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BRS NEUROLOGY > Cells of the Nervous System and Neuromuscular Junction > Flashcards

Cells of the Nervous System and Neuromuscular Junction Flashcards

1
Q

What are the cells of the nervous system?

A

Oligodendrocyte
Astrocyte
Microglia
Ependyma
Neuron

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2
Q

What is the morphology of neurones?

A

Unipolar: 1 axonal projection

Psuedo-unipolar: Single axonal projection that divides into two

Bipolar: 2 projections from cell body

Multipolar: Numerous projections from cell body

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3
Q

What are the types of multipolar neurones?

A
  • Pyramidal cells: ‘pyramid’ shaped cell body
  • Purkinje cells: GABA neurons found in the cerebellum
  • Golgi cells: GABA neurons found in the cerebellum
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4
Q

What are neurones?

A

Excitable cells of CNS
Heterogeneous morphology
Non-dividing cells

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5
Q

What are common features of neurones?

A

Soma (cell body, perikaryon):
Contains nucleus & ribosomes
Neurofilaments-> structure & transport

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

Dendrites: (receives communication from other neurones)
Highly branched cell body - NOT covered in myelin
Receive signals from other neurons

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6
Q

What is the direction of transmission in a neurone?

A

dendrite to axon

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7
Q

What are oligodendrocytes?

A

Glial cell - produces myelin in the CNS

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8
Q

What are astrocytes?

A

Most abundant cell type in CNS
Tend to stay in one place
Removes neurotransmitter and waste
Provides structure
Provides support to neurones

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9
Q

What are microglia?

A

Neuronal macrophages
Usually move around when activated

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10
Q

What are ependyma?

A

Epithelial cells lining the ventricles

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11
Q

What cells produce myelin in the PNS?

A

Schwann cells

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12
Q

What are the 4 major physiological ions?

A

Potassium, sodium, chloride, calcium

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13
Q

How do they major physiological ions pass membranes?

A

Membranes are impermeable to these ions
Transportation is regulated by channels and pumps

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14
Q

What do the channels and pumps of these ions cause in terms of ions?

A

high extracellular Na+ and Cl-
low extracellular K+
High concentration gradient for Ca2+

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15
Q

What does the difference in concentration of ions across a membrane cause?

A

creates a potential difference across the membrane

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16
Q

What is the charge of neuronal cells?

A

Negative charge inside compared to outside
RMP of between -40 to -90mV

Positive and negative charges are concentrated around the membrane

17
Q

Are the channels open or closed at resting membrane potential?

A

Voltage-gated Na+ channels (VGSCs) & voltage-gated K+ channels (VGKCs) are closed

18
Q

What happens when there is a membrane depolarisation in terms of Na and K?

A

1) opening of VGSC -> Na+ influx -> further depolarisation

2) VGKCs opens at a slower rate and causes -> efflux of K+ from cell -> membrane repolarisation

19
Q

What happens to the balance on ions when there is an action potential and how is it restored?

A

Ap leaves Na+ and K+ imbalance–> needs to be restored

Na+K+ATPase pump restores the ion gradient

20
Q

How many Na+ in/ out and how many K+ in/out normally?

A

3Na+ out
2K+ in

21
Q

What is the resting configuration and active configuration?

A

1) Resting configuration - Na+ enters vestibule & upon phosphorylation -> ions are transported through protein

2) Active configuration - Na+ removed from cell -> K+ enters the vestibule

3) Pump returns to resting configuration -> K+ is transported back into the cell

22
Q

What is saltatory conduction?

A

Saltatory conduction:

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

23
Q

What happens with neurotransmission at synapses?

A
  1. Propagation of the action potential:
    - AP is propagated by VGSCs opening
    - Na+ influx -> membrane depolarisation ->AP ‘moves along’ neurone
    - VGKC opening -> K+ efflux -> repolarisation
  2. Neurotransmitter (NT) release from vesicles
    - AP opens voltage-gated Ca2+ channels at presynaptic terminal
    - Ca2+influx -> vesicle exocytosis
  3. Activation of postsynaptic receptors
    - NT binds to receptors on postsynaptic membrane
    - Receptors modulate post-synaptic activity
  4. Neurotransmitter reuptake
    - NT dissociates from receptor and can be:
    Metabolised by enzymes in synaptic cleft
    Recycled by transporter proteins
24
Q

What are the types of communication between nerve cells?

A

Autocrine and paracrine: neurotransmitter release

25
Q

Describe potential synaptic organisation?

A

Axodendritic synapse: connection between presynaptic terminal-> neuronal dendrite

Axosomatic synapse: connection between presynaptic terminal -> neuronal soma

Axoaxonic synapse: connection between presynaptic terminal -> neuronal axon

26
Q

What is the neuromuscular junction?

A

Specialised structure incorporating axon terminal & muscle membrane allowing unidirectional chemical communication between peripheral nerve & muscle

27
Q

What is the communication between nerve and effector cells?

A

paracrine: neurotransmitter release

28
Q

What happens at the neuromuscular junction?

A

Action potential propagated along axon (Na+ & K+) -> Ca2+ entry at presynaptic terminal

Ca2+ entry -> acetylcholine (ACh) release into synapse

ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle —> change in end-plate potential (EPP)

Miniature EPP: quantal ACh release

29
Q

What is excitation-contraction coupling?

A

The skeletal muscle membrane: nAChR
activation -> depolarisation – action potential (AP) -> muscle contraction

30
Q

What happens at the sarcolemma during excitation-contraction coupling?

A

Sarcolemma:

  • The skeletal muscle membrane: nAChR activation -> depolarisation – action potential (AP)
  • T-tubules: continuous with sarcolemma & closely connected to sarcoplasmic reticulum
  • AP travels through T-tubules
31
Q

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

A

Location: surrounds myofibrils – contractile units of muscle

Function: Ca2+ storage -> Ca2+ release following sarcolemma depolarisation

Effect: Ca2+ -> myofibril contraction & muscle contraction

32
Q

What are disorders of the neuromuscular junction? (3)

A

Botulism

Myasthenia Gravis (MG)

Lambert-Eaton myasthenic syndrome (LEMS)

33
Q

What is Botulism?

A

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

34
Q

What is myasthenia gravis (MG)?

A

Autoimmune disorder: antibodies directed against ACh receptor

Cause fatigable weakness (i.e. becomes more pronounced with repetitive use)

35
Q

What is Lambert-Eaton myasthenic syndrome (LEMS)?

A

Autoimmune disorder: antibodies directed against VGCC

BRS NEUROLOGY (22 decks)

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