1. Introduction
Human motion results from the relationship between anatomy and physiology.
This chapter’s goal is to provide a basic understanding of neural physiology as it relates to kinesiology.

2. Introduction Types of nerves
Afferent (sensory)—incoming sensory information
Efferent (motor)—outgoing response to muscles

3. Nervous System Anatomy
Nerve fibers
Motor and sensory nerves wrapped in myelin
Myelin = phospholipid that speeds conduction

4. Nervous System Anatomy
Nerve fibers—motor classification in PNS
Alpha motor neurons
Innervate extrafusal muscle fibers
Gamma motor neurons
Innervate intrafusal muscle fibers

5. Nervous System Anatomy
Nerve fibers—classification
Upper motor neurons
Located within CNS
Carry impulses from brain to spinal cord
Lower motor neurons
Carry impulses from spinal cord to muscle fibers

6. Muscle and muscle fiber structure
Muscular System
Muscle and muscle fiber structure
Muscle is surrounded by epimysium.
Perimysium subdivides muscle into sections.
Each “section” is composed of muscle fibers.
Muscle fibers = muscle cells.

7. Muscle and muscle fiber structure
Muscular System
Muscle and muscle fiber structure
Muscle fibers are composed of myofibers.
Myofibers are covered by the sarcolemma.
Myofibers are composed of units—sarcomeres.
Sarcomeres lie between to Z-lines.
Recommend inserting Figure 3-5D

8. Muscle and muscle fiber structure
Muscular System
Muscle and muscle fiber structure
Myofibers or filaments are composed of:
Actin (thin)—provides binding site for myosin
Myosin (thick)—two crossbridges at each end
Thick and thin filaments give “striated” appearance.
Recommend inserting Figure 3-5E

9. Muscle contraction and relaxation
Muscular System
Muscle contraction and relaxation
Sarcomeres decrease in length from 2.5 µm at rest to 1.5 µm when contracted.
Sarcomere may increase in length to 3.0 µm when stretched.

10. Muscle contraction and relaxation
Muscular System
Muscle contraction and relaxation
Sliding filament model
Recommend inserting Figures 3-5 E, L , H

11. Muscular System Muscle relaxation
Calcium concentration drops and relaxation occurs.
Calcium is actively “pumped” back to SR.
Troponin returns to its original shape.

12. Muscular System Muscle fiber types Type I—postural muscles
Dark in appearance (myoglobin and mitochondria)
Small diameter; fatigue slowly
Slow twitch, tonic, or slow oxidative
Fibers depend on aerobic metabolism

13. Muscular System Muscle fiber types
Type II (subdivided into IIa and IIb)—rapid brief motion
White
Larger diameter; fatigue quickly
Fast-twitch, phasic, fast oxidative
Associated with anaerobic metabolism

14. Muscular System The motor unit
Alpha motor nerve and all the muscle fibers it innervates
Various sizes of motor units (5–1000 fibers)
“All or none”
Muscle fibers from respective motor units spread throughout muscle

15. Gradation of contraction strength
Muscular System
Gradation of contraction strength
Size principle
Recruitment principle
Input/coding rate principle

16. Joint, Tendon, and Muscle Receptors
Joint receptors—sensory
Found in joint capsule and ligaments
Mechanically activated with motion
Adapt after motion ceases
Provide information related to joint position and rate of movement

17. Joint, Tendon, and Muscle Receptors
Golgi tendon organs (GTOs)
Located near muscle-tendon junction
10–15 muscle fibers connected in series with GTOs
Provide information related to muscle tension
Send afferent information via BI axons

18. Joint, Tendon, and Muscle Receptors
Muscle spindle
Embedded parallel within muscle
Consists of intrafusal fibers (nuclear chain and bag)
Provides information related to muscle length
Transmits afferent information via IA and II axons

19. Joint, Tendon, and Muscle Receptors
Muscle spindle—stretch reflex
Abrupt stretch activates spindle and ultimately extrafusal muscle fibers of same muscle.
Recommend inserting Figure 3-12

20. Joint, Tendon, and Muscle Receptors
Muscle spindle—motor function
Gamma (γ) motor neurons innervate intrafusal fibers
Responsible for maintaining muscle tone
Recommend inserting Figure 3-11

21. Joint, Tendon, and Muscle Receptors
Kinesthesia and proprioception
Kinesthesia—dynamic joint motion
Position sense—awareness of static position
Proprioception—use of sensory input to detect joint position and movement

22. Joint, Tendon, and Muscle Receptors
Kinesthesia and proprioception
Postural equilibrium
Visual
Vestibular
Somatosensory