Unit 3_Motor Systems and Motor Units

Question 1

How does a single neuron work and how do neurons talk to eachother?

Answer 1

Sensory systems
Sensorimotor integration

Question 2

How does information get into the nervous system and what do we perceive based on this information?

Answer 2

Sensory systems

Question 3

How do we respond to sensory inputs, use sensory inputs for planning movements and how do we execute movements?

Answer 3

Sensorimotor integration

Question 4

What does purposeful reaching for an object require?

Answer 4

The nervous system to interact with and/or control the physical machine- our musculoskeletal system - and the musculoskeletal system’s interaction with a varying environment

Question 5

What is it called when the nervous system can solve problems in many ways and this flexibility is normal?

Answer 5

Motor Equivalence

Question 6

Loss of flexibility is what?

Answer 6

Dysfunctional

Question 7

What mechanisms help us prepare for movement and respond to perturbations of movement, respectively?

Answer 7

Feed-forward and feedback control

Question 8

What axons of alpha motor neurons innervate skeletal muscle (extrafusal muscle fibers) and form part of motor units? These axons form the motor part of peripheral nerves (from spinal cord and cranial nerves).

Answer 8

Alpha Motor Neurons (lower motor neuron; LMN’s)

Question 9

What are located in the ventral horn of every spinal cord segment and motor nuclei for cranial nerves in the brainstem?

Answer 9

Cell bodies

(note: Gamma motor neurons for the spindle also have cell bodies in ventral horn)

Question 10

What axons travel in spinal and cranial nerves that have a motor component and innervate skeletal muscle?

Answer 10

Alpha motor neuron (LMN)

Question 11

What are known as each spinal cord segment that has its own set of alpha motor neurons (LMN) whose axons form the ventral root of the spinal nerve at that segment only?

Answer 11

Myotomes

Question 12

What type of organization is found in the spinal cord where alpha motor neuron cell bodies are located?

Answer 12

Topographic organization

Question 13

What are organized in a way to most easily access the motor neurons they impact?

Answer 13

Descending pathways

Question 14

What is a motor neuron (motoneuron) [including its cell body (soma), dendrites and axon] and all of the (extrafusal) muscle fibers it innervates?

Answer 14

Motor unit

Question 15

There are usually _____ motor units within a named muscle.

Answer 15

many

Question 16

There are _________ types of motor units that allow us to do things for a long time and to generate large forces for short times.

Answer 16

different

Question 17

What are the three types of motor units that allow us to do things for a long time and to generate large forces for short times?

Answer 17

Slow, fast fatigue-resistant, fast fatigable

Question 18

Most muscles are a mixture of what?

Answer 18

slow and fast twitch muscle fibers

Question 19

Motor units from muscles that need to generate a lot of force tend to have ______ muscle fibers in the motor unit (e.g., MG) while those used for fine control have _______ muscle fibers in the motor unit (e.g., lateral rectus and tensor tympani).

Answer 19

more
fewer

Question 20

Are there distinct types of motor units?

Answer 20

It is more of a continuum. Not all motor units fall into a specific force to twitch ratio.

Question 21

What governs recruitment of motor units into action? Small motor units with small alpha motor neurons are recruited before larger motor units with larger motor neurons.

Answer 21

The size principle

Question 22

What motor units are recruited first?

Answer 22

Small motor units with small alpha motor neurons are recruited before larger motor units with larger motor neurons

Question 23

Force can be increased by what two mechanisms that are like sensory mechanisms?

Answer 23

Population coding (recruiting more motor units)

Frequency coding (rate coding; each motor unit firing faster)

Question 24

What mechanism increases force by recruiting more motor units?

Answer 24

Population coding

Question 25

What mechanism increases force by rate coding; each motor unit firing faster?

Answer 25

Frequency coding

Question 26

What are Common Signs and Symptoms of Alpha Motor Neuron and Motor Unit Neuropathology?

Answer 26

(“Lower Motor Neuron”) Disorders Weakness (paresis) Hypotonia Hyporeflexia Muscle atrophy Fasciculations and fibrillations

Question 27

What are the following disorders? Weakness (paresis) Hypotonia (floppy/lax) Hyporeflexia (decreased/absent reflex responses) Muscle atrophy Fasciculations (small muscle twitches that you can see) and fibrillations (small muscle twitches that you necessarily can't see)

Answer 27

“Lower Motor Neuron” Disorder

Question 28

The distribution of problems, when one has a lesion causing “LMN” signs and symptoms, is always what (i.e. only in that segment or nerve)? For example, a lesion in the ventral horn of C6 will give you “lower motor neuron” signs in those muscles supplied by C6 only. NOT in all muscles below the lesion like when a pathway is cut.

Answer 28

Segmental and ipsilateral

Question 29

Diseases of the motor unit do what? They may also affect the smoothness of contraction and demonstrate plasticity within the neuromuscular system.

Answer 29

change the force output

Question 30

What is caused by a viral infection that affects the alpha motor neurons in the ventral horn of the spinal cord and cranial nerve motor nuclei in the brainstem? It is an alpha motor neuron (lower motor neuron) disorder that affects muscles in the body and well as muscled supplied by cranial nerves. The affected muscles exhibit lower motor neuron signs and symptoms (weakness (paresis), hypotonia, hyporeflexia, muscle atrophy, fasciculations and fibrillations). The viral infection is self-limiting and the destruction of cells occurs within the first few weeks of infection.

Answer 30

Polio

Question 31

What syndrome do patients usually recover up to a certain extent and is left with residual deficits? This is a syndrome that occurs many years after a person first experiences polio. Individuals who have been stable and functioning with their residual deficits for years begin to experience new weakness and muscle fatigue. These new symptoms are likely due to a combination of overuse and aging. This condition is usually not life threatening but it often requires individuals to make significant lifestyle changes to reduce fatigue and conserve remaining muscle strength.

Answer 31

Post-polio syndrome

Question 32

What disease destroys alpha motor neurons in the spinal cord and brainstem and is also classified as a lower motor neuron disorder? However, unlike polio this disease is progressive and usually fatal within an average of 5 years. It is also multisegmental with destruction of the ventral horn alpha motor neurons in many spinal segments as well as cranial nerve motor nuclei. Unlike polio, in the later stages of this disease it may also affect the lateral white matter columns of the spinal cord and the patient may present with UMN signs such as spasticity.

Answer 32

ALS (Amyotrophic Lateral Sclerosis; Lou Gehrig’s)

Question 33

What disease may be caused by spinal cord injuries, spinal cord tumors, and damage caused by inflammation in and around the spinal cord? In some cases, the cause is unknown (idiopathic).

Answer 33

Syringomyelia

Question 34

What can sensory input evoke?

Answer 34

reflex activation of muscle

Question 35

What helps coordinate postural control?

Answer 35

Long propriospinal pathway

Question 36

What helps coordinate limb movement?

Answer 36

Short propriospinal pathway

Question 37

What is responsible for much of movement?

Answer 37

The spinal cord

Question 38

Much of what you see as movement is the result of patterns of motor unit activity generated by what? Reflexes give us a hint of the patterns that can be generated. Reflexes are more flexible than previously thought and they are not rigidly fixed. That said many neurologic diseases/injuries result in loss of flexibility.

Answer 38

The spinal cord

Question 39

What are the following primary functions for? 1. To adjust for unexpected perturbations 2. To organize patterns for coordinated movement (examples are flexor withdrawal and crossed extension; reciprocal inhibition) 3. To allow for rapid protection from painful or damaging stimuli (not a major function)

Answer 39

Reflexive motor control at the level of the spinal cord

Question 40

You do not need what to obtain a reflex contraction? Any lesions in the sensory cortex or ascending sensory white matter tracts that affect our ability to detect a sensation will not abolish a reflex, but it will not have its normal flexibility.

Answer 40

perception of sensation

Question 41

What can influence or regulate reflexes by increasing or decreasing the size of the reflex response but you do not need descending motor pathways to have a reflex present? You don't need descending motor or ascending sensory white matter pathways for a reflex to be present.

Answer 41

Descending control from the cerebral cortex and brainstem

Question 42

What may be used to obtain a motor response in a patient?

Answer 42

Stimulation of a spinal reflex pathway

Question 43

What occurs over a very short time frame and usually does not last much longer after the removal of the stimulus? The only way to lose or abolish a reflex is to remove the sensation that stimulates it or denervate the muscles that contract.

Answer 43

The motor response

Question 44

What will not abolish reflexes? They may make the spinal reflex presentation abnormal and less flexible.

Answer 44

Descending pathway (UMN) lesions

Question 45

What may be used to initiate movements for rehabilitation? They may be of particular relevance in the acute phase of rehabilitation to stimulate muscle activity and give the patient a proprioceptive sense of movement.

Answer 45

Reflexes

Question 46

What may be used to inhibit spastic muscles?

Answer 46

Certain reflexes

Question 47

What help us prepare for movement and respond to perturbations of movement, respectively?

Answer 47

Feedback and feed-forward control (mechanisms)

Question 48

What are 3 ways reflexes can help you adjust?

Answer 48

1. Can adjust for unexpected perturbations 2. To organize patterns for coordinated movement (i.e. reciprocal inhibition) 3. To allow for rapid protection from painful or damaging stimuli. The stretch reflex acts to protect muscles from over stretching.

Question 49

What do the following relate to in regards to reflexes? If an object is placed in your hand is unexpectedly heavy, you will not exert enough force to hold the weight and your biceps may be stretched. This triggers a reflexive contraction of biceps to support the weight of the object correctly. If you are standing and you are displaced posteriorly, the muscles on the anterior aspect of your lower leg (anterior tibialis) will be stretched. They will contract in response to your stretch and dorsiflex the ankle to assist in bringing you back to midline. However, longer latency responses are more involved in controlling large perturbations in humans.

Answer 49

Can adjust for unexpected perturbations

Question 50

What do the following relate to in regards to reflexes? Many movement patterns require coordination of agonist and antagonist so that as the agonist is excited the antagonist is inhibited. Descending pathways use the components of the stretch reflex loop to organize these activation patterns for reciprocal inhibition.

Answer 50

To organize patterns for coordinated movement (i.e. reciprocal inhibition)

Question 51

What does the following relate to in regards to reflexes? The GTO regulates the force of a contraction and is regulated by descending pathways. - For example, if you are holding a videotape in your hand and it starts to slip, the reflex can be inhibited to allow you to develop more force to hold the tape. That said cutaneous input has been shown to be the key to prevent slip.

Answer 51

To organize patterns for coordinated movement

Question 52

What type of reflex is a painful stimulus stimulates nociceptors, the cutaneous afferent nerve fibers (flexor reflex afferents or FRA’s) transmit the signal to the spinal cord and synapse on alpha motor neurons. The reflex is an example of an intersegmental reflex as many muscles are coordinated to activate at once to withdraw the limb. Clinically, this reflex may be used to stimulate muscle contraction in the flexors. For example, it may be used in comatose patients for arousal and to initiate a motor response. In normal life these reflexes may utilize similar circuitry as locomotion (walking).

Answer 52

Flexor Withdrawal Reflex and Crossed Extension

Question 53

What reflex do the following relate to? 1. Can adjust for unexpected perturbations 2. To organize patterns for coordinated movement 3. To allow for rapid protection from painful or damaging stimuli

Answer 53

Flexor withdraw and Crossed Extension

Question 54

What flexor withdraw/crossed extension reflex support the following: Response to pain or nociceptive stimulus?

Answer 54

Can adjust for unexpected perturbations

Question 55

What flexor withdraw/crossed extension reflex support the following: - The flexor withdrawal reflex is an example of an intersegmental reflex as many muscles are coordinated to activate at once to withdraw the limb. - Clinically, this reflex may be used to stimulate muscle contraction in the flexors. For example, it may be used in comatose patients for arousal and to initiate a motor response. - In normal life the flexor withdrawal and crossed extension may utilize similar circuitry as locomotion (walking)

Answer 55

To organize patterns for coordinated movement

Question 56

What flexor withdraw/crossed extension reflex support the following: Flex away from the stimulus but also maintain body support and positioning.

Answer 56

To allow for rapid protection from painful or damaging stimuli

Question 57

What type of reflex involves fast cutaneous sensory stimulation such as fast "icing", brushing, or stroking to the skin will cause the muscle underneath the stimulated area to contract? In this case, the cutaneous afferent excites the homonymous muscle. Therefore, one would want to avoid using these types of stimuli over a spastic muscle. However, these techniques would be appropriate for a hypotonic muscle. Other forms of cutaneous stimulation, such as maintained heat, cause the muscle under the skin that is heated to relax or be inhibited. This might be a good technique to apply to the skin over a spastic muscle.

Answer 57

Cutaneous Surface Stimulation