L11 Cerebral Hemispheres

Question 1

What is the neocortex and where is it found?

Answer 1

Also called the cortex.

• Thin sheet of neurons lying just beneath the pia mater of the cerebral hemispheres
• Associated with higher level functions
• Only found in mammals and the most developed primates

Question 2

Describe the structure of the neocortex.

Answer 2

• Highly folded to increase SA
• Ridges called gyri occupy 2/3rds of the cortex area
• Grooves called sulci occupy 1/3rd of the cortex area

Question 3

Name the cortical lobes.

Answer 3

• Frontal lobe
• Parietal lobes
• Occipial lobes
• Temporal lobes

Question 4

Describe the funciton of the neocortex.

Answer 4

• Recieves sensory info associated with the primary cortical areas
• Info sent to sensory association cortical areas which integrates info
• Info then relayed to primary and secondary motor areas where we plan and command voluntary movements
• At the frontal lobe association cortex we formulate desires, intentions, beliefs and decision making

Question 5

How many layers is the neocortex composed of?

Answer 5

6 layers.

Question 6

Describe layer I.

Answer 6

• The molecular layer
• Closest to the pia mater
• Contains very few neurons or cell bodies

Question 7

Describe layer II.

Answer 7

• Contains small neuron soma and intra-hemisphere cortical circuits

Question 8

Describe layer III.

Answer 8

• Contains small pyramidal neurons connected to other cortical areas (intra and inter hemisphere connections)

Question 9

Describe layer IV.

Answer 9

• Contains small neurons which recieve input from the thalamus

Question 10

Describe layer V.

Answer 10

• Contains large pyramidal neurons with large axons projecting to areas outside of the neocortex

Question 11

Describe layer VI.

Answer 11

• Small spindle like neurons which make efferent connections to the thalamus, and intra-cortical connections to other cortical layers

Question 12

What percentage of cortical connections are intra cortical and what percentage are sub-cortical?

Answer 12

• 99% of cortical connections are intra-cortical, both intra and inter hemisphere.
• 1% of cortical connections are to sub-cortical areas.

Question 13

What are the 4 primary cortices?

Answer 13

• Primary motor cortex in the frontal lobe (M1)
• Primary somatosensory cortex in the parietal lobe (S1)
• Primary visual cortex in the occipital lobe (V1)
• Primary auditory cortex found on top of the temporal lobe

Question 14

How have researchers been able to assign functions to specific cortical areas?

Answer 14

Non-invasive imaging e.g. MRI, fMRI, CT, PET.

Historical records of patients with traumatic brain injuries.

Question 15

The cortex is divided into…

Answer 15

Functional columns

Question 16

Functional columns make up a cortical map of the body called…

Answer 16

A somatotopic map

Question 17

Describe the somatotopic map.

Answer 17

• A map which displays the spatial organisation of body parts correspongin to the mammalian primary somatosensory cortex and innervation
• Higher density fof sensory innervation = larger erea of somatotopic map occupied
• Lips and oral cavity highly innervated = large

Question 18

When sensory info is recieved by the primary sensory cortices (e.g. visual and auditory) where is it sent to?

Answer 18

The sensory association areas, integrated and processed, allowing us to form a perception of the outside world

Question 19

Where is info sent from the sensory association areas?

Answer 19

Sent to the primary motor cortex which executes voluntary movement.
Or sent to supplementary second motor areas.

Question 20

What is the internal capsule?

Answer 20

A white matter structure containing the axons which comprise the principle fibre tracts to and from the cortex.

Question 21

Describe the stucture of the internal capsule.

Answer 21

• V-shaped

- Anterior limb, posterior limb and apex called the genu

Question 22

What are the 3 major axon types found in the internal capsule?

Answer 22

• Extrapyramidal motor neurons
• Thalamo-cortical fibres
• Corico-spinal and cortico-bulbar fibres

Question 23

What structure connects the two cerberal hemispheres?

Answer 23

The corpus callosum

Question 24

Which hemisphere is dominant in right handed people?

Answer 24

The left hemisphere

Question 25

What is the limbic system?

Answer 25

A conceptual term for a number of inter-connected brain regions that are thought to co-operate to generate emotions of:

• Fear
• Aggression
• Anger
• Hopelessness

And the ability to recognise these emotions in others.

Question 26

What are the 5 components of the limbic system?

Answer 26

• Cigulate gyrus/cortex
• Hippocampus
• Amygdala
• Septum
• Ancient olfactory cortex

Question 27

How is the limbic system connected to the ANS?

Answer 27

Via the fornix (a fibre tract).

Plays a role in allowing the ANS to generate the fight or flight response.