Neural Tissue Part 2 (Action Potential)

Action Potential

Large depolarization that affects the entire axolemma. Doesn’t diminish as it moves away from point of stimulation

All-or-none principle

If action potential forms- it influences the entire axon

All action potentials are the same- no matter the stimulus

Step 1 of Action Potential

Depolarization to threshold (from -70mV to -55mV)

1A: Chemically-gated. Na+ channels open

1B: Na+ enters cell

1C: Depolarization

1D: If depolarized to -55mV (threshold) = action potential

Step 2 of Action Potential

Rapid depolarization from -55mV to +33mV

2A: Voltage- gaited sodium channels open

2B: MORE Na+ enters cell

2C: MORE depolarization (towards +33mV)

Step 3 of Action Potential

Repolarization from +30mV towards -70mV

3A: Voltage gated Na+ channels close, Na+ cannot enter.

3B: Channel/cell cannot respond to additional stimuli

3C: Voltage fated K+ channels open

3D: K+ leaves

3E: Cell repolarizes (more negative) towards resting MP -70 mV

Step 4 of Action Potential

Hyperpolarization from -70 mV to -90 mV

4A: Voltage-gated K+ channels begin to close

4B: Channels close slowly

4C: K+ keeps leaving causing brief hyperpolarization to -90mV

4D: Voltage-gated K+ channels finish closing, the resting membrane potential is restored by the sodium- potassium exchange pump

4E: Cell can respond to larger than normal stimuli

Refactory Period

Membrane can’t respond normally to stimuli

Absolute Refactory Period

Can’t respond to any further stimuli AT ALL

Relative Refactory Period

Can only respond to larger than normal stimuli

Propagation (conduction)

Moving the action potential along the axon. Repeat depolarization, repolarization, hyperpolarization down axon

Types of Propagation

Continuous: Unmyelinated axons

Saltatory: Myelinated axons

Propagation Speed

Myalin: Faster

Larger axon diameter: Faster

Synapse

Where a neuron communicated with another cell

Parts of a Synapse

1: Presynaptic- Sends the message

2: Synapatic Cleft- Gap between 2 neurons or between neuron and effector cell

3: Postsynaptic- Receives the message

Types of synapses

Electrical: Signal transmitted using direct physical contact between cells (Brain and eye)

Chemical: Signal transmitted using a chemical signal. Most common

Cholingeric Synapse

A type of chemical synapse that uses the neurotransmitter acetylcholine to transmit signals between neurons or between neurons and muscles.