Physiology Unit 1.4 Action Potentials and Synapses

Draw an action potential

Draw a neuron and identify where the trigger zone is

What are the 5 steps of an AP?

1) Local potential depolarizes the axolemma of the trigger zones to a certain threshold

2) Voltage-gated Na+ channels open, Na+ enters, and the axon section depolarizes

3) Na+ channels inactivate anad voltage-gated K+ channels activate, so Na+ stops coming in and K+ exits. The axon repolarization begins.

4) Na+ channels return to resting state and repolarization continues as K+ flows out

5) The axolemma may hyper polarize before K+ channels return to the resting state. After, the axolemma returns to the RMP

What is the absolute refractory period?

No matter how strong the stimulus is, there can be no more APs

What is the relative refractory period?

We don’t want one, but if the stimulus is torn enough we can do another AP

Na+ entry during an AP creates a ___ feedback loop that doesn’t stop until the __. Draw what stops it.

Postive, Na+ inactivation gates close.

What is a synapse?

A junction between two neurons

What are the two types of synapses?

1. Electrical: gap junctions between pre and post-synaptic membranes allow current to pass through passively through intercellular channels

2. Chemical: One neuron secretes a NT that binds to a receptor found on the adjacent neuron

Draw the synapse and describe what happens when an AP is introduced

What type of receptors are involved in electrical responses?

Ionotropic receptors

What type of receptors are involved in chemical responses?

Metabotropic receptors

What is involved in presynaptic transmission?

Transmits electrical signals to chemical signals

What is involved in postsynaptic transmission?

Transmits chemical signals to electrical signals

APs are a type of __ signal, while NTs are a type of __. So APs can basically be converted into NTs

Electrical, chemical

Describe the process of transmission from electrical to chemical and back

1) AP is fired in the presynaptic neuron

2) It travels down to the axon terminal

3) the presynaptic neuron releases NTs (so now the presynaptic side has turned an electrical signal into a chemical one)

4) The NTs cross the synaptic cleft and bind to receptors on the postsynaptic neuron

5) The new chemical message from the NTs changes the electrical activity of the postsynaptic neuron (so now the postsynaptic side has turned a chemical signal into an electrical one)