Block 2 100812 Reflexes

Front 1

What is the stimulus, response, and neural circuitry of the myotatic (stretch) reflex?

Back 1

Stimulus= stretch of tendon/muscle
response=contraction of that same muscle
neural path= stretch receptors depolarize from membrane distortion and APs down to neuron body in dorsal root ganglia. The afferent axons from the muscle spindles make excitatory synapses on alpha motoneurons. There is an interneuron that inhibits the antagonist muscles

Front 2

Describe the organization of muscle spindle organ.

Back 2

Muscle spindle organ is a sensory receptor that is arrangled in parallel with striated skeletal extrafusal fibers. Smaller intrafusal fibers are surrounded by a capsule and have actin and myosin at the ends of the intrafusal cells because in the middle they are innervated by afferent nerves (type Ia) primary afferent axon endings called annulospiral endings. Type II axons that are secondary endings called flower spray innervate intrafusal cells too and are sensitive to tonic stretch.

Front 3

What stimulus are Ia axons sensitive to?
What are Type II axons sensitive to?

Back 3

Ia: rapid (phasic) stretch

II: tonic stretch

Front 4

What is the role of the gamma motor system?

Back 4

gamma motor neurons synapse with intrafusal cells at the ends and when synapse excitatory responses they deform the center by contracting the ends and stretching the center of the fibers that increase afferent discharge which makes spindles more sensitive to change in muscle length and increases muscle tone

Front 5

What is alpha-gamma co-activation?

Back 5

Descending motor pathways excite alpha motor neurons and gamma motor neurons so spindles are response to stretch while muscle is shortening and prevents the spindles from being unloaded

Front 6

WHat is the functional role of stretch reflex?

Back 6

This negative feed back system responds to loads and keep the muscle length optimal by increasing muscle tone when a spindle afferent excites motoneurons and restores the muscle to its original length

Front 7

What descending inputs control gamma-motor neurons?

Back 7

This is subconsciously controlled by the CNS and travel down vestibulospinal tracks and reticulospinal tracks

Front 8

What is reciprocal inhibition?

Back 8

When a reflex causes a muscle to contract and inhibitory interneurons are activated to relax antagonist muscles

Front 9

What is the stimulus, response, and neural circuity of the Golgi Tendon reflex?

Back 9

stimulus: large increase in tension at the muscle tendon detected by golgi tendon organ
response: relaxation of the same muscle
Circuit: during passive stretch GTO have weak/no response but during active shortening of muscle GTO fires frequencey proportional to the contractile force through Ib afferent ***through interneurons to motor neurons

Front 10

What are the functional roles for golgi tendon organ?

Back 10

They are sensory receptors that have axon terminals in town fibers that :
compensates for muscle fatigue
protects from over-stress of a muscle
reduces contraction upon contact of a limb with an object
reduces contraction at the limits of joint movement

Front 11

What are the sensory transducers, stimulus, reponse, and neural path for the Withdrawl (Flexion) reflex?

Back 11

transducers: nociceptors
stimulus: pain (nociceptors)
response: contraction of muscles appropriate to remove body from harm
path: afferent---> interneurons---> motor neurons (interneurons inhibit antagonistic motor neurons

Front 12

What is crossed extension reflex?

Back 12

When nociceptor input increases more neuron groups are recruited to produce a bigger response
ex) small stim: activate flexors at joint. medium stim: activate flexors at neighboring joints. big stim: activate extensors of opposite limb to support body

Front 13

What is the extensor thrust reflex?

Back 13

stimulus: pressure receptors on plantar surface
response: extension of limbs

occurs only up until 1yo

Front 14

What is spinal shock?

Back 14

loss of reflexes below a lesion caused by a spinal injury but gradually recovers

Front 15

What is the babinski sign?

Back 15

When after an upper motor injury an adult reverts back to the infact response of the plantar reflex. When a baby (<1yo) has their foot scrapped their toes fan while an adult flexes the toes because their corticospinal tract is myelinated

Front 16

Describe the interneuronal organization underlying rhythmic movements like stepping.

Back 16

Movement is initiated by descending tracts but also may have a central pattern generator that generate locomotor rhythms in the absence of corticomotor control