Introduction to Human Anatomy

Nawfal K. Al-Hadithi, Chairman, Anatomy Dept., College of Medicine, University of Baghdad

ANATOMY ?

- Anatomy is one of the cornerstones of a doctor’s medical education.

- What is being taught today may differ in content significantly from the past but the methods used to teach this have not really changed that much

- It includes the study of those structures that can be seen grossly (without the aid of magnification) and microscopically (with the aid of magnification).

- Typically, when used by itself, the term 'anatomy' tends to mean gross or macroscopic anatomy.

- Microscopic anatomy, also called 'histology', is the study of cells and tissues using a microscope

- Embryology, Molecular Biology, Histochemistry … were included

- Sectional Anatomy, Radiologic Anatomy, Surgical Anatomy … are evolving

How can gross anatomy be studied?

- Prosection:

A prosection is the dissection of a cadaver (human or animal) or part of a cadaver by an experienced anatomist in order to demonstrate for students anatomic structure

- Dissection:

Dissection (also called anatomization) is usually the process of disassembling and observing something to determine its internal structure and as an aid to discerning the functions and relationships of its components.

The anatomical position:

- This position is the standard reference position of the body used to describe the location of structures

- Standing upright

- Feet together

- Hands by the side

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- Face looking forward

- Mouth is closed

- Facial expression is neutral

- Palms face forward with the fingers straight and together and with the pad of the thumb turned 90° to others

- Toes point forward

Anatomical planes:

1- Coronal planes are oriented vertically and divide the body into anterior and posterior parts.

2- Sagittal planes are oriented vertically and divide the body into right and left parts.

The plane that divides the body into equal right and left halves is termed the median plane.

3- Transverse, horizontal, or axial planes divide the body into superior and inferior parts.

Sections:

- Longitudinal sections: run parallel to the long axis of the body or of any of its parts regardless of the position of the body

- Transverse sections: or cross sections, are slices of the body or its parts that are cut at right angles to the longitudinal axis of the body or of any of its parts

- Oblique sections: are slices of the body or any of its parts that are not cut along the previously listed anatomical planes

Terminology:

Terms of relationship:

These are terms used to describe the location of structures relative to the body as a whole or to other structures

- Anterior & posterior: describe the position of structures relative to the 'front' and 'back' of the body.

. Anterior; nearer to the front

. Posterior; nearer to the back

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. Ventral Vs dorsal; in the trunk

. Palmar Vs dorsal ; in the palm

. Plantar Vs dorsal; in the foot

- Medial and lateral: describe the position of structures relative to the median plane

. Medial; nearer to the median plane

. Lateral; away from the median plane

- Superior and inferior: describe structures in reference to the vertical axis of the body.

. Superior; nearer to the vertex

. Inferior; nearer to the sole

- Proximal & distal: used with reference to the origin or attachment of a structure, particularly in the limbs.

Proximal; nearer to origin

Distal; away from origin

- Superficial & deep: used to describe the relative positions of structures with respect to the surface of the body.

Superficial; nearer to surface

Deep; away from surface

- External & internal: used to describe the position in relation to the center

External; away from center

Internal; nearer to center

Terms of laterality:

- Bilateral; paired strucures present on both sides (kidneys)

- Unilateral; unpaired structure present on one side (spleen)

- Ipsilateral; same thing present on the same side of the body (thumb & big toe)

- Contralateral; same thing present on the other side of the body (Rt & Lt hands)

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The skin (integumentum):

- The largest body organ

- Excellent indicator of the body health

- Needs careful examination

Acts for:

- Protection

- Sensation

- Cosmetic

- Thermal regulation

- Vit D sybthesis

Made of:

- Epidermis

- Dermis

Appendages:

- Hair

- Nails

Langer (cleavage) lines

Fasciae:

- Fibro-areolar or aponeurotic laminæ, of variable thickness and strength

- They act as wrapping, packing & insulating materials in the tissues

- They have been subdivided into superficial and deep

Superficial fascia (subcutaneous tissue):

- Found immediately beneath the skin

- Consists of fibroareolar tissue, containing in its meshes pellicles of fat in varying quantity.

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Deep fascia:

- Is a dense, inelastic, fibrous membrane, forming sheaths for the muscles, and in some cases affording them broad surfaces for attachment.

- They form compartments & intermuscular septa

- Potential spaces are sometimes present between folds of deep fascia

- Fascia is thick in unprotected situations, as on the lateral side of a limb

- May assist muscle action by increasing the degree of tension

- May surround special structures (carotid, parotid fascia…)

Muscles:

Classification:

1- Voluntary muscles (skeletal):

- Parallel fibers with peripheral nuclei

- Characteristic striation across fibers

- Supplied by somatic nerves

- Without motor supply they cannot contract

2- Involuntary muscles:

A) Cardiac muscles:

- Fibers not parallel

- Show striation

- Usually have autonomic control

- Contract automatically

B) Smooth muscles:

- Fibers show no striation with big central nuclei

- Supplied by autonomic system

- Need autonomic supply to contract

C) Skeletal muscles:

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- Muscle is for movement

- They are connected to bones, cartilages, ligaments, and skin

- Muscle is composed of a belly & tendon

- Muscles vary extremely in their shape:

• Long muscles

• Flat muscles

• Diaphragms

Fiber arrangement:

- Flat muscles: have parallel fibers often with an aponeurosis

- Fusiform muscles: spindle shaped with a round belly and tapered ends

- Convergent muscles: from a broad origin fibers converge to a single tendon

- Circular or sphincter muscles: surround a body opening or orifice, constricting it when contracted

- Multi-headed muscles: have more than one head or more than one contractile belly

- Quadrate muscles: have four equal sides

- Pennate muscles: Oblique fibers converge to a tendon:

.Unipennate; fibers converge to one side of the tendon (FHL)

.Bipennate; fibers converge to both sides of a central tendon (tibialis posterior)

.Multipennate; fibers pass between septa within the muscle in 2 opposite directions, as in deltoid

Muscle tendons:

- White, glistening, inelastic fibrous cords

- They consist almost entirely of collagen fibers

- Their blood supply is very spares.

- Their nerves have special modifications of their terminal fibers (organs of Golgi).

Aponeuroses:

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- The non fleshy part of flat muscles

- They appear white color, iridescent, glistening, and similar in structure to the tendons.

- They are only sparingly supplied with blood vessels

- Muscle names, derived from:

(1) Situation, as tibialis, radialis ...

(2) Direction, as rectus, obliqus …

(3) Function, as flexor, supinator …

(4) Shape, as deltoid, rhomboid

(5) Number of heads, as biceps, triceps

(6) Points of attachment, as sternocleidomastoid

Terms related to muscles:

- Origin: is meant to imply its more fixed or central attachment

- Insertion: the movable point

* The origin is absolutely fixed in only a small number of muscles

* Accurate knowledge of these is of great importance in the understanding their mechanics

Muscle action:

- Prime mover: direct action

- Synergist: complemets the prime mover

- Antagonist: opposes or inhibits the prime mover

- Fixator; a muscle which fixes certain parts to promote the action of the acting muscle & reduce power loss

Bones:

• 206 named bines

• Axial & appendicular skeleton

* Ossification:

1- O. in cartilage

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2- O. in membrane

* Bone vasculature & nerve supply:

- Periosteum

- Nutrient arteries

- Nerves

* Compact & spongy bones

Bone shapes:

1- Long bones: have shaft & 2 ends

2- Short bones: cube like

3- Flat bones: thin, flattened, with slight curvature

4- Irregular bone: complicated shapes

5- Sesamoid: within tendons

Ligaments:

- A ligament is a cord of connective tissue uniting two structures

- Usually associated with joints

- Histologically divided into fibrous & elastic

Bursae:

- A bursa is a lubricating device consisting of a closed fibrous sac lined with a delicate smooth membrane & filled with a jelly-like fluid

- They are found where tendons rub against hard structures

Synovial Sheath:

- A synovial sheath is a tubular bursa that surrounds a tendon

- It is a lubricating & protective structure

Cartilage:

A type of elastic connective tissue of three main histological types:

1- Elastic:

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- Flexible, contains mainly elastic fibers

- Never ossifies

- Not seen in joints

2- Fibrocartilage:

- Cartilage containing collagen fibers

- It is very tough structure, never fracture

3- Hyaline:

- Tough but brittle

- May ossify with age

- Is the most common type

Joints:

Joints are the meeting points between:

• Two bones

• Two cartilages

• Bone & cartilage

Structural types:

1- Fibrous J.

2- Cartilagenous J.

3- Synovial J.

Morphological types:

1- Ball & socket J.

2- Condaloid J.

3- Gliding J.

4- Hinge J.

5- Pivot J.

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6- Saddle J.

I) Fibrous joints:

Articulating surfaces are fastened together by dense connective tissue containing collagen:

II) Cartilaginous joints:

Articulating bones are connected by hyaline cartilage or fibrocartilage:

III) Synovial (diarthrotic) joints:

Characterized by:

- Surrounded by a joint capsule

- Supported by ligaments

- Lined with synovial membrane

- Covered by hyaline cartilage

- Contains synovial fluid

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Joint movements:

Four types of movements are conducted on joints:

1- Gliding movement:

- One surface glides over the other

- It is common to all movable joints

- This movement may exist between any two contiguous surfaces (not confined to joints)

2- Angular movement:

- Occurs only between the long bones

- The angle between the two bones is increased or diminished

- It may take place:

(1) Forward and backward, constituting flexion and extension

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(2) Toward and away from the median plane (or a specific axis), constituting adduction and abduction.

(3) Circumduction:

- A combination of the four angular movements

- Best seen in the shoulder and hip-joints

(4) Rotation:

- Movement around a central axis without any displacement

- The axis of rotation may lie in a separate bone or the bone itself

- Rotation could be medial or lateral

* Special movements:

- Inversion – eversion

- Pronation – supination

- Opposition

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The nervous system:

Division of the nervous system:

I- The somatic nervous system:

1- The central nervous system (CNS):

a) Brain

b) Spinal cord

2- The peripheral nervous system (PNS)

a) Cranial nerves

b) Spinal nerves

II- The autonomic nervous system

1- Sympathetic NS

2- Parasympathetic NS

Cells in the nervous system:

Neuron:

- Are the nerve cells. They form the basic building unit in the NS

- Parts:

1- The soma

2- The processes:

- Dendrites: the short processes of the, usually bring impulses toward the soma

- Axon: the longest process of the soma, usually takes impulses away from it

Schwann cells:

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Form the myelin sheath envelop of the axon

Neuroglia:

Are the supporting cells of the NS

Gray & white matters:

The interior of the central nervous system is organized into gray and white matter

- Gray matter consists of nerve cells embedded in neuroglia

- White matter consists of nerve fibers (axons) embedded in neuroglia

Schwann cells:

- Large, flat cells wrap the nerve processes

- They contain an insulating material, the myelin which preserves the nerve potential

- The space between two adjacent Schwann cells is called the node of Ranveir

- Electrical potentials travel from one node to another

- Impulse passes in myelinated nerves faster than non-myelinated nerves

Neuroglia:

They are of four types:

1- Astrocytes

2- Oligodendrocytes

3- Microglia

4- Ependyma (lining brain ventricles)

Divisions of the CNS:

1- The Brain:

A) Forebrain:

- Cerebrum

- Diencephalon

B) Midbrain

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C) Hindbrain:

- Pons

- Medulla oblongata

- Cerebellum

2- The spinal cord

The brain:

- The brain receives information from, and controls the activities of, the trunk and limbs through connection with spinal cord

- It also possesses 12 pairs of cranial nerves through which it communicates mostly with structures of the head and neck.

- In addition to sensory perception & issuing motor commands, the brain is responsible for maintaining visceral activities, & functions which characterizes human beings like thinking & personality

The spinal cord (medulla spinalis):

- This long tubular structure is continuous with the brainstem

- It is 45 cm long in mature male

Gray matter of the cord lies interior & arranged in an (H) shaped fashion:

. Anterior horn neurons are motor

. Posterior horn neurons are sensory

. Lateral horn is present in a part of the cord for sympathetic function

White matter constitutes bundles of fibers called (tracts) providing complex connections

Peripheral Nervous System:

• Mainly formed of nerves (axons)

• Collection of soma in the PNS form ganglia

The cranial nerves:

- 12 pairs of nerves arise from the brain or brain stem

- May be sensory, motor or mixed

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- 4 of them carry autonomic supply (III, VII, IX & X)

- Their destination is variable & may reach as far as the colon

- Collection of nerve cells outside the CNS is called ganglion

ModalityNameNerve number

Sense of smellOlfactoryI

Sense of visionOpticII

Motor to ocular muscles + parasympathetic

OculomotorIII

Motor to superior obliqueTrochlearIV

Sensory to face + motorTrigeminalV

Motor to lateral rectusAbducentVI

Motor to face muscles + parasympathetic

FacialVII

Sense of hearing & equilibriumVestibulocochlearVIII

MixedGlossopharyngealIX

Motor + parasympatheticVagusX

MotorAccessoryXI

Motor to tongue muscleHypoglossalXII

The spinal nerves:

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- 31 pairs of nerves spring from the spinal cord, and are transmitted through the intervertebral foramina

Number of vertebraeNumber of nervesRegion

78Cervical

1212Thoracic

55Lumbar

55Sacral

11Coccygeal

Nerve Roots:

- Each nerve is attached to the cord by two roots, an anterior & a posterior, the latter being characterized by the presence of a ganglion, the spinal ganglion

- The anterior root (MOTOR): formed by axons of neurons in the anterior horn of gray matter

- The posterior root (SENSORY): formed by axons of neurons in the spinal ganglion

- Both roots unite in the intervertebral foramen to form the spinal nerve (mixed)

The spinal (dorsal root) ganglia:

- Collections of nerve cells on the posterior roots of the spinal nerves.

- Ganglia are usually placed in the intervertebral foramina

- The ganglia contain unipolar neurons whose single process divides into two:

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* Peripheral process, represents the dendrites & conveys information from the body to the nerve cell

* Central process, represents the axon & conveys these information into the posterior horn cells of S.C

Structure of the spinal nerve:

- The spinal nerve contains:

• Motor fibers

• Sensory fibers

• Sympathetic fibers; given to the nerve in the intervertebral foramen

- Immediately after its formation, the spinal nerve divides into anterior & posterior rami

- Each ramus contains the three modalities

- Dorsal rami supply skin & muscles of the back of trunk

- Ventral rami supply the ventral side of trunk & limbs

Synapses:

- The small cleft between 2 adjacent neurons which represents site of functional interneuronal communication

- Most neurons may make synaptic connections to a 1000 or more other neurons and may receive up to 10,000 connections from other neurons

- Synaptic transmission is a chemical process

- The neurotransmitter passes across the synapse affecting the charge (potential) of the post-synaptic cell

- This change will liberate neurotransmitter from the cell to affect the coming one & so on

The spinal reflex:

- A sudden stimulation of the sensory nerve fiber is conveyed to the dorsal horn neurons

- These neurons have a direct communication with their corresponding ventral horn neurons via a connector cell called interneurones

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- These interneurones will stimulate the ventral horn cells unconsciously

- Involuntary movement of the injured area away from the stimulus will result

- The higher centers will receive information about what happened later!

Terms related to spinal nerves:

- The spinal segment:

It is the part of spinal cord which gives origin to a single pair of spinal nerves

- The dermatome:

It is the amount of skin supplied by a single spinal nerve

- The myotome:

Is the amount of muscle fibers supplied by a single spinal nerve

Autonomic N.S:

Sympathetic N.S:

- All parts of the body needs sympathetic innervation

- Therefore it is distributed widely through these ways:

1- With spinal nerves (somatic)

2- Directly to viscera (visceral)

3- With blood vessels (vascular)

- Sympathetic ganglia are present on each side of the vertebral column & distribute these branches

- This system is under control of the CNS through nerves called preganglionic nerves & enter sympathetic ganglia

- Its direct branches to the target are called postganglionic nerves & leave these ganglia

- The system provides motor & sensory functions

Functions of the sympathetic system:

- The function of the sympathetic system is to prepare the body for an emergency.

- The heart rate is increased, arterioles of the skin and intestine are constricted, arterioles of skeletal muscle are dilated, and the blood pressure is raised.

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- There is redistribution of blood; thus, it leaves the skin and GIT to go to the brain, heart, and skeletal muscle.

- Sympathetic stimulation dilates the pupils; inhibit smooth muscle of the bronchi, intestine, and bladder wall; and close the sphincters.

- The hair is made to stand on end, and sweating occurs.

Parasympathetic system:

- Not all parts of the body needs this innervation

- P.S system does not have the well defined structure like the S. system

- Most of P.S innervation is distributed with cranial nerves & sacral spinal segment

- Like S. system it is under control of the CSN by preganglionic nerves & its target branches are called postganglionic nerves

- Like S. system, it provides sensory & motor functions

Functions of the P.S system:

- The activities of the parasympathetic part of the autonomic system are directed toward conserving and restoring energy.

- The heart rate is slowed

- Pupils are constricted

- Peristalsis and glandular activity is increased

- Sphincters are opened

- The bladder wall is contracted.

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