nerves and receptors Flashcards
what are the 3 types of neuron
sensory intermediate and motor
what do neurons have
cell body dendrites axon schwann cells myelin sheath
nodes of ranvier
electrical impulse moves from dendrite to axon
describe the reflex arc
stimulus - receptor - sensory neuron - intermediate neuron - motor neuron - effector ( muscle or gland) allows rapid reaction. prevent damage to body tissues
resting potential is maintained how
sodium ions pumped out of axon by sodium potassium pump using active transport so ATP is needed
3 sodium ions out for every 2 potassium in
membrane is more permeable to potassium
what are the stages of an action potential
some K+ channels always open with k+ leaving from axon out of cell by diffusion
voltage gated sodium ion channels open
sodium ions enter axon by diffusion
axon becomes depolarised (have a +40 mv charge)
more Na+ channels open through pos feedback
potassium ion channels open
potassium ions leave axon by diffusion
axons become hyperpolarised (-85 mv)
some potassium ion channels close
k na pump restores resting potential of (-65 mv)
what do myelinated axons do
saltatory conduction myelin insulates axon
ions can only pass through plasma membrane of the axon at the nodes of ranvier so action potentials are only generated here so the impulse jumps from node tp node which is much faster
what would an unmyelinated axon have to be like
whole length of membrane must be depolarised
whats the refractory period
time during which a new action potential cannot be generated as the cell is in hyperpolarisation. sodium ion channels are closed so sodium cannot enter. helps action potentials pass in one directon and form discrete impulses
whats the all or nothing principle
if enough sodium ions enter cell and reaches the threshold it will cause more sodium ion voltage gated channels to open and cause depolarisation - if not, no impulse. all action potentials are the same size (+4o mv)
what happens if a neuron transmits a series of impulses
oxygen consumption increases
more respiration
more ATP supplied for active transport in k+ na+ pump
what are the stages of synaptic transmission
action potential causes calcium ion channels to open and calcium ions diffuse into synaptic knob
causes synaptic vesicles to fuse with membrane and release neurotransmitter into synaptic cleft
they diffuse across the synapse
bind with specific glycoprotein receptor site on post synaptic neuron
opens either sodium channels (excitatory) or chloride channels (inhibitory) which either increase or decrease action potentials in post synaptic neuron
whats the Pacinian corpuscle
receptor or skin in joint that detects pressure
how does the Pacinian corpuscle stimulate an action potential
membrane layers around the end of the neuron are distorted it causes the stretch mediated Na+ channels to open
Na + move into the neuron, if enough enter for the charge to reach the generator potential then an action potential will be transmitted along the sensory neuron
describe synapses
gaps between neurons. are unidirectional due to neurotransmitter only being stored in presynaptic neurone and receptors only on post synaptic neuron
what is a cholinergic synapse
one that uses acetylcholine as the ntm
mostly as neuromuscular junctions
drugs can affect synaptic transmission
