Lecture 8

Question 1

Autonomic NS

Answer 1

functions without conscious control to maintain homeostasis. it controls; cardiac and smooth muscles and exo/endocrine nerves. divided into sympathetic (fight/flight), supplies tissues inc. adrenal gland. parasympathetic (rest)

Question 2

Action potential

Answer 2

all action potential have same charge. a stronger stimuli increase frequency of action potentials

Question 3

saltatory conduction

Answer 3

the way an electrical impulse skips from one node to the next

Question 4

temporal summation

Answer 4

Repeated stimuli, occurring quickly at the same synapse

Question 5

action potential steps

Answer 5

1. The neuron is at rest, maintained by the Na⁺/K⁺ ATPase pump. The inside of the neuron is more negative than the outside due to high intracellular K⁺ and high extracellular Na+.
2. Depolarization (Threshold ~ -55 mV)
   A stimulus (e.g., neurotransmitter binding) causes some voltage-gated Na⁺ channels to open. If the threshold potential (~ -55 mV) is reached, a rapid influx of Na⁺ occurs.
3. The membrane potential rises sharply toward +30 mV.
4. Peak of Action Potential (+30 to +40 mV) is reached
   Na⁺ channels inactivate.The inside of the neuron is now positive relative to the outside.
5. Repolarisation occurs where voltage-gated K⁺ channels open, allowing K⁺ to exit the cell. This restores the negative membrane potential.
6. Hyperpolarization (Refractory Period)
   K⁺ channels remain open longer than necessary, causing an overshoot (~ -80 mV). The neuron is temporarily more negative than the resting potential.
7. During this time the absolute refractory period occurs where no new action potential can be triggered (Na⁺ channels are inactivated). Or, relative refractory period: A stronger-than-normal stimulus can trigger an action potential.
8. Na⁺/K⁺ ATPase pump restores ion gradients. K⁺ channels close, bringing the neuron back to -70 mV.
9. The neuron is now ready for another action potential.

Question 6

summations

Answer 6

Action potentials adhere to the all-or-none principle, meaning that if the threshold is reached, a full action potential occurs, regardless of stimulus strength. They propagate along the length of the axon without losing intensity, ultimately triggering neurotransmitter release at the synaptic terminals. The action potential is initiated at the trigger zone (axon hillock and initial segment) if the membrane potential reaches threshold (~ -55 mV).

Question 7

Spatial summation

Answer 7

stimuli are applied at the same time, but in different areas, with a cumulative effect upon membrane potential.