segmental motor circuits

Question 1

what are the classes of movement

Answer 1

1. Reflex (stereotyped)
2. Voluntary (motor cortex)
3. Cyclical (programed)

Question 2

what is a motor unit

Answer 2

alpha motor neuron and the skeletal muscle fibers that it controls and has
NMJs with.

Question 3

how many fibers do alpha motor neurons innervate

Answer 3

Each alpha motor neuron will innervate a few skeletal muscle fibers. Some neurons control more
skeletal muscle fibers than others.

Question 4

what are the 3 types of inputs of a LMN

Answer 4

1. From local interneurons
2. From sensory afferents (periphery)
3. From higher centers (descending
   tracts)

Question 5

what are the segmental reflexes

Answer 5

• Monosynaptic, disynaptic, polysynaptic
• Reciprocal inhibition

Question 6

what is the monosynaptic reflex

Answer 6

• 2 neurons and 1 synapse in between
• stretch reflex

Question 7

what is a disynaptic reflex

Answer 7

inverse stretch reflex

Question 8

what are are polysynaptic reflexes

Answer 8

• Withdrawal (flexion) reflex
• Reciprocal (antagonist) inhibition

Question 9

what does the stretch reflex involve

Question 10

Muscle spindle pathway

Answer 10

• Sensory axons from the muscle spindle goes to the dorsal root ganglion,
• synapses to the motor
  neuron in the ventral horn of grey matter, and causes the alpha motor neuron to fire and contract
  the muscle that was stretched.

Question 11

what is the stretch reflex also called

Answer 11

Stretch reflex has other names: myotatic reflex or deep tendon
reflex.

Question 12

steps of muscle stretch

Answer 12

step 1) stretching of the muscle stimulates muscle spindles
step2) activation of sensory neuron
step 3) information processing at motor neuron
step4) activation of motor neuron
step5) contraction of the muscle

Question 13

what happens when during the knee jerk reflex test

Answer 13

• when Dr taps the tendon you stretch the muscle which stretches the spindle and reflex goes through spinal cord which causes alphamotor neuron to fire and contraction of quads and jerk of the leg

Question 14

what are the functions of the stretch reflex

Answer 14

 Holds muscle length constant
 Maintenance of erect posture
 Responsible for muscle tone

Question 15

what is muscle tone

Answer 15

• the basal level of contraction of a muscle due to gravity

Question 16

what is the gamma motor system

Answer 16

• it adds to the reflex story
• controls the spindle itself, its sensitivity
• stetch the muscle spindle itself

Question 17

what is the gamma motor neuron pathway

Answer 17

-CNS stimulates gamma motor neuron to stretch the muscle spindle
 muscle
spindle axon enters the DRG to the spinal cord, where it synapses with the alpha motor
neuron that innervates the muscle  alpha motor neuron fires, and the muscle in
contracted
 this low level contraction adds to muscle tone

Question 18

intrafusal vs extrfusal muscle fibers

Answer 18

• extrafusal - bulk of the muscle
• intrafusal - muscle spindle

Question 19

what does the inverse stretch reflex involve ( Disynaptic reflex)

Answer 19

 Golgi tendon organ
 Senses muscle tension
- 3 neurons 2 synapses

Question 20

what is the inverse stretch reflex pathway

Answer 20

GTO measures muscle tension. It synapses with an inhibitory interneuron in the segmental pool
of neurons within the spinal cord. The inhibitory interneuron acts on the alpha motor neuron,
causing the muscle to relax.
- overall decresases contraction of EXTRAFUSAL muscle fibers

Question 21

example of inverse stretch

Answer 21

• overloading muscle with a weight if its too heavy the inverse stretch reflex inhibits and drop the weight

Question 22

what does the flexor ( withdrawl) reflex respond to

Answer 22

• respond to painful stimulus

Question 23

what is the pathway of the flexor reflex

Answer 23

• Free nerve ending in the skin synapse in the gelatinosa.
• Polysynapstic connections of interneurons to the alpha motor neuron.
• There’s also the ascending spinothalamic tract, which goes through the anterior
  commissure and up the spinothalamic tract.
• Pain afferents synapse with interneurons which converge on an alpha motor neuron
  and typically cause reflexive flexion withdrawal.

Question 24

what is a example of a flexor reflex

Answer 24

• touching a hot stove
• remove the hand even before you feel the pain

Question 25

what are antagonist muscles

Answer 25

- biceps - reflexer - tricpes - extencer - there needs to be reciprocal inhibition

Question 26

what is reciprocal inhibiton

Answer 26

- if you reflex biceps alpha motor neurons of triceps need to be inhibited and vice versa

Question 27

what are the 2 routed of reciprocal inhibiton

Answer 27

1. Classic muscle spindle reflex. Muscle spindle in the extensor muscle excites the alpha motor neuron, which goes back to the same muscle and causes it to contract. 2. Muscle spindle in the extensor muscle branches and connects with an inhibitory interneuron. This inhibitory interneuron acts on the flexor muscle and causes it to relax.

Question 28

what are the cranial nerve reflexes

Answer 28

- jaw jerk - corneal reflex

Question 29

what is the jaw closing reflex

Answer 29

- If you stretch the masseter muscle by tapping the chin, there’s a reflex that contract the masseter - usually, this reflex is inhibited - But if there is some abnormality of the central motor pathway, this reflex may become apparent.

Question 30

jaw closing reflex pathway

Answer 30

- masseter muscle has muscle spindle - spindle afferent goes to mesencephalic nicleus - - The muscle spindle fiber synapses with the alpha motor neuron in the motor nucleus of V and causes the masseter to contract, closing the jaw.

Question 31

where is the mesecephalic nucleus of V in the pons

Answer 31

Question 32

what is the cornal refelx

Answer 32

- if you touch the cornea you blink

Question 33

what is the corneal reflex pathway

Answer 33

- receptors in the cornea go through V1 and synapse in the brainstem at the chief sensory nucleus of V. - There is an interneuron that goes to the motor nucleus of 7 (facial muscles), which causes a contraction of the eye muscles  blinking reflexively

Question 34

what are central pattern gernators

Answer 34

Neuronal networks in spinal cord or brain stem that generate, rhythmic alternating activity. -

Question 35

examples of central pattern gerneators

Answer 35

 Walking  Swimming  Chewing  Breathing  Eye movements  Sneezing & coughing

Question 36

mastication

Answer 36

- exerts huge forces - also can execute precise movements such as for speech with speed - mandible moves rapidly

Question 37

what reflexes are included in mastication

Answer 37

 Central Pattern Generator  Stretch reflexes (spindles in jaw closing muscles)  Mandibular rest position  Periodontal reflexes  Joint reflexes