Nervous Coordination Flashcards
1
Q
Types of neurones
A
- Sensory neurone (single long dendron, single short axon)
- Relay neurone (many short dendron, many short axons)
- Motor neurone (single short axon, ends with a neurotransmitter junction)
2
Q
1) Resting potential
A
- Sodium potassium pump actively transports 3 Na+ out neurone and 2 K+ into neurone using ATP
- Potassium ion channels are open so some K+ diffuses out of neurone down the electrochemical gradient by facilitated diffusion
- Voltage gated sodium ion channels are closed and membrane is not permeable to Na+ so a sodium ion electrochemical gradient is created
3
Q
2) Generator potential
A
- Weak stimulus causes some Na+ channels to open
- Some Na+ diffuses in but threshold not reached
- Sodium potassium pump restores resting potential
4
Q
3) Threshold
A
- Generator potential reaches threshold
- Many voltage gated sodium ion channels open
- Na+ diffuses into axon
5
Q
4) Depolarisation
A
- Sodium ion channels are open
- Na+ diffuses in
6
Q
5) Repolarisation
A
- Potassium ion channels open
- K+ diffuses out of neurone
- Voltage gated sodium ion channels close
7
Q
6) Hyperpolarisation
A
- Membrane potential is more negative than resting potential
- Potassium ion channels are slow to close
8
Q
What is the refractory period?
A
Period where another action potential can’t be started, making action potentials discrete and unidirectional
9
Q
What causes waves of depolarisation?
A
- Na+ diffuse along the neurone (sideways)
- Ahead of the action potential the neurone is at resting potential
- Na+ triggers threshold, causing action potential to move along neurone in a wave of depolarisation
10
Q
All or Nothing Law
A
- If a generator potential reaches threshold, an action potential is triggered
- All action potentials are the same size but a stronger stimulus generates more frequent action potentials
11
Q
What factors increase speed of conduction?
A
- Myelination (electrical insulator prevents depolarisation)
- Nodes of Ranvier (lots of Na+ and K+ channels for depolarisation)
- Large diameter of axon (larger SA, less resistance)
12
Q
Saltatory conduction
A
- Action potential jumps between nodes of Ranvier, speeding up transmission of nerve impulses
- Cytoplasm conducts enough charge to depolarise the next node
13
Q
Synaptic transmission
A
- Action potential arrives at pre-synaptic knob
- Voltage gated calcium ion channels open and Ca2+ diffuses in
- Vesicles full of neurotransmitter (ACh) fuse with the pre-synaptic membrane
- ACh diffuses across synaptic cleft and binds to receptors on the post-synaptic membrane
- Some sodium ion channels open and Na+ diffuses in
- If threshold is reached, voltage gated sodium ion channels open
- Action potential is triggered in the post-synaptic membrane
- Enzyme acetylcholinesterase breaks down ACh, stopping the response
- Products are reabsorbed into the pre-synaptic knob and recycled
14
Q
Roles of synapses
A
- Synaptic divergence, spreading action potential to the rest of body
- Synaptic convergence, amplifying signal
- Spatial summation
- Temporal summation
15
Q
Summation
A
- Spatial summation (neurotransmitters from multiple neurones combine to trigger an action-potential in the post-synaptic neurone)
- Temporal summation (more frequent action potentials release more neurotransmitter which combine to trigger an action potential in the post-synaptic membrane)
16
Q
What is a neuromuscular junction?
A
A synapse between a motor neurone and muscle fibre
17
Q
What makes a neuromuscular junction different to a cholinergic synapse?
A
- More receptors on the post-synaptic membrane so an action potential is always generated in the post-synaptic membrane
- Acetylcholinesterase found in pits on the post-synaptic membrane
- Receptors are called nicotinic cholinergic receptors
