sensory systems and cpg's (lecture 5 motor control)notes on web)
TRANSCRIPT
Proprioception and KinesthesiaSpinal Control of Movement
Proprioceptive SensationsDefinition-an awareness of body position and of movements of parts of the body. Proprioception tells us the location and rate of movement of one body part in relation to others. Proprioceptive sense informs us of: the degree to which our muscles are being contracted the amount of tension created in the tendons change of position of a joint the orientation of the head relative to the ground and in response to movements
Proprioceptors
Only slight adaptation-this allows the brain to be informed continually of the status of different parts of the body so that adjustments can be made. Receptors for Proprioception:
Muscle Spindles Tendon organs Joint kinesthetic receptors
Proprioceptors ContdThe three types of receptors are located in skeletal muscle, tendons, joint capsules and within the inner ear. Impulses for conscious proprioception pass along ascending tracts in the spinal cord to the thalamus and from there to the cerebral cortex. The sensation is perceived in the somatosensory area in the parietal lobe of the cerebral cortex.
Joint Kinesthetic Receptors
There are several types of joint kinesthetic receptors within and around the capsules of synovial joints:
Encapsulated receptors-present in the joint capsules and respond to pressure. Receptors inside connective tissue-outside of the joint capsule and respond to acceleration and deceleration of joint movement.
Additional forms of Proprioception
Receptors in the joint capsule
Mechanosensitive neurons
Angle direction velocity sensitive
Combine with spindle and GTO, in addition to receptors in the skin Loss of one or more systems
Total hip or knee replacement
Cutaneous ReceptorsThere are other receptors related to movement perception which are located in various places within the skin. These receptors can signal sensations to the body, such as pain, pressure, heat, and cold. For the purposes of this class, these receptors are important for movement control because they signal information about touch and deep pressure.
Types of Cutaneous ReceptorsPacinian Corpuscle-located deep in the skin and are stimulated by heavy pressure. Other receptors inside the skin: Meissner Corpuscles, Merkels disks and Ruffinis corpuscles. Hair follicle Receptors-located close to hair follicle and are stimulated when the hairs on the body are deformed by light touch. Fingertip Receptors-provide information about the surfaces of objects through touch.
Input to the CNSThe major pathways for transmitting signals from the periphery to the brain are the spinal tracts, which are located along the vertebrae. Input to the CNS goes through roots that collect and guide the information to the spinal cord. And the input from the receptors comes together in the periphery into spinal nerves.
Spinal nerves are collections of neurons that carry information toward and away from the spinal cord.
Proprioception and the CNS
Proprioception enables us to tell where our limbs are and how they are acting The CNS combines and integrates information in a way to resolve any ambiguity received by the signals from the receptors.
Proprioception and Motor Control
The expanded Closed-loop model for movement control Muscle contractions cause the limbs and the body to move, which causes change within the environment. The contracting muscles and the movement of the body produce sensations from the different receptor systems.
Sensory Components of Movement
Vision
Horizontal and vertical cue Orientation to environment Inner ear Head movement and position
Vestibular
Sensory Integration
Spinal Cord Level
Reflexes Cyclical Movements Cerebellum Brain Stem Motor Cortex
Higher Brain Centers
ROLE OF PRIOPRIOCEPTIVE FEEDBACK
Affects the degree of movement accuracy Influences the timing of the onset of motor commands Coordinates body and limb segments (to self and environment)
Muscle Receptors
Sensory Components of Movement
Sensory Receptors (Mechanorecpetors)
Joint Receptors
Joint capsule and ligaments Joint position and rate of movement Only at extreme ranges of motion
Sensory Components of Movement
Sensory Receptors (Mechanorecpetors)
Muscle Receptors
Golgi Tendon Organs Muscle Spindles
Types of Spindle FibersBag fibers Chain fibers Different fibers are responsible for static (chain) and dynamic (bag1) movements
Physiology of Muscle Spindles
Proprioception from Muscle SpindlesMiddle section is swollen and contains group Ia sensory axons wrapped around spindle Sensitive to muscle stretch Ia neurons are the largest and therefore the fastest sensory neurons in the body
Enters dorsal horn synapse in the spinal cord with interneurons and alpha motor neurons exits ventral horn with motor command.
Muscle SpindlesSpecialized groupings of muscle fibers interspersed among regular skeletal muscle fibers and oriented parallel to them. One Muscle spindle = 3-10 specialized muscle fibers called intrafusal muscle fibers. Surrounding the muscle spindle are regular skeletal muscle fibers called extrafusal fibers. These fibers contract when stimulated by small neurons called gamma motor neurons.
MUSCLE SPINDLE
Why
do muscle spindles contain their own contractile elements?
MUSCLE SPINDLE
Muscle Spindles ContdMuscle spindles monitor changes in the length of a skeletal muscle by responding to the rate and degree of change in length. This information is relayed to the cerebrum, which allows conscious perception of limb position. Also, passes to the cerebellum to aid in the coordination and efficiency of muscle contraction.
MUSCLE SPINDLE
MUSCLE SPINDLE
MUSCLE SPINDLE
Muscle fiber vs. Muscle spindle
Skeletal muscle
Muscle Spindle
Extrafusal fibers Alpha motor neuron
Intrafusal fibers Gamma motor neuron
Activation causes muscle to contract
Activation causes muscle spindle to reset
Function:
Function:
Shorten or lengthen to cause or control movement
Contraction occurs from cortical drive or muscle spindle activation
sense changes in muscle length Provide moment to moment control of movement
Alpha-Gamma Coactivation
Simultaneous activation of Alpha and Gamma motor neurons
Alpha shortens the muscle Spindle would become slack and unable to sense further stretch Gamma motor neuron keeps spindle taught and able to sense movement
During this simultaneous contraction possible decreased sensitivitywhy?
Movement Detection
Contracting muscle 2.4 times larger movement required
GTO
Golgi Tendon Organs
Function as a strain gauge, measuring tension in the muscle Situated in series with muscle fibers Located close to the tendon's attachment to the muscle Information carried via Ib neurons Enter spinal cord synapse on interneurons, and inhibitory neurons Even senses small changes in tension Inhibit contracting (agonist) muscles and excite antagonist muscles to prevent injury Sensory (afferent) Type Ib fibers penetrate the tendon organ capsule.
Golgi Tendon OrgansCan protect from overload, or regulate contraction in optimal range They also function as, contraction receptors by monitoring the force of contraction of associated muscles. Important for fine motor control
Help to maintain optimal contraction force to manipulate fine objects
Golgi Tendon Organ
GOLGI TENDON ORGAN
GOLGI TENDON ORGAN
Sensory Motor Integration
http://www.learner.org/resources/series142.html
CPGs
Central Pattern GeneratorsRhythmic movements can be controlled by the SC Following an initial stimulus to start, the CPG can cause alternating bursts of activity Higher brain centers can intervene if adjustments are needed Gait patters are possible without higher brain centers
CPGs
CPG cntd.
The CPG is under influence of loosely defined higher brain center and also receives inputs from peripheral sensors and possibly other structures. Afferent inputs into a CPG may bring about changes in the pattern of its activity, leading to changes in gait.
Locomotor Centers
In the 1960s a group of researchers in Moscow stimulated the reticular formation of the midbrain of decerebrate cats. Stimulation of certain areas led to rhythmic locomotor-like movements of the cats limbs. The frequency of the stimulation was not related to the frequency of locomotion, so it was assumed the CPG is activated by descending signals generated by the stimulation. An increase in amplitude led to an increase in locomotor speed, eventually leading to a change in gait.
Decerebrated Cat
Would locomotor movements such as walking, trotting, and galloping require different CPGs?
Control of LocomotionWhat benefit comes from CPGs? Think in terms of control requirements!
Spinal Locomotion
If the spinal cord of an animal is cut acutely, a locomotor pattern is typically observed for a few seconds.
This is best explained as a release of the activity of a spinal CPG from the tonic descending inhibitory influence.
A chronic spinal animal will not display locomotion without external stimuli, but will when placed on a treadmill display stepping of the limbs with shifts in gait to alternating speeds. Spinal locomotion is observed in animals in which all of the dorsal roots have been cut (without afferent inflow), proving the spinal cord capable of producing movement without feedback.
Spinal Locomotion cntd.
It has also been demonstrated that individual CPGs may exist for each limb. Recent data have suggested a spinal locomotor generator located at a lower thoracic-upper lumbar level in humans.
Patients will display involuntary stepping movements of the legs, when unable to do so voluntarily.
Although coordinated locomotor activity is displayed, the movements are not meaningful for many reasons.
The animal needs information about the environment, control of posture, and needs to handle perturbations.
Interneurons
Spinal InterneuronsGTOs action on alpha motor neurons is polysynaptic (what was the spindles synapse?) Interneurons receive input from:
Primary sensory axons Axons from the brain Collaterals of lower motor neuron axons
Interneurons are interconnected allowing for coordinated movement of multiple spinal levels
Reciprocal InhibitionMuscle is stretched Ia neuron synapses with alpha motor neuron stretched muscle contracts what is missing from this? Now what about a voluntary contraction?
Biceps contracts tricep stretches tricep spindle stretches causing tricep to contract
If this happened would we have smooth movement Descending command also tells antagonist to relax via interneurons
Flexor & Crossed-extensor reflexInterneurons can also facilitate contractions Response to adverse stimuli
Flexors of affected limb contract Reflex is slower that myotatic necessitating interneurons Response also involves extensors of opposite limb to contract Building block for locomotion
Central pattern generator
Illusory Movement
Perceptions of movement or movement mismatch can occur
Efferent/control process illusion
Distorted signals from receptors, or processing of afferent signals Muscle vibration creates a distorted signal, and causes the spindle to fire repeatedly appears that muscle has lengthened
Distorted efferent copy signal Commands that differ from what was expected by the brain
Remote Controlled Human???
Purpose
What effect do illusory changes in head position have on joint position sense in the elbow
Novel in that they were not using any biomechanical changes in muscle length
Vibration effects
What is the general feeling with muscle vibration in general
What is the general feeling with galvanic vestibular stimulation?
Feeling that the muscle in lengthening
What was the result of low GVS stim?
Lateral body tilt toward the anode
Increased GVS resulted in head shift sense
Postural shift but no changes in head position sense Sense is away from but sway is towards the anode??? What Page 94 vs. 97
Results/Discussion
Significant difference in reporting Joint angle in mid range of movement
Why not extremes?
How is this related to integration and movement?
What implication were made based on this study to perception and action coupling?
Position of the head plays an important role in joint proprioception Since the head did not move it is more than biomechanical changes in head position
Why were the results inconsistent?
Most studies showed that individuals exposed to the GVS will exhibit changes in sensation of head position
What was reported to suggest that something else may have contributed to the mixed findings?
Supine vs. upright
Off to the Lab!!!