Human Anatomy & PhysiologyNinth Edition

PowerPoint® Lecture Slidesprepared byBarbara Heard,Atlantic Cape Community College

C H A P T E R

© 2013 Pearson Education, Inc.© Annie Leibovitz/Contact Press Images

11

Fundamentals of the Nervous System and Nervous Tissue: Revised by Dr. Par Mohammadian

The Nervous System

• Master controlling and communicating system of body

• Cells communicate via electrical and chemical signals– Rapid and specific

Functions of the Nervous System

• Sensory input– Information gathered by sensory receptors

about internal and external changes

• Integration– Processing and interpretation of sensory input

• Motor output– Activation of effector organs (muscles and

glands) produces a response

Sensory input

Integration

Motor output

Divisions of the Nervous System

• Central nervous system (CNS) – Brain and spinal cord of dorsal body cavity– Integration and control center

• Interprets sensory input and dictates motor output

• Peripheral nervous system (PNS)– The portion of the nervous system outside

CNS– Consists mainly of nerves that extend from

brain and spinal cord• Spinal nerves to and from spinal cord• Cranial nerves to and from brain

Peripheral Nervous System (PNS)

• Two functional divisions

– Sensory (afferent) division

• Somatic sensory fibers—convey impulses from skin, skeletal

muscles, and joints to CNS

• Visceral sensory fibers—convey impulses from visceral organs

to CNS

– Motor (efferent) division

• Transmits impulses from CNS to effector organs– Muscles and glands

• Two divisions– Somatic nervous system

– Autonomic nervous system

Motor Division of PNS:

Somatic Nervous System– Conscious control of skeletal muscles

Autonomic Nervous System

• Regulates smooth muscle, cardiac muscle, and glands

• Two functional subdivisions– Sympathetic– Parasympathetic

Central nervous system (CNS)Brain and spinal cord

Integrative and control centers

Peripheral nervous system (PNS)Cranial nerves and spinal nerves

Communication lines between the CNSand the rest of the body

Sensory (afferent) divisionSomatic and visceral sensorynerve fibers

Conducts impulses fromreceptors to the CNS

Motor (efferent) divisionMotor nerve fibers

Conducts impulses from the CNSto effectors (muscles and glands)

Somatic sensory fiber SkinSomatic nervous

systemSomatic motor(voluntary)

Conducts impulsesfrom the CNS toskeletal muscles

Autonomic nervoussystem (ANS)Visceral motor(involuntary)

Conducts impulsesfrom the CNS tocardiac muscles,smooth muscles,and glandsVisceral sensory fiber

Motor fiber of somatic nervous system

StomachSkeletalmuscle

Sympathetic divisionMobilizes body systemsduring activity

Parasympatheticdivision

Conserves energy

Promotes house-keeping functionsduring rest

Sympathetic motor fiber of ANS Heart

Parasympathetic motor fiber of ANS Bladder

Structure

Function

Sensory (afferent) division of PNS

Motor (efferent) division of PNS

Histology of Nervous Tissue

• Highly cellular; little extracellular space

– Tightly packed

• Two principal cell types

– Neuroglia – small cells that surround and

wrap delicate neurons

– Neurons (nerve cells)—excitable cells that

transmit electrical signals

Histology of Nervous Tissue: Neuroglia

• Astrocytes (CNS)

• Microglial cells (CNS)

• Ependymal cells (CNS)

• Oligodendrocytes (CNS)

• Satellite cells (PNS)

• Schwann cells (PNS)

Astrocytes

• Most abundant and highly branched glial cells

• Cling to neurons, synaptic endings, and capillaries

• Functions include

– Support neurons

– Play role in exchanges between capillaries and neurons

– Control chemical environment around neurons

– Respond to nerve impulses and neurotransmitters

Capillary

Neuron

Astrocyte

Astrocytes are the most abundant CNS neuroglia.

Neuron

Microglialcell

Microglial cells are defensive cells in the CNS.

Microglial Cells

Small, ovoid cells with thorny processes

Can transform to phagocytize

Fluid-filled cavityCilia

Ependymalcells

Brain orspinal cordtissue

Ependymal cells line cerebrospinal fluid–filled cavities.

Ependymal Cells

• Range in shape from squamous to columnar• May be ciliated

– Cilia beat to circulate cerebrospinal fluid (CSF)• Line the central cavities of the brain and spinal column• Form permeable barrier between CSF in cavities and tissue fluid bathing

CNS cells

Myelin sheath

Process ofoligodendrocyte

Nervefibers

Oligodendrocytes have processes that form myelinsheaths around CNS nerve fibers.

Oligodendrocytes

• Branched cells• Processes wrap CNS nerve fibers, forming insulating myelin

sheaths thicker nerve fibers

Satellite Cells and Schwann Cells (PNS)

• Satellite cells– Surround neuron cell bodies in PNS– Function similar to astrocytes of CNS

• Schwann cells (neurolemmocytes)– Surround all peripheral nerve fibers and form

myelin sheaths in thicker nerve fibers• Similar function as oligodendrocytes

– Vital to regeneration of damaged peripheral nerve fibers

Satellitecells Cell body of neuron

Schwann cells(forming myelin sheath)

Nerve fiber

Satellite cells and Schwann cells (which form myelin)surround neurons in the PNS.

Neurons

• Structural units of nervous system

• Large, highly specialized cells that conduct impulses

• High metabolic rate—requires continuous supply of O2 and glucose – cannot survive for more than a few minutes without O2!

• All have cell body (soma) and one or more processes

Dendrites(receptiveregions)

Cell body(biosynthetic center& receptive region)

Nucleus

Nucleolus

Axon hillock

Chromatophilicsubstance (roughendoplasmicreticulum)

Axon(impulse-generatingand -conductingregion)

Impulsedirection

Schwann cell

Myelin sheath gap(node of Ranvier)

Terminal branches

Axonterminals(secretoryregion)

• Armlike extensions from the soma

• Called tracts in the CNS and nerves in the PNS

• There are two types:

axons and dendrites

Processes

• Contains the nucleus and a nucleolus

• Is the major biosynthetic center

• Is the focal point for the outgrowth of neuronal

processes

• Has well-developed Nissl bodies (rough ER)

• Contains an axon hillock – cone-shaped area from

which axons arise

Nerve Cell Body (Perikaryon or Soma)

Nuclei & Ganglia

• Most neuron cell bodies located in the CNS – protected by the bones, skull, and vertebral column: Nuclei

• Cell bodies located in the PNS: ganglia

Dendrites• In motor neurons

– 100s of short, tapering, diffusely branched processes

• Receptive (input) region of neuron

Neuron cell body

Dendriticspine

The Axon: Structure

• One axon per cell arising from axon hillock• Long axons called nerve fibers• Occasional branches (axon collaterals)• Branches profusely at end (terminus)• Distal endings called axon terminals or terminal

boutons

Function:• Generates nerve impulses• Transmits them along axolemma (neuron cell

membrane) to axon terminal• Secrete neurotransmitters from the axonal terminals

Myelin Sheath

Whitish, fatty (protein-lipoid), segmented sheath

around most long axons

It functions to:

– Protect the axon

– Electrically insulate fibers from one another

– Increase the speed of nerve impulse transmission

• Formed by Schwann cells in the PNS and Oligodendrocytes in the CNS

• A Schwann cell:

– Envelopes an axon in a trough

– Encloses the axon with its plasma membrane

– Has concentric layers of membrane that make up the myelin sheath

• Neurilemma – remaining nucleus and cytoplasm of a Schwann cell

• Nodes of Ranvier: Gaps in the myelin sheath between adjacent Schwann cells

Myelin Sheath and Neurilemma: Formation

Schwanncell plasmamembrane

Schwann cellcytoplasm

Axon Schwann cellnucleus

A Schwann cell envelops an axon.

The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers.

Myelinsheath

Schwann cell cytoplasm

The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath.

Myelination of a nerve fiber (axon)

1

2

3

Myelin Sheaths in the CNS

• White matter– dense collections of myelinated fibers

• Gray matter– Mostly neuron cell bodies and nonmyelinated fibers

Structural Classification of Neurons

– Multipolar – 3 or more processes• 1 axon, others dendrites

• Most common; major neuron in CNS

– Bipolar – 2 processes• 1 axon and 1 dendrite

• Rare, e.g., Retina and olfactory mucosa

– Unipolar – 1 short process• Divides T-like – both branches now considered axons

– Distal (peripheral) process – associated with sensory

receptor

– Proximal (central) process – enters CNS

© 2013 Pearson Education, Inc.

Table 11.1 Comparison of Structural Classes of Neurons (2 of 3)

Table 11.1 Comparison of Structural Classes of Neurons (3 of 3)

Functional Classification of Neurons

• Sensory

– Transmit impulses from sensory receptors toward

CNS

• Motor

– Carry impulses from CNS to effectors

• Interneurons (association neurons)

– Shuttle signals through CNS pathways; most are

entirely within CNS

– 99% of body's neurons

– Most confined in CNS