Transcript Nerve activates contraction

Essentials of Anatomy and Physiology
Fifth edition
Seeley, Stephens and Tate
Chapter 8: Nervous System
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Slide 2.1
Functions of the Nervous System
 Sensory input – gathering information
 Changes occurring inside and outside the
body
 Changes = stimuli
 Integration
 Process and interpret sensory input
 Determine action needed
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Slide 7.1a
Functions of the Nervous System
 Motor output
 A response to integrated stimuli
 Activates muscles or glands (effectors)
 May be voluntary
 May be involuntary
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Slide 7.1b
Structural Classification of the
Nervous System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerves attached to brain and spinal cord
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Slide 7.2
Functional Classification of the PNS
 Sensory (afferent) division
 Nerve fibers that carry information to the
central nervous system
Figure 7.1
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Slide 7.3a
Functional Classification of the PNS
 Motor (efferent) division
 Nerve fibers that carry impulses away from
the central nervous system
Figure 7.1
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Slide 7.3b
Functional Classification of the PNS
 Motor (efferent) division
 Two subdivisions
 Somatic nervous system = voluntary
 Autonomic nervous system = involuntary
Figure 7.1
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Slide 7.3c
Organization of the Nervous System
Figure 7.2
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Slide 7.4
Nervous Tissue: Support Cells
(Neuroglia = “Nerve Glue”)
 Astrocytes
 Star-shaped cells
 Support neurons
 Form blood-brain
barrier
 Control the chemical
environment
Figure 7.3a
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Slide 7.5
Nervous Tissue: Support Cells
 Microglia
“little glue” cells
 Spider-like phagocytes
 Dispose of debris
Figure 7.3b, c
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Slide 7.6
Nervous Tissue: Support Cells
 Ependymal cells
 Line cavities of the
brain and spinal
cord
 Circulate
cerebrospinal
fluid (CSF)
Figure 7.3b, c
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Slide 7.6
Nervous Tissue: Support Cells
 Oligodendrocytes
 “few branch” cells
 Produce myelin
sheath in the CNS
Figure 7.3d
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Slide 7.7a
Nervous Tissue: Support Cells
 Schwann cells
 Form myelin sheath in the PNS
Figure 7.3e
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Slide 7.7b
Nerve Fiber Coverings: Schwann Cells, con’t…
 Wrap around axons
 Nodes of Ranvier:
gaps in myelin
sheath
Figure 7.5
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Slide 7.12
Nervous Tissue: Neurons
 Neurons = nerve cells
Functional cells of the nervous system
 Specialized to transmit messages
 Anatomy
 Cell body – nucleus and organelles
 Processes – fibers that extend from the
cell body
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Slide 7.8
Neuron Anatomy
 Cell body
 Nissl
substance:
 specialized RER
 Neurofibrils:
 cytoskeleton
 maintains cell
shape
Figure 7.4a
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Slide 7.9a
Neuron Anatomy
 Cell body, con’t.
 Nucleus
 Large
nucleolus
Figure 7.4a
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Slide 7.9b
Neuron Anatomy
 Processes
 Dendrites:
conduct
impulses toward
the cell body
 Axons: conduct
impulses away
from the cell
body
Figure 7.4a
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Slide 7.10
Axons and Nerve Impulses
 Axons end in axon terminals
 Axonal terminals
house vesicles with neurotransmitters
 Synaptic cleft – gap between adjacent
neurons
 Synapse – junction between nerves
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Slide 7.11
Neuron Cell Bodies: Location
 Most are in the CNS
 Gray matter = cell bodies and unmyelinated
fibers
 Nuclei = clusters of cell bodies within the
white matter of the central nervous system
 Ganglia = collections of cell bodies outside the
CNS
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Slide 7.13
Functional Classification of Neurons
 Sensory (afferent) neurons
 Carry impulses from sensory receptors
 Cutaneous sense organs
 Proprioceptors: detect stretch or tension
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Slide 7.14a
Functional Classification of Neurons
 Motor (efferent) neurons
 Carry impulses from the central nervous
system
 To an effector (muscle or gland)
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Slide 7.14a
Functional Classification of Neurons
 Interneurons (association neurons)
 Found in neural pathways in the CNS
 Connect sensory and motor neurons
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Slide 7.14b
Functional Classification of Neurons
Figure 7.6
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Slide 7.15
Structural Classification of Neurons
 Multipolar neurons – many extensions
from the cell body
 Most common: these are motor neurons
Figure 7.8a
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Slide 7.16a
Structural Classification of Neurons
 Bipolar neurons – one axon and one
dendrite
 Rare: these are sensory neurons (eye, ear)
Figure 7.8b
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Slide 7.16b
Structural Classification of Neurons
 Unipolar neurons – short single
process leaving the cell body
 These are Sensory neurons in the PNS
Figure 7.8c
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Slide 7.16c
Nerve Impulse Transmission
 Two mechanisms involved
Transmission along a neuron
An electrical process
Transmission between neurons
A chemical process
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Slide 7.17
Functional Properties of Neurons
 Irritability – ability to respond to stimuli
 Conductivity – ability to transmit an
impulse
 The plasma membrane at rest is
polarized (like a resting muscle fiber)
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Slide 7.17
Transmission of a Nerve Impulse
along a Neuron
 Depolarization –
stimulus causes a
change in membrane
permeability
 Allows sodium (Na+) to
enter the neuron
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Figure 7.9a–c
Slide 7.18
Transmission of a Nerve Impulse
along a Neuron
 The exchange of ions
creates an action
potential in the neuron
 “potential to do work”
 Sound familiar??
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Figure 7.9a–c
Slide 7.18
The Action Potential
 Once the action potential (nerve
impulse) begins, it spreads along the
entire neuron
“all-or-none” law: sound familiar??
 Potassium ions (K+) leave the neuron
after Na+ enters
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Slide 7.19
The Action Potential
 Exchange of Na+ and K+ repolarizes the
membrane
 The sodium-potassium pump restores
ions to their original location
 Protein pump in the membrane
 This action requires ATP
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Slide 7.19
Nerve Impulse Propagation
 The impulse
continues to move
along the neuron
 Impulses travel
faster along
myelinated fibers
Figure 7.9c–e
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Slide 7.20
Nerve Impulse Propagation
 Myelinated fibers:
~200 feet/second
 Unmyelinated fibers:
~10 feet/second
Figure 7.9c–e
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Slide 7.20
Transmission of the Nerve Impulse
between Neurons
 Impulses can cross the synapse to
another nerve
 Depolarization activates vesicles in axon
terminal
 Requires Ca++
 Neurotransmitter is released
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Slide 7.21
Transmission of the Nerve Impulse
between Neurons
 The dendrite of the “next” neuron has
receptor sites
 Neurotransmitter attaches to receptors
 If enough molecules of NT attach:
 A new action potential is generated
 Sound familiar??
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Slide 7.21
How Neurons Communicate at
Synapses
Figure 7.10
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Slide 7.22