Chapter 4: The Neuromuscular Basis of Human Motion

1. Chapter 4:The Neuromuscular Basis of Human Motion KINESIOLOGY Scientific Basis of Human Motion, 10th edition Luttgens & Hamilton Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University

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 • 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 Fig 4.1

6. Motor Neurons • Situated in anterior horns of spinal cord • Dendrite that synapse with sensory neurons • 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

7. 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

8. Connector Neurons • Exist completely within the CNS • Serve as connecting links • 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

9. Nerves • A bundle of fibers, enclosed within a connective tissue sheath, for transmission of impulses • 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 • Posterior root bears a ganglion – a collection of cell bodies Fig 4.2

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

12. The Synapse • Connection between neurons • May be thousands between any two neurons • 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 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 • Substance diffuses synapse and produces an action potential in postsynaptic neuron Fig 4.3

14. Action Potentials • Threshold level is the minimum level of stimulus (chemical transmitter) necessary to initiate or propagate a signal • Facilitation – an excitatory stimulus • Inhibition – an inhibitory stimulus • 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

15. THE MOTOR UNIT (MU) • 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 Fig 4.4

16. Size of Motor Units • Vary widely in the number of muscle fibers • Gastrocnemius: 2,000 or more muscle fibers • Eye muscles: may have fewer than 10 fibers • Small ratio of muscle fibers to MU is capable of more precise movements • 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 How do they adjust to such extremes? 1. Number of motor units that are activated 2. Frequency of stimulation

18. All-or-None PrincipleRecruitment of Motor Units • 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 • 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 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

20. SENSORY RECEPTORS • Respond to different stimuli • Exteroceptors: near body surface stimuli come from outside the body • Interoceptors: sense heat, cold, pain and pressure Fig 4.5

21. Proprioceptors • Respond to degree, direction, & rate of change of body movements • Transmit information to CNS • Muscle receptors • Joint & skin receptors Fig 4.6

22. Muscle ProprioceptorsMuscle Spindles • 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 • More spindles are located in muscle controlling precise movements

23. Muscle ProprioceptorsMuscle Spindles • Extrafusal fibers “regular” muscle fibers • Intrafusal fibers muscle fibers inside spindles • Noncontractile central portion Fig 4.7

24. Muscle ProprioceptorsMuscle Spindles • Spindles contains two type of nerve endings • 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 • Respond to static muscle length • Impulses directly proportional to length

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

26. Muscle ProprioceptorsGolgi Tendon Organ (GTO) • Embedded “in series” in the tendon • As tension in tendon increases GTO is activated • Signals CNS to relax muscle • Protective mechanism Fig 4.8

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

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

29. Joint and Skin ProprioceptorsCutaneous Receptors • Meissner corpuscles: touch • Pacinian corpuscles: pressure • Free nerve endings: pain • 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 • 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 • Receptor organ, Sensory neuron, Motor neuron, Muscle • Connector neurons Fig 4.10

32. Exteroceptive ReflexesExtensor Thrust Reflex • Pressure on sole of stimulates reflex contraction of extensor muscles Fig 4.11

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

34. Proprioceptive ReflexesStretch Reflex • A reflex contraction of stretched muscle and synergists and relaxation of antagonists • Phasic Type: Knee jerk reflex • Weight placed in hand elbow at 900 Biceps Fig 4.12-1 Triceps

35. Proprioceptive ReflexesStretch Reflex • Tonic Type: muscle is gradually stretched and will result in a more tonic response Biceps Triceps Fig 4.12-3

36. Proprioceptive ReflexesStretch Reflex • Phasic preparatory phase can take advantage of the stretch reflex • Result in a stronger contraction Fig 4.13a

37. Proprioceptive ReflexesStretch Reflex • Slow preparatory phase should be used when the desired outcome is accuracy • Result in a stronger contraction Fig 4.13b

38. Tendon Reflex • 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 • Feedback mechanism to control tension • May effect skills of beginners until GTO threshold develops

39. VOLITIONAL MOVEMENTCNS: 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 MOVEMENTCNS: 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 MOVEMENTPyramidal & Extrapyramidal Tracts • The two tracts originate in cerebral cortex and end at the spinal cord • 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

42. Kinesthesis • 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 • 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 • Antagonist remain relaxed & agonists contract without opposition • Automatic in reflexes & familiar movements • 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 • Practice increases familiarity, and coactivation decreases in favor of reciprocal inhibition • Efficiency of movement increase • 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 • After repeated viewing, students should be able to name and discuss the reflexes that could be acting at various points in each phase