nervous system
DESCRIPTION
NERVOUS SYSTEM. HONORS ANATOMY & PHYSIOLOGY. excitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue. together with endocrine system: responsible for maintaining homeostasis. - PowerPoint PPT PresentationTRANSCRIPT
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NERVOUS SYSTEMHONORS ANATOMY & PHYSIOLOGY
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Nervous Tissue & Homeostasis
excitable characteristic of nervous tissue allows for generation of nerve impulses (action potentials) that provide communication & regulation of most body tissue.
together with endocrine system: responsible for maintaining homeostasis
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Differences in Nervous & Endocrine Control of Homeostasis
NERVOUS ENDOCRINE
rapid responderaction potentials
slow, prolonged response
releases hormones
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Structures of the Nervous System
total mass of 2 kg (~3% of total body mass)
SkullSpinal CordSpinal NervesCranial NervesGangliaEnteric PlexusSpecial Senses & other Sensory Receptors
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Major Structures of the Nervous System
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Functions of the Nervous System
3 basic functions:1. Sensory2. Integrative3. Motor
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Sensory Function
sensory receptors detect internal & external stimuli
sensory (afferent) neurons carry this sensory information to spinal cord & brain thru cranial & spinal nerves
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Integrative Function
integrate: processnervous system takes information from
sensory neurons & processes that information, analyzes it, stores some of it & makes decisions for appropriate responses
served by interneurons (connect 1 neuron to another neuron
Perception:◦ conscious awareness of sensory stimuli◦occurs in brain
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Motor Function
served by motor (efferent) neuronscarry info from brain/spinal cord
effectors (muscle or gland) thru cranial or spinal nerves
results in muscles contraction or gland secreting
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Quick Quiz
What terms are given to neurons that carry input spinal cord & brain?
What terms are given to neurons that carry output out of the brain & spinal cord?
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Organization of the Nervous System
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Histology of the Nerrvous System
2 cell types1. Neurons2. Neuroglia
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Neurons
nerve cells that possess electrical excitability:◦ability to respond to a stimulus & convert it into an action potential
◦stimulus: any change in environment that is strong enough to initiate an action potential
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Direction Action Potential Travels
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Action Potential
electrical signal that propagates along surface of neurolema (membrane)◦begins & travels due to movement of ions between interstitial fluid & inside of neuron thru specific ion channels
◦once begun it travels rapidly @ constant strength
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Parts of a Neuron
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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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Nerve Fiber
general term for any neuronal process or extension that emerges from cell body
most neurons have 2:1. Dendrites2. Axons
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Dendrites
“little trees”input portion of neuronusually, short, tapering, highly branchedtheir 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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Axonal Transport
2 types:◦for moving materials from cell body axon
terminals
1. slow◦ 1-5 mm/d◦ replenishes new axoplasm to developing or
regenerating axons
2. fast◦ 200 – 400 mm/d◦ moves materials to/from cell body
organelles or membranes needed in axon terminal
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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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Sheath of Schwann = Neurolemma
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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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