Motor System 2.0 Flashcards
Motor unit = ?
Motor System
Motor Unit: An alpha motor neuron AND the muscle fibers it innervates.
Types of Muscle Fibers
- Extrafusal fibers are innervated by = ?
- Intrafusal fibers are innervated by = ?
Motor System
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
Two types of lower motor neurons = ?
Motor System
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.
Upper Motor Neurons
Four UMN Medial tracts = ?
Motor System
Upper Motor Neurons - Medial tracts:
- Medial corticospinal tracts = Neck, shoulder and trunk muscles
- Reticulospinal tract = Bilateral postural muscles and gross limb movements
- Lateral vestibulospinal tract = Postural muscles
- Medial vestibulospinal tract = Neck muscles
Upper Motor Neurons
Two UMN Lateral tracts = ?
Motor System
Upper Motor Neurons - Lateral tracts:
- Lateral corticospinal tracts = Fine distal movements
- Rubrospinal tract = Extension of wrist and fingers
Upper Motor Neurons
UMN Lateral tracts = ?
Motor System
Upper Motor Neurons - Lateral tracts:
- Lateral corticospinal tracts = Fine distal movements
Lower Motor Neurons
What are the four LMN pools located in the ventral horn/anterior horn = ?
Motor System
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
Lower Motor Neurons
Posteriorly located pools in ventral horn innervate = ?
Motor System
(LMN) Posteriorly located pools in ventral horn innervate = Flexors
Lower Motor Neurons
Laterally located pools in ventral horn innervate = ?
Motor System
(LMN) Laterally located pools in ventral horn innervate = Distal Muscles
Lower Motor Neurons
Anteriorly located pools in ventral horn innervate =
Motor System
(LMN) Anteriorly located pools in ventral horn innervate = Extensors
Lower Motor Neurons
Medially located pools in ventral horn innervate = ?
Motor System
Medially located pools in ventral horn innervate = Axial and Proximal Muscles
Upper Motor Neurons
Corticobrainstem tract fibers arise in the cerebral cortex then project to ?
Motor System
Upper Motor Neurons
- Corticobrainstem tracts:
- Fibers arise in the cerebral cortex then project to the cranial nerve nuclei in the brainstem.
From Decision → Skeletal Muscles
Decision
↓
(1) = ?
↓
(2) =?
↓
(3) =?
↓
(4) =?
↓
(5) =?
↓
Skeletal Muscles
Motor System
(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.
Signs of Motor Neuron Lesions = ?
Motor System
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
Signs of Motor Neuron Lesions
Paresis vs. Paralysis
Motor System
- 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
Muscle Atrophy
Disuse atrophy vs. Denervation
Motor System
- 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.
“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
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”
Abnormal Muscle Tone
hypertonia vs. hypotonia
BONUS: Flaccidity = ?
Motor System
- 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
Involuntary Muscle Contractions
Fasciculations vs. Fibrillations
Motor System
- 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.
Abnormal Muscle Tone
Hypotonia or flaccidity can be caused by = ?
Motor System
- LMN lesions
- ACUTE UMN lesions like stroke, SCI
hypotonia will usually be temporary
Abnormal Muscle Tone
Hypertonia can be caused by = ?
Motor System
- 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.
Velocity-Dependent hypertonia limits = ?
Motor System
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.
What is the Clasp-Knife response = ?
Motor System
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
Normal Reflex Order
*click to view**
Motor System
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.
Abnormal Reflexes
Four most common abnormal reflexes are = ?
Motor System
Four most common abnormal reflexes are:
- Hyperreflexia (UMN)
- Clonus (UMN)
- Babinski Sign (UMN)
- Hyporeflexia (LMN)
What’s the difference (B & C) ?
Motor System
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.
- 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.
Involuntary, repeating, and rhythmic muscle contractions = ?
Motor System
- 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.
Extension of the great toe, accompanied by fanning of the other toes = ?
Motor System
Babinski Sign (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.
Myoplasticity = ?
UMN or LMN
Motor System
Myoplasticity = 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
Common Impairments in UMN Lesions = ?
Motor System
Common Impairments in UMN Lesions:
- Abnormal synergy
- Abnormal co-contraction
- Hyperreflexia
- Muscle contracture
- Hypertonia
- Muscle overactivity
- Muscle tone
- Myoplasticity
- Paresis
- Spasticity
Common Impairments in UMN Lesions
Abnormal synergy = ?
Motor System
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.
Common Impairments in UMN Lesions
Abnormal co-contraction = ?
Motor System
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.
Common Impairments in UMN Lesions
Hyperreflexia = ?
Motor System
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.
Common Impairments in UMN Lesions
Muscle contracture = ?
Motor System
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.
Common Impairments in UMN Lesions
Hypertonia = ?
Motor System
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}.
Common Impairments in UMN Lesions
Muscle overactivity = ?
Motor System
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.
Common Impairments in UMN Lesions
Muscle tone = ?
Motor System
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.
Common Impairments in UMN Lesions
Myoplasticity = ?
Motor System
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.
Common Impairments in UMN Lesions
Myoplasticity = ?
Motor System
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.
Common Impairments in UMN Lesions
Paresis or Paralysis= ?
Motor System
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.
Common Impairments in UMN Lesions
Spasticity = ?
Motor System
Common Impairments in UMN Lesions - Spasticity:
- Neuromuscular overactivity secondary to MT lesion
Progressive neurodegenerative disease that affects both UMN and LMNs = ?
Motor System
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
