Warm Up

• List the events in the nervous system that occur if you accidentally get a paper cut. How does your body respond?

The Nervous System

Chapter 7 (pg 229-237)

Objective Checklist

• List the general functions of the nervous system.

• Explain the classifications of the nervous system.

• Define central and peripheral nervous systems.

• Classify neurons according to their structure and function.

Introduction to the Nervous System

Provides for sensation, higher mental functioning, and emotion; activates muscles and glands

Nervous System Functions

• Sensory input– To monitor changes (stimuli) occurring inside and

outside the body• Integration– To process and interpret sensory input and decide if

action is needed• Motor output– Respond to integrated stimuli by activating muscles

or glands

Structural Classification of the Nervous System

• Central nervous system (CNS)– Brain– Spinal cord

• Peripheral nervous system (PNS)– Nerves outside the central

nervous system– Cranial and spinal nerves

Functional Classification of the PNS

• Sensory (afferent) division– Nerve fibers that carry information to the central

nervous system• Motor (efferent) division– Nerve fibers that carry impulses away from the

central nervous system; two subdivisions• Somatic nervous system = voluntary skeletal muscle• Autonomic nervous system = involuntary

smooth/cardiac muscle

Functional Classification(PNS only)

Functional Classification

(PNS only)

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

Neurons• Outside the cell body– Dendrites – conduct impulses toward the cell

body– Axons – conduct impulses away from the cell body– Axon terminals – contain neurotransmitters to

signal to other nerve cells– Myelin sheaths – protects nerve fibers and helps

conduct nerve impulses– Synapse – gap between axon terminal and

dendrites of the next neuron

Neurons

DendritesCell bodyAxon TerminalsMyelin sheathAxonNucleus

DRAW AND LABEL

Dendrites

Cell body

Axon Terminals

Myelin sheathAxon

Nucleus

Terminology

• Cell bodies in the CNS are in clusters called nuclei.• In the PNS, these collections are known as ganglia.• Bundles of nerve fibers (nerve processes in the CNS

are called tracts.• In the PNS, they are known as nerves!

Functional Classification of Neurons

• Sensory (afferent) neurons– Carry impulses from the sensory receptors

• Cutaneous sense organs of the skin • Proprioceptors of the muscles and tendons • Special sense organs

• Motor (efferent) neurons– Carry impulses from the central nervous system

• Interneurons (association neurons)– Found in the central nervous system– Connect sensory and motor neurons

Functional Classification of Neurons

Structural Classification of Neurons

Mainly interneurons and motor neurons

Rare; some sensory neurons

Mainly sensory neurons

CNS Neuroglia

Line brain/spinal cavities; cilia circulate cerebrospinal fluid

Insulate nerve fibers with myelin sheath; Schwann cells do a similar job in the PNS Account for ½ of neural tissue; anchor neurons to

nutrient supply (capillaries)

Phagocytes that dispose of dead brain cells and bacteria

Myelin Sheath

• Fatty cells that protect/insulate nerve axons and increase the transmission rate of nerve impulses

• Schwann cells in PNS; Oligodendrocytes in CNS

• Breaks in the sheath are known as Nodes of Ranvier

Disease Associated with the Myelin Sheath

• Multiple Sclerosis – Causes destruction of the

myelin sheath– Electrical current is short-

circuited.– Causes visual and speech

disturbances, inability to control muscles, and progressive disablement

– An autoimmne disease caused by WBC attack of the myelin sheath

Objective Checklist

• List the general functions of the nervous system.

• Explain the classifications of the nervous system.

• Define central and peripheral nervous systems.

• Classify neurons according to their structure and function.

Questions? Comments?

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