11 - Motor Control of Body Movement Flashcards
What is the function of the Cerebellum?
- Compares motor signals sent out and sensory information received to monitor and adjust the execution of movement
- Major role in the timing of motor activities, and in executing rapid and smooth transitions between successive movements.
(no direct ability to cause muscle contractions, exerts its effects via connections to other motor areas)
What are the types of movement?
- Reflex, voluntary, rhythmic
What parts of brain control voluntary movement?
- Cerebral cortex
- Cerebellum
- Basal ganglia
What are the steps of voluntary movement?
- Decision making & planning (cerebral cortex, cerebellum)
- Initiating the movement (cerebral cortex)
- Executing the movement (cerebellum and cerebral cortex)
What are the motor areas in the cerebral cortex?
- Primary motor cortex:
- Triggers discrete patterns of muscle activation (finger movements)
- direct connection to motor neurons in spinal cord - Premotor area
- plans more complex patterns of movement (position shoulders)
- sends these patterns to the primary motor cortex for execution - Supplementary motor area
- body-wide adjustments to provide the “background” for the more specific movement plans in the premotor and primary motor cortex (eyes, head, coordinating hands)
- This region is involved in the planning of movement but does not itself send out direct commands
What are the 3 parts of the cerebellum and their function?
- Vestibulocerebellum: Regulation of muscle tone, coordination of skilled voluntary movement
- Spinocerebellum: Planning and initiation of voluntary activity, storage of procedural memories
- Cerebrocerebelum: Maintenance of balance, control of eye movement
What does Basal Ganglia do?
- Important in the planning of learned subconscious complex patterns of activity( ie: writing, throwing a ball, aspects of speech, etc.)
- Part of the neural circuit involved in the cognitive control of motor activity (linking thoughts to action)
What sensory input do muscles provide?
- Proprioceptive input from skin and muscles combine with visual, auditory and vestibular input to describe body position in space.
What issues motor output?
Based on integrated sensory info:
- Motor cortex via the corticospinal tracts (spinal cord) to the skeletal muscles for execution of the throw
- Brain stem (reflexes involved in equilibrium and posture)
What is the corticospinal tract?
- A group of interneurons that runs from the motor cortex to the spinal cord
- These tracts cross to the opposite side of the body in the brain stem (aka pyramids)
- they synapse directly with the somatic motor neurons, which innervate the muscles to produce movement
What is the brainstem’s function?
- Responsible for several specialized motor tasks (respiration, cardio, eye movements)
- Connects higher motor areas and the spinal cord
- Send out direct connections to motor neurons in the spinal cord, which are important for whole-body movements (related to posture and equilibrium)
How does feedforward postural adjustments work?
- brain initiates movement
- each movement activates sensory receptors that feed info back into the spinal cord, brain stem and cerebellum, activating postural reflexes
What are the parts and functions of the ear?
- External ear
- Middle ear
- Inner ear
- Cochlea
- Vestibular Apparatus -> Semicircular canals, Utricle, Saccule
What are the components of the Vestibular Apparatus?
- Semicircular canals: Detects rotation or angular acceleration or deceleration
- Utricle: Detects changes in head position away from vertical and horizontal
- Saccule: Detects changes in head position away from vertical and horizontal
What activates hair cells in the semicircular canals?
Head rotation
How does the ultricle work?
- When you tilt your head in another direction (not vertical) the hairs bend in the direction of the tilt because of gravity
- The bending depolarizes of hyperpolarizes the receptor
- The CNS receives different patterns of neural activity depending on the head position
**Located between the cochlea and the semicircular canals
- When you start walking, otolith membrane first lags, then catches up for constant speed, and when you stop, the hairs bend toward the front
What is Vestibular input and output?
Input: visual, cutaneous, proprioceptive, vestibular
Output: output to motor neurons of limb and torso muscles, output to motor neurons of external eye muscles, output to CNS
What is the Internal Model?
- The brains representation of body posture and position (aka current state of body)
- When a motor command is sent out, a “duplicate” of that command is also used to update the internal model (efferent copy)
- ‘Forward modelling’: Use the internal model (current state) and efferent copy (current input) to predict expected movement that will result from a motor command
- Once feedback is received from sensory organs, measurements are compared to the prediction and internal model is corrected and updated
What are the two types of neural reflexes?
- Negative feedback (more common) - response conteracts the stimulus
- Positive feedback - response reinforces the stimulus
What are the types of joint/muscle proprioception receptors?
- Muscle spindles
- Golgi Tendon Organs
- Located in Capsules and ligaments around joints
- Stimulated by mechanical distortion that accompanies changes in the relative positioning of bones linked to flexible joints
- Sensory information from joint receptors is integrated in cerebellum
What are the different states of the Muscle Spindles?
- Relaxed: stimulation of gamma motor neuron ensures that correct tension is maintained in the muscle spindle at rest
- Contracted muscle: The spindle fibers are not sensitive to stretch because of lack of tension in the muscle spindle
- Contracted muscle: when there is co-activation of the alpha and gamma motor neuron systems
What is the structure/function of muscle spindles?
- Consists of a collection of specialized intrafusal fibres
- Aligned parallel to extrafusal skeletal muscle fibres
- innervated by gamma motor neurons
- Afferent sensory endings are activated by stretch
- monitors muscle length (each muscle has many muscle spindles)
- Sensory neurons project to the spinal cord and synapse directly with the alpha motor neurons innervating the muscle where the spindles lie
What do the Gamma motor neurons do?
- Adjust the stretch sensitivity of the muscle spindles so that the spindles are active no matter what the muscle length is
- When the gamma motor neurons fire, the ends of the fibres contract and shorten, so that central region maintains stretch
What is alpha-gamma coactivation?
- Alpha motor neurons fire and gamma motor neurons fire
- Muscle contracts
- Stretch on centers of intrafusal fibers unchanged (firing rate of afferent neuron remains constant)
What are the components of a reflex arc?
- Receptor
- Afferent Pathway
- Integrating centre
- Efferent Pathway
- Efferent Organ
Are spindles firing when muscle is relaxed?
Yes.
Muscle tone: the amount of tension in a muscle at rest due to tonic stimulation activity
What is a stretch reflex?
- Muscle stretch initiates a contraction response (prevents damage from overstretching)
- Caused by any movement that increases muscle length as it stretches the muscle spindles and causes their sensory fibres to fire more rapidly
What is the patellar tendon reflex?
- A monosynaptic stretch reflex in the quadriceps muscle
- “classic knee-jerk”
What is the withdrawal reflex?
- the response to a painful stimulus
Afferent neuron causes 3 diff types of interneurons:
1. Excitatory: Stimulates the efferent motor neurons to retract the limb from the painful stimulus
2. Inhibitory: prevents counterproductive contraction of the antagonistic muscle
3. Interneuron: carries signal up to the spinal cord via ascending pathways to the brain for awareness of pain, memory
What is the crossed extensor reflex?
- occurs in the other limb to compensate from a withdrawal reflex (one leg moves, the other prepares to bear all the persons weight)
What are the Golgi Tendon Organs (GTO)?
- Consist of sensory nerve endings interwoven among collagen fibres
- Type of muscle proprioceptor
- Are in series with the muscle fibres, respond to changes in muscle tension
- When muscle fibres contract, there is more tension on the bone and GTO afferent receptors are stretched, causing afferent fibres to fire
- Info from GTO reaches conscious awareness (aware of tension but not length)
Where is the CPG for locomotion located?
The spinal cord.
each limb has at least one CPG - so they are coupled
Ex: What are the control systems involved in the Control of Grip Function?
Feedback: (uses tactile receptors in hand)
Feed-forward: muscle activates before hand comes into contact with object in anticipation
Need both control systems because feedback alone is too slow, and feed-forward alone is difficult to compensate when predictions are incorrect
