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Objective 4. Outline the steps of a nerve impulse, and its conduction from one neuron to the next. Action Potential. A nerve impulse, signal, electrical impulse… Is correctly called an “Action Potential” “Potential” is from the chemistry…the potential charges of the + and – ions involved

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Objective 4
Objective 4

Outline the steps of a nerve impulse, and its conduction from one neuron to the next.


Action potential
Action Potential

  • A nerve impulse, signal, electrical impulse…

    • Is correctly called an “Action Potential”

    • “Potential” is from the chemistry…the potential charges of the + and – ions involved

    • Are received from the dendrites…pass down an axon…to the axon terminals.


Starting a nerve impulse
Starting a Nerve Impulse

  • Resting State – all ion gates closed… Na+ outside, K+ inside

  • Depolarizing - membrane allows sodium (Na+) to flow inside the membrane

Figure 7.9a–c


Nerve impulse propagation
Nerve Impulse Propagation

3. Repolarizing – Na channels close. K+ channels open

4. “Undershoot” – K+ channels are open too long, there is a ‘dip’ in the charge

5. Sodium/Potassium Pump – energy is used to pump Na & K back to normal state

Figure 7.9d–f


The action potential
The Action Potential

  • If the action potential (nerve impulse) starts, it is passed over the entire axon (“all or none”)

  • Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane

  • The sodium-potassium pump restores the original configuration

    • This action requires ATP



Continuation of the nerve impulse between neurons
Continuation of the Nerve Impulse between Neurons

  • Impulses are able to cross the synapse to another nerve

    1. Ca+ Gates open when action potential (nerve impulse) reaches the axon terminal


How neurons communicate at synapses1
How Neurons Communicate at Synapses

2. Ca+ causes vesicles (vacuoles) to dump Neurotransmitters into the synapse (gap)



How neurons communicate at synapses3
How Neurons Communicate at Synapses

3. Neurotransmitters bind to the receptors of the next cell (can be another neuron, a muscle, or a gland)



How neurons communicate at synapses5
How Neurons Communicate at Synapses

4. Binding causes Na+ ion channels to open so …

- (if neuron) action potential can continue

- (if muscle/gland) trigger the appropriate response


  • The Neurotransmitter can “hang around” causing ‘after-effects’ after the stimulus is removed.

  • Some medications work on this process…

    • Pain killers can prevent neurotransmitters from binding to receptors

    • Depression medication can take the place of neurotransmitters


Objective 5
Objective 5 ‘after-effects’ after the stimulus is removed.

List the main components of a reflex arc.


The reflex arc
The Reflex Arc ‘after-effects’ after the stimulus is removed.

  • Reflex – rapid, predictable, and involuntary responses to stimuli

  • Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector

Figure 7.11a


Simple reflex arc
Simple Reflex Arc ‘after-effects’ after the stimulus is removed.

Figure 7.11b–c


Types of reflexes and regulation
Types of Reflexes and Regulation ‘after-effects’ after the stimulus is removed.

  • Autonomic reflexes

    • Smooth muscle regulation

    • Heart and blood pressure regulation

    • Regulation of glands

    • Digestive system regulation

  • Somatic reflexes

    • Activation of skeletal muscles


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