Disorders Of Electrical Excitability

Question 1

Hyponatremia

Answer 1

Decrease in sodium concentration outside the cell <135mmol/L

Causes: Diuretics, renal disease (inadequate reabsorption of salts)
Liver cirrhosis (alcoholism)
Congestive heart failure (water retention)

Symptoms: Muscle cramps
Weakness, fatigue
Altered mental state (confusion, hallucinations, decreased consciousness, possible coma)
brain oedema

Question 2

Hypernatremia

Answer 2

Increase in Na+ above 145mmol/L

Causes: Renal failure (water loss and dehydration)
Fever, diarrhoea (water loss in elderly or infants)

Symptoms: Tremor
Seizure
Hyper-reflexia
Convulsions
Intense thirst leading to lethargy, stupor and coma
Brain shrinkage and bleeding through damage ton blood vessels in the brain

Question 3

Hypokalemia

Answer 3

Decrease in potassium concentration <3.5mmol/L

Causes: Diuretics
Renal disease (inadequate reabsorption of salts)
Liver cirrhosis (chronic alcoholism)
Malnutrition (or malabsorption in GI tract)
Mild symptoms: Muscle weakness, fatigue, constipation, cardiac arrhythmia
Severe symptoms: Muscle paralysis, respiratory paralysis, paralysis of GI tract, potentially fatal abnormal heart rhythms

Question 4

Hyperkalemia

Answer 4

Increase in potassium concentration >5.5mmol/L

Causes: Decreased kidney function or drug interactions during the treatment of kidney infections (interferes with urinary excretion)

Symptoms: impairment of neuromuscular, cardiac and GI organ systems
Ventricular fibrilation
Increased risk of cardiac arrest

Question 5

Channelopathies

Answer 5

Diseases that disrupt the activity of the ion channel

Question 6

Na+ channel blockers as local anaesthetics

Answer 6

Block Na+ channels to block action potential generation so pain information cannot be transferred

Question 7

Peripheral nerve block

Answer 7

Injection of local anaesthetic around single nerves

Question 8

Regional or epidural nerve block

Answer 8

Injection of local anaesthetic around the dorsal and ventral roots at the appropriate level of the spinal cord

Question 9

Bier’s block

Answer 9

Infusion of a large volume of local anaesthetic into a limb during temporary interruption of blood circulation

Question 10

Mutations in K+ channels

Answer 10

Prolong the depolarisation of action potentials

Serious cardiac arrhythmia, ventricular fibrillation and risk of cardiac arrest

Question 11

Demyelinating diseases

Answer 11

Damage to Schwann cells and loss of myelin, often due to auto-immune reaction

Question 12

Multiple sclerosis

Answer 12

Patches of inflammation in the brain
Loss of myelin and damage to axons
Repeated episodes leads to permanent damage
Possible stem cell repair

Question 13

Charcot Marie-Tooth disease

Answer 13

Most common inherited disease
Affects peripheral nerve conduction
Progressive loss of myelination in legs then in arms and hands

Question 14

Guilian-Barre syndrome

Answer 14

Inflammatory attack on the myelin and peripheral nerves
Tingling, abnormal sensation, muscle weakness
Possible paralysis and risk of respiratory failure

Question 15

Peripheral neuropathies

Answer 15

Diabetic neuropathy - damage to sensory and motor axons in distal limbs due to dysregulation of glucose levels in the blood - lead to ulceration, infections and gangrene

Autonomic neuropathy - loss of sympathetic and parasympathetic nerves, leads to poor circulation, GI tract motility and healing, risk of gangrene in severe cases

Question 16

Neuritis

Answer 16

Inflammation of cranial nerves - leads to compression in the bony canals

Optic - loss of vision in eyes over a few hours

Vestibular - loss of vestibular function on one or both sides
Loss of balance and control of movement

Question 17

Bells Palsy

Answer 17

Weakness or paralysis of facial muscles - usually temporary

Caused by viral inflammation (herpes simplex) of facial nerve

Question 18

Trigeminal neuralgia

Answer 18

Stabbing or electric-shock like pain in parts of the face or surface of the eye - usually on one side and lasting for a few seconds but can become constant

Triggered by touch/loud sounds/ chewing/brushing teeth

Compression of the trigeminal nerve which carries pain and somatosensory information from the face to trigeminal nuclei in the brain stem and midbrain

Question 19

Myasthenia gravis

Answer 19

Autoimmune disorer - loss of function of ACh receptors on skeletal muscles disrupting synaptic transmission

Fluctuating muscle weakness and fatigue which worsens with activity and improves with rest

Symptoms: difficulties breathing, talking, chewing, swallowing
difficulties with locomotion (climbing stairs, walking)
Facial paralysis or weakness or facial muscles
Double vision, difficulty maintaining a steady daze

Question 20

Hyporeflexia

Answer 20

Depressed or absent reflexes

Caused by: lower motor neuron lesions, loss of motor neurons, denervation of muscles, thyroid deficiency

Question 21

Hypereflexia

Answer 21

Exaggerated reflexes, spatiscity and rigidity

Causes: upper motor neuron lesions, spinal trauma or trans-section, brain haemorrhage, drug misuse

Question 22

Spinal shock

Answer 22

Loss of sensation and motor paralysis

Follows partial or complete transaction of spinal cord