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Medicine > Cells of the Nervous system and Neuromuscular junction > Flashcards

Cells of the Nervous system and Neuromuscular junction Flashcards

1
Q

Anatomy of CNS

A

Consists of :

  1. Cerebral hemispheres
  2. Brainstem
  3. Cerebellum
  4. Spinal cord
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2
Q

Neurons in CNS

A
  1. Non-dividing excitable cells

2. Share common features: Soma, Axon and Dendrites

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3
Q

Neuroglia

A
  1. Astrocytes (support cells)
  2. Oligodendrocytes (myelin)
  3. Microglia
  4. Ependyma
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4
Q

Cerebral hemispheres

A
  • Highly convoluted surface of ridges; gyri and valleys ; sulci
  • 4 functional regions: frontal, parietal, temporal, occipital
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5
Q

Brainstem

A
  • Consists of: Midbrain, Pons, Medulla (in descending order)

- Target or source of all cranial nerves and has numerous important functions

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6
Q

Cerebellum

A
  • Hindbrain structures attached to brainstem

- Important role in motor coordination, balance and posture

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7
Q

Spinal cord

A

Extends down from medulla

  • Conduit for neural transmission
  • Coordinates some reflex actions
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8
Q

Neurons morphology

A
  1. Unipolar : 1 axonal projection
  2. Pseudo-unipolar : Single axonal projection that divides into two
  3. Bipolar : 2 projections from cell body
  4. Multipolar : 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
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9
Q

Soma

A

(cell body, perikaryon)

  • Contains nucleus and ribosomes
  • Neurofilaments -> structure and transport
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10
Q

Axon

A
  • Long processes (aka nerve fibre) -> originates from some at axon hillock
  • Can branch off into ‘collaterals’
  • Usually covered in myelin sheath
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11
Q

Dendrites

A
  • Highly branched cell body - NOT covered in myelin

- Receive signals from other neurons

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12
Q

Astrocytes

A

Most abundant cell type within CNS
Able to proliferate

Functions:

  • Structural cells : blood-brain barrier
  • Cell repair : synthesise neurotrophic factors
  • Homeostasis : neurotransmitter removal and reuptake
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13
Q

Oligodendrocytes

A
  • Variable morphology and function
  • Numerous projections that form internodes of myelin
  • One oligodendrocytes -> myelinates many axons
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14
Q

Schwann cells

A
  • Produce myelin for peripheral nerves

- One Schwann cells -> myelinates one axon segment

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15
Q

Oligodendrocytes vs. Schwann cells

A

Oligodendrocytes are in the BRAIN whereas Schwann cells are found in the peripheral NS

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16
Q

Microglial cells

A
  • Specialised cells : similar to macrophages

- Perform immune functions in CNS

17
Q

Ependymal cells

A
  • Epithelial cells : Line fluid filled ventricles

- Regulate production and movement of cerebrospinal fluid

18
Q

CSF production and movement

A

Ependymal cells produce CSF

CSF is produced in the ventricles (by choroid plexus) 
It flows through the ventricular system and into the subarachnoid space. 
Small structures (arachnoid granulations, located along the superior sagittal sinus) permit the drainage of CSF from the sub-arachnoid space into the venous blood
19
Q

Resting membrane potential

A
  • 4 major physiological ions : K+, Na+, Cl-, Ca2+
  • Cell membranes: impermeable to these ions; transportation by channels and pumps
  • This causes an uneven ion distribution:
    1. High Extracellular Na+ and Cl-
    2. Low Extracellular K+
    3. High conc. gradient for Ca2+
  • Difference in concentration creates a potential difference across the membrane
  • Neuronal cells : Negative charge inside compared to outside; RMP of between -40 to -90 mV
  • Positive and negatice charges are concentrated around the membrane
20
Q

Action potential

A

Na+ and K+ have important roles in generation of neuronal action potential

At RMP

  • Voltage-gated Na+ channels (VGSCs) and voltage-gated K+ channels (VGKCs) are closed
    1) Membrane depolarisation - opening of VGSC -> Na+ influx -> further depolarisation
    2) VGKCs open at a slower rate and causes -> efflux of K+ from cell -> membrane repolarisation
21
Q

Restoring RMP

A

AP leaves Na+ and K+ imbalance -> need to be restored
Na+-K+-ATPase (pump) restores ion gradients

1) Resting configuration - Na+ enters the vestibule and 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

Around half of our energy is used for this process of restoring the K+/Na+ balance

22
Q

Saltatory conduction

A
  • AP spreads along the axon by ‘cable transmission’
  • Myelin prevents AP spreading because; it has high resistance and 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

4 steps of neurotransmission

A
  1. Propagation of the action potential (AP)
  2. Neurotransmitter (NT) releases from vesicles
  3. Activation of postsynaptic receptors
  4. Neurotransmitters uptake
24
Q
  1. Propagation of AP
A
  • AP is propagated by VGSCs opening
  • Na+ influx -> membrane depolarisation -> AP ‘moves along’ neuron
  • VGKC opening -> K+ efflux -> repolarisation
25
Q
  1. Neurotransmitter release from vesicles
A
  • AP opens voltage-gated Ca2+ channels at presynaptic terminal
  • Ca2+ influx -> vesicle exocytosis
26
Q
  1. Activation of postsynaptic receptors
A
  • NT binds to receptors on post-synaptic membrane

- Receptors modulate post-synaptic activity

27
Q
  1. Neurotransmitter uptake
A
  • NT dissociate from receptor and can be:
    • Metabolised by enzymes in synaptic cleft
    • Recycled by transporter proteins
28
Q

Communication between nerve cells

A

Autocrine and paracrine: Neurotransmitter release

29
Q

Post-synaptic cell - synaptic organisation

A
  1. Axodendritic synapse : connection between presynaptic terminal; neuronal dendrite
  2. Axosomatic synapse : connection between presynaptic terminal; neuronal soma
  3. Axoaxonic synapse : connection between presynaptic terminal; neuronal axon
30
Q

Nerve and muscle cells

A

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

Communication between nerve and effector cells : Paracrine; neurotransmitter release

31
Q

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

*EPP is same as membrane potential; Need a summation of EPPs to get an action potential

32
Q

Sarcolemma

A
  • The skeletal muscle membrane: nAChR activation -> depolarisation - action potential
  • AP travels through T-tubules
33
Q

T-tubules

A

Continuous with sarcolemma and closely connected to sarcoplasmic reticulum

34
Q

Sarcoplasmic reticulum

A

Location: surrounds myofibrils - contractile units of muscle

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

Effect: Ca2+; myofibril contraction and muscle contraction

35
Q

Botulism

A

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

36
Q

Myasthenia Gravis

A

Autoimmune disorder: antibodies directed against ACh receptors

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

37
Q

Lambert-Eaton myastenic syndrome

A

Autoimmune disorder: antibodies directed against VGCC

Medicine (8 decks)

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