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Integrative Physiology and Control of Body Movement

This chapter explores the neural reflexes involved in controlling body movement, including somatic and autonomic reflexes, skeletal muscle reflexes, and the integration of reflexive and voluntary behavior. It also covers the movement in visceral muscles.

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Integrative Physiology and Control of Body Movement

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  1. Chapter 13 Integrative Physiology I: Control of Body Movement

  2. About this Chapter • Neural Reflexes: types & pathways • Autonomic Reflexes pathways and functions • Skeletal Muscle reflexes, myotactic units and movement • Combining reflexive and voluntary behavior into locomotion • Movement in visceral muscles

  3. Neural Reflexes: Overview • Stimulus • Sensory receptor • Sensory (afferent) neuron • CNS integration • Efferent (motor) neuron • Effector (target tissue) • Response (movement) • Feedback to CNS

  4. Neural Reflexes: Overview Figure 13-1a: Monosynaptic and polysynaptic somatic motor reflexes

  5. Neural Reflexes: Classification of Pathways • Effector Division • Somatic • Autonomic • Integration site • Spinal • Brain • Neurons in pathway • Monosynaptic • Polysynaptic

  6. Neural Reflexes: Classification of Pathways Figure 13-1: Monosynaptic and polysynaptic somatic motor reflexes

  7. Autonomic Reflexes: “visceral reflexes” • Regulate internal organs • Integrate in spinal cord or lower brain • Coordinate with hormones & pacemakers

  8. Autonomic Reflexes: “visceral reflexes” Figure 13-2: Autonomic reflexes

  9. Examples of Autonomic Reflexes • Cold Water Immersion causing tachycardia • Pupillary Reflex-Pupil Constricting in response to light • Baroreceptor Reflex- Low BP in carotid sinus results in tachycardia and blood vessel constriction • Carotid Sinus Reflex- Increased pressure within or external manipulation of carotid sinus results in bradycardia • Dilation of Blood vessels as body temperature increases • Secretion of epinephrine and norepinephrine from the adrenal medulla in response to fear or stress • Sweating in response to increased body temperature

  10. Skeletal Muscle Reflex Sensory Receptors: Proprioceptors • Muscle spindle • In muscles • Sense stretch • Golgi tendon organ • Near tendon • Sense force • Joint receptors • Sense pressure • Position

  11. Skeletal Muscle Reflex Sensory Receptors: Proprioceptors Figure 13-3: Sensory receptors in muscle

  12. Alpha motoneuronsextrafusal fibers bigger and more numerous than intrafusal myofibrils all along length this causes muscle contraction Gamma motoneurons intrafusal fibers tightens spindles enhances sensitivity of spindles

  13. Upper motoneurons usually stimulate both simultaneously ( Alpha-Gamma Coactivation) Alpha motoneurons promote muscle contracting Gamma motoneurons help maintain muscle tone Reflexes are produced as an unconscious response to particular stimuli Can be simple or complex Golgo tendon organs monitor tension

  14. Muscle Spindles: Mechanism • Muscle tone • Stretch reflex

  15. Stretch Reflex and the Muscle Spindle Apparatus Figure 13-6b: Muscle reflexes

  16. Golgi Tendon Reflex: Response to Excessive Force • Force pulls collagen fibers which squeeze sensors • Overload causes inhibition of contraction

  17. A Myotactic Unit • Myotactic unit: all pathways controlling a joint • Example: elbow joint – all nerves, receptors, muscles

  18. Knee Jerk Reflex: Stretch & Reciprocal Inhibition Reflexes • Tendon strike stretches quads-reflexive contraction • Reciprocal (hamstring) muscle is inhibited

  19. Knee Jerk Reflex: Stretch & Reciprocal Inhibition Reflexes Figure 13-7: The knee jerk reflex

  20. Flexion Reflex: Pull away from Painful Stimuli • Pain stimulus • Nocioceptors • Spinal integration • Flex appendage away • Signal to brain (feel pain)

  21. Double reciprocal innervation stimulus on one side of the body, reaction on another Step on tack- affected foot withdraws (flexes), Other foot extends to support weight (crossed-extensor reflex) Take-home lesson: some reflexes are simple; affect and are controlled by a small part of the spinal cord Some are more elaborate

  22. Flexion Reflex: Pull away from Painful Stimuli Figure 13-8: Flexion reflex and the crossed extensor reflex

  23. Cross Extensor Reflex: To Keep Balance • Opposite leg • Extensors stimulated • Flexors inhibited • Body supported

  24. Movement: Coordination of Several Muscle Groups • Reflexive Movement • Spinal integration • Input to brain • Postural reflexes • Cerebellum integration • Maintains balance • Input to cortex Figure 13-9: Integration of muscle reflexes

  25. Voluntary Movement: “Conscious” • Cortex at top of several CNS integration sites • Can be initiated with no external stimuli • Parts can become involuntary: muscle memory

  26. Voluntary Movement: “Conscious” Figure 13-11: Control of voluntary movements

  27. Rhythmic Movements • Cortex initiation • Central pattern generators • In spine • Maintain motion • Combines movements • Reflexive • Voluntary Figure 13-12: The corticospinal tract

  28. Feed Forward: Postural Reflex • Anticipates body movement • Reflexive adjustment to balance change • Prepares body for threat: blink, duck, "tuck & roll" • Combines with feedback Figure 13-13: Feedforward reflexes and feedback of information during movement

  29. Visceral Movement: Heart & Organs • Moves products in hollow organs • Act as valves (sphincters): digestive tract or blood vessels • Multiple controls: autonomic neurons, hormonal and paracrine

  30. Summary • Reflex pathways: spinal, cranial • Sensor, afferent, integration, efferent, effector • Classified by effector, integration site or synapses

  31. Summary • Proprioceptor types, functions, role in reflexes & balance • Motor reflex pathways: stretch, Golgi tendon, flexion, reciprocal inhibition & crossed extensor • Myotatic unit structure and coordination • Movement coordination: reflexive, voluntary, rhythmic • Feed forward and feedback coordination • Visceral movement of body organs

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