9.2 Flashcards
(44 cards)
Somatic nervous system
1) Afferent:
-sensory
2) Efferent:
-motor
Nervous system
Central -brain and spinal chord.
Peripheral - pairs of nerves which originate from the brain or spinal chord.
Peripheral nervous sytem
1) Somatic:
-under voluntary control
2) Autonomic:
-involuntary
Autonomic nervous system
1) Sympathetic:
-positive stimulation
-speed up
-fight or flight
2) Parasympathetic:
-inhibitory
-slows down activity
-resting and digesting
Compare and contrast symp and parasymp
Similarities:
-NS fibres leave the CNS in a ganglion (collection of nerve fibres).
Differences:
-Symp: ganglia close to the CNS.
-Para: ganglia close to the effector organ.
Compare and contrast symp and parasymp funtions
Symp:
-produces noradrenaline
-fight or flight response
-activated in times of stress or active
-adrenergic synapses
Parasymp:
-slower, inhibitory effect
-acetychloine neurotransmitter produced
-maintains normal functioning of the body
-chloinergic synapses
Resting potential
- Inside of the axon is negatively charged compared to the outside of the axon.
- Outside ions more concentrated.
- Axon is polarised.
- -70mV.
Sodium potassium pump
- Requires energy
- 3 Na+ ions moved out of the membrane for every 2 K+ ions in.
- ATPase in pump uses ATP to move cations.
How is resting potential maintained?
- Sodium potassium pump
- Na+ out K+ in
- K+ move through potassium channels
- NA channels close
- Outside more positive than inside
Action potential
- Stimulus recieved.
- Causes a temporary reversal of the charge on the axon membrane - inside less negative.
- Moves to about +40mv.
- Membrane depolarised
Depolarisation
- Resting potential some K voltage-gated channels are open but Na channels are closed.
- The stimulus causes some Na gates in the axon membrane to open and ∴ some Na+ move into the axon via facilitated diffusion.
- As they are +vly charged they trigger a reversal in the potential difference.
- As it is more +ve more voltage-gated sodium channels open - +ve feedback.
- Once the action potential is around +40mv the voltage-gated sodium ion channels close.
- Excess sodium ions are pumped out by Na-K pump.
Repolarisation
- Voltage-gated potassium channels open so K ions move out the axon by facilitated diffusion down the conc. grad.
- Cell is repolarised and becomes more negative.
Hyperpolarisation
- More potassium flows out.
- The inside is more negative than the outside so more negative than the resting potential.
After hyperpolarisation
- Gates on K+ channels now close and Na-K pumps Na to be out and K in.
- -70 mv is re-established.
Action potential simplified
1) Na+ voltage gated channels open.
2) Na+ diffuse rapidly into axon.
3) Potential difference reversed.
4) Na+ voltage gates close.
5) K+ voltage gated chanells open.
6) K+ diffuse out of axon.
7) Inside axon returns to negative.
8) Resting potential restored.
Absolute refractory period
- Sodium chanells are completly blocked and the resting potential hasnt been restored.
- Milisecond.
- Second stimulus will not trigger a second action potential.
Relative refractory period
- K channels are able to repolarise the membrane and pottasium ions difuse out of axon.
- Normal resting potential can not be restored until these K channels are closed.
- Last several milliseconds.
- During this time, a greater than normal stimulus is required to initiate an action potential.
Refractory period
- Time taken for an area of the axon membrane to recover after an action potential.
- Depends on:
-Na/K pump.
-Membrane permeability to potassium ions.
Purpose of a refractory period
- Ensure action potentials are only in one direction.
- Produce discrete impulses- action potentials are separated.
- Limits the number of action potentials.
Events at synapse
1) Action potential depolarises the presynaptic neuron (increases the permeability).
2) Calcium channels open and calcium diffuses in down conc. grad.
3) Synaptic vesicles move to and fuse with the pre-synaptic membrane.
4) The neurotransmitter is released into the synaptic cleft.
5) Neurotransmitter moves across cleft by diffusion.
6)Neurotransmitter binds to specific protein receptors on the sodium channel on the post synaptic membrane.
7) Sodium channels open and sodium diffuses in.
8) This causes a change in the potential difference of the membrane and an excitatory post-synaptic potential (EPSP) to be set up.
9) If there are enough EPSP the +ve charge exceeds the threshold level and an action potential is set up.
Types of synapse
Cholinergic
Adrenergic
-use noradrenaline
Inhibitory post-synaptic potential (IPSP)
- Is a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potential.
- Different ion channels open in the membrane, allowing inward movement of negative ions.
- This makes the post-synaptic cell more negative than normal resting potential.
- This means an action potential is less likely to occur.
Saltatory conduction
- Mylenated neurones ions can only pass in and out of the axon freely at the nodes of ranvier.
- Action potential can only occur at the nodes
so apear to jump. - Speed up transmition as the ionic movemetns happen less frequently taking less time.
Transmission in unmylenated axons
- A current (change in potential difference) occurs in a part of the neuron.
- This is detected in the adjacent part of the membrane.
- When it detects the current, it causes voltage gated channels to open and an action potential will occur when the threshold is reached.
- The nerve impulse is transmitted as a self-propagating wave of depolarisation.
