Kinesthesis Receptors responsible for Kinesthesis Muscle Spindle Golgi Tendon Organs Pacinian Corpuscle Ruffini Receptors Free Nerve Endings Muscle Spindle Comprised of different types of Muscle Fibers Extrafusal Fibers (EF) Typical Skeletal Fibers on the outside of spindle Intrafusal Fibers (IF) Fibers on the inside of the spindle that are not striated Types of IF: Nuclear Bag Fibers up to a dozen nuclei clustered in the center of the fiber usually two fibers (2) per spindle located on the outsides Nuclear Chain Fibers three (3) to seven fibers (7) per spindle nuclei centered, but arranged single file fibers are shorter and thinner than Nuclear bag Fibers Ends of all IF Fibers have Motor Poles striated myofibrils capable of contractions nucleated area of IF Fibers does not contract Contains 2 Receptors (that respond to stretching) Send messages to the CNS to CONTRACT a muscle - contracts both Extrafusal and Intrafusal Fibers Annulospiral Ending (primary receptor - one per spindle) wraps around Nuclear Bag fibers & other less developed fibers primarily around the non-contractile portion sends impulse through Type Ia (fast) Afferent Nerve excited by BOTH phasic (jerky) and tonic (static) stretching Flower Spray Receptor (secondary receptor - one or two per spindle) branches to / wraps around Nuclear Chain fibers responds to the amount of stretch sends impulse through Type II (slow) Afferent Nerve excited ONLY by static stretching requires more stimulation than the Annulospiral Ending Golgi Tendon Organs (GTO) Are located in Tendons Respond to Stretching (BOTH Active and Passive) Requires a higher level of stimulation than does the Muscle Spindle Stimulation during Active Stretching DAMPENS contraction of Muscle Inverse Myotatic Reflex - allows the stretched muscle to stretch further - protective effect - Occurs in BOTH the fiber of origin, AND the whole Muscle Group Pacinian Corpuscles Large Organ in Joints Capsules and Sheaths of Muscle and Tendon Several layers of Connective Tissue where Nerve Endings Ramify Excited by Deformation and Deep Pressure May be more important to Kinesthesis than Spindles and Golgi Tendon Organs Ruffini Receptors Scattered throughout the skin and the Collagenous Fibers of Joint Capsules Excited by joint movement Each receptor senses some degree of movement Stimuli from numerous receptors integrated by the Nervous System Free Nerve Endings Freely Distributed in the Muscles, Tendons, Joints, Fascia, and Ligaments Function as Kinesthetic Receptors not understood Alpha and Gamma Fibers Alpha Efferent Fibers (Axons) stimulate Extrafusal (Skeletal) Muscle Fibers - fibers are larger and faster Gamma Efferent Fibers stimulate Intrafusal Muscle Fibers Gamma Afferent Fibers move information from the muscle to the CNS Two-thirds of the Efferent fibers are Type Alpha Reflex's Reflex Arc - signals that cause motion but do not require higher processing by the CNS - initiated by the Spinal Cord Thrust Reflex - heels of palms feels pressure - foot plantarflex's, wrist flex's Flexor Reflex - pain in extremities causes flexion - causes retraction of extremity through stimulation of flexor muscles Crossed Extensor Reflex - opposite of Flexor Reflex - occurs simultainously - opposing limb extends to provide support during phase Stretch Reflex - does not use interneurons of CNS - sensory ==> motor - simplest type of Reflex Arc - Two Types (Phasic = Fast; and Tonic = slow) Phasic = Knee Jerk used in activities when fast motions are required - pitching, kicking stimulates only the primary ending results in rapid, brief contractions of the muscle being stretched Tonic used in activities when accuracy is desired - putting, free throws stimulates both the primary and secondary endings primary stimulation results in contraction of the muscle being stretched secondary stimulation results in: contraction of that muscle if it is a flexor, or dampening the contrction of the flexor if the extensor is stretched Voluntary Contractions Contraction of Extrafusal Fibers causes innervation of Intrafusal Fibers Innervation of Intrafusal Fibers causes shortening and resetting of spindle length This causes/allows FURTHER stimulation of the Extrafusal Fibers Feedback Loop in Muscular Contraction (Renshaw Cell) When Alpha Efferent Neurons fire, another Axon is also innervated Causes a synapses with an Association Neuron in the Renshaw Cell The Renshaw Cell Synapses with and Inhibits other Motor Neurons Thus, the rate of Contraction can be controlled by a Servomechanism