Motor 2 Flashcards
Hierarchical organization of the motor system
- Has control pathways organized in series and in parallel
- 2 control loops: cerebellar and basal ganglia
Diagram of organization of motor system
What are the purposes of the organization of the motor system?
Strategy: what movement is relevant?
■ Cortex (area 6), basal ganglia, higher order association areas
Tactics: how do we do this movement smoothly? (right sequence of contractions)
■ Motor cortex (area 4), cerebellum ○
Execution: doing the movement
■ Brainstem, cerebellum, spinal cord
What type of motor neurons control motor output?
Upper motor neurons (brain & above superior colliculus)
What are the two main descending motor pathways?
- Lateral pathway descends down lateral sections of spinal cord
- Ventromedial pathway descends down ventral and medial sections
Lateral pathway
- Voluntary movement
- Distal muscles (e.g. hands and arms)
- Corticospinal tract (and rubrospiunal)
Ventromedial pathway
- Posture, gait, balance, head position
- Axial/proximal muscles (e.g. trunk, upper arm, legs)
Diagram of descending motor pathways
Which pathway is responsible for voluntary movement?
Lateral
Which pathway is responsible for posture, gait, balance, head position
Ventromedial
Which pathway involves the corticospinal tract?
Lateral
Which pathway controls the distal muscles (e.g. hands and arms)?
Lateral
Which pathway controls the axial/proximal muscles (e.g. trunk, upper arm, legs)?
Ventromedial
Detail on ventromedial pathways
● AKA ventromedial descending spinal tract
● Originates in brainstem
○ Collect info from superior
colliculus, cerebellum, vestibular
nucleus
○ Integrate with info from visual and
vestibular systems → posture,
gait, balance, head position
● You DO NOT need to know individual tracts
Detail on lateral pathways/corticospinal tract
● We focus mostly on the corticospinal tract
○ AKA: pyramidal tract
○ Largest descending motor pathway
○ 1 mil (106) axons on each side
● Purpose: voluntary movements
○ Esp of distal muscles (hands, digits)
● Contralateral control: decussates at caudal medulla (medullary pyramids)
Motor cortex - area 4
● Anterior to S1 (somatosensory cortex is on the other side of central sulcus)
● M1 activity → movement and movement control (usually voluntary)
● Lesioning M1 damages movement
● Stimulating specific parts of M1 → moves a specific body part
○ Demonstrates somatotopy like S1
○ Discovered through Walter Penfield’s experiments
● Important for movement execution
○ Moving your fingers
Motor cortex - area 6
● Sub-motor area, pre-motor area
● Involved in motor planning, intent to move, strategy
○ Thinking about moving your fingers rather than actually moving them
What areas does the middle cerebral artery supply blood to?
Cortical areas key to sensation and movement
Stroke in middle cerebral artery
- Stroke stops blood flow → brain damage
- Broca’s area (speech, langauge production) is close to middle cerebral artery
- Stroke symptoms: slurred/difficult speech
Signs of damage to long motor tracts
- Paresis (weakness)
- Plegia (paralysis)
- Spasticity
- Sign of Babinski
Paresis (weakness)
Diminished speed, power, agility
Plegia (paralysis)
- Caused by more extensive legions
■ Hemiplegic gait: weakness on one side
Spasticity
Hypertonia, hyperreflexia, clonus (rhythmic, involuntary muscle reflexion
Sign of Babinski
- Babies (<2 yrs): running a pen across the bottom of the foot causes toes to splay out
● Long motor tracts not fully developed yet - Adults: toes should curl in unless damage to tracts
What is the cerebellum made up of?
Folia, not gyri
Input and output in cerebellum
- Input: motor control
- Output to premotor and motor systems
○ cerebral cortex and brainstem (areas of direct spinal cord control)
Functions of cerebellum
- Modulates motor learning: modifies synaptic circuits/connections to allow adaptation and learning
- Key to execution (esp timing and metrics of movement)
Layers of neurons of cerebellum
- Molecular layer
- Purkinje cells
- Granule cell layer
Diagram of cerebellar loop
Cerebellar loop
- Sensorimotor cortex (area 4/6, S1, PPC): layer V pyramidal cells project to the pons (pontine nuclei)
- Pontine nuclei project to contralateral (from the cortex) cerebellum
- Lateral cerebellum projects to contralateral VLc (thalamus) then to ipsilateral cortex
L cortex → R cerebellum → L cortex → R motor control
● Cerebellum controls the ipsilateral side of the
body!
○ So contralateral from cortex, but since cortex controls the contralateral side of the body, cerebellum controls the ipsilateral side
Cerebellar Damage: Ataxia
Cerebellar damage causes effects on the side ipsilateral to the lesion
Ataxia: poor coordination of voluntary movements, disruption of timing and spatial accuracy
● Used to diagnose cerebellar damage
● Other symptoms:
○ Slow to begin/end movement
○ Intention tremor: not at rest, but tremor when doing
voluntary movements
○ Drunken gait: alcohol affects cerebellum, and
cerebellar
○ MEGALOGRAPHIA: large handwriting
○ Hypotonia: pendular knee jerks
○ Disrupted balance
Ataxia is NOT: paralysis, rigidity, worsened cognitive sensation, less muscle strength, involuntary movement disorders
Basal ganglia
Made up of: caudate nucleus, putamen, globus pallidus
○ Caudate is lateral to the lateral ventricles
○ Putamen and globus pallidus separated from caudate by internal capsule
○ Caudate and putamen make up striatum
Diagram of basal ganglia loop
Inputs and outputs of basal ganglia loop
- Input: large areas of cortex
○ Premotor areas (prefrontal cortex), motor areas, sensory areas - Output: premotor and motor cortex, esp SMA (Area 6)
○ Movement initiation
○ filters out irrelevant/inappropriate movements
Basal ganglia loop
- Cortex projects to striatum
- Striatum projects to globus pallidus
- Globus pallidus projects to VLo (thalamus)
- VLo projects to cortex
Basal ganglia simplified circuit
Basal ganglia circuit
● Includes a double negative (inhibiting an inhibitor):
○ Globus pallidus neuron consistently inhibits VL thalamus
○ Striatum neuron inhibits globus
pallidus
○ Activating cortex excites striatum
→ inhibits GP → relieves inhibition on VL thalamus → cortical activation
● Subthalamic neuron excites GP neuron – inhibits cortex and acts to filter out inappropriate movements
● Substantia nigra neurons excite striatum → cortical activation
○ Dopamine from substantia nigra key to circuit function
Subthalamic damage to basal ganglia circuit
- Normally, the subthalamic nucleus stimulates the inhibitory globus pallidus neuron, which inhibits the Vl thalamic neuron
- Damage subthalamic nucleus: = less excitation of globus palladium inhibitory neurons = less inhibition of VL thalamus = more action potentials from VL to motor cortex = HYPERKINESIS (excess movements)
Substantia Nigra Damage (Parkinson’s Disease)
- Substantia nigra excites the putamen inhibitory neuron.
- Lesion substantia nigra. Substantia nigra was exciting the inhibitory neuron from putamen. Less excitation of putamen inhibitory neurons, so less inhibition of globus pallidus. Globus pallidus fires at a faster frequency. It inhibits the VL neuron more, so the SMA fires less (hypokinesis)
Basal Ganglia Diseases
VLo thalamus inhibition/excitation correlated with basal ganglia output
○ Increased inhibition by GP neuron → hypokinesia (not enough movement)
■ Parkinson’s disease
○ Decreased inhibition by GP neuron → hyperkinesia (excess movement)
■ Huntington’s disease ● Symptoms:
○ Dyskinesias: involuntary movements (dys = difficult/bad → bad movement)
○ Akinesia: difficulty with movement initiation (a = lack of → lack of movement)
○ Difficulty continuing/stopping movement
○ Rigidity (problems w/ muscle tone), dystonia (problems w/ posture of limbs/trunk)
○ Ballism: excessive, uncontrolled movement
■ Caused by damage to subthalamic nucleus → no inhibition of VL thalamus → overactivation of cortex
● Suggest that basal ganglia is involved in initiation and support of movement
Cause and manifestation of Parkinson’s Disease
- Caused by death of dopaminergic neurons in substantia nigra
- Chronic, progressive neurodegenerative disease
- Late onset usually (found in ~1% of people >60 yrs old)
Symptoms of Parkinson’s
Symptoms: caused by circuit being too inhibitory
- Akinesia: difficulty initiating voluntary movement Bradykinesia: slowness of movement
- Rigidity: increased muscle tone
- Asymmetric resting tremor - mechanism still unknown (retrorubral field?)
■ Not intention tremor, happens when not moving
- Masked face (stiff face), stooped posture, shuffling gait
- Some dementia in late stages
Treatment of Parkinson’s
- L-Dopa: increase levels of dopamine
- Pallidotomy: lesion parts of globus pallidus
- Deep Brain Stimulation (DBS): addresses tremor, bradykinesia, rigidity
Disease summary table
What happens when you damage right above the rostral region of your right medulla?
Loss of movement control of left hand, fingers, and foot
Damage to the cerebellum results in deficits to the ___ side of the body
Ipsilateral
Unlike the cerebral cortex, the cerebellum receives input from, and controls output to, the ipsilateral side of the body, and damage to the cerebellum therefore results in deficits to the ipsilateral side of the body.
Ataxia and intention tremor in movements of the right arm is caused by damage to
a) the right half of the cerebellum
b) the left half of the cerebellum
c) the right substantia nigra
d) the left substantia nigra
a) The right half of the cerebellum
The cerebellum is the part of the brain responsible for coordinating movements, and damage to one side of the cerebellum affects the ipsilateral side of the body, meaning damage to the right cerebellum impacts the right arm.
Damage to the ventromedial pathways will cause ________ in ______.
a) weakness or paresis; muscles of posture
b) weakness or paresis; muscles of the hands and feet
c) resting tremor; muscles of posture
d) resting tremor; muscles of the hands and feet
a) Weakness or paresis in muscles of posture
Loss of coordination and intention tremor are signs of damage to the ___
Cerebellum
Damage to posterior parietal cortex is associated with
a) blindness
b) ataxia
c) hemineglect syndrome
d) hemiplegia
c) Hemineglect syndrome
Damage to the corticospinal tract in the left side of the cervical spinal cord would lead to
a) inability to feel mechanical stimuli in the right foot
b) sign of Babinski in the right foot
c) inability to feel mechanical stimuli in the left foot
d) inability to move the toes of the right foot
d) inability to move the toes of the right foot
corticospinal is contralateral
Which of the following is most rostral in the brain?
a) Primary motor cortex
b) Primary visual cortex
c) Primary somatosensory cortex
d) Posterior parietal cortex
a) Primary motor cortex
You are sitting in bed, thinking about a particular finger sequence to play a piano piece that you
are just learning. While thinking about this complicated sequence of finger movements, but not
executing the movements, you would expect activity in
a) SMA (supplementary motor area)
b) M1 (primary motor cortex)
c) S1 (primary somatosensory cortex)
a) SMA (supplementary motor area)
Area 6 is located in ___
The supplementary motor area (SMA)
The cerebellum is attached to your brainstem by the cerebellar peduncles. If Peter were to stop
all activity in the cerebellar peduncles this would lead to
a) Hyperkinesis (excessive movements)
b) Ataxia
c) Resting tremor
d) Paralysis
b) Ataxia
Stimulating the subthalamic nucleus of the basal ganglia on one side of the brain would likely
cause
a) Ballism, or, random, excessive movements of half the body when voluntary movements
are made
b) Decrease in movement in half the body
c) Paralysis in half the body
d) Ataxia in half the body
b) Decrease in movement in half the body
Paresthesia is induced when your foot “falls asleep” (i.e. Blood flow is cut off to your leg and
then returning blood flow triggers an immediate strange set of affects.) Paresthesia is
associated with all of the following EXCEPT
a) Weakness in leg muscles when you try to stand on the affected leg
b) a “pins and needles” or “foot in a beehive” sensation in the affected foot
c) weak sensory stimuli produce larger than normal sensory responses in the affected foot
d) stronger sensory stimuli are required in the affected foot to elicit a sensation
d) stronger sensory stimuli are required in the affected foot to elicit a sensation
Peter being Peter, he injects local anesthetic into the left half of your thoracic spinal cord at T7.
While the anesthetic is functioning, you would experience all of the following deficits EXCEPT
a) Loss of movement in your left foot
b) Loss of touch in your left foot
c) Loss of sensation to pain in your right foot
d) Loss of knee jerk reflex in your left leg
d) Loss of knee jerk reflex in your left leg
The knee jerk reflex is a monosynaptic reflex, which involves sensory neurons (afferent) and motor neurons (efferent) within the same side of the spinal cord.
A common symptom of Parkinson’s disease is
a) rigidity
b) hyperkinesia
c) spasticity
d) staccato speech
a) rigidity
Per Roland used PET imaging of the human brain to study the cortical control of movement.
What brain area did he find was activated by mentally imagining moving one’s fingers
a) primary motor cortex
b) posterior parietal cortex
c) prefrontal cortex
d) supplementary motor area
d) supplementary motor area
The sign of Babinski is most likely a result of damage to the ___
Long motor tracts
Cutting through the left half of the thoracic spinal cord would result in loss of
a) movement of the fingers of the right hand
b) sensation to touch in the right foot
c) sensation to pain in the right foot
d) More than one of the above
c) sensation to pain in the right foot
b) Sensation to touch in the right foot
This is incorrect. The pathway for touch and proprioception (dorsal column-medial lemniscal pathway) crosses over at the level of the brainstem, not in the spinal cord. Therefore, a lesion on the left side of the spinal cord at the thoracic level would affect touch sensation on the left side of the body below the lesion, not the right side.
c) Sensation to pain in the right foot
This is correct. The spinothalamic tract, which carries pain and temperature sensation, crosses to the opposite side of the spinal cord within a few segments of its entry point. Therefore, a lesion on the left side of the thoracic spinal cord would disrupt pain sensation for the right side of the body below the lesion, including the right foot.
Which of the following manipulations is most likely to produce motor deficits that are similar
to those of Parkinson’s disease?
a) blocking dopamine receptors on neurons in the substantia nigra
b) overexcitation of neurons in the subthalamic nucleus
c) blocking dopamine receptors in neurons of the putamen
d) overexcitation of neurons in the putamen
c) blocking dopamine receptors in neurons of the putamen
Damage to the corticospinal tract on the left side of the brainstem at the level of the pons will lead to which of the following symptoms?
a) hemiplegic gait impacting the right leg and arm
b) hemiplegic gait impacting the left leg and arm
c) hyperkinetic movements in the right leg and arm
d) hyperkinetic movements in the left leg and arm
a) hemiplegic gait impacting the right leg and arm
A midline (mid sagittal) cut along the length of the medulla would cut axons in the
a) DCML pathway
b) corticospinal pathway
c) spinothalamic pathway
d) More than one of the above
e) All of the above
d) More than one of the above
DCML and corticospinal
If it’s got a C in it, it decussates at the __
Medulla!
DCML and Corticospinal decussate at the medulla
