Motor control Flashcards
How can voluntary movement be classed?
according to the amount of conscious input required to initiate them
- involuntary
- voluntary
what are two factors that are important in muscle activation
- need to be activated in an appropriate sequence
- need the appropriate amount of force
What is a crucial aspect of motor control?
Motor learning and rehersal
What is motor learning
- Motor learning stores motor skills
- not accessible to the consciousness
- less easily formed than declarative memory
What is the difference between motor learning and declarative memory?
New motor skills need to be continuously rehearsed, but once learnt, they are not as easily forgotten as declarative memory
What is declarative memory?
- factual information
- life events
- available to consciousness
- easily formed/forgotten
What strategies are used by the nervous system for controlling movement?
- ballistic (pre-programmed) movements
- Pursuit or visual feedback movements
What are ballistic movements?
(pre-programmed)
- movement based largely on a set of pre-programmed instructions
- rapid but at the expense of accuracy
- movement cannot be interrupted or corrected
What are pursuit or visual feedback movements?
- motor command continually updated according to sensory feedback
- highly accurate and can be modified in progress but slow
What areas of the neocortex are involved in planning and instruction of movement?
- the motor cortex proper
- the prefrontal cortex
- the primary motor cortex
What areas of the motor cortex proper are involves in controlling movement?
M1 - primary motor cortex
SMA - supplementary motor area
PMA - premotor area
What is the function of the prefrontal cortex in relation to control of movement?
involved in the decision to make the movement, thoughts in response to the environment
What is the function of the primary motor cortex in relation to control of movement?
Is the main output of the motor cortex
What is a platinum grid array electrode
Used for seizure monitoring and brain mapping on subdural cortical surface in conscious patients
Possible to record from awake patients
What is the somatotopic map?
Mapping between ares of the motor cortex and muscles of the body
Which areas of the body require fine motor control?
face and hands
Which areas of the body have the largest representation on the motor homunculus
The face and hands
What is decussation?
Crossing of pathways
Which pathways are decussated?
Pathways providing connections between primary sensory and motor areas and the periphery are crossed
At what level do pathways decussate?
At the level of the medulla
What side of the body does the right motor cortex control?
The left side of the body
What side of the body does the left motor cortex control?
The right side of the body
What is the outcome of a stroke?
Functions may be lost following a stroke depending on the extent of the haemorrhage
The paralysis and loss of sensation will be on the contralateral side to the haemorrhage because of decussation
What are the areas of the neocortex involved in planning and instruction of voluntary movement?
Area 6 = supplementary motor area & pre motor area
What is area 6 of the neocortex involved in?
Important in the planning of movements
In what part of the sequence is activity in area 6 of the neocortex found?
Activity occurs in this area before activity in M1 and movement
What is the evidence for the function of the supplementary motor cortex?
Imaging studies show activity in the SMA, M1 and S1 during finger movement task, but only in the SMA when the movement is mentally rehearsed (without actual movement)
Why is S1 activity present during movement?
Due to sensory input from the movement
Why is SMA isolated in mental rehearsement?
- no movement therefore no activity in M1
- no sensation therefore no activity in S1
Activity in SMA because of planning movement - passes information to M1 so that M1 can send signals via motor neurons to produce muscle contraction
How is isolated SMA movement used clinically?
Can assess patients in a persistent vegetative state to asses activity in the SMA when told to mentally rehearse a movement
Can determine whether the patient is conscious and aware
What is the difference between the premotor area and the SMA?
Essentially the same, but premotor area is for more proximal parts of the body
Both are involved in motor planning and communicating their motor plan to the adjacent M1
Remember PPP!
Premotor area works to Plan movements for Proximal parts of the body
What other areas of the cortex are involved in the control of movement?
Sensory information is crucial for coordinated movement as the brain requires continual input about what is happening to different parts of the body
Vision: eyes, visual system, visual cortex
Vestibular: feedback from organs of balance, essential for maintaining an upright posture
- subcortical
What is proprioception?
Feedback from peripheral sensory receptors on the positions and movement of limbs to he somatic sensory cortex
What happens when there is loss of proprioception?
Inability to create movements, not through paralysis, but through lack of control
What non-cortical brain structures are involved in the control of movement?
The basal ganglia and cerebellum
Where does the basal ganglia receive input from?
Mainly from the prefrontal cortex -> intended movement
`Where does the basal ganglia send output to?
The pre-motor area via the thalamus
What is the function of the basal ganglia in control of movement?
- initiation of movement
- putting mottor plan to action
- planing of complex voluntary movement
Describe the route of signals for movement in relation to the basal ganglia
prefrontal cortex => basal ganglia => thalamus => premotor area => M1
How does the basal ganglia control movement
Basal ganglia receive afferent input from prefrontal cortex and motor areas about intended movement
Relays through subthalamic and thalamic nuclei back to area 6
Allow the instructions from within area 6 to be passed to M1 in order to send signals to the muscles to initiate
movement
Name common disorders of the basal ganglia
- Parkinson’s disease
- Huntington’s disease
What are the symptoms of parkinson’s disease?
tremors hypokinesia shuffling gait progressing to general cognitive decline difficulty initiating movement difficulty changing direction
How does Parkinson’s disease occur?
Pathology in the basal ganglia - loss of dopaminergic neurones (degenerate) => loss of dopaminergy signalling
What are the treatments for Parkinson’s disease and how do they work?
L-dopa - boosts dopaminergic signalling by administering precursors
Deep brain stimulation - place electrodes close to subthalamic nuclei and provide electric stimulation
What is Huntington’s disease?
Sporadic uncontrolled involuntary movements (choreas)
What are the symptoms of huntington’s disease?
choreas
difficulty speaking and swallowing
progressing to general cognitive decline
How does Huntington’s disease occur?
Affects the basal ganglia
Inherited - triplet repeat disease CAG base pair is repeated an abnormal number of times in the genetic code
The number of repeats can vary between patients and is correlated with age of onset
(more repeats= earlier age of onset)
Where does the cerebellum receive its input from?
Mainly from the sensory cortex
Where does the cerebellum send its output to?
The primary motor cortex (via the thalamus)
What is the function of the cerebellum in motor control?``
co-ordination and smooth execution of movements
Compares the intended movement to the actual movement
Motor learning (error detection system that allows for correction of the output from the motor cortex
Describe the route of signals for movement in relation to the cerebellum
Sensory cortex => Cerebellum => primary motor cortex
What is the result of damage to the cerebellum?
Cerebellar ataxia: poor coordination
What can cause cerebellar ataxia?
Can occur as a result of many diseases
What symptoms do patients commonly present with, with cerebellar ataxia?
Inability to coordinate balance, gait, extremity and eye movements
What can lesions to the cerebellum cause?
- dyssynergia
- dysmetria
- dysdiadochokinesia
- dysarthria
- ataxia of stance and gait
What is dyssynergia?
Disturbance of muscular coordination, resulting in uncoordinated and abrupt movements
What is dysmetria?
Lack of coordination of movement typified by the undershoot or overshoot of intended position with the hand, arm, leg, or eye
What is dysdiadochokinesia?
impaired ability to perform rapid, alternating movements
What is dysarthria?
motor speech disorder resulting from neurological injury of the motor component of the motor-speech system
What are the descending pathways for motor control?
Descending pathways providing inputs to motorneurons
What are the two descending pathways for voluntary control?
- lateral pathways
- ventromedial pathways
What is the lateral pathway?
Main function is control of voluntray movement and distal muscle groups
What do the lateral pathways supply?
more lateral (distal) muscles such as limbs, and are therefore involved in controlling voluntary movement
What is the ventromedial pathway?
Mainly controls the proximal and axial (trunk) muscles and maintain posture
What do the ventromedial pathways supply?
medial (midline) muscles, and therefore maintain posture
What are the two tracts of the lateral pathways?
- corticospinal
- rubrospinal
Where do corticospinal pyramidal neurones in M1 project to?
The spinal cord
Where do rubrospinal pyramidal neurons in M1 project to?
Red nucleus
Where are cotricospinal and rubrospinal tracts found?
In lateral white matter tracts
Where do ventromedial descending systems synapse?
on interneurones in the spinal cord
Where are ventromedial tracts found?
In the medial white matter tracts
What are intrinsic circuits?
Responsible for the generation of certain sterotypes of patterns of activity
What is a tendon jerk reflex?
reflex muscle contractions produced by muscle stretch
Which muscles can elicit a tendon jerk reflex
any muscle where the tendon is accessible
Describe the tendon jerk reflex
a monsynaptic reflex - simple as only one synapse
What is the tendon jerk reflex important for?
Maintaining muscle tone in response to muscle stretch
What are the stages of the tendon jerk reflex?
- Afferent impulses from stretch receptor travel to the spinal cord
- Efferent impulses to alpha motor neurons cause contraction of the stretched muscle that resists/reverses the stretch
- Efferent impulses to antagonist muscles are damped (reciprocal inhibition)
Where are the sensory receptors for the tendon jerk reflex found?
Muscle spindles contain the sensory receptors for the stretch monosynaptic stretch reflex
Where is sensory input received from in the tendon jerk reflex?
segmental afferents
How does the stretch reflex maintain muscle tone and upright posture?
- stretch reflexes are initiated by muscle spindles and must maintain healthy muscle tone
The brain sets a muscles length by sensing commands to the motor neurons
The stretch reflex makes the muscle stay at that length
The stretch reflex is therefore important for maintaining muscle tone and upright posture
Which spinal reflexes contribute to the control of movement?
The stretch reflex
What are the parts of a reflex arc?
- receptor
- sensory neuron
- inerneuron
- motor neuron
- effector
What is the receptor in a reflex arc?
receptor - detects the stimulus
It is the receptor end of a particular dendrite or a specialised receptor cell in a sensory organ
It is able to function due to being sensitive to a specific type of internal or external change
What is the sensory neuron in a reflex arc?
- conveys the sensory info to brain or spinal cord
- It is the dendrite, cell body and axon of a sensory neuron
- functions through transmitting nerve impulses from the receptor into the brain or spinal cord
What is the interneuronin a reflex arc?
- relay neurons
- a dendrite, cell body and axon of a neuron within the brain or spinal cord
- Serves as a processing centre, conducts nerve impulses from the sensory neuron to the motor neuron
What is the motor neuron in a reflex arc?
- conducts motor output to the periphery
- is a dendrite, cell body and axon of a motor neuron
- transmits nerve impulses from the brain or spinal cord out to an effecter
What is the effecter in a reflex arc?
- a muscle or a gland
- responds to stimulation by the motor neuron and produces the reflex or behavioural action
How do muscle spindles operate?
- stretching the muscles activates the muscle spindle and there is an increased rate of action potential in Ia fibers
- Contracting the muscle reduces tension on the muscle spindle and there is a decreased rate of action potential on Ia fibers
What is rhythmic activity useful for and how is it achieved?
Spinal pattern generators produce rhythmic activity for stepping
- intrinsic circuits of the spinal cord can produce rhythmic motorneuron activity, which drives stepping
- It consists of alternating activity in flexor and extensor muscles coordinated across the two (in bipid) limbs
Describe the possible circuit for rhythmic alternating activity
- two sets of pattern-generating neurons project to flexor and extensor pools, respectively
- separate populations of rhytmically active central pattern generators project to different muscles
- recipricol inhibitory connections between the two sets of pattern-generating neurones help to co-ordinate their activity, so that there is alternating excitation of flexors and extensors
- I.e the separate populations are inhibited by input from the brain depending on desired movement
Which motorneurones innervate skeletal muscle fibers?
alpha motoneurons
What is a motor unit?
A motoneuron and the muscle fibers it innervates
How many muscle fibers are innervated by a motoneuron?
between 3-1000
What are motornuclei?
Collections of motoneurons in the ventral horn
What is a motoneuron pool?
consists of all individual motor neurons that innervate a single muscle that forms columns in the ventral horn
Describe the segmental distribution of motor neurons controlling muscles in different parts of the body
- cervical: arms and upper body
- Thoracic: trunk
- Lumbar and sacral: legs
How can graded control of muscle contraction be adjusted, and which of these has a bigger effect?
By changing:
- the AP frequency (limited effect)
- motor unit requirement (bigger effect)
