Topic 6 Flashcards
What are advantages of simple reflexes
- Help escape from predators
- Rapid
- Do not need to be learned
- Protects the body from harm
What are the general parts of a motor neurone
Cell body = this contains organelles such as the nucleus and RER
Axon = long, unbranched fibre which carries nerve impulses away from the cell body
Dendrons = branch into dendrites which carry impulses
Additional features of a myelinated motor neurone
Schwann cells = wrap around the axon
Myelin sheath = made from a fatty substance for insulation
Nodes of ranvier = short gaps between Schwann cells where there is no myelin sheath
Order of a reflex arc
Receptor - Sensory Neurone - Relay Neurone - Motor Neurone - Effector
How do you know a reflex arc is simple?
There are 3 neurones
What is resting potential?
The electrical potential of a neuron or other excitable cell relative to its surroundings when at rest
Value for resting potential
-65 mV
How is resting potential established
3 Na+ are pumped out of the cell
2 K+ pumped into the cell
The axon is overall losing positive ions
How is resting potential established using channels
K channels are open (leaky) and Na channels are closed
More K+ leaves the axon by facilitated diffusion than Na+ entering
Axon losing positive ions therefore maintaining the -65 mV
What are the 4 stages for generating an action potential
Depolarisation
Repolarisation
Hyperpolarisation
Return to resting potential
What happens during depolarisation
More sodium channels open therefore more sodium ions diffuse
This reverses the p.d. to +40mV
Once +40 mV is reached, sodium channels close so no more sodium ions diffuse in
What happens during repolarisation
Voltage-gated potassium channels open
Potassium ions diffuse out leading to repolarisation
The p.d. across membrane becomes more negative
What happens during hyperpolarisation
Outward movement of potassium ions causes a temporary ‘overshoot’
The axon becomes more negative causing potassium gates to close
Importance of the refractory period
Ensures unidirectional impulse
Ensures discrete impulses
Limits frequency of impulse transmission
The passage of an action potential
Known as saltatory conduction
Na+ move into axon, causes nearby channels to open
Creates a wave of depolarisation
Positive sodium ions move into the axon further along it, triggers more voltage-gated channels to open
