Meninges and Cerebral Hemispheres

Question 1

What spaces do the meninges separate?

Answer 1

epidural space,subarachnoid space, and thesubdural space

Question 2

What is the epidural space?

Answer 2

The epidural space is a potential space located between the inner surface of the skull and the tightly adherent dura. Themiddle meningeal arteryenters the skull through the foramen spinosum and runs between the dura and the skull. Injury to this artery can result in an acuteepidural hematoma

Question 3

What is the subdural space?

Answer 3

The subdural space is also a potential space between the inner layer of the dura and the loosely adherent arachnoid mater. The bridging veins traverse the subdural space to drain into the several largedural venous sinuses. Disruption of the bridging veins is the principal cause ofsubdural hematoma

Question 4

What is the subarachnoid space?

Answer 4

The space between the arachnoid and pia is called the subarachnoid space, which is filled withcerebrospinal fluid. In addition, the major arteries of the brain also run within the subarachnoid space, and rupture of an aneurysm of these major arteries in the subarachnoid space may causesubarachnoid hemorrhage

Fluid filled space between pia mater and arachnoid mater
Web like arachnoid trabeculae pass between arachnoid mater and pia mater

Question 5

What is the external periosteal layer of dura mater?

Answer 5

Formed by periosteum
Adheres to internal surface of skull

Fused internal and external layers can be easily stripped from the cranial bones, and a blow to the head can detach the periosteal layer from the calvaria without fracturing the cranial bones

Question 6

What is Internal Meningeal layer of dura mater?

Answer 6

Strong fibrous membrane
Continuous at foramen magnum with spinal dura mater
Fused with periosteal layer and cannot be separated from it

Fused internal and external layers can be easily stripped from the cranial bones, and a blow to the head can detach the periosteal layer from the calvaria without fracturing the cranial bones

Question 7

What is Falx Cerebri - Dura Mater?

Answer 7

Dural septa extending into the longitudinal fissure between the cerebral hemispheres
Continuous with tentorium cerebelli

Question 8

What is Tentorium Cerebelli - Dura mater?

Answer 8

Separates occipital lobes from cerebellum
Toward the midline it slopes upward and fuses with falx cerebri

Question 9

What is arachnoid mater?

Answer 9

Proximal to dura mater
Not attached to dura
Held against inner surface of dura mater by pressure of CSF
Avascular

Question 10

What is pia mater?

Answer 10

Proximal to arachnoid mater
Thin membrane
Adheres to brain and follows all of its contours
Highly vascularized

Question 11

What are Gyri?

Answer 11

crests of cortical folds

Question 12

What are sulci?

Answer 12

furrows

Question 13

Explain the significance of Gyri, Sulci and Fissures in cerebral hemispheres?

Answer 13

Gyri (crests of cortical folds) are separated by sulci (furrows) or deeper fissures

Folding of cortex in this way allows cranial vault to contain a large area of cortex

Separates frontal, parietal, occipital, temporal and insula lobes from each other

Question 14

What is the Lateral Cerebral Fissure?

Answer 14

Separates temporal lobe from frontal & parietal lobes

Insula, portion of cortex that did not grow much during development, lies deep within this fissure

Question 15

What is Circular Sulcus (circuminsular fissure)?

Answer 15

Surrounds insula & separates it from adjacent frontal, parietal & temporal lobes

Question 16

What is Longitudinal Cerebral Fissure?

Answer 16

Separates hemispheres

Question 17

Where is the central sulcus?

Answer 17

Arises near middle of hemisphere, beginning near longitudinal cerebral fissure and extending downward and forward to 2.5 cm above lateral cerebral fissure
Separates frontal lobe from parietal lobe

Question 18

Where is Precentral Sulcus?

Answer 18

Parallel to central sulcus and lies anterior to precentral gyrus

Question 19

Where is Postcentral Sulcus?

Answer 19

Parallel to central sulcus and lies posterior to postcentral gyrus

Question 20

What artery supplies the blood for the primary motor cortex?

Answer 20

middle cerebral artery

Question 21

Lesions of the precentral gyrus result in?

Answer 21

paralysis of the contralateral side of the body (facial palsy, arm-/leg monoparesis, hemiparesis) - see upper motor neuron.

Question 22

The medial aspect (leg areas) is supplied by branches of the what artery?

Answer 22

anterior cerebral artery

Question 23

Where is the Parietooccipital Fissure?

Answer 23

Medial surface of posterior portion of cerebral hemisphere > downward and forward

Separates parietal and occipital lobes

Question 24

Where is the Calcarine Fissure?

Answer 24

Medial surface of hemisphere near occipital pole  below splenium of corpus callosum

Above fissure is visual cortex for bottom half of ones vision, below fissure is visual cortex for top half of ones vision

Question 25

Where is Cingulate Sulcus?

Answer 25

Cingulate gyrus is between this sulcus and corpus callosum

Separates frontal and limbic lobes

Question 26

How many Lobes of Cerebral Cortex are there?

Answer 26

6

Question 27

Where is the frontal lobe?

Answer 27

Extends from frontal pole to central sulcus

Superior and inferior frontal sulci divide the superior, medial and inferior frontal gyri

Precentral gyrus is continuous on medial surface of hemisphere as anterior paracentral gyrus

Question 28

What is the primary motor complex?

Answer 28

Precentral & anterior paracentral gyri form primary motor cortex

Controls contralateral voluntary movements of skeletal muscle via corticonuclear and corticospinal tracts  efferent nuclei in brain stem & ventral horn of spinal cord

Lesions result in spastic paralysis of contralateral extremity, affecting mainly fine and skilled movements

Irritative lesions of motor centres may cause seizures that begin as focal twitching and spread to large muscle groups (Jacksonian epilepsy)

Question 29

What forms the primary motor complex?

Answer 29

Precentral & anterior paracentral gyri

Question 30

Where is the premotor area?

Answer 30

Anterior part of precentral gyrus and posterior parts of superior, middle and inferior frontal gyri

Stores programs of motor activity assembled from past experiences and thus programs activity of primary motor area

Involved with coarse postural movements

Question 31

Where is the frontal eye field?

Answer 31

Extends forward from facial area of precentral gyrus into middle frontal gyrus

Controls voluntary scanning (conjugate) movements of eye

Lesions in one hemisphere causes two eyes to deviate to side of lesion and an inability to turn eyes toward opposite side

Connected to occipital visual cortex by association fibres

Question 32

Where is Broca’s Motor Speech Area? What does it do?

Answer 32

In inferior frontal gyrus

Allows formation of words via connections to adjacent primary motor area and muscles of larynx, tongue, soft palate and respiration

Dominant in left hemisphere forming words or speaking fluently. Damage = Expressive Aphasia

If the opposite side is damaged, speech is not affected

The anterior, or frontal, part of Broca’s area is responsible for understanding the meaning of words; in linguistics, this is known as semantics. The posterior, or back, part of Broca’s area is responsible for helping people understand how words sound, something known as phonology in linguistic terms

Question 33

Where is the Prefrontal Cortex?

Answer 33

Anterior to precentral area

Includes most of superior, medial and inferior frontal gyri and anterior half of cingulate gyrus

Concerned with individuals personality and influences initiative and judgement

Damage does not result in any marked loss in intelligence

Emotional changes includes tendency to euphoria
Patient no longer conforms to accepted mode of social behaviour & becomes careless of dress & appearance

planning complex cognitive behaviour, personality expression, decision making, and moderating social behaviour

Question 34

Where is the parietal lobe?

Answer 34

Extends from central sulcus to parietooccipital fissure
Laterally it extends to level of lateral cerebral fissure

Postcentral gyrus is continuous with posterior paracentral gyrus on medial surface of hemisphere

Question 35

What is the primary sensory cortex?

Answer 35

Postcentral gyrus and posterior paracentral gyri form primary somatosensory cortex

Receives fibres from thalamus conveying touch & proprioception from other side of body
Cortical taste area receives gustatory information (via thalamus from solitary nucleus in medulla)

Irritative lesions produce numbness, tingling, electric shock or pins and needles on opposite side of body

Destructive lesions produce subjective and objective impairments in sensibility of light touch/pain perception, and texture/size/shape discrimination

Question 36

Where is the occipital lobe?

Answer 36

Pyramid shaped

Situated behind parietooccipital fissure

Question 37

What is the Primary visual cortex?

Answer 37

In posterior part of calcarine sulcus

Receives fibres from temporal ½ of ipsilateral retina and nasal ½ of contralateral retina
Right ½ of vision is represented in left visual cortex, and vice versa
Superior retinal quadrants (inferior field of vision) pass superior to calcarine sulcus
Inferior retinal quadrants (superior field of vision) pass inferior to calcarine sulcus

Irritative lesions  visual hallucinations of light, rainbows, brilliant stars or bright lines
Destructive lesions  contralateral homonymous visual field defects

Question 38

What is the Visual Association Cortex?

Answer 38

Surrounds primary visual area

Relates visual information received by primary visual area to past visual experiences, thus enabling the individual to recognise and appreciate what he or she is seeing

Question 39

Where is the temporal lobe?

Answer 39

Below lateral cerebral fissure and extends back to level of parietooccipital fissure on medial surface of hemisphere

Its anterior part, most medial portion of temporal lobe, curves in the form of a hook, known as the uncus

Primary auditory cortex

Question 40

What are the functions of the temporal lobe?

Answer 40

Help in formation of long-term memories and processing new information
Fomation of visual and verbal memories
Interpretation of smells and sounds
Object and face recognition – communication with occipital lobe more posterior in temporal lobe
Thetemporal lobeis involved in processing sensory input into derived meanings for the appropriate retention ofvisual memory,language comprehension, and emotion association.
Medial temporal lobe – long term memory –with hippocampus
Impaired new memory formation – antegrade amnesia

Question 41

Where is Wernicke’s Sensory Speech Area? What does it do?

Answer 41

In superior temporal gyrus of left (dominant) hemisphere
Connected to Broca’s area by arcuate fasciculus

Permits understanding of written and spoken language and allows a person to read a sentence and understand it

Lesions of dominant hemisphere produces loss of understanding of the spoken and written word
Speech is unimpaired (Broca’s area unaffected), but patients are unaware of the meaning of words they use, and use incorrect/non existent words
Patients are unaware of their mistakes

Question 42

Where is the Insula Lobe?

Answer 42

Sunken portion of cerebral cortex

Lies deep within lateral cerebral fissure
Exposed by separating upper and lower lips of lateral fissure

Insula receives nociceptive and viscerosensory input

Question 43

Where is the limbic lobe?

Answer 43

Ring of cortex that makes up the medial-most rim of the cerebral hemisphere
Part of limbic system

Includes:
Subcallosal, cingulate gyrus, isthmus of the cingulate gyrus, parahippocampal gyrus and the uncus

Question 44

What is the limbic system?

Answer 44

Includes components of the “Papez Circuit”:
Hippocampus > fornix > mammillary bodies > mamillo-thalamic tract > anterior nucleus of the thalamus (internal capsule)  cingulate gyrus (cingulum) > hippocampus

Appears to play crucial roles in memory, emotional responses and integration of behaviour

Question 45

What is Cerebral White Matter?

Answer 45

Association Fibres
Connects cells of cortex of same cerebral hemisphere

Permits cortex to function as a co-ordinated whole

Short association fibres link neighbouring gyri

Long association fibres link more distant gyri (E.g. superior longitudinal fasciculus links occipital and temporal poles)

Commissural Fibres
Connects gyri of one hemisphere with corresponding gyri of the other

Allow co-ordination of activities of right and left halves of the brain

Largest example is corpus callosum

Question 46

What is the Corpus Callosum?

Answer 46

Largewhite matter tract that connects the 2 hemispheres of the brain

200 million myelinated & non myelinated fibres

Crosses longitudinal cerebral fissure
Interconnects large portions of the hemispheres and holds two cerebral hemispheres together

Body of corpus callosum is arched
Genu is anterior curved portion
Rostrum is forward continuation of genu
Splenium is thick posterior portion, which lies over the midbrain

Commissural fibres are very closely packed in the midline and radiate (fan out) towards the various parts of the cortex

Fibres from frontal lobe must therefore pass backwards and medially to reach genu of corpus callosum

Forceps minor is the arch formed by the genu and bundles of fibres converging from the frontal pole

Forceps major is the arch formed by the fibres passing forwards and medially in order to converge on the splenium of the corpus callosum linking the occipital lobes

Question 47

What are Projection Fibres?

Answer 47

Connect cerebral cortex with lower portions of brain/spinal cord

Question 48

What is the Internal Capsule?

Answer 48

Majority of projection fibres of cerebral cortex, both afferent and efferent, pass through a very restricted region, the internal capsule
Consists of an anterior limb, a genu and a posterior limb

myelinated fibre bundles that runs through the basal nuclei

Separates lentiform nucleus (lateral to internal capsule) from caudate nucleus (medial to internal capsule & anterior to thalamus) and thalamus (medial to internal capsule and posterior to head of caudate nucleus)

Frontal projection fibres are placed most anteriorly
Temporal and occipital fibres most posteriorly
Parietal fibres in-between

Contains virtually all cerebral cortical projection fibres, except for fornix and olfactory projection fibres, including fibres to and from thalamus, corpus striatum, pontine nuclei, tectum of midbrain, reticular formation, cranial nerve nuclei and spinal cord

“Motor” fibres comprise largely of corticopontine fibres, & much smaller, but more clinically important number of corticospinal and corticonuclear fibres

Exact position of corticospinal and corticonuclear fibres in posterior limb of internal capsule depends on level of horizontal section
Somatotopic arrangement, with head regions most anterior and leg regions most posterior

Question 49

What are the clinical correlations of stroke?

Answer 49

Haemorrhage or blockage of the blood supply to the corpus striatum and internal capsule results in a “stroke”

Since the cerebral cortex deals primarily with sensations and movements of the contralateral side of the body, fibres of the internal capsule are also primarily concerned with functions of the contralateral side

Lesions of the posterior limb of the internal capsule causes contralateral spastic paralysis and sensory loss, with associated exaggerated deep (myotatic) spinal reflexes and limited muscular wasting

Question 50

What are the clinical correlations of an internal capsule lesion?

Answer 50

An internal capsule lesion will not effect equally the motor functions of the cranial nerves
Most cranial nerve nuclei receive bilateral input from the cerebral cortex and so will be relatively spared following a unilateral supranuclear lesion

However, the input is solely from the contralateral cortex for the part of the facial nucleus dealing with the lower facial musculature, for most of the hypoglossal nucleus and for the part of the spinal nucleus of the accessory nerve innervating trapezius
The remainder of the spinal nucleus of XI, which innervates the sternocleidomastoid muscle receives fibres solely from the ipsilateral cortex

Supranuclear lesions in the frontal eye field will temporarily impair voluntary eye movements to the contralateral side, otherwise eye movements are little affected by unilateral lesions of descending fibres