Anatomy, cell physiology and CSF

Question 1

Do the dorsal and ventral roots belong to the CNS or PNS?

Answer 1

PNS

Question 2

Give 2 differences between grey matter and white matter

Answer 2

• grey matter is cell bodies and white matter is axons
• grey matter is highly vascular giving it a grey appearance, white is less so and appears white due to lots of fatty myelin present

Question 3

How many spinal segments are there?

Answer 3

31

Question 4

Which part of the spinal cord will the lateral horn be found and what types of fibres are found within in it?

Answer 4

the thoracic region and sympathetics

Question 5

Describe the reflex arc of the knee

Answer 5

1a- muscle spindle detect stretch and relay this to L3/4. This stimulates the a motor fibres in the ventral horn to cause contraction of the quadricep. The 1a-muscle spindles also descend to L5/S1 and synapse with inhibitory interneurones which inhibit a- motor neurone going to hamstrings, allowing flexion of the knee.

Question 6

What is the jedraddiks maneuver?

Answer 6

Voluntary movement elsewhere (clenching teeth, pulling hands apart) to increase sensitivity of tendon stretch

Question 7

What is a funiculus?

Answer 7

A segment of white matter containing multiple distinct tracts, with impulses travelling in multiple directions. There are three; ventral, dorsal and lateral.

Question 8

What is a tract?

Answer 8

An anatomically and functionally defined white matter pathway connecting two distinct regions of white matter, impulses travel in one direction.

Question 9

What is a fasiculus?

Answer 9

a subdivision of a tract supplying a distinct region of the body.

Question 10

What is the name of a grey matter tract/ column?

Answer 10

Rexed’s laminae

Question 11

What is a nucleus?

Answer 11

A collection of functionally related cell

Question 12

Describe the difference between association fibres, commissural fibres and projection fibres

Answer 12

Association: connect regions in same hemisphere.
Commissural: connects left and right hemisphere.]
Projection: project down to cerebral hemisphere and cord/ brain stem.

Question 13

Describe the layout of the brains ventricles

Answer 13

2 lateral ventricles with the third ventricle sitting inferior to them, between the thalamus, The third ventricle continues downwards as the cerebral aqueduct which dilates in the pons as the 4th ventricle. This extended down through the spinal cord. There are lateral and medial aperatures though which CSF drains into the subarachnoid space.

Question 14

Where is CSF created and absorbed?

Answer 14

Created in choroid plexus cells of the ventricles and is absorbed into arachnoid granulations which feed into dural venous sinuses and also into lymphatics around the brain and spinal cord.

Question 15

What is the difference between T1 and T2 MRI?

Answer 15

T1= fluid black and fat bright
T2= fluid white and fat intermediate

Question 16

Describe the three roles of astrocytes other than maintaining blood brain barrier

Answer 16

• provide energy for neurones (neurones can acquire glucose from blood but also need lactate from astrocytes- glucose lactate shuttle)
• Removal of neurotransmitters (some neurotransmitters such as glutamate are toxic at high concentrations, so astrocytes mop it up and convert it into glutamine and give it back to presynaptic neurones)
• maintain low K+ in brain (neurones release K+ on firing, so NaKCCT on astrocytes needed to keep K+ low, if this didnt happen, neurones would be depolarised by the high K+ concentrations, leading to epilepsy (inappropriate firing)

Question 17

What do oligodendrocytes do?

Answer 17

Myelinate the CNS, one oligodendrocyte myelinates many axons

Question 18

What is the function of microglial cells?

Answer 18

They are activated by foreign material to become phagocytic and remove debris and foreign material, they also present antigens to T cells. They also inhibit initiation of pro-inflammatory T cell response this is because you dont want inflammation within the skull- this is called immune privilege.

Question 19

Describe how and why the blood brain barrier is created?

Answer 19

• tight junctions between endothelial cells, induced by astrocytes
• also basement membrane and end feet of astrocytes fusing to ensure nothing can diffuse from blood to brain
• ensures toxins and aminoacids which may act as neurotransmitters cannot pass into brain
• also means concentrations of glucose, K+, AA etc can be controlled as have to diffuse through cells.

Question 20

What are the 3 classes of neurotransmitters?

Answer 20

• aminoacids (glutamate, GABA, glycine)
• biogenic amines (Ach, NA, dopamine, serotonin and histamine)
• peptides (dynorphin, substanceP, somatostatin, neuropeptide Y, cholecystokinin)

Question 21

Name 3 ionotrophic glutamate receptors and what their activation causes

Answer 21

AMPA receptors, Kainate receptors and NMDA receptors.

All lead to Na, K and Ca channel opening (NMDA only), leading to depolarisation.

Question 22

How does the metabotrophic glutamate receptor work?

Answer 22

It is a GPCR leading to IP3 and more Ca2+ influx or inhibition of AC so less cAMP

Question 23

Describe what long term potentiation is?

Answer 23

• Glutamatergic synapses have both AMPA and NMDA receptors, AMPA are activated 1st leading to fast depolarisations
• NMDA receptors will only be activated when glutamate binds and the cell is depolarised
• NMDA receptor activation leads to up regulation of AMPA (maybe todo with more Ca2+ entry)
• therefor strong, high frequency stimulation leads to easier transmission of action potential across synapse
• important for learning and memory

Question 24

Why is too much glutamate toxic?

Answer 24

It activates NMDA receptors leading to increased Ca2+ influx, which is toxic to cells.

Question 25

What is the main inhibitor neurotransmitter in the brain and in the brain stem and spinal cord? How do they both work?

Answer 25

Brain= GABA
Brain stem and spinal cord= glycine
Both work by opening Cl- channels.

Question 26

Where do the neurones releasing Ach originate?

Answer 26

Nucleus basalis (forebrain) and septohippocampal pathway (midbrain), some are also found in corpus striatum.

Question 27

What is the role of Ach release?

Answer 27

arousal, learning, memory, motor control

Question 28

What disease is associated with nucleus basalis degeneration?

Answer 28

alzheimers disease- which is why acetylcholinesterase inhibitors (neostigmine) may be given to help symptoms

Question 29

Give two pathways which use dopamine and what that pathway is involved in?

Answer 29

Nigrostriatal pathway- motor control

Mesolimbic pathway- mood, arousal and reward

Question 30

Name two centres from which noradrenaline is released and their function?

Answer 30

Locus coreulus- found in brainstem, projects throughout brain, is inactivated during sleep
Reticular formation- associated with arousal and wakefullness

Question 31

From where do serotonin neurones originate and what are they involved in?

Answer 31

originate from raphe nucleus, projects throughout brain and involved in modulation of sleep, wakefullness and mood.

Question 32

Name the inputs to the anterior and posterior circulations of the brain

Answer 32

anterior= internal carotid artery
posterior= vertebral artery

Question 33

Describe the blood supply to the cerebellum

Answer 33

there is posterior inferior cerebellar artery, anterior inferior cerebellar artery and a superior cerebellar artery

Question 34

Describe the blood supply to the cerebral hemispheres

Answer 34

the medial portion of the frontal and parietal lobes are supplied by the anterior cerebral artery. the lateral portions of the medial and parietal lobes and the temporal lobes are supplied by the middle cerebral artery and the occipital lobes are supplied by the posterior cerebral artery.

Question 35

Describe the consequence of transection of many pontine arteries, during neurosurgery for example.

Answer 35

may get locked in syndrome

Question 36

What are the lenticulostriate arteries a branch of?

Answer 36

the middle cerebral artery, supply the internal capsule