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Year 1 - Organisation of the Body > 6.1 Tissues of the Peripheral Nervous System > Flashcards

6.1 Tissues of the Peripheral Nervous System Flashcards

1
Q

What is the CNS?

A

Central nervous system, composed of the brain and spinal cord

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2
Q

What is the PNS?

A

Peripheral nervous system, composed of cranial and spinal nerves that make up the somatic and autonomic nervous system. The autonomic system also splits into sympathetic, parasympathetic and enteric divisions

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3
Q

From where is the PNS derived?

A

Migratory neural crest cells, migrate away from the neural tube to form the peripheral nervous system

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4
Q

What are sensory nerves?

A

Afferent nerves, can be visceral or somatic

  • Visceral: conveys impulses from a particular tissue or organ to the CNS
  • Somatic: respond and convey stimuli in the external environment to the CNS
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5
Q

What are motor nerves?

A

Efferent nerves, can be somatic or autonomic, convey information from the CNS to the tissues

  • Somatic: conveys impulses that result in voluntary movements of skeletal/striated muscle
  • Autonomic: visceral, not under voluntary/conscious control, conveys information to cardiac and smooth muscles (smooth muscle also lines blood vessels) as well as stimulating glands
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6
Q

Which nervous systems maintain homeostasis?

A

The sympathetic, parasympathetic and enteric systems

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7
Q

Which system is the enteric nervous system controlled by?

A

Various sections of the parasympathetic and sympathetic nervous systems - essentially the autonomic nervous system

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8
Q

Do sympathetic and parasympathetic nerves show the same effects in tissues they both innervate?

A

No, they generally show opposing actions

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9
Q

What is the saying describing the general action of the sympathetic nervous system?

A

Fight or flight

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10
Q

What is the saying describing the general action of the parasympathetic nervous system?

A

Rest and digest

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11
Q

Give three features of neurons.

A
  • Excitable (responsive to change)
  • Conductive (able to transmit nerve impulses)
  • Secretory (communicate with other cells using chemical messengers)
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12
Q

What is a perikaryon?

A

The cell body or soma of a neuron, containing the nucleus

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13
Q

What are Nissl bodies?

A

Clumps of rough ER in the cytoplasm of neurons, highly basophilic

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14
Q

What are dendrites?

A

Threadlike processes/extensions from the cell body which branch profusely and conduct electrical signals transmitted through synapses (with other nerve cell processes) towards the cell body
Longer in sensory nerves than motor (cell body is further from synapse in a sensory nerve)
Known generally as nerve fibres

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15
Q

What is a dendritic spine?

A
  • A small membranous protrusion from a neuron’s dendrite that typically receives input from a single synapse of an axon
  • Serve as a storage site for synaptic strength and help transmit electrical signals to the neuron’s cell body
  • Thin neck with a bulbous head, neck connects to shaft of dendrite
  • Suggested to aid plasticity and learning
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16
Q

What are axons?

A
  • Known generally as nerve fibres
  • Long threadlike structures that conduct impulses away from the cell body to the cell’s target/next synapse
  • Lack protein synthesis machinery so all proteins and organelles must be transported down them to the synapse via the cytoskeleton (microtubules)
  • This is ANTEROGRADE AXONAL TRANSPORT
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17
Q

What is anterograde and what is retrograde axonal transport?

A
  • Anterograde is where products are transported from the cell body to the synapses
  • Retrograde is where products are transported from the synapses to the cell body

Processes are allowed by ‘rail-like’ microtubules

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18
Q

What is kinesin?

A

A special motor protein associated with microtubules that allows anterograde transport

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19
Q

What is dynein?

A

A special motor protein associated with microtubules that allows retrograde transport

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20
Q

What are glial cells?

A

Specialised non-neuronal support cells, e.g. Schwann and satellite cells

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21
Q

What are the features and function of glial cells?

A
  • Provide peripheral nerves with support, protection and a suitable microenvironment
  • Individual Schwann cells wrap around the axon (in myelinated neurons) to form the myelin sheath
  • Myelin is mostly lipid
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22
Q

What are the gaps between Schwann cells along the axon?

A

Nodes of Ranvier

  • Interdigitating extensions of Schwann cell cytoplasm
  • External base lamina
  • Regular gaps in the myelin sheath
  • Increases rate of conduction
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23
Q

What type of disease is Guillain-Barre syndrome and what causes it?

A
  • Autoimmune demyelinating neuropathy
  • Caused by antibodies to glycosphingolipids
  • Usually triggered by acute infections
  • Myelin regeneration occurs but there may also be some axon damage
  • Many patients become paralysed and unable to breathe
  • 5% die from respiratory paralysis
  • Random onset, but usually self limiting
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24
Q

How do neurons remain at rest?

A

They expend energy to maintain a resting membrane potential/electrical polarisation across the plasma membrane
Inner surface is slightly more negative that the exterior

25
Q

What causes the resting membrane potential?

A
  • Unequal distribution of sodium and potassium ions
    • > more sodium outside
    • > more potassium inside
  • Permeability of the membrane to the charged ions (membrane potential will trend to equilibrium potential of whichever ion is most permeable, as seen in an action potential)
  • Membranous sodium-potassium pumps that export 3 sodium for every 2 potassium cells imported (net loss of charge)
  • Establishes a resting potential of around -70mV
26
Q

Which way do sodium ions flow in response to a stimulus?

A

Into the axon, causing the membrane potential to increase/tend towards the equilibrium potential for sodium ions

27
Q

How does repolarisation occur?

A

The delayed rectifier channels (potassium) open, increasing potassium permeability (moves out) causing the membrane potential to decrease again

28
Q

What is a nerve impulse?

A

A wave of electric excitation caused by the propagation of an action potential

29
Q

What two factors affect speed of impulse conduction?

A
  • Axon diameter (wider = faster)

- Presence of myelin sheath (unmyelinated = slowed except in very thin and small nerves)

30
Q

What is saltatory conduction?

A

Where the sideways diffusion of ions allows action potentials to be propagated at adjacent nodes of Ranvier

31
Q

How are impulses transferred between neurons?

A

Through the release and effect of neurotransmitters - end bulbs of axons contain synaptic vesicles packed with neurotransmitters, they release their contents into the synaptic cleft when stimulated by the arrival of an action potential. The process by which they do this is exocytosis. Postsynaptic membranes have receptors that bind to the neurotransmitter and this will in some cases trigger depolarisation and excitation of the trigger cells (although some neurotransmitters can be inhibitory and have the opposite effect)

32
Q

What is the NMJ and the motor end plate?

A

The NeuroMuscular Junction is the synapse/axon terminal of a motor neuron with a motor end plate

  • Motor end plate = highly excitable region of the muscle plasma membrane/sarcolemma
  • Responsible for initiations of action potentials across the muscle’s surface, causing it to contract
33
Q

What is the neurotransmitter at the NMJ?

A

ACh, acetylcholine

34
Q

What ion triggers vesicles to bind to the pre-synaptic membrane and release their contents into the synaptic cleft?

A

Calcium ions, enter via voltage-dependant calcium channels upon the arrival of an action potential

35
Q

Where does ACh bind to on the motor end plate?

A

To NICOTINIC ACh receptors, which are ligand-gated ion channels, so once the neurotransmitter has bound, the pore opens and allows the rapid influx of ions into the cell (sodium) whilst also allowing potassium ions to flow out of the muscle cell’s cytosol
Due to electrochemical gradients, more sodium flows in that potassium out, producing local depolarisations along the end plate, which will then trigger an action potential in the adjacent sarcolemma

36
Q

What is the EPP?

A

End Plate Potential

  • Spreads along the end plate to the sarcolemma where it is then propagated
  • Travels down the T-tubules
  • Initiates the release of calcium from the sarcoplasmic reticulum
  • Initiates muscle contraction
37
Q

What terminates the action of ACh?

A

Acetylcholinesterase (AChase) degrades the neurotransmitter, choline is taken back up whilst acetate is allowed to diffuse away

38
Q

What is the structure of a nerve?

A

Multiple axons bound together by connective tissue

Mix of myelinated and unmyelinated nerves, with the latter usually predominating

39
Q

What is the epineurium?

A

Complete outer layer of connective tissue surrounding a nerve, also contains loose connective tissue beneath it with blood vessels and adipose tissue within the loose connective tissue

40
Q

What are fascicles?

A

Structures present in many nerves where axons are gathered together in bundles, with each bundle being surrounded by a connective tissue sheath known as the perineurium

41
Q

What is the perineurium?

A

Connective tissue sheath surrounding fascicles/bundles of axons

42
Q

What is the endoneurium?

A

The membrane covering individual axons and Schwann cells that contain fibroblasts, the occasional macrophage and reticular fibres
Capillaries can supply essential nutrients/neural elements through these layers

43
Q

What are ganglia?

A
  • Groups of neuronal cell bodies
  • Associated with glial cells
  • Often with a connective tissue capsule
  • Act as relay or integrative stations along sensory and motor pathways
44
Q

Where are cell bodies of sensory neurones found?

A

In the dorsal root ganglia of each spinal nerve
- contains many hundreds or thousands of pseudounipolar neurons that are surrounded by many satellite (glial) cells
Communication in a DRG does not require transmission through a synapse

45
Q

Where are the cell bodies of the autonomic system found?

A

In autonomic ganglia - associated with both the sympathetic and the parasympathetic nervous systems
Cell bodies are dispersed and only a few satellite cells present, otherwise structure is similar to those of the DRG
Neurons here are multipolar, with their dendrites synapsing with motor signals transmitted by the preganglionic signals, that have originated in the CNS

46
Q

What is a pseudounipolar neuron?

A

A neuron that has only one extension from its cell body, an axon that has split into two branches, one to the PNS (afferent) and one to the CNS (efferent)

47
Q

Which are the sympathetic ganglia?

A
  • Sympathetic chain (paravertebral) ganglia (allows communication up and down the trunk)
  • Mesenteric ganglia (part of mesenteric plexus)
48
Q

Which are the parasympathetic ganglia?

A
  • Cranial (associated with cranial nerves)

- Terminal (near or within the internal organs that are supplied by these nerves)

49
Q

What are the ganglia of the enteric system?

A

Very small
- Ganglia of Auerbach’s
- Meissner’s plexus
Often considered part of the parasympathetic nervous system but in functional terms operate independently and is also modified by the sympathetic nervous system

50
Q

What is Wallerian degeneration?

A
  • Axonal degeneration that can cause muscle paralysis

- Occurs when a nerve is damaged and a distal region atrophies

51
Q

Is it possible to achieve some regeneration in the PNS?

A

Yes, due to the presence of Schwann cells

  • They can divide and produce a hollow tube enclosed by the endoneurium
  • Proximal end of nerve fibre sends out sprouts towards these tubes
  • Sprouts are attracted by growth factors produced by the Schwann cells
  • Growth is very slow, however - ~3-4mm a day
52
Q
  • What are some more names for and features of peripheral nerve disorders?
A
  • Peripheral neuropathies
  • Neuropathies
  • Neuritis
  • Peripheral neuritis
  • Mononeuropathy (affect one nerve)
  • Polyneuropathy (affect many nerves, causes neuropathic pain)

Can be chronic (long-term) or acute (sudden and rapid onset, slow resolution)

Can also be genetic or idiopathic

Symptoms are usually tingling, numbness and pain

53
Q
  • What can cause peripheral nerve disorders?
A
  • Pre-existing conditions, e.g. diabetes, immune mediated diseases
  • Injury
  • Medication
  • Excess alcohol consumption
  • Nerve compression (e.g. carpal tunnel syndrome, = mononeuropathy, or thoracic outlet syndrome)
  • Brachial plexus injuries or complex regional pain syndrome can be problems that begin after an injury
54
Q
  • What is Charcot-Marie-Tooth disease (CMT)?
A
  • Hereditary motor and sensory neuropathy
  • Characterised by progressive loss of muscle tissue and touch sensation across multiple parts of the body
  • One of a group of varied inheritable disorders of the PNS
55
Q
  • What are the general treatments for neuropathic diseases?
A
  • Eliminating the cause (where possible)
  • Maintaining muscle strength
  • Limiting pain
56
Q
  • What is Pelizaeus-Merzbacher disease?
A
  • Mutation in myelin protein
  • X-linked
  • Causes reduction in myelin and therefore reduced speed of transmission in peripheral nerves
57
Q
  • What is Myasthenia Gravia (MG)?
A
  • Autoimmune disease caused by antibodies affecting
    acetylcholine receptors
  • Affects control of voluntary muscle
  • Characterised by fatigable muscle weakness
58
Q
  • What are congenital myasthenic syndromes?
A
  • Mutations in genes of proteins at the NMJ that can also cause disease, e.g. mutations in rapsyn, a protein that encodes for the acetylcholine receptor

Year 1 - Organisation of the Body (20 decks)

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