Ch7bppt nerve impulses and reflexes

PowerPoint® Lecture Slide Presentation by Patty Bostwick-Taylor, Florence-Darlington Technical College

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings

PART B7

The Nervous System


Functional Properties of Neurons

Irritability

Ability to respond to stimuli

Conductivity

Ability to transmit an impulse


Nerve Impulses

Resting neuron

The plasma membrane at rest is polarized

Fewer positive ions are inside the cell than outside the cell

Depolarization

A stimulus depolarizes the neuron’s membrane

A depolarized membrane allows sodium (Na+) to flow inside the membrane

The exchange of ions initiates an action potential in the neuron


Nerve Impulses

Figure 7.9a–b


Nerve Impulses

Action potential

If the action potential (nerve impulse) starts, it is propagated over the entire axon (all or none)

Impulses travel faster when fibers have a myelin sheath


Nerve Impulses

Figure 7.9c–d


Nerve Impulses

Repolarization

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

The sodium-potassium pump, using ATP, restores the original configuration


Nerve Impulses

Figure 7.9e–f


Transmission of a Signal at Synapses

Impulses are able to cross the synapse to another nerve

Neurotransmitter is released from a nerve’s axon terminal

The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter

An action potential is started in the dendrite



Figure 7.10, step 1

Axonterminal

Vesicles

Synapticcleft

Actionpotentialarrives

Synapse

Axon oftransmittingneuron

Receivingneuron



Figure 7.10, step 2

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron

Vesiclefuses withplasmamembrane

Synaptic cleft

Ion channels Receiving neuron

Transmitting neuron



Figure 7.10, step 3

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron

Neurotrans-mitter is re-leased intosynaptic cleft


Synaptic cleftNeurotransmittermolecules


Transmitting neuron



Figure 7.10, step 4

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron


Neurotrans-mitter bindsto receptoron receivingneuron’smembrane




Transmitting neuron



Figure 7.10, step 5

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Receptor

Neurotransmitter

Na+

Ion channel opens



Figure 7.10, step 6

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Receptor

Neurotransmitter

Na+Na+

Neurotransmitterbroken downand released

Ion channel opens Ion channel closes



Figure 7.10, step 7

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Receptor

Neurotransmitter

Na+Na+

Neurotransmitterbroken downand released

Ion channel opens Ion channel closes


The Reflex Arc

Reflex—rapid, predictable, and involuntary response to a stimulus

Occurs over pathways called reflex arcs

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


The Reflex Arc

Figure 7.11a

Stimulus at distalend of neuron

Skin Spinal cord(in cross section)

Interneuron

Receptor

Effector

Sensory neuron

Motor neuron

Integrationcenter

(a)


Simple Reflex Arc

Figure 7.11b, step 1

Spinal cord

Sensory receptors(stretch receptorsin the quadricepsmuscle)

(b)


Simple Reflex Arc


Spinal cord

Sensory (afferent)neuron


(b)


Simple Reflex Arc


Spinal cord



Synapse inventral horngray matter

(b)


Simple Reflex Arc


Spinal cord


Motor(efferent)neuron



(b)


Simple Reflex Arc


Spinal cord




Effector(quadricepsmuscle ofthigh)


(b)


Simple Reflex Arc

Figure 7.11c, step 1

Spinal cord

Sensory receptors(pain receptors inthe skin)

(c)


Simple Reflex Arc


Spinal cord



(c)


Simple Reflex Arc


Spinal cord

Inter-neuron



(c)


Simple Reflex Arc

Figure 7.11c, step 4a

Spinal cord

Inter-neuron




(c)


Simple Reflex Arc

Figure 7.11c, step 4b

Spinal cord

Inter-neuron




Effector(bicepsbrachiimuscle)

(c)


Types of Reflexes and Regulation

Somatic reflexes

Activation of skeletal muscles

Example: When you move your hand away from a hot stove



Autonomic reflexes

Smooth muscle regulation

Heart and blood pressure regulation

Regulation of glands

Digestive system regulation



Patellar, or knee-jerk, reflex is an example of a two-neuron reflex arc

Figure 7.11d