how are APs graded
the frequency (more or less rapid - like bullets from a machine gun or a vibration)
where do APs occur
mainly in axons are start at the axon hillock near the cell body
Schwann cell
found in the peripheral nervous system and act as the myelin sheath
Oligodendrocytes
provide myelination in the CNS
Saltatory Jumping conduction
jumps along nodes in sections and resumes a fresh at each one
unmyelinated nerve fibres trend for the speed of conduction
larger the diameter the faster the conduction
if there is any slowing in the speed of conduction this would be consistent with
demyelination
When neurotransmitters are released they are inactivated, why?
- diffusion
- re-uptake
- enzymes inactivation
what’s the difference between inotropic and metabotropic receptors
inotropic - directly gate ion flow
metabotropic - indirectly gate ion flow or activate other pathways
Post-synpatic (PSPs) are caused by
the passage of ions through ion channels which have been opened following receptor/neurotransmitter interactions
after a PSP what happens
a NET flow of positive ions into he cell depolarises the membrane (bringing it closer to the threshold) and is thus termed EXCITORY EPSP. single EPSP rarely result in an action potential
summation
if multiple EPSPs summate together they can cause an action potential
This means stronger external signals result in a
higher frequency of APs in the axon
SNAP
sensory nerve action potential
CMAP =
compound muscle action potential
Autoimmune channelopathies
Myasthenia gravis
Lambert-Eaton myasthenic syndrome (associated with small cell lung Ca) Limbic encephalitis (memory loss; associated with underlying neoplasm)
Compression syndromes include
carpal tunnel syndrome, ulnar nerve compression at elbow
Less axons means
reduced size of compound action potential
