1. 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

2. 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

3. 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

4. Anatomical Divisions of the Nervous System
Figure 7.1

5. Relationship Between PNS and CNS
Figure 7.2

6. Structure of a Neuron Cell body Dendrites Axon Synapse
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

7. The Parts of a Neuron
Figure 7.3

8. Synaptic Transmission
Figure 7.4

9. 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

10. 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

11. The Resting Membrane Potential in Cells
Figure 7.5

12. Concentrations of Ions Across a Cell Membrane
Figure 7.6

13. Illustration of Ion Channels
Figure 7.7

14. The Sodium-Potassium Pump
Figure 7.8

15. 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

16. An Action Potential
Figure 7.9

17. Depolarization and Repolarization of a Nerve Fiber
Figure 7.10

18. 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

19. Basic Structure of a Chemical Synapse
Figure 7.11

20. 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

21. 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

22. 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

23. 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

24. The Crossed-Extensor Reflex
Figure 7.12

25. 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

26. Illustration of a Motor Unit
Figure 7.13

27. Vestibular Apparatus and Equilibrium
Located in the inner ear
Responsible for maintaining general equilibrium and balance
Sensitive to changes in linear and angular acceleration

28. Role of the Vestibular Apparatus in Maintaining Equilibrium and Balance
Figure 7.14

29. Motor Control Functions of the Brain
Brain stem
Responsible for:
Many metabolic functions
Cardiorespiratory control
Complex reflexes
Major structures:
Medulla
Pons
Midbrain
Reticular formation

30. 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

31. 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

32. 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

33. Structures and Processes Leading to Voluntary Movement
Figure 7.16

34. 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

35. Neurotransmitters of the Autonomic Nervous System
Figure 7.17

36. 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)