Topic Six Flashcards
what is a stimulus?
a change in the environment that is detected by a receptor
what is a receptor?
transforms environmental stimuli into electrical nerve impulses
what is an effector
organs that produce a response to a stimulus
what is the order
receptor -> sensory -> relay (CNS) -> motor -> effector
what is a reflex?
rapid + involuntary response to a stimulus
what are dendrites?
short-branched fibres that convert chemical info from neurones/receptors into electrical signals
what is the function of an axon?
elongated fibre that transmits electrical signals to terminal regions for communication
what is a soma?
the cell body containing nucleus and organelles
what is the purpose of myelin sheath?
improves electrical conduction via saltatory conduction
what is; membrane potential?
unequal distribution of ions on different sides of membrane, creating a potential difference
what is resting potential?
the charge difference when a neutron is at rest, ~ 70 mV
how is resting potential maintained?
1) there is a higher conc. of K+ inside & higher conc. of Na+ outside
2) 3 Na+ out for every 2 K+ in
- creates an electrochemical gradient = cell is more -ve then outside
3) cell is more permeable to K+
4) Na+ is actively transported out & K+ in (using ATP)
What are the 3 steps making an action potential?
- depolarisation
- repolarisation
- refectory period
what happens in depolarisation?
- in response to stimulus, Na+ channels open up
- as Na+ have higher conc. outside, Na+ diffuses down the electrochemical gradient into the cell
- influx of sodium causes membrane potential to be more positive
what happens in repolarisation?
- increase in Na+ inside = K+ channels open
- K+ is more conc. inside, K+ diffuses down the electrochemical gradient out of the cell
- efflux of k+ causes membrane potential to go back to -ve.
what happens in the refectory period?
- At rest, Na+ = outside & K+ = inside
- after depolarisation + repolarisation, ionic distribution is reversed
- before neurone can re-fire; resting potential has to be restored by using sodium-potassium pump
- It pumps Na+ out and K+ in
how are nerve impulses “1D”?
- depolarisation = when ion channels open + cause a change in membrane potential
- ion channels are voltage-gated
- so depolarisation at one point of axon, triggers the opening of ion channels in the next segment
- causes depolarisation to spread along the length of an axon as a unidirectional “wave”
what is the all-or-nothing principle?
an action potential of the same magnitude (-55mV) will generate as long as threshold potential is reached.
what is myelin made of?
protein + phospholipids made by Schwann cells
what is the difference in myelinated vs non-myelinated neurones?
in myelinated: action potentials ‘hop’ between nodes of ranvier
in non-mylenated: action potentials move along in a continuous wave of depolarisation
what is the process of synaptic transfer?
- Action potential arrives at axon terminal + triggers opening of voltage-gated Ca2+ channels
- Ca2+ diffuses into the cell + promotes the fusion of vesicles with cell-membrane, = exocytosis happens, releasing neurotransmitters.
- Neurotransmitters bind to specific receptors on post-synaptic membrane & opens ion channels
- channel openings generates an electrical impulse in post-synaptic neurone
- neurotransmitters are recycled or broken down
what do neurotransmitters do?
- released in response to depolarisation of axon terminal of a pre-synaptic neurone
- they bind to receptors on post-synaptic cells + trigger (excitatory) or prevent (inhibitory) a response
what do excitatory neurotransmitters do?
cause depolarisation by opening Na+ or Ca2+ channels
what do inhibitory neurotransmitter do?
cause hyperpolarisation by opening K+ or Cl- channels
