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Nervous System (Sensory-Motor Integration (Sensory Input (Complexity of…

- - - - Spinal cord
        Lower brain stem
        Cerebellum
        Thalamus
        Cerebral cortex (primary sensory cortex)
  - - - Spinal cord
        
        Lower region of brain
        
        Motor area of cerebral cortex
  - - - Instant, preprogrammed response to a given stimulus
        
        Response to stimulus identical each time
        
        Occurs before conscious awareness
  - - - Different from normal (extrafusal) muscle fibers
        Innervated by g-motor neurons
        Sensory receptors for muscle fiber stretch
    - - Synapses in spinal cord with an a-motor neuron
        Triggers reflex muscle contraction
        Prevents further (damaging) stretch
        Stretch reflex
  - - - Associated with 5 to 25 muscle fibers
        
        Sensitive to tension in tendon (strain gauge)
    - - Inhibit agonists, excite antagonists
        
        Prevent excessive tension in muscle/tendon
        
        Reduce potential for injury
- - - - High [Na+] outside cell, medium [K+] inside cell
        Inside more negative relative to outside
- - - - Uses acetylcholine (ACh) as its neurotransmitter
        Excitatory: passes AP along to muscle
    - - ACh binds to receptor at motor end plate
        
        Causes depolarization
        
        AP moves along plasmalemma, down T-tubules
        
        Repolarization, refractory period
- - - - Brain stem
        
        Relays information between brain and spinal cord
        
        Midbrain, pons, medulla oblongata
        
        Reticular formation
        
        Coordinates skeletal muscle function and tone
        
        Controls cardiovascular and respiratory function
        
        Analgesia system
        
        Opioid substances modulate pain here
        
        b-endorphin release with exercise
      - Cerebrum
        
        Left and right hemispheres
        
        Connected by corpus callosum, which allows interhemisphere communication
        
        Cerebral cortex
        
        Outermost layer of cerebrum
        
        Gray matter (nonmyelinated)
        
        Conscious brain (mind, intellect, awareness)
        
        5 Lobes
        
        Four superficial (outer) lobes
        
        Frontal: general intellect, motor control
        
        Temporal: auditory input, interpretation
        
        Parietal: general sensory input, interpretation
        
        Occipital: visual input, interpretation
        
        One central (deep) lobe
        
        Insular: emotion, self-perception
        
        Regions of Interest for Exercise Physiology
        
        Primary motor cortex (frontal lobe)
        
        Conscious control of skeletal muscle movement
        
        Pyramidal cells → corticospinal tract → spinal cord
        
        Basal ganglia (cerebral white matter)
        
        Clusters of cell bodies deep in cerebral cortex
        
        Help initiate sustained or repetitive movements
        
        Walking, running, posture, muscle tone
        
        Primary sensory cortex (parietal lobe)
      - Diencephalon
        
        Thalamus
        
        Major sensory relay center
        
        Determines what we are consciously aware of
        
        Hypothalamus
        
        Maintains homeostasis, regulates internal environment
        
        Neuroendocrine control
        
        Appetite, food intake, thirst/fluid balance, sleep
        
        Blood pressure, heart rate, breathing, body temperature
      - Cerebellum
        
        Controls rapid, complex movements
        
        Coordinates timing, sequence of movements
        
        Compares actual to intended movements and initiates correction
        
        Accounts for body position, muscle status
        
        Receives input from primary motor cortex, helps execute and refine movements
    - - Continuous with medulla oblongata
      - Tracts of nerve fibers permit two-way conduction of nerve impulses
        
        Ascending afferent (sensory) fibers
        
        Descending efferent (motor) fibers
  - - - Transmits information from periphery to brain
      - Major families of sensory receptors
        
        Mechanoreceptors: physical forces
        
        Thermoreceptors: temperature
        
        Nociceptors: pain
        
        Photoreceptors: light
        
        Chemoreceptors: chemical stimuli
      - Special Families of Sensory Receptors
        
        Joint kinesthetic receptors
        
        Sensitive to joint angles, rate of angle change
        Sense joint position, movement
        
        Muscle spindles
        
        Sensitive to muscle length, rate of length change
        Sense muscle stretch
        
        Golgi tendon organs
        
        Sensitive to tension in tendon
        Sense strength of contraction
    - - Somatic: voluntary, to skeletal muscles
        
        stimulates skeletal muscle activity
      - Autonomic: involuntary, to viscera
        
        Sympathetic
        
        Parasympathetic
        
        regulates visceral activity
      - Transmits information from brain to periphery
      - Autonomic Nervous System
        
        Controls involuntary internal functions
        
        Exercise-related autonomic regulation
        
        Heart rate, blood pressure
        Lung function
        
        Two complementary divisions
        
        Parasympathetic nervous system
        
        Rest and digest
        
        Active at rest
        Opposes sympathetic effects
        
        Parasympathetic stimulation includes
        
        ↑ Digestion, urination
        Conservation of energy
        – ↓ Heart rate
        – ↓ Diameter of vessels and airways
        
        Sympathetic nervous system
        
        Fight or flight: Prepares body for exercise
        
        Sympathetic stimulation
        
        – ↑ Heart rate, blood pressure
        – ↑ Blood flow to muscles
        – ↑ Airway diameter (bronchodilation)
        – ↑ Metabolic rate, glucose levels, FFA levels
        – ↑ Mental activity
    - - 12 pairs of cranial nerves (connect to brain)
        
        31 pairs of spinal nerves (connect to spinal cord)
        
        Both types directly supply skeletal muscles
- - - - Cell body (soma)
        
        Contains nucleus
        
        Cell processes radiate out
      - Dendrites
        
        Receiver cell processes
        
        Carry impulse toward cell body
      - Axon
        
        Sender cell process, starts at axon hillock
        
        End branches, axon terminals, neurotransmitters
- - - - Help cell body decide whether to pass signal to axon
        
        Can excite or inhibit a neuron
        
        Localized changes in membrane potential
        
        Generated by incoming signals from dendrites
        
        Inhibitory signal = K+ efflux = hyperpolarization
        
        Excitatory signal = Na+ influx = depolarization
        
        Strong GP → AP
        
        How strong? Must depolarize to threshold mV
        
        AP will be propagated down axon
        
        AP will be transmitted to next cell
    - - Pass signal down axon
        
        Only excitatory
        
        Rapid, substantial depolarization
        
        Last ~1 ms
        
        Begin as GPs
      - Generate an AP
        
        If GP reaches threshold mV, AP will occur
        
        ~−55 mV
        
        Threshold mV not reached = no action potential
        
        All-or-none principle
        
        − 70 mV → +30 mV → − 70 mV again
        
        − 70 to −55 mV: depolarizing GP, Na+ influx
        
        − 55 to +30 mV: depolarizing AP, Na+ influx
        
        +30 to −70 mV: repolarizing AP, K+ efflux
      - Refractory Periods
        
        Absolute refractory period
        
        During depolarization
        
        Neuron unable to respond to another stimulus
        
        Na+ channels already open, can’t open more
        
        Relative refractory period
        
        During repolarization
        
        Neuron responds only to very strong stimulus
        
        K+ channels open (Na+ closed, could open again)
      - Propagation Down Axon
        
        Myelin: speeds up propagation
        
        Fatty sheath around axon (Schwann cells)
        
        Not continuous (nodes of Ranvier)
        
        Saltatory conduction
        
        Multiple sclerosis: degeneration of myelin
        
        Axon diameter: larger = faster
- - - - Fine motor control: fewer fibers per motor unit
        
        Gross motor control: more fibers per motor unit
    - - Fiber types not mixed within a given motor unit
        
        Either type I fibers or type II fibers
        
        Motor neuron may actually determine fiber type