Week 110- Peripheral Neuropathy

Question 1

Resting membrane potential

Answer 1

-65mV

polarised at rest by the Na/K pump. Pumps Sodium out and Potassium in.

Two gradient forces: Chemical and Electrical

Question 2

Action potential

Answer 2

Rising phase, falling phase, hyperpolarisaton.

Ligand gated Na channels open. Na in.
Opens Voltage gated Na channels.
Triggers rising phase. Voltage reaches 40mV.
Na channels close at peak of action potential.
Voltage gated K channels open and K rushes out.
Restore membrane potential.

Question 3

Myelin

Answer 3

80% Lipid

20% protein

Allows faster conduction of action potential.

myelinated neurons= white.

Schwann cells- peripheral CNS
Oligodendrocytes- Central CNS

Question 4

Multiple Sclerosis

Answer 4

Demylination of central nerves.

Question 5

Guillan-Barre syndrome

Answer 5

– Inflammatory demyelination of peripheral nerves
– Progressive motor and sensory function loss
- Characterised by high protein in CSF

treatment:

• IV imunoglobulin
• Plasma washout (rarely used)

general:
Assess risk of VTE (heparin needed)
monitor Lung function and consult ITU if necessary
treat pain but avoid resp depressants

Question 6

Charcot-Marie tooth disease

Answer 6

genetic mutation in Schwann cells.

Question 7

Lambert-Eaton syndrome

Answer 7

Genetic condition where antibodies are raised against voltage gated Calcium channels.

Question 8

gamma-Amino butyric acid (GABA) neurotransmitter.

Answer 8

Inhibitory neurotransmitter.

acts through ligand gated chloride channels to hyperpolarize neurone.

Question 9

glycine neurotransmitter

Answer 9

Inhibitory neurotransmitter.

acts through ligand gated chloride channels to hyperpolarize neurone.

Question 10

Central Nervous system

Answer 10

• sympathetic
• parasympathetic
• enteric

Question 11

sympathetic system

Answer 11

arises T1-L2. Preganglionic neurons located lateral horn.

Sympathetic chains run length of spinal cord as paravertebral ganglia.
Origin of many postganglionic neurons.

Pass through the para-vertebral column without synapsing.

Question 12

Sympathetic system- preganglionic neurones

Answer 12

– Short
– Myelinated
– Release Acetylcholine
– Connect with several (~ 10) postganglionic neurones

Question 13

Sympathetic system- postganglionic neurones

Answer 13

Long
– Unmyelinated
– Release Noradrenaline
• except in sweat glands (acetylcholine)

Question 14

Parasympathetic system- preganglionic neurones

Answer 14

Located either in brainstem (some cranial nerves) or S2-S4 segments of the spinal cord.

Question 15

Ionotropic receptors

Answer 15

– Predominantly postsynaptic
– Conduct ions
– Which may also activate intracellular signalling pathways
– Act fast

Question 16

Metabotropic receptors

Answer 16

(Do not conduct ions)
– Predominantly presynaptic
– Coupled to intracellular signalling pathways
– May also be coupled to ionotropic receptors
– Act (more) slowly

Question 17

Sympathetic system- Neurotransmitters

Answer 17

Acetylcholine

Noradrenaline

Question 18

Parasympathetic system- Neurotransmitters

Answer 18

Acetylcholine

Muscarinic Acetylcholine receptors on effector muscles

Question 19

Acetylcholine

Answer 19

Nicotinic receptors
– Ligand-gated channels
– Excitatory
– Multiple subtypes
• Each receptor composed of 5 subunits
• Each subunit may occur in multiple forms
• Tissue-specific expression
– On postganglionic neurons
– Also neuromuscular junction
• Muscarinic receptors
– Metabotropic receptors - are NOT channels
– On effectors of parasympathetic system
• Except adrenal medulla which has nicotinic receptors

Question 20

Adrenal Medulla

Answer 20

• Directly innervated by preganglionic neurons
• Cells of the adrenal medulla are basically
modified postganglionic sympathetic neurons
– Secrete noradrenaline and adrenaline

Question 21

Atropine

Answer 21

Muscarinic antagonist.

Muscle relaxant, used to dilate pupil for eye exams.

Question 22

Acetylcholinesterase as a drug target

Answer 22

Reversible inhibitors have clinical uses
– Myasthenia gravis
• Neostigmine, pyridostigmine
– Glaucoma
• Physostigmine, demecarium

irreversible inhibitors such as organophosphates very bad.

Question 23

Adrenergic receptors

Answer 23

Alpha receptors- alpha-1 antagonist doxazosin (treat hypertension).

Beta receptors- Salbutamol B2 agonist

antagonists- timolol- non specific blocker used to treat glaucoma
Bisoprolol- selective B1 antagonist

Question 24

Orthostatic/postural hypotension

Answer 24

Autonomic system doesn’t react quickly/enough to drop in blood pressure
when person stands up (from sitting)
– May be side effect of a1 adrenergic blockers

Question 25

Horner Syndrome

Answer 25

Cranial nerve damage (tumour, stroke etc)
– Unilateral
• Ptosis
• Decreased pupil size
• Anhidrosis

Question 26

Frey syndrome

Answer 26

– Parasympathetic fibres (branch of Trigeminal nerve) that supply parotid gland
becomes “diverted”
• Surgery or trauma
– Instead supply sweat glands of skin overlying parotid gland
– Sweat when should salivate

Question 27

Carpel tunnel syndrome

Answer 27

 Diagnosis:
 Nerve conduction studies
 Treatment
 Short term
 Wrist splints
 Local steroid injection
 Carpel tunnel decompression
 Day case procedure
 Good success rate
 What doesn’t work!
 Diuretic drugs
 Non-steroidal anti-inflammatory drugs

Question 28

Chronic peripheral neuropathy

Answer 28

 Common
 Slow progression
 Axonal (dying back) neuropathy
 Sensory, motor or mixed; sensory most
common
 Variable aetiology
 Idiopathic
 Diabetes
 Drugs (statins, cytotoxic drugs)
 B12 deficiency
 Alcohol
 Inherited

Question 29

Myasthenia Gravis

Answer 29

Autoimmune disease against acetylcholine receptor

Typically women 40s to menarche
May be related to hyperthyroidism (can have it out).

treatment:
IV immunoglobulin
Acetylcholinesterase inhibitors
immunosupressants.

Question 30

Bells palsy

Answer 30

Facial paralysis from dysfunction of cranial nerve 7 unilaterally.