chapter 7 the nervous system: structure and control of movement
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Chapter 7 The Nervous System: Structure and Control of Movement. EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley. General Nervous System Functions. Control of the internal environment With the endocrine system - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 7
The Nervous System: Structure and Control of
Movement
EXERCISE PHYSIOLOGYTheory and Application to Fitness and Performance,
6th editionScott K. Powers & Edward T. Howley
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General Nervous System Functions
• Control of the internal environment– With the endocrine system
• Voluntary control of movement• Programming spinal cord reflexes• Assimilation of experiences necessary for
memory and learning
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Organization of the Nervous System
• Central nervous system (CNS)– Brain and spinal cord
• Peripheral nervous system (PNS)– Neurons outside the CNS– Sensory division
• Afferent fibers transmit impulses from receptors to CNS– Motor division
• Efferent fibers transmit impulses from CNS to effector organs
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Anatomical Divisions of the Nervous System
Figure 7.1
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Relationship Between PNS and CNS
Figure 7.2
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Structure of a Neuron• Cell body• Dendrites
– Conduct impulses toward cell body• Axon
– Carries electrical impulse away from cell body– May be covered by Schwann cells
• Forms discontinuous myelin sheath along length of axon
• Synapse – Contact points between axon of one neuron and
dendrite of another neuron
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Figure 7.3
The Parts of a Neuron
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Synaptic Transmission
Figure 7.4
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Electrical Activity in Neurons
• Neurons are “excitable tissue”• Irritability
– Ability to respond to a stimulus and convert it to a neural impulse
• Conductivity– Transmission of the impulse along the axon
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Resting Membrane Potential
• Negative charge inside cells at rest– -5 to -100 mv (-40 to -75 mv in neurons)
• Determined by: – Permeability of plasma membrane to ions– Difference in ion concentrations across membrane
• Na+, K+, Cl-, and Ca+2
• Maintained by sodium-potassium pump– Potassium tends to diffuse out of cell– Na+/K+ pump moves 2 K+ in and 3 Na+ out
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The Resting Membrane Potential in Cells
Figure 7.5
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Concentrations of Ions Across a Cell Membrane
Figure 7.6
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Illustration of Ion Channels
Figure 7.7
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The Sodium-Potassium Pump
Figure 7.8
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Action Potential• Occurs when a stimulus of sufficient strength
depolarizes the cell– Opens Na+ channels and Na+ diffuses into cell
• Inside becomes more positive
• Repolarization– Return to resting membrane potential
• K+ leaves the cell rapidly• Na+ channels close
• All-or-none law– Once a nerve impulse is initiated it will travel the length of
the neuron
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An Action Potential
Figure 7.9
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Depolarization and Repolarization of a Nerve Fiber
Figure 7.10
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Neurotransmitters and Synaptic Transmission
• Synapse– Small gap between presynaptic neuron and
postsynaptic neuron• Neurotransmitter
– Chemical messenger released from presynaptic membrane
– Binds to receptor on postsynaptic membrane– Causes depolarization of postsynaptic
membrane
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Basic Structure of a
Chemical Synapse
Figure 7.11
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Neurotransmitters and Synaptic Transmission
• Excitatory postsynaptic potentials (EPSP)– Causes depolarization – Temporal summation
• Summing several EPSPs from one presynaptic neuron
– Spatial summation• Summing from several different presynaptic neurons
• Inhibitory postsynaptic potentials (IPSP)– Causes hyperpolarization
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Proprioceptors
• Provide CNS with information about body position and joint angle– Free nerve endings
• Sensitive to touch and pressure• Initially strongly stimulated then adapt
– Golgi-type receptors• Found in ligaments and joints• Similar to free nerve endings
– Pacinian corpuscles• In tissues around joints• Detect rate of joint rotation
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Muscle Chemoreceptors
• Sensitive to changes in the chemical environment surrounding a muscle– H+ ions, CO2, and K+
• Provide CNS about metabolic rate of muscular activity– Important in regulation of cardiovascular and
pulmonary responses
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Reflexes
• Rapid, unconscious means of reacting to stimuli• Order of events:
– Sensory nerve sends impulse to spinal column– Interneurons activate motor neurons– Motor neurons control movement of muscles
• Reciprocal inhibition– EPSPs to muscles to withdraw from stimulus– IPSPs to antagonistic muscles
• Crossed-extensor reflex– Opposite limb supports body during withdrawal of injured limb
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The Crossed-Extensor Reflex
Figure 7.12
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Somatic Motor Function
• Somatic motor neurons of PNS– Responsible for carrying neural messages from
spinal cord to skeletal muscles• Motor unit
– Motor neuron and all the muscle fibers it innervates
• Innervation ratio– Number of muscle fibers per motor neuron
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Illustration of a Motor Unit
Figure 7.13
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Vestibular Apparatus and Equilibrium
• Vestibular apparatus– Located in the inner ear – Responsible for maintaining general equilibrium
and balance– Sensitive to changes in linear and angular
acceleration
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Role of the Vestibular Apparatus in Maintaining Equilibrium and Balance
Figure 7.14
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Motor Control Functions of the Brain
• Brain stem – Responsible for:
• Many metabolic functions• Cardiorespiratory control• Complex reflexes
– Major structures:• Medulla • Pons• Midbrain• Reticular formation
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Motor Control Functions of the Brain
• Cerebrum– Cerebral cortex
• Organization of complex movement• Storage of learned experiences• Reception of sensory information
– Motor cortex• Motor control and voluntary movement
• Cerebellum– Coordinates and monitors complex movement
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Motor Functions of the Spinal Cord
• Withdrawal reflex• Other reflexes
– Important for the control of voluntary movement• Spinal tuning
– Voluntary movement translated into appropriate muscle action
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Control of Motor Function• Subcortical and cortical motivation areas
– Sends a “rough draft” of the movement • Cerebellum and basal ganglia
– Coverts “rough draft” into movement plan– Cerebellum: fast movements– Basal ganglia: slow, deliberate movements
• Motor cortex through thalamus– Forwards message sent down spinal neurons for “Spinal
tuning” and onto muscles– Feedback from muscle receptors and proprioceptors
allows fine-tuning of motor program
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Structures and Processes Leading to Voluntary Movement
Figure 7.16
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Autonomic Nervous System
• Responsible for maintaining internal environment– Effector organs not under voluntary control
• Smooth muscle, cardiac muscle, and glands
• Sympathetic division– Releases norepinephrine (NE)– Excites an effector organ
• Parasympathetic division– Releases acetylcholine (ACh)– Inhibits effector organ
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Neurotransmitters of the Autonomic Nervous System
Figure 7.17
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Exercise Enhance Brain Health
• Exercise improves brain function and reduces the risk of cognitive impairment associated with aging
• Regular exercise can protect the brain against disease (e.g. Alzheimer’s) and certain types of brain injury (e.g. stroke)