Objective 4

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

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

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


Starting a Nerve Impulse1.Resting State – all ion

gates closed… Na+ outside, K+ inside

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

Figure 7.9a–c


Nerve Impulse Propagation3. 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 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


How Neurons Communicate at Synapses

Figure 7.10


Continuation of the Nerve Impulse between NeuronsImpulses are able to cross the

synapse to another nerve

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



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



(Ignore the numbers!)



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





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

List the main components of a reflex arc.


The Reflex Arc 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

Figure 7.11b–c


Types of Reflexes and Regulation Autonomic reflexes

Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation

Somatic reflexes Activation of skeletal muscles

Documents

Objective 4