elaine n. marieb eighth edition 7 copyright © 2006 pearson education, inc., publishing as benjamin...

ELAINE N. MARIEB

EIGHTH EDITION

7

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

PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University

ESSENTIALSOF HUMANANATOMY

& PHYSIOLOGY

PART A

The Nervous System


Functions of the Nervous System Sensory input – gathering information

To monitor changes occurring inside and outside the body

Changes = stimuli = sensory input

Integration

To process and interpret sensory input and decide if action is needed


Functions of the Nervous System Motor output

A response to integrated stimuli

The response activates muscles or glands


Structural Classification of the Nervous System Central nervous system (CNS)

Brain

Spinal cord

Act as integrating & command centers (interpret sensory input & issue commands)

Peripheral nervous system (PNS)

Nerve outside the brain and spinal cord

Spinal nerves carry impulses to & from spinal cord

Cranial nerves carry impulses to & from brain

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 7.1

Functional Classification of the Peripheral Nervous System Sensory (afferent) division

Nerve fibers that carry information to the central nervous system


Functional Classification of the Peripheral Nervous System Sensory fibers that carry impulses from skin,

skeletal muscle & joints = somatic sensory fibers.

Those that carry impulses from the visceral organs = visceral sensory fibers


Functional Classification of the Peripheral Nervous System Motor (efferent) division

Nerve fibers that carry impulses away from the central nervous system to effector organs, the muscles & glands


Functional Classification of the Peripheral Nervous System

Motor (efferent) division

Two subdivisions

Somatic nervous system = voluntary

Autonomic nervous system = involuntary


Functional Classification of the Peripheral Nervous System

Autonomic nervous system = involuntary

2 parts

Sympathetic – mobilizes the body during extreme situations – called the “fight or flight” division

Parasympathetic – allows us to “unwind” & conserve energy – called the craniosacral division


Organization of the Nervous System

Figure 7.2

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 7.3a

Nervous Tissue: Support Cells (Neuroglia = literally “nerve glue”) Astrocytes

Abundant, star-shaped cells

Brace neurons; anchor to capillaries

Form barrier between capillaries and neurons

Control the chemical environment of the brain


Nervous Tissue: Support Cells Microglia

Spider-like phagocytes

Dispose of debris(dead brain cells, bacteria)

Ependymal cells

Line cavities of the brain and spinal cord

Beating cilia circulate cerebrospinal fluid

Figure 7.3b–c


Nervous Tissue: Support Cells Oligodendrocytes

Produce myelin sheath around nerve fibers in the central nervous system

Unable to transmit nerve impulses

Never lose their ability to divide

Most brain tumorsare gliomas -tumors formed byneuroglia

Figure 7.3d

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin CummingsFigure 7.3e

Nervous Tissue: Support Cells Satellite cells

Protect neuron cell bodies

Schwann cells

Form myelin sheath in the peripheral nervous system


Nervous Tissue: Neurons Neurons = nerve cells

Cells specialized to transmit messages

Major regions of neurons

Cell body – nucleus and metabolic center of the cell

Processes – fibers that extend from the cell body


Neuron Anatomy Cell body

Nissl substance – specialized rough endoplasmic reticulum

Neurofibrils – intermediate cytoskeleton that maintains cell shape

Figure 7.4a


Neuron Anatomy Cell body

Nucleus

Large nucleolus

Lacks centrioles – confirms amitoticnature of most neurons

Figure 7.4a–b


Neuron Anatomy Extensions outside

the cell body – frommicroscopic to 3-4feet in length

Dendrites – conduct impulses toward the cell body – may number in the 100’s

Axons – conduct impulses away from the cell body – only one

Figure 7.4a


Axons and Nerve Impulses Axons end in axon terminals

Axon terminals contain vesicles with neurotransmitters – impulses stimulate their release

Axon terminals are separated from the next neuron by a gap

Synaptic cleft – gap between adjacent neurons

Synapse – junction between nerves


Nerve Fiber Coverings Schwann cells –

produce myelin sheaths in jelly-roll like fashion on axons outside the CNS

Neurilemma – part of Schwann cell external to myelin sheath

Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7.5


Nerve Fiber Coverings Oligodendrocytes form CNS myelin sheaths

CNS sheaths lack a neurilemma

Because the neurilemma remains intact (for the most part) when a peripheral nerve fiber is damaged, it plays an important role in fiber regeneration, an ability that is largely lacking in the CNS


Neuron Cell Body Location Most are found in the central nervous system

Gray matter – cell bodies and unmylenated fibers

Nuclei – clusters of cell bodies within the white matter of the central nervous system

Ganglia – collections of cell bodies outside the central nervous system

Bundles of nerve fibers in the CNS are called tracts; whereas in the PNS they are called nerves


Functional Classification of Neurons Sensory (afferent) neurons

Cell bodies always found in the ganglion outside the CNS

Carry impulses from the sensory receptors to CNS

Cutaneous sense organs (skin)

Pain receptors – bare dendrite endings – most numerous

Proprioceptors – detect stretch or tension (muscles & tendons) – help maintain balance & normal posture


Functional Classification of Neurons Motor (efferent) neurons

Carry impulses from the CNS to viscera, &/or muscles & glands

Cell bodies of motor neurons are always located in the CNS


Functional Classification of Neurons Interneurons (association neurons)

Found in neural pathways in the central nervous system

Connect sensory and motor neurons

Cell bodies are always located in the CNS


Neuron Classification

Figure 7.6


Structural Classification of Neurons Multipolar neurons – many extensions

from the cell body

All motor & interneurons (association neurons) are multipolar

Most common

Figure 7.8a


Structural Classification of Neurons Bipolar neurons – one axon and one dendrite

Rare in adults - found only in some special sense organs (eye, nose)

Figure 7.8b


Structural Classification of Neurons Unipolar neurons – have a short single

process leaving the cell body

Figure 7.8c


Structural Classification of Neurons Short, divides almost immediately into

proximal (central) & distal (peripheral) processes

Dendrite = small process at end of peripheral process; remainder = axon

Axon conducts impulses both away from & toward cell body

Sensory neurons found in PNS ganglia are unipolar


Functional Properties of Neurons Irritability – ability to respond to stimuli

Conductivity – ability to transmit an impulse

The plasma membrane at rest is polarized

Fewer positive ions are inside the cell than outside the cell


Starting a Nerve Impulse Depolarization – a

stimulus depolarizes the neuron’s membrane

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

The exchange of ions initiates an action potential in the neuron

Figure 7.9a–c


The Action Potential If the action potential (nerve impulse) starts,

it is propagated over the entire axon

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


Nerve Impulse Propagation The impulse

continues to move toward the cell body

Impulses travel faster when fibers have a myelin sheath

Figure 7.9d–f


Continuation of the Nerve Impulse between Neurons 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


How Neurons Communicate at Synapses

Figure 7.10

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