Module 10 - Motor System

What is the flow of information between components of the motor system?

1. Decide to move - prefrontal cortex

2. Plan and regulate movements - motor planning areas, cerebellum, basal ganglia

3. Initiate descending signal - primary motor cortex

4. Carry signal through spinal cord - UPNs

5. Transmit signal to skeletal muscles - LMNs

6. Muscle contraction - skeletal muscles

What is the function of the lateral corticospinal tract?

• Most important tract for voluntary movement; normal movement

• Fractionation of movement and distal limb movement

What is muscle tone?

Unconscious resistance to stretch in resting muscle

Normal = minimal resistance to passive stretch

Types: flaccidity, hypotonicity, hypertonicity → spasticity and rigidity

What is flaccidity?

Complete loss of muscle tone

What is hypertonicity and hypotonicity?

Hypertonicity: abnormal increase in muscle tone

Hypotonicity: abnormal decrease in muscle tone

What is spasticity?

Velocity dependent, moving affected limb quickly; present in flexion or extension (not both)

What is rigidity?

Velocity independent, difficulty moving limb on both sides of a joint (flexion and extension)

What is the clasp-knife phenonmenon?

Severe spasticity at a joint that suddenly relaxes with sustained stretch

What is clonus?

Rhythmic contraction of spastic muscle, usually caused by quick stretch or light touch

What are the functions of the cerebellum?

• Nonconscious coordination of movement, maintenance of posture, and equilibrium; coordinate movement of eyes and body

• Integrates information, compares intended movements with actual movement, and makes corrections as needed

• Damage: ataxia (lack of coordination)

What are the functions of the basal ganglia?

• Precise regulation of movement

• Balancing inhibition and disinhibition to allow for fine tuning of muscle contraction, muscle force, multi-joint movements, and sequencing of movements

What is cogwheel and lead pipe?

Cogwheel: Jerky, alternating movements

Lead-pipe: continuous, sustained resistance

What are the common causes of upper motor lesions?

• Cerebral pasly

• SCI

• Stroke

• TBI

• Mulitple sclerosis

• Brain or spinal cord tumors

What are the common causes of lower motor lesions?

• Trauma

• Infection

• Chronic neuropathy

• Tumors in PNS

• Guillain Barre

What are the signs of an upper motor neuron lesion?

• Paresis

• Hyperreflexia

• Hypertonia

• Disuse atrophy (loss of muscle mass)

What are the signs of lower motor neuron lesions?

• Paralysis

• Hyporeflexia

• Hypotonia

• Denervation atrophy

What is the Romberg Test?

• Standing balance test; eyes open and eyes closed

• Inability to maintain balance with eyes open and closed = cerebellar ataxia → damage to cerebellum

• Inability to maintain balance with eyes closed = sensory ataxia → damage to somatosensory nerves and tracts

• Sense of vibration is intact with cerebellar ataxia and impaired with sensory ataxia

What is truncal ataxia?

Difficulty maintaining sitting and standing balance; unable to walk on toes or hells and/or tandem

What is an ataxic gait?

Wide-based, unsteady, staggering gait

What are the different types of limb ataxia?

Limb movement/fine motor is affected

• Dysdiadochokinesia: inability to perform rapid alternating movements Ex: nose to finger

• Movement decomposition: moving each joint separately during an activity

• Dysmetria

• Action (intention) tremor; oscillations : shaking of limb during voluntary movement 

What are the neurotransmitters involved in normal function of the basal ganglia?

• Glutamate: input;excitatory → stimulates activity inside the basal ganglia

• GABA: output; inhibitory → to the thalamus

• Dopamine: internal; both excitatory and inhibitory 

• Basal ganglia is dependent on dopamine which is produced by substantia nigra (normal function of basal ganglia)

What is the concept of disinhibition?

• Default is inhibition

• Disinhibition decreases inhibition to increase movement → just right movement; allows for fine tuning of neural output

What is Parkinson’s Disease?

• Basal ganglia motor disorder

• Interferes with voluntary and automatic movements as a result of DA and ACh producing cells

• Types: postural instability gait difficulty and tremor-dominant

What is Postural Instability Gait Difficulty?

• Muscular rigidity (cogwheel rigidity)

• Postural unsteadiness

• Difficulty standing from sitting

• Abnormal gait

• Mask like facial expression

• Resting tremor

• Freezing gait (getting to door and stopping)

• Parkinsons dementia, depression, autonomic dysfunction

What is Tremor-Dominant?

• Resting and action tremors

• Rigidity and slowing of movement are relitively mild

• Slower progression than PIGD

What is Huntington’s Disease?

• Progressive degneration of striatum and cerebral cortex → diminished GABA, increased dopamine, decreased inhibition from basal ganglia, and causes excessive motor output

• Signs: chorea (involuntary, jerky, rapid movements) and dementia, depression, and behavioral changes

What is Amyotrophic Lateral Sclerosis (ALS)?

• Progressive destruction of bilateral UMNs and LMNs

• Paresis, paralysis, spasticity, loss of fine motor control, muscl atrophy, hyporeflexia, dysphagia, dysarthria, dysphonia

• Spreads everywhere; sensation remains intact