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What are the spaces on the axon between myelination called?

Nodes of Ranvier


What are the signs and symptoms of motor neuropathy?

Weakness, Wasting, Muscle fasciculation, loss of reflexes.


What are the signs and symptoms of sensory neuropathy?

anaesthesia, paraesthesia, burning, hypersensitivity, ataxia (loss of proprioception), ulcers, areflexia.


What are the signs and symptoms of autonomic neuropathy?

Dry mouth, dry eyes, orthostatic hypotension, loss of heart rate variability, GI disturbance, bladder urgency/frequency, impotence, dry skin/ excess sweating, pupil reactions.


What are the three main types of peripheral nerve damage?

Axonal neuropathy, demyelinating and axonotmesis.


What change would you get in conducting velocity in a demyelinating neuropathy?



What changes would you get to the conducting velocity and compound motor action potential in an axonal neuropathy?

Normal CV but a slow CMAP.


Which type of neuropathy tends to be demyelinating and which tend to be axonal?

Inflammatory neuropathies tend to be demyelinating whilst chronic conditions tend to be axonal.


What is the likely cause of a mononeuropathy?



How does compression cause damage to a nerve?

Conduction velocity is slowed or blocked, the AP may also be dispersed. Damage is also caused to the myelin.


What are the symptoms and signs of carpal tunnel syndrome?

Numbness - waking at night, lateral 3 1/2 fingers.
Weakness - Thumb abduction
Wasting - Thenar eminence


What are the treatment options for carpal tunnel syndrome?

Wrist splints, injection of steroids.
Carpal tunnel decompression.


A man presents with 3/7 h/o of sensory loss in hands and feet, has progressively got weaker and can't lift arms above head, bladder and bowel function is normal. What is the likely diagnosis?

Guillain Barre Syndrome.


What is Guillain Barre Syndrome?

An acute, demyelinating, polyridiculo neuropathy, with preceding infection, vaccination, trauma, surgery. (Inflammation of spinal roots)


What are the investigations for Guillain Barre Syndrome?

Lumbar puncture - high level of protein will indicate inflammation.
Never conduction studies - show reduced CV and AP delayed and dispersed.


What are the treatment options for Guillain Barre Syndrome?

Intravenous immunoglobin - probably blocks pathogenic antibodies but reactions are relatively common, expensive and there is a world wide shortage.
Plasma exchange - Washes out pathogenic antibodies, venous access may be restricted, electrolyte disturbances common, BP fluctuations common.


A lady presents with numbness and burning sensation in her feet to the ankles it has progressed over the last few years, she is a controlled type II diabetic. What is the likely diagnosis?

Chronic diabetic neuropathy.


What are some of the aetiologies of chronic peripheral neuropathy?

Idiopathic, diabetes, drugs (statins,cytotoxic drugs) B12 deficiency, Alcohol, Inherited.


At resting membrane potential where are the higher concentrations of Na, K and Cl.

Na and Cl are at higher concentrations outside of the cell. K is at higher concentration inside the cell.


How does the membrane of a nerve cell maintain the resting potential?

A pump, using ATP, exchanges 3 Na out of the cell and brings 2 K into the cell.


What if the resting potential of a neurone?



What triggers an action potential?

A neurotransmitter binds to a ligand-gated channel allowing sodium to enter the cell.


What is the threshold potential and what is its value in mV?

The threshold potential is the level of depolarisation that is required to open voltage-gated Na channels, it is followed by the rising phase of an action potential. It has a value between 40-55mV.


At which point to the rising phase of an action potential end?

At approximately +40mV the Na channels close so no more Na can enter the cell.


Explain the falling phase of an action potential.

Depolarisation of the membrane also opens K channels after a slight delay, there is now an eflux of K which begins to restore the resting membrane potential and there is a slight hyper=polarisation.


Why can an action potential not fire straight after a previous one?

The Na and K are in the wrong place, there is a period where this is restored by the ion exchanger, this period is called the refractory period.


What are the insulating cells of the central nervous system?



What are the insulating cells of the peripheral nervous system called?

Schwann cells.


Which disease is caused by the genetic mutation of Schwann cells?

Charcot Marie Tooth disease.


What occurs at the synapse when an action potential arrives?

Voltage gated Ca2+ gates open allowing an influx of calcium ions. This causes vesicles of neurotansmitter to exocytose. This then diffuses across the synaptic cleft and binds to receptors on the postsynaptic terminal which triggers an action potential.