1. The Role of the Nervous System Applied Kinesiology 420:151

2. Agenda Introduction to the nervous system Structural considerations Motor efferents and gradations of force Sensory afferents Reflex movement

3. Introduction to the NS Functions: Sensory input  afferent neurons Integration Motor output  efferent neurons Properties: Irritability Conductivity

4. Introduction to NS Levels of Control: Cerebral cortex Consciousness Basal ganglia Homeostasis  posture and equilibrium Cerebellum Timing and intensity  smooth and precise motion Brain stem Arousal and cardiorespiratory function Spinal cord Link b/w CNS and PNS  interneurons and synapses

5. Figure 4.14, Hamilton Cerebral cortex Basal ganglia Cerebellum Brain stem Spinal cord Overide?

6. Introduction to the NS Basic divisions of the nervous system:

7. Figure 14.1, Marieb & Mallett (2003)

8. Agenda Introduction to the nervous system Structural considerations Motor efferents and gradations of force Sensory afferents Reflex movement

9. Structural Considerations The neuron The nerve The synapse The motor unit

10. The Neuron Functional unit of nervous tissue Three main types of neurons Sensory/afferent neurons Motor/efferent neurons Interneurons Common structures

11. DendritesCell BodyAxon Differences: Peripheral body, location of dendrites/synaptic knobs, direction of transmission Figure 12.11, Marieb & Mallett (2003)

12. The Neuron Other considerations Cell body Nucleus Almost all cell bodies are in spinal cord (ganglia?) Dendrites Afferents  cell body via peripheral body Efferents  cell body via axon Axon Myelin sheath Axon collaterals Extensive terminal branching (10,000) Synaptic knobs

13. Figure 12.4, Marieb & Mallett (2003)

15. Structural Considerations The neuron The nerve The synapse The motor unit

16. The Nerve Nerve = bundle of neurons Not unlike skeletal muscle architecture Figure 12.17, Marieb & Mallett (2003)

17. The Nerve Nerves can contain both afferent and efferent neurons. Spinal/peripheral nerves connect to the spinal cord via: Anterior root (motor efferent neurons) Posterior root (sensory afferent neurons)

18. Anterior root Posterior root

19. The Nerve Thirty one pairs of spinal/peripheral nerves: Cervical  8 Thoracic  12 Lumbar  5 Sacral  5 Coccygeal  1 Figure 13.29, Marieb & Mallett (2003)

20. Structural Considerations The neuron The nerve The synapse The motor unit

21. The Synapse Synapse: Area between the synaptic knob of one neuron and the membrane of another neuron Figure 12.7, Marieb & Mallett (2003)

22. Neurons have thousands of synaptic knobs Some neurons are excitatory, some inhibitory Competition between excitation and inhibition occurs  Threshold stimulus reached? Neurotransmitter NMJ or motor end plate Figure 12.8, Marieb & Mallett (2003)

23. Excitatory and Inhibitory Postsynaptic Potentials: EPSP, IPSP EPSP - IPSP = Stimulus Stimulus > Threshold = Excitation of impulse Stimulus < Threshold = Inhibition of impulse Impulse itself can be excitatory or inhibitory in nature

24. Structural Considerations The neuron The nerve The synapse The motor unit

25. The Motor Unit Functional unit of neuromuscular system Consists of: Neuron + all muscle fibers Eye muscles vs. gastrocnemius (10-2000) Fewer fibers/neuron = precision More fibers/neuron = force

26. Figure 14.6, Marieb & Mallett (2003)

27. Agenda Introduction to the nervous system Structural considerations Motor efferents and gradations of force Sensory afferents Reflex movement

28. Efferents: Gradations of Force Motor efferent: Sends signal away from the CNS (skeletal muscle) Dendrites in spinal cord Synaptic knobs  muscle Excitatory or inhibitory Gradation of force: Concept: Muscles are able to activate with varying degrees of force

29. Efferents: Gradations of Force Two factors influence the gradation of force: Number coding: The number of motor units participating Rate coding: The frequency of stimulation

30. Number Coding All-or-none principle of single motor units  threshold Gradation of force Small force = fewer motor units or motor units with less fibers Large force = more motor units or motor units with more fibers Orderly sequence  Size principle

31. Figure 19.13, Plowman & Smith (2003) Resting muscle tonus achieved via alternating activation of some muscle fibers

32. Rate Coding Effects of different stimulus frequencies on motor units: Single stimulus  twitch Second stimulus added prior to full relaxation  temporal summation Multiple stimuli added so that any relaxation is prohibited  irregular and fused tetanus

33. As frequency increases, force/tension increases Maximum number coding + maximum rate coding = maximum force

34. Agenda Introduction to the nervous system Structural considerations Motor efferents and gradations of force Sensory afferents Reflex movement

35. Sensory Afferents Sensory afferents: Sends signal towards the CNS Dendrites are all over body (not in CNS) Synaptic knobs are in spinal cord Classifications of afferents: Exteroceptors Interoceptors (visceroceptors) Proprioceptors

36. Figure 14.1, Marieb & Mallett (2003) Proprioceptors are main concern

37. Proprioceptors Location: Tendons, skeletal muscle, ligaments, joint capsules and inner ear Functions: Transmit movement information  CNS CNS integrates and initiates appropriate response (consciously/subconsciously) Provide sense of body awareness Provide stimulus for reflexes

38. Proprioceptor Classification Muscle proprioceptors: Muscle spindles Golgi tendon organs Joint and skin proprioceptors Ruffini endings Pacinian corpuscles Labyrinthine and neck proprioceptors Labyrinthine proprioceptors Neck proprioceptors

39. Muscle Proprioceptors: Muscle Spindles Location: Lay between and parallel to muscle fibers Structure: Tiny capsules (1 mm) Filled with fluid and intrafusal muscle fibers Nucleated and supplied with afferent neuron Function: Sensitive to stretch and tension of skeletal muscle tissue Transmit to CNS Excitatory impulse  agonist and synergists Inhibitory impulse  antagonists (reciprocal inhibition)

40. Stretch Interneurons Excitatory activation of agonists Activation of synergists Reciprocal inhibition of antagonists Figure 14.5, Knutzen & Hamill (2004)

41. Muscle Proprioceptors: GTOs Location: Musculotendon junction of skeletal muscle Structure: Mass of terminal endings in connective tissue capsule Connections both with tendon and fibers Function: Sensitive to tension in tendon due to both stretch and shortening of muscle Transmit to CNS: Inhibitory impulse  agonists and synergists Excitatory impulse  antagonists

42. 1. High muscle tension 2. High tendon tension 3. GTO activation 4. Inhibition of agonist

43. Joint and Skin Proprioceptors: Ruffini Endings Location: Beneath skin, joint capsules Structure: Spray of dendrites in flattened connective tissue capsule Functions: Sensitive to  Rapid changes in joint angle Constant pressure resulting in deformation of capsule

44. Skin and Joint Proprioceptors: Pacinian Corpuscles Location: Beneath skin, joint capsules, ligaments and tendons Structure: Relatively large (naked eye) Tip of single dendrite in connective tissue capsule Function: Sensitive to  Rapid changes in joint angle Rapid, short-term changes in pressure resulting in deformation of capsule

45. Ruffini endings Pacinian corpuscle Free nerve endings

46. Labyrinthine Proprioceptors Location: Inner ear Structure: Several structures within the ear Function: Detect orientation and movements of the head

47. Neck Proprioceptors Location: Ligaments of cervical vertebrae Function: Head/neck movement  transmit opposite signals Prevents sense of imbalance

48. Agenda Introduction to the nervous system Structural considerations Motor efferents and gradations of force Sensory afferents Reflex movement

49. Reflexes Reflex: Specific pattern response that occurs without volition The reflex arc consists of: Receptor organ Afferent neuron Interneuron (sometimes) Efferent neuron

50. Figure 12.18, Marieb & Mallett (2003)

51. Classification of Reflexes Exteroceptive reflexes: Respond to external stimuli Extensor thrust reflex Flexor reflex Crossed extensor reflex Proprioceptive reflexes: Response to internal stimuli Stretch (myotatic) reflex Tendon reflex Righting reflex Tonic neck reflex Labyrinthine reflex

52. Exteroceptive: Extensor Thrust Reflex General mechanism: Pressure stimulates pacinian corpuscles  excitatory impulse to extensors Examples: Standing Shifting weight  preparation for motion Hands  cartwheel or back handspring

53. Exteroceptive: Flexor Reflex General mechanism: Typically in response to pain  excitatory impulse to flexors Examples: Pricking or burning hand

54. Exteroceptive: Crossed Extensor Reflex General mechanism: Functions cooperatively with flexor reflex Contralateral limb is extended Examples: Stepping on tack Pricking or burning hand

55. Proprioceptive: Stretch Reflex General mechanism: Stretched muscle results in stretched muscle spindle  Excitatory impulse to agonist for protection Inhibitory impulse to antagonists Two types: Phasic: Rapid stretching  rapid powerful contraction that ends rapidly Tonic: Slow stretching  smooth, less powerful contraction that lasts as long as the stretch

56. Elbow flexed 90 degrees while holding a bucket 1. Object dropped into bucket 2. Object dropped in from lesser height 3. Object placed into bucket Figure 14.12, Hamilton

57. Explosive movements: Long and rapid prep phases (phasic stretch reflex) Precise movements: Short and slow prep phase (tonic stretch reflex)

58. Proprioceptive: Tendon Reflex General mechanism: Sensitive to tension in tendon due to: Muscle lengthening Tendon reflex vs. stretch reflex Muscle shortening Very sensitive (low threshold) Threshold stimulus  inhibitory impulse to agonists Extreme cases  total relaxation Training or extreme stress can increase the threshold

59. Proprioceptive: Righting Reflex General mechanism: Body tilting  thrusting of limbs to restore balance Example: A gentle push with eyes shut

60. Proprioceptive: Tonic Neck Reflex General mechanism: Head movement results in flexion or extension of limbs Obvious in infants Surpressed in adults  evident under stress Examples: Symmetric vs. asymmetric Neck flexion: Upper extremities flex Neck extension: Upper extremities extend Neck rotation: Extension/Abduction of contralateral arm Flexion/abduction of ipsilateral arm.

61. Proprioceptive: Labyrinthine Reflex General mechanism: Movements of the head  activation of limbs to maintain balance