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Chapter 4: The Neuromuscular Basis of Human Motion Lecture Notes.

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1 Chapter 4: The Neuromuscular Basis of Human Motion Lecture Notes

2 Objectives 1. Name and describe the function of the basic structure of the nervous system 2. Explain how gradations in strength of muscle contraction and precision of movements occur 3. Name and define the receptors important in musculoskeletal movement 4. Explain how the various function, and describe the effect each has on musculoskeletal movement

3 Objectives 5. Describe reflex action, and enumerate and differentiate among the reflexes that affect musculoskeletal action 6. Demonstrate a basic understanding of volitional movement by describing the nature of the participation of the anatomical structures and mechanisms 7. Perform an analysis of the neuromuscular factors influencing the performance of a variety of motor skills

4 THE NERVOUS SYSTEM AND BASIC NERVE STRUCTURES I. Central nervous system (CNS) A. Brain B. Spinal cord II. Peripheral nervous system (PNS) A. Cranial nerves (12 pairs) B. Spinal nerves (31 pairs) III. Autonomic nervous system A. Sympathetic B. Parasympthetic

5 Neurons Is a single nerve cell consisting of a cell body and one or more projections Is a single nerve cell consisting of a cell body and one or more projections

6 Motor Neurons Situated in anterior horns of spinal cord Situated in anterior horns of spinal cord Dendrite that synapse with sensory neurons Dendrite that synapse with sensory neurons Axon emerges from spinal cord, travels by way of a peripheral nerve to muscle Axon emerges from 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 Each terminal branch ends at the motor end plate of a single muscle fiber

7 Sensory Neurons Situated in a dorsal root ganglion just outside the spinal cord Situated in a dorsal root ganglion just outside the spinal cord Neuron may terminate in spinal cord or brain Neuron may terminate in spinal cord or brain A long peripheral fiber comes from a receptor A long peripheral fiber comes from a receptor

8 Connector Neurons Exist completely within the CNS Exist completely within the CNS Serve as connecting links Serve as connecting links May be a single neuron, connecting sensory to motor neurons May be a single neuron, connecting sensory to motor neurons To an intricate system of neurons, whereby a sensory impulse may be related to many motor neurons To an intricate system of neurons, whereby a sensory impulse may be related to many motor neurons

9 Nerves A bundle of fibers, enclosed within a connective tissue sheath, for transmission of impulses A bundle of fibers, enclosed within a connective tissue sheath, for transmission of impulses A typical spinal nerve consist of A typical spinal nerve consist of –Motor outgoing fibers –Sensory incoming fibers

10 Nerves Each spinal nerve is attached to spinal cord by an anterior (motor) root and a posterior (sensory) root Each spinal nerve is attached to spinal cord by an anterior (motor) root and a posterior (sensory) root Posterior root bears a ganglion – a collection of cell bodies Posterior root bears a ganglion – a collection of cell bodies

11 Spinal Nerves 31 pairs – exit both sides of the vertebral column 31 pairs – exit both sides of the vertebral column –8 Cervical –12 Thoracic –5 Lumbar –5 Sacral –1 Coccyx Table 4.1 outlines spinal Table 4.1 outlines spinal

12 The Synapse Connection between neurons Connection between neurons May be thousands between any two neurons May be thousands between any two neurons Proximity of the membrane of one axon to another dendrites Proximity of the membrane of one axon to another dendrites The more often a synapse is used the faster a signal will pass through it The more often a synapse is used the faster a signal will pass through it The greater the number of synapses for receptor to effector, the longer the time form stimulus to response The greater the number of synapses for receptor to effector, the longer the time form stimulus to response

13 The Synapse Transmission across depends on a chemical transmitter Transmission across depends on a chemical transmitter Substance diffuses synapse and produces an action potential in postsynaptic neuron Substance diffuses synapse and produces an action potential in postsynaptic neuron

14 Action Potentials Threshold level is the minimum level of stimulus (chemical transmitter) necessary to initiate or propagate a signal Threshold level is the minimum level of stimulus (chemical transmitter) necessary to initiate or propagate a signal Facilitation – an excitatory stimulus Facilitation – an excitatory stimulus Inhibition – an inhibitory stimulus Inhibition – an inhibitory stimulus Stimulus may be from more than one neuron Stimulus may be from more than one neuron The sum total of excitatory and inhibitory determine if the postsynaptic neuron will produce an action potential The sum total of excitatory and inhibitory determine if the postsynaptic neuron will produce an action potential

15 THE MOTOR UNIT (MU) Consist of a single MU and all the muscle fibers its axon supplies Consist of a single MU and all the muscle fibers its axon supplies All muscle fibers in a MU are of the same muscle fiber type All muscle fibers in a MU are of the same muscle fiber type

16 Size of Motor Units Vary widely in the number of muscle fibers Vary widely in the number of muscle fibers Gastrocnemius: 2,000 or more muscle fibers Gastrocnemius: 2,000 or more muscle fibers Eye muscles: may have fewer than 10 fibers Eye muscles: may have fewer than 10 fibers Small ratio of muscle fibers to MU is capable of more precise movements Small ratio of muscle fibers to MU is capable of more precise movements Size of MU has direct bearing on the precision of movement Size of MU has direct bearing on the precision of movement

17 Gradations in the Strength of Muscular Contractions Experience tells us that the same muscles contract with various gradations of strength Experience tells us that the same muscles contract with various gradations of strength How do they adjust to such extremes? 1. Number of motor units that are activated 2. Frequency of stimulation

18 All-or-None Principle Recruitment of Motor Units All-or-None Principle: If the stimulus is of threshold value, all muscles of MU will contract All-or-None Principle: If the stimulus is of threshold value, all muscles of MU will contract –Applies to muscle fibers not whole muscle MU recruitment: has an orderly sequence to MU recruitment: has an orderly sequence to –Smaller slow twitch fibers are recruited first  They have lower thresholds –Larger fast twitch fibers are recruited later  They have higher thresholds

19 Frequency of Stimulation At low frequency, muscle fibers relax between impulses At low frequency, muscle fibers relax between impulses At high frequency, fibers do not have time to relax and result in summation or maximal contraction At high frequency, fibers do not have time to relax and result in summation or maximal contraction A combination of maximum number of fibers stimulated and high frequency results in a maximal strength of contraction A combination of maximum number of fibers stimulated and high frequency results in a maximal strength of contraction

20 SENSORY RECEPTORS Respond to different stimuli Respond to different stimuli –Exteroceptors: near body surface stimuli come from outside the body –Interoceptors: sense heat, cold, pain and pressure

21 Proprioceptors Respond to degree, direction, & rate of change of body movements Respond to degree, direction, & rate of change of body movements Transmit information to CNS Transmit information to CNS Muscle receptors Muscle receptors Joint & skin receptors Joint & skin receptors

22 Muscle Proprioceptors Muscle Spindles Located in muscle belly, parallel with fibers Located in muscle belly, parallel with fibers When stretched, sensory nerve sends impulses to CNS, which activates the motor neurons causing contraction of the muscle When stretched, sensory nerve sends impulses to CNS, which activates the motor neurons causing contraction of the muscle More spindles are located in muscle controlling precise movements More spindles are located in muscle controlling precise movements

23 Muscle Proprioceptors Muscle Spindles Extrafusal fibers “regular” muscle fibers Extrafusal fibers “regular” muscle fibers Intrafusal fibers muscle fibers inside spindles Intrafusal fibers muscle fibers inside spindles –Noncontractile central portion

24 Muscle Proprioceptors Muscle Spindles Spindles contains two type of nerve endings Spindles contains two type of nerve endings Primary or annulospiral endings: coiled around noncontractile midsection Primary or annulospiral endings: coiled around noncontractile midsection –Sensitive to velocity of change (phasic) –Sharp decline in impulses to static changes Flower-spray endings: at end of noncontractile midsection Flower-spray endings: at end of noncontractile midsection –Respond to static muscle length –Impulses directly proportional to length

25 Muscle Proprioceptors Muscle Spindles Gamma motor neurons: stimulate the intrafusal fibers to contract, shortening the muscle spindle Gamma motor neurons: stimulate the intrafusal fibers to contract, shortening the muscle spindle

26 Muscle Proprioceptors Golgi Tendon Organ (GTO) Embedded “in series” in the tendon Embedded “in series” in the tendon As tension in tendon increases GTO is activated As tension in tendon increases GTO is activated Signals CNS to relax muscle Signals CNS to relax muscle Protective mechanism Protective mechanism

27 Joint and Skin Proprioceptors Pacinian Corpuscles In regions around joint capsules, ligament, and tendons sheaths In regions around joint capsules, ligament, and tendons sheaths End-organ has concentric layers of capsule End-organ has concentric layers of capsule Activated by joint angle changes & pressure Activated by joint angle changes & pressure Transmits impulses for only a very brief time Transmits impulses for only a very brief time Predict where body part will be at any time Predict where body part will be at any time Appropriate adjustment in position can be anticipated and effected Appropriate adjustment in position can be anticipated and effected

28 Joint and Skin Proprioceptors Ruffini Endings In deep layers of skin and joint capsule In deep layers of skin and joint capsule Activated by mechanical deformation Activated by mechanical deformation Signal continuous states of pressure Signal continuous states of pressure Adapt slowly, then transmit a steady signal Adapt slowly, then transmit a steady signal Stimulated strongly by sudden joint movement Stimulated strongly by sudden joint movement Sense joint position and changes in joint angle Sense joint position and changes in joint angle The CNS knowing which receptors is stimulated can tell the joint angle The CNS knowing which receptors is stimulated can tell the joint angle

29 Joint and Skin Proprioceptors Cutaneous Receptors Meissner corpuscles: touch Meissner corpuscles: touch Pacinian corpuscles: pressure Pacinian corpuscles: pressure Free nerve endings: pain Free nerve endings: pain Serve as proprioceptors when they show sensitivity to texture, hardness, softness and shape, and participate in reflexes Serve as proprioceptors when they show sensitivity to texture, hardness, softness and shape, and participate in reflexes

30 Labyrinthine and Neck Proprioceptors Cochlea: is concerned with hearing Cochlea: is concerned with hearing Semicircular canals: sense balance Semicircular canals: sense balance –Labyrinth filled with fluid and is lined with hair cells, senses motion of fluid as head moves Joint receptors of the neck: sensitive to angle between the body and the head –Prevent labyrinthine proprioceptors from producing feeling of imbalance

31 REFLEX MOVEMENT A specific pattern of response without volition form the cerebrum A specific pattern of response without volition form the cerebrum Receptor organ, Sensory neuron, Motor neuron, Muscle Receptor organ, Sensory neuron, Motor neuron, Muscle Connector neurons Connector neurons

32 Exteroceptive Reflexes Extensor Thrust Reflex Pressure on sole of stimulates reflex contraction of extensor muscles Pressure on sole of stimulates reflex contraction of extensor muscles

33 Exteroceptive Reflexes Flexor Reflex: Flexor Reflex: –Most frequent in response to pain –Quick withdraw from source of pain Crossed Extensor Reflex: Crossed Extensor Reflex: –As flexor reflex respond to pain, extensor muscle muscle of opposite ling contract to support additional weight

34 Proprioceptive Reflexes Stretch Reflex A reflex contraction of stretched muscle and synergists and relaxation of antagonists A reflex contraction of stretched muscle and synergists and relaxation of antagonists Phasic Type: Knee jerk reflex Phasic Type: Knee jerk reflex –Weight placed in hand elbow at 90 0

35 Proprioceptive Reflexes Stretch Reflex Tonic Type: muscle is gradually stretched and will result in a more tonic response Tonic Type: muscle is gradually stretched and will result in a more tonic response

36 Proprioceptive Reflexes Stretch Reflex Phasic preparatory phase can take advantage of the stretch reflex Phasic preparatory phase can take advantage of the stretch reflex Result in a stronger contraction Result in a stronger contraction

37 Proprioceptive Reflexes Stretch Reflex Slow preparatory phase should be used when the desired outcome is accuracy Slow preparatory phase should be used when the desired outcome is accuracy Result in a stronger contraction Result in a stronger contraction

38 Tendon Reflex The reflex Inhibit impulses form motor neuron to the muscle and synergists, causing muscle to relax, antagonists is facilitated The reflex Inhibit impulses form motor neuron to the muscle and synergists, causing muscle to relax, antagonists is facilitated Protective mechanism to prevent muscles from being torn or ruptured Protective mechanism to prevent muscles from being torn or ruptured Feedback mechanism to control tension Feedback mechanism to control tension May effect skills of beginners until GTO threshold develops May effect skills of beginners until GTO threshold develops

39 VOLITIONAL MOVEMENT CNS: Levels of Control 1. Cerebral cortex: where consciousness occurs, initiation of voluntary movement 2. Basal ganglia: responsible for homeostasis, coordination & some learned acts of posture 3. Cerebellum “little brain”: key role in sensory integration, regulates timing & intensity of muscle contraction

40 VOLITIONAL MOVEMENT CNS: Levels of Control 4. Brain stem: arousal and monitoring of physiological parameters, key facilitory and inhibitory centers 5. Spinal cord: contains cell bodies of lower motor neurons, common pathway between CNS & PNS, final point for integration and control Functions of the 5 levels overlap depending on classification scheme used

41 VOLITIONAL MOVEMENT Pyramidal & Extrapyramidal Tracts The two tracts originate in cerebral cortex and end at the spinal cord The two tracts originate in cerebral cortex and end at the spinal cord Pyramidal Tracts: predominately axon of motor neurons, controls muscles for precision Pyramidal Tracts: predominately axon of motor neurons, controls muscles for precision Extrapyramidal Tracts: synapse with all levels of CNS, functions in stabilization and control of posture Extrapyramidal Tracts: synapse with all levels of CNS, functions in stabilization and control of posture

42 Kinesthesis The conscious awareness of position of body parts and the amount and rate or joint movement The conscious awareness of position of body parts and the amount and rate or joint movement Without rapid transmission & processing, accurately controlled movements could not proceed Without rapid transmission & processing, accurately controlled movements could not proceed Kinesthetic perception and memory are the basis for voluntary movement and motor learning Kinesthetic perception and memory are the basis for voluntary movement and motor learning

43 Reciprocal Inhibition When motor neurons are transmitting impulses to an agonist, antagonistic are simultaneously & reciprocally inhibited When motor neurons are transmitting impulses to an agonist, antagonistic are simultaneously & reciprocally inhibited Antagonist remain relaxed & agonists contract without opposition Antagonist remain relaxed & agonists contract without opposition Automatic in reflexes & familiar movements Automatic in reflexes & familiar movements More complicated movements depends on the degree of skill developed by performer More complicated movements depends on the degree of skill developed by performer

44 Coactivation or Reciprocal Activation Most frequently appears in movement when there is uncertainty about movement task Most frequently appears in movement when there is uncertainty about movement task Practice increases familiarity, and coactivation decreases in favor of reciprocal inhibition Practice increases familiarity, and coactivation decreases in favor of reciprocal inhibition Efficiency of movement increase Efficiency of movement increase Coactivation also occurs to maintain joint stiffness Coactivation also occurs to maintain joint stiffness

45 NEUROMUSCULAR ANALYSIS Muscle-response patterns of well-learned motor skills involve the integrated action of many reflexes and the inhibition of others Muscle-response patterns of well-learned motor skills involve the integrated action of many reflexes and the inhibition of others After repeated viewing, students should be able to name and discuss the reflexes that could be acting at various points in each phase After repeated viewing, students should be able to name and discuss the reflexes that could be acting at various points in each phase

46 Summary 1. Know the function of the basic structure of the nervous system 2. Know how gradations in strength of muscle contraction and precision of movements occur 3. Name and define the receptors important in musculoskeletal movement 4. Know various neurological function, and describe the effect each has on musculoskeletal movement

47 Summary 5. Know reflex action, and enumerate and differentiate among the reflexes that affect musculoskeletal action 6. Have a basic understanding of volitional movement by describing the nature of the participation of the anatomical structures and mechanisms 7. Be able to perform an analysis of the neuromuscular factors influencing the performance of a variety of motor skills

48 Summary KNOW THE NERVOUS SYSTEM AND BASIC NERVE STRUCTURES (CNS, PNS, ANS) KNOW THE NERVOUS SYSTEM AND BASIC NERVE STRUCTURES (CNS, PNS, ANS) KNOW THE PROPRIOSEPTORS, REFLEXES, CARPUSLES KNOW THE PROPRIOSEPTORS, REFLEXES, CARPUSLES


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