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HONORS ANATOMY & PHYSIOLOGYCHAPTER 11
Fundamentals of the
Nervous System
Functions of the Nervous System
3 overlapping functions:1. Sensory input
monitor changes in & outside of body information gathered called sensory input which is
carried to #2 on afferent nerves
2. Integration processing & interpreting sensory input
3. Motor output activation of effector organs (muscles or glands) to
cause a response called motor output which is carried on efferent nerrves
Divisions of the Nervous System
1. Central Nervous System(CNS) Brain Spinal Cord
2. Peripheral Nervous System (PNS) Sensory neurons: specialized endings to detect a
particular sense Motor neurons:
Somatic: CNS skeletal muscle (voluntary) Autonomic:1. Sympathetic2. Parasympatheric
Organization of the Nervous System
Histology of Nervous Tissue
very cellular, ~20% extracellular material2 cell types:1. Neurons
excitable (respond to stimuli) able to transmit electrical impulses (action
potentials)
2. Neuroglia: supporting cells
Parts of Neuron: Cell Body
contains nucleus, cytoplasm, typical organelles,
+ Nissl bodies clusters of RER make materials
for: growth of neuron regenerate
damaged axons in PNS
Dendrites
“little trees”input portion of
neuronusually, short,
tapering, highly branched
their cytoplasm contains Nissl bodies, mitochondria
Axon
propagates action potentials another neuron muscle fiber gland cell
Parts of an Axon
joins cell body @ cone-shaped elevation: axon hillock
part of axon closest to hillock = initial segment
jct of axon hillock & initial segment where action potential arises so is called the trigger zone
Parts of an Axon
axoplasm: cytoplasm of an axonaxolemma: plasma membrane of axonaxon collaterals: side branches along length
of axon (most @ 90°)axon terminals: axon divides into many fine
processes
Synapse
site of communication between 2 neurons or between a neuron & effector cell
synaptic end bulbs: tips of some axon terminals swell into bulb-shaped structures
synaptic vesicles: store neurotransmitter many neurons have >1 neurotransmitter,
each with different effects on postsynaptic cell
Types of Neurons
Functional Classification
Structural Classification
SensoryInterneuronsMotor
use # processes extending from cell body
1. Multipolar neurons2. Bipolar neurons3. Unipolar neurons
Multipolar Neurons
several dendrites with 1 axonincludes most neurons in brain & spinal cord
Bipolar Neuron
1 main dendrite & 1 axonretina, inner ear, olfactory area of brain
Unipolar Neuron
are sensory neurons that begin in embryo as bipolar
during development axon & dendrite fuse then divide into 2 branches (both have characteristic structure & function of an axon)
1 branch ends with dendrites (out of CNS)2nd branch ends in axon terminal (in CNS)cell bodies of most found in ganglia
Unipolar Neuron
Purkinje Cells
found in cerebellum
Pyramidal Cells
in cerebral cortex of brain
Neuroglia (Glia)
~50% vol of CNS“glue”do not generate or propagate action
potentialsmultiply & divide in mature nervous systemsglioma:
brain tumors derived from glial cells very malignant, grow rapidly
Glial Cells of the CNS
1. ASTROCYTES2. OLIGODENDROCYTES3. MICROGLIA4. EPENDYMAL CELLS
Astrocytes
star-shapedlargest & most numerous of glial cellsfunctions:1. physically support neurons2. assist in blood-brain-barrier (bbb)3. in embryo: regulate growth, migration, &
interconnections between neurons4. help maintain appropriate chemical
environment for propagation of action potentials
Oligodendrocytes
“few trees”smaller & fewer branches than astrocytesFunctions:1. form & maintain myelin sheath on axons in
CNS2. 1 oligo. myelinates many axons
Microglia
small cells with slender processes giving off many spine-like projections
function:1. phagocytes
remove cellular debris made during normal development
remove microbes & damaged nervous tissue
Ependymal Cells
single layer of cuboidal to columnar cellsciliated & have microvillifunction:1. line ventricles of brain & central canal of
spinal cord2. produce, monitor, & assist in circulation of
cerebrospinal fluid (CSF)3. form bbb
Neuroglial Cells of the PNS
Schwann cellsSatellite cells
Schwann Cells
functions:1. myelinate axons in PNS
1 Schwann cell myelinates 1 axon
2. participate in axon regeneration
Satellite Cells
flat cells that surround cell bodies of neurons in PNS ganglia
functions:1. structural support2. regulate exchange of materials between
neuronal cell bodies & interstitial fluid
Myelination
myelin sheath: made up of multilayered lipid & protein (plasma membrane) covering
function:1. electrically insulates axon2. increases speed of nerve impulses
Myelinated & Unmyelinated Axons
Nodes of Ranvier
gaps in myelin sheath1 Schwann cell wraps axon between nodes
of Ranvier
Myelin
amount increases from birth to maturity infant‘s responses slower & less coordinated
as older child or adult in part because myelination is a work in progress thru infancy
Demyelination
loss of myelin sheathsee in disorders:
multiple sclerosis Tay-Sachs side effect of radiation therapy & chemotherapy
Gray Matter of the Nervous System
contains: neuronal cell bodies dendrites unmyelinated axons axon terminals neuroglia
White Matter of the Nervous System
composed of: myelinated axons