Download ActionPotential and Synapse

Objective 4
Outline the steps of a nerve
impulse, and its conduction
from one neuron to the next.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Starting a Nerve Impulse
1.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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
How Neurons Communicate at Synapses
Figure 7.10
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
How Neurons Communicate at Synapses
2. Ca+ causes vesicles
(vacuoles) to dump
Neurotransmitters into the
synapse (gap)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
How Neurons Communicate at Synapses
(Ignore the
numbers!)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
How Neurons Communicate at Synapses
3. Neurotransmitters bind to
the receptors of the next cell
(can be another neuron, a
muscle, or a gland)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
How Neurons Communicate at Synapses
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
 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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Objective 5
List the main components of a
reflex arc.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Simple Reflex Arc
Figure 7.11b–c
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings