KINESTHESIA

KINESTHESIA

sense of movement and position of limbs and other body parts

KINESTHESIA

is crucial for sensing jaw movements and positioning.

proprioceptors

receptors that respond to internal stimuli

exteroceptors

receptors that respond to external stimuli

joint receptors

are once the main contributors to kinesthesia

muscle receptors

are not believed to play a role in conscious movement sensation

joint receptors

only respond to extreme joint angles

joint receptors

arent the main source of kinesthesia

Muscle Spindle

help sense muscle movement and position noe

Muscle Spindle

provide sensory feedback for controlling muscle movements and adjusting to loads

limb muscles

focus on load compensation

eye muscles

focus on movement control.

Fusiform Capsule

spindle is shaped like a spindle (fusiform) and encased in a capsule

Fusiform Capsule

Attached to either muscle fibers (extrafusal fibers) or tendons

Sensory Receptors

spindles contain modified muscle fibers and sensory endings

Sensory Receptors

have dual innervation

Sensory Receptors

Carries signals from the central nervous system (CNS) to the spindle.

Sensory Receptors

Sends sensory information from the spindle to the CNS

Nuclear-bag fibers

Nuclei concentrated in the middle (equatorial region)

Nuclear-chain fibers

Nuclei distributed along the length

Intrafusal Fibers

contains 2-3 nuclear bag fibers. 4-6 nuclear chain fibers

y1 fusimotor fibers

End in a plate-like arrangement

y2 fusimotor fibers

End in a fine network called trail endings

annulospiral endings

sensory terminals ng Nuclear-bag and nuclear-chain fibers

annulospiral endings

These endings wrap around the middle (equatorial region) of the intrafusal fibers

annulospiral endings

are supplied by large-diameter group Ia afferent axons

group II afferent axons

These endings are located next to the annulospiral endings

group II afferent axons

secondary endings

annulospiral endings

primary endings

dynamic phase

when the muscle is being stretched

dynamic phase

the primary endings show a much greater increase in firing rate compared to the secondary endings

static phase

when the muscle is held at a new length

static phase

both types of endings fire at similar rates

Static Fusimotor

Reduces the sensitivity of the primary ending during the dynamic phase of stretching the spindle

Dynamic Fusimotor

Enhances the sensitivity of the primary ending during the dynamic phase of stretching the spindle

Dynamic y fusimotor fibers

innervate bag1 fibers at one or both poles of the muscle spindle

Dynamic b axon

innervates about one-third of the bag1 fibers and innervates the subset of extrafusal fibers

dynamic fusimotor system

combination of both dynamic b and y axon

fusimotor system

helps maintain muscle spindles' tension

fusimotor system

provides continuous feedback to adjust movements with precision

γ fusimotor system

allows for subtle adjustments to muscle tone, enabling fine adjustments that keep the muscles in an optimal position without over-contracting or relaxing

proprioception

this s feedback mechanism is especially important in complex oral tasks where precise movements, such as controlling the tongue and jaw during speech and eating, are necessary.

stretch reflex

an important protective mechanism that prevents overstretching

γ motor neurons

ensure the muscle spindle remains responsive

Golgi tendon organ

consists of a thinly encapsulated bundle of small tendon fascicles with a fusiform (spindlelike) shape

Golgi tendon organ

are situated at the junction between a muscle and its tendon

Tendon organs

respond with a steady frequency of action potentials

Tendon organs

responds when a single muscle motor unit connected to the tendon organ is activated

active contraction

most effective stimulus for tendon organs

IN THE LIGAMENTS

slowly adapting responses arise mainly from Golgi tendon organ-type endings

Golgi tendon organ-type endings

where the slowly adapting responses arise mainly from pag IN THE LIGAMENTS

IN THE CAPSULE

slowly adapting response originate from Ruffini type endings.

Ruffini type endings.

where the slowly adapting responses arise mainly from pag IN THE CAPSULE

joint receptors

provides a fast mechanism to prevent hyperextension of the joint such as when a person tries to kick a ball and misses

Muscle spindles

are present in the masseter, temporalis, and medial pterygoid muscles and are therefore found in jaw elevator, but not depressor, muscles

Muscle spindles

are not evenly distributed in the muscles and are concentrated in the deep and anterior parts of the muscles

Muscle spindles

are absent from the tongue in most species but have been reported in primates

temporomandibular joint

translates jaw movements

temporomandibular joint

move together simultaneously but not symmetrically

cell bodies

are located in the trigeminal mesencephalic nucleus

Electrophysiologic recordings

have shown responses to the rotation of the temporomandibular joint.

Muscle spindles

are complex sensory organs containing specialized, muscle fibers, sensory endings, and a specialized motor innervation

Afferent sensory information

derived from muscle spindles reaches conscious levels and is important in the control of muscle length.