Introduction to CNS lec11

Question 1

Which part of the brain of the CNS is in charge of programming?

Answer 1

basal ganglia, cerebellum, thalamus

Question 2

What are the receptors that provide information regarding the position of the limbs and their movements relative to each other and to the surroundings?

Answer 2

proprioreceptors?

Question 3

The muscle fibers of the muscle spindles are called:

Answer 3

intrafusal fibers

Question 4

Which fiber and its endings wrap around the intrafusal fibers?

Answer 4

the group Ia fiber and its primary ending

Question 5

Which fiber and its ending touch the surface of the intrafusal fiber?

Answer 5

group II fiber and its secondary ending

Question 6

Which two fibers are connected to the furthest end on the intrafusal fiber and closest to the extrafusal fiber?

Answer 6

the gamma fibers/motoneurons and their fusimotor endings.

Question 7

Are the fusimotor fibers myelinated?

Answer 7

yes

Question 8

What does the gamma motoneuron innervate?

Answer 8

the contractile regions of both the nuclear chain and nuclear bag fibers to bring about contraction of the peripheral regions of the muscle spindles.

Question 9

True of false, that the intrafusal fibers contract in response to fusimotor stimulation, their sensory endings are stimulated by the stretch?

Answer 9

True

Question 10

Two ways that the muscle spindles can be stimulated:

Answer 10

1. stretching of entire skeletal muscle

2. by causing the intrafusal fibers to contract while the extrafusal fibers remain at the same length

Question 11

One most studied reflex is the stretch reflex–knee tendon jerk reflex. The muscles of the knee and ankle act in antagonistic manner. Describe this reflex.

Answer 11

• sharp tap on the knee stretches the quadriceps muscle.
• stretch stimulates the dynamic nuclear bag muscle (innervated by the gamma motoneurons)
• increase rate of firing of group Ia afferents in the spindle
• this informs the spinal cord that the quadriceps muscles have been stretched
• some afferent fibers branch and enter the grey matter and make monosynaptic contact with alpha-motoneurons supplying the quadriceps, causing them to discharge in synchrony.
• resulting contraction quickly extends the lower leg
• collaterals of the Ia fibers make synaptic contact with inhibitory interneurons which in turn inhibit flexing of the knee.

Question 12

Describe the withdrawal reflex

Answer 12

• a threatening object, source, like heat
• afferent fibers arise from cutaneous nociceptors
• small diameter fibers synapse with number of interneurons
• in the dorsal horn of the spinal cord
• then synapse with and excite flexor neurons. which causes the muscle to flex
• reciprocal inhibition is also seen
• inhibition of motoneurons to extensor muscles so that the muscles do not extend
• limb away from object
• protection reflex.