university of manitoba brain stuff

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U of M - Medicine - Human Anatomy and Cell Science -

Anatomy of the Brain & Spinal Cord

Human Anatomy and Cell Science

Anatomy of the Brain & Spinal Cord

Reading resources:

Moore and Agur, pp 358 - 366, 446 - 465

Netter's Atlas, Figures 1 - 9, 96 - 103, 132 - 135

Objectives:

On specimens you should be able to:

1. Identify the major lobes and fissures of the brain.

Be able to state the function of the major lobes.

2. Identify the parts of the brain stem

3. Name and identify the three meninges of the brain

4. Identify the major blood vessels supplying the brain

5. Name and identify the major cranial nerves

6. Identify the spinal cord, spinal nerves and dorsal root ganglia.

__________________

The Brain

Before we get into the details of the gross features of the brain, note that the left and right sides appear anatomically

more or less the same. For the most part there are two of almost everything in the brain. Although the two sides look

the same, functionally they are different. For example, the left side of the brain controls movement of the right hand, and

the right side of the brain controls movement of the left hand. For most of us, the left side of the brain is the side

necessary for speech. Functionally, then, there are two brains, a right brain and a left brain.

Dorsal surface

We will study the top surface of the brain, the dorsal surface, separately from the bottom surface, the ventral surface.

We will also look at a brain that has been split into right and left sides, so that we can identify the structures on the

medial surface of the brain.

Lets begin by examining the dorsal surface of the brain. Identify the three major parts, the cerebrum, the cerebellum,

and the brain stem. Note that the two cerebral hemispheres are separated by a deep groove, the longitudinal fissure

rsi ty of Manitoba: U of M - Medicine - Human Anatomy and Cell Sc... http://www.umanitoba.ca/faculties/medicine/units/anatomy/jvbmrgr

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. On the floor of the

longitudinal fissure you will see a mass of tissue, the corpus callosum, connecting the two cerebral hemispheres. The

corpus callosum is easily seen on the medial surfaces of a brain that has been cut into two equal halves. The brain stem

is continuous with the spinal cord. When the brain was removed the spinal cord was cut just below the brain stem. The

cerebellum , as you

can see, is located on the dorsal surface of the brain stem.

The cerebral hemispheres consist of several lobes separated by fissures or grooves called sulci (sulci are the grooves

between the strange folds (gyri) of cerebral cortex. Now that we know what fissures, sulci, and gyri are, we can use

them as landmarks to identify the boundaries of the various lobes (Netter, 99). Find the lateral fissure (also known as


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the 6.Sylvian fissure)

, which separates the

frontal and temporal lobes. The cortex located deep in the Sylvian fissure is the insula (isle of Reil). You may need the

instructors help to find the 2. central sulcus , which separates the frontal and parietal lobes. On the dorsal surface of

the cortex the temporal lobe merges with the parietal lobe without a distinct groove between the two.

Look on the medial surface of the cortex to identify the parietooccipital fissure , which is the landmark separating the

parietal and occipital lobes. At the posterior margin of the temporal lobe you can find the preoccipital notch, a landmark

between the parietal and occipital lobes. On the dorsal surface of the cortex the anterior border of the occipital lobe is

an imaginary line from the parietooccipital fissure across the cortex to the preoccipital notch. As you can see, the cortex

of parietal and temporal lobes merge imperceptibly into the cortex of the occipital lobe. Also locate the calcarine

fissure on the medial surface of the occipital cortex.

Some functions can be localized to specific gyri of the brain. The precentral gyrus


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is the primary motor

cortex. The postcentral gyrus is the primary sensory cortex. The auditory cortex is located in the superior gyrus of the

temporal lobe. Motor speech requires an intact inferior frontal lobe. The visual cortex is located on the gyri bordering

the calcarine fissure . Follow the superior temporal gyrus to the gyrus in which it ends, the angular gyrus, a visual

association area. Damage to the angular gyrus results in the loss of the ability to read and write (alexia and

agraphia). Follow the lateral fissure to the gyrus in which it ends, the supramarginal gyrus , a sensory association

area. Damage to this gyrus results in the loss of the ability to recognize common objects (agnosia).

Meninges of the brain

The three membranes which cover the brain and spinal cord, the meninges, are the dura

, the arachnoid, and

the pia mater.

The dura consists of two layers, an outer layer, which forms a periosteum of the bones of the skull, and an inner layer

covering the brain. In many of the brain specimens the dura was left in the skull at the time the brain was removed. Try


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to find a specimen that has at least some of the dura attached to the brain.

Identify the following folds of the dura: There may be a skull prosection available in which the brain has been removed to

demonstrate the folds of dura.

1. the falx cerebri- a

fold formed from the inner layer of dura between the two cerebral hemispheres. Note that the falx encloses a venous

sinus, the superior sagittal sinus in the upper margin and the inferior sagittal sinus in the lower margin (Netter, 97).

2. the tentorium cerebelli - a fold of dura covering the cerebellum like a tent. Note that the transverse sinuses are

enclosed in the tentorium at its junction with the inner surface of the skull (Netter, 98). The junction of the superior

sagittal sinus and the transverse sinuses is the confluence of sinuses. Also note that the straight sinus is located at the

junction of the falx cerebri and the tentorium cerebelli. This sinus runs between the inferior sagittal sinus and theconfluence of sinuses.

3. the falx cerebelli - a fold of dura between the cerebellar hemispheres (Netter, 97).

The arachnoid is a thin transparent membrane covering the gyri of the brain. It does not extend into the sulci as does the

pia mater, which follows the contours of the sulci and gyri. You will notice that the cerebral veins are located deep to

the arachnoid membrane.

Ventral surface

Turn the brain over so that you can study the ventral, or basilar surface of the brain. Note that the frontal and temporal

lobes of the cerebrum make up a large portion of the basilar surface of the brain. Identify the frontal pole


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of the cerebrum, the

temporal pole and the occipital pole (Netter, 101). Identify also various parts of the brain stem visible from this point

of view. You can see the floor of the hypothalamus between the optic chiasm and the mamillary bodies . Note the

cerebral peduncles , part of

the midbrain. The previous photograph is of a brain in which the pons and medulla have been removed. Identify the

pons and the medulla on your specimen. On the surface of the pons and medulla you can observe the cranial nerves

and blood vessels as described below.

Cranial nerves

Now lets identify some of the major cranial nerves. The first cranial nerve is the olfactory nerve. You will not be able to

see this nerve in your brain specimen; however you should be able to identify the olfactory bulb , into which the fibers of

the olfactory nerve normally enter. You can also easily see the olfactory tract (Netter, 101).


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The second cranial nerve is the optic nerve (Netter, 101). Find the large optic nerves, the optic chiasm

and the optic tracts on the

specimen. Netter's atlas shows that the pituitary gland located just posterior to the optic chiasm. You will not see a

pituitary gland in your specimen. What happened to it? You should see the cut ends of the internal carotid arteries

(one on each side) posterior to the optic chiasm. The carotid arteries are one of the main sources of blood to the brain.

The oculomotor nerve can be identified in the interpeduncular fossa (Netter, 101, 108). If it has been torn off in your

specimen try another brain. The oculomotor nerve is one of 3 cranial nerves (III, IV and VI) that innervate the

extraocular muscles which control eye movement. The


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fourth cranial nerve, the trochlear

nerve is quite small and is often no longer intact in laboratory brain specimens. Look for the sixth cranial nerve, the

abducens nerve, at the pontomedullary junction.

The trigeminal nerve is easy to find - it is the largest of the cranial nerves. It exits the brain stem from the side of the

pons (Netter, 108).


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The facial nerve (cranial nerve VII) and the

vestibulocochlear nerve (cranial nerve VIII) can be found lateral to the abducens nerve at the angle between the

cerebellum, brainstem and pons. You may have difficulty distinguishing the two on your specimen.

To locate the remainder of the cranial nerves you will need to identify a bulge on the medulla named the olive. In the

groove anterior to the olive you can see rootlets that contribute to form the glossopharyneal nerve (CN IX), the vagus

nerve (CN X), and the spinal accessory nerve (CN XI). Don't spend a lot of time trying to distinguish these separate

nerves. In the groove posterior to the olive the rootlets forming the hypoglossal nerve (CN XII) can be found. This

important nerve supplies the muscles of the tongue.

Blood supply of the brain

There are two major sources of blood supply to the brain, the


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vertebral

arteries and the internal carotid arteries (Netter, 133).

On your specimen note that the two vertebral arteries combine at the junction of pons and medulla to form a single

artery, the basilar artery . The basilar artery has branches which supply the cerebellum, brain stem and part of the

cerebrum. Find the terminal branches of the basilar artery, the two posterior cerebral arteries (Netter, 132).

Now identify the internal carotid arteries (Netter, 132). Also find the two terminal branches of each internal carotid, the

anterior cerebral artery and the middle cerebral artery.

Note on your specimen that branches of the verterbral-basilar system are connected to branches of the internal carotid

system to form a 'traffic circle' for blood, the circle of Willis (Netter, 133).. The oculomotor nerve exits the

interpeduncular fossa between the posterior cerebral artery and the superior cerebellar artery.

Medial surface of the brain

Find a brain split in halves to review the medial surface


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of the brain.

Identify frontal, parietal, and occipital cortex and the corpus callosum. Also identify the cerebellum, the thalamus,

hypothalamus, pons and medulla (Netter, 100).

The ventricular system of the brain can also be studied in brain halves. Identify the location of the lateral ventricles

, the third ventricle,

the cerebral aqueduct and the fourth ventricle (Netter, 100, 102).

Now identify the anterior and posterior cerebral arter ies on half brains using the atlas (Netter, 135) as a guide. On the


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lateral surface of the brain identify the middle cerebral artery deep in the lateral fissure.

Prosection of spinal cord

Examine a prosection of the spinal cord in situ and study using the atlas (Netter 148). As you can see, the spinal cord

also has meninges, dura, arachnoid and pia mater. The meningeal layers that have been cut and reflected to expose the

cord are the dura and arachnoid. The pia mater closely follows the contours of the spinal cord. The space between the

dura and the vertebral canal is the epidural space. The space between arachnoid and the spinal cord is the subarachnoid

space.

Identify on the specimen the (http://www.umanitoba.ca/faculties/medicine/anatomy/bmr/graphics/cervical%20cord.html)


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identify the dorsal and ventral roots of one of the spinal nerves, as well as the dorsal root ganglion (Netter, 155, 156).

Note that the vertebral artery ascends lateral to the spinal cord through the vertebral foramina of the cervical

vertebrae. The spinal cord ends as the conus medullaris . You will note that the spinal nerves continue past the end

of the spinal cord as a group of nerve fibers referred to as the


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Review questions

1. Which lobes of the cerebral hemispheres contain the primary motor cortex?

2. Which lobes of the cerebral hemispheres contain the visual cortex?

3. Which lobes of the cerebral hemisphers contain the auditory cortex?

4. What is the function of the meninges?

5. What are the names of the dural folds which divide the cranial cavity?

6. Name the venous sinuses associated with the the falx cerebri and the tentorium cerebelli.

7. Tearing of cerebral veins at the point of entry into the dural venous sinuses would result in bleeding into which space?

8. Which cranial nerves control movement of the eyes via innervation of the extraocular eye muscles?

9. Which cranial nerve controls the muscles of facial expression?10. Name the terminal branches of the basilar artery.

11. What are the terminal branches of the internal carotid artery?

12. Which vessels make up the circle of Willis (circulus arteriosus cerebri)?

13. Which artery supplies most of the lateral surface of the cortex?

14. What are the cauda equina?

15. Which of the roots of a spinal nerve contains a sensory ganglion?

Answers:

1. frontal lobes

2. occipital lobes

3. temporal lobes

4. protect, support and nourish the CNS. They also contain venus sinuses.

5. falx cerebri, falx cerebelli, tentorium cerebelli, diaphragma sellae6. superior sagittal sinus, inferior sagittal sinus, superior petrosal sinus, transverse sinus, straight sinus

7. subdural space (resulting in a subdural hematoma)

8. cranial nerves III (oculomotor), IV (trochlear), and VI (abducens).

9. cranial nerve VII, the facial nerve

10. posterior cerebral arteries

11. anterior cerebral artery and middle cerebral artery

12. posterior cerebrals, posterior communicating arteries, middle cerebrals, anterior cerebrals, and anterior

communicating arter ies

13. the middle cerebral

14. A collection of spinal nerve roots caudal to the termination of the spinal cord.

15. the dorsal root

@copyright Dr. J. VriendDo not copy without permission.

Comments or questions may be directed to :Dr. J. Vriend(mailto:[email protected])

Department of Human Anatomy & Cell Science

Basic Medical Science Building, Rm130 - 745 Bannatyne Avenue

University of Manitoba, Winnipeg, MB R3E 0J9 Canada

Tel 204 789 3652 Fax 204 789-3920 Email [email protected]


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