Cells of Nervous System and Neuromuscular Junction

Question 1

What does the CNS consist of?

Answer 1

• Cerebral hemispheres
• Brainstem (pons, medulla and midbrain)
• Spinal cord
• Cerebellum

Question 2

What are the different types of nervous cell?

Answer 2

1. Unipolar - 1 axonal projection
2. Psuedo-unipolar - 1 axonal projection with divides into 2
3. Bipolar - 2 projections from cell body
4. Multipolar - Numerous projections from cell body

Question 3

What is a neuron made up of?

Answer 3

• Soma (cell body)
• Axon (nerve fibre)
• Dendrite (highly branched cell body from soma)

Question 4

What are the key features of a neuron?

Answer 4

• Non-dividing
• Excitable cells of CNS
• Heterogenous morphology

Question 5

What is an astrocyte and what is it function?

Answer 5

• Glial cell
• Most abundant cell type in CNS
• Blood brain barrier
• Synthesise neurotrphic factors
• Neurotrasmitter removal and reuptake

Question 6

What are oligodendrocytes and what is their function?

Answer 6

• Produce myelin for peripheral nerves
• One schwan cell -> one axon segment
• Glial cell

Question 7

What is the function of microglial cells?

Answer 7

• Similar to macrophages

- Perform immune functions in the CNS

Question 8

What are and what is the function of ependymal cells?

Answer 8

• Epithelial cells - line fluid filled ventricles

- Regulate production and movement of CSF

Question 9

What are 4 major ions in neurotrasnsmission?

Answer 9

• K+
• Cl-
• Na+
• Ca2+

Question 10

What is the relative concentrations of ions inside and outside of a neuron?

Answer 10

K+ Higher inside
Na+ Higher outside
Cl- Higher outside
Ca2+ Higher outside

Question 11

What occurs during an action potential?

Answer 11

1. Membrane depolarisation - Opening of VGSC -> Na+ in
2. Membrance repolarisation - VGKC opens slower -> K+ out
3. Resting configuration - Na+ enters vestibule & upon phosphorylation -> ions transported through Na+K+ATPase
4. Active configuration - Na+ removed from cell -> K+ enters vestibule
5. Pump returns to resting configuration -> K+ is transported back into the cell

Question 12

What is saltatory conduction?

Answer 12

• Between myelin sheaths are Nodes of Ranvier

- AP ‘jumps’ between nodes

Question 13

How is an action potential propagated?

Answer 13

1. VGSC open -> Na+ influx
2. Membrane depolarisation -> AP ‘moves along’ neuron
3. VGKC open -> K+ efflux -> repolarisation

Question 14

How is neurotransmitter released?

Answer 14

1. Neurotransmitter in vesicles
2. Action potential opens Ca2+ channels at presynaptic terminal
3. Ca2+ influx -> vesicle exocytosis

Question 15

How are postsynaptic receptors activated?

Answer 15

NT binds to receptors

Question 16

How is neurotransmitter reuptaken?

Answer 16

1. Neurotransmitter dissociates from receptor and can be:
   - Metabolised by enzymes in synaptic cleft
   - Recycled by transporter proteins

Question 17

What are the types of synaptic organisation?

Answer 17

• Axodendritic
• Axosomatic
• Axoaxonic

Question 18

What occurs at a neuromuscular junction?

Answer 18

1. Action potential propagated along neuron to presynaptic terminal
2. Ca2+ influx -> ACh release into synapse
3. ACh binds to nicotinic receptors on skeletal muscle
4. Miniature EPP: quantal ACh release

Question 19

What is the location, function and effect of sarcoplasmic reticulum?

Answer 19

Location: Surrounds myofibrils
Function: Ca2+ storage -> Ca2+ release following sarcolema depolarisation
Effect: Myofibril and muscle contraction