Muscle innervation and motor unit Flashcards
1A muscle fiber receptor
primary spindle endings, measures length and rate of change length
1b muscle fiber receptor
receptor is on golgi tendon organ measures tension
II muscel fiber receptor
receptor on secondary spindle endings measures length receptor on non-spindle endings measures deep pressure
III and IV(unmyelinated) muscle fiber receptor
free nerve ending that measures pain, chemicals and temp.
changes in muscle length are related to
changes of the angle of the joint(joint position)
muscle spindles emit axons that serve as
afferent components of muscle stretch reflexes
motor innervation of muscle spindle organs
gamma neurons that adjust sensitivity of the spindle stretch
components of spindle
small group of fine intrfusal muscle fibers -myelinated sensory axons with receptive endings on the central regions of intrafusal fibers -myelinated motor axons that innervate the contractile regions adjacent to the central regions of the intrafusal fibers.
intrafusal fibers lie
within the spindle which is attached to connective tissue running parralle to and between the extrafusal fibers
each spindle indrectly connects to
the tendons
when muscles are stretched the spindle
also is stretched with an increase of firing rate of muscle spindle afferents.
types of itnrafusal fibers
dynamic nuclear bag- change in length and rate of change nuclear chain- changes in length static nuclear bag- changes in length
dynamic nuclear bag innervated by
Group 1a afferent dynamic and static Dynamic A gamma motor neurons- end on contractile portions
nuclear chain and static nuclear bag innervated by
group II afferent Static A gamma neurons ends on contractile portions.
extrafusal innervation of extrafusal fibers
large A Alpha (myelinated with large diameter.
role of muscle spindle
stretch reflex, proprioceptive info regarding movement and position of body parts, regulating muscle contraction under influence of descending motor pathways and afferent feedback.
role of muscle spindle in stretch reflex
1a fibers conduct action potentials towards excitator alpha motor neurons . these muscles contract while collaterals of the excited 1a fibers excite interneurons that inhibit firing of alpha neurons on antagonist muscle
muscle spindle activity during sustained stretch
some spindles fire tonically instead of phasically
muscle spindle activity during alpha motor stimulation
the spindle becomes inactive and the afferent discharge ceases leading to reduced activity of alpha motor neurons.
coactivation of alpha and gamma motor neurons
both extrafusal and intrafusal fibers contract, the spindles remain loaded and sensitive to stretch. enables muscle spindle to measure muscle length continuously
role of gamma motor activity on spindle performance.
stimulation of effernet fibers sensitizes the spindle to changes in muscle length. ( contraction of the ends of the intrafusal fibers exerts tension on the sensory components of these fibers. at any length of the spindle the firing rates are enhanced during periods of gamma motor neuron stimulation and the spindle remains sensitive to further increases in length
golgi is innervated by
a single large 1B fibers, within the organ it looses it’s myelin sheath. leaving naked nerve endings to interweave among the collagen fibers.
when golgi organ is deformed during muscle contraction
the ner ve endings undergo distortion which opens the membrane spanning stretch sensitive vation channels and the rate of action potential firing thus increases in the 1b fibers.
golgi organ monitors
tension
at great tensions the golgi organ mediates
inhibition of over active alpha motor neurons (inverse myotatic reflex) that relaxes teh muscles and excites the antagonist muscle
Renshaw cells
inhibitory interneurons that connect to the alpha motor neurons
the major collateral of the lower motor neurons leaves
the CNS and runs to the skeletal muscle branching extensively to innervate the multiple muscle fibers distributed within a muscle belly.
motor neuron pools
lower motor neurons that control individual muscle troups. are located in the columns sometimes bridging several cord segments and are scattered along the derivatives of the basal plate of the brainstem.
large populations of motor neurons on the ventral horns of the cervical and lumbar segements serve
the muscles of the upper and lower limbs. with fewer motor neurons located in the thoracic segments of the cord.
input to motor neurons
muscle spindle afferents, interneurons, upper motor neurons.
neuromuscular junction is located in
the middle of the muscle fiber.
hypotonia
detectable by palpation. caused by damage to 1a fibers or alapha motor neurons . can also arise from lesions in other parts of the motor system like the cerebellum.
