Week 110: Peripheral Neuropathy Flashcards
What are action potentials in nerve and skeletal muscle initiated by?
Activation of ligand-gated Na+ channels by neurotransmitters
What are ligand-gated channels?
Ion channels gated by the presence of a specific signal molecule
What are voltage-gated channels?
Ion channels that are opened or closed according to the potential difference (voltage) across the cell membrane
What is the Na+-K+ATPase or Na+ pump?
Produces the uneven distribution go Na+ ions across the cell membrane
How does the Na+-K+ATPase/Na+ pump work?
- Uses metabolic energy to move Na+ ions out of the cell and K+ ions into the cel AGAINST their concentration gradients
- The ATPase binds extracellular K+ and intracellular Na+ ions (usually in 2:3) and hydrolyses adenosine triphosphate (ATP) to provide energy needed to change its conformation
- This leads to the ejection of Na+ into the extracellular medium and K+ into the cytosol thus allowing the cell to maintain high levels of K+ ions and low concentration of Na+ ions in the cell
What are ion channels?
The route by which ions can diffuse across cell membranes down their electrochemical gradient
How are neurone activated?
- Starting polarisation of -65mV
- Activations starts when sodium channels open and Na+ goes into the cell, making it positively charged
- K+ then starts to leak out and Na+ stops going in - this is the REFRACTORY PERIOD
- The pump then corrects so it can be repeated
- Cannot be activated again if Na_ is in the cell
- Propagation: travels along the axon - as the polarity of membrane changes, the next part of the cell membrane notices and does the same
- Nodes of Ranvier: jumping
- Continuous usually vs saltatory (jumping)
- Then the next cell/organ is activated:
- Calcium comes into the cell at the synaptic cleft/synapse
- Presynaptic vesicles move towards the cell membrane due to the Ca, attach to the cell membrane (exocytosis) so it opens up and releases contents into the synaptic cleft (usually something like acetylcholine)
What produces myelin for the central nervous system?
Oligodendrocytes
What produces myelin for the peripheral nervous system?
Schwann cells
What do photoreceptors do?
Light
What do thermoreceptors do?
Heat
What do barareceptors do?
Stretch
What do nociceptors do?
Pain
What do chemoreceptors do?
Chemicals
What is always present at neuromuscular junctions?
Acetylcholine
What is the sympathetic nervous system responsible for?
Fight or flight
What is the parasympathetic nervous system for?
Rest and digest
Which nerve is most likely for the digestive system?
Vagus
Which nerve is most likely for the pelvis?
Podendal
What do both pre sympathetic and sympathetic preganglionic nerves use as a transmitter?
Acetylcholine
What do parasympathetic post ganglionic neurone use as a transmitter?
Acetylcholine
Act on muscarinic receptors on target organs
What do sympathetic post ganglionic neurones use as a transmitter?
Noradrenaline
What is Horner’s syndrome?
⇒ Damage to cranial nerves on one side ⇒ Results in one sided: - Decreased pupil size - Ptosis - Anhydrosis (not sweating) ⇒ Can be caused by a stroke
What is orthostotic or postural hypertension?
⇒ Causes drop of blood pressure when standing causing syncope
What is Frey syndrome?
⇒ Damage to nerves of side of the head that supply the parotid gland (they can become diverted)
⇒ End up innervating sweat glands of skin over parotid gland
⇒ Results in sweat rather than saliva
What is Guillaume-barré syndrome?
⇒ Immune reaction against peripheral nervous system
⇒ Eventually gets to the point you can’t breath
⇒ Treatment: washing out of fluid in patient to rid them of antibodies
- Treatment lasts a couple of months and then they deteriorate
⇒ Can be cause by a virus, often influenza
⇒ Immune repression
What is herpes/varicella zoster?
- 1st time: chicken pox
- 2nd time: shingles
- Painful
- Blisters
- Travels along the course of one nerve
What can happen in diabetics?
- Damage to axons, starts far away and then progress centrally without being noticed
- Crucial to keep blood sugar under control
What is Charcot Marie Tooth disease?
- Genetic deficiency of the myelin sheath
- Toe drop
- Hammer toes
- Lack of sensation in arms and feet
- Generally clumsiness
What happens in distal axonal degeneration?
- Occurs in diabetes: end gets damaged and retreats towards CNS
- Dying back of axons
What happens in Wollarian axonal degeneration?
- Cut nerve and the whole part dies but myelin sheath remains, providing a sheath to rebuild the neurone
- All degenerates together
- COmplete death
What is Myasthenia Gravis?
⇒ A neuromuscular junction disorder
- Weakness of muscles from overuse
- Caused by antibodies against acetylcholine receptors
- The more the nerve is used, the more antibodies produced, hence fatiguable weakness
What is Lambert Eaton Myasthenia Gravis
⇒ A neuromuscular junction disorder
- Antibodies against voltage-gated calcium channels
What is Neuromyotonia?
⇒ A neuromuscular junction disorder
- Antibodies against voltage-gated potassium channels
What is carpal tunnel syndrome?
- Affects thumb and 2.5 fingers
- Hypothenar eminence
- Tingling
- Can be painful
- Wake at night and shake hands out
- Can be associated with pregnancy
- Can be operated on
- While that hand is recovering, the other hand gets it
- Weakness of thumb (sensory difference for other fingers)
- Risk: diabetes, arthritis…
What is ulnar nerve compression?
- Truck drivers
- Usually in the right arm
- Hypothenar wasting
- Weakness in hand except thumb
- Tingling/loss of sensation over innervated areas
- Claw hand
What is radial nerve palsy?
- Loss of sensation over back of hand/back of forearm
- Drop arm
What is most likely to damage the radial nerve?
Fracture of humerus
What can cause loss of sensation over the lateral thigh?
Lateral cutaneous nerve of thigh goes through inguinal ligament
- Myalgia parysthetica
What happens when the common perennial nerve is injured?
- It is round the head of the tibia
- Can get foot drop
- Can be painful to lift foot up
