Motor System Impairments Flashcards
Motor System Impairments - what are the primary motor system impairments?
- Motor Weakness [paresis]
- Muscle tone abnormalities
- Coordination problems
Motor Weakness:
- strength = generate sufficient force for posture/movement
- weakness = inability to generate normal levels of force
Motor System Impairments - describe some neural factors that influence motor weakness:
- Decreased number of motor units (MUs) recruited
- Predominantly type 1 MUs recruited
- Decreased MU firing rate [remember, firing rate influences Ca and thus muscle force]
Motor Weakness: Paresis
‘Paresis’ results from decreased MU recruitment; difficultly in recruiting or modulating output of motor neurones
Results from lesion/s within descending motor pathways= decreased descending drive
Because of decreased descending drive, including serotonergic/noradrenergic drive to SC
- cant recruit high threshold motor units [remember PICs]
- difficulty modulating firing rate when increasing force
More apparent in distal muscles
Produces peripheral changes in muscle, exacerbates problems
Incorrectly used to believe:
- ST training would cause problems with muscle tone
- no reason to examine, evaluate or treat weakness
[motor weakness seen more in distal segments - distal segments more affected]
Motor Weakness: Treatments:
Biofeedback e.g. Sensory amplitude electrical stimulation over muscles (10s on/10s off)
Functional electrical stimulation [FES]
- applied to wrist extensors for 30min 3x/day to strengthen extensors
- combined with task training of upper extremity [for lifting weight] for 15 min 2x/day to improve hand function
- applied to perineal nerve in hemiplegic patients with foot drop for tib ant muscle during gait.
Muscle Tone Abnormalities:
Muscles tone is characterised by a muscle’s resistance to passive stretch
A certain level of muscle tone is normal
Flaccidity[Spasticity>Rigidity]- hypertonicity
Damage to descending tracts results in increased alpha motor neurone excitability that causes:
- increased muscle tone [enhanced tonic stretch reflex activity; velocity dependent]
- exaggerated tendon jerks [hyper excitability of physical stretch reflexes]
Clinical Term - spasticity
Results in hyperactive stretch reflex, abnormal limb postures, excessive coactivation, clonus and stereotyped movement synergies
Muscle Tone Abnormalities: Rigidity
Another form of hypertonicity
Increased resistance to passive limb movement, not velocity dependent
Predominantly affects flexor muscles of trunk and limbs
Problems with gait, speech, posture, eating
{may result from disinhibition of basal ganglia}
Muscle Tone Abnormalities: Hypotonicity
Decreased stiffness in muscle lengthening
Flaccidity is a total loss of muscle tone
Exhibited by many patients, e.g. Spinocerebellar lesions, Down syndrome.
Muscle Tone Abnormalities: Spasticity
What does altering a patients position do?
Mild spasticity treated with therapeutic ex, splinting and orthotics
Severe spasticity treated with chemodenervation [e.g. Botox], surgery and medications
Ex treatments can be combined with muscle stimulation [high or low freq]
Altered position:
Supine facilitates extensor tone
Prone facilitates flexor tone
Side-lying inhibits effect of asymmetrical tonic neck reflex; facilitates bilateral symmetrical activation
Coordination Problems: Name 2 activation and sequencing problems
Results from disruption of activation, sequencing, timing and scaling of muscle activity
- Flexion synergy of upper extremity in stroke:
Scapular retraction
Shoulder abduction & external rotation
Elbow flexion
Forearm supination
Wrist & finger flexion
2. Extension synergy of lower extremity: Hip extension, addiction & internal rotation Knee extension Ankle plantar flexion & inversion Toe plantar flexion
Coordination Problems: Timing Problems
Initiating problems, slowed movement time, and problems terminating movement. [initiation problems - Reaction time]
Neuromuscular:
- inadequate force generation
- rate of force generation
- insufficient ROM to allow movement
- motivation to move
- abnormal postural control
Cognitive:
- cant recognise command or signal to move
- difficulty recalling and selecting movement plan
- difficulty assembling and initiating plan
Coordination Problems: Name some problems patients have terminating movement:
- inability to stop movement
- inability to change direction
- inability to control appropriate forces of the agonist muscle at end of ROM
- inadequate timing and force generation of antagonist muscle
Coordination Problems: Name the 3 scaling force problems
- Dysmetria = problems judging distance or ROM, cant scale forces appropriately, patients with cerebellar lesions
- Hypermetria = overestimation of force or ROM
- Hypometria = underestimation of force or ROM
Coordination Problems Helped by?
Repetition and practice of functional task specific movement [therapist provides correction feedback]
Weight bearing activity for coordination in lower extremities [e.g. Yoga]
Repetition of timed coordination tasks [e.g. Tai Chi]
Ataxia - definition?
Why is the Cerebellum important ?
Lack of movement coordination, motor dysfunction condition with neurological basis, often involves cerebellum.
Cerebellum important for:
- Planning of a movement
- Control of posture & equilibrium
- Control of smooth limb movement, coordination [compares descending with ascending info]
Ataxia - Cerebellar
May exhibit all of the below:
- Vestibulo cerebellar dysfunction = postural instability, wide stance
- Spino cerebellar dysfunction = ‘drunken sailor’, gait, gaze nystagmus [stare or gaze at object]
- Cerebrospinal cerebellar dysfunction = intention, tremor, slurred speech, unpredicatable and inconsistent hand writing.
