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!!!