Copyright 2009 Pearson Education, Inc., publishing as Benjamin Cummings Functional Properties of...

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

Functional Properties of Neurons Irritability

Ability to respond to stimuli & convert to nerve impulse

Conductivity Ability to transmit an impulse to other

neurons, muscles, or glands


Nerve Impulses: Electrical Conditions Resting neuron

The plasma membrane at rest is polarized Fewer positive ions are inside the cell than

outside the cell so cell interior is more negative Major ion inside cell is K+ Major ion outside cell is Na+

As long as inside remains more negative than outside, neuron stays inactive


Nerve Impulse: Action Potential & Generation Many types of stimuli excite neurons: light, sound,

pressure, smell, temperature, neurotransmitters Most neurons are excited by neurotransmitters

released by other neurons Result is always the same:

Na+ channels open & Na+ diffuses into the cell This causes Depolarization (inside becomes

more positive) This causes the neuron to transmit a signal

called an Action Potential (AKA Nerve Impulse)


Nerve Impulses

Figure 7.9a–b


Nerve Impulse: Action Potential & Generation Action potential

If the action potential (nerve impulse) starts, it is propagated over the entire axon

Impulses travel faster when fibers have a myelin sheath


Nerve Impulses

Figure 7.9c–d


Nerve Impulse: Action Potential & Generation Repolarization

K+ ions rush out of the neuron after Na+ ions rush in, which repolarizes the membrane

The sodium-potassium pump, using ATP, restores the original ion concentrations

This must happen before the neuron can conduct another impulse


Nerve Impulses

Figure 7.9e–f


Transmission of a Signal at Synapses Impulses are able to cross 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 Nerve impulse neurotransmitter nerve impulse

neurotransmitter effector “Electrochemical Event” because impulse is

electrical but next neuron is stimulated by a neurotransmitter, which is chemical


Transmission of a Signal at Synapses

Figure 7.10

Axonterminal

Vesicles

Synapticcleft

Actionpotentialarrives

Synapse

Axon oftransmittingneuron

Receivingneuron

Neurotrans-mitter is re-leased intosynaptic cleft

Neurotrans-mitter bindsto receptoron receivingneuron’smembrane

Vesiclefuses withplasmamembrane

Synaptic cleftNeurotransmittermolecules

Ion channels Receiving neuron

Transmitting neuron

Receptor

Neurotransmitter

Na+Na+

Neurotransmitterbroken downand released

Ion channel opens Ion channel closes



Figure 7.10, step 1

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron



Figure 7.10, step 2

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron


Synaptic cleft


Transmitting neuron



Figure 7.10, step 3

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron



Synaptic cleft Neurotransmittermolecules


Transmitting neuron



Figure 7.10, step 4

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron



Figure 7.10, step 5

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

ReceptorNeurotransmitter

Na+

Ion channel opens



Figure 7.10, step 6

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron


Na+Na+





Figure 7.10, step 7

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron




Synaptic cleftNeurotransmittermolecules


Transmitting neuron


Na+Na+




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


Types of Reflexes and Regulation Somatic reflexes

Stimulation of skeletal muscles Example: When you move your hand away

from a hot stove


Types of Reflexes and Regulation Autonomic reflexes

Regulate activity of: Smooth muscle Heart and blood pressure Glands

Example: saliva secretions, change in eye pupil size, digestion, excretion, blood pressure, sweating


5 Elements of a 3 Neuron Reflex 1. Sensory Receptor (reacts to a stimulus) 2. Sensory Neuron (afferent) 3. Integration Center (CNS) 4. Motor Neuron (efferent) 5. Effector Organ (stimulated to react)


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)


The Reflex Arc

Figure 7.11a, step 1


Skin

Receptor

(a)


The Reflex Arc



Skin

ReceptorSensory neuron

(a)


The Reflex Arc




Interneuron


Integrationcenter

(a)


The Reflex Arc




Interneuron


Motor neuron

Integrationcenter

(a)


The Reflex Arc




Interneuron

Receptor

Effector

Sensory neuron

Motor neuron

Integrationcenter

(a)


Simple Reflex Arc

Figure 7.11b–c

Spinal cord

Sensory (afferent)neuron

Inter-neuron

Motor(efferent)neuron


Sensory receptors(stretch receptorsin the quadricepsmuscle)


Sensory receptors(pain receptors inthe skin)

Effector(quadricepsmuscle ofthigh)

Effector(bicepsbrachiimuscle)

Synapse inventral horngray matter

(c)

(b)


Simple Reflex Arc

Figure 7.11b, step 1

Spinal cord


(b)


Simple Reflex Arc


Spinal cord



(b)


Simple Reflex Arc


Spinal cord




(b)


Simple Reflex Arc


Spinal cord





(b)


Simple Reflex Arc


Spinal cord






(b)


Simple Reflex Arc

Figure 7.11c, step 1

Spinal cord


(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





(c)


Simple Reflex Arc

Figure 7.11b–c

Spinal cord


Inter-neuron









(c)

(b)


Types of Reflexes and Regulation Patellar, or knee-jerk, reflex is an example of a

two-neuron reflex arc

Figure 7.11d

Copyright 2009 Pearson Education, Inc., publishing as Benjamin Cummings Functional Properties of...

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