1. Chapter 2 Neuromuscular Fundamentals PPT Series 2C
EXSC 314
Chapter 2 Neuromuscular Fundamentals PPT Series 2C

2. Neural Control of Voluntary Movement
Overview:
Muscle contraction results from stimulation by the central nervous system (CNS). Every muscle fiber is innervated by a somatic motor neuron, and when an stimulus is provided, results in muscle contraction.

3. Neural Control of Voluntary Movement
The genesis/stimulus for skeletal muscle action is processed in varying degrees at different levels of the CNS
The CNS may be divided into five levels of control
Cerebral cortex
Basal ganglia
Cerebellum
Brain stem
Spinal cord

4. Neural Control of Voluntary Movement - Cerebral Cortex
The cerebral cortex (word origin = bark) is the outer layer of the cerebrum and maintains the greatest level of control.
Provides for the creation of voluntary movement as aggregate muscle action, but not as specific muscle activity
Interprets sensory stimuli from the body, to a degree, to determine desired response

5. Neural Control of Voluntary Movement - Basal Ganglia
Basal ganglia are a group of structures at the top of the midbrain
Basal ganglia communicate with the cerebral cortex, thalamus, and brainstem, and other several areas.
Associated with the control of voluntary movements
Controls maintenance of postures and equilibrium, integrates balance, rhythmic movements.
Controls procedural learning movements such as driving a car.

6. Neural Control of Voluntary Movement - Cerebellum
Located in the posterior inferior brain.
Function is to coordinate and regulate muscular activity.
The Cerebellum does not initiate movement.
The Cerebellum does play a major role in coordination, precision, and accurate timing of movement
The Cerebellum integrates sensory impulses as it receives input from the spinal cord and from other parts of the brain.
This integration allows the cerebellum to fine-tune motor activity by controlling timing and intensity of muscle activity.
FYI – The Cerebral and cerebellar peduncles (stalk like connecting structures) communicate with other regions of the brain and CNS to integrate and coordinate movement

7. Neural Control of Voluntary Movement - Brain Stem
Lower region of the CNS that “connects” the brain to the spinal cord. Includes midbrain, pons, and medulla. Transmits sensory neural impulses from the periphery and motor impulses to the periphery Reticular functions, integrating cardiorespiratory control, arousal and alertness, consciousness.
Brain Stem

8. Neural Control of Voluntary Movement - Spinal Cord
Is a cylindrical bundle of neural fibers that is the common pathway between CNS and peripheral nervous system (PNS)
It extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column
Integrates various simple and complex spinal reflexes
There are different tracts within the cord. Ascending and tracts transmit different forms of sensory information, whereas descending tracts carry motor signals to the musculature.

9. Neural Control of Voluntary Movement - Peripheral Nervous System (PNS)
Functionally, the PNS is divided into sensory and motor divisions
Sensory or afferent nerves bring impulses from receptors in skin, joints, muscles, and other peripheral aspects of the body to the CNS
Motor or efferent nerves carry impulses to outlying regions of the body from the CNS

10. Neural Control of Voluntary Movement - Spinal Nerves
- Provide both motor and sensory function for their respective portions of the body
- Named for the location from which they exit the vertebral column
- From each of side of spinal column there is/are:
8 cervical nerves
12 thoracic nerves
5 lumbar nerves
5 sacral
1 coccygeal nerve

11. Neural Control of Voluntary Movement – Sensory Function
Dermatome Map
Sensory function ( one of the ascending tracts of the spinal cord relays this information) of spinal nerves is to provide information to the CNS regarding skin sensation
Dermatome - Defined area of skin supplied by a specific spinal nerve

12. Neural Control of Voluntary Movement
Myotome - a group of muscles innervated by a single spinal nerve root
Myotomes are are clinically useful as they can determine if damage has occurred to the spinal cord, and at which level the damage has occurred
Certain spinal nerves are also responsible for reflexes

13. Neural Control of Voluntary Movement - Neurons
Basic functional units of the nervous system responsible for generating and transmitting impulses
Consist of:
A neuron cell body
One or more branching projections known as dendrites, which transmit impulses to the neuron and cell body
An axon, which is an elongated projection that transmits impulses away from neuron cell bodies

14. Neural Control of Voluntary Movement – Neuron Types
Neurons are classified into three types according to the direction in which they transmit impulses
Sensory neurons transmit impulses to the spinal cord and brain from all parts of the body
Motor neurons transmit impulses away from the brain and spinal cord to muscle and glandular tissue
Sensory neurons
Motor neurons
Interneurons
Interneurons are central or connecting neurons that conduct impulses from sensory neurons to motor neurons

15. Proprioception and Kinesthesis
Proprioception is an awareness of the position of the body and body segments.
Activity performance is significantly dependent on proprioception which also incorporates the “senses”
Example: Seeing when to lift our hand to catch a flying ball
Proprioceptors Internal receptors located in skin, joints, muscles, and tendons that provide feedback relative to tension, length, and contraction state of muscle, position of body and limbs, and movements of joints

16. Proprioception and Kinesthesis
Kinesthesis - Conscious awareness of the position and movement of the body in space (ie. is sensation or perception of motion)
Proprioceptors work in combination with other sense organs to accomplish kinesthesis.

17. Proprioception and Kinesthesis
Proprioceptors specific to joints and skin
Meissner’s corpuscles
Ruffini’s corpuscles
Pacinian corpuscles
Krause’s end-bulbs
Proprioceptors specific to muscles
Muscles spindles
Golgi tendon organs (GTO)

18. Proprioception and Kinesthesis - Muscle Spindles
Concentrated primarily in muscle belly between the fibers
Sensitive to stretch and rate of stretch
Insert into connective tissue within muscle and run parallel with muscle fibers
Number of spindles varies depending upon level of control needed
Greater concentration of muscle spindles in the hands than in the thighs
Muscle Spindle

19. Proprioception and Kinesthesis - Muscle Spindles
Muscle spindles and myotatic or stretch reflex
Rapid muscle stretch occurs
Impulse is sent to the CNS
CNS activates motor neurons of the muscle and cause the spindle to contract

20. Proprioception and Kinesthesis - Muscle Spindles
Example - Knee jerk or patella tendon reflex
Reflex hammer strikes the patella tendon
Causes a quick stretch of the musculotendinous unit of the quadriceps
In response, the quadriceps fires and the knee extends
The more forceful the tap, the greater the reflexive contraction

21. Proprioception and Kinesthesis - Muscle Spindles
Stretch reflex may be utilized to facilitate a greater response
Example - Quick, short squat before attempting a jump
Quick stretch placed on muscles in the squat enables the same muscles to generate more force in subsequently jumping off the floor

22. Proprioception and Kinesthesis - Golgi Tendon Organ (GTO)
Found serially in the tendon close to the muscle–tendon junction
Sensitive to both muscle tension and active contraction
Much less sensitive to stretch than muscle spindles are
Requires a greater stretch to be activated

23. Proprioception and Kinesthesis - Golgi Tendon Organ (GTO)
Tension in tendons and GTO increases as the muscle contracts, which activates GTO
GTO stretch threshold is reached
Impulse is sent to the CNS
CNS causes the muscle to relax and facilitates activation of the antagonists as a protective mechanism
GTO protects us from an excessive contraction by causing its muscle to relax

24. Proprioception and Kinesthesis – Pacinian, Ruffini's, and Meissner’s Corpuscles

25. Proprioception and Kinesthesis - Pacinian Corpuscles
Concentrated around joint capsules, ligaments, tendon sheaths, and beneath the skin. External pressure causes the Pacinian Corpuscle to deform.
Activated by rapid changes in the joint angle and by pressure changes affecting the capsule
Activation lasts only briefly and is not effective in detecting constant pressure
Helpful in providing feedback regarding the location of a body part in space following quick movements such as running or jumping

26. Proprioception and Kinesthesis - Ruffini’s Corpuscles
Located in deep layers of the skin and the joint capsule
Activated by strong and sudden joint movements and pressure changes
Reaction to pressure changes are slower to develop.
Activation is continued as long as pressure is maintained
Essential in detecting even minute joint position changes and providing information as to the exact joint angle.

27. Proprioception and Kinesthesis - Meissner's Corpuscles
Located in the skin and other subcutaneous tissues
Important for receiving stimuli from touch
Not as relevant to the discussion of kinesthesis

28. Muscle Tension Development - All or None Principle
When a muscle contracts, contraction occurs at all fibers within a particular motor unit
Motor unit - Consists of a single motor neuron and all muscle fibers it innervates and functions as a single unit

29. Muscle Tension Development - All or None Principle
Typical muscle contraction
The number of motor units responding, thus, the number of muscle fibers contracting within the muscle may vary significantly from relatively few to virtually all, depending on the number of muscle fibers within each activated motor unit and the number of motor units activated
Regardless of number, individual muscle fibers within a given motor unit will either fire and contract maximally or not at all.

30. Factors Affecting Muscle Tension Development
Difference between a muscle contracting to lift a minimal resistance versus lifting a maximal resistance is the number of muscle fibers recruited
The number of muscle fibers recruited may be increased by:
Activating those motor units containing a greater number of muscle fibers
Activating more motor units
Increasing the frequency of motor unit activation

31. Factors Affecting Muscle Tension Development
Number of muscle fibers per motor unit varies significantly
(Fine Control) From less than ten in muscles requiring a precise and detailed response such as the muscles of the eye
(Strength Control) To as many as a few thousand in large muscles that perform less complex activities such as the quadriceps

32. Factors Affecting Muscle Tension Development
Motor unit must first receive a stimulus via an electrical signal known as an action potential for the muscle fibers in the unit to contract
Subthreshold stimulus
Not strong enough to cause an action potential
Does not result in a contraction
Threshold stimulus
Stimulus becomes strong enough to produce an action potential in a single motor unit axon
All of the muscle fibers in the motor unit contract
Submaximal stimulus
Stimuli that are strong enough to produce action potentials in additional motor units
Maximal stimulus
Stimuli that are strong enough to produce action potentials in all motor units of a particular muscle

33. Factors Affecting Muscle Tension Development
As stimulus strength increases from threshold up to maximal, more motor units are recruited, and the overall muscle contraction force increases in a graded fashion

34. Factors Affecting Muscle Tension Development
Greater contraction forces may also be achieved by increasing the frequency or motor unit activation
Phases of a single muscle fiber contraction or twitch
Stimulus
Latent period
Contraction phase
Relaxation phase

35. Factors Affecting Muscle Tension Development
Latent period
Brief period of a few milliseconds following a stimulus
Contraction phase
Muscle fiber begins shortening
Lasts milliseconds
Relaxation phase
Follows the contraction phase
Last about 50 milliseconds

36. Factors Affecting Muscle Tension Development
Summation
When successive stimuli are provided before the relaxation phase of the first twitch is complete, the subsequent twitches combine with the first to produce a sustained contraction
Generates a greater amount of tension than a single contraction would produce individually
As the frequency of stimuli increase, the resultant (wave) summation increases accordingly producing increasingly greater total muscle tension
Tetanus
Occurs when the stimuli are provided at a frequency high enough that no relaxation can occur between contractions.

37. Factors Affecting Muscle Tension Development
Treppe ( German for “stairs”)
Occurs when a series of maximal stimuli delivered to the muscle at a frequency just below tetanizing frequency immediately following the previous stimulus.
The tension with each twitch during each twitch increases until maximal height is reached and a plateau has formed.
This gradual rise is believed to result form the gradual increase in Ca++ ion concentration in the sarcoplasm

38. Muscle Length–Tension Relationship
Maximal ability of a muscle to develop tension and exert force varies depending upon the length of the muscle during contraction.
Greatest amount of tension can be developed when a muscle is stretched between 100% and 130% of its resting length
When a muscle is stretched beyond 100% to 130% of its resting length, amount of active tension generated significantly decreases

39. Muscle Length–Tension Relationship
Generally, depending on muscle involved:
A proportional decrease in ability to develop tension occurs as a muscle is shortened
The ability to develop contractile tension is essentially reduced to zero when shortened to around 50% to 60% of resting length
Example - Increasing the ability to exert force
Squatting slightly to stretch the calf, hamstrings, and quadriceps before contracting the same muscles concentrically to jump

40. Muscle Length–Tension Relationship
Example- Reducing the ability to exert force
Isolating the gluteus maximus by maximally shortening the hamstrings with knee flexion

41. Muscle Force–Velocity Relationship
When a muscle is contracting (concentrically or eccentrically) the rate (velocity) of muscle length change is related to the amount of force that can be produced by the muscle and the amount of resistance applied
When contracting concentrically against a light resistance, a muscle is able to contract at a high velocity

42. Muscle Force–Velocity Relationship
As resistance increases, the maximal velocity at which a muscle is able to contract decreases
Eventually, as the load increases, the velocity decreases to zero resulting in an isometric contraction
As the load increases beyond the muscle’s ability to maintain an isometric contraction, the muscle begins to lengthen resulting in an eccentric contraction

43. Muscle Force–Velocity Relationship
Increases in the load results in the velocity of lengthening
Eventually, the load may increase to a point where the muscle can no longer resist, resulting in an uncontrollable lengthening or dropping of the load
Inverse relationship between concentric velocity and the amount of force production (ie. Lighter resistance = Higher velocity)

44. Muscle Force–Velocity Relationship
As the force needed to cause the movement of an object increases, the velocity of concentric contraction decreases
Somewhat proportional relationship between eccentric velocity and force production
As force needed to control an object’s movement increases, the velocity of eccentric lengthening increases, at least until when control is lost

45. Stretch-Shortening Cycle
Sequencing and timing of contractions can enhance the total amount of force produced
When a muscle is suddenly stretched, resulting in an eccentric contraction that is followed by a concentric contraction of the same muscle, the total force generated in the concentric contraction is greater than that of an isolated concentric contraction
Functions by integration of the GTO and the muscle spindle (see previous slides)

46. Stretch-Shortening Cycle
Elastic energy is stored during the eccentric stretch phase, transitioned, and utilized in the concentric contraction phase
A stretch reflex is elicited in the eccentric phase of the motion, which subsequently increases activation of the muscle that was stretched, resulting in a more forceful concentric contraction
To be effective, the transition phase must be immediate. The shorter the transition phase, the more effective the force production

47. Reciprocal Inhibition or Innervation
Antagonist muscle groups must relax and lengthen when the agonist muscle group contracts
This reciprocal innervation effect occurs through reciprocal inhibition of the antagonists
Activation of the motor units of the agonists causes a reciprocal neural inhibition of the motor units of the antagonists
This reduction in neural activity of the antagonists allows them to subsequently lengthen under less tension

48. Reciprocal Inhibition or Innervation
Example - Compare the ease of:
Stretching hamstrings when simultaneously contracting the quadriceps
Stretching hamstrings without contracting the quadriceps

49. Angle of Pull
Angle between the line of pull of the muscle and the bone on which it inserts (angle toward the joint)
With every degree of joint motion, the angle of pull changes
Joint movements and insertion angles involve mostly small angles of pull

50. Angle of Pull
Angle of pull decreases as the bone moves away from its anatomical position through the local muscle group’s contraction
Range of movement depends on the type of joint and bony structure
Most muscles work at angles of pull less than 50 degrees
Amount of muscular force needed to cause joint movement is affected by the angle of pull

51. Angle of Pull
Rotary component (vertical component) - Component of muscular force that acts perpendicular to the long axis of the bone (lever)
When the line of muscular force is at 90 degrees to the bone on which it attaches, all of the muscular force is rotary force (100% of the force is contributing to movement)
All of the force is being used to rotate the lever about its axis
The closer the angle of pull to 90 degrees, the greater the rotary component

52. Angle of Pull
At all other degrees of the angle of pull, one of the other two components (non-rotary) of force are operating in addition to the rotary component
Rotary component continues with less force to rotate the lever about its axis
Second force component is the horizontal or non- rotary component and is either a stabilizing component or a dislocating component, depending on whether the angle of pull is less than or greater than 90 degrees

53. Angle of Pull
If the angle is less than 90 degrees, the force is a stabilizing force because its pull directs the bone toward the joint axis

54. Angle of Pull
If angle is greater than 90 degrees, the force is dislocating because its pull directs the bone away from the joint axis

55. Angle of Pull
Sometimes, it is desirable to begin with the angle of pull at 90 degrees
Chin-up (pull-up)
Angle makes the chin-up easier because of the more advantageous angle of pull
Compensate for the lack of sufficient strength

56. Uniarticular, Biarticular, and Multiarticular Muscles
Uniarticular muscles
Cross and act directly only on the joint that they cross
Example - Brachialis, which can only pull the humerus and ulna closer together
Biarticular muscles - Cross and act on two different joints
Depending on certain factors, biarticular muscles may contract and cause motion at either one or both of its joints
Two advantages over uniarticular muscles
Can cause and/or control motion at more than one joint
Are able to maintain a relatively constant length due to shortening at one joint and lengthening at another joint

57. Uniarticular, Biarticular, and Multiarticular Muscles
Muscle does not actually shorten at one joint and lengthen at the other
Concentric shortening of the muscle to move one joint is offset by the motion of the other joint, which moves its attachment of the muscle farther away
This maintenance of a relatively constant length results in allows the muscle a continuous exertion of force (examples follow)

58. Uniarticular, Biarticular, and Multiarticular Muscles
Example 1 - Hip and knee biarticular muscles
Concurrent movement pattern occurs when both the knee and hip extend at the same time
If only the knee were to extend, the rectus femoris would shorten, and its ability to exert force similar to the other quadriceps muscles would decrease,
However, relative length of the rectus femoris and subsequent force production capability are maintained due to its relative lengthening at the hip joint during extension of the hip with the knee

59. Uniarticular, Biarticular, and Multiarticular Muscles
Example 2 - Hip and knee biarticular muscles
Countercurrent movement pattern occurs in kicking
During the lower extremity forward movement phase, the rectus femoris concentrically contracts to flex the hip and extend the knee
These two movements, when combined, increase the tension or stretch on the hamstring muscles both at the knee and hip

60. Uniarticular, Biarticular, and Multiarticular Muscles
Multiarticular muscles act on three or more joints due to the line of pull between their origin and insertion crossing multiple joints
Principles relative to biarticular muscles apply to multiarticular muscles; however, multiarticular muscles can reduce work load of muscles with less articulations

61. Active and Passive Insufficiency
As a muscle shortens, its ability to exert force diminishes
Active insufficiency is reached when the muscle becomes shortened to the point that it cannot generate or maintain active tension
The muscle cannot shorten any further
Passive insufficiency is reached when the opposing muscle becomes stretched to the point where it can no longer lengthen and allow movement

62. Active and Passive Insufficiency
Easily observed in either biarticular or multiarticular muscles when the full range of motion is attempted in all the joints crossed by the muscle
Example - Rectus femoris contracts concentrically to both flex the hip and extend the knee
Can completely perform either action one at a time but actively insufficient to obtain the full range at both joints simultaneously (countercurrent movement pattern)

63. Active and Passive Insufficiency
Similarly, hamstrings cannot usually stretch enough to allow both maximal hip flexion and maximal knee extension because of passive insufficiency
As a result, it is virtually impossible to actively extend the knee fully when beginning with the hip fully flexed or vice versa
END OF PPT SERIES 2C