Motor System 2.0

Question 1

Motor unit = ?

Motor System

Answer 1

Motor Unit: An alpha motor neuron AND the muscle fibers it innervates.

Question 2

Types of Muscle Fibers

• Extrafusal fibers are innervated by = ?
• Intrafusal fibers are innervated by = ?

Motor System

Answer 2

Types of Muscle Fibers

(1) Extrafusal:

• Constitute majority of muscle fiber
• Innervated by α motorneuron
• Used to generate force

(2) Intrafusal:

• Encapsulated in sheaths, forming muscle spindles that run parallel to extrafusal muscle fiber.
• Innervated by Υ motor neuron
• Too small to generate significant force
• No or few actin/ myosin filaments
• Innervated by sensory and motor fibers

Question 3

Two types of lower motor neurons = ?

Motor System

Answer 3

Two Types of Lower Motor Neuron’s

(1) Alpha:

• Axons of alpha motor neurons project to extrafusal skeletal muscle
• Normally, an alpha motor neuron releases enough ACh that all of the muscle fibers it innervates contract.

(2) Gamma:

• Axons of gamma motor neurons project to intrafusal fibers in the muscle spindle.

Question 4

Upper Motor Neurons

Four UMN Medial tracts = ?

Motor System

Answer 4

Upper Motor Neurons - Medial tracts:

1. Medial corticospinal tracts = Neck, shoulder and trunk muscles
2. Reticulospinal tract = Bilateral postural muscles and gross limb movements
3. Lateral vestibulospinal tract = Postural muscles
4. Medial vestibulospinal tract = Neck muscles

Question 5

Upper Motor Neurons

Two UMN Lateral tracts = ?

Motor System

Answer 5

Upper Motor Neurons - Lateral tracts:

1. Lateral corticospinal tracts = Fine distal movements
2. Rubrospinal tract = Extension of wrist and fingers

Question 6

Upper Motor Neurons

UMN Lateral tracts = ?

Motor System

Answer 6

Upper Motor Neurons - Lateral tracts:

• Lateral corticospinal tracts = Fine distal movements

Question 7

Lower Motor Neurons

What are the four LMN pools located in the ventral horn/anterior horn = ?

Motor System

Answer 7

Lower Motor Neurons

- LMN pools are groups of cell bodies in the spinal cord whose axons project to a single muscle.

• LMN pools located in the ventral horn/anterior horn

- Actions of these pools are arranged in the order:

• Medially located pools innervate axial and proximal muscles
• Laterally located pools innervate distal muscles
• Anteriorly located pools in ventral horn innervates extensors
• Posterior pools innervate flexors

Question 8

Lower Motor Neurons

Posteriorly located pools in ventral horn innervate = ?

Motor System

Answer 8

(LMN) Posteriorly located pools in ventral horn innervate = Flexors

Question 9

Lower Motor Neurons

Laterally located pools in ventral horn innervate = ?

Motor System

Answer 9

(LMN) Laterally located pools in ventral horn innervate = Distal Muscles

Question 10

Lower Motor Neurons

Anteriorly located pools in ventral horn innervate =

Motor System

Answer 10

(LMN) Anteriorly located pools in ventral horn innervate = Extensors

Question 11

Lower Motor Neurons

Medially located pools in ventral horn innervate = ?

Motor System

Answer 11

Medially located pools in ventral horn innervate = Axial and Proximal Muscles

Question 12

Upper Motor Neurons

Corticobrainstem tract fibers arise in the cerebral cortex then project to ?

Motor System

Answer 12

Upper Motor Neurons

- Corticobrainstem tracts:

• Fibers arise in the cerebral cortex then project to the cranial nerve nuclei in the brainstem.

Question 13

From Decision → Skeletal Muscles

Decision
↓
(1) = ?
↓
(2) =?
↓
(3) =?
↓
(4) =?
↓
(5) =?
↓
Skeletal Muscles

Motor System

Answer 13

(1) Neural activity begins with a decision made in the anterior part of the frontal lobe.

(2) Next, motor planning areas are activated, followed by control circuits.

(3) Control circuits, consisting of the cerebellum and basal ganglia, regulate the activity in upper motor neuron tracts.

(4) Upper motor neuron tracts deliver signals to spinal interneurons and lower motor neurons (LMNs).

(5) LMNs transmit signals directly to skeletal muscles, eliciting a contraction.

Question 13

Signs of Motor Neuron Lesions = ?

Motor System

Answer 13

Signs of Motor Neuron Lesions:

• Paresis
• Paralysis
• Involuntary muscle contractions
• Muscle atrophy
• Abnormal muscle tone
• Abnormal reflexes
• Disturbances of movement efficiency and speed
• Impaired postural control

Question 14

Signs of Motor Neuron Lesions

Paresis vs. Paralysis

Motor System

Answer 14

• Paresis is the partial loss of voluntary contraction.
• Paralysis is the complete loss of voluntary contraction (such as complete spinal cord injury - SCI).
• BOTH UMN and LMN

Question 14

Muscle Atrophy

Disuse atrophy vs. Denervation

Motor System

Answer 14

• Disuse atrophy is the result of a lack of muscle use (UMN).
• Denervation of skeletal muscle produces the most severe atrophy, because frequent neural stimulation, even at a level inadequate to produce muscle contraction, is essential for the health of skeletal muscle (LMN).

• Atrophy is the loss of muscle bulk.

Question 14

“A motor disorder, characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex as one component of the upper motor neuron (UMN) syndrome” = ?

Motor System

Answer 14

Spasticity - Velocity-Dependent Hypertonia:

• “A motor disorder, characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex as one component of the upper motor neuron (UMN) syndrome”

Question 14

Abnormal Muscle Tone

hypertonia vs. hypotonia

BONUS: Flaccidity = ?

Motor System

Answer 14

- Muscle tone is the resistance to stretch in the resting muscle

- Spasticity = hypertonia (UMN)

• Usually more resistance to stretch in one direction (leads to posturing)

- Hypotonia is an abnormally low resistance to passive stretch (LMN).

Flaccidity is the lack of resistance to passive stretch

• Complete loss of muscle tone
• Initially in UMN and also in LMN

Question 15

Involuntary Muscle Contractions

Fasciculations vs. Fibrillations

Motor System

Answer 15

- Spontaneous involuntary contractions include:

Fasciculations = Quick twitches of muscle fibers of a single motor unit visible on the skin surface (LMN).

Fibrillations (always pathologic) = Brief contractions of single muscle fibers not visible.

• EMG can detect.

• Muscular dystrophy, peripheral nerve injuries, conditions in which muscle fiber regeneration and /or denervation are often or very often present.

Question 16

Abnormal Muscle Tone

Hypotonia or flaccidity can be caused by = ?

Motor System

Answer 16

• LMN lesions
• ACUTE UMN lesions like stroke, SCI

hypotonia will usually be temporary

Question 17

Abnormal Muscle Tone

Hypertonia can be caused by = ?

Motor System

Answer 17

• Chronic UMN lesions

- Velocity-dependent: The amount of resistance to passive movement depends on the velocity of movement.

• Resistance during slow stretch is low, with greater resistance occurring with faster stretch.

Question 18

Velocity-Dependent hypertonia limits = ?

Motor System

Answer 18

Spasticity - Velocity-Dependent Hypertonia:

• Limits joint range of motion, interferes with function, and may cause deformity.

Example:

• Significant bilateral plantarflexor hypertonia may allow only toe-walking because lack of ankle dorsiflexion prevents the heels from touching the ground.

Question 19

What is the Clasp-Knife response = ?

Motor System

Answer 19

Clasp-Knife Response:

• Occurs when a paretic muscle is slowly and passively stretched and resistance drops at a specific point in the range of motion.
• Change in resistance is similar to the opening of a pocketknife.
• The initial strong resistance to opening the knife blade gives way to easier movement.
• Clasp knife phenomenon or response/spasticity

Question 20

Normal Reflex Order

*click to view**

Motor System

Answer 20

Myotatic/ Stretch Reflex/DTRs:

• Whenever a muscle is stretched, excitation of the spindle causes reflex contraction of the muscle.
• Stimulus: stretch of the muscle (mechanical);
• Sensor: spindles
• Involving alpha (and gamma) motor neurons, local circuit interneurons, and afferent somatic sensory input.

Question 21

# Abnormal Reflexes Four most common abnormal reflexes are = **?** ## Footnote Motor System

Answer 21

Four most common abnormal reflexes are: * Hyperreflexia (UMN) * Clonus (UMN) * Babinski Sign (UMN) * Hyporeflexia (LMN)

Question 22

What's the difference (B & C) **?** ## Footnote Motor System

Answer 22

**Hyperreflexia**: * Loss of inhibitory corticospinal input combined with LMN and interneuron development of enhanced excitability results in excessive LMN response to afferent input from stretch receptors. * Excessive muscle contraction occurs when spindles are stretched as a result of excessive firing of the LMNs. ## Footnote * Hyperreflexia may limit walking speed, interfere with positioning, mobility, hygiene, comfort, and sleep. * Positive aspect is that it can intentionally trigger to elicit involuntary muscle contraction during transfers, preventing muscle atrophy.

Question 23

Involuntary, repeating, and rhythmic muscle contractions = **?** ## Footnote Motor System

Answer 23

[**Clonus**](https://app.clinicalpattern.com/neuroexam/p6059/): * Involuntary, repeating, and rhythmic muscle contractions. * Unsustained clonus fades after a few beats, even with maintained muscle stretch. * ***Sustained clonus*** is always pathologic in origin and is produced when a ***lack of UMN control*** allows the activation of oscillating neural networks in the spinal cord.

Question 24

Extension of the great toe, accompanied by fanning of the other toes = **?** ## Footnote Motor System

Answer 24

[**Babinski Sign**](https://app.clinicalpattern.com/neuroexam/p6060/) (UMN): * Babinski’s sign is the extension of the great toe, accompanied by fanning of the other toes. * To test for abnormal reflexes, firmly stroke the lateral sole of the foot, from the heel to the ball of the foot, then across the ball of the foot.

Question 25

Myoplasticity = **?** | *UMN or LMN* ## Footnote Motor System

Answer 25

**[Myoplasticity](https://www.athleticlab.com/myoplasticity-how-muscle-adapts-by-kristen-koltun/#:~:text=Myoplasticity%20is%20the%20ability%20of,Energy%20intake%20refers%20to%20nutrition.)** = The ability of a muscle to change and adapt. * Is an adaptive structural changes within a muscle in response to changes in neuromuscular activity level and to prolonged positioning (**UMN**). * Weak actin myosin bonds * Contractures

Question 26

Common Impairments in UMN Lesions = **?** ## Footnote Motor System

Answer 26

**Common Impairments in UMN Lesions**: * Abnormal synergy * Abnormal co-contraction * Hyperreflexia * Muscle contracture * Hypertonia * Muscle overactivity * Muscle tone * Myoplasticity * Paresis * Spasticity

Question 27

# Common Impairments in UMN Lesions Abnormal synergy = **?** ## Footnote Motor System

Answer 27

Common Impairments in UMN Lesions - **Abnormal synergy**: * Abnormal coupling of movements due to stereotyped coactivation of muscles. An example is shoulder abduction and external rotation combined with elbow flexion when the person is attempting to reach forward. * ***Mechanism*** : Loss of lateral corticospinal fractionation of movement plus loss of cortical inhibition of reticulospinal tracts. Abnormal co-contraction.

Question 28

# Common Impairments in UMN Lesions Abnormal co-contraction = **?** ## Footnote Motor System

Answer 28

Common Impairments in UMN Lesions - **Abnormal co-contraction**: * Temporal overlap of agonist and antagonist muscle contraction. * Cocontraction is normal when learning a new motor skill and when stability is required. * Cocontraction is abnormal only when it interferes with achieving the movement goal. * Abnormal cocontraction is prevalent in spastic cerebral palsy, due to persistence of developmental corticospinal inputs to motor neurons innervating agonist, synergist, and antagonist muscles.

Question 29

# Common Impairments in UMN Lesions Hyperreflexia = **?** ## Footnote Motor System

Answer 29

Common Impairments in UMN Lesions - **Hyperreflexia**: * Excessive reflex response to passive muscle stretch. * Hyperreflexia is caused by reduced descending inhibition of MNs and the subsequent development of MN excessive excitability. * Hyperreflexia often contributes to movement disorders post spinal cord injury and in spastic cerebral palsy. * Hyperreflexia usually does not interfere with functional movement post stroke.

Question 30

# Common Impairments in UMN Lesions Muscle contracture = **?** ## Footnote Motor System

Answer 30

Common Impairments in UMN Lesions - **Muscle contracture**: * Adaptive shortening of muscle, caused by the muscle remaining in ashortened position for prolonged periods of time. * The decrease in length is caused by loss of sarcomeres.

Question 31

# Common Impairments in UMN Lesions Hypertonia = **?** ## Footnote Motor System

Answer 31

Common Impairments in UMN Lesions - **Hypertonia**: * Excessive resistance to stretch of a muscle at rest. * Produced by neural input to muscles (overactive stretch reflex or overactivity of reticulospinal and/or vestibulospinal tracts resulting in active muscle contraction) and/or by changes within the muscle (*myoplasticity* : contracture and weak actin-myosin bonding}.

Question 32

# Common Impairments in UMN Lesions Muscle overactivity = **?** ## Footnote Motor System

Answer 32

Common Impairments in UMN Lesions - **Muscle overactivity**: * Muscle contraction that is excessive for the task. * Caused by excess neural input to the muscle(s}. May be due to reticulospinal tract overactivity, vestibulospinal tract over activity, pain, anxiety, or lack of skill in task performance.

Question 33

# Common Impairments in UMN Lesions Muscle tone = **?** ## Footnote Motor System

Answer 33

Common Impairments in UMN Lesions - **Muscle tone**: * Amount of tension In resting muscle. Muscle tone Is examined passively and Is not an Indicator of ablllty to move actively.

Question 34

# Common Impairments in UMN Lesions Myoplasticity = **?** ## Footnote Motor System

Answer 34

Common Impairments in UMN Lesions - **Myoplasticity**: * Adaptive changes within muscle secondary to a MT lesion and/or prolonged positioning. * Produced by contracture and Increased weak actin-myosin bonding.

Question 35

# Common Impairments in UMN Lesions Myoplasticity = **?** ## Footnote Motor System

Answer 35

Common Impairments in UMN Lesions - **Myoplasticity**: * Adaptive changes within muscle secondary to a MT lesion and/or prolonged positioning. * Produced by contracture and Increased weak actin-myosin bonding.

Question 36

# Common Impairments in UMN Lesions Paresis or Paralysis= **?** ## Footnote Motor System

Answer 36

Common Impairments in UMN Lesions - **Paresis**: * Decreased or lost ability to generate the level of force required for a task. * Occurs in all MT lesions.

Question 37

# Common Impairments in UMN Lesions Spasticity = **?** ## Footnote Motor System

Answer 37

Common Impairments in UMN Lesions - **Spasticity**: * Neuromuscular overactivity secondary to MT lesion

Question 38

Progressive neurodegenerative disease that affects both UMN and LMNs = **?** ## Footnote Motor System

Answer 38

**Amyotrophic Lateral Sclerosis** (ALS): * Condition that affects both UMN and LMNs – patients will have wide range of symptoms * Progressive neurodegenerative disease- most people develop ALS between 40-70 years of age; average age is 55. * ALS - 20% more common in men than women * ALS - 90% of cases occur without family history (sporadic); other 10% - Familial