Chapter 7—The Nervous System Part 1
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Transcript of Chapter 7—The Nervous System Part 1
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Chapter 7—The Nervous SystemPart 1
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General Functions of the Nervous System
Sensory input – Gathering Information Monitor changes occurring inside and
outside the body Changes = stimuli
Integration of stimuli To process and interpret sensory input
and decide if action is needed Motor output—Responding to Stimuli
Sending instructions to activate muscles or glands
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General Functions of the Nervous System
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Central nervous system (CNS) Brain Spinal cord
Peripheral nervous system (PNS) Nerves that extend from the brain and spinal
cord Spinal nerves—carry impulses to & from the
spinal cord Cranial nerves—carry impulses to & from
brain Carry impulses from sensory receptors to CNS &
from CNS to appropriate muscles & glands
Structural Classification of the Nervous System
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Figure 7.1
Functional Classification of the Peripheral Nervous System
Sensory (Afferent) Division Nerve fibers that carry information to the
central nervous systemSomatic – fibers from skin, muscles &
jointsVisceral – fibers from internal organs
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Figure 7.1
Functional Classification of the Peripheral Nervous System
Motor (efferent) division Nerve fibers that carry impulses away
from the central nervous systemTo effector organs, muscles, glands
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Figure 7.1
Functional Classification of the Peripheral Nervous System
Motor (efferent) division Two subdivisions
Somatic nervous system = voluntary (skeletal muscle)
Autonomic nervous system = involuntary (smooth & cardiac muscle, glands)2 parts: sympathetic & parasympathetic
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Organization of the Nervous System
Figure 7.2
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Nervous tissue made of 2 kinds of cells: Supporting cells = neuroglia (aka glial
cells)Cannot transmit nerve impulsesCan divideMost brain tumors are gliomasFunction – to support, insulate, and protect neurons
Neurons
Nervous Tissue—Structure & Function
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Figure 7.3a
Nervous Tissue: Support Cells of CNS
Astrocytes (half of neural tissue) Abundant, star-shaped cells Brace neurons Form barrier
between capillaries and neurons
Control the chemical environment of the brain
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Nervous Tissue: Support Cells Microglia
Spider-like phagocytes
Dispose of debris, including bacteria & dead brain cells
Figure 7.3b–c
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Nervous Tissue: Support Cells
Ependymal Cells Line cavities of the brain and spinal
cord Circulate cerebrospinal fluid Cushions CNS tissue
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Nervous Tissue: Support Cells
Oligodendrocytes Wrap around nerve fibers in the central
nervous system Produce myelin sheath that insulates
nerve fibers
Figure 7.3d
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Figure 7.3e
Nervous Tissue: Support Cells of PNS
Satellite Cells Cushion & protect neuron cell bodies
Schwann Cells Form myelin sheath in the peripheral
nervous system
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Nervous Tissue: Neurons
Neurons = Nerve Cells Cells specialized to transmit messages Major regions of neurons
Cell Body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell bodyNerve fibers covered in whitish, fatty
material = myelin Protects & insulates & increases
transmission rate of nerve impulse
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Neuron Anatomy Cell Body
Nissl substanceSpecialized rough endoplasmic
reticulum Neurofibrils
Intermediate cytoskeleton Maintains cell shape
NucleusLarge nucleolus
Figure 7.4a
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Neuron AnatomyExtensions outside the cell body (can be 3-4’ long)Dendrites – conduct impulses toward the cell body
Axons – conduct impulses away from the cell body
Neuron has 100’s of dendrites, but only 1 axon
Figure 7.4a
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Figure 7.4a–b
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Axons and Nerve Impulses
Axons end in axonal terminals Axonal terminals contain vesicles
with neurotransmitters Axonal terminals are separated from
the next neuron by a gap Synaptic cleft – gap between
adjacent neurons Synapse – junction between nerves
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Nerve Fiber Coverings
Myelin sheath—whitish, fatty material covering axons
Schwann cells – produce myelin sheaths that form in jelly-roll like fashion around nerve Found in PNS only Neurilemma – cytoplasm on outside
Nodes of Ranvier – gaps in myelin sheath along the axon
Figure 7.5
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Neuron
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Neuron Cell Body Location Most neuron cell bodies are found in the
central nervous system Gray matter – cell bodies and
unmyelinated fibers Nuclei – clusters of cell bodies within
the gray matter of the central nervous system
White matter – myelinated fibers Ganglia – collections of cell bodies
outside the central nervous system
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Functional Classification of Neurons Sensory (Afferent) Neurons
Cell bodies in ganglia of PNS Carry impulses from the sensory
receptors to CNSCutaneous sense organs (skin)Proprioceptors – detect stretch or tension (muscle)
Motor (Efferent) Neurons Cell bodies in CNS Carry impulses from the central
nervous system to viscera, muscles, glands
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Functional Classification of Neurons
Free nerve endings (pain & temperature receptors)
Meissner’s Corpuscles (touch receptors
Lamellara Corpuscles (deep pressure receptors)
Golgi Tendon Organ (proprioceptors)
Muscle Spindle (proprioceptor)
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Functional Classification of Neurons
Interneurons (Association Neurons)Cell bodies in CNSFound in neural pathways in the central nervous system
Connect sensory and motor neurons
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Neuron Complex
Figure 7.6
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Structural Classification of Neurons
Multipolar neurons – many extensions from the cell body (all motor & association neurons)
Figure 7.8a
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Structural Classification of Neurons
Bipolar neurons – one axon and one dendrite Rare in adults In special sense organs (eye, nose)
Figure 7.8b
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Structural Classification of Neurons Unipolar neurons – have a short, single
process leaving the cell body Axon conducts nerve impulses both toward
& away from cell body In PNS ganglia
Figure 7.8c
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Functional Properties of Neurons Irritability – ability to respond to stimuli &
convert it into a nerve impulse Conductivity – ability to transmit an
impulse Resting Neuron (Baseline Anatomy):
The plasma membrane (of a neuron) at rest is polarized
Fewer positive ions are inside the cell than outside the cell (K+ inside, Na+ outside)
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Starting a Nerve Impulse
Depolarization – a stimulus depolarizes the neuron’s membrane A depolarized membrane allows
sodium (Na+) to flow inside the membrane
The exchange of ions initiates an action potential (aka “nerve impulse”) in the neuron
Figure 7.9a–c
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Nerve Impulses
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The Action Potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon (all or none)
Impulses travel faster when fibers have a myelin sheath Saltatory conduction – impulse can’t
flow through myelin sheath, so it jumps across from node to node
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Nerve Impulses
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Repolarization Potassium ions rush out of the neuron
after sodium ions rush in, which repolarizes the membrane Restores electrical conditions at
membrane to polarized or resting state
The sodium-potassium pump restores the original configuration (Na+ outside, K+ inside) This action requires ATP
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Nerve Impulses
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Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a
nerve’s axon terminal The dendrite of the next neuron has
receptors that are stimulated by the neurotransmitter
An action potential is started in the next dendrite
Transmission of a Signal at Synapses
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Transmission of a Signal at Synapses
Figure 7.10