Lower Motor Neurons

Question 1

What disease is this?

Degnerative disease of both upper and lower motor neurons in the nervous system?

Answer 1

Amyotrophich Lateral Sclerosis

Question 2

Which motor activity system is this? (lower or upper)

Sum of the supraspinal descending influences on the lower motor neuron

Answer 2

Upper Motor Neuron System

Question 3

What part of the brain do descending motor tracts arise from?

Answer 3

Cortex and brainstem

Question 4

What motor tracts are from the cortex?

Answer 4

• Corticospinal
• Corticobular

Question 5

What motor tracts are from the brainstem?

Answer 5

• Vestibulospinal
• Reticulospinal
• Rubrospinal
• Tectospinal

Question 6

How is voluntary movement controlled?

Answer 6

Top-down; from the brain to spinal cord to muscle

Question 7

Where does the descending motor system start with a decision when starting an action?

Answer 7

In the anterior region of the frontal lobe or the motor cortex to activate upper motor neurons

Question 8

What makes up the descending control center?

Answer 8

Upper motor neurons in the motor cortex and brainstem

Question 9

What actions is the motor cortex involved in?

Answer 9

Planning, initiating, and directing voluntary movements

Question 10

What actions are the brainstem centers invovled in?

Answer 10

Rhythmic, sterotyped movements and postural control

Question 11

What happens after a decision is made in the anterior region of the frontal lobe?

Answer 11

Motor planning areas and control circuits are activated

Question 12

Where are the control circuits found?

Answer 12

Cerebellum and basal ganglia

Question 13

What does the control center do?

Answer 13

Regulate activity of descending upper motor neurons in the motor cortex and brainstem centers

Question 14

What action is the basal ganglia invovled in?

Answer 14

Initiation of intended movement and suppression of unwanted movement

Question 15

What action is the cerebellum involved in?

Answer 15

Coordinates ongoing movement

Question 16

What happens after motor areas and control circuits are activated?

Answer 16

Upper motor neurons deliver singals to local spinal and brainstem circuits and motor neuron pools (lower motor neurons)

Question 17

What processs occur in the local circuit neurons?

Answer 17

Sensorimotor integration and central pattern generation processes

Question 18

Where do the local circuit neuron proccesses occur?

Answer 18

Brainstem and spinal interneurons

Question 19

What is the final event in activation of voluntary movement?

Answer 19

Transmission of signals from the lower motor neurons directly to skeletal muscles, eliciting contraction of muscle fibers

Question 20

What is the following a definiton of?

Composite of voluntary and involuntary motor activity

Answer 20

Movement

Question 21

Where are voluntary movements directed?

Answer 21

Distal muscle groups

Question 22

How is lower motor neuron innervation mediated?

Answer 22

Through the lateral corticospinal tract

Question 23

What muscle groups does involuntary movement involve?

Answer 23

Proximal and truncal muscle groups

Question 24

Why is involuntary movement critical?

Answer 24

Critical for postural stability

Question 25

What tract are postural adjustments under?

Answer 25

Anterior Corticospinal tract

Question 26

What are the tracts that mediate postural stability?

Answer 26

- Vestibulospinal - Reticulospinal - Rubrospinal - Tectospinal

Question 27

What tract does the brainstem pathway recieve input from?

Answer 27

Corticospinal pathways

Question 28

Lower motor neurons are the only neurons that convey signals to ____ and ____ skeletal muscle fibers

Answer 28

extrafusal; intrafusal

Question 29

What neurons are the final common pathways for signal transduction

Answer 29

Lower motor neurons

Question 30

Where are LMN located?

Answer 30

Anterior horn of the spinal cord and motor nuclei of cranial nerves in the brainstem

Question 31

LMN are organized into circuits to do what?

Answer 31

Sort and regulate the multitude of descending influences so that activity of truncal, proximal, and distal muscle groups are coordinated

Question 32

Where are cell bodies of the spinal lower motor neurons located?

Answer 32

Ventral horn

Question 33

Where do the cell bodies of the spinal LMN leave the spinal cord?

Answer 33

Ventral root

Question 34

Cell bodies whose axons project to a single muscle are clustered in ____ ____

Answer 34

Motor pools

Question 35

Medially located pools of motor cells bodies innervate what muscles?

Answer 35

Axial and proximal muscles

Question 36

Anteriorly located pools innervate what muscle?

Answer 36

Extensor muscles

Question 37

Posterior pools within ventral horn innervate what?

Answer 37

Flexor muscles

Question 38

Where are the cell bodies of alpha and gamma motor neurons located?

Answer 38

Ventral horn of the spinal cord

Question 39

Alpha and gamma motor neuron axons leave the spinal cord via ____ ____ then travel through the ____ ____ and then travel through the ____ ____ to reach skeletal muscle

Answer 39

ventral rool; spinal nerve; peripheral nerve

Question 40

# Is the following alpha or gamma motor neuron? large cell bodies and large myelinated axons

Answer 40

Alpha

Question 41

# Is the following alpha or gamma motor neuron? Medium sized myelinated axons

Answer 41

Gamma

Question 42

Where do the axons are alpha motor neurons project to?

Answer 42

Extrafusal skeletal muscles branching into numerous terminals

Question 43

Where do gamma motor neurons project to?

Answer 43

Intrafusal fibers in the muscle spindle

Question 44

What does a motor unit consist of?

Answer 44

Alpha motor neuron and the muscle fibers it innervates

Question 45

# What is the following a definition of? Activated pattern that maintains the stretch on the central region of the muscle spindle intrafusal fiberes by contracting the ends of the intrafusal fibers when the extrafusal fibers actively contract

Answer 45

Alpha-gamma coactivation

Question 46

What is the purpose of the alpha-gamma coactivation?

Answer 46

Maintain stretch sensivity of the muscle spindle when extrafusal muscle fibers contract

Question 47

Why does alpha-gamma coactivation occur?

Answer 47

Because most sources of input to alpha MN have collaterals to gamma MN | MN = motor neurons

Question 49

What neurotransmitter is released when alpha MN is activated?

Answer 49

ACh

Question 50

Smaller diameter slower conducting alpha MN innervates what type of motor unit?

Answer 50

Slow twitch

Question 51

Large diameter and faster conducting alpha MN innervated what type of motor unit?

Answer 51

Fast twitch

Question 52

# What is the following a defintion of? Order of recruitment from smaller to larger alpha motor neurons

Answer 52

Henneman's size principle

Question 53

What does resistance to stretch that muscles generated depend on?

Answer 53

Muscle length

Question 54

A stretched muscle generates ____ resistance to stretch than when its ____

Answer 54

more; shortened

Question 55

What factors determine the total resistance to muscle stretch?

Answer 55

- Active contraction - titin - connective tissue - weak actin-myosin bonds

Question 56

# What is the following a defintion of? Resistance to stretch in a resting muscle

Answer 56

Muscle tone

Question 57

When muscle tone is normal, resistance to passive stretch is what?

Answer 57

Minimal

Question 58

What is normal resistance to slow passive stretch in relaxed muscle produced by?

Answer 58

Weak actin-myosin bonds and titin

Question 59

# The following functions are of what chemical? Maintains the position of myosin relative to actin and prevents sacromere from being pulled apart

Answer 59

Titin

Question 60

How are weak actin-myosin bonds formed?

Answer 60

Myosin attaches to actin but myosin head doesn't swivel so there is no power stroke

Question 61

What are the two forces that act on a joint to determine its resistance to movement called?

Answer 61

Elastic and contractile forces

Question 62

What does upper limb contraction allow for?

Answer 62

Precise movements

Question 63

What does lower limb contractions allow for?

Answer 63

Enables person to stand on unstable surface