Week 4 Content

A collection of vocabulary flashcards related to motor control concepts and mechanisms, based on the lecture notes.

Primary Motor Cortex area number and location

Area 4 or M1, located in the pre-central gyrus

Primary motor cortex function

Houses upper motor neurons, executes commands to motor neurons

Pre-Motor Cortex

Receives input from sensory areas, role in planning movement related to sensory input, spatial guidance of movement

Supplementary Motor Cortex

Involved in sequencing movement by feeding motor instructions to primary motor cortex, active during mental rehearsal of coordinated movements

Reflexes

Involuntary, rapid, stereotyped movements initiated by external stimuli

Rhythmic motor patterns

Combines voluntary and reflexive acts, initiated and terminated voluntarily but become reflexive once initiated

Voluntary movements

Complex and purposeful actions that can improve with practice, initiated at the cerebral cortex level, requires planning, programming and execution

Stepping pattern generator (SPG)

Adaptable networks of spinal interneurons that activate lower motor neurons, activated when conscious signal is sent from brain to initiate walking

Output of SPG

Adapted to task, environment, stage of walking cycle

Motor Control

Ability to regulate mechanisms essential to movement, relies on sensory information to alter motor patterns according to external stimuli

Proprioception

Sensory feedback from muscle spindles and other receptors that provides information about limb position and movement

Visual system

Provides information about visual cues for movement, guides movement

Vestibular system

Input from inner ear receptors, provides information about head position relative to gravity and during movement

Hierarchical model

A model where organization control is top down, suggests higher centers control lower centers

Hierarchial model limitations

Cannot explan dominance of reflex behaviour in certain situations (withdrawal reflex), must be cautious about assumptions that low level behaviours are immature vs high level behaviours are mature

Dynamical systems theory (DST)

Views body as a mechanical system subject to external and internal forces, see variability necessary for function

Degrees of freedom in DST

Human beings have many degrees of freedom that need to be controlled such as joints, human movement has inherit variability

Optimal variability in DST

Provides for flexible, adaptive strategies and allows adjustments to environment, too little = lead to injury, too much = impaired movement performance, small amount = indicates highly stable behaviour

Limitations of DST

Can presume nervous system has less important role, gives mathematical formulas and principles of body mechanics more dominant role, understanding application or relevance to clinical practice can be difficult

Ecological theory

Suggests motor control evolved to cope with environmental demands and requires perceptual information to perform within specific environment

Ecological theory limitations

Gives less acknowledgement to structure and function of nervous system

Need to recognise about motor control theories

Movement emerges from interaction between individual, task and environment in which task is occurring, results from dynamic interplay between perception, cognition and action systems

Upper Motor Neurons (UMN)

Neurons with cell bodies in primary motor cortex or brainstem, responsible for sending motor commands

UMN pathways originating in cortex

Corticospinal tract and corticobrainstem tract

UMN pathways originating from brainstem

Vestibulospinal, reticulospinal, rubrospinal, tectospinal

Corticospinal Tract

Originates from the primary motor cortex, involved in voluntary and skilled movements of limbs, major role in fractionated movements

Corticospinal tract pathway

Primary motor cortex, posterior limb of internal capsule, pyramidal decussation, lateral column of spinal cord, anterior horn of spinal cord, LMN of limbs

Corticobrainstem tract

Originates from lateral aspect of primary motor cortex, contralateral fibres decussate at level of brainstem where cranial cell bodies are, facilitates voluntary control of all motor cranial nerves

Innervation of motor cranial nerves via CBT

Most cranial nerves receive bilateral innervation except VII (only lower half of face) and XII

Reticulospinal tract

Reflexive head movement response to visual or auditory input

Vestibulospinal tract

Arises from vestibulocochlear nerve nucleus to help control neck and upper back muscles, aids in balance

Rubrospinal tract

Areas from red nucleus in midbrain, minimal contribution to upper limb extensor muscles

Tectospinal tract

Originates from superior colliculus of midbrain, mediates reflex postural movements of the head, neck, and upper trunk in response to sudden visual or auditory stimuli

Lower Motor Neurons (LMN)

Neurons that directly transmit signals to skeletal muscles, causing contraction, only neurons that convey signals to skeletal muscle fibres

Pathway of LMN depending on where cell body lies in CNS

Cell body in ventral horn of spinal cord = axons travel with peripheral nerves, cell body in brainstem = axons travel with cranial nerves

Alpha LMN

Large cell body, large myelinated axon, project to extrafusal muscle fibres

Gamma LMN

Medium sized myelinated axons, project to intrafusal muscle fibres in muscle spindles

Motor unit

One alpha LMN and all muscle fibres it innervates, when one neuron fires all muscle cells stimulated by the neuron contract

Large vs small motor unit

Large motor unit = increased muscle fibres for gross control, small motor unit = decrease muscle fibres for precise control

Large vs small cortical tissue (+relationship to motor unit)

Large cortical tissue = more UMN cell bodies = small motor unit for precise control, small cortical tissue = less UMN cell bodies = large motor unit for gross control

UMN lesion

Paralysis or paresis, absent atrophy or resulting from disuse, hyperreflexia or abnormal reflexes, babinski’s reflex present, hypertonia - spasticity or rigidity, fasciculations and fibrillations absent

LMN lesion

Paralysis or paresis, atrophy may be marked, hyporeflexia or areflexia, babinski’s reflex absent, hypotonia or flaccidity, fasciculations and fibrillations may be present

Decerebrate rigidity in UMN injury

Rigid extension of limbs and trunk, internal rotation of upper limbs, planterflexion

Decorticate rigidity in UMN injury

Rigid flexed upper limbs, extended neck and lower limbs, plantarflexion

Reflexes

Involuntary motor response to external stimulus, can be protective, can integrate motor movements to function in coordinated manner, can be monosynaptic or polysynaptic

Phasic stretch reflex

Muscle contraction in response to quick stretch

Cutaneous reflex

Afferent information from skin, muscles and or joints can elicit variety of withdrawal movements modulated in spinal cord

Gag reflex

Protective mechanism to prevent unwanted entry of foreign body to respiratory passage, receives sensory input form IX, motor response from X

Abnormal reflexes = Babinski's sign

Extension of great toe with stimulation of lateral sole of foot, considered normal for new born babies but abnormal in adults

Abnormal reflexes - areflexia

Absence of reflexes

Abnormal reflexes - Hyperreflexia

Increased or overactive reflexes due to excessive LMN response to afferent input

Abnormal reflexes - Hyporeflexia

Decreased reflexes due to lower motor neuron dysfunction.