Anatomy of the Head, Neck & Spine

LCRS Year 2

Anil Chopra

ContentsHead Neck and Spine 1 – Vertebral Column and Spinal Cord...............................1Head, Neck and Spine 2 – Cranium and Brain.........................................................7Head Neck and Spine 3 – Root of the Neck.............................................................14Head, Neck and Spine 4 – Biting, Chewing and Swallowing.................................23Head, Neck and Spine 5 – Breathing, Voice and Hearing.....................................34Head Neck and Spine 6 – Eye and Sight..................................................................40

Head Neck and Spine 1 – Vertebral Column and Spinal CordAnil Chopra

1. Recognise and name the following parts of a typical vertebra in osteological specimens or in suitable imaging: body, pedicle, lamina, transverse process, spinous process, articular surfaces

2. Recognise the distinctive features of cervical, thoracic and lumbar vertebrae3. Explain the roles of intervertebral discs, ligaments and muscles in load bearing in

the vertebral column4. Describe the relative extents of antero-posterior flexion, lateral flexion and axial

rotation in the major regions of the vertebral column and explain this in terms of skeletal anatomy

5. Identify the atlas and axis and explain their functions in head movement6. Demonstrate on each other the location of C7, T3, T7, L2 and L4 vertebrae7. State the number of vertebrae in each region of the spine, and how the pairs of

spinal nerves are related to them 8. Explain the arrangement of the meninges around the spinal cord and roots, and

indicate any differences from the cranial meninges9. Identify two major reasons for carrying out lumbar puncture, and explain the basis

for the puncture site10. Explain the danger of carrying out lumbar puncture without excluding the

presence of raised intracranial pressure11. Outline the steps taken to avoid neurological complication in casualties with a

possibility of cervical spine injury12. Explain in anatomical terms the most common causes of back pain13. Describe the most common abnormalities of spinal curvature

The vertebrae are different depending on whereabouts in the spinal cord they lie:

Cervical Vertebrae: there are 7 cervical vertebrae. They are characterised by:o the foramen transversarium in the transverse processes through which the

vessels run, o very small vertebral bodieso a short and bifid spinous processo triangular vertebral foramen

Thoracic vertebrae are characterised by facets used for articulations with the ribs (the transverse processes) and are at more of an angle with the vertebral body. They are smaller than the lumbar vertebrae. Their vertebral foramen is circiular.

Lumbar vertebrae are characterised by their large bodies and have rounded pper and lower facets to prevent rotation.

Sacrum is one fused set of five vertebrae that articulate with the pelvic bone. Coccyx is usually a set of 4 fused bones inferior to the sacrum.

Intervertebral Discs

The intervertebral disc forms the cartilagous symphyses between vertebral bodies in the vertebral column. It consists of 2 layers, the Anulus fibrosus (outer ring of collagen surrounding fibrocartilage) and the Nucleus pulposus. (gelatinous filling in the centre which absorbs compression between the vertebrae). As we get older, the anulus fibrosus can degenerate resulting in herniation of the nucleus pulposus. These

can press on the sciatic nerve root ( L5 and S1) and so cause pain in the lower back radiating to the back of the thigh.

The lumbar region is the most common site of back pain because it is subjected to stress during weight bearing. Trying to extend the spine from a fully flexed position (bending over) places a lot of stress of the intervertebral discs and so the joints can become inflamed. This is even more dangerous if the spine is rotating at the same time.

In order to prevent this, when lifting heavy loads, the load should be held close to the body and the knees should be extended rather than the spine so that the load can be lifted.

NB: there are no discs between the skull and CI or between CI and CII due to specialised movements that occur at these joints

Each vertebra articulates with the one above and below via; The midline cartilaginous joint – the intevertebral disc Two lateral synovial joints between the transverse processes – facet joints

The movements permitted are flexion, extension, and lateral flexion to both sides

Ligaments

There are 2 main ligaments running up either side of the vertebral bodies: the anterior and posterior longitudinal ligaments.

Whip-lashneck hyperextensiondamage to anterior longitudinal ligament

Ligamenta flava: run in between each vertebral body. (pierced during a lumbar puncture)Suproaspinous ligament: runs up posterior to the spinous processes (i.e. along the ends).Interspinous ligaments: pass between the adjacent vertebral spinous processes. Articular Ligaments: surrounds all facet joints.

Back Movement4 main movement of vertebral column:

- Extension- Flexion- Lateral Flexion- Rotation

The amount of movement between two adjacent vertebrae is limited, the additive effect of them all moving allows posture change. There is more limited movement in the thoracic part of the column because of the articulation with the ribs.

Flexion/extension Lateral flexion Rotation

C1-C7 ++ ++ ++T1-T6 0 + +

T7-T12 + ++ ++L1-sacrum ++ + 0

MusclesContraction of the muscles of the abdominal wall causes flexion and lateral flexionThere are two main groups of muscle: Superficial extrinsic muscles including trapezius and latissimus dorsi Deep intrinsic muscles, particularly the erector spinae, which are important in controlling the movement of the vertebral column. The large muscle bulk posterior and lateral to the vertebral column

Atlas and AxisAtlas: is the top bone (CI) in the vertebral column that articulates with the head. It lacks a vertebral body and is located just posterior to the mouth. The skull sits on top of the lateral masses

Axis: the second bone in the vertebral column (CII) on which the atlas rests and contains the dens (allows head rotation) which slots nicely into the faced in the atlas and is held together by the transverse ligament of the atlas. It has no emerging spinal roots.

The CI-CII atlanto-axial joint: In the midline A synovial joint between the dens and the back of the anterior arch of the atlas, and a synovial bursa between the dens and the cruciate ligament behind Laterally the articular surfaces are flat to allow gliding The cruciate ligament separates the dens from the spinal meninges

Atlanto-occiptal joints – between CI and the occipital bone of the skull form synvial joints linked by apical ligaments to allow nodding of the head

Spinal Nerves: Nerve C1 is between the skull and CI vertebra. Nerves C2 – C7 emerge superior to the vertebral peduncles Nerve C8 emerges inferior to the vertebral peduncle CVII Nerves T1 downward emerge inferior to their respective vertebrae.

Number of vertebrae

Number of spinal nerves Relationship of nerve to vertebra

Cervical 7 8 All above corresponding vertebra except for C8

Thoracic 12 12 All below corresponding vertebra

Lumbar 5 5 All below corresponding vertebra

Sacral 5 5 All below corresponding vertebra

Coccyx 1 fused (or up to 4 unfused) 1 Below (or between if unfused)

Total 30 31

Meningeal Layers

Dura Mater – thick external covering. In the brain this is attached to the skull but in the spinal cord it is not attached to any bone.Arachnoid mater – against (but not adherent to) inner surface of dura mater

Subarachnoid Space - the subarachnoid space is in between the pia and arachnoid mater and contains CSF. Continuous with foramen magnumPia Mater – a vascular membrane that is adherent to the spinal cord although has denticulate ligaments that attach it to the arachnoid mater.

NB: the filum terminale is at the lower end of the spinal cord (L2) and is attached to the coccyx. It is formed when the spinal cord withdraws upward during development - the Pia mater surrounding the cord is prolonged. Together with the nerve roots, it forms the cauda equine below L2.

Lumbar Puncture- Used for obtain a sample of CSF for examination- Used to inject anaesthetics for patients with operations on their legs.- Used to asses CSF pressure.- It is done between L4 and L5 because the spinal cord stops but the CSF is still

in the meninges.NB: lumbar punctures should not be done in the presence of raised intra-cranial pressure. This is because herniation of the cerebellum through the foramen magnum may occur.

Epidural anaesthesia – a liquid agent can be injected into the epidural space to anaesthetise the spinal nerve roots.The sacral hiatus allows administration of caudal epidural anaesthesia

Spinal Curvature Abnormalities

Scoliosis – vertebral column is laterally deviated.Kyphosis – thoracic curvature is bigger than normal (hump-back)Lordosis – lumbar curvature is bigger than normal (e.g. obesity)

Head, Neck and Spine 2 – Cranium and BrainAnil Chopra

1. Demonstrate on a skull and in radiographs the following bones: frontal, parietal, temporal (squamous, petrous and mastoid process), ethmoid, sphenoid (body and wings) and occipital

2. Identify both on the brain and in x-ray, CT and MR images the following: ventricles, cerebral hemispheres, thalamus, hypothalamus, internal capsule, basal ganglia, brainstem, optic chiasm and pituitary gland

3. Identify the different tissue components of the scalp4. Demonstrate the relationship between the brain and the different cranial fossae5. Describe the structure and function of the meninges6. Draw a simple diagram to explain the flow of cerebrospinal fluid in and around

the brain7. Explain the term herniation with respect to the brain and give examples of its

neurological consequences8. Identify on a skull the main exit/entry routes for the cranial nerves and the major

blood vessels9. Draw a simple diagram of the Circle of Willis 10. Demonstrate the main venous sinuses11. Outline how venous anatomy presents opportunities for intracranial infection12. Identify the pterion and explain the clinical importance of its relationship to the

middle meningeal artery

Problems can occur when you get a space occupying lesion. – Herniation Herniation can occur in 3 main places:

1) Sub-falcine herniation – 2) Uncal Herniaton - Medial end of Tentorium3) Tonsilar herniation

Tissue Layers in the Scalp

SkinConnective TissueAponeurosisLoose areolar tissuePeriosteum

Relationships of Brain to Cranial Fossa

Anterior (frontal, ethmoid and sphenoid bones) – frontal lobes of cerebral hemispheres.

1 Lateral ventricle [may be cut through twice in horizontal or coronal plane]

2 Third ventricle [may look like a hole or a slit in coronal and horizontal plane, depending on angle of section]

3 Fourth ventricle4 Aqueduct

5 Corpus callosum [may be cut through twice in horizontal plane]

6 Frontal lobe7 Occipital lobe8 Parietal lobe9 Temporal lobe

10 Basal ganglia [may be more than one part]11 Thalamus

12 Internal capsule [both anterior and posterior limbs seen in horizontal plane]

13 Optic chiasma14 Midbrain15 Pons16 Medulla17 Cerebellum

Middle (sphenoid and temporal bones) – temporal lobes rest in the greater wing of the sphenoid bone and anterior part of the temporal bone, pituitary gland sits in the hypophysial fossa.

Posterior (occipital and temporal bones) – contains brainstem (midbrain pons and medulla) which all travel through the foramen magnum, and the cerebellum which rests mainly on the occipital bone.

MeningesDura Mater Thick outer layer, a tough covering for the brain which itself is split into 2 layers.

o Outer periosteal layer – attached to the skull and continuous with skull through foramen magnum and others.

o Inner meningeal layer – in close contact with arachnoid mater and is continuous with the spinal cord at the foramen magnum.

These layers split up at various different dural partitions including:o Falx cerebri – separates the two cerebral hemispheres.o Tentorium cerebelli – separates cerebellum and posterior cerebral

hemispheres.o Falx cerebelli – separates cerebellar hemispheres.o Diaphragma sellae – covers the hypophysial fossa in the sella turcica.

There is an opening through which the infundibulum runs. This connects the base of the brain with the pituitary gland along with any blood vessels.

The function of the dural folds is to make sure brain does not move around in the cranium. (made from dense connective tissue).

Arachnoid Mater Thin avascular membrane against the inner surface of dura mater. Has projections into the superior sagittal sinus called arachnoid granulations. Does not enter grooves or fissures in the brain except for the longitudinal fissure

between the two cerebral hemispheres.

Pia Mater Thin delicate membrane that is adherent to the brain itself It enters grooves and origins and runs right into nerve roots.

Extradural Space The space between the bone and the outer periosteal layer of the dura mater.

Normally this shouldn’t exist but if there is a bad injury, then this space can become filled with fluid.

Subarachnoid Space The space between the arachnoid mater and pia mater. Normally has some fluid although this amount can increase in injury.

Cerebrospinal Fluid

CSF is produced by the choroids plexus – a vascular plexus formed where the vesself of the pia mater come into contact with the Ependymal lining of the central canal

Lateral ventricles → through the foramina of Monro → third ventricle → through cerebral aqueduct → fourth ventricle → some enters the central canal of the spinal cord, most enters the subarachnoid space through foramina in the roof of the fourth ventricle → flows to the flows around the brain and is absorbed back into the venous circulation through arachnoid villi/granulations in the venous sinuses

Hydrocephalous is over production of CSF or reduced absorption

Herniation

(Diagram from notes on holes in base of skull)

Blood Supply to the Brain

Vertebral Arteries – arise from the left and right subclavian arteries. They pass through the transverse foramina of the cervical vertebrae up to the cranial cavity. (through the foramen magnum). The left and right vertebral arteries join to form the basilar artery.

Basilar Artery – bifurcates to form the two posterior cerebral arteries.

Circle or Willis – this is formed at the base of the brain by interconnecting the branch of the posterior cerebral artery which is the posterior communicating arteries along with the anterior communicating arteries (which connects the two anterior cerebral arteries).

Internal Carotid arteries – arise from the two common carotid arteries, proceeding through the carotid canal. Branches out into the ophthalmic, posterior communicating artery, middle cerebral and anterior cerebral arteries.

Venous DrainageEventually all blood in the brain enters the dural venous sinus through a range of different veins:

- diploic veins : from bone- cerebral veins: from the cerebral hemispheres- meningeal veins: from meninges- cerebellar veins: from cerebellum e.t.c.- emissary veins : from outside the cranial cavity

NB: emissary veins are a conduit for infections to spread from the scalp to the cranial cavity because they have no valves. This is why it is important to avoid infection of lacerations of the scalp.

There are many different dural sinuses that they can drain into: Superior sagittal sinus: superior border of the falx cerebri. It empties into the

right transverse sinus. Inferior Saggital sinus: drains the inferior part of the cerebral hemispheres and

ends in the straight sinus Straight sinus: runs right from the centre of the brain (from the great cerebral

vein) posteriorly into the confluence of the sinuses). Transverse sinus: run round the outer posterior ring of the cerebral hemispheres

and drain into the confluence of sinuses. As they make their way round to the cavernous sinus, they form the sigmoid sinus.

Cavernous sinus: receive blood from emissary, ophthalmic and cerebral veins. There are also many structures running through the cavernous sinus including:

o Internal carotid arteryo Abducent nerve (VI)o Oculomotor nerve (III)o Trochlear nerve (IV)o Ophthalmic division of trigeminal nerve (V1)o Maxillary nerve division of trigeminal nerve (V2)

Petrosal Sinuses: these drain the cavernous sinuses into the transverse sinuses.

NB: if the middle meningeal artery becomes damaged, then an Extradural haemorrhage can result. This typically occurs in the region of the pterion as the bone is very thin around this area.

Head Neck and Spine 3 – Root of the NeckAnil Chopra

1. Sketch the thoracic inlet to show the relations of the following structures at the neck-chest interface: 1st thoracic vertebra, 1st ribs and cartilages, manubrium, pleura and lungs, oesophagus, trachea, brachiocephalic veins, vagus nerves, brachiocephalic artery, left common carotid and subclavian arteries, sympathetic trunks, left recurrent laryngeal nerve, phrenic nerves

2. Locate the carotid pulse and explain the main uses of this central pulse3. Demonstrate the technique for palpation of the cervical lymph nodes and define

their field of drainage4. Define the boundaries of the anterior and posterior triangles of the neck5. Identify the infrahyoid (strap) muscles, mylohyoid and the digastric muscle 6. Demonstrate on the living subject and on suitable prosections the position of the

roots and trunks of the brachial plexus7. Demonstrate in prosections the position and key relations of the subclavian artery

and vein, and brachial plexus 8. Demonstrate the courses of the internal thoracic and vertebral branches of the

subclavian artery 9. Explain the uses of central venous lines and indicate the landmarks for insertion

of a central line into the internal jugular vein10. List the possible complications of insertion of central venous lines11. Describe the origin, course and function of the phrenic and spinal accessory

nerves

Blood Supply to Thyroid

2 Main Arteries:- Superior thyroid artery (branch of external carotid)- Inferior thyroid artery (branch of thyrocervical trunk)

3 Main veins:- Superior thyroid vein drains into the internal jugular vein.- Middle thyroid vein drains into internal jugular vein.- Inferior thyroid vein drains into brachiocephalic vein.

1st Rib

Manubrium

Functions of the neck: Structural – support and movement of head Visceral functions – trachea, etc Conduit for blood vessels and nerves

3 main compartments in the column of the neck – visceral compartment (trachea, oesophagus, thyroid) carotid sheath (vagus nerve, carotid artery, jugular veing, associated with sympathetic chain behind) vertebral compartment (vertebral column, nuchal muscles)

Vertebral Levels of the neck: C1 – open mouth C2 – superior cervical ganglion C3 – body of hyoid C4 – upper border of thyroid cartilage, bifurcation of the common carotid artery C6 – cricoid cartilage, middle cervical ganglion C7 – inferior cervical ganglion

Taking Pulses

A pulse can be felt at 4 main locations on the face. These are: Anterior temporal pulse – on temples. Temporal pulse – anterior to the ear Facial pulse – inferior border of mandible (jaw) Carotid pulse – anterior triangle of the neck. It is one of the strongest pulses in

the body, and is important as it is used in the assessment of pulse rhythm, rate, character and timing of murmurs.

Lymph Node PalpationThere are several sets of lymph nodes in the head and neck: Occipital Nodes – situated and drains the posterior scalp and neck. Mastoid nodes – just posterior to ear and drains postero-lateral part of the scalp Parotid nodes – anterior to ear, drains the anterior auricle. Submandibular nodes – inferior to the mandible. These are most commonly

palpated in order to check for infection or lymphoma. This is done by running the fingers round the jaw, behind the ears and down the neck.

Deep Cervical nodes – all lymph from head and neck eventually drains into these which then empties either into the right lymphatic duct (on the right) or the thoracic duct (on the left).

Triangles in the NeckAnterior Triangle – defined:- anteriorly by the midline of the

neck- inferior and posteriorly by the

sternocleidomastoid muscle- superiorly by the mandible

Contains: Mainly muscles – lower facial Platysma Anterior jugular veins Cutaneous branches of cervical plexus Strap muscles – thyrohyoid, sternohyoid, sternothyroid, omohyoid Digastric muscle Larynx and trachea Thyroid gland Cervical plexus C1-C3

Posterior Triangle – defined:- anteriorly by the sternocleidomastoid muscle- posteriorly by the trapezius muscle- inferiorly by the clavicle- superiorly by the occipital bone just posterior to the mastoid process.

Contains: Mainly nerves and blood vessels External jugular vein Spinal accessory nerve Trunks of the brachial plexus, emerging posterior to scalenus anterior Subclavian artery posterior to scalenus anterior Subclavian vein anterior to scalenus anterior Phrenic nerve lying in the anterior surface of scalenus anterior

Muscles In the Neck

The main muscles in the anterior triangle of the neck are situated around the hyoid bone:

Muscle Origin Insertion Innervation FunctionStylohyoid Base of styloid

processLateral area of body of hyoid bone

Facial nerve [VII] Pulls hyoid bone upward in a posterosuperior direction

Digastric-Anterior belly

Digastric fossa on lower inside of mandible

Attachment of tendon between two bellies to body of hyoid bone

Mylohyoid nerve from inferior alveolar branch of mandibular nerve [V3]

Opens mouth by lowering mandible; raises hyoid bone

-Posterior belly

Mastoid notch on medial side of mastoid process of temporal bone

  Facial nerve [VII]  

Mylohyoid Mylohyoid line on mandible

Body of hyoid bone and fibres from muscle on opposite side

Mylohyoid nerve from inferior alveolar branch of mandibular nerve [V3]

Support and elevation of floor of mouth; elevation of hyoid

Geniohyoid Inferior mental spine on inner surface of mandible

Anterior surface of body of hyoid bone

Branch from anterior ramus of C1 (carried along the hypoglossal nerve [XII])

Fixed mandible elevates and pulls hyoid bone forward; fixed hyoid bone pulls mandible downward and in-ward

Sternohyoid Posterior aspect of sternoclavicular joint and adjacent manubrium of sternum

Body of hyoid bone medial to attachment of omohyoid muscle

Anterior rami of C1 to C3 through the ansa cervicalis

Depresses hyoid bone after swallowing

Omohyoid Superior border of scapula medial to suprascapular notch

Lower border of body of hyoid bone just lateral to attachment of sternohyoid

Anterior rami of C1 to C3 through the ansa cervicalis

Depresses and fixes hyoid bone

Thyrohyoid Oblique line on lamina of thyroid cartilage

Greater horn and adjacent aspect of body of hyoid bone

Fibers from anterior ramus of C1 carried along hypoglossal nerve [XII]

Depresses hyoid bone, but when hyoid bone is fixed raises larynx

Sternothyroid

Posterior surface of manubrium of sternum

Oblique line on lamina of thyroid cartilage

Anterior rami of C1 to C3 through the ansa cervicalis

Draws larynx (thyroid cartilage) downward

There are various other muscles in the posterior triangle of the neck:Muscle Origin Insertion Innervation FunctionSternocleidomastoid-Sternal head Upper part of

anterior surface of manubrium of sternum

Lateral one-half of superior nuchal line

Accessory nerve [XI] and branches from anterior rami of C2 to C3 (C4)

Individually-will tilt head to-wards shoulder on same side rotating head to turn face to opposite side; acting to-gether, draw head forwards

-Clavicular head

Superior surface of medial one-third of clavicle

Lateral surface of mastoid process

   

Trapezius Superior nuchal line; external occipital protuberance; ligamentum nuchae; spinous processes of vertebrae CVII to TXII

Lateral one-third of clavicle; acromion; spine of scapula

Motor-accessory nerve [XI]; proprioception-C3 and C4

Assists in rotating the scapula during abduction of humerus above horizontal; upper fibers-elevate, middle fibers-adduct, lower fibers- depress scapula

Splenius capitis

Lower half of ligamentum nuchae; spinous processes of vertebrae CVII to TIV

Mastoid process, skull below lateral one-third of superior nuchal line

Posterior rami middle cervical nerves

Together, draw head back-wards; individually, draw and rotate head to one side (turn face to same side)

Levator scapulae

Transverse processes of CI to C4

Upper part of medial border of scapula

C3,C4; and dorsal scapular nerve (C4, C5)

Elevates scapula

Posterior scalene

Posterior tubercles of transverse processes of vertebrae CIV to CVI

Upper surface of rib II Anterior rami of C5 to C7

Elevation of rib II

Middle scalene

Transverse processes of vertebrae CII to CVII

Upper surface of rib I between tubercle and groove for subclavian artery

Anterior rami of C3 to C7

Elevation of rib I

Anterior scalene

Anterior tubercles of the transverse processes of vertebrae CIII to CVI

Scalene tubercle and upper surface of rib I

Anterior rami of C4 to C7

Elevation of rib I

Omohyoid Superior border of scapula medial to

Inferior border of body of hyoid bone

Ansa cervicalis; anterior rami of C1

Depress the hyoid bone

scapular notch to C3Roots and Trunks of the Brachial Plexus

There are other nerves that also run through the root of the neck:

Phrenic Nerves : arise from C3 C4 and C5 and keep the diaphragm alive. Vagus Nerves: continue downward and control visceral autonomic function. Recurrent laryngeal Nerves: split into left and right, they are both branches of the

vagus nerves that descend beside the trachea to the larynx. Accessory Nerve: this exits the cranial cavity through the jugular foramen and

descends to and innervates the sternocleidomastoid muscle. It then crosses the posterior triangle to the trapezius where it innervates that muscle.

Cervical Ganglion of the Sympathetic Nervous System: there are 3 of these (inferior, middle and superior). The superior cervical ganglion is the start of the sympathetic chain and begins around area vertebrae CI.

Other Arteries

Subclavian: the left subclavian arises from the aortic arch and lies posterior to the left common carotid artery. The right subclavian arises as a branch of the brachiocephalic artery and begins posterior to the sternoclavicular joint. Both become auxiliary arteries as they pass the outer border of rib I (as they enter the arm).

Vertebral: first branch of the both the left and right subclavian arteries as they enter the roof of the neck. They ascend through the foramina in the cervical vertebrae. It passes through the foramen magnum to enter the cranial fossa.

Internal Thoracic: the third branch of the subclavian. It descends into the thoracic cavity posterior to the clavicle giving off numerous branches.

Central Venous Lines

Normally go in the internal jugular or subclavian veins. (also in femoral and brachial veins)

They are used to monitor venous pressure, administer irritant drugs, and also for intravenous feeding.

The insertion point is normally found as the midpoint of the mastoid process and the sternal notch.

Can also be found as the apex of the triangle formed by the two heads of the sternocleidomastoid muscle, and the clavicle.

Various complications can arise from insertion of central venous lines:o Arterial punctureo Pneumothoraxo Nerve damage o Air embolismo Thrombosiso Misplacemento Infection

Head, Neck and Spine 4 – Biting, Chewing and SwallowingAnil Chopra

1. Outline the main neuromuscular systems involved in biting, chewing, salivation and swallowing

2. Identify the major branches of the external carotid artery (superior thyroid, ascending pharyngeal, lingual, facial, posterior auricular, occipital, superficial temporal, maxillary)

3. Assess those functions of the trigeminal, facial, glossopharyngeal, vagus and hypoglossal nerves which relate to biting chewing and swallowing

4. Demonstrate how the temporo-mandibular joint and muscles of mastication produce chewing movements

5. Demonstrate the routes by which the maxillary, mandibular, facial, glossopharyngeal, vagus and hypoglossal nerves leave the skull, and indicate the courses of the lingual and inferior alveolar nerves

6. Describe the relationship between the facial nerve and the parotid gland7. Identify the positions of the parotid and submandibular glands and the lymph

nodes draining the oral and oropharyngeal structures 8. Identify the teeth in the living mouth and record them accurately; recognise

characteristic dental patterns for children and adults9. Be able to identify the following structures in the living mouth: hard and soft

palate, uvula, faucial pillars, palatine tonsils, lingual papillae, parotid and submandibular papillae, sublingual glands, frenulum, genioglossal ridge

Opening the mouth depends on the mandibular branch of the trigeminal and facial nerves – mandibular supplies the muscles that open the jaw and the facial supplies the muscles that part the lips Chewing involves the facial, mandibular and hpoglossal The facial nerve keeps the lips closed The mandibular innervates the muscles that chew and grins The facial and hypoglossal maintain the food in the occlusal plane by innervating buccinator and the tongue The maxillary and mandibular branches of the trigeminal sense the position and consistency of the food and regulate the force of contraction of the muscles Taste perception is provided by the trigeminal and facial

Mastication (chewing): Elevation – the mandible is suspended from the skull by a muscular sling formed internally by the medial pterygoid and laterally by masseter. Temporalis is a powerful elevator of the tongue Depression is brought about in two ways:

Anterior traction on the head of the mandible by lateral pterygoid Inferior traction on the mandible by the anterior belly of digastric and mylohyoid

Grinding – lateral and rotary movements are produced by muscles of the two sides working co-operatively Protraction – lateral pterygoid, anterior fibres of temporalis Retraction – posterior fibres of temporalis

Swallowing: Once the bolus of food has been propelled to the posterior 1/3 of the oral cavity by buccinator (Facial VII) and the tongue (hypoglossal XII):

Lift and retract tongue (styloglossus, intrinsic) Bolus into oropharynx (palatoglossus) Close off nasopharynx by raising soft palate Raise the larynx, closed off by epiglottis Peristaltic wave of constrictor muscles Relax cricopharyngeus, open oesophagus

Salivation: The parotid gland is supplied by the glossopharyngeal (IX) and opens into the parotid duct which opens at the upper second molar The submandibular salivary gland is located beneath and medial to the angle of the mandible The submandibular duct passes forwards to open out either side of the frenulum of the tongue The sublingual salivary glands are scattered along the submandibular duct into which some of them open. Some open directly into the oral cavity Secretomotor impulses to both glands originate in the superior salivary nucles and pass through the VII (facial), the chorda tympani, lingual nerve and the submandibular ganglion

The External Carotid Artery There are numerous branches of the external carotid artery:

Branch SuppliesSuperior thyroid artery

Thyrohyoid muscle, internal structures of the larynx, sternocleidomastoid and cricothyroid muscles, thyroid gland

Ascending pharyngeal artery

Pharyngeal constrictors and stylopharyngeus muscle, palate, tonsil, pharyngotympanic tube, meninges in posterior cranial fossa

Lingual artery Muscles of the tongue, palatine tonsil, soft palate, epiglottis, floor of mouth, sublingual gland

Facial artery All structures in the face from the inferior border of the mandible anterior to the masseter muscle to the medial corner of the eye, the soft palate, palatine tonsil, pharyngotympanic tube, submandibular gland

Occipital artery Sternocleidomastoid muscle, meninges in posterior cranial fossa, mastoid cells, deep muscles of the back, posterior scalp

Posterior auricular artery

Parotid gland and nearby muscles, external ear and scalp posterior to ear, middle and inner ear structures

Maxillary artery External acoustic meatus, lateral and medial surface of tympanic membrane, temporomandibular joint, dura mater on lateral wall of skull and inner table of cranial bones, trigeminal ganglion and dura in vicinity, mylohyoid muscle, mandibular teeth, skin on chin, temporalis muscle, outer table of bones of skull in temporal fossa, structures in infratemporal fossa, maxillary sinus, upper teeth and gingivae, infra-orbital skin, palate, roof of pharynx, nasal cavity.

Superficial Parotid gland and duct, masseter muscle, lateral face, anterior part of external ear,

temporal artery temporalis muscle, parietal and temporal fossae

Remember by Some Anatomists Like Freaking Out Poor Medical Students

Muscles Used in Biting Chewing and Swallowing

Mylohyoid Muscle: Situated on the floor of the oral cavity. It is used to elevate and pull forward the hyoid bone in swallowing. It also pulls the mouth open when the hyoid bone is held in place.

Geniohyoid Muscle: also on the floor of the oral cavity from the hyoid bone and used to pull forward the hyoid bone in swallowing as well as pulling the mouth open when the hyoid bone is held in place.

Tongue: there are various different muscles in the tongue:Muscle Origin Insertion Innervation FunctionIntrinsicSuperior longitudinal

Submucosal connective tissue at the back of the tongue and from the median septum of the tongue

Muscle fibers pass forward and obliquely to submucosal connective tissue and mucosa on margins of tongue

Hypoglossal nerve [XII]

Shortens tongue; curls apex and sides of tongue

Inferior longitudinal

Root of tongue (some fibers from hyoid)

Apex of tongue Hypoglossal nerve [XII]

Shortens tongue; uncurls apex and turns it down-ward

Transverse Median septum of the tongue

Submucosal connective tissue on lateral margins of tongue

Hypoglossal nerve [XII]

Narrows and elongates tongue

Vertical Submucosal connective tissue on dorsum of tongue

Connective tissue in more ventral regions of tongue

Hypoglossal nerve [XII]

Flattens and widens tongue

ExtrinsicGenioglossus Superior mental

tuberclesBody of hyoid; entire length of tongue

Hypoglossal nerve [XII]

Protrudes tongue; depresses centre of tongue

Hyoglossus Greater horn and adjacent part of body of hyoid bone

Lateral surface of tongue Hypoglossal nerve [XII]

Depresses tongue

Styloglossus Styloid process (anterolateral surface)

Lateral surface of tongue Hypoglossal nerve [XII]

Elevates and retracts tongue

Palatoglossus Inferior surface of palatine Aponeurosis

Lateral margin of tongue Vagus nerve [X] (via pharyngeal branch to pharyngeal plexus)

Depresses palate; moves palatoglossal fold toward midline; elevates back of the tongue

Soft Palate Muscles: there are many muscles in the soft palate. In order to swallow the soft palate must be raised. Most are innervated by the vagus nerve (X).

Masseter: this is a powerful muscle that originates form the zygomatic arch and the maxillary process of the zygomatic – innervated by mandibular branch of trigeminal nerve (V). It is attached to the mandible and its function is to elevate it.

Temporalis: this is a large fan-shaped muscle that fills the temporal fossa. It is attached to the bony surfaces of the temporal fossa and to the coronoid process (front of the mandible) Its function is to elevate and retract the jaw and it is also supplied by then mandibular branch of the trigeminal (V).

Medial Pterygoid: has 2 heads. The superficial head, is attached to the posterior of the maxilla and inserts into the deep part of the mandible. The deep head attaches at the pterygoid process and inserts in the deep part of the mandible. It is used in elevating and protruding (moving forward) the jaw and it is also supplied by the mandibular branch of the trigeminal (V)

Lateral Pterygoid: has 2 heads. The upper head originates from the infratemporal fossa and the lower head originates from the pterygoid process (the same place as the medial pterygoid). They both insert into the articular disc and are used in elevation, protraction and lateral movement of the mandible for fast chewing. It is also supplied by the mandibular branch of the trigeminal (V).

Constrictor Muscles in the Pharynx: these 3 main muscles found in the pharynx that contract sequentially from top to bottom to push the food down into the oesophagus:

MusclePosterior attachment Anterior attachment Innervation Function

Superior constrictor

Pharyngeal raphe

Pterygomandibular raphe and adjacent bone on the mandible and pterygoid hamulus

Vagus nerve [X]

Constriction of pharynx

Middle constrictor

Pharyngeal raphe

Upper margin of greater horn of hyoid bone and adjacent margins of lesser horn and stylohyoid ligament

Vagus nerve [X]

Constriction of pharynx

Inferior constrictor

Pharyngeal raphe

Cricoid cartilage, oblique line of thyroid cartilage, and a ligament that spans between these attachments and crosses the cricothyroid muscle

Vagus nerve [X]

Constriction of pharynx

The Temporo Mandibular Joint Divided into two separate synovial cavities by a fibrocartilaginous disc – gliding and hinge movements Sensory supply from mandibular branch of trigeminal (V) which is why pain, like from the teeth can be referred to the external acoustic meatus or tympanic membrane Mandibles tethered by the sphenomandibular ligament which extends from the spine of the sphenoid to the lingual of the mandible As the mouth opens the mandible moves forwards, as it closes it moves back During opening and closing the condyle of the mandiblearticulates with the mandibular fossa of the temporal bone in a hinge movement During protrusion and retraction the condyle of the mandible glides forward to articulate with the articular tubercle of the temporal boneMovements:

Depression is brought about in two ways: Anterior traction on the head of the mandible by lateral pterygoid Inferior traction on the mandible by the anterior belly of digastric and mylohyoid

Grinding – lateral and rotary movements are produced by muscles of the two sides working co-operatively Protraction – lateral pterygoid, anterior fibres of temporalis Retraction – posterior fibres of temporalis

Muscles involved: Temporalis – under zygomatic arch Masseter – superficial to zygomatic arch (one you can feel while chewing) Materal and medial pterygoid Mylohyoid Anterior belly of digastric

Nerves in Biting Chewing and SwallowingMandibular Branch of Trigeminal Nerve: supplies all the muscles involved in chewing (masseter, temporalis and the pterygoids) as well as one of the muscles in the soft palate (tensor veli palatini). It is the only branch of the trigeminal nerve which is both motor and sensory. (the maxillary and ophthalmic are purely sensory).

The trigeminal nerve originates from the trigeminal ganglion in the middle cranial fossa and passes down through the foramen ovale after which it splits into posterior and anterior:

Meningeal – sensory for dura mater Medial pterygoid – innervates medial pterygoid. Buccal – generally sensory but also innervates lateral pterygoid and part of the

temporalis muscle.

Masseteric – innervates masseter. Deep temporal – usually 2, innervate temporalis muscle from its deep surface. Auriculotemporal – sensory for areas of skin around the temples as well as

external ear, external auditory meatus, tympanic membrane and temporomandibular joint.

Lingual – the major sensory branch of the posterior mandibular nerve, it is sensory for the anterior two thirds of the tongue and is joined by the chorda tympani from the facial nerve. It also carries parasympathetic fibres for all glands below the level of the oral fissure. It descends between the tensor veli palatini and the lateral pterygoid (where it is joined by the chorda tympani) into the oral cavity. It enters the oral cavity between the posterior attachment of the mylohyoid muscle and the superior constrictor of the pharynx. It is palpable through the oral mucosa on the medial side of the mandible just inferior to the last molar tooth. It attaches to the submandibular ganglion.

Inferior Alveolar – another major sensory branch of the posterior part of the mandibular nerve. Sensory to all the lower teeth, lower of lower lip, chin and innervates the mylohyoid muscle and the anterior belly of the digastric muscle. It descends on the lateral surface of the medial pterygoid and passes between the sphenomandibular ligament and the ramus of the mandible. It enters the mandibular canal through the mandibular foramen and then continues inferior to the molar teeth. The roots can sometimes curve around the canal making the extraction of these teeth difficult. It branches into the incisive nerve which supplies the front teeth, and the mental nerve which exits through the mental foramen and supplies the lower lip. This is palpable through the oral mucosa adjacent to the roots of the premolars.

Glossopharyngeal: carries taste and general sensation from the pharyngeal part of the tongue as well as taste and general sensation from the vallate papillae. It also innervates one of the longitudinal muscles of the pharynx, the stylopharyngeus, which elevates the pharynx just before swallowing.

Vagus Nerve: supplies muscles in the larynx used in swallowing (apart from stylopharyngeus), as well as the pallatoglossus muscle of the tongue.

Hypoglossal: supplies all the muscles in the tongue except for the palatoglossus.

Facial Nerve: facial nerve emerges from the skull through the stylomastoid foramen in the temporal bone, travels through the parotid gland after which it has 5 main braches. These are involved with carrying taste and general sensation from the oral part of the tongue (the front 2/3), motor innervation to facial muscles and parasympathetic fibres to the lacrimal and salivary glands:

Temporal – to frontal belly of occipitofrontalisZygomatic – to orbicularis oculi and upper faceBuccal – to buccinatorm orbicularis oris and mid faceMandibular – to orbicularis oris and the corner of the mouthCervical – to platysma

Remember by Ten Zulus Buggered My Cat As the nerve is superficial is is easy to damage leading to facial palsy. The mandibular branch is particulary in danger as it passes just below the lower margin of the mandible.

Bell’s palsy = a lower motor lesion of the facial nerve – lesion of cell bodies or the nerve itself causing the muscles of the face to sag on the affected sideSalivary GlandsParotid Gland Largest of the three main salivary glands in the head. It is anterior to the lower part of the ear and just deep to the ramus of the

mandible. The parotid gland lies at the side of the face behind the mandible, it lies

superficially (parotid swellings, i.e. mumps) The parotid duct emerges from the anterior border and passes forwards on

masseter, then turns medially and penetrates buccinator and opens into the mouth opposite the second upper molar tooth

Parasympathetic secretomotor impulses come from the glossopharyngeal (IX) – the lesser petrosal nerve

The parotid duct leaves the anterior edge of the parotid gland half way down the gland and passes the medial border of the masseter and then pierces the buccinator muscle entering the inside of the mouth.

Through it travels the facial nerve dividing into its upper and lower trunks. These travel through the substance of the parotid gland which makes the removal of the parotid gland very difficult.

Submandibular Gland Hook shaped – round the mylohyoid muscle; the superficial part also runs against

the deep part of the body of the mandible. The submandibular ducts run from the deep part of the gland to the base of the

mouth. Sublingual Gland Smallest of the three main salivary glands

Immediately lateral to the submandibular duct and associated lingual nerve. Lies against the medial surface of the mandible. Drains the oral cavity with numerous small ducts which open into the crest of the

sublingual fold.

LymphaticsAll lymphatic vessels from the oral cavity and oropharynx lead to the deep cervical nodes. These include the retropharyngeal, paratracheal, infrahyoid and jugulodigastric nodes.

Teeth and Gingivae

There are normally 32 adult teeth (16 on the upper and lower jaws).

There are normally 20 deciduous teeth (10 on upper and lower jaws).

Gingivae (gums) are specialised regions that cover the oral mucosa and surround the teeth.

Uvula

Palatopharangeal fold

Palatine tonsil

Palatoglossalfold

Posterior wall oforopharynx

Faucil pillars - a pair of curved ridges running down the soft palate Parotid papillae – small raised patch neer the 2nd upper molar – opening of parotid duct Submandibular papillae – felshy tag with a forked tip found as you run doen the low gums and mandibular symphysis – where the submandicular salivary ducts open Sublingual glands – bumpy bit on the lower lateral buccal floor (the lingual papillae) Genioglossal ridge – a smooth, firm rounded ridge running along the midline of the floor of the mouth to the tongue formed by the genioglossus muscle

Head, Neck and Spine 5 – Breathing, Voice and HearingAnil Chopra

1. List the mechanisms which protect the lungs and bronchi against aspiration of food and drink

2. Explain (in terms of sensory and motor pathways and muscle groups) the sneeze and cough reflexes

3. Demonstrate in dissected specimens the landmarks of the nasal cavities, nasopharynx and soft palate

4. Demonstrate in living subjects the body of the hyoid, the thyroid and cricoid cartilages, the cervical part of the trachea, and the thyroid isthmus

5. Demonstrate in living subjects and imaging the positions of the paranasal sinuses; define their sensory nerve supply; explain the clinical significance of their drainage routes

6. Explain the importance of the relationship of the maxillary sinus to the roots of the upper teeth, and of the sphenoid sinus to the pituitary fossa

7. Explain pressure equalisation between the pharynx and the middle ear8. Explain the clinical importance of the relationship of the mastoid antrum and the

mastoid air cells to the middle ear cavity in the skull 9. Identify the features of the external auditory meatus and eardrum that can be seen

through an auroscope10. Outline the contributions of the structures and spaces of the airway and oral cavity

to voice production11. List the actions that may be taken to restore patency of the airway in an

emergency12. Describe the anatomical basis of tracheotomy and cricothyroidotomy13. Explain likely consequences of disease or injury of a recurrent laryngeal nerve

and of the superior part of the cervical sympathetic chain

Larynx – the hollow area between the mouth and the trachea. Consists of - three unpaired cartilages: thyroid, cricothyroid and epiglottis- three small cartilage pairs: arytenoids, corniculate and cuneiform- fibroelastic membranes and intrinsic muscles.

When the larynx is raised in swallowing the epiglottis shuts and the entry to the oesophagus is opened. This stops food going into the trachea. The gag reflex also plays an important role in the prevention of food and drink entering the trachea.

Coughing and SneezingCoughing: receptors in the larynx and trachea become irritated (sensed by branches of vagus nerve X) which causes the phrenic nerves (C3-5) and thoracic nerves (T1-12) to initiate deep inhalation. There is a build up of pressure against a closed glottis and then forced exhalation. The oropharyngeal isthmus is open so the air escapes through the mouth.

Sneeze: receptors in the nasal mucosa are irritated (sensed by branches of trigeminal V1 and V2) which causes the phrenic nerves (C3-5) and thoracic nerves (T1-12) to initiate deep inhalation. There is a build up of pressure against a closed

glottis and then forced exhalation. The oropharyngeal isthmus is closed so the air escapes through the nose.

Paranasal Air Sinuses

There are 4 paranasal air sinuses: Frontal sinus : these are just superior to the nose on the anterior side of the frontal

bone. They are triangular in shape and drain into the middle meatus by the frontonasal duct. They are innervated by the branches of the supra-orbital nerve (from the ophthalmic nerve V1) and are supplied with blood by the anterior ethmoidal arteries.

Ethmoidal cells : these make up the ethmoidal labyrinth which is situated between the two orbits (in the ethmoidal bone). The number of small air chamber is variable. Their three constituent parts drain into different places:

o Anterior ethmoidal cells empty into infundibulum or frontonasal duct.o Middle ethmoidal cells empty into ethmoidal bulla.o Posterior ethmoidal cells empty into the lateral wall of the superior nasal

meatus.It is innervated by the ethmoidal branches of the nasociliary nerve (of the ophthalmic nerve V1) and the maxillary nerve (V2). They receive blood from the posterior and anterior ethmoidal arteries.

Maxillary Sinuses : these are the largest of the paranasal sinuses and take up most of the room in the maxillae. Its anterolateral surface is related to the upper molar and premolar teeth, which means there is a possibility of infection from the tooth roots of upper teeth spreading into the maxillary sinus. They are pyramidal in shape and empty into the middle nasal meatus. They are innervated by the infra-orbital and alveolar branches of the maxillary nerve (V2) and receive blood through the branches of the infra-orbital and alveolar branches of the maxillary arteries.

Sphenoidal Sinuses : situated on either side in the body of the sphenoid bone, the sphenoidal sinuses open up into the roof of the nasal cavity. It lies just inferior to the pituitary gland and is only separated by thin bone, surgeons use this as a route to the pituitary gland and hypothalamus. They are innervated by the posterior ethmoidal branch of the ophthalmic nerve (V1) and the maxillary nerve (V2) and are supplied by the pharyngeal branches of the maxillary arteries.

NB: If an auroscope is shined through the external acoustic meatus, then a cone of light is normally seen as a reflection on the tympanic membrane at the 5 o’clock position. This is not seen in infection.

The Ear

The anatomy of the ear is split up into 3 main sections:External Ear containing:

- Pinna/ Auricle- External acoustic meatus

Middle Ear containing:- 3 Auditory ossicles

o Malleuso Incuso Stapes

- Typanic membrane Inner Ear containing:

- Oval and round windows- Utricle and saccule- Cochlea- Auditory nerve (VIII)- Phanygotympanic tube- Semicircular canals

The posterior wall of the middle ear is the mastoid wall which contains the mastoid air cells. These continue throughout the temporal bone including the mastoid process. These are only separated from the middle cranial fossa by the thin tegmen tympani. The mucous membrane lining the mastoid air cells is the continuous with the mucus membrane of the middle ear and therefore infections can spread easily from the middle ear to the mastoid area.

Equalisation of pressure between the two sides of the tympanic membrane is achieved by the pharyngotympanic tube. This tube connects the middle ear with the nasopharynx

and it has two parts; a bony part and a cartilaginous part. Vocal ProductionWhen phonating, the arytenoids cartilages and the vocal folds are adducted and air forced out through the rima glottidis. The vestibule is open. The sounds are then modified by the upper parts of the airway.

Phonation = vocal sound created when air is forced between vocal folds Pitch depends on the relative position and tension in the vocal folds by the

movement of arytenoid cartilages and cricothyroid joint Intensity of sound depends on the force with which air is pushed through the

glottis Quality of sound depends on resonation in pharynx, mouth and paranasal sinuses Words depend on shaping of sound with mouth, particular tongue and lips

These are supplied by the superior and inferior laryngeal arteries, and drained by the inferior and superior laryngeal veins. The cricothyroid muscle is supplied by the external branch of the superior laryngeal nerve and the internal laryngeal nerve is sensory to the laryngeal cavity above the level of the vocal folds.

The recurrent laryngeal nerve is sensory for the laryngeal cavity below the vocal folds and also innervates all the intrinsic muscles of the larynx (except the cricothyroid). As this nerve passes very close to the thyroid gland, it can be damaged in thyroid surgery and as a result can cause hoarseness and problems with speech.

Airway Blockage

Airway patency can be restored by a variety of different methods:• Chin lift/ jaw thrust• Endotracheal intubation - tube is inserted into a patient's trachea in order to

ensure that the airway is not closed off and that air is able to reach the lungs. It is regarded as the most reliable available method for protecting a patient's airway. Requires general anaethesia.

• Cricothyroidotomy - an emergency incision through the skin and cricothyroid membrane (between the thyroid cartilage and the cricoid cartilage). A tube is then inserted into the incision and then the patient is ventilated using a bag.

• Tracheotomy – emergency incision but directly into the trachea; between the sternal notch and the thyroid cartilage.

Head Neck and Spine 6 – Eye and SightAnil Chopra

1. Describe briefly the margin and walls of the bony orbit and name its important contents

2. Test function of the following cranial nerves: oculomotor, trochlear, abducens, ophthalmic division of trigeminal, facial (to orbicularis oculi)

3. Identify the rectus and oblique muscles, levator palpebrae superioris and orbicularis oculi in suitable specimens

4. Identify on a skull the superior orbital fissure and the optic canal and name the nerves and vessels passing through them

5. Explain the clinical significance of the close relationship between the superior orbital fissure and the cavernous sinus

6. Describe briefly the arterial supply and venous drainage of the eye, including the retina

7. Understand how to test corneal and consensual light reflexes and explain the afferent and efferent components of these

8. Identify the optical and neural parts of the eye9. Outline the mechanisms of tear secretion,

tear-film maintenance and tear drainageBony Orbit

The bony orbit is made up of 7 bones which form a pyramid shape with its apex as the optical foramen. It contains the visual apparatus including the nerves and vessels which supply it. The walls are formed by a number of bones (shown in the diagram) – NB: its posterior wall is made up mainly of the sphenoid bone which has a number of holes for vessels and nerves that travel to and from the brain.

Testing the Cranial Nerves

Oculomotor, trochlear and Abducens

Look for eyelid drooping. Shine light in the eye and test the pupil reflex

(both direct and consensual). Light can be moved from eye to eye. Ask patient to follow your finger without moving head. Make an H shape using

the 6 cardinal points. Test accommodation by asking patient to look at distant object and then focus on

closer one.

Ophthalmic Division of the Trigeminal

Ask patient to clench their mouth and look for the prominence of the masseter muscle.

Other trigeminal includeo Ask patient to look up and away and touch cotton wool on one side (assess

patient reaction – should blink).o Ask patient to look away and touch sterile sharp item on their cheek/head.

(Assess patient reaction).

Facial Ask patient to look up and wrinkle forehead (examine muscle strength) Ask patient to shut eyes tightly. (compare each side) – This is testing the

orbicularis oculi. Ask patient to grin (look for facial movement)

Muscles of the Eye

2 Groups of muscles within the orbit:Extrinsic: move the eyelid and eyeball itself.

Muscle Origin Insertion Innervation FunctionLevator palpebrae superioris

Lesser wing of sphenoid anterior to optic canal

Anterior surface of tarsal plate; a few fibers to skin and superior conjunctival fornix

Oculomotor nerve [III]- superior branch

Elevation of upper eyelid

Superior rectus

Superior part of common tendinous ring

Anterior half of eyeball superiorly

Oculomotor nerve [III]- superior branch

Elevation, adduction, medial rotation of eyeball

Inferior rectus

Inferior part of common tendinous ring

Anterior half of eyeball inferiorly

Oculomotor nerve [III]- inferior branch

Depression, adduction, lateral rotation of eyeball

Medial rectus Medial part of common tendinous ring

Anterior half of eyeball medially

Oculomotor nerve [III]- inferior branch

Adduction of eyeball

Lateral rectus

Lateral part of common tendinous ring

Anterior half of eyeball laterally

Abducent nerve [VI]

Abduction of eyeball

Superior oblique

Body of sphenoid, superior and medial to optic canal

Outer posterior quadrant of eyeball

Trochlear nerve [IV]

Depression, abduction, medial rotation of eyeball

Inferior oblique

Medial floor of orbit posterior to rim; maxilla lateral to nasolacrimal groove

Outer posterior quadrant of eyeball

Oculomotor nerve [III]- inferior branch

Elevation, abduction, lateral rotation of eyeball

NB: loss of oculomotor nerve (III) causes loss of function of levator palpebrae superioris and hence eyelid drooping.

Intrinsic:

These include the ciliary muscle, the sphincter pupillae, and the dilator pupillae and control the shape and size of the lens.

Holes in the Bony Orbit

Optic Canal: this is the round opening at the apex of the pyramid and contains the optic nerve and the ophthalmic artery.

Superior Orbital Fissure: this is a longer triangular shaped gap in the lateral wall of the bony orbit. There are a number of structures that pass through the superior orbital fissure:

- superior branch of oculomotor nerve (III) - inferior branch of oculomotor nerve (III)- trochlear nerve (IV)- abducent nerve (VI)- lacrimal, frontal and nasociliary branches of the ophthalmic nerve (V1)- superior ophthalmic vein.

Because the superior ophthalmic vein drains into the cavernous sinus there is a potential route for the spread of infection from around the orbit or nasal sinuses. This

may lead to cavernous sinus thrombosis and subsequent impairment of all structures running through it.Inferior Orbital Fissure: begins from the inferior part of the superior orbital fissure and runs downward. Passing through it are:

- maxillary nerve (V2)- infra-orbital vessels- vein communicating with the pterygoid plexus of veins

Infra-Orbital Foramen: this begins about half way along the inferior orbital fissure and contains the infra-orbital nerve (a branch of the maxillary).

Blood Supply and Drainage of the Eye

Orbit is mainly supplied by ophthalmic artery which passes through he optic canal. It has many branches: Lacrimal artery: supplies lacrimal glands,

muscles, the anterior ciliary branch to the eyeball and the lateral sides of the eyelid.

Central retinal artery: enters through the optic nerve itself to supply the cells in the retina.

Posterior ciliary arteries: there are 2, long and short, which supply the structures in the eyeball.

Muscular arteries: supply the intrinsic muscles of the eyeball.

Supra-orbital arteries: passes out of the orbit through the supra-orbital foramen to supply scalp.

Ethmoidal arteries: also pass out of the orbit to supply ethmoidal cells of nasal cavity as well as the septum and lateral wall.

Medial palpebral arteries: supply eyelids Dorsal Nasal and supratrochlear arteries:

leave orbit to supply nose and forehead.

The venous drainage mainly takes place between 2 main channels; the superior ophthalmic vein and the inferior ophthalmic vein.

Superior ophthalmic vein collects from angular vein and supra-orbital vein to pass through the superior orbital fissure into the cavernous sinus.

Inferior ophthalmic vein collects from the inferior part of the orbit and then either joins with the superior ophthalmic vein, enters the cavernous sinus directly, or

passes through the inferior orbital fissure to the pterygoid plexus in the infratemporal fossa.

The vorticose veins drain the eyeball itself.

Nerves in the Eye

Optic Nerve (II): carries afferent fibres from retina to brain. It is surrounded by cranial meninges and is really an extension of the brain. If there is increased intracranial pressure then the subarachnoid space may become filled with fluid and so venous drainage is impeded from the retinal veins.

Oculomotor Nerve (III): this leaves the anterior surface of the brainstem between the midbrain and the pons. It splits into superior and inferior branches as it enters the orbit through the superior orbital fissure and then supplies the various different intrinsic and extrinsic muscles of the eye.

Trochlear Nerve (IV): leaves the posterior surface of the midbrain and travels round the brainstem and into the orbit via the superior orbital fissure. It supplies the superior oblique muscle.

Abducent Nerve (VI): leaves the brainstem between the pons and medulla, runs through the cavernous sinus and into the orbit through the superior orbital fissure. It supplies the lateral rectus muscle.

Postganglionic Sympathetic fibres: these pass through the ciliary ganglion of the oculomotor nerve and then go on to innervate the dilator pupillae muscle (an intrinsic muscle).

Ophthalmic Nerve (V1): passes into the orbit through the lateral wall of the cavernous sinus and then splits into three branches; nasociliary, lacrimal and frontal. The lacrimal nerve goes on to the lacrimal gland. The nasociliary nerve continues anteriorly giving off many branches which are sensory to other parts of the nose and sinuses, as well as the long ciliary nerve which is involved with pupil dilation. The frontal nerve splits into two in the middle of the orbit; the supratrochlear nerve and the supra-orbital nerve supply the conjunctiva and the skin on the upper eyelid and forehead.

Ciliary Ganglion: this is where pre- and post-ganglionic parasympathetic fibres synapse before making their way to the eyeball. There are also some sensory and sympathetic fibres that make their way through the ganglion. The postganglionic fibres enter the posterior part of the eyeball through short ciliary nerves and innervate the sphincter pupillae muscle (pupil constriction) and the ciliary muscle which widens the lens for near vision.

Light ReflexesPupillary Light Reflex: A light shone into either eye causes both pupils to constrict Involves the optic nerve → optic chiasm → optic tract → midbrain → oculomotor

nerve (parasympathetic) → ciliary ganglion → iris muscles

It is consensual as commissural connections mean light in one eye leads to both responding

It does not involve cortical function and so works on unconscious people – a test of brainstem function

Fixed dilated pupils are those which do not respond and are a likely indicator of death

Accommodation Reflex: Focusing on a near object and then looking away, or vice-versa causes changes in

pupil size and lens shape Pupil - near = constricted, far = dilated Lens – near = fatter, far = thinner In accommodation there is some degree of perception and so the cortex is

involved There is also some voluntary control and you decide what to focus on Pathway: Retina → optic nerve → optic chiasm → optic tract → lateral

geniculate bodies → visual cortex → frontal cortex → midbrain Edinger-Westphal nuclei → III (occulomotor) → ciliary ganglion → ciliary and iris muscles

Horner’s Syndrome

This is a condition where the innervation of the sympathetic cervical ganglion in the neck is blocked (normally by a lesion or tumour). It is characterised by:

- constriction of pupil (miosis)- drooping of eyelid (ptosis)- absence of sweating (anhidrosis)

Lacrimation

The lacrimal gland is a small exocrine gland in the upper part of the orbit that consists of two parts:

- orbital part: above the tendon of levator palpebrae superioris- palpebral part: below the tendon of levator palpebrae superioris.

Glandular secretions are continually secreted (innervated by facial nerve VII, pterygopalatine ganglion and branches of the trigeminal nerve V) into the lateral part of the superior fornix of the conjunctiva, this is then moved across the eyeball as we blink.

The fluid accumulates in the lacrimal lake and then drained by the lacrimal sac by the lacrimal canaliculi. This is then forced through the nasolacrimal duct with blinking, which then drains into the inferior meatus of the nasal cavity.

- Lacrimal nerve (of the ophthalmic) is sensory for the lacrimal gland.- Parasympathetic secretomotor nerves innervate the lacrimal gland to

produce tears.

Infection of the lacrimal canaliculi blocks tears leading to dripping down cheeks (excessive production also produces the same effect).