Cerebrum

Question 1

Define the three types of mammalian cortex

Answer 1

1. Archicortex (3 layers, hippocampus)
2. paleocortex (3-5 layers, olfactory/pyriform cortex)
3. neocortex (6 layers, everything else)

Question 2

Answer 2

Question 3

What are the major principle cells of cerebral cortex?

Answer 3

1. Pyramidal cells (excitatory, 2/3 of all neurons, glutamatergic)
2. Fusiform cells (atypical, irrgular, elliptical)

Question 4

What are the major interneurons in the cerebral cortex?

Answer 4

1. Stellate (excitatory, layer IV, star)
2. Basket cell (inhibitory, lateral branching axons)
3. Retzius-cajal cells (aka horizontal cells, molecular layer)
4. Cells of martinotti (deep layers, axons project up to plial layer)

Question 5

What are the 6 layers of cortex & the cells found in each

Answer 5

1. Molecular
   * synaptic layer, retzius-cajal cell bodies, terminal dendrites/axons, pyramidal dendritic branches)
2. External Granular
   * small pyramidal & interneurons
3. External Pyramidal
   * small/medium pyramidal (forms association & commissural fibres)
4. Internal Granular
   * stellate, some other interneurons & pyramidal
5. Internal Pyramidal
   * large pyramidal (form projection fibres)
6. Multiform
   * cells of martinotti, fusiform, few interneurons, pyramidal cells that project to thalamis/claustrom

Question 6

Describe some of the variations in cytoarchitecture and how they can be used to identify different regions of the cerebrum

Answer 6

• primary visual, auditory and somatosensory cortex (layers 2-5 merge into one)
• Primary motor & premotor (layers 2-6 merge into one)

Question 7

Describe the organisation of intracortical circuits.

Answer 7

• Cortical cell axons excite pyramidal apical dendrite
• input from thalamus excites pyramidal basal dendrites & stellate cells
• stellate cells excite pyramidal cells
• input from thalamus & pyramidal cells excite basket cells
• basket cells inhibit currounding pyramidal cells

Question 8

Describe and identify the cerebral localisation and circuitry of general somatic sensation

Answer 8

Primary somatic = Brodman 1,2,3 (postcentral gyrus)
* input from ventral posterior thalamus
* homunculus (localisation of sensation)

Somatic association = Areas 5&7 (superior parietal lobule & precuneus)
* input from primary somatic, lateral posterior thalamus and pulvinar
* allows object recognition without visual aid

Question 9

Describe and identify the cerebral localisation and circuitry of vision

Answer 9

Primary visual = area 17 (surrounding calcarine sulcus)
* input form lateral geniculate thalamus via geniculocalcarine tract
* LHS visual field represented in RHS brain (and vice versa)

Visual association = areas 18 & 19 (occipital surrounding primary area)
* input from contralateral area 17, thalamus & pulvinar
* complex visual processing, recognition & significance

Question 10

Describe and identify the cerebral localisation and circuitry of hearing

Answer 10

Primary auditory = areas 41 & 42 (ventral wall of lateral sulcus, herschl’s convolutions)
* input from medial geniculate thalamus

Question 11

Describe and identify the cerebral localisation and circuitry of taste

Answer 11

Taste = Area 43 (inferior postcentral gyrus)
* input from medial ventral posterior thalamus

Question 12

Describe and identify the cerebral localisation and circuitry of olfaction

Answer 12

Olfactory = Area 34 (limen insulae & uncus)
* input from olfactory tubercle & medial dorsal thalamus

Question 13

Describe and identify the cerebral localisation and circuitry of vestibular

Answer 13

No defined cortical area.
* intraparietal sulcus (in somatosensory cortex) & posterior insular
* integrates vestibular & proprioceptive signals

Question 14

Describe and identify the cerebral localisation and circuitry of motor systems

Answer 14

Primary moto = area 4 (precentral gyrus)
* input from other motor cortex, posterior ventral lateral thalamus

Supplementary/cingulate motor
* area 6 (PMA/SMA) & anterior cingulate
* Area 8 frontal eye fields for control of eye movements.
* input from many cortical areas, ventral anterior thalamus & ventral lateral thalamus

Question 15

Identify the localisation of language areas that control both comprehension of language and motor speech areas.

Answer 15

Wernicke’s Area
* Area 22 - Left posterior superior temporal gyrus
* receptive language area - comprehension of spoken and written language

Broca’s area
* Areas 44 & 45 - inferior frontal gyrus
* expressive speech area - motor speech

Question 16

What are the 3 types of cerebral fibre tract?

Answer 16

1. Association tracts (within 1 hemisphere)
2. Commissural tracts (between 2 hemispheres
3. Projection tracts (between cortical & subcortical, ie internal capsule)

Question 17

Identify the major association fasciculi and their connections.

Answer 17

1. Cingulum - cingulate gyrus, parahippocampal gyrus & septum
2. superior longitudinal fasciculus - parietal, temporal, occipital lobes to frontal lobe
3. superior occipitofrontal fasciculus - anterior frontal and posterior frontal cortex
4. inferior occipitofrontal fasciculus - orbital frontal cortex and temporal lobe

Question 18

Identify the major commissural tracts and their connections.

Answer 18

1. Corpus callosum (enourmous, majority of neocortical fibres)
2. anterior commissure (additional comms between paleocortical temporal lobes)

Question 19

Identify the major projection fibres and their connections.

Answer 19

all travel along internal capsule
1. thalamic radiations (between thalamus and cortex)
2. motor (corticofugal) - (from motor cortex to basal ganglia, cerebellum & spinal tracts)

Question 20

Answer 20