Cells of the nervous system

Question 1

What is a unipolar neurone?

Answer 1

A neurone with 1 axonal projection

Question 2

What is psuedo-unipolar neurone?

Answer 2

Single axonal projection that divides into two

Question 3

What is a bipolar neurone?

Answer 3

2 projections from cell body

Question 4

What is a multipolar neurone and give 3 examples

Answer 4

Numerous projections from cell body
Pyramidal cells: ‘pyramid’ shaped cell body
Purkinje cells: GABA neurons found in the cerebellum
Golgi cells: GABA neurons found in the cerebellum

Question 5

What are neurones

Answer 5

Excitable cells of CNS
Heterogeneous morphology
Non-dividing cells
Share common features:

Question 6

What is contained in a soma?

Answer 6

Contains nucleus & ribosomes
Neurofilaments for structure & transport

Question 7

What is an axon?

Answer 7

Long process (aka nerve fibre) - originates from soma at axon hillock
Can branch off into ‘collaterals’
Usually covered in myelin

Question 8

What are dendrites?

Answer 8

Highly branched cell body - NOT covered in myelin
Receive signals from other neurons

Question 9

What is a oligodendrocyte?

Answer 9

Glial cell - produces myelin

Question 10

What is an astrocyte?

Answer 10

Most abundant cell type in CNS

Involved in clearing excess neurotransmitters, stabilizing and regulating the blood-brain barrier, and promoting synapse formation.

Question 11

What is a microglia?

Answer 11

Neuronal macrophages

Question 12

What is an ependyma?

Answer 12

Epithelial cells lining CNS ventricles

Question 13

What does membrane impermeability to Ca2+, K+, Na+ and Cl- cause?

Answer 13

Transport is regulated by ion pumps
This causes an uneven ion distribution:
High extracellular - Na+ & Cl-
High intracellular - K+
High concentration gradient for Ca2+
Difference in concentration → creates a potential difference across the membrane

Question 14

What is the range for resting membrane potential for neuronal cells?

Answer 14

-40mV to -90mV

Question 15

How is an action potential reached?

Answer 15

Membrane depolarisation - opening of VGSC → Na+ influx → further depolarisation

VGKCs opens at a slower rate and causes → efflux of K+ from cell → membrane repolarisation

Question 16

How is resting potential regained after an AP?

Answer 16

AP leaves Na+ & K+ imbalance → need to be restored
Na+-K+-ATPase (pump) restores the ion gradients

Resting configuration - Na+ enters vestibule & upon phosphorylation → ions are transported through protein
Active configuration - Na+ removed from cell → K+ enters the vestibule
Pump returns to resting configuration → K+ is transported back into the cell

Question 17

Describe the process of saltatory conduction

Answer 17

AP spreads along the axon by ‘cable transmission’
Myelin prevents AP spreading because it has- high resistance & low capacitance
Nodes of Ranvier - Small gaps of myelin intermittently along axon:
AP ‘jumps’ between nodes - saltatory conduction
AP is unable to ‘jump’ across the gap at the axon terminal

Question 18

How does a synapse function?

Answer 18

Propagation of the action potential (AP)
AP is propagated by VGSCs opening
Na+ influx → membrane depolarisation → AP ‘moves along’ neurone
VGKC opening → K+ efflux → repolarisation

Neurotransmitter (NT) release from vesicles
AP opens voltage-gated Ca2+ channels at presynaptic terminal
Ca2+ influx → vesicle exocytosis

Activation of postsynaptic receptors
NT binds to receptors on post-synaptic membrane
Receptors modulate post-synaptic activity

Neurotransmitter reuptake
NT dissociates from receptor and can be:
Metabolised by enzymes in synaptic cleft
Recycled by transporter proteins

Question 19

What 2 types of intercellular signalling are neurones involved in?

Answer 19

Paracrine and autocrine

Question 20

What is an axodendritic synapse

Answer 20

A synapse between the presynaptic terminal and neuronal dendrite

Question 21

What is an axosomatic synapse

Answer 21

A synapse between between presynaptic terminal and a neuronal soma

Question 22

What is an axoaxonic synapse

Answer 22

A synapse between the presynaptic terminal and neuronal axon

Question 23

What type of communication is it in a neuromuscular junction?

Answer 23

Paracrine

Question 24

Outline what occurs at an NM junction

Answer 24

Action potential propagated along axon (Na+ & K+) causes Ca2+ entry at presynaptic terminal
Ca2+ entry causes acetylcholine (ACh) release into synpase
ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle causes change in end-plate potential (EPP)

Question 25

What does a minimal EPP cause?

Answer 25

A quantal(non-continuous) ACh release

Question 26

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

Answer 26

Location: surrounds myofibrils – contractile units of muscle

Function: Ca2+ storage causes Ca2+ release following sarcolemma depolarisation

Effect: Ca2+ causes myofibril contraction & muscle contraction

Question 27

What occurs in botulism?

Answer 27

Botulinum toxin (BTx): irreversible disruption of stimulation-induced ACh release from presynaptic nerve terminal

Question 28

What occurs in myasthenia gravis?

Answer 28

Autoimmune disorder: antibodies directed against ACh receptor
Cause fatigable weakness (i.e. becomes more pronounced with repetitive use)

Question 29

What occurs in Lambert-Eaton myasthenic syndrome (LEMS)

Answer 29

Autoimmune disorder: antibodies directed against VGCC