Introduction To Motor Control
Motor control evolves from a complex set of neutral, physical and behavioral processes that govern posture and movement
In motor learning and motor skill development, interaction and exploration of the environment facilitate the acquisition of motor skills, with practice and feedback playing crucial roles in defining the process.
The development of motor programs is guided and shaped by using sensory information.
An abstract representation that, when initiated, results in the production of a coordinated movement sequence defines a motor program.
for example : the complex neural circuitry in the spinal cord known as central pattern generators that control locomotion and gait
Generalized motor programs contain information about order of events, the timing of events, overall force of contractions, and the muscle or limb used in movements
An idea or plan for purposeful movement, comprising several component motor programs, constitutes a motor plan.
A motor memory involves the recall of motor programs or subroutines and include information on
- initial movement conditions
- sensory parameters (how the movement felt, looked, and sounded)
- specific movement performance parameters
- outcome of the movement
System theory, a distributed model or motor control, defines the cooperative actions of multiple systems that accommodate movement to match the specific demands of the task and the environment.
The central concept is that many systems interact to produce coordinated movement, not just the nervous system
The actions of the central nervous system (CNS) acquire and modify motor skills through processes of motor learning.
Practice or experience leads to relatively permanent changes in the capability for skilled behavior, defining motor learning as a set of internal processes.
Components of Motor Examination
The examination of motor function involves three component
- patient history
- a review of relevant systems
- specific tests and measures are used that allow formulation of the diagnosis, prognosis, and POC.
During the patient/client history, the healthcare provider gathers information on general demographics, social history, employment/work, living environment, general health status, social health habits, family history, medical surgical history, current condition or chief complaint, functional status, and activity level.
A system review serves a purpose of screening examination that is a brief or limited examination of body system.
A physical therapist then can use this information to identify potential problems that will require more extensive testing.
Elements of Motor Function Examination
Some important elements of motor function examination are
- tone
- hypertonia
- spasticity
- rigidity
- decorticate and decerebrate rigidity
- dystonia
- hypotonia
TONE
The resistance of muscle to passive elongation or stretch defines tone as a state of slight residual contraction in normally innervated, resting muscle, or steady-state contraction.
A number of factors influence tone, including:
- physical inertia
- intrinsic mechanical-elastic stiffness of muscle and connective tissue
- spinal reflex muscle contraction
Some clinicians prefer to use the term “postural tone” to describe a pattern of muscular tension that exists throughout the body and affects groups of muscles.
Tonal abnormalities categorize as hypertonia, hypotonia, and dystonia.
HYPERTONIA
Spasticity
Spasticity characterizes a motor disorder where there’s a velocity-dependent increase in muscle tone with increased resistance to stretch.
the larger and quicker the stretch the stronger the resistance of spastic muscle.
During rapid movement, the limb may initially exhibit high resistance, followed by a sudden inhibition or letting go in response to a stretch stimulus, which is termed as the clasp-knife response.
Chronic spasticity associates with contracture, abnormal posturing and deformity, functional limitations, and disability.
Spasticity arise from injury to descending motor pathways from the cortex or brainstem, producing disinhibition of spinal reflexes with hyperactive tonic stretch reflexes or a failure of reciprocal inhibition.
A clonus characterizes cyclical, spasmodic alternation of muscular contraction and relaxation in response to sustained stretch of a spastic muscle.
Rigidity
Rigidity embodies a state of heightened muscle tension, manifesting as stiffness and resistance to movement, regardless of how swiftly one moves
it is associated with lesions of basal ganglia and is seen in parkinson’s disease
rigidity is the result to excessive supraspinal drive acting on alpha motor neurons; spinal reflex mechanism are typically normal
Leadpipe rigidity refers to a constant increase in muscular tone and stiffness of affected muscles
Cogwheel rigidity refers to the coexistence of rigidity with tremor, producing stiffness and a ratchet-like jerkiness when manipulating a body part.
DYSTONIA
it is a prolonged involuntary movement disorder characterized by twisting or writing repetitive movements and increased muscular tone
Dystonia posturing refers to sustained abnormal postures caused by co-contraction of muscles that may last for several minuted or hours, or may be permanent
A CNS lesion, commonly in the basal ganglia, results in it and it can be inherited, associated with neurodegenerative disorders (Wilson’s disease, Parkinson’s disease), or metabolic disorders.
Dystonia can affect only one part of the body as seen in spasmodic torticollis
segmental dystonia affects two or more adjacent areas.
HYPOTONIA
Hypotonia and Flaccidity are terms used to define abnormally low tone or absent muscular tone
Limbs become easily movable (floppy) due to reduced resistance to passive movement and dampened or absent stretch reflexes
Lower Motor Neuron Syndrome results from lesions that affect the anterior horn cell and peripheral nerve
for example : peripheral neuropathy, cauda equina lesion, radiculopathy.
it produces symptoms of decreased or absent tone, decreased or absent reflexes, paresis, muscle fasciculation and fibrillations with denervation, and neurogenic atrophy