Cortex (from cortex, thalamus & hypothalamus)

Question 1

Raised fold in the cortex

Answer 1

Gyrus

Question 2

Fissure in the cortex

Answer 2

Sulcus

Question 3

Discuss the cerebral microstructure

Answer 3

1. cell bodies of cortical neurones are always arranged in layers, that usually lie parallel to the surface of the brain
2. the layer of neurons closest to the surface (the most superficial layer) is separated from the pia mater by a zone that lacks neurons → the molecular layer
3. at least one cell layer contains pyramidal cells that emit large dendrite (apical dendrites) that extend up to layer I where they form multiple branches → pyramidal cells in the prefrontal cortex have up to 23 times more dendritic spines than those in the primary visual area (may allow for more extensive sampling of inputs, as required by higher-order processing of visual information)

Question 4

What two divisions may the cortex consist of?

Answer 4

1. the neocortex (differentiated into 6 horizontal layers)

2. the allocortex, which contains the hippocampus (which has 3 cortical layers) and olfactory cortex

Question 5

How many layers does the hippocampus have?

Answer 5

3 at most

Question 6

Discuss cortical columns

Answer 6

Neurons in various layers connect vertically to form small microcircuit → these are cortical columns

also known as hypercolumns

they consist of groups of neurons that have nearly identical receptive fields

Question 7

What are Broadmann’s areas distinguished by?

Answer 7

Differences in histological structure and functional roles in:
- sensation, cognition and behaviour

Question 8

What neurons are the most common in the cortex?

Answer 8

Pyramidal

Question 9

What neurotransmitter do pyramidal neurons utilise?

Answer 9

Glutamate

Question 10

Discuss the 3 different fibres types in the cortex

Answer 10

Commissural (transverse fibres) → connect the two hemispheres
Association → connect regions in the same hemisphere
Projection → leave the cortex and project to different regions of the CNS - e.g. thalamus & spinal cord

Question 11

How many layers does the cortex have?

Answer 11

6

Question 12

Mnemonic for layers of the cortex

Answer 12

From the outside to the inside:
Molecular (plexiform), external granular, external pyramidal, internal granular, internal pyramidal, multiform (fusiform) layers (‘Miles Per Gallon Is Gallon Per Miles’)

Question 13

Descibre the molecular layer (layer I)

Answer 13

1. Contains few scattered neurons and consists mainly of extensions of apical dendritictufts of
   pyramidal neurons and horizontally oriented axons, as well asglial cells
2. Also, some spinystellate cellscan be found here.
3. Inputs to the apical tufts are thought to be crucial for the ‘‘feedback’’ interactions in the
   cerebral cortex involved in associative learning and attention
4. While it was once thought that the input to layer I came from the cortex itself, it is now
   realized that layer I across the cerebral cortex mantle receives substantial input from ‘‘matrix’’
   or M-type thalamus cells (in contrast to ‘‘core’’ or C-type that go to layer IV)

Question 14

Describe the external granular layer (layer II)

Answer 14

Contains smallpyramidal neuronsand numerous stellate neurons

Can be long enough to be association fibres

Question 15

Describe external pyramidal layer (layer III)

Answer 15

Contains predominantly small and medium-sizepyramidal neurons

• The apical dendrites of these cells extend superficially and reach the molecular layer
• the basal processes join the subcortical white matter and then project again to the cortex, so they serve as both association and commissural corticocortical fibers.

Question 16

Describe the interal granular layer (layer IV)

Answer 16

• Contains different types ofstellateandpyramidal neurons,
• is the main target of
  thalamocortical afferents from thalamus type C neurons as well as intra-hemispheric
  corticocortical afferents
• main input to cortical station (most stimuli from the periphery arrive here)
• therefore contains sensory areas:
• Stellate cells of the primary sensory cortex receive fibers from the ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei of the thalamus
• Primary visual cortex receives fibers from the lateral geniculate nucleus
• Stellate cells from primary auditory cortex receive projections from the medial geniculate nucleus

Question 17

Describe the internal pyramidal layer (layer V)

Answer 17

Contains LARGEpyramidal neuronswhich give rise to axons leaving the cortex and running
down to subcortical structures (such as thebasal ganglia).

• In the primary motor cortex of the frontal lobe, layer V containsBetz cells, whose axons travel
  through theinternal capsule, thebrain stemand the spinal cord forming the corticospinal
  tract, which is the main pathway for voluntary motor control.

Question 18

Describe the multiform layer (layer VI)

Answer 18

• Contains few largepyramidal neuronsand many small spindle-like pyramidal and multiform
  neurons
• Layer VI sends efferent fibers to the thalamus, establishing a very precise reciprocal
  interconnection between the cortex and the thalamus – layer VI neurons from one cortical column connect with thalamus neurons that provide input to the same cortical column; these
  connections are both excitatory and inhibitory
• Neurons sendexcitatoryfibers to neurons in the thalamus and also send collaterals to
  thethalamic reticular nucleusthatinhibitthese same thalamus neurons or ones adjacent to
  them – one theory is that because the inhibitory output is reduced by cholinergicinput to the
  cerebral cortex, this provides thebrainstemwith adjustable “gain control for the relay
  oflemniscalinputs
• Cortical areas that lack a layer IV are called agranular; cortical areas that have only a
  rudimentary layer IV are
  called dysgranular

Question 19

Which layers are the output pyramidal cells located in?

Answer 19

3, 5 and 6

Question 20

What do the columns represent?

Answer 20

The functional units of the cortex

Question 21

Describe the anatomy of the corpus callosum

Answer 21

1. Theposterior(back) portion of the
   corpus callosum is called thesplenium
2. theanterior(front) is called thegenu(or knee)
3. between the two is the truncus, or body
4. The part between the body and the splenium is often markedly narrowed – isthmus

Question 22

Describe the area of the brain connecting the prefrontal cortex between the two halves

Answer 22

Thinner axons in the genu

These fibres arise from a fork-like bundle of fibres in the tapetum (main body of fibres), called the forceps anterior

Question 23

Describe the connection of the motor cortex between the two hemispheres

Answer 23

• Thicker axons in the mid-body or trunk, innerconnect areas of the motor cortex
• proportionately more of the corpus callosum is dedicated to supplementary motor regions, including Broca’s area

Question 24

Describe the part of the the allows exchange of somatosensory information between the two hemispheres?

Answer 24

The posterior body of the corpus, known as the splenium, communicates somatosensory information between the two halves of the parietal lobe and the visual cortex at the occipital lobe

These are the fibres of the forceps posterior

Question 25

What is the internal capsule?

Answer 25

A white matter structure situated in the inferomedial part of each cerebral hemisphere (boomerang shape)

Question 26

What does the internal capsule separate?

Answer 26

The caudate nucleus and the thalamus from the putamen and globus pallidus

Question 27

What does the internal capsule consist of?

Answer 27

Both ascending and descending axons

Question 28

What forms a large part of the internal capsule? What does this carry?

Answer 28

Corticospinal tract | Motor info from the primary motor cortex to the lower motor neurons of the spinal cord

Question 29

What does the anterior limb of the internal capsule contain?

Answer 29

a) Frontopontine (corticofugal) fibers project from frontal cortex to pons b) Thalamocortical fibers (part of the thalamocortical radiations) connect the medial and anterior nuclei of the thalamus to the frontal lobes (these are severed during a prefrontal lobotomy).

Question 30

What can the internal capsule be divided into?

Answer 30

Anterior limb Genu Posterior limb

Question 31

What does the genu contain?

Answer 31

contains corticobulbar fibers, which run between the cortex and the brainstem.

Question 32

What does the posterior limb contain?

Answer 32

contains corticospinal fibers, sensory fibers (including | the medial lemniscus and the anterolateral system) from the body and a few corticobulbar fibers

Question 33

What is the fornix?

Answer 33

The fornix is a C-shaped bundle of nerve fibers in the brain that carries signals from the hippocampus to the mammillary bodies and then to the anterior nuclei of thalamus it is part of the limbic system

Question 34

What connects the fornix to the corpus callosum?

Answer 34

Septum pellucidum

Question 35

What are the posterior bifurcations of the fornix called?

Answer 35

Columns of the fornix

Question 36

What does the fornix pass through to reach the mamillary body?

Answer 36

Hypothalamus

Question 37

Describe the precommisurral fornix

Answer 37

composed of the fibers that descend in front of the anterior commissure. They relay onto the septal nuclei (medial olfactory area), the ventral striatum, and the cingulate gyrus.

Question 38

Describe the postcommisurral fornix

Answer 38

the postcommissural fornix are the fibers that pass behind the anterior commissure and relay onto the mammillary bodies and the anterior nuclei of the thalamus. A small amount of fornical fibers pass above the splenium of corpus callosum to reach the structures above the corpus callosum. Those fibers constitute the dorsal fornix.

Question 39

Main function of the fornix

Answer 39

the primary role of the fornix is to transmit the information from the hippocampus to the mammillary bodies and to the anterior nuclei of thalamus thought to play a key role in memory

Question 40

Functional anatomy areas of the cortex → draw as well

Answer 40

``` Somatosensory - Motor and pre-motor - Visual - Auditory - Posterior parietal - Orbitofrontal - Olfactory - Limbic Look on OneNote ```

Question 41

Describe thalamocortical projections

Answer 41

Thalamocortical fibers have a bush or tree-like appearance as they extend into the internal capsule and project to the layers of the cortex. - The main thalamocortical fibers extend from different nuclei of the thalamus and project to the visual cortex, somatosensory (and associated sensori-motor) cortex, and the auditory cortex in the brain. - Visual input from the optic tract is processed by the lateral geniculate nucleus of the thalamus - auditory input processed in the medial geniculate nucleus - Somatosensory input processed in the ventral posterior nucleus - Thalamocortical radiations also innervate the gustatory pathways, as well as pre-frontal motor areas

Question 42

Describe corticothalamic projections. Which nucleus recieves corticothalamic feedback? From which layer of the cortex do these mainly come?

Answer 42

Thalamic nuclei project to cortical areas of distinct architectural organization and relay the processed information back to the area of original activity in the thalamus via corticothalamic (CT) fibres - The thalamic reticular nucleus (TRN) receives incoming signals via corticothalamic pathways and regulates activity within the thalamus accordingly - Cortico-thalamic feedback neurons are mostly found in layer VI of the cortex. - Reciprocal CT projections to the thalamus are of a higher order than, and synapse with the TRN in much greater number than do thalamocortical projections to cortex – this suggests that the cortex has a much bigger role in top down processing and regulation of thalamic activity than do the processes originating in thalamic interneurons.

Question 43

What s the arterial cerebral circulation normally divided into?

Answer 43

Anterior cerebral circulation and posterior cerebral circulation

Question 44

What are the two main pairs of arteries that supply the cerebral arteries and the cerebrum?

Answer 44

- internal carotid | - vertebral

Question 45

What are the anterior and posterior cerebral circulations interconnected via?

Answer 45

Bilateral posterior communicating arteries - part of the circle of Willis - this provides backup circulation

Question 46

Describe the anterior cerebral circulation - what is it supplied by?

Answer 46

1. Internal carotid arteries – these large arteries are the left and right branches of the common carotid arteries in the neck which enter the skull, as opposed to the external carotid branches which supply the facial tissues. The internal carotid artery branches into the anterior cerebral artery and continues to form the middle cerebral artery 2. Anterior cerebral artery (ACA) – left and right anterior cerebral arteries connected by anterior communicating artery, within and along the floor of the cerebral vault. 3. Middle cerebral artery (MCA)

Question 47

What arteries form the posterior cerebral circulation?

Answer 47

1. Vertebral arteries: These smaller arteries branch from the subclavian arteries; within the cranium the two vertebral arteries fuse into the basilar artery - Posterior inferior cerebellar artery (PICA) is largest branch off of vertebral arteries 2. Basilar artery: Supplies midbrain, cerebellum, and usually branches into posterior cerebral artery - Anterior inferior cerebellar artery (AICA) - Pontine branches - Superior cerebellar artery (SCA) 3. Posterior cerebral artery (PCA) 4. Posterior communicating artery

Question 48

What is the structure of the venous drainage of the brain?

Answer 48

Drainage by veins which empty into dural venous sinuses

Question 49

Where do the dural venous sinuses lie?

Answer 49

Between the periosteal and meningeal layers of the dura mater

Question 50

What do all the dural sinuses ultimately drain into?

Answer 50

The internal jugular vein

Question 51

How many venous sinuses are there in total?

Answer 51

11

Question 52

Describe the venous sinuses

Answer 52

The straight, superior, and inferior sagittal sinuses are found in the falx cerebri of the dura mater. They converge at the confluence of sinuses (overlying the internal occipital protuberance). The straight sinus is a continuation of the great cerebral vein and the inferior sagittal sinus. From the confluence, the transverse sinus continues bi-laterally and curves into the sigmoid sinus to meet the opening of the internal jugular vein. The cavernous sinus drains the ophthalmic veins and can be found on either side of the sella turcica. From here, the blood returns to the internal jugular vein via the superior or inferior petrosal sinuses Draw them! OneNote

Question 53

What may the veins of the brain be divided into?

Answer 53

Superficial and deep gorups

Question 54

Discuss the superficial venous system

Answer 54

1. Superior cerebral veins: Drain the superior surface, carrying blood to the superior sagittal sinus. 2. Superficial middle cerebral vein: Drains the lateral surface of each hemisphere, carrying blood to the cavernous or sphenopalatine sinuses. 3. Inferior cerebral veins: Drain the inferior aspect of each cerebral hemisphere, depositing blood into cavernous and transverse sinuses. 4. Superior anastamotic vein (Trolard): Connects the superficial middle cerebral vein to the superior sagittal sinus. 5. Inferior anastamotic vein (Labbé): Connects the superficial middle cerebral vein to the transverse sinus

Question 55

Discuss the deep venous system

Answer 55

1. Subependymal veins – There are numerous subependymal veins, which will not be described here in detail. These receive blood from the medullary veins and carry it to the dural venous sinuses. The great cerebral vein (vein of Galen) is worthy of a mention; it is formed by the union of two of the deep veins, and drains into the straight sinus. 2. Medullary veins: Originate 1-2cm below the cortical grey matter, and drain into subependymal veins. These drain the deep areas of the brain.

Question 56

Consequences of lesion to visual cortex

Answer 56

Scotoma (hole in visual field)

Question 57

Consequences of lesion to motor cortex

Answer 57

Lesions of the precentral gyrus (primary motor cortex) result in paralysis of the contralateral side of the body

Question 58

Consequences of lesion to somatosensory cortex

Answer 58

Lesions in S1 impair somatosensation (dysfunction in texture, size and shape discrimination)

Question 59

Consequences of lesion to posterior parietal cortex

Answer 59

``` the two most striking consequences of PPC lesions are apraxia and hemospatial neglect (neglect syndromes and acquired dyslexias) ``` Left hemisphere lesions cause Broca’s aphasia Right hemisphere lesions cause hemispatial neglect (failure to perceive and process stimuli from one side of the body, most commonly contralateral side) – hemispatial neglect occurs more commonly in right hemisphere, so often left-sided neglect