7. Introduction to the cortex of the brain.pdf

Question 1

What is the cerebral cortex?

Answer 1

The grey matter covering the surface of the cerebral hemispheres
I.e. the grey matter covering the white matter

Question 2

All sensory information goes through the…

Answer 2

Thalamus

Question 3

Other name for pituitary?

Answer 3

Hypophysis

Question 4

How many layers are in the cerebral cortex?

Answer 4

5 rows

Also in columns which are associated with different modalities of sensation for a given part of the body.
Some areas of the columns mingle so interpretation can begin here

Question 5

What are the 4 sources of inputs to the neocortex? i.e. the AFFERENTS

Answer 5

1. Ascending information from the thalamus. Topographical thalamic information is routed to specific areas of the cortex for primary processing (e.g. somatosensory sensation, hearing), Non topographical information is routed to the appropriate areas in the cortex.
2. Ascending information from other sub-cortical structures. These include the hypothalamus, basal parts of the forebrain and the brain stem (involved in sleep/arousal amongst other things).
3. Commissural fibres (from pyramidal neurons) which travel between hemispheres
4. Association fibres (from pyramidal neurons) which travel from the ipsilateral cortex, either from distant areas or from neighbouring cortical columns.

Question 6

What 2 features of characteristic to output signals from the neocortex?

Answer 6

Always excitatory in nature

Always via pyramidal cells, i.e. uses excitatory neurotransmitters.

Question 7

What are the outputs of the neocortex? i.e. the EFFERENTS

Answer 7

• All parts of the cortex project to the thalamus
• Projections from the somatosensory and motor cortices provide most of the input to the
basal ganglia
• Cortex projects to the brainstem nuclei (which deal with motor and sensory information)
• Cortex projects to spinal cord (onto motor neurons in the anterior horn)
• The cortex in one hemisphere can project to the contralateral hemisphere
• There are ipsilateral hemispheric projections of differing lengths (longer ones between
association cortices and shorter ones for example between sensory and motor cortex)

Question 8

How did we learn about the functions of the neocortex?

Answer 8

1. HISTOLOGY: Map and divide the brain up using forms of anatomy
   • Brodmann divided the brain into 52 REGIONS based on cortical cell prevalence and distribution of the different cortical layers (histology) Note that most cortex is actually NEOCORTEX (relatively new evolutionarily, comprising 6 layers)
2. MEASURE THE EFFECTS OF LOCALISED DAMAGE following trauma/stroke (association and disassociation) or DURING ELECTRICAL STIMULATION of a particular area in an awake patient.

3. SCAN THE ACTIVITY OF THE BRAIN during defined tasks.
• EEG – poor spatial resolution
• CT (computerised tomography)
• MRI & fMRI
• PET

Question 9

What are the three functional divisions of the cortex

Answer 9

1. Motor
2. Association areas
3. Sensory

Question 10

What defines the “primary areas” of the cortex functionally?

What are the 5 primary areas?

Answer 10

Primary areas receive thalamic input with relatively little processing

1. Primary SOMATOSENSORY AREA is post central gyrus of the parietal lobe
2. Primary MOTOR AREA is just anterior of the central sulcus
3. Primary VISUAL CORTEX is located in the occipital lobe
4. Primary OLFACTORY CORTEX is located in the anterior temporal lobe (piriform cortex)
5. Primary AUDITORY AREA is located in the medial temporal lobe

Question 11

What is the functional role of the association areas of the cortex?

Answer 11

Association areas integrate and pass on information from all relevant areas of the CNS – largest portion of the cortex.

Consists of 2 types, UNIMODAL (one type of modality input ie vision) and POLYMODAL (multiple modal input ie vision and hearing)

Question 12

What is the functional role of the cerebellar cortex of the cortex?

Answer 12

Integrates ascending proprioceptive information with descending movement intent, and feeds back to cerebral cortex to refine movement

Question 13

Function of cerebellum?

Answer 13

The cerebellum primarily functions to modify movement by comparing sensory information with pre-motor information, and affecting change

Question 14

How many layers of the cerebellar cortex?

Answer 14

3 principal layers
Top= Molecular layer
Middle= Purkinje cell layer
Centre/lower= Granule cell layer

Question 15

Which cells are found in the 3 layers of the cerebellar cortex?

Answer 15

Molecular layer: Stellate cells
Purkinje cell layer: Purkinje cells, basket cells
Granule cell layer: Golgi cell, granule cell

Question 16

Role of climbing fibre in the cerbellar cortex?

Answer 16

Can up or down regulate the purkinje cell to control stimulation. Purkinje cell in middle layer but climbing fibres extend into molecular layer above and granule layer below.

Question 17

Mode of input into cerebellum?

Answer 17

Via 3 peduncles (sup, middle, inf)

Question 18

What are the inputs into the cerebellum?

Answer 18

• PROPRIOCEPTIVE INFO from the skin, muscles and joints of the body and head
• SPINAL REFLEX information
• Some types of VISUAL, AUDITORY and MOTION information are projected to the
cerebellum.
• Large numbers of different fibres and tracts from the BRAINSTEM (nuclei and
reticulum).
• SENSORY INFO from the somatosensory cortex via the OLIVES
• Motor PLANNING INFO from the pre-motor cortex via the OLIVES

Question 19

What are the outputs (efferents) of the cerebellum?

Answer 19

• Projects onto the brainstems postural motor nuclei
• Projects to the vestibular nuclei (balance and motion)
• Projects to muscle spindles for reflex and postural control
• Project to motor and pre-motor cortices via thalamus for motor control and motor
learning of complex sequences

Question 20

How can lesions in primary cortex by mitigated?

Answer 20

Lesions in the primary cortex produce obvious deficits which can occasionally be mitigated by neuronal plasticity

Question 21

How do lesions in associations areas differ from those in primary cortex?

Answer 21

Lesions in association cortices produce a wide variety of symptoms and are less stereotypical in nature.

Question 22

What is an Agnosia ?

Answer 22

Agnosia is the inability to process sensory information

Question 23

3 examples of visual agnosias?

Answer 23

• Ocular ataxia
• What - Where pathway disorientation
• Prosopagnosia (or face blindness)

Question 24

2 examples of auditory agnosias?

Answer 24

• Wernicke’s and Brocca’s aphasias

* Amusia

Question 25

Role of the association area?

Answer 25

The association areas integrate information from different receptors or sensory areas and relate the information to past experiences. Then the brain makes a decision and sends nerve impulses to the motor areas to generate responses.

e.g. Wernickes (at temporal lobe) and Broca’s (at frontal lobe)