Cerebrum excluding Limbic System, Basal Ganglia and Diencephalon

Question 1

[9-minute video]: anatomy of the Internal Capsule

Answer 1

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Question 2

[3-minute video]: cadaveric demonstration of the Circle of Willis

Answer 2

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Question 3

[13-minute video]: applied anatomy - Surgical Removal of Brain Tumor

Answer 3

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Question 4

Each cerebral hemisphere has three poles, three surfaces and three borders. List the three poles.

Answer 4

1. Frontal pole anteriorly
2. Occipital pole posteriorly
3. Temporal pole that lies between the frontal and occipital poles and points forward and downward

Question 5

List the three borders of the cerebral hemispheres.

Answer 5

1. Superomedial border
2. Inferolateral border (orbital part of this border is called superciliary border)
3. Inferomedial border, divided into:
   - an anterior part, medial orbital border
   - a posterior part, medial occipital border

Question 6

List the three surfaces of the cerebral hemisphere.

Answer 6

a) superolateral surface
b) medial surface
c) inferior surface (it is subdivided into orbital and tentorial surfaces by the stem of the lateral sulcus)

NOTE:
A little anterior to the occipital pole, the inferolateral border shows a slight indentation called the preoccipital notch (or preoccipital incisure).

Question 7

The surface of the cerebral cortex is highly convoluted into gyri and sulci. Sulci can be categorised into 4 categories. List them, giving examples.

Answer 7

1. Limiting sulcus: Such a sulcus separates two functionally different areas, e.g. central sulcus.
2. Axial sulcus: A sulcus growing in the long axis of a rapidly growing homogeneous area, e.g. posterior part of calcarine sulcus.
3. Operculated sulcus: A sulcus, which has one particular type of functional area on the surface and has another functional area in its depth, which is concealed, e.g. posterior part of calcarine sulcus which has primary visual area in its depth and has peristriate and parastriate areas which are secondary visual areas on the surface.
4. Complete sulcus: A sulcus, which is deep enough to produce an elevation on the ventricular wall, e.g. collateral sulcus which produces collateral eminence in the floor of the inferior horn of lateral ventricle.

Question 8

What are some of the key sulci?

Answer 8

✓ median longitudinal fissure, separating the two cerebral hemispheres (remember the dural fold that goes through it?)
✓ Rolandic fissure (central sulcus)
✓ Sylvian fissure (lateral sulcus)
✓ parieto-occipital sulcus (on the surface it gives a parietoccipital notch)

NB: You can identify the central sulcus since it’s the most continuous sulcus from medial to lateral.

Question 9

State the 4 major lobes of the cerebral cortex.

Answer 9

(a) Frontal lobe:
Extents:
Anteriorly - frontal pole
Posteriorly - central sulcus
Laterally - lateral sulcus
Medially - longitudinal fissure

(b) Temporal lobe (it’s inferior to the lateral sulcus)
(c) Parietal lobe: extends from the central sulcus to an imaginary line joining pre-occipital notch to parietoccipital notch
(d) Occipital lobe

Question 10

What are the 2 other “special” lobes?

Answer 10

1. The insula or insular lobe (island of Reil) is an area of the cortex that lies deep to the lateral sulcus and is hence hidden from the surface view. You’ll have to retract the frontal, parietal and temporal opercula to view it.
2. The limbic lobe is a part of limbic system, forming a border (Limbus = Border) between telencephalic and diencephalic structures and comprising of cingulate, subcallosal and parahippocampal gyri. The limbic lobe is seen on the medial and inferior surfaces of the cerebral hemisphere.

Question 11

Generally, the cerebrum can be divided into 2 parts. Name them.

Answer 11

(a) Cerebral hemispheres (which consist of):
✓ cerebral white matter
✓ cerebral cortex
✓ basal nuclei/basal ganglia
(b) Diencephalon

Question 12

This card shows labelled cadaveric images of the gyri of the superolateral surface of the cerebral hemisphere. Click Answer to view them.

Answer 12

[Diagram 1] [Diagram 2]

Question 13

Primary Motor Cortex
1. Brodmann number
2. location
3. fibres that arise from this area
4. function
5. effect of lesion

Answer 13

(1) Area 4 of Brodmann
(2) precentral gyrus on the superolateral surface and on the anterior part of the paracentral lobule on the medial surface of the cerebral hemisphere
(3) [about 40% of] pyramidal fibres (corticospinal and corticonuclear)
(4) execution of voluntary movements
(5) spastic paralysis of the extremeties of the opposite half of the body (contralateral hemiplegia)

Further notes:
☛ Cortical control is mainly contralateral except for; muscles of the upper part of the face, tongue (genioglossus), mandible, larynx, pharynx, and axial musculature.
☛ The paracentral lobule is located on the medial surface of the cerebral hemisphere, and includes parts of both the frontal and parietal lobes. It is the medial continuation of the precentral and postcentral gyri. It has motor and sensory functions related to the lower limb.
☛ Spastic paralysis refers to a state of increased muscle tone leading to muscle stiffness and involuntary spasms. It is usually caused by damage to the part of the brain or spinal cord that controls voluntary movement. This damage can result in an imbalance in the signals that tell the muscles to contract or relax, causing the muscles to become tight and hard.

Question 14

1. What is the cerebral cortex?
2. What are three types of functional areas found in the cerebral cortex?

Answer 14

1. The cerebral cortex is the surface layer of grey matter covering the cerebral hemisphere.
2. Motor areas, sensory areas, association areas

Question 15

Premotor Cortex
1. Brodmann number
2. location
3. function
4. effect of lesion

Answer 15

1. Area 6 of Brodmann
2. anterior to the primary motor area in the posterior parts of superior, middle, and inferior frontal gyri and extends on to the medial surface of the hemisphere
3. programming and fine-tuning of voluntary movements
4. deficits in contralateral fine motor control

Question 16

Frontal Eye Field
1. Brodmann number
2. location
3. function
4. effect of lesion

Answer 16

1. Area 8 of Brodmann
2. posterior part of middle frontal gyrus
3. conjugate movement of the eyes to the opposite side [in the sense that one turns medially and the other laterally] (horizontal conjugate gaze)
4. deviation of the eye towards the side of the lesion

Further notes:
Conjugate eye movements: refers to the motor coordination of the eyes that allows for bilateral fixation on a single object. In other words, it’s a movement of both eyes in the same direction to maintain binocular gaze.
Diplopia: Double vision, which is also called diplopia, causes people to see two of the same image—whether horizontal, vertical or diagonal—instead of one. Sometimes double vision can just be an irritating but benign problem called strabismus.

Question 17

Motor Speech Area of Broca
1. Brodmann number
2. location
3. function
4. effect of lesion

Answer 17

1. Area 44 and 45
2. inferior frontal gyrus of the frontal lobe of the dominant hemisphere [i.e. the left hemisphere in right handed and most left handed individuals]; specific areas of the inferior frontal gyrus: pars triangularis (area 45) and pars opercularis (area 44)
3. motor speech
4. expressive aphasia aka. Broca’s aphasia: loss of the ability to produce proper speech. The patient faces difficulty in finding the right words to express what they wish to say but they can understand what others say. [Video]

Further notes:
✓ The inferior frontal gyrus is divided into 3 parts: pars opercularis, pars triangularis, and pars orbitalis. Click here for a diagram.
✓ Broca’s area is present ONLY on the dominant hemisphere.

Question 18

Supplementary Motor Cortex
1. Brodmann’s number
2. Location
3. Function
4. Effect of lesion

Answer 18

1. Areas 4, 6, and 8 of Brodmann (medial aspect)
2. Medial frontal gyrus
3. Coordinating bilateral movements and voluntary movements that are time based i.e. with temporal sequence e.g. riding a bike or signing signatures
4. Motor deficits

Question 19

Prefrontal cortex
1. Brodmann number
2. Location
3. Function
4. Effect of lesion

Answer 19

1. Areas 9, 10, 11, 12, 46 and 47 of Brodmann
2. Frontal pole: the part of the frontal lobe excluding the motor and premotor areas (includes the parts of the frontal gyri anterior to the premotor area, the orbital gyri, most of the medial frontal gyrus)
3. Higher “cognitive” functions e.g. thinking, reasoning, intelligence, memory
4. Impaired cognition

Further notes:
✓ Unlike Broca’s area, prefrontal cortex is bilaterally represented.
✓ This area is concerned with the individual’s personality. It exerts its influence in determining the initiative and judgement of an individual.
✓ It is also concerned with depth of emotions, social, moral and ethical awareness, concentration, orientation, and foresightedness.
✓ Another effect of lesion is Phineas Gage syndrome.

Question 20

Briefly discuss Phineas Gage syndrome.

Answer 20

This syndrome is characterized by uninhibited, impulsive and socially unacceptable behaviour as well as poor decision making. It is as a result of lesions in the cortex of the frontal lobe.

Further reading:
Phineas Gage Syndrome refers to the set of alterations observed in Phineas Gage, an American railroad construction foreman, after he survived a severe brain injury. In 1848, a large iron rod was driven completely through his head during an accident, destroying much of his brain’s left frontal lobe. Remarkably, Gage survived the accident, but his personality and behaviour reportedly changed significantly.

Question 21

State other functions of the frontal lobe other than those performed by the primary motor, premotor, frontal eye field, Broca’s area, supplementary motor, and prefrontal cortices.

Answer 21

• perceives taste sensations (primary gustatory cortex, hidden by frontal and parietal opercula)
• limbic functions: part of the limbic lobe is in the frontal lobe
• autonomic functions

Question 22

Primary Sensory Cortex/Primary Somatosensory Cortex
1. Brodmann number
2. location
3. function
4. it receives projections from which nuclei of the thalamus?
5. effect of lesion

Answer 22

1. Areas 3, 1 and 2 of Brodmann
2. postcentral gyrus and extends into the posterior part of the paracentral lobule on the medial surface of the hemisphere
3. The primary sensory area is concerned with the perception of exteroceptive (pain, touch, and temperature) and proprioceptive (vibration, muscle, and joint sense) sensations from the opposite half of the body.
4. ventral posterolateral and ventral posteromedial nuclei [which convey impulses received through the medial, spinal and trigeminal lemnisci]
5. loss of appreciation of exteroceptive and proprioceptive sensations from the opposite half of the body (contralateral anaesthesia)

Question 23

Somatosensory Association Area
1. Brodmann’s number
2. Location
3. Function
4. Effects of lesion

Answer 23

1. Area 5 and 7
2. Superior parietal lobule
3. Recognition of general sensations perceived by the primary somatosensory cortex.
4. Sensory agnosia: occurs when dominant hemisphere is affected, so one won’t be able to recognise sensations from the environment
   Self-neglect: occurs when the non-dominant hemisphere is affected, so one won’t be able to recognise self

Question 24

Wernicke’s area/Wernicke’s sensory speech area
1. Brodmann’s numbers
2. Location
3. Function
4. Effect of lesion

Answer 24

1. Areas 39 and 40 of parietal lobe, area 22 of temporal lobe
2. Supramarginal gyrus (area 40), angular gyrus (area 39) and superior temporal gyrus (area 22)
3. Understanding of speech, i.e. interpretation of language (both spoken and written)
4. Receptive aphasia (aka. Wernicke’s aphasia/Fluent aphasia): one is able to speak well and use long sentences, but what they say may not make sense [Click here for a video]

Note:
The Wernicke’s area is connected to the Broca’s area by a bundle of nerve fibres called arcuate fasciculus.

Question 25

Primary Gustatory Cortex
1. Broadmann’s number
2. Location
3. Function
4. Effect of lesion

Answer 25

1. Area 43
2. Parietal operculum
3. Perception of taste
4. Loss of taste sensation (ageusia)

Further notes:
☛ The parietal lobe perceives and recognizes all sensations except vision, smell and hearing.
☛ The parietal operculum is a part of the brain that covers the upper part of the insular cortex, which is a region involved in various functions such as emotion, perception and self-awareness. The parietal operculum is located between the inferior part of the postcentral gyrus and the posterior branch of the lateral sulcus.

Question 26

What is the homunculus?

Answer 26

It is a graphical representation of the whole body on the pre-central and post-central gyri.
Diagram: Homonculus

(Note that some body regions are given a larger surface area on the homunculus based on the functions. Also note that the lower part of the body is represented medially, the upper part more laterally. That is very important when discussing effects of arterial injury to the cortex.)

Question 27

Primary Visual Cortex
1. Brodmann number
2. Location
3. Function
4. Effect of lesion

Answer 27

1. Area 17
2. Banks of calcarine sulcus (these are just very close to the calcarine sulcus, but part of the cuneal and lingual gyri) and around occipital pole
3. Perception of light input
4. Anopia (blindness)

Question 28

The Primary Visual Cortex is also known as the ________ cortex.

Answer 28

striate

Question 29

Visual Association Cortex
1. Brodmann’s number
2. Location
3. Function
4. Effect of lesion

Answer 29

1. Areas 18 and 19
2. Cuneal gyrus (cuneus) (on posteromedial surface), lingual gyrus (on posteromedial surface), superior and inferior occipital gyri (on posterolateral surface) [Additional image]
3. Recognition of light input
4. Visual agnosia: an impairment in recognizing visually presented objects despite having normal vision

[NB: Rays that land on the occipital pole come from that of the central visual field/macular vision.]

Further notes:
~ Cuneus vs Occipital gyri: The occipital gyri and the cuneus are different parts of the occipital lobe of the brain. The occipital gyri are three gyri on the lateral surface of the occipital lobe, separated by the superior and inferior occipital occipital sulci. The cuneus is a wedge-shaped area on the medial surface of the occipital lobe, bounded by the parieto-occipital sulcus and the calcarine sulcus.

Question 30

Choose the correct answer:
On the superolateral surface of the cerebrum, which sulcus limits the primary visual area?
A. Calcarine
B. Parieto-occipital
C. Lunate
D. Lateral occipital

Answer 30

Choice C: Lunate sulcus

Question 31

Primary Auditory Cortex
1. Brodmann’s number
2. Location
3. Function
4. Effect of lesion

Answer 31

1. Areas 41 and 42
2. Transverse temporal gyri (both anterior and posterior)/Transverse gyri of Heschl
3. Perception of sound
4. Hearing loss

Question 32

Primary olfactory cortex
1. Brodmann’s number
2. Location
3. Function
4. Effect of lesion

Answer 32

1. Areas 28, 34
2. Parahippocampal gyrus [with the uncus (area 34) and entorhinal cortex (area 28)]
3. Perception of smell
4. Anosmia

Question 33

Anterior, middle and posterior cerebral arteries give origin to two types of branches. Name them.

Answer 33

1. Central branches
2. Cortical branches

Question 34

What is the recurrent artery of Heubner, and what is its clinical significance?

Answer 34

Recurrent branch of the anterior cerebral artery (also called the recurrent artery of Heubner) is one of the anteromedial group of arteries. It supplies the caudate nucleus, anterior limb and genu of the internal capsule. Thrombosis in the artery of Heubner results in contralateral paralysis of the face and upper extremity (faciobrachial monoplegia).

Question 35

Discuss Charcot’s artery of cerebral haemorrhage.

Answer 35

One of the lateral striate arteries (lenticulostriate arteries) is usually larger than the others. It is called Charcot’s artery of cerebral haemorrhage. Rupture of this artery, in elderly hypertensive individuals, results in loss of blood supply to internal capsule leading to contralateral spastic hemiplegia, paralysis of lower half of face and altered sensorium (due to involvement of genu and posterior limb of internal capsule).

Further notes:
~ The internal capsule is a two-way tract for the transmission of information to and from the cerebral cortex. It lies in the inferomedial portion of each cerebral hemisphere. On transverse sections of the brain, the internal capsule is a V-shaped structure with the apex pointing medially.
~ What is altered sensorium? This is a medical condition characterized by the inability to think clearly or concentrate.

Question 36

What are cortical branches of cerebral arteries?

Answer 36

Cortical branches ramify on the surface of the cerebral hemispheres and supply the cortex. They give off branches that run perpendicularly into the substance of the cerebral hemisphere. Some of these are short and end within the grey matter of the cortex. Others are longer and penetrate into the subjacent white matter.

Question 37

While cortical branches may anastomose with each other on the surface of the brain, the perpendicular branches (both long and short) behave as terminal or end arteries. What is the clinical significance of this information?

Answer 37

Each branch supplies a limited area of brain tissue and does not anastomose with neighboring arteries. As a result, blockage of such a branch leads to death (necrosis) of brain tissue in the region of supply.

Question 38

a) Briefly describe the course of the anterior cerebral artery.
b) State its cortical branches and areas of supply.

Answer 38

a) This artery arises from the internal carotid artery below the anterior perforated substance as one of the terminal branches and lateral to the optic chiasma. It crosses the optic chiasma to reach the median longitudinal fissure. At the anterior end of the longitudinal fissure, the anterior communicating artery connects the right and left anterior cerebral arteries. Inside the longitudinal fissure, the anterior cerebral artery winds around the genu of the corpus callosum and then runs posteriorly on the superior aspect of the body of corpus callosum.

b)
* Orbital branches: Supply olfactory system and medial
half of orbital surface of frontal lobe
* Frontopolar branch: Supplies frontal pole
* Callosomarginal branch: Supplies medial frontal gyrus, paracentral lobule and precuneus
* Pericallosal branch: Supplies corpus callosum and cingulate gyrus

Question 39

a) Briefly describe the course of the middle cerebral artery.
b) State its cortical branches and areas of supply.

Answer 39

a) It is one of the terminal branches of the internal carotid artery. It turns laterally on the anterior perforated substance to enter the stem of the lateral sulcus, where it divides into four to five cortical branches.
b)
Branches to frontal lobe:
* Orbitofrontal branch: Supplies lateral half of orbital
surface of frontal lobe
* Pre-Rolandic or precentral branch: Supplies
premotor area and Broca’s area (in left cerebral cortex)
* Rolandic or central branch: Supplies primary motor
cortex and primary sensory cortex

Branches to parietal lobe:
* Anterior parietal branch: Supplies anterior part of
parietal lobe
* Posterior parietal branch: Supplies posterior part of
parietal lobe and anastomoses with posterior cerebral artery to supply macular region of visual field of occipital lobe

Branches to temporal lobe:
* Anterior temporal branch: Supplies temporal pole
and anterior part of temporal lobe
* Posterior temporal branch: Supplies posterior part
of temporal lobe and Wernicke’s area (in left cerebral cortex)

Question 40

a) Briefly describe the course of the posterior cerebral artery.
b) State its cortical branches and areas of supply.

Answer 40

a) The right and left posterior cerebral arteries are the terminal branches of basilar artery. Each passes laterally around the crus cerebri of the midbrain, where it receives the posterior communicating artery. It continues along the lateral aspect of the midbrain and enters the supratentorial compartment through the tentorial notch. Then, it courses on the tentorial surface of the brain giving out its branches.

b)
* Temporo-occipital branch: Supplies inferior surface of temporal lobe and lateral surface of the occipital lobe
* Internal occipital branch: Divides into parieto-occipital branch and calcarine branch and supplies cuneus and the rest of medial surface of the occipital lobe

Question 41

The anterior cerebral artery has three segments: A1, A2 and A3. State the extents of each segment.

Answer 41

A1 segment: from internal carotid artery to anterior communicating artery
A2 segment: from end of A1 upto where it divides into pericallosal and callosomarginal arteries
A3 segment: also termed the pericallosal artery, is one of the (or the only) main terminal branches of the ACA, which extends posteriorly in the pericallosal sulcus to form the internal parietal arteries (superior, inferior) and the precuneal artery.

Question 42

The middle cerebral artery has 4 segments; M1, M2, M3 and M4. State the extents of each segment.

Answer 42

M1: from its origin upto the Sylvian fissure
M2:
M3:
M4: cortical branches of middle cerebral artery

Question 43

The posterior cerebral artery has three segments, P1, P2, and P3. State the extents of each segment.

Answer 43

P1: from basilar artery bifurcation up to where it gives the posterior communicating artery
P2: from PComA to origin of inferior temporal arteries (goes around and under midbrain)
P3: the part of the artery that runs through the quadrigeminal cistern. It often divides into its two terminal branches, the calcarine and parieto-occipital arteries between.

Question 44

State the effects of unilateral occlusion of anterior cerebral artery.

Answer 44

✈ Contralateral monoplegia of lower limb—involvement of the upper part of the motor area [since in the homonculus, lower limb is represented on the medial surface, and MCA supplies the lateral surface while medial surface of homonculus is supplied by ACA]
✈ Contralateral anaesthesia of lower limb—involvement of the upper part of the sensory area
✈ Astereognosis—involvement of superior parietal lobule

Astereognosis - inability to know and tell what you’re holding is a 3D object

Question 45

State the effects of occlusion of one anterior cerebral artery when only one anterior cerebral artery is present [i.e. unpaired ACA].

Answer 45

• Personality changes, i.e. attention deficit, difficulty in planning, emotional lability, (excessive emotional reactions and frequent mood changes), inappropriate social behaviour, apathy, abulia (loss of willpower)—involvement of prefrontal cortex
• Uninhibited bladder—involvement of medial frontal cortex
• Cortical paraplegia—involvement of paracentral lobule

Check out the various forms of paralysis here.

Question 46

State the effects of occlusion of middle cerebral artery.

Answer 46

• Contralateral hemiplegia and loss of sensations (the face and arms are most affected while lower limb shows slight weakness due to cerebral oedema that is associated with a large infarct)—involvement of primary motor and somatosensory cortex
• Astereognosis or tactile agnosia—involvement of somatosensory association area
• Hearing may be slightly affected in both ears—involvement of primary auditory area
• Aphasia, if the thrombosis is in the left hemisphere—involvement of Broca’s, Wernicke’s areas and/or involvement of arcuate fasciculus connecting the two areas
• Aprosodia (prosody means rhythm, pitch, stress, intonation of speech), if the thrombosis is in the right hemisphere—involvement of similar areas of right hemisphere
• Word deafness/auditory verbal agnosia—involvement of auditory association area of left side
• Acalculia, anomia, finger agnosia, left-right confusion—involvement of left inferior parietal lobule
• Left hemineglect, construction apraxia, dressing apraxia, anosognosia (unaware of the existence of the disability)—involvement of right inferior parietal lobule

Further notes:
Apraxia - inablity of someone to perform skilled movements even though the person desires and is willing to do them.
Astereognosis is used to describe both the inability to discriminate shape and size by touch and the inability to recognize objects by touch.
Aprosodia is a deficit in comprehending or expressing variations in tone of voice used to express both linguistic and emotional information.

Question 47

State the effects of occlusion of posterior cerebral artery.

Answer 47

• Contralateral homonymous hemianopia with macular sparing—involvement of primary visual area
• Visual hallucinations, distortion of colour vision—involvement of visual association area
• Pure word blindness/alexia—involvement of visual association area of left hemisphere
• Peripheral visual loss with macular sparing/Gun-barrel vision—bilateral involvement of primary visual area

[Point to consider: If PCA is occluded, the person may end up having tunnel vision. Why not anopia instead? (Hint: dual blood supply of the occipital pole)]

Question 48

The veins of the cerebral hemisphere consists of two sets; superficial and deep. List the superficial veins of the cerebrum on the superolateral surface, stating where each drain into.

Answer 48

Superior cerebral veins - Superior sagittal sinus
Superficial middle cerebral vein
Anteriorly, cavernous sinus
Posteriorly, superior anastomotic vein (of Trolard) to superior sagittal sinus
Posteriorly, inferior anastomotic vein (of Labbe) to transverse sinus
Inferior cerebral veins - Transverse sinus, straight sinus, superior petrosal sinus, cavernous sinus

(Refer to Indebir Neuroanatomy p.g. 252 for a good diagram on the same)

Question 49

The superficial veins at the base of the cerebral hemisphere are the basal veins.
a) What two veins unite to form the basal veins?
b) The basal veins drain into which vein?

Answer 49

a) anterior cerebral vein and deep middle cerebral vein
b) great cerebral vein (of Galen)

Question 50

a) What comprises the deep veins of the cerebral hemisphere?
b) All the deep veins drain into their corresponding ________ vein.
c) Two ________ veins join to form the great cerebral vein of Galen, which drains into straight sinus.

Answer 50

(a) septal, choroidal and thalamostriate veins on each side
(b) internal cerebral
(c) internal cerebral
(d) [Diagram for reference]

Question 51

Lateralisation of cerebral hemispheres
[Important for understanding, but just rate it a 5 … don’t stress 😎 …]

a) The two cerebral hemispheres show bilateral asymmetry both in structure and function. Give examples of bilateral asymmetry in structure and in function.
b) Functional specialization has been studied in split-brain patients (who had corpus callosotomy due to severe epilepsy). New methods that allow in vivo comparison of the two hemispheres in normal individuals include __________(a)__________ and __________(b)__________.
c) What functions are lateralised to what hemisphere?
d) What are the functional and evolutionary advantages of lateralisation?

Answer 51

a) Structurally, the posterior ramus of lateral sulcus generally is longer in the left hemisphere (planum temporale) than in the right hemisphere.
Functionally, Broca’s area and Wernicke’s area are located in the left cerebral hemisphere in almost all right-handed individuals and most left-handed as well.

b)
(a) positron emission tomography (PET)
(b) functional magnetic resonance imaging (fMRI).

c)
- Language functions such as grammar, vocabulary, and literal meaning are typically lateralized to the left hemisphere.
- The rhythm, stress, intonation of speech, the emotional state of the speaker, the presence of irony or sarcasm, emphasis, contrast and focus (all together called prosody), are comprehended and expressed by the right hemisphere.
- Arithmetic ability (numerical calculation) and fact retrieval are associated with left hemisphere.
- Geometric understanding, facial perception, and artistic ability (including music) are predominantly right- sided.
- Analytical, sequential, and logical thinking are by left hemisphere.
- Synthetic, spatial and creative thinking (lateral thinking/thinking out-of-the-box) are predominantly by the right hemisphere.

d)
The functional advantage of lateralization allows each hemisphere to hone its specialization rather than be a jack-of-all-and-master-of-none.
The evolutionary advantage of lateralization comes from the ability to perform separate parallel tasks, simultaneously, in each hemisphere of the brain. (Put all the eggs in one basket and watch that basket!)

Question 52

Brodmann numbers and gyri:
a) Primary Visual Cortex
b) Visual Association Cortex

Answer 52

a) 17; banks of calcarine sulcus and occipital pole
b) 18 and 19; cuneal gyrus, lingual gyrus, superior and inferior occipital gyri

Question 53

Outline the blood supply of the superolateral surface of the cerebral hemisphere.

Answer 53

The greater part of the superolateral surface is supplied by the middle cerebral artery. Areas not supplied are as follows:
1. A strip half to one inch wide along the superomedial border, extending from the frontal pole to the parieto-occipital sulcus is supplied by the anterior cerebral artery.
2. The area belonging to the occipital lobe is supplied by the posterior cerebral artery.
3. The inferior temporal gyrus (excluding the part adjoining the temporal pole) is also supplied by the posterior cerebral artery.
4. [Diagram]

Question 54

Outline the blood supply of the medial surface of the cerebral hemisphere.

Answer 54

1. Most of the medial surface (anterior 2/3rd) is supplied by the anterior cerebral artery. The region of cerebral cortex supplied includes the parts of motor and sensory areas (paracentral lobule) concerned with perineum, leg, and foot.
2. Temporal pole of the temporal lobe is supplied by the middle cerebral artery.
3. Occipital lobe is supplied by the posterior cerebral artery. The area supplied includes the visual cortex.
4. [Diagram]

Question 55

Outline the blood supply of the inferior surface of the cerebal hemisphere.

Answer 55

1. The lateral part of the orbital surface is supplied by the middle cerebral artery and the medial part by the anterior cerebral artery.
2. The tentorial surface is supplied by the posterior cerebral artery. The temporal pole is, however, supplied by the middle cerebral artery.
3. [Diagram]

Question 56

What artery is:
(a) least likely to cause olfactory disturbance?
(b) most likely to cause split brain syndrome?
(c) most likely to cause motor aphasia?

Hints:
📝 split brain syndrome: a condition involving a cluster of neurological abnormalities caused by partial or complete severing or lesioning of the coropus callosum
📝 motor aphasia: the inability to speak or to recognize the muscular movements of speech

Answer 56

(a) Middle Cerebral Artery
(b) Anterior Cerebral Artery
(c) Middle Cerebral Artery

Question 57

Brodmann numbers and gyri
(a) Wernicke’s Area
(b) Primary Auditory Cortex

Answer 57

(a) Areas 39 (angular gyrus) and 40 (suparamarginal gyrus) of temporal lobe and area 22 (superior temporal gyrus) of parietal lobe
(b) 41 and 42; transverse temporal gyri

[Note the sequence: 22, 39, 40, 41, 42 … 😁]

Question 58

The interior of each cerebral hemisphere consists of a core of white matter, which is composed of myelinated nerve fibres. The fibres of white matter are classified into three types. Name them.

Answer 58

1. association fibres
2. commissural fibres
3. projection fibres

Question 59

What are association fibres?

Answer 59

These are white matter fibres that connect different parts of the cerebral cortex of the same hemisphere to each other.

Question 60

State the two types of association fibres.

Answer 60

1. Short association fibres, which connect the adjacent gyri to each other
2. Long association fibres, which connect the gyri located at a distance from each other

Question 61

List the long association bundles (fibres).

Answer 61

1. Cingulum: located within the cingulate gyrus. It extends from the paraterminal gyrus to the uncus. The cingulum is part of the Papez circuit of the limbic system.
2. Uncinate fasciculus: a curved fibre bundle. It connects the inferior frontal gyrus and the orbital gyri of the frontal lobe to the hippocampus and amygdaloid nucleus of the temporal lobe. Thus, it connects the limbic areas of the cerebral hemispheres.
3. Superior longitudinal fasciculus: long bundle that begins in the frontal lobe and arches back via the parietal lobe to the occipital lobe, from where it turns into the temporal lobe. Thus, it connects the occipital lobe to the frontal eye field. (The arcuate fasciculus is a bundle of axons that forms part of the superior longitudinal fasciculus that connects temporal lobe and the frontal lobe. Thus, it connects the sensory and motor speech areas to each other in the dominant hemisphere).
4. Inferior longitudinal fasciculus: connects the occipital lobe to the temporal lobe.
5. Fronto-occipital fasciculus: connects frontal to occipital and temporal lobes. It is lateral to caudate nucleus, lies medial to the superior longitudinal fasciculus and is separated from it by corona radiata.
6. Perpendicular fasciculus: connects the parietal lobe to the occipital lobe and the posterior part of temporal lobe.
7. [Cadaveric image 1] [Cadaveric image 2] [Cadaveric image 3]

Question 62

What are commissural fibres?

Answer 62

These are white matter fibres that ross the midline and connect functionally identical parts of the two hemispheres.

Note: Not all fibres crossing from one side of the brain or spinal cord to the opposite side are commissural fibres. When fibres originating in a mass of grey matter in one-half of the central nervous system (CNS) end in some other mass of grey matter in the opposite half, they are referred to as decussating fibres, and the sites where such crossings take place are referred to as decussations.

Question 63

State the important commissures in the cerebrum.

Answer 63

• The corpus callosum is the largest commissure of the brain connecting various parts of neocortex of both the hemispheres.
• The anterior commissure connects the right and left temporal lobes. It is in the shape of a cupid’s bow. It crosses the midline in the upper part of the lamina terminalis anterior to the columns of fornix.
• The habenular commissure is located in the superior lamella of the pineal stalk and is a part of epithalamus. It connects the habenular nuclei of both sides.
• The posterior commissure is located in the inferior lamella of the pineal stalk and is a part of brainstem. It connects the nuclei of III, IV, VI and VIII cranial nerves.
• The hippocampal commissure or commissure of fornix connects the hippocampus of the two sides to each other.

Question 64

Name the parts of the corpus callosum.

Answer 64

✓ rostrum (prolongation from the genu to the upper end of lamina terminalis) (ACA)
✓ genu (anterior part of corpus callosum) (ACA)
✓ trunk/body (central part) (ACA)
✓ splenium (posterior bulbous part) (PCA)

✓ [Diagram]: parts of the corpus callosum in sagittal view
✓ [Diagram]: forceps minor and forceps major of the corpus callosum (transverse section)

Question 65

Corpus callosum may be surgically divided in cases of intractable epilepsy. State the anatomical basis for this surgery.

Answer 65

To disconnect the transfer of impulses from an irritable focus of one cerebral hemisphere to another.

Question 66

What are projection fibres?

Answer 66

These are cerebral white matter fibres connecting the cerebral cortex to subcortical regions by corticopetal/ascending and corticofugal/descending fibres.

Question 67

Briefly discuss Gerstmann’s syndrome.

Answer 67

This syndrome is caused by a lesion affecting the angular gyrus, such as in occlusion of the middle cerebral artery. The primary symptoms of Gerstmann’s are:
☯︎ Dysgraphia/agraphia: a deficiency in the ability to write
☯︎ Dyscalculia/acalculia: difficulty in learning
☯︎ Finger agnosia: inability to distinguish the fingers of the hand
☯︎ Left-right disorientation
☯︎ Wernicke’s aphasia: difficulty in expressing oneself when speaking, in understanding speech, or in reading and writing