Motor Systems

Question 1

What do lower motor neurons innervate?

Answer 1

skeletal muscles (provide motor innervation to the contractile elements in the muscle

Question 2

Where are the lower motor nueron cell bodies located in?

Answer 2

1) ventral horn of spinal cord gray in lamina IX of rexed

2) brainstem in motor nuclei of cranial nerves

Question 3

Where do lower motor neurons send axons out of the CNS in?

Answer 3

1) Ventral rootlets of all spinal nerves

2) All cranial nerves except I, II & VIII

Question 4

What do the lower motor neurons innervate?

Answer 4

skeletal muscle cells

Question 5

What do lower motor neurons serve as a link between?

Answer 5

CNS and somatic effector cells

Question 6

What are lower motor neurons known as?

Answer 6

final common pathway neurons

Question 7

In general, what controls lower motor neurons?

Answer 7

Motor control areas of the brain and the brain stem by various kinds of sensory inputs that come in at sensory segmental levels

Question 8

What are the parts of the brain and brainstem that influence lower motor neurons known as?

Answer 8

supranuclear motor control areas

Question 9

Where do some of the supranuclear motor control areas send axons to terminate on?

Answer 9

Lower Motor Neurons

Question 10

What do the fibers of the supranuclear motor control areas that send axons to terminate on lower motor neurons form?

Answer 10

Descending motor control pathways

Question 11

What are the pathways of the neurons of the descending motor control called?

Answer 11

Upper motor Neurons

Question 12

What do Upper Motor Neurons exert influence on?

Answer 12

Lower Motor Neurons

Question 13

What can influence the activity of the lower motor neurons?

Answer 13

Direct sensory input at a segmental level

Question 14

In the spinal cord what can modify the activity of lower motor neurons?

Answer 14

somatosensory and visceral information that enters the cord segmentally

Question 15

What do the modification of lower motor neuron activity by somatosensory and visceral information form?

Answer 15

form the basis of spinal cord reflexes

Question 16

Can sensory input to the brain areas from cranial nerves active reflex responses involving lower motor neurons of cranial nerves?

Answer 16

yes

Question 17

What are the two major types of lower motor neurons?

Answer 17

Alpha motor neurons

Gamma motor neurons

Question 18

What do the major types of lower motor neurons comprise in the spinal cord?

Answer 18

Cell bodies that comprise lamina IX in the spinal cord and cranial nerve motor nuclei in the brainstem

Question 19

what fibers are part of the alpha motor neurons?

Answer 19

A-alpha fibers

Question 20

Where are the alpha motor neuron axons found?

Answer 20

Spinal cord or brainstem in spinal or cranial nerves

Question 21

What do alpha motor neurons provide innervation to?

Answer 21

Extra fusal muscle fibers in skeletal muscle

Question 22

Do alpha motor neurons innervate one or several extra fusal fibers?

Answer 22

Many extra fusal fibers are innervated by a single alpha motor neuron

Question 23

What make up a motor unit?

Answer 23

An alpha motor neuron and the muscle fibers it supplies

Question 24

What type of neurons are gamma motor neurons?

Answer 24

Fusimotor neurons

Question 25

Which are larger, alpha motor neurons or gamma motor neurons?

Answer 25

Alpha motor neurons

Question 26

What type of axon fibers are gamma motor neurons?

Answer 26

Group A gamma fibers

Question 27

What do gamma motor neuron fibers exit and via what means?

Answer 27

Exit spinal cord and brain via spinal & cranial nerves

Question 28

What do gamma motor neurons provide innervation to?

Answer 28

Intrafusal muscle fibers in a neuromuscular spindle

Question 29

Where are neuromuscular spindles found?

Answer 29

in skeletal muscle

Question 30

How are alpha and gamma motor neurons arranged in the ventral horn?

Answer 30

Somatopically arranged

Question 31

Where are Lower motor neurons that innervate muscles of the trunk located?

Answer 31

Medially in the ventral horn

Question 32

Where are Lower motor neurons that innervate extremity located?

Answer 32

Positioned laterally in the ventral horn

Question 33

List the pathway of motor neurons

Answer 33

Upper motor neurons -> descending motor control pathways -> influence lower motor neurons (as ventral spinal tract, medial lateral fasciculus, tectospinal and tectobulbar tracts) -> skeletal muscle cells (via spinal nerves of certain cranial nerves