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Ch.8-1 8-2Introduction

Neurons

Basic unit of nervous system

All functions involve communication between neurons and with other cells

Neuroglia (Glial cells)

Regulate environment around neurons

Provide supporting framework

Act as phagocytes

Retain ability to divide (most of them)

Monitors internal & external environments

Integrates sensory information

Coordinates voluntary & involuntary responses of many organ systems

Central Nervous System (CNS)

(Brain & Spinal Cord)

Integrates & coordinates processing of sensory data and transmission of motor commands

Seat of higher function(intelligence, memory, emotion)

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Peripheral Nervous System (PNS)

(All neural tissue outside CNS – the peripheral nerves)

Links communication between CNS and rest of the body

Afferent Division

Sensory information detected by receptors

Transmitted to CNS for processing

Efferent Division

Motor commands sent from CNS to other areas (effectors)

Efferent Division

Motor commands send from CNS to other areas (effectors)

Somatic (SNS) –

Autonomic (ANS) –

Control over skeletal muscle contractions

Involuntary regulation of smooth &cardiac muscle, glandular secretions

• Contains sympathetic & parasympathetic divisionsaffecting rates of activity in various structures

Nervous System

Peripheral Central

Autonomic(organs, glands)

Somatic(skeletal muscle)

Parasympathetic(calming)

Sympathetic(arousing)

Efferent(from CNS to PNS)

Afferent(from PNS to CNS)

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Cell Body

Contains Organelles

Large nucleus (prominent nucleolus)

Lack centrioles

Numerous mitochondria

Clusters of ribosomes (free & fixed) & ER

Give gray color to those areascalled Nissl bodies

Dendrites

Numerous branched extensions

Sensitive to stimulation(chemical, mechanical, or electrical)

RECEIVE incoming signals

Axon

Elongated projection(often only one is present)

Sensitive to stimulation(chemical, mechanical, or electrical)

CARRIES INFORMATION AWAY from cell body

Axon

Action potentials begin at thickened region of cell body called axon hillock

Many branch producing collaterals

Synaptic Terminals

Located at end of each branch

Part of a synapse

Synapse – Site where neuron communicates with another cell

Multipolar

Two or more dendrites

Single axon

Most common in CNS

All motor neurons that control skeletal muscles

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Unipolar

Dendrites & axon are continuous

Cell body lies to one side

Most common in sensory neurons

Bipolar

One dendrite & one axon

Cell body lies between the two

Rare, but found in special sense organs (parts in sight, smell, hearing)

Sensory (~10 million total in body)

Form afferent division of PNS

Receive information from sensory receptors monitoring external & internal environments(May be dendrite or specialized cell of other tissue)

Relay information to CNS

Motor (~0.5 million total in body)

Form efferent division of PNS

Carry instructions from CNS to other tissues, organs, or organ systems

Interneurons (~20 billion total in body)

Located entirely within brain & spinal cord

Form connections between neurons

Responsible for distribution of sensory information & coordination of motor activity (More complex the stimulus, greater the number of interneurons involved)