Motor Control Flashcards
What are the 2 broad principles of motor control?
- Hierarchical organisation - higher order areas = higher order tasks, lower order areas = lower order tasks
- Functional segregation - motor system divided into different areas that control different aspects
How is voluntary and automatic movement brought about?
What is the difference between upper and lower motor neurons?
Interaction between the 2 principles of control
Upper motor neurons originate in the cerebral cortex and travel down to the brain stem or spinal cord, while lower motor neurons begin in the spinal cord and go on to innervate muscles and glands throughout the body
What are the 2 major descending tracts from the brain?
Where do they pass through and what are their functions?
- Pyramidal - pass through the pyramids in the medulla, output neurons in the motor cortex to spinal cord / cranial nerve nuclei in the brainstem. Voluntary movement of body and face.
- Extrapyramidal - do not pass through the pyramids of the medulla, begin in the brainstem and project to the spinal cord, where they synapse. They project to muscles for involuntary actions e.g. balance, posture
Where is the primary motor cortex located and what is its function?
Located in the pre-central gyrus
Controls fine and discrete movements, via the spinal cord
Where is the pre-motor cortex located and what is its function?
Located just anterior to the primary motor cortex
Planning of movements - regulated externally cued movements e.g. reaching out to grab something
Where is the supplementary motor area located and what is its function?
Located anterior and medial to primary motor cortex
Becomes active prior to voluntary movements occurring
Complex movements that are internally driven e.g. speech
What are the names of the 2 pyramidal tracts?
Corticospinal and corticobulbar
What is the corticospinal tract?
Where it is located, what is its structure and what does it innervate?
Upper motor neurons in the primary motor cortex, cerebral peduncles in the midbrain, and medulla located further down
Vast (90%) crossing over of the upper motor neurons to the other side of the body in the medulla
These then synapse onto lower motor neurons in the spinal cord
Crossed over neurons make up lateral corticospinal tract = limb muscles
Non-crossed over neurons make up anterior corticospinal tract = trunk muscles
This tract contains upper and lower motor neurons
What is meant by somatotopic control?
Certain region of the brain corresponds to controlling a certain region of the body
What is the corticobulbar tract?
What is its function? What is its structure and what does it innervate?
Provides voluntary movements of the face
Primary motor cortex = upper motor neurons
These synapse with brainstem nuclei onto the lower motor neurons of the cranial nerves that go out to control movements of the face e.g. eyes, jaw
i.e. trigeminal nulei = muscles of mastication, oculomotor and abducens and trochlear nuclei = eyes, facial nuclei = facial expression, hypoglossal nuclei = tongue
This tract contains upper and lower motor neurons
What are the 4 extrapyramidal tracts and what are their functions?
Vestibulospinal = originates in lateral vestibular nucleus (Deiters nucleus), projects to ipsilateral motor neurons in spinal cord. Stabilising head, moving eyes within head to keep vision fixed on the retina, coordinates head and eye movements, mediates postural adjustment
Reticulospinal = most primitive descending tract - from medulla (medial reticulospinal) and pons (lateral reticulospinal); changed in muscle tone associated with voluntary movement, postural stability
Tectospinal = originates from superior colliculus in the midbrain and projects to cervical spinal cord. Orientation of head and neck during eye movements
Rubrospinal = from red nucleus in the midbrain to lateral cervical spinal cord. Seen active in primates but in humans mainly taken over by the corticospinal tract (does come into play when there are lesions in the CNS, leads to posture and balance disorders)
What occurs if there is a lesion in the upper motor neuron?
HINT: negative and positive symptoms, what is the difference
Both signs = bad: negative = loss of activity, positive = extra unwanted activity
Negative signs: Loss of voluntary motor function e.g. paresis (graded weakness of movements) or paralysis (complete loss of voluntary muscle activity)
Positive signs: Increased abnormal motor function due to loss of inhibitory descending input, spasticity = increased muscle tone, hyper-reflexia (exaggerated reflexes), babinski’s sign
What is apraxia?
Disorder of a skilled movement - consequence of a lesion e.g. stroke, dementia
Dysfunction in the supplementary motor area
Patients are not paralysed, but lose the ability to perform skilled movements
What occurs if there is a lesion in the lower motor neurons?
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy (muscle wasting)
Fasciculations: damaged motor units produce spontaneous action potentials, results in a visible (to the naked eye) twitch
Fibrillations: spontaneous twitching of individual muscle fibres, not visible to the naked eye, seen during EMG testing
What is Motor Neuron Disease?
AKA Amyotrophic Lateral Sclerosis [ALS]
Affects upper and lower motor neurons
Progressive neuro-degeneration of the motor system - results in death, no cure
Issues with voluntary contraction of the tongue, upper and lower limbs etc.
Issues with respiratiory musces e.g. intercostal muscles
What are the upper motor neuron signs and lower motor neuron signs in MND?
Upper motor neuron signs: Spasticity (increased tone of limbs and tongue) Brisk limbs and jaw reflexes Babinski’s sign Loss of dexterity Dysarthria (difficulty speaking) Dysphagia (difficulty swallowing)
Lower motor neuron signs: Muscle atrophy Weakness in the muscles Twitching (fasciculations) and wasting of tongue muscles Dysphagia (difficulty swallowing) Nasal speech
What is the basal ganglia and what makes up the basal ganglia?
A group of subcortical nuclei responsible primarily for motor control
Globus pallidus (external and internal) Striatum - made up of the caudate and putamen nuclei Substantia nigra (midbrain)
What is the function of the basal ganglia?
Decision to move (intention)
Elaboration associated movements (e.g. swinging arms when walking, facial expressions to match emotions)
Moderating and coordinating movement (suppressing unwanted movements)
Performing movements in order
What are some disorders associated with the basal ganglia?
e.g. Parkinson’s and Huntington’s disease and Ballism
Parkinsons = associated with substantia nigra (midbrain)
What is the order of the basal ganglia structures: caudate nucleus, putamen, external globus pallidus and thalamus in a coronal section from anterior to posterior?
Caudate nucleus, putamen, external globus pallidus and thalamus
What is the basal ganglia circuitry?
Cortex communicates with the striatum
Striatum then communicates with the substantia nigra, internal globus pallidus and external globus pallitus
What is Parkinson’s disease?
How does it present clinically?
Degeneration of the dopaminergic neurons that originate from the sunstantia nigra and project to the striatum
Bradykinesia - affects ability making small dextrous movements
Hypomimic face - expressionless face
Akinesia - difficulty producing intention of movement
Rigidity - increased muscle tone causing resistance to externally imposed joint movements
Tremor at rest - 4-7 cycles per second (slow tremor)
What is Huntington’s Disease?
How does it present clinically?
Degeneration of GABAergic neurons (inhibitory neurons) in the striatum, caudate and the putamen
Choreic movements = rapid, jerky, involuntary movements
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages = cognitive decline and dementia
What is Ballism?
Associated with a stroke affecting the subthalamic nucleus
Usually one sided symptoms (contra-lateral)
Uncontrolled flinging of the extremities - rotatory movement of the limbs
What is the cerebellum? Where is it located and what is its function?
Located in the posterior cranial fossa
Separated from the cerebrum above by the tentorium cerebelli
Co-ordinator and predictor of movement - compares what is going out of the CNS (signals on the way down to the muscles of the body) to what is returning from sensory receptors from the PNS (leads to fluid movement)
What connects the two cerebellar lobes?
What is the purpose of the cerebral peduncles?
Where do the corticospinal tracts cross over?
Pons
Cerebral peduncles take the large motor tracts (from the erebrum) down to the pyramids (brainstem)
In the medulla 90% of the corticospinal fibres cross over
What is the function of the vestibulocerebellum?
What happens if there is damage to this area?
At the posterior cerebellum
Regulates gait, posture and equilibrium
Co-ordinates movement of the head and movement of the eyes
Lesions = similar to symptoms of vestibular disease = poor co-ordination when walking (gait ataxia), tendency to fall even when patient is sitting still with eyes open
What is the function of the spinocerebellum?
What happens if there is damage to this area?
Responsible for co-ordinating speech and limb movements, adjustment of muscle tone
Damage (can occur with chronic alcoholism ) = affects mainly legs, gait (wide based)
What is the function of the cerebrocerebellum?
What happens if there is damage to this area?
Lateral part of the cerebellum
Co-ordinated skilled movements, cognitive control (attention, language processing, emotional control)
Damage = affects skilled and co-ordinated movements and speech (e.g. tremor)
What are the main signs of cerebellum disorders?
Reveals itself when a person tries to make movements:
Ataxia - disturbances in posture and gait, legs wider apart, patients may appear drunk
Dysmetria - unable to predict the amount of force required for target directed movement e.g. move the hand to pick up an object
Intention tremor - tremor when trying to reach for something e.g. nose-finger tracking test (touch clinician’s finger, then touch your nose - repeat this)
Dysdiadochokinesia - inability to do rapidly alternating mvoements (e.g. rapid pronation and supination of the hands)
Scanning speech - staccato = lack of co-ordination of the speech muscles
