Motor Control Flashcards
-> Organisation of the nervous system: Compare and contrast the structure of the central, peripheral and autonomic (sympathetic and parasympathetic) nervous systems -> Nervous system disorders: Describe the clinical features and treatment options of central and peripheral nervous system disorders
What are the major descending tracts divided into?
- Pyramidal tracts: Pass through the pyramids of the medulla
- Extrapyramidal tracts: Do not pass through the pyramids of the medulla
What are the 2 pyramidal descending tracts?
- Lateral corticospinal tract
- Anterior corticospinal tract
What is the general path followed by the pyramidal tracts?
- Motor cortex to spinal cord or cranial nerve nuclei in brainstem
What is the function of the pyramidal tracts?
- Voluntary movements of body and face
What is the general path followed by the extrapyramidal tracts?
- Brainstem nuclei to spinal cord
What is the function of the extrapyramidal tracts?
- Involuntary (automatic) movements for balance, posture and locomotion
What type of tracts are the corticospinal and corticobulbar tracts?
- Pyramidal tracts (major descending)
Outline the journey of the corticospinal tract until it divides into the lateral corticospinal tract and the anterior corticospinal tract (8 steps).
- Originate in the cell bodies of the first-order neurons in the primary motor cortex.
- The axons descend via through the cerebral peduncle of the midbrain.
- Through the ventral aspect of the pons to reach the ventral aspect of the medulla.
- At the medulla these fibres bundle together and create swellings known as the pyramids, and the majority of the corticospinal fibers cross over to the opposite side at the level of the caudal medulla, in what’s known as the pyramidal decussation.
- At this level, the corticospinal tract divides into the lateral corticospinal tract, and the anterior corticospinal tract.
- The decussated fibers form the lateral corticospinal tract, while the uncrossed fibers continue as the anterior corticospinal tract.
- The lateral corticospinal tract continues through the contralateral lateral column of the spinal cord, and synapse in the ventral horn on the lower motor neurons.
- The anterior corticospinal tract descends uncrossed within the anterior column, with its fibers decussating only after they reach the desired spinal cord level, where they synapse with lower motor neurons in the ventral horn.
What do the corticospinal tracts do? What are the corticospinal tracts responsible for?
- The corticospinal tract is a motor pathway that carries efferent information from the cerebral cortex to the spinal cord
- It is responsible for the voluntary movements of the limbs and trunk
What is the function of the lateral corticospinal tracts?
- Innervate muscles of the limbs
Where does the corticobulbar tract originate?
- Cell bodies of the upper motor neurones of the motor cortex
What is the function of the anterior corticospinal tracts?
- Supply muscles of the trunks
What is the function of the corticobulbar tract?
- Provides voluntary movements of body and face
What are the 4 extrapyramidal tracts?
- Rubrospinal tract
- Reticulospinal tract
- Tectospinal tract
- Vestibulospinal tract
Where does the vestibulospinal tract originate?
- Originates in vestibular nuclei
- Does not decussate
- Synapses on interneurons in ventral horn of spinal cord
What is the funciton of the vestibulospinal tract?
- Receives info about the position & motion of the head
- Carries motor commands to extensor muscles of trunk & extremities
- Helps maintain balance
Where does the reticulospinal tract originate?
- Originates from reticular formation in pons & medulla
What is the function of the reticulospinal tract?
- Excite or inhibit motor neurones to influence:
- Voluntary movements
- Posture
- Reflexes
Where does the tectospinal tract originate?
- Originates in suprior colliculi
- Decussates
- Synapses on intraneurones in ventral horns of cervical region
What is the function of the tectospinal tract?
- Mediates postural reflexes of head & neck in reticuloendothelial system (RES)
Where does the rubrospinal tract originate?
- Originates from red nucleus in midbrain
- Decussates
- Synapses within interneurons in ventral horn
Where does the rubrospinal terminate?
- Cervical region
What is the function of the rubrospinal tract?
- Regulates flexor & extensor muscle activity in upper limb (produces smoother & more coordinated movement)
What are the negative signs of an upper motor neuron (UMN) lesion (3)?
- Loss of voluntary motor function
- Paresis: graded weakness of movements
- Paralysis (plegia): complete loss of voluntary muscle activity
What are the positive signs of an upper motor neuron (UMN) lesion (5)?
- Increased abnormal motor function due to loss of inhibitory descending inputs
- Spasticity: increased muscle tone
- Hyper-reflexia: exaggerated reflexes
- Clonus: abnormal oscillatory muscle contraction
- Babinski’s sign
What is a Babinski reflex?
- Sole of the foot is stimulated with a pointed instrument → hallux flexion (normal) or extension (sign of pathology)
What is apraxia?
- A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements
Which cerebral lobe lesions are commonly associated with apraxia?
- Lesion of inferior parietal lobe, frontal lobe (premotor cortex and supplementary motor area)
Which motor areas are affected in apraxia?
Supplementary motor area (SMA) and premotor cortex
What is the function performed by the premotor cortex?
Concerned with movement planning and regulates externally cued movements
What area is responsible for planning internally cued movements?
Supplementary motor area
What are the most common causes of apraxia?
Strokes and dementia
What are the 6 main signs of a lower motor neurone lesion?
- Weakness
- Hypotonia (reduced muscle tone)
- Hyporeflexia (reduced reflexes)
- Muscle atrophy
- Fasciculations
- Fibrillations
What are fasciculations?
- Damaged motor units produce spontaneous action potentials resulting in a visible twitch
What are fibrillations?
- Spontaneous twitching of individual muscle fibres; recorded during electromyography examination
What is the motor neurone disease (MND)?
- Progressive neurodegenerative disorder of the motor system (upper and lower motor neurones)
What is another term used to describe motor neurone disease (MND)?
- Amyotrophic lateral sclerosis
What are the upper motor neurone signs in motor neurone disease (MND) (6)?
- Spasticity (Increased tone of limbs and tongue).
- Brisk limbs and jaw reflexes
- Babinski’s sign
- Loss of dexterity
- Dysarthria (Difficulty speaking)
- Dysphagia (Difficulty swallowing)
What are the lower motor neurone signs in motor neurone disease (MND) (5)?
- Weakness
- Muscle wasting
- Tongue fasciculations and wasting
- Nasal speech
- Dysphagia
What are the 7 main structures of the basal ganglia?
- Caudate nucleus (C)
- Putamen (P)
- Globus pallidus (G)
- Thalamus (T)
- Nucelus accumbens (Acc)
- Amygdala (Am)
- Anterior commisure (AC)
What are the functions of the basal ganglia (4)?
- Decision to move
- Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
- Moderating and coordinating movement (suppressing unwanted movements)
- Performing movements in order
What is the Parkinson’s Disease?
- Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum
Which basal ganglia structure is predominantly affected in Parkinson’s disease?
- Substania nigra
What are the 5 main clinical presentations of Parkinson’s disease?
- Bradykinesia
- Hypomimic face
- Akinesia
- Rigidity (muscle tone increases, causing resistance to externally imposed joint movements)
- Tremor at rest
What is bradykinesia?
- Slowness of small movements
What is a hypomimic face?
- Expressionless (absence of movements that normally animate the face)
What is akinesia?
- Difficulty in the initiation of movements because cannot initiate movements internally
What is the Huntington’s Disease?
- Degeneration of GABAergic neurons in the striatum, caudate and then putamen
Which basal ganglia structures are affected in patients with Huntington’s disease?
- Striatum
- Caudate
- Putamen
What are the presenting symptoms in a patient with Huntington’s disease (5)?
- Choreic movements (chorea) - rapid jerky involuntary movements of the body hands and face a
- Speech impairment
- Difficulty swallowing (dysphagia)
- Unsteady gait
- Later stages, cognitive decline and dementia
What is the inheritance pattern of Huntington’s disease?
- Autosomal dominant
What type of mutation is inherited in a patient with Huntington’s disease?
- CAG repeat
What is ballism?
- Sudden uncontrolled flinging of the extremities, symptoms occur contralaterally
Usually from stroke affecting the subthalamic nucleus
Which basal ganglia structure is associated with Ballism?
- Subthalamic nucleus
Where is the cerebellum located?
- Posterior cranial fossa
Which structure separates the cerebrum from the cerebellum?
- Tentorium cerebelli
What is the main function of the cerebellum?
- Coordinator and predictor of movement
Which cerebellum structure is associated the regulation of gait, posture and equilibrium?
- Vestibulocerebellum
A tumour to the vestibulocerebellum can cause what type of symptoms (3)?
- Gait
- Ataxia
- Tendency to fall
What is the function of the spinocerebellum (3)?
- Coordination of speech
- Adjustment of muscle tone
- Coordination of limb movements
A lesion to the spinocerebellum can lead to what?
- Abnormal gait and stance (wide-based)
- Affects mainly legs
Chronic alcoholism affects which part of the cerebellum?
- Spinocerebellum
Which cerebellar region is the most lateral?
- Cerebrocerebellum
What is the function of the cerebrocerebellum (5)?
- Coordination of skilled movements
- Cognitive function
- Attention
- Processing of language
- Emotional control
A lesion to the cerebrocerebellum affects what?
- Arms / skilled coordinated movements (tremor)
- Speech
What are the main signs of cerebellar dysfunction (5)?
- Ataxia
- Dysmetria
- Intention tremor
- Dysdiadochokinesia
- Scanning speech
Define ataxia.
- General impairments in movement coordination and accuracy: Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Define dysmetria.
- Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Define intention tremor.
- Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Define dysdiadochokinesia.
- Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms).
Define scanning speech.
- Staccato, due to impaired coordination of speech muscles.
What is a motor unti?
- A single motor neurone with all the muscle fibre that it innervates.
- It is the smallest functional unit with which to produce force.
Fun fact: On average each motor neuron supplies about 600 muscle fibres
What are the 3 types of motor units?
- Slow (S, type I)
- Fast, fatigue resistant (FR type IIA)
- Fast, fatiguable (FF type IIB)
How are the 3 different motor unit types classified?
- Amount of tension generated
- Speed of contraction
- Fatiguability
What are the two mechanisms by which the brain regulates the force that a single muscle can produce?
- Recruitment
- Rate coding
What is recruitment when it comes to producing muscle force?
- Smaller units are recruited first (these are generally the slow twitch units).
- As more force is required, more units are recruited.
This allows fine control (e.g. when writing), under which low force levels are required.
What is rate coding
when it comes to producing muscle force?
- A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency.
- As the firing rate increases, the force produced by the unit increases.
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.
Outline the monosynaptic reflex (3 steps).
- Tendon hammer causes stretch of the muscle
- Sensory neurone embeded within the muscle signals the CNS via the monosynaptic reflex
- Reflex contraction of the muscle
What is the supraspinal control of reflexes?
-
The signal travels above the spinal cord before traveling back down to the same segment it entered the spinal cord from
- Inhibitroy control dominates in normal condition
- Excitatory control from supraspinal areas is visible only after cerebration
- Can cause rigidity & spasticity
What are the mechanisms of control of the supraspinal control of reflexes (5)?
- Activating alpha motor neurones
- Activating inhibiting interneurones
- Activating propiospinal neurones
- Activating gamma motor neurones
- Activating terminals of afferent fibres
How to increase the effect of the monosynaptic reflex?
- Jendrassik manoeuvre
What is the Jendrassik manoeuver?
- Clenching the teeth, making a fist or pulling against locked fingers when having platella tendon tapped
- Increases the reflexes speed & strength
What are the signs of hyperreflexia (3)?
- Overactive reflexes
- Clonus
- Babinski’s sign
Loss of descending (supraspinal) inhibition
What is clonus?
Involuntary and rhythmic muscle contractions
Loss of descending inhibition
What is the main cause of hyperreflexia?
- Upper Motor Neurone (UMN) Lession
What are the signs of hyporeflexia?
- Below normal / absent reflexes
What is the main cause of hyporeflexia?
- Lower Motor Neurone (LMN) Lession
