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

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

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

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

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

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

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

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

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

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

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

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

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

Muscle Spindles: Mechanism Muscle tone Stretch reflex

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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