Cerebral cortex from cells to function

Question 1

What are the components of a neuron and their function?

Answer 1

Dendrites which direct stimulus towards cell

Dendritic spines principal axon target

Nucleus + (nucleolus)

Cell Body

Axon hillock

Axons direct unitary digital output away from the cell

Question 2

What are neurons used for?

Answer 2

Neurons are used for;
- Networking
- Vectorial impulse transmission/propagation
- Dissociative secretion/synapse formation
- Chemical Transmission
- Inhibitory or excitatory

Question 3

How are neurons classified and what is the main neuron we have and its function?

Answer 3

Based upon how many processes they have

Pseudo-Unipolar Cell (dorsal root ganglion) - they bring conduction towards the cell body (structurally this is an axon as its got a myelin sheath but functionally its a dendrites as its bringing information to a cell body)
- has a peripheral and central process

We also have “Modified” bipolar cells - commonly found in ear, eyes and nose

Question 4

What is a multipolar neuron, its features and 2 types of it?

Answer 4

Multipolar - lots of dendrites with 1 single axon

Interneuron (local processing)
- Has a SHORT axon
- Can be inhibitory or excitatory

Pyramidal cell (sending info from cerebral cortex)
- Has a LONG axon

Question 5

What is the Schwann cells job?

Answer 5

It builds only 1 internode in the PNS

They all envelope unmyelinated axons contacting 1 or more axons (cf myelinating ones)

Question 6

What is the Oligodendrocyte cells job?

Answer 6

It builds multiple internodes in the CNS

Question 7

What are some features of unmyelinated axons in the CNS + examples?

Answer 7

• They are not associated with myelinating cells (not embedded)
• Have continuous conduction f action potentials due to passive current flow (low conduction speed)

Examples - sensory fibres carrying pain, temp and itch

Question 8

What occurs in multiple sclerosis ?

Answer 8

Phasic disease
Demyelination
Inflammation (T cell/macrophage mediated)
Conduction block (slowing propagation)
Cross talk (paraesthesia - burning sensation)
Some re-myelination can occur
Permanent loss (due to cell death/axonal loss)

Can see white spots on MRI - signs of demyelination

More common in northern hemispheres that lack Vit D

Question 9

What is white matter?

Answer 9

Collections of nerve fibres many of which are coated in insulating fatty myelin

White matter also contains neuron processes Schwann/oligodendrocyte cells and myelin

Question 10

What is grey matter?

Answer 10

Processing

Contains: Neuron cell bodies, processes and synapses

Question 11

What are the Glial cells of the CNS?

Answer 11

Oligodendrocytes (myelination)
Astrocytes
Microglia
Ependyma (lining cells of the CNS cavities)

Question 12

What are the Glial cells of the PNS?

Answer 12

Schwann Cells (myelination)
Satellite Cells (support cells in ganglia)

Question 13

What are astrocytes and their function?

Answer 13

Astrocytes are star shaped cells and they appear in the white matter as fibrous astrocytes (longer and more extended) and as protoplasmic astrocytes in the grey matter (looks blobby)

They provide metabolic and mechanical support (and in the CNS scar tissue also).

Details;
- Control water distribution
- Potassium buffering
- ROS scavenging (Reactive oxygen species)
- Define architecture
- Regulate migration / pruning /synaptogenesis
- Help maintain but do not take upper the BBB

Question 14

What are astrocytes role in the BBB?

Answer 14

BBB is a barrier composed of endothelial cells and their tight junctions

Integrity is highly dependent on astrocyte ‘end feet

So the barriers consists of endothelial cells and their tight junctions and the astrocytes help to maintain it

Question 15

What is the function of microglial cells?

Answer 15

Microglial cells are described as the resident macrophages of the CNS

Their role is for;
- Phagocytosis and antigen presentation (immune response)
- Synaptic pruning

Question 16

What is the function of Ependymal cells?

Answer 16

Ependymal cells are ciliated cuboidal cells, that line the ventricle as part of a plexus and secrete (also reabsorb) CSF

Question 17

What its CSF?

Answer 17

CSF (cerebrospinal fluid)
- Clear, cell-free fluid partly produced in specialised ependyma on choroid plexus

Question 18

What are the 4 main lobes of the cerebrum and what separates them?

Answer 18

Frontal, parietal, temporal and occipital

Central sulcus separates the frontal and parietal lobes

Lateral sulcus/fissure separates the frontal and parietal lobes from the temporal lobe

Preoccipital notch separates the Occipital lobe from the Parietal and Temporal lobe

Parieto-occipital sulcus separates the parietal and occipital lobes

Calcarine sulcus separates the occipital lobe into two parts:
1) lingual gyrus (inferior part)
2) cuneus (superior part)

Question 19

How is the cerebral cortex sorted into layers?

Answer 19

They are sorted into layers by lamination during tissue development

The cerebral cortex external grey matter - convoluted shaped gyro increased packing per volume

Most cerebral cortex 6 layered neocortex (recent evolution) - e.g hippocampus has less layers

There is much less area within the 3rd and 4th layers as evolutionary they are old

Question 20

What are the 2 main neurons found in the main layers?

Answer 20

Stellate interneurons mostly in granular layers 2 + 4 - For inputs and local processing

Pyramidal neurons in pyramidal layers 3 + 5 - For outputs to local and distant targets

Question 21

What are the different layers of the cerebellum called from 1 - 6 and what functions and neurons would you find here?

Answer 21

Layer 1) - Molecular layer

Layer 2) - External Granular - INPUT from other cortex

Layer 3). External Pyramidal - OUTPUT local to other cortex

Layer 4). Internal Granular - INPUT from thalamus

Layer 5). Internal pyramidal - OUTPUT to brainstem and spinal cord

Layer 6). Multiform layer

External layers nearer brain, internal further away from brain!

Question 22

How do the layers of the cerebellum vary from region to region of the cerebellum?

Answer 22

Layers vary in thickness/cellular composition and also function from region to region

Stellate cells (interneurons) are more numerous in the sensory cortex (in layer 4) - more input

(also in primary visual cortex layers 4 is well developed/prominent and makes a striped appearance and this is why we call it the striate cortex!)

Whereas in the motor cortex you will see more pyramidal cells (layer 5) - more output

Question 23

What its brodmann’s areas ?

Answer 23

Its a map based on histological differences in structure across the cerebral cortex. It relates closely to function.

E.g motor function in area 4 (primary motor cortex) and area 1 (primary visual cortex) for input

Question 24

Tell me about the primary visual cortex and its association cortex

Answer 24

Primary visual cortex is located on the median area of the occipital lobe, receives input and does simple processing

The association visual cortex is adjacent to the primary visual cortex and carries out more complex processing of visual information (in rest of occipital lobe and beyond)

E.g Motion, object recognition, depth, binocular, patters and faces

Can get an impairment called Prosopagnosia which is a blindness for faces

Question 25

Describe the dual stream mode of the visual cortex?

Answer 25

The dual stream mode of the visual cortex starts off in the primary visual cortex then splits off into dorsal and ventral streams of visual information processing (by association cortexes); Dorsal Stream runs along the posterior parietal lobe; - Vision for action (movement, spatial) - Integrates motion vs object locations - Coordinates visual guided action for skilled movements - Guides visual attention (basically more awareness) Ventral stream; - Vision perception (object recognition) - Recognition inferno-temporal cortex - Distinguishes spatial patters, objects and faces - Stores visual memory - Recognises significance of objects and faces (Basically more recognition of objects and faces)

Question 26

What are the general principles for function localisation across the cerebral cortex?

Answer 26

The cerebral cortex can be split into primary and association cortex (majority of cerebral cortex in humans is association cortex) The primary motor cortex is the principle exit in motor and entry points in sensory In the association cortex there is integration, complex processing often cognate primary cortex info

Question 27

What are the 2 types of modes that you can get from the association cortex?

Answer 27

Unimodal - one top of modality input/output Polymodal - multiple modal input (e.g vision and somatic sensation in the dorsal stream)

Question 28

What is the function of the primary motor cortex and where is it located?

Answer 28

The primary motor cortex is located just anterior to the central sulcus. It has more direct control of motor activity than other motor areas Force, direction and speed of muscle contraction

Question 29

What do body region maps show (homunculus)?

Answer 29

This is called homunculus Areas of the brain showing how much of it controls what body parts. Certain parts are enlarged to show fine sensory and motor skills and the quantity needed e.g hands

Question 30

Where are the association cortex regions for the primary motor cortex and what do they do?

Answer 30

- Supplementary motor area - Premotor cortex - Posterior parietal cortex

Question 31

Where is the Supplementary motor area and what is its function?

Answer 31

Supplementary motor area; - Planning complex tasks! - Simple movement - Complex movement (especially two hand movements) - Mental rehearsal of complex movement It is located on the midline surface of the hemisphere just in front of (anterior to) the primary motor cortex and superior to the premotor cortex

Question 32

Where is the Premotor cortex and what is its function?

Answer 32

Its just anterior to the Primary motor cortex and inferior to the supplementary motor area. Its function is; - to prepare for action - Posture and gait - Integration of spatial information - Planned movement - Grasping

Question 33

Where is the Posterior parietal cortex and what is its function?

Answer 33

Its located in the superior region of the parietal lobe Its function is; - To integrate visual information to formulate motor commands (hence why is in parietal!)

Question 34

What is the function of the primary somatosensory cortex and where is it located?

Answer 34

Its located just posterior to the central sulcus It senses touch, pain, etc It has different modalities, based upon the depth of the gyrus. The deepest part is for tactical info/muscle spindle, more superficially is for basic processing, even more superficially is for size, shape and texture and more posteriorly is for motion, direction and orientation!

Question 35

What is the function of the association somatosensory cortex and where is it located ?

Answer 35

Its located in the parietal lobules superior and inferior Its mainly responsible for awareness and perception in space (orientation) It is also responsible for rearrangement of memories, organising grasping reaching movement, number processing, mirror neurons here!

Question 36

What happens if the association somatosensory cortex is damaged?

Answer 36

If you damage the inferior parietal lobule you will deny an existence of your left hand side of body, will draw a clock with one side missing To do with awareness of self in space Also asterognosis (inability to recognise objects by touch) Damage in superior parietal lobule will cause problems with visuomotor integration (optic ataxia - affects co-ordination, balance and speech).

Question 37

What happened in the Boston Crow Bar Case?

Answer 37

A guy was tamping on the railway and the rod bounced and managed to go through the mans skull and brain and he still somehow lived! The rod had been driven through his frontal lobe hence how he still lived but there was a huge change in his personality and motivation which are functions associated with the frontal lobe

Question 38

What can damage to the frontal lobe cause?

Answer 38

- Personality changes - Deficits in planning - Perseveration - Primitive reflexes - Abulia (slowlessness of intellect)

Question 39

What are the functions of the prefrontal lobes?

Answer 39

- Contributes to attention - Morality - Planning - Working memory - Conscious decision making - Social behaviour regulation

Question 40

What did Paul Pierre Broca discover?

Answer 40

He had a patient called Tan (or so he thought as this is all the patient could mutter) and he suffered from Expressive Aphasia - Language is reduced to disjointed words and instance construction is poor but comprehension is okay. Once Tan died Broca dissected Tan's brain and discovered a lesion in an area that is now called Broca's area and it is for executing speech. It is located in the inferior frontal gyrus of the frontal lobe

Question 41

Where is Wernicke's area and what is its function?

Answer 41

Wernicke's area is fo comprehension of speech Wernicke's area is located in the posterior section of the superior temporal gyrus (STG), usually in the left cerebral hemisphere. This area encircles the auditory cortex on the lateral sulcus, the part of the brain where the temporal lobe and parietal lobe meet

Question 42

What would a lesion to Wenicke's area cause?

Answer 42

Receptive aphasia - unable to understand/generate meaningful language

Question 43

Where is the primary auditory area and what is its function?

Answer 43

Used for hearing; integrating and processing complex auditory signals, which includes language comprehension The primary auditory cortex is located on the superior temporal gyrus in the temporal lobe

Question 44

What connects Wernicke and Broca's areas together and what does damage to this cause?

Answer 44

Wernicke and Broca's areas are connected together by DTI of acute fasciculus (association bundle). Damage to this area causes conduction aphasia (difficulty repeating words/phrases)

Question 45

How was the classical model wrong about right and left handers and the side of the brain they use?

Answer 45

Most processing does happen in left even in left and right handers 4% there's usually damage Most have a dominant left hemisphere Language processing 96% in left

Question 46

How does the dual stream mode work in language specialisation?

Answer 46

The stream starts in Wernicke's area and the Dorsal stream (sensorimotor) maps acoustic speech to articulatory networks through the angular and supra marginal gyrus to the the frontal lobe and Broca's area for Articulation The ventral stream is for comprehension bilaterally. It starts in Wernicke's area and travels into the primary auditory cortex for word sound recognition.

Question 47

How do we know specialisation of the hemispheres occurs and what different things do they do?

Answer 47

Hemispheres are specialised Left is mostly dominant where language and calculation is done Right is mainly drawing, music and spatial perception In 96% of the population... We know this due to corpus callosum slicing People get corpus callosum cut when they have really bad epilepsy If you ask someone with split brain to feel their keys in their pockets the left hand feels and the right cortex recognises but cannot activate the language centres too speak the word keys as they are in the left hemisphere.

Question 48

Why does a small percentage of people have rights sided language control?

Answer 48

Many of the 4% with right sided language control have damaged left hemisphere or it can b completely missing. Therefore hemispheric specialisation can switch sides

Question 49

What is important in stroke recovery?

Answer 49

Brain plasticity

Question 50

How do brain cells and regions talk to one another?

Answer 50

Commissural - cortex to cortex cross over the midline (largest commissural bundle of fibres is the corpus callosum) Association - cortex to cortex cross "stay"on the same side Projection - communicate with other structures inside and outside the brain - By projections fibres lik bundle of nerve fibres in internal capsule and corona radiata

Question 51

What happens to the corticospinal tract after corona radiata stroke?

Answer 51

You get a reduced corticospinal tract as projections don't work the same