Separation of the hemispheres & the IIIrd ventricle

Question 1

What borders the IIIrd ventricle anteriorly, above and below?

Answer 1

anteriorly - lamina terminalis
above - tela choroida
below - optic chiasm, pituitary stalk, mamillary bodies and tegmentum of midbrain

Question 2

What does the interventricular foramen allow communication between?

Answer 2

lateral ventricles and IIIrd ventricle

Question 3

What is the interventricular foramen almost entirely filled with?

Answer 3

choroid plexus - produces CSF

Question 4

What does the cerebral aqueduct allow communication between?

Answer 4

IIIrd and IVth ventricles

Question 5

What is the paracentral lobule?

Answer 5

U shaped gyrus surrounding the medial extension of the central sulcus which contains representations of the lower limb within the primary motor and somatic sensory areas of the cortex which on the lateral surface of the brain represent the pre-central and post-central gyri respectively

Question 6

What is the cingulate sulcus?

Answer 6

separates the cingulate gyrus, which runs above the corpus callosum, from the rest of the hemisphere

Question 7

What is the parieto-occipital sulcus?

Answer 7

lies mainly on the medial surface of the hemisphere where it forms a Y shaped arrangement with the calcarine sulcus - divides the internal occipital lobe from the parietal and internal temporal lobes

Question 8

What is the calcarine sulcus?

Answer 8

roughly at right angles with the parieto-occipital sulcus - separates the occipital lobe into the lingual gyrus (inferior) and cuneus (superior)

Question 9

What are the striae of genari?

Answer 9

a white band in the primary visual cortex, running parallel with the pial surface in the mid-depth of the grey matter - prominent feature gives the name striate cortex to the primary visual area

Question 10

What is the corpus callosum?

Answer 10

a broad arched band of white matter - largest of the fibre bundles connecting the two halves of the brain, enabling communication between the two hemispheres

Question 11

The corpus callosum can be divided into different regions - what are they called?

Answer 11

• genu = anterior curved end
• body = central main curve
• rostrum = leads downwards from the genu
• splenium = rounded posterior end

Question 12

What is the fornix?

Answer 12

C shaped bundle of white matter beneath the body of the corpus callosum

Question 13

What system is the fornix involved in?

Answer 13

limbic system - therefore associated with the processes of cognition, memory consolidation, emotions and sexual responses

Question 14

Outline the structure of the fornix

Answer 14

• begins in the hippocampus as the alveus
• aggregate to form the fimbria of the hippocampus
• main bulk of fimbriae continue on each side of the cerebral hemisphere to form the crus of the fornix
• the two crura arch anterosuperiorly under the splenium of the corpus callosum
• establish a connection with each other across the midline by the partially decussating fibres called the commissure of the fornix/hippocampal commissure
• both crura continue anteriorly and merge in the midline to form the body of the fornix
• body of the fornix arches over the thalamus and under the septum pallucidum, which connects it to the corpus callosum
• body of the fornix extends anteriorly and bifurcates into the right and left halves called the columns of the fornix. They extend vertically downwards to the mamillary bodies

Question 15

What is the anterior commissure?

Answer 15

thick bundle of white matter crossing the midline horizontally between the lamina terminalis and the fornix to interconnect the temporal lobes and olfactory structures on each side

Question 16

What is the septum pallucidum?

Answer 16

two thin vertical sheets made primarily of glia with a few white fibres, sparse grey matter and a covering of ependyma - acts as a partition between the lateral ventricles/separates the anterior horns of the two lateral ventricles

Question 17

What is the lamina terminalis?

Answer 17

thin sheet of ependyma and pia which extends downwards from the rostrum of the callosum and fornix to the anterior wall of the IIIrd ventricle

Question 18

The thalamus is made up of two symmetrical structures formed from what?

Answer 18

the diencephalon

Question 19

What is the role of the thalamus?

Answer 19

major subcortical relay station for information ascending to the cerebral cortex. Also plays a role in sleep, wakefulness, consciousness, learning and memory

Question 20

How are the two thalami connected?

Answer 20

via the interthalamic adhesion - is behind the interventricular foramen and may be absent in some people (10%)

Question 21

What is the medial geniculate nucleus/body?

Answer 21

relays auditory information from the midbrain to the auditory cortex and passes some fibres via the inferior brachium to the inferior colliculi

Question 22

What is the lateral geniculate nucleus/body?

Answer 22

relays visual information from the optic nerve to both the visual cortex via the optic radiation (for vision) and the superior colliculi via the superior brachium (for pupillary reflexes)

Question 23

What is the hypothalamic sulcus?

Answer 23

forms the boundary between the thalamus and hypothalamus - shallow groove on the lateral wall of the IIIrd ventricle extending from the cerebral aqueduct to the interventricular foramen

Question 24

What is the role of the hypothalamus?

Answer 24

principal visceral control centre of the brain and mediates a broad range of functions via its connections with the endocrine, autonomic, somatic motor and limbic systems, maintaining a state of homeostasis

Question 25

Where is the hypothalamus located?

Answer 25

- extends from the lamina terminalis - superior border is marked by the hypothalamic sulcus - inferior surface bears the optic chiasm anteriorly, the tuber cinereum centrally and the mamillary bodies posteriorly

Question 26

What is the tuber cinereum?

Answer 26

region of grey matter extending from the optic chiasm to the mamillary bodies, from which the funnel shaped infundibulum becomes continuous with the infundibular stalk attached to the pituitary gland

Question 27

What is the subthalamus?

Answer 27

ventral part of the diencephalon below the thalamus and lateral to the hypothalamus merging with the tegmentum functionally its closely associated with the basal ganglia - subthalamic nucleus is involved in the integration of somatic motor function

Question 28

What is the preoptic area?

Answer 28

adjacent to the lamina terminalis and in front of the optic chiasm - essential brain region to coordinate sleep and body temperature

Question 29

Different areas of the cortex are connected by myelinated axons - these form white matter. There are three main types - what are they?

Answer 29

1. association fibres = link cortical regions within one cerebral hemisphere 2. commissural fibres = link similar functional area of the two hemispheres (eg: corpus callosum) 3. projection fibres = link the cortex with subcortical structures such as the thalamus and spinal cord via the internal capsule and corona radiata

Question 30

What do association fibres do?

Answer 30

link cortical regions within one cerebral hemisphere

Question 31

What do commissural fibres do?

Answer 31

link similar functional regions of the two hemispheres (eg: corpus callosum)

Question 32

What do projection fibres do?

Answer 32

link the cortex with subcortical structures such as the thalamus and spinal cord via the internal capsule and corona radiata

Question 33

There are two basic functions in uniting the two cerebral hemispheres - what are they?

Answer 33

1. bringing together separate representations of the two halves of the body, the visual field and the auditory surround 2. uniting areas of the cortex which have functions specialised to one hemisphere

Question 34

Clinical link - thalamic lesions (eg: strokes or tumours) destroying the thalamus could cause what symptoms?

Answer 34

loss of sensation in the contralateral face and limbs, accompanied by distressing discomfort in the paradoxically anaesthetic areas (thalamic pain)