NMS

7/1/1999

Muscle Spindle

• In w/in skeletal mm
• Found in some involuntary mm, such as diaphragm
• Major function is to maintain tone
• Have to have a healthy nervous system
• Reciprocal inhibition—secondary function—contract biceps and relax triceps
• More powerful than GTO
• More numerous than GTO
• Monosynaptic reflex—go through on synapse for message to be heard
• Muscle cells surround the muscle spindle—individually attached
• What fires a spindle? Stretch—it is a stretch receptor
• Prevents over stretch of the muscle
• Increase tone when contract muscle
• Normal tone is that the muscle spindle does not like to stretch and it constantly fires
• Tone is the balance b/w agonist and antagonist muscles
• Controlled by the cerebellum
• GroupA—flexors, internal rotators, adductors—primary muscles—fetal position
• If CNS fails, start to return to this position
• White, fast twitch
• Do not respond well to stretch
• Stretch will cause contraction and spasm

• Opposite muscles are posture muscles—GroupB—passive stretch works the best—red, slow twitch
• Extensors, abductors, external rotators
• Hybrids—hamstrings—flex the knee, extend the thigh

• Inside every muscle spindle there are:
• Nuclear chain
• At the end there are sarcomeres—contractile ends—intrafusal muscle fiber
• Wrapped around the center is annulospiral sends a monosyaptic fiber to the cord—responsible for DTR—sends signal for facilitation
• Juxtaequatorial nerve endings—land on top of the intrafusal muscle fibers—multisynaptic to the cord along w/the annulospiral—flower spray—inhibitory when it fires in a certain group of muscles—posture muscles—provides very little input
• Maximum stretch and sustained on the muscle

• g motor neuron—fusimotor system
• motor to contracting sarcomere of the nuclear chain
• need g to maintain tone of the muscle no matter what position the muscle is in—isotonic contraction
• cerebellum is aware of what the muscle
• it gets message from spinocerebellar pathway
• it from mechanocreceptors in the area of the muscle
• through the extrapyramidal pathways where it lands on the g motor neurons
• w/an upper motor neuron lesion only indirectly affect the a motor neuron, it directly affects g motor neurons

Parkinson's

• messes everything up
• pt is rigid
• loss of message flow through the cerebellum

Barry Wyke

• mechanoreceptors in capsules
• type I
• type II
• type IV
• these land on g motor neurons

• Nuclear bag

Golgi Tendon Organ

• Relaxes muscle tone
• Essentially the opposite of muscle spindle
• Multisynaptic reflex—goes through several synapses and takes longer for its message to be heard