chapter 4: the neuromuscular basis of … · a typical spinal nerve ... sensory, incoming...

CHAPTER 4:THE NEUROMUSCULAR

BASIS OF HUMAN MOTION

KINESIOLOGYScientific Basis of Human Motion, 12th edition

Hamilton, Weimar & LuttgensPresentation Created by

TK Koesterer, Ph.D., ATCHumboldt State University

Revised by Hamilton & Weimar

Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/Irwin

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Motor Cortex Sensory Cortex

CEREBRAL CORTEX

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NEURONS

A single nerve cell consists of a cell body and one or more projections. Axons: Carry impulses away

from cell body. Dendrites: Carry impulses

toward cell body.

Fig 4.1

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MOTOR NEURONS

Situated in anterior horns of spinal cordDendrite that synapses with sensory neurons

or connector neurons.Axon emerges from the spinal cord, travels by

way of a peripheral nerve to muscle. Each terminal branch ends at the motor

end plate of a single muscle fiber

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SENSORY NEURONS

Situated in a dorsal root ganglion just outside the spinal cord.

Neuron may terminate in spinal cord or brain.

A long peripheral fiber comes from a receptor.

Fig 4.1b

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CONNECTOR NEURONS

Exist completely within the CNS. Serve as connecting links. May be a single neuron, connecting

sensory to motor neurons.OR

An intricate system of neurons, whereby a sensory impulse may be relayed to many motor neurons.

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NERVES

A bundle of fibers, enclosed within a connective tissue sheath, for transmission of impulses.

A typical spinal nerve consists of: Motor, outgoing (efferent) fibers Sensory, incoming (afferent) fibers

Each spinal nerve is attached to spinal cord by an anterior (motor) root and a posterior (sensory) root

Posterior root bears a ganglion

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SPINAL NERVES

31 pairs – exit both sides of the vertebral column 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 1 Coccyx

9A-9

SPINAL COLUMN: STRUCTURE

7 Cervical Vertebrae 12 Thoracic

Vertebrae 5 Lumbar Vertebrae Sarcrum Coccyx

Fig 9.1

(7)

(12)

(5)

(5)

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THE SYNAPSE Connection between neurons. May be thousands between

any two neurons. Is a proximity of the membrane

of an axon to the membrane of a dendrite or cell body.

The more often a synapse is used the faster a signal will pass through it.

The greater the number of synapses from receptor to effector, the longer the time from stimulus to response.

Transmission across the synapse depends on a chemical transmitter.

Substance diffuses the synapse and produces an action potential in the postsynaptic neuron.

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MUSCLE INNERVATION

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GRADATIONS IN THE STRENGTH OF MUSCULAR CONTRACTIONS

Experience tells us that the same muscles contract with various gradations of strength.

How do they adjust to such extremes?Number of motor units that are activated.Frequency of stimulation.

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SENSORY RECEPTORS

Respond to different stimuliExteroceptors: near

body surface stimuli come from outside the body.

Interoceptors: sense heat, cold, pain and pressure.

Fig 4.5

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PROPRIOCEPTORS

Stimulated by body movements.

Transmit information to CNS.

Two primary categories:Muscle receptors Joint & skin receptors

Fig 4.6

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LABYRINTHINE SYSTEM

Utricle

Semicircular Canals

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REFLEX MOVEMENT

A specific pattern of response without volition from the cerebrum.

Stimulus - receptor organ - sensory neuron -motor neuron - muscle (response)

Connector neurons often used.

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PROPRIOCEPTIVE REFLEXESSTRETCH REFLEX Knee jerk response Sudden addition of weight to hand, elbow at

90°.Biceps stretches, then contracts.

Weight dropped Muscle contracts