Nerves Flashcards
describe the neurone at resting potential.
the outside is + the inside - , the membrane is polarised, the voltage is approx - 70mV,
describe how the Na/K pumps maintain the resting potential
Na is moved out using active transport, Na cannot diffuce back in = electrochemical gradient, pottasium is pumped in but can move out via facilitated diffusion - making the outside + compared to the inside
when is a neurone depolarised?
when it is stimulated
describe what happens when the neurone is stimulated
the stimulus excites the cell membrane, causing Na ion channels to open. Na diffuses down the electrochemical gradient, making the inside less negative
describe depolarisation
if the threshhold is reached (-55mV) more channels open and Na diffuses rapidly into the membrane
describe repolarisation
when +3mV is reached the sodium channels close up. K diffuses out through the opened channels, returning the membrane to resting potential
describe the nervous system in comparison to the endocrine system
nervous system is short lived, fast and localised (endocrine opposite)
what is included in the CNS?
brain and spinal cord
what is the peripheral system?
all other neurones
what do we dived the peripheral into?
sematic and autonomic
what is the sematic nervous system?
concious decision eg) muscle movement
what is the autonomic nervous system?
unconcious eg) heart rate
what 2 sections can we divide the autonomic system into?
parasympathetic and sympathetic
describe the parasympathetic
decreases/ slows things down eg) heart rate
what neurotransmitter controls the parasympathetic?
acetylcholine
describe the sympathetic
increases/ speeds things up eg) heart rate
what neurotransmitter controls the sympathetic?
noradrenaline
describe the route from stimulus to response
stimulus - receptor - sensory - intermediate (cns) - motor - effector - response
describe the receptor
specific, cell or protein, transforms stimulus into nerve impulse
describe the sensory neurone
Single long dendron, single short axon, (draw a diagram and check)
decribe the intermediate neurone
within cns, many short dendrites/ axons (draw a diagram)
describe the motor neurone
many short dendrites, single long axon, ends at neuromuscular junction
describe the effector
muscle/gland
describe the sodium pottassium pump
maintains the resting potential by active transport of Na+ out and K+ in. some K+ diffuse out by facilitated diffusion
what happens at generator potential?
a weak stimulus causes some voltage gated Na+ channels to open, some Na+ diffuses in, threshold isnt reached so returns to resting potential.
what happens at threshold?
many voltage gated Na+ channels open, Na+ diffuse into axon, positive feedback (rapid depolarisation)
describe repolarisation
K+ channels open, K+ diffuses out, sodium ion channels close
what is hyperpolarisation?
membrane potential is more negative than resting potential because K+ channels are slow to close
what is the refractory period?
another action potential cannot be started, ensuring action potentials are discrete, unidirectional nervous impulse
Describe how resting potential is established in an axon by the movement of ions across the membrane
Active transport of sodium out, diffusion of K in
making the inside more negative than the outside
why can sodium and pottasium ions only pass through the membrane through proteins?
because they are polar, and not lipid soluble
why doesn’t every stimulus produce an action potential?
because it has a refractory period
because it doesn’t reach threshold
not all the sodium channels open
describe the role of calcium ions in synaptic transmission.
in the presynaptic neurone, calcium ions increase membrane fluidity allowing vesicles to fuse with it for exocytosis.
describe the all or nothing principal
if a generator potential reaches threshold an action potential is triggered, all AP are the same size, stronger stimulus = higher frequency
what is hyperpolarisation’s role?
creates a refractory period as so ions diffusing Bck don’t diffuse out. Ahead the AP is in resting potential ensuring undirectionality.
what is the myelin sheath?
it is made up of schwann cells and acts as an electical insulator - so ions can not move in and out of the nuerone.
describe the nodes of ranvier
they are gaps in the myelin sheath with high levels of Na/K channels, AP jump between nodes of ranvier.
what is saltatory conduction?
AP jumps between the nodes of ranvier + speed and - distance
How can we speed up transfer?
more Schwann cells increases saltatory conduction, increase temperature faster diffusion of action potential, diameter of the axon - increasing the diameter increases the speed, greater surface area for ion movement
Describe the process of cholinergic synaptic transmission
AP at pre synaptic knob
voltage gated calcium ion channels open and calcium ions diffuse in
vesicles containing acetylcholine fuse with the presynaptic membrane (exocytosis)
acetylcholine diffuses across the synaptic cleft
acetylcholine binds with the receptor on the post synaptic membrane triggering an action potential
acetylcholineesterase breaks down acetylcholine to stop the response
acetylcholine is reabsorbed into the presynaptic knob
How do synapses ensure that the nerve impulse is unidirectional
only receptors on the post synaptic membrane
neurotransmitters diffuse from high to a low conc
What is synaptic divergence?
when one neurone joins many neurones –> spreads AP to other parts of the body
What is synaptic convergence?
many neurones join a single neurone - amplifies a signal
What is a neuromuscular junction?
a synapse between a motor neurone and a muscle fibre
What is different about a neuromuscular junction compared to a cholinergic synapse?
- more receptors on the post synaptic membrane so an AP is always triggered
- acetylcholine-esterase is found in pits on the post synaptic membrane
What is the name of the receptors on the post synaptic membrane?
nicotinic cholinergic recepters
What does the sartcolema connect with that causes the release of calcium ions for muscle contraction?
the transverse tubules on the sarcolema connect with the sarcoplasmic reticulum
