Neuronal Communication Flashcards
what features are common to all sensory receptors
act as energy transducers which establish generator potential
respond to specific stimuli
describe the basic structure of a pacinian corpuscle
single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
stretch mediated sodium channels on membrane
capillary runs along base layer of tissue
what stimulus do a pacinian corpuscle respond to and how
pressure deforms membrane causing channels to open
influx of sodium raises membrane to threshold potential, a generator potential is produced
action potential moves along sensory neurone
describe the features of all neurones
cell body-contains organelles
dendrons-branch into dendrites which carry impulses towards cell body
axon-long unbranched fibre carries nerve impulses away from cell body
describe the structure and function of a sensory neurone
cell body in the middle of axon
transmits impulses from receptors to CNS
describe the structure and function of a relay neurone
transmits impulses between neurones
describe the structure and function of a motor neurone
cell body at the end of axon
transmits impulses from relay neurones in CNS to efefctor
describe the additional features of a myelinated neurone
schwann cells-wrap around axon
myelin sheath-made of myelin rich membranes of schwann cells
nodes of ranvier- very short gaps between neighbouring schwann cells where there is no myelin sheath
name 3 processes schwann cells are involved in
phagocytosis
nerve regeneration
electrical insulation
explain why myelinated neurones conduct impulses faster
saltatory conduction-impulse jumps from one node to another
depolarisation cannot occur where myelin acts as electrical insulator
nerve impulse does not travel whole length of axon
where are myelinated and non myelinated neurones found
myelinated-most neurones in central and peripheral nervous systems non-myelinated-group C nerve fibres involved in transmitting secondary pain
what is resting potential
potential difference across neurone membrane is about -70mV
how is resting potential established
membrane is more permeable to potassium than sodium
sodium potassium pump actively transports 3 sodium out of cell and 2 potassium into cell
establishes electrochemical gradient
name the stages in generating an action potential
depolarisation
Repolarisation
hyperpolarisation
what happens during depolarisation
stimulus –>facilitated diffusion of sodium into cell down electrochemical gradient
potential difference across membrane becomes more positive
if membrane reaches threshold potential (-50) sodium voltage gated channels open
influx of sodium ions reverses potential difference to +40
what happens during repolarisation
sodium voltage gated channels close and potassium voltage gated channels open
Facilitated diffusion of potassium ions out of cell down electrochemical gradient
potential difference becomes more negative
what happens during hyperpolarisation
potassium ions diffuse out so potential difference becomes more negative than resting potential
refractory period:no stimulus large enough to raise membrane to threshold
voltage gated potassium channels close and sodium potassium pump restablishes resting potential
explain the importance of the refractory period
no action potential can be generated in hyperpolarised sections of membrane
ensures unidirectional impulses
discrete impulses
why is the frequency of impulse transmission significant
organism can distinguish size of stimulus
what is the function of synapses
electrical impulse cannot pass junction
neurotransmitters send impulses between neurones
summation of sub threshold impulses
describe the structure of a synapse
presynaptic neurone ends in synaptic cleft
contains lots of mitochondria, RER and vesicles of neurotransmitter
postsynaptic neurone has complementary receptors to neurotransmitter
what happens in the presynaptic neurone when an action potential is transmitted
wave of depolarisation travels down presynaptic neurone causing calcium voltage gated channels to open
vesicles move and fuse with presynaptic membrane
exocytosis of vesicle
what happens in the post synaptic neurone when an action potential is transmitted
neurotransmitter binds to specific receptor on post synaptic membrane sodium gated channels open
influx of sodium ions raises membrane to threshold potential-action potential generated
what happens in an inhibitory synapse
neurotransmitter binds to opens chloride channels on post synaptic membrane-triggers potassium channels to open
chloride moves in and potassium moves out
potential difference becomes more negative
what is the difference between temporal and spatial summation
temporal- one presynaptic neurone releases neurotransmitter several times in quick succession
spatial- multiple presynaptic neurones release neurotransmitter
what are cholinergenic synapses
use acetylcholine as primary neurotransmitter
what happens to acetyl choline from synaptic cleft
hydrolysis into acetyl and choline by acetylcholinesterase
acetyl and choline diffuse back into presynaptic membrane
ATP used to reform acetylcholine for storage in vesicles
