Neuro Atlas

Proprioception and Reflex Pathways: II
NEUROPHYSIOLOGY
Alpha motor neurons to extrafusal
striated muscle end plates
Gamma motor neurons to intrafusal
striated muscle end plates
Ia (A) fibers from annulospiral
endings (proprioception)
II (A) fibers from flower spray
endings (proprioception);
from paciniform corpuscles (pressure)
and pacinian corpuscles (pressure)
III (A) fibers from free nerve endings
and from some specialized endings
(pain and some pressure)
IV (unmyelinated) fibers from free
nerve endings (pain)
Ib (A) fibers from Golgi tendon
organs (proprioception)
Alpha motor neuron to extrafusal
muscle fiber end plates
A fibers from
Golgi-type
endings
A fibers from
paciniform corpuscles
and Ruffini terminals
A and C fibers
from free nerve
endings
Gamma motor neuron to intrafusal
muscle fiber and plates
II (A) fiber from flower spray endings
Ia (A) fiber from annulospiral endings
Detail of
muscle spindle
Sheath
Lymph space
Nuclear bag fiber
Nuclear chain fiber
Extrafusal
muscle fiber
Intrafusal
muscle fibers
©
Efferent fibers
Afferent fibers
FIGURE 2.26
MUSCLE AND JOINT RECEPTORS •
Muscle spindles and Golgi tendon organs send afferent signals to
the brain to convey the position of limbs and help coordinate muscle
movement. Muscle spindles convey information on muscle tension
and contraction (dynamic forces) and muscle length (static
forces). The nuclear bag fibers respond to both dynamic and static
forces, whereas the nuclear chain fibers respond to static forces.
Intrafusal fibers maintain appropriate tension on the nuclear bag
and nuclear chain fibers. If the muscle tension is too great (e.g.,
overstretching of muscle or too heavy a load), activation of the
Golgi tendon organ causes a reflex relaxation of the muscle.
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