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.

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

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

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

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

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.

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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