ESSENTIALS

OF HUMAN

ANATOMY

& PHYSIOLOGY

Unit

4The Nervous System and

Nervous Tissue

Nervous System Functions

�Sensory input- gathering information�Monitor stimuli inside and outside the body

�Integration�Process and interpret sensory input and decide

if action is needed

�Motor output�Response to integrated stimuli�Activates muscles or glands

Nervous System Structural Classification

�Central nervous system (CNS)�Brain�Spinal cord

�Peripheral nervous system (PNS)�Nerves outside the brain and spinal cord

Functional Classification of the PNS

�Sensory (afferent) division�Nerve fibers carry information to the CNS

�Motor (efferent) division� Nerve fibers carry impulses away from the

CNS

�Two subdivisions�Somatic nervous system = voluntary

�Autonomic nervous system = involuntary

Organization of the Nervous System

Nervous Tissue: Support Cells (Neuroglia)

�Astrocytes�Abundant, star-shaped cells�Brace neurons�Form barrier between capillaries and neurons�Control chemical environment of

the brain

Nervous Tissue: Support Cells

�Microglia�Spider-like phagocytes�Dispose of debris

�Ependymal cells�Line cavities of the

brain and spinal cord�Circulate cerebrospinal

fluid

Nervous Tissue: Support Cells

�Oligodendrocytes�Produce myelin sheath around nerve fibers in

the CNS

Nervous Tissue: Support Cells

�Satellite cells�Protect neuron cell bodies

�Schwann cells�Form myelin sheath in the PNS

Nervous Tissue: Neurons

�Neurons = nerve cells�Cells specialized to transmit messages�Major regions�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 ER�Neurofibrils- intermediate cytoskeleton that

maintains cell shape�Nucleus�Large nucleolus

Neuron Anatomy

�Extensions outside the cell body�Dendrites- conduct impulses toward cell body�Axons- conduct impulses away from cell body

Axons and Nerve Impulses

�Axons end in axonal terminals

�Axonal terminals:�Contain vesicles with neurotransmitters�Separated from next neuron by a gap�Synaptic cleft- gap between adjacent neurons

�Synapse- junction between nerves

Nerve Fiber Coverings

�Myelin sheaths- jelly roll like

covering (schwann cells)

�Nodes of Ranvier- gaps in

myelin sheath along the

axon

Neuron Cell Body Location

�Most are found in the CNS�Gray matter- cell bodies and unmylenated

fibers�Nuclei- clusters of cell bodies within the white

matter of the CNS

�Ganglia- collections of cell bodies outside

the CNS