The Nervous System Chapter 4

Learning Objectives Know how the nervous system is organized. Know how motor neurons innervate muscle fibers. Understand the role of the nervous system in simple reflexes. Understand proprioception and kinesthesis. Understand the involvement of higher brain centers during voluntary movement. Understand the role of the nervous system in maintaining posture and balance. Know the effects of exercise on several neurological disorders.

Organization of the Nervous System Anatomical divisions:  Central nervous system  Peripheral nervous system Functional divisions:  Autonomic nervous system  Somatic nervous system

Diagram of the Peripheral Nerves

Functional Divisions of the Nervous System

Neurons Sensory (afferent) neurons:  Conduct sensory impulses from the periphery to the central nervous system Motor (efferent) neurons:  Conduct impulses from the central nervous system to the muscles

The Neuron and Its Components

Your Perspective Knowing what you now know about exercise and autonomic tone, how would you counsel someone who: Has recently had a heart attack Has undergone eight weeks of endurance training And now wants to quit exercising

Reflexes An involuntary motor response to a sensory stimulus Types:  Simple reflexes  Reciprocal inhibition  Crossed extensor reflex  Conditioned reflex Simple reflexes:  Spinal reflex  Myotatic reflex (e.g., knee jerk response)  Flexion reflex (e.g., moving a hand away from a hot surface)

Diagram of a Two-Neuron Reflex Adapted from Gardner (1958). From a spindle in a muscle back to the muscle fibers of the same muscle.

How Impulses from a Cutaneous Receptor Reach an Effector (Skeletal Muscle) Adapted from Gardner (1958).

Proprioception Receptors throughout the body provide sensory information about movement and body position. Two types: 1.Vestibular 2.Kinesthetic

Structural Relations of Innervation of the Human Labyrinth

Muscle Spindles Widely distributed throughout muscle tissue The stretch reflex that originates in muscle spindles is the basis for unconscious muscular adjustments of posture.

Muscle Spindle

Golgi Tendon Organ Provides sensory information Inhibits further contraction and stimulation of a muscle’s antagonist Acts as a protective device

Golgi Tendon Organ

Higher Nerve Centers and Muscular Control Pyramidal system Extrapyramidal system Proprioceptive–cerebellar system

Areas of the Human Cerebral Cortex Involved in the Extrapyramidal System In the frontal lobe are areas 4, 6, and 8. In the post central region are areas 1, 2, 3, and 5. In the temporal lobe, area 22 is concerned with the extra- pyramidal pathways.

Importance of These Systems for the Coach/Physical Educator Electrical stimulation of the pyramidal system produces specific movements. Stimulation of the extrapyramidal system produces large, general movement patterns. Learning a new skill involving conscious attention to the movements involves area 4. As skill progresses, the origin of the movement shifts to area 6.

The Role of the Cerebellum Receives constant sensory information from receptors:  Muscles, joints, tendons, skin  Visual, auditory, and vestibular end organs May modify muscular activity during movement.

Posture Upright posture is brought about mainly through reflexes. If a knee joint starts to collapse and stretches muscle spindles, an impulse is generated and sent to a motor neuron. The motor neuron innervates fibers and causes the muscles to contract and reextend the joint into proper position.

Balance The righting reflex Seen in a cat being dropped from a height; also divers and gymnasts. Coordination of the otolith system and muscle and tendon receptors provide a perception of the body’s orientation and position of body parts in space.

Clinical Application Exercise and Neurological Disorders/Injuries Many chronic disorders/injuries involve the central or peripheral nervous system. Neuromuscular weakness:  Leads to reduced ability to perform daily living activities. A small change in muscle function can improve functional performance. Resistance training may improve strength and muscle function.

Electromyography and Neuromuscular Function Contraction of muscle tissue is accompanied by an electrical charge (muscle action potential; MAP) Recorded and measured via electromyography Two types: 1.Qualitative 2.Quantitative

MAP Recordings Differences between recordings of single motor-unit potentials with needle electrodes (left) and summated potentials from many motor units with surface electrodes (right).

Frequency Domain of Quantitative EMG The rate at which the waveform fluctuates above and below the baseline; expressed in hertz (Hz). Power density spectrum (PDS)—the amount of power that exists in the EMG signal at each frequency.  Mean power frequency (MPF)  Median power frequency (MDPF)

Diagram of the Power Density Spectrum of a Surface EMG Signal

Time Domain Involves determining the amplitude (voltage) of electrical current that exists during a specific period of time. Provides information regarding:  Muscle relaxation, motor unit activation strategies, and neuromuscular fatigue  The magnitude and sequence of activation of muscles during activities such as walking, sit ups, and various weight-lifting exercises.

Integration of Muscle Action Potentials

Where to Learn More Peripheral nervous system, neuromuscular junction and muscle; neurons:  P/PNS.html P/PNS.html Nervous system:  NERV.html#Nervous%Systems NERV.html#Nervous%Systems

NASPE Guideline— D8 Understand the reflex actions related to activation of the muscle spindle and golgi tendon organ.  If you were a coach, what would you recommend to your athletes who are warming up by performing bouncing or jerking movements while stretching?  How would you explain the problem so they could understand it?