Disorders Of Electrical Excitability Flashcards
Hyponatremia
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
Hypernatremia
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
Hypokalemia
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
Hyperkalemia
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
Channelopathies
Diseases that disrupt the activity of the ion channel
Na+ channel blockers as local anaesthetics
Block Na+ channels to block action potential generation so pain information cannot be transferred
Peripheral nerve block
Injection of local anaesthetic around single nerves
Regional or epidural nerve block
Injection of local anaesthetic around the dorsal and ventral roots at the appropriate level of the spinal cord
Bier’s block
Infusion of a large volume of local anaesthetic into a limb during temporary interruption of blood circulation
Mutations in K+ channels
Prolong the depolarisation of action potentials
Serious cardiac arrhythmia, ventricular fibrillation and risk of cardiac arrest
Demyelinating diseases
Damage to Schwann cells and loss of myelin, often due to auto-immune reaction
Multiple sclerosis
Patches of inflammation in the brain
Loss of myelin and damage to axons
Repeated episodes leads to permanent damage
Possible stem cell repair
Charcot Marie-Tooth disease
Most common inherited disease
Affects peripheral nerve conduction
Progressive loss of myelination in legs then in arms and hands
Guilian-Barre syndrome
Inflammatory attack on the myelin and peripheral nerves
Tingling, abnormal sensation, muscle weakness
Possible paralysis and risk of respiratory failure
Peripheral neuropathies
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
Neuritis
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
Bells Palsy
Weakness or paralysis of facial muscles - usually temporary
Caused by viral inflammation (herpes simplex) of facial nerve
Trigeminal neuralgia
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
Myasthenia gravis
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
Hyporeflexia
Depressed or absent reflexes
Caused by: lower motor neuron lesions, loss of motor neurons, denervation of muscles, thyroid deficiency
Hypereflexia
Exaggerated reflexes, spatiscity and rigidity
Causes: upper motor neuron lesions, spinal trauma or trans-section, brain haemorrhage, drug misuse
Spinal shock
Loss of sensation and motor paralysis
Follows partial or complete transaction of spinal cord
