Lecture 5: Spinocereballar Tracts

Question 1

What is the general purpose of the cerebellum?

Answer 1

coordinates willed muscular contractions for study movements and steady posture

Question 2

What is the purpose of the spinocerebellar pathway?

Answer 2

conveys information to the cerebellum about limb and joint position (unconscious proprioception) using a two neuron pathway

Question 3

What are the two types of receptors for the spinocerebellar system?

Answer 3

muscle spindles and golgi tendon receptors

Question 4

What types of fibers are contained in muscle spindles and what do they sense?

Answer 4

1a (length and change in length) and 2 (length)

Question 5

Do second order neurons of the spinocerebellar tract cross the midline?

Answer 5

most do not cross but simply enter the cerebellum via the inferior cerebellar peduncle (lesser and more complex runs contra laterally in the sc but then crosses gain int eh brain stem)

Question 6

Where do DRG synapse if they come from L4 and below?

Answer 6

fibers ascend in the faciculus gracilis and synapses in Clarke’s column (mostly leg muscles)

Question 7

Where do DRG synapse if they come from C8-L3?

Answer 7

synapse on Clarke’s column (mostly trunk muscles)

Question 8

Where do DRG that enter C7 and above synapse?

Answer 8

travel cranially in the fascicles cuneatus and synapse in accessory cuneate nucleus (mostly arm muscles)

Question 9

How are golgi tendon fibers arranged?

Answer 9

they are encapsulated receptors that include nerve terminals that wind their way between collagen fibers and mechanorecptors are acted by pinching of collagen fibers

Question 10

Describe the fibers that serve the golgi receptors.

Answer 10

1b fibers are large diameter, myelinated and very high speeds

Question 11

What parameter do golgi receptors measure?

Answer 11

only tension, without regard to length, increased firing with increased tension

Question 12

What are the two types of muscle spindle fibers?

Answer 12

nuclear bag or nuclear chain fibers

Question 13

Describe the fibers of a muscle spindle and how they are arranged.

Answer 13

modified muscle fibers called intrafusal fibers wrap around the muscle fiber and are accompanied by a gamma fiber that is important (allows spindle fibers to contract with muscle so spindle fibers are responsive to changes in length- removes slack)

Question 14

What type of fibers carry information from the muscle spindles?

Answer 14

1a (huge and fast myelinated fibers send info about rate of change and length) and 2 (large and fast send info about length) )types of fibers gamma neurons carry motor innervation to the spindle)

Question 15

How are sensory fibers innervating intrafusal muscle fibers activated?

Answer 15

by mechanosensory channels (spectrin fibers are physically tugged when there is a change in length)

Question 16

What is the difference in signaling of type 1a and 2 fibers that conveys their respective detective sense?

Answer 16

1a increase firing initially and then lessens over time while 2 gradually increase firing with change

Question 17

What are the two types of nuclear bag fibers?

Answer 17

Static nuclear bag fibers and dynamic nuclear bag fibers (detect change in length)

Question 18

Describe the myotatic reflex

Answer 18

spindle fibers sense muscle is stretched resulting activation of sensory directly on motor neurons to same muscle being stretched and also signaling to interneurons that inhibit apposing group muscles (antagonistic) (higher centers can modulate this action)

Question 19

What are Renshaw cells?

Answer 19

they “turn down” reflex by limiting the reaction of alpha motor neurons and shutting off 1a interneurons

Question 20

Describe the inverse stretch (autogenic inhibition) reflex.

Answer 20

gogli sensors sense excessive muscle tension and 1b activate activates muscle opposite of stretch reflex and also inhibits motor neuron to the same muscle (can inhibit excitatory interneurons that activate a motor neuron to opposing muscle)… suddenly activates at very high tension but appears to be active under normal conditions)

Question 21

Describe the flexor reflex to a painful stimulus.

Answer 21

painful stimulus activates LMN that will take foot away from the painful stimuli and inhibit those that bring it closer by activating appropriate excitatory and inhibitory muscles; those reflexes can activate many muscles in multiple limbs so you don’t fall over when you move away from original stimuli