Ch 13 & 14 Motor Systems and Spinal Region Neuroscience Exam 2

Flashcards for lecture notes on motor control and spinal regions.

Skeletal Muscle Structure

Skeletal muscle is excitable, contractile, extensible, and elastic.

Skeletal Muscle Function

Individual muscle fibers consist of myofibrils arranged parallel to the long axis of the muscle fiber.

Muscle Contraction Mechanism

Muscle contraction is produced when actin slides relative to myosin. Repeated attachement of myosin head on actin, swiveling, and detachment of myosin heads produce contraction of the muscle

Muscle Contraction

The shortening of a muscle.

Muscle Contracture

Stuck in a position; can't move joint through full ROM; can't elongate.

Causes of Muscle Contractures

Coma, Stroke, Immoblization, and Upper Motor Lesions

Sacromeres in Muscle Contractures

Disappear from the ends of myofibrils when in shortened position or add sacromeres when immobile in a lengthened position

Cocontractions

Simultaneous contraction of agonist and antagonist muscles.

Cocontractions are normal when…

meeting a movement goal

Cocontractions are compensatory when..

used to compensate for weakness

Cocontractions are pathologic when….

in cerebral palsy, contract the agonist, anatagonist, and synergists that interfere with movement

Alpha Motor Neurons

Axons project to extrafusal skeletal muscles; have large cell bodies and large myelinated axon; release enough Ach to all of the muscle fibers it innervates

Gamma Motor Neurons

Consist of medium-sized myelinated axons; axons project to intrafusal fibers in muscle spindle

Alpha-Gamma Coactivation

Maintains stretch of the muscle spindle by contracting the ends of the intrafusal fibers when the extrafusal fibers contract; maintain the sensitivity of the muscle spindle

Myotome Levels-Arm Abd.

Suprascapular Nerve and Axillary Nerve; C5

Myotome Levels-Elbow Flex.

Musculocutaneous Nerve and Radial Nerve; C6

Myotome Levels-Elbow Extension

Radial nerve; C6 & C7

Myotome Levels-Wrist Flex.

Median and Ulnar Nerve; C7

Myotome Levels-Wrist Extension

Radial Nerve; C6,C7,C8

Myotome Levels-Finger movements

Median, Ulnar, Radial Nerve; C8

Myotome Levels-Thumb Movements

Median, Radial, Ulnar; C8

Myotome Levels- Hip Flex.

Lumbar Spinal Nerves, Femoral; L2

Myotome Levels-Hip ext.

Inferior gluteal nerve; S1

Myotome Levels- Knee flex.

Sciatic Nerve; L5 and S1

Myotome Levels- Knee ext.

Femoral Nerve; L3 and L4

Myotome Levels-Ankle DF

Sciatic Nerve and Peroneal; L4 and L5

Myotome Levels-Ankle PF

Sciatic Nerve and Tibial Nerve; S1

Spinal Cord Mechanisms

Spinal mechanisms organize and synchronize muscle activation.

Neural communication within the spinal cord contributes to coordination of…

movement

Types of Mechanisms of Spinal Coordination

Recipirocal Inhibition, Muscle Synergies, and Proprioceptive Input, and stepping pattern generators

Reciprocal inhibition

muscle contraction

muscle spindles sent signals to SC

signal activates interneurons

inhibits MNs of the antagonist

Muscle Synergies

Pattern of activation across muscles.

Proprioceptive Input

Input from joint capsules, ligament receptors, muscle spindle receptors, and GTOs.

Stepping Pattern Generators

adapatable networks of spinal movements that active MNs to elicit alternating flex./ext. of hips and knees; each lower limb has its own; different input adjusts timing, facilitates transition from stance to swing phase of gait, and reinforces muscle activation

Spinal Reflexes

Involuntary motor response to an external stimulus; clinical examination provides info about the peripheral CNS.

Types of Spinal Reflexes

phasic stretch reflex, cutaneous reflex, recirpocal inhibition

Phasic Stretch Reflex

Muscle contraction in response to quick stretch; quick muscle stretch activates signal from muscle spindles to alpha MNs of the same muscle

Withdrawal Reflex

Cutaneous stimulation can elicit reflexive movements; circuitry responsible for the withdrawal reflex is located within the spinal cord

Reciprocal inhibition

muscle contraction

muscle spindles to SC

signal activates interneurons

inhibit the MNs of the antagonist

Involuntary muscle contraction

muscle cramps, fasciuluations, myoclonus, fibrillations, and tremors

Muscle Cramps

Severe, painful muscle contractions lasting seconds to minutes.

Fasciculations

Quick twitches of all muscle fibers in a single motor unit.

Myoclonus

Brief, involuntary contraction of a muscle or group of muscles.

Fibrillations

Contractions of single muscle fibers.

Tremors

involuntary, rhymthmic movements of a body part; types: resting, action, physiologic

Sensory Input in Motor Control

Need sensation to learn new movements; relies on somatosensation and proprioception in absence of vision; we are a visually dominant species; sensation necessary to learn new movements and keeps well learned movements on track

Gross Movements/Postural Control

Occur automatically without conscious effort;

Motor tracks involved with postural control and gross movements…

medial motor tracts

Medial Motor Tracks

Reticulospinal Tract

Medial and Lateral Vestibulospinal Tract

Medial Corticiospinal Tract

Reticulospinal Tract

Facilitates bilateral MN innervating postural and gross limb movement of the muscles throughout the body

Medial and Lateral Vestibulocospinal Tract

med: receives info. about head movement and position from vestibular apparatus

lat: responds to gravity info. from the vestibular apparatus

Medial Corticospinal Tract

has a direct connection from cerebral cortex to the spinal cord; controls axial movement

Isolated distal limb movements

selective motor control; activate individual muscles independently.

Motor tracks involved with isolated distal limb movements….

lateral motor tracks

Lateral Motor Tracks

Lateral Corticospinal Tract

Rubrospinal Tract

Lateral Corticospinal Tract

starts in the motor planning area of the primary motor cortex; through internal capusle, cerebral peduncle, and anterior pons, decussates in the pyramids of the lower medulla, to the SC then specific muscles

Fractionated Movement

Ability to produce isolated, independent movements of individual body parts.

What areas are responsible for fractioned movement?

primary motor cortex and lateral corticospinal tract

Hemiplegia

Paralysis affecting one side of the body.

paraplegia

affects the body below the arms

quadpleiga

affects all four limbs

Abnormal Reflexes

Babinski’s sign, stretch reflex hypereflexia, clonus

Babinski’s sign

ext. of the great toe and often accompanied by fanning of other toes

stretch reflex hyperreflexia

phasic stretch hyperreflexia; high velocity stretch by midrange; loss of inhibitory cortciopsinal input combined with enhanced excitability of MNs and interneurons which causes excessive MN response to afferent input from stretch receptors

Clonus

Interferes with gait; involuntary, repeating rhythmic muscle contraction; unsustained and sustained clonus

Myoplasticity

Adaptive changes in muscle in response to changes in neuromuscular activity level and prolonged positioning.

Myoplasticity Contributing Factors and Impacts on Movement

mechanical loading, unloading disuse, neural input, hormonal influence, nutrition, age, genetics, disease, satellite cell activity, activity type

abnormal muscle tone

flaccidity, hypotonia, hypertonia, spasticity, rigidity

muscle tone

resistance to stretch in resting muscle

Flaccidity

Complete lack of resistance, caused by MN lesions/developmental disorders/acute ML lesions.

hypotonia

abnormally low resistance; aused by MN lesions/developmental disorders/acute ML lesions.

Hypertonia

Increased resistance to passive movement.

spasticity

velocity-dependent hypertonia; abnormally high resistance that increases with faster movemeent

Rigidity

Resistance to passive movement remains constant regardless of speed or force application.

Decerebrate Rigidity

Rigid extension of upper limbs.

Decorticate Rigidity

Flexed upper limbs, extended neck, lower limbs, and plantarflexion.

Signs of Motor Tract Lesions

Paresis, paralysis, abnormal reflexes, myoplasticity, muscle atrophy, loss of fractionated movements.

common causes of motor tract lesions

stroke, tbi, sci, ms, als, cp, tumors, infections, neurodegernative disease, vascular malformations, neuropathy/periphereal nerve injury

Denervation Atrophy

Complete denervation of skeletal muscle produces severe muscle atrophy because frequent neural stim. even at level inadequate to prodcue muscle contraction is essential for the health of skeletal muscle

Paresis

Weakness; occurs in both upper motor neuron (UMN) and lower motor neuron (LMN) lesions.

Paralysis

Complete loss of voluntary contraction; occurs in both UMN and LMN lesions.