Proprioceptors

Proprioception

sense of position and movement, integrated with other senses

Active joint position sense

muscles are activated by pathways made by you

Passive joint position sense

muscles are moved for you

Joint matching task

someone moves one side of your body, and you can match with the other side

Kinesthesia

active joint position, movements

Sense of Force

how much force is applied to a muscle/joint, and being able to match it

Sense of change in velocity

detects vibration of oscillating objects, not able to detect absolute velocity

Intrafusal fibers

not contractile, found in the middle of the muscle

Extrafusal fibers

contractile

Nuclear bag

center of muscle spindle, intrafusal, contains many nuclei, causes excitation of sensory fibers

Dynamic nuclear bag (bag1)

for fast contraction speeds, sensitive to length

Static nuclear bag (bag2)

for slow contraction speeds, sensitive to length

Nuclear chain

nuclei in chain wrapped around intrafusal fibers, measures stress and strain on muscle

gamma motor neuron function

activated to keep muscle spindle taut and sensitive to length changes, contract intrafusal fibers

gamma motor neuron origination

from reticular formation of pons

taut gamma motor neuron

allows alpha motor neuron to fire/contract muscle

Ia afferent

medial sensory fibers of muscle spindle, wraps around intrafusal fibers medially

II afferent

sensory fibers of muscle spindle, end laterally (near bag2)

Afferent stretch info transduction

via mechanically-gated ion channels (similar to hearing)

Bag2 and chain fibers

increase firing rate of sensory afferents at a given muscle length

Bag1 fibers

increase sensitivity of Ia by stiffening fibers

lacking gamma motor neurons

lacking Ia afferent so no outgoing info

Fusimotor set

static gamma for routine movements, dynamic gamma for difficult tasks

Fusimotor template

static gamma is for temporal expected movement, dynamic gamma for controlling timing

Goal-directed preparatory control

dynamic gamma proactively prepares for movement, static gamma active when plan not executed

alpha-gamma coactivation

both dynamic and static gamma stimulated at the same time

Golgi tendon organs structure

tree-like sensory ending in a spindle-like connective tissue capsule

Golgi tendon organ afferents

Ib fibers, discharges with passive and active stretch

1b fiber arrangement

in series to fibers, myelinated

Golgi tendon organ detection

tension, transduces muscle force into AP

Golgi tendon organ efferent

not present

Activity of GTO

corresponds to whole muscle force

1b afferent paths

supraspinal response and reflexive control

Supraspinal response

throughout entire physiological range, regulates extensor activity and postural control

GTO transduction

muscle belly shortens, tendon lengthens, collagen fibers straighten

Reflexive control of GTO

reciprocal innervation during excessive force, relaxation of overworked muscle, and contraction of its antagonist

purpose of GTO reflexive control

protect against overstraining muscles/tendons