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

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

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

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

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

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

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 Principle Recruitment 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

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

22. Muscle Proprioceptors Muscle 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 Proprioceptors Muscle Spindles
Extrafusal fibers “regular” muscle fibers
Intrafusal fibers muscle fibers inside spindles
Noncontractile central portion

24. Muscle Proprioceptors Muscle 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 Proprioceptors Muscle Spindles
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
As tension in tendon increases GTO is activated
Signals CNS to relax muscle
Protective mechanism

27. Joint and Skin Proprioceptors Pacinian 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 Proprioceptors Ruffini 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 Proprioceptors Cutaneous 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

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

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 Reflexes Stretch 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

35. Proprioceptive Reflexes Stretch Reflex
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
Result in a stronger contraction

37. Proprioceptive Reflexes Stretch Reflex
Slow preparatory phase should be used when the desired outcome is accuracy
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
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 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
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

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 PROPRIOSEPTORS, REFLEXES, CARPUSLES