Ch7bppt nerve impulses and reflexes

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

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

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

Simple Reflex Arc

Figure 7.11b, step 1

Spinal cord

Sensory receptors(stretch receptorsin the quadricepsmuscle)

Simple Reflex Arc

Spinal cord

Sensory (afferent)neuron

Simple Reflex Arc

Spinal cord

Synapse inventral horngray matter

Simple Reflex Arc

Spinal cord

Motor(efferent)neuron

Simple Reflex Arc

Spinal cord

Effector(quadricepsmuscle ofthigh)

Simple Reflex Arc

Figure 7.11c, step 1

Spinal cord

Sensory receptors(pain receptors inthe skin)

Simple Reflex Arc

Spinal cord

Simple Reflex Arc

Spinal cord

Inter-neuron

Simple Reflex Arc

Figure 7.11c, step 4a

Spinal cord

Inter-neuron

Simple Reflex Arc

Figure 7.11c, step 4b

Spinal cord

Inter-neuron

Effector(bicepsbrachiimuscle)

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

Ch7bppt nerve impulses and reflexes

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