EYE BALL AND BRAIN LAB REPORTStella Onsare

Ivy Tech Community College

SHEEP BRAIN AND EYE• The sheep brain/eye are used to study human

anatomy because they are both mammals; therefore, have many comparative similarities in structure and function to the human brain/eye.

• I was able to identify similar and common structures like the cerebellum, pons, corpus callosum, medulla oblongata, spinal cord, thalamus, hypothalamus, optic nerve, white and gray matter.

• The sheep is also a familiar animal that can be readily obtained. It’s brain and eye are of convenient size making it neither too large to handle nor too small to make dissection.

Significance

The significance of this investigative question is that;• The eye and brain function in the working memory

which takes place in the frontal cortex and coordinates long term memories with sights, sounds, and feelings.

• It is also more humane to use an animal to examine and obtain physical experience in the composition of the brain/eye than using an actual human brain/eye for the study.

Initial Thoughts on investigative question

• The inhumane conditions that test animals are exposed to are terrible because the brain/eye are very sensitive parts of an animals body, therefore cause intense pain. In addition, those animals are killed by being loaded into a carbon dioxide gas chamber or having their necks broken making it very harsh. I believe such conditions can affect the mammals emotionally and physically before death; therefore yielding false test results.

• With technology, scientists should find another way of examining and obtaining physical experience with human anatomy hence avoiding the unethical treatment of these animals with needless repetition of experiments.

Visual ApparatusThe Eyeball dissection

Tunic of the eye

The three layers of the eye are referred to as “tunics” • Fibrous tunic• Vascular tunic• Nervous tunics

The fibrous tunic of the eye is composed of cornea and sclera.

• The Cornea is the transparent anterior covering of the eye. The cornea is curved and helps to focus on light entering the eye.

• The sclera (white of the eye) covers the majority of the eyeball with the exception of the region covered by the cornea. Sclera is composed primarily of collagen fibers. The extrinsic muscles of the eye attach to the sclera.

CorneaTransparent covering

ScleraWhite of the eye

Adipose tissueCushions the eye

The Vascular Tunic is composed of iris, choroid, and ciliary bodies.

• The Iris is the colored are of the eye surrounding the pupil. The diameter of the pupil is changed by the action of the muscles in the iris.

• The Choroid is a highly vascularized layer of the eye and provides nourishment to the retina.

• The Ciliary bodies begins at the junction of the sclera and cornea. The ciliary bodies are connected to suspensory ligaments, which attach to the lens.

choroidVascularized layer of the eye.

Tapetum lucidum

retina

IrisColored area of the eye when the lens is pushed aside

Ciliary bodiesSuspensory ligaments

Vitreous humorGelatinous material

The Nervous Tunic consists of the retina and optic nerves

• The Retina is made up of receptors called rods and cones.

• The Optic Nerves ( cranial nerve II) receives impulses from the rods and cones and passes these visual information along the optic tract to the primary visual cortex within the occipital lobe of the brain

Optic nerve

Other structure in the eyeball1. Aqueous humor- is a thin fluid located in the anterior of the eye.

The anterior cavity is formed from the anterior and posterior chambers of the eye. The anterior chamber of the eye is the space between the cornea and the iris. The posterior chamber is the space between the iris and the lens.

2. Vitreous humor- is the gelatinous material in the posterior cavity. The posterior cavity extends from behind the lens to the retina of the eye.

3. The Pupil is the opening surrounded by the iris. Light passes through the pupil and then the lens to stimulate the rods and cones of the retina.

4. The lens focuses images on the retina. It is a clear most spherical structure that is attaches by suspensory ligaments to the ciliary body. The lens changes shape based on whether one is focusing on objects at a distance or viewing nearby objects.

lensFocuses image

pupilOpening surrounded by iris when the lens is pushed aside.

Accessory structures of the eyes

1. Extraocular muscles are six small skeletal muscles attached to the bony orbit and directly to the eyeball. They function to produce eye movements. They include superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique and inferior oblique.

2. Eyebrows and eyelashes serve to prevent debris from entering the eyes.

3. Eye lids prevent dust and debris from entering the eyes and also keeps the eyes lubricated.

The Brain and related Structures.

MENINGESThe cranial meninges are layers of membranes that surrounds the brain and act to protect it. They include:1. Dura mater2. Subdural space3. Arachnoid mater4. Subarachnoid mater5. Pia mater

Dura Mater is the outermost of the meninges. This thick, durable layer is tough protective sleeve for the brain. In the cranium the dura mater is made up of two layers between which are formed the dural venous sinuses. One of the sinuses is the superior sagittal sinus, which courses through the double layered dura mater. The outer layer of the dura mater is continuous with the cranial periosterum.2

Subdural Space is the space between the arachnoid mater and the dura mater. This space may not exist in a living human.

Arachnoid mater is the middle meninx. It has a gauzy spidery-cobweb like consistency. It is distinguishable at the gross level, and covers the brain.

Subarachnoid space is the space between the arachnoid mater and the pia mater in which cerebrospinal fluid (CSF) circulates. Cerebral blood vessels are located within the subarachnoid space.

Pia mater is the inner most meninx. This thin, soft and transparent layer is intimately associated with the neural tissue and is not distinguishable at the gross anatomical level. It gives the neural tissue a shiny appearance. Pia mater follows convulsions of the gyri and Sulci of the cerebral hemisphere.

BLOOD SUPPLY OF THE BRAIN

Arterial blood

Arterial blood reaches the brain from two sources:1. The internal coratid artery, which is a branch of the

common coratid artery that enters the cranium through the coratid canal. The artery reaches the base of the brain through either side of the sella turcica.

2. The vertebral artery is the first branch of the subclavian artery. It passes through the transverse foramina of cervical vertebrae to enter the cranium through the foramina magnum.

Circle of Willis

It is also called cerebral arterial circle. It is a circular anastomosis between the internal coratid and the vertebral arteries, which provide a continuous blood supply to the brain. It consists specifically named and communicating arteries.• Vertebral arteries enter the cranial cavity through the foramina magnum.• Basilar artery forms from the union of the vertebral arteries, and passes

over the ventral surface of the pons.• Posterior cerebral arteries are branches of the basilar arteries. They supply

the posterior of the brain.• Posterior communicating arteries are branches of the posterior cerebral

arteries.• Internal coratid arteries enter the cranium through the coratid canal.• Middle cerebral arteries are branches of the internal coratid arteries.• Anterior cerebral arteries are also branches of the internal coratid arteries.• Anterior Communicating artery connects the anterior cerebral arteries with

each other.

Venous BloodRoute of drainage of venous blood from the brain:• The cerebral veins carry deoxygenated blood from the brain into

the system of dural venous sinuses.• Dural venous sinuses form a network of channels formed between

the two layers of dura mater. Only the cranial dura mater contains sinuses and therefore the 2-layered regions are present only in the cranium.

• These sinuses receive venous drainage from the cerebral veins and ultimately carry the deoxygenated blood out of the cranium through the jugular foramina and into the internal jugular veins.

• The inner surface of the cranium has grooves formed by some of the dural venous sinuses.

• Some of the major structures in the cranial meninges are: superior sagittal sinus, transverse sinuses, jugular foramina and internal jugular vein.

CEREBRAL HEMISPHERES

• The Cerebral hemispheres are two convoluted masses of neural tissue separated in the midsagittal plane by the longitudinal fissure. In the whole brain, gently spread the longitudinal fissure and look from above to see the superior surface of the corpus callosum.

• Gray Matter of the cerebral hemispheres comprises the cerebral cortex. The cerebral cortex is made up primarily of neural cell bodies.

Gray MaterGyri are the ridges which rise between the sulci of the cerebral cortex. Two important gyri are:• The precentral gyrus which is located just anterior to the central sulcus. It is the

primary motor cortex and functions in conscious, voluntary movements of the skeletal muscles. Pyeramidal cells are a type of neuron located in the precentral gyrus.

• The Postcentral gyrus is located just posterior to the central sulcus. The postcentral gyrus is the primary somatosensory cortex. The postcentral gyrus receives sensory information from touch, pressure, pain, and temperature receptors

Sulci are conspicuous grooves etched in the cerebral cortex. Especially deep sulci are called fissures.• The central sulcus is a deep groove between the precentral and postcentral gyrus. It

separated the frontal and parietal lobes of the brain. • The lateral sulcus is a deep groove separating the parietal and frontal lobes from the

temporal lobe. The insula lobe of the brain is located deep to the lateral sulcus.

Lateral sulciConspicuous grooves

Longitudinal fissureSeparates the two hemispheres of the brain

Gyriridges

Lobes of the cerebral hemispheres1. The frontal lobe is anterior to the central sulcus. The posterior domain

of the precentral gyrus in the frontal lobe controls tasks as voluntary movement and learned motor skills. Motor control over muscles of the tongue and lips also resides in the frontal lobe. Areas in the anterior frontal lobe are involved in cognition, emotion and personality.

2. The parietal lobe is located between the central sulcus and the occipital lobe. It contains the primary sensory cortex and taste interpretation.

3. The occipital lobe is posterior to the parietal lobe. It contains the primary visual cortex and visual association area.

4. The temporal lobe is inferior to the lateral sulcus. The speech area is located in the temporal lobe.

5. The insula is located deep within the lateral sulcus, between the parietal and temporal lobes.

Occipital lobe

Frontal lobe

Temporal lobe

Parietal lobe

White matter of cerebral hemisphere

White matter is located in the deep regions of the cerebral hemisphere. It is made up of neuronal axons grouped in functionally related tracts that pass to other parts of the CNS.• Association tracts connect structures within a single

cerebral hemisphere.• Commissural tracts connects structures between the

two cerebral hemispheres e.g. The corpus callosum.• Projection tracts connects structures between one

cerebral hemisphere and spinal cord.

Structures within the cerebral hemisphere

Basal nuclei are nuclear masses of gray matter surrounded by white matter deep within the cerebral hemisphere. Nuclei are collections of nerve cell bodies within the CNS. They include:• Caudate nucleus• Globus pallidus• Putamen

Lateral ventricles are spaces within each cerebral hemisphere that are filled with cerebrospinal fluid (CSF). They are separated by the thin septum pellucidum layer. All ventricles contain Choroid pluxes, which is a collection of permeable capillaries overlain with a layer of ependymal cell. Choroid plexus is the tissue that produces CSF.

THE DIENCEPHALON

The diencephalon is also called the between brain.Consists mainly of two masses of nuclei i.e.1. Thalamus which is composed of two egg

shaped structures, each consisting of over a dozen individual nuclei. It is located just rostal (toward the nose) to the midbrain.

2. The Hypothalamus which is a bilaterally located group of nuclei lying inferior to the thalamus. It also forms part of the wall of the third ventricle.

Corpus callosum

Thalamus

1. The thalami function primarily as somatosensory relay station and send somatosensory information to the cerebral cortex for processing.

2. The thalami also form part of the walls of the third ventricle.

3. The intermediate mass is a connection between the two thalami across the third ventricle. This structure is not present in all people.

Intermediate mass

Pituitary gland

Pituitary gland

Hypothalamus

The hypothalamusHypothalamus controls release of a number of hormones, controls output of the ANS (sympathetic and parasympathetic divisions). It includes1. The Optic chiasm is formed by the decussation of fibers of

the optic nerve and is located inferior to the hypothalamus. The optic chiasm forms the anterior boundary of the hypothalamus

2. Hypothalamus is connected to the pituitary gland by the infundibulum. It is located along inferior aspect of hypothalamus.

3. The mammillary bodies are a pair of rounded nuclear masses located inferior to the hypothalamus. They resemble small peas and are part of the Limbic system. They function in the sense of smell.

The Third VentricleIt is a thin slit at the midline, formed between the thalamus and hypothalamus on both sides. It is connected to the lateral ventricle on each side by an interventricular foramen. It contains the choroid plexus for CSF production.

The Pineal GlandIt is a small, cone-shaped gland located posterior to the thalamus. It involved in control of sleep-wake cycles. It secretes the hormone melatonin.

Third Ventricle

Lateral ventricle

THE CEREBELLUM

• The cerebellum is located inferior to the posterior part of the cerebrum.

• It functions in posture, coordination and balance.

• White matter within the cerebellum branches extensively and is called the arbor vitae.

• The cerebellum has neural connections with the pons and medulla oblongata.

Cerebellum Processes skill memories

Arbor vitae

Corpus callosum

THE BRAINSTEM

• The brainstem is a lower brain region consisting of the midbrain, pons and the medulla oblongata.

• It is continuous superiorly with the thalamus and inferiorly with the spinal cord.

• The brainstem contains nuclei of cranial nerves III-XII.

• The Fibers of these same cranial nerves may be seen along the ventral surface of the brainstem.

Brain stemConsists pons, medulla oblongata and midbrain

Third Ventricle

The Midbrain

The mid brain is the portion of the brainstem inferior to the thalamus. It contains nuclei of the oculomotor and trochlear nerves. 1. The cerebral peduncles are columns of neural tissue consisting primary of

descending motor tracts. They form the neck of the midbrain and are located just above the pons and below the thalamus.

2. The substantia nigra is pigmented tissue located deep to the cerebral peduncles consisting of dopamine-producing cells.

3. The corpora quadrigemina are two pairs of rounded structures with nuclei involved in visual and auditory pathways. They are located along the dorsal aspect of the mid brain. Superior colliculi is involved in eye movements when tracking a moving object whereas the inferior colliculi is involved with head movement in response to auditory stimuli.

4. The cerebral aqueduct is a long tube-like structure connecting the third and fourth ventricles; located just ventral to the superior and inferior colliculi. CSF from third and fourth ventricles flows through the cerebral aqueduct.

The Pons

The pons is inferior to the midbrain. It contains nuclei of the trigeminal (V), abducens (VI) and facial (VII) nerves. It also includes projection fibers that make connections between various parts of the brain, especially the cerebellum.1. The basilar pons is a rounded ventral region made of

many nuclei and tracts.2. Cerebellar peduncles are 3-paired (superior, middle and

inferior) bundles of tracts, which pass to and from the cerebellum. The middle cerebellum is the largest.

3. The dorsal surface of the pons forms part of the ventral wall of the fourth ventricle.

Pons

Medulla Oblongata

The Medulla oblongata is inferior to the pons and contains the nuclei of the cranial nerves: vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII).1. The pyramids of the medulla are ventrally located columns

containing descending motor neurons. Crossing over of motor tracts causes voluntary movement on one side to be controlled by opposite side of the brain.

2. The medulla oblongata houses nuclei of the respiratory and cardiovascular control centers.

3. The dorsal surface of the medulla oblongata forms part of the ventral wall of the fourth ventricle as does the pons.

Medulla oblongata

The Fourth Ventricle

• The fourth ventricle is a triangle shaped space located posterior to the pons and medulla.

• It is connected to the third ventricle by the cerebral aqueduct.

• It contains choroid plexus and three foramina, which allow CSF to flow into subarachnoid space.

• These foramina are median aperture and two lateral apertures.

Fourth Ventricle

Cranial Nerves

• Cranial nerves originate from the brain and extend to peripheral organs.

• They contain sensory, motor or parasympathetic fibers, either singly or in some combination.

• They are located within the brainstem and the fibers of cranial nerves III-XII appear to emerge from the brainstem along its ventral and lateral surfaces.

Cranial Nerve Function

I – Olfactory Sensory – special sense of smell

II – Optic Sensory – special sense of sight

III – Oculomotor Motor

IV – Trochlear Motor

V - Trigeminal Both sensory & motor

VI – Abducens Motor

VII – Facial Both sensory & motor

VIII – Vestibulocochlear Sensory – special sense of hearing

IX - Glossopharyngeal Both sensory & Motor

X – Vagus Both sensory &motor

XI – Accessory Motor

XII – Hypoglossal Motor