HONORS ANATOMY & PHYSIOLOGY CHAPTER 11 Fundamentals of the Nervous System.
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Transcript of HONORS ANATOMY & PHYSIOLOGY CHAPTER 11 Fundamentals of the Nervous System.
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HONORS ANATOMY & PHYSIOLOGYCHAPTER 11
Fundamentals of the
Nervous System
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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
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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
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Organization of the Nervous System
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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
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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
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Dendrites
“little trees”input portion of
neuronusually, short,
tapering, highly branched
their cytoplasm contains Nissl bodies, mitochondria
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Axon
propagates action potentials another neuron muscle fiber gland cell
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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
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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
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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
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Types of Neurons
Functional Classification
Structural Classification
SensoryInterneuronsMotor
use # processes extending from cell body
1. Multipolar neurons2. Bipolar neurons3. Unipolar neurons
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Multipolar Neurons
several dendrites with 1 axonincludes most neurons in brain & spinal cord
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Bipolar Neuron
1 main dendrite & 1 axonretina, inner ear, olfactory area of brain
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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
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Unipolar Neuron
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Purkinje Cells
found in cerebellum
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Pyramidal Cells
in cerebral cortex of brain
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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
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Glial Cells of the CNS
1. ASTROCYTES2. OLIGODENDROCYTES3. MICROGLIA4. EPENDYMAL CELLS
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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
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Oligodendrocytes
“few trees”smaller & fewer branches than astrocytesFunctions:1. form & maintain myelin sheath on axons in
CNS2. 1 oligo. myelinates many axons
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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
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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
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Neuroglial Cells of the PNS
Schwann cellsSatellite cells
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Schwann Cells
functions:1. myelinate axons in PNS
1 Schwann cell myelinates 1 axon
2. participate in axon regeneration
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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
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Myelination
myelin sheath: made up of multilayered lipid & protein (plasma membrane) covering
function:1. electrically insulates axon2. increases speed of nerve impulses
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Myelinated & Unmyelinated Axons
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Nodes of Ranvier
gaps in myelin sheath1 Schwann cell wraps axon between nodes
of Ranvier
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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
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Demyelination
loss of myelin sheathsee in disorders:
multiple sclerosis Tay-Sachs side effect of radiation therapy & chemotherapy
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Gray Matter of the Nervous System
contains: neuronal cell bodies dendrites unmyelinated axons axon terminals neuroglia
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White Matter of the Nervous System
composed of: myelinated axons
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