L15 - Control of Body Movement Flashcards
reflex vs voluntary movement
reflex movements:
- rapid reproducible, automatic motor response to external stimulus
- employs simple neural circuit involving peripheral nerves and spinal cord
- does not require involvement of higher brain centres
voluntary movements:
- wide variety of movements of varying speed, duration, and complexity
- typically involves complex patters of sensory and motor processing
- initiated on demand (voluntarily) in brain and many higher centres involved in control
describe the stretch reflex (use image on slide)
Important for maintaining balance and posture
Muscle stretch detected by muscle spindles (modified fibres wrapped in afferent nerve fibres)
Alpha-motor neurons of same and synergistic muscles stimulated (A+C)
Interneuron stimulated (B; inhibitory)
Opposing muscle group(s), on the opposing side of the limb, are inhibited due to cell body being hyperpolarised
Jaw-jerk reflex is used to test activity of trigeminal nerve.
describe the tension reflex (use image on slide)
Prevents damage to muscle caused by excessive tendon tension
Triggered through activation of golgi tendon organ:
- afferent nerve fibres wrapped around collagen bundles in tendons
- tension in tendon distorts receptor endings -> activation
- results in inhibition of the muscle -> reduce force -> protect muscle
Passive stretch of relaxed muscle results in less tendon stretch and fewer APs generated compared to muscle comtraction
describe the withdrawal reflex (can use diagram in lecture)
Purpose is to withdraw from a painful stimulus
Nociceptor is stimulated (pain signal)
Lower limb process is more complex than upper limb: (maintain balance)
- alpha-motor neurons of ipsilateral flexors are stimulated
- alpha-motor neurons of ipsilateral extensors are inhibited
- alpha-motor neurons of contralateral flexors are inhibited
- alpha-motor neurons of contralateral extensors are stimulated
Interneurons required:
- some lead to depolarisation of alpha-motor neurons
- others lead to hyper polarisation of alpha-motor neurons
Jaw unloading reflex is bilateral and leads to depression of mandible
- biting something hard that cracks suddenly, reflex prevents teeth clash and damage
describe the motor control hierarchy (three levels, also diagram on sides)
Highest level: command neurons
- consciously planned action decided
Middle level: sensorimotor cortex, basal nuclei, thalamus, cerebellum, brainstem
- create a motor programme: pattern of neural activity required to properly perform desired action
- specify specific postured and movement required for action -> subprograms
- receive input from receptors in muscles, tendons, joints, skin, vestibular system, eyes: information about surrounding environment and body position in space
Lower level: brainstem and spinal cord interneurons, receptors, muscle fibres
- active specific motor neurons
- specify tension in muscles, angles of joints at specific times necessary to complete motor programmes
descibe motor control heirachy in terms of how they adjust
Motor programmes are continuously adjusted during the course of movements
- middle level nuclei receive updated afferent information about body position in space - proprioception
- modify and control the movement: adjust strength of muscle contraction, adjust posture etc
As complex actions/skills are practiced the motor program is refined. become more accurate, fewer corrections will need to be made
describe the role of the prefrontal cortex
Organises thoughts and actions
Intimately involved in “executive functions”
- cognitive function - acquiring knowledge through thought and experience
- social behaviour (incl predicting consequences and deciding on social acceptablity of actions), planning, language, decision making, risk assessment, personality, emotion etc)
- used to recall and consider information not currently available from the environment
- recall of past events can be used to help plan future events
describe the role of the primary motor cortex
Spatial ‘map’ of body (somatotopy)
Area devoted to muscles in each region related to level of fine control and movement complexity (ie. not to muscle size)
Area may change as a function of use (ie. it is ‘plastic’)
Damage to a specific region (eg. stroke) results in movement defects in the associated muscles
Located on both sides of the brain, outputs are crossed (ie. left brain controls right side of body)
Regulates spinal cord motor systems via corticospinal tract
describe the role of the corticospinal tract
From the cortex to the spine
- efferent motor signals
- 2 neurons in pathway
1st neuron:
- cell body in primary motor cortex
- descends to brainstem
- decussates (crosses midline of body) in medulla oblongata
- continues down spinal cord to level of exit
- terminates in ventral horn of spinal cord
2nd neuron (alpha-motor neuron):
- cell body in ventral horn of spinal cord
- exits spine and has stimulatory synapse at NMJ of target muscle fibre(s)
describe the branistem pathway
From the brainstem’
Key pathway for maintenance of balance and posture
efferent motor signals
2 neurons in pathway
some neurone decussate, but most do not
1st neuron:
- cell body in brainstem
- descends down spinal cord level of exit
- terminates in ventral horn of spinal cord
2nd neuron (alpha-motor neuron):
- cell body in ventral horn of spinal cord
- exits spine and has stimulatory synapse at NMJ of target muscle fibres
how does coordination and correction happen in the brain (diagram on slides)
Need to monitor progress
Continue to compare goal with changes due to progress through motor programme and changes in the envrionment
Involves both conscious and unconscious changes
Basal nuclei adjust patterns of movement in two ways:
1. they alter the sensitivity of the pyramidal cells to adjust the output along the coriticospinal tract
2. they change the excitatory or inhibitory output of the medial and lateral patways
Cerebellum monitors balance and equilibrium and adjusts upper motor neurons activity
what is the role of the cerebellum
Helps plan, execute and learn motor programmes.
Integrates sensory info with planned events
Organises timing of muscle contractions
Compares planned movement with actual result, modifies ongoing activity to make movements smooth and accurate
Cerebellar injury results in movements that are slow and uncoordinated (ataxia)
- drunken gait
- dysmetria - inability to judge distances and stopping points
- tremors
- muscular weakness (hypotonia)
- slurred speech (ataxic dysarthria)
- abnormal eye movements (nystagmus)
describe the basal nuclei’s role and what the diff ones are called
Deep cerebral nuclei:
- caudate nucleus
- putamen
- globus pallidus
Mid-brain nuclei:
- substantia nigra
Planning, initiating and monitoring of movements
Involves excitatory and inhibitory processing loops: cortex - basal nuclei - cortex
how do basal nuclei signal (input from where, output from where, pathways, etc) - also diagram on slides that need to understand but not memorise
Basal nuclei help establish appropriate motor programmes
- sequence of movements to accomplish desired actions for smooth movement
Input from cortex to caudate-putamen
Output frim caudate-putamen to globus pallidus via 2 pathways:
- Direct pathway: enhances motor activity
- Indirect pathway: reduces activation of cortical neurons
Neurons inn substantia nigra release dopamine which is essential for proper basal nuclei function and resultant movement
how does parkinson’s disease occur
Neurodegeneraton of dopamine neurons in substance nigra reduces DA output:
- difficulties with movement initiation
- slowed movements (bradykinesia)
- siffness
- tremor
Less dopamine:
- decreased activity of direct pathway
- increased activity of the indirect pathway
- decreased stimulation of motor cortex
Treatments:
- dopamine precursor medication
- deep brain stimulation
describe central pattern generators
Central pattern generators are networks of neurons in brainstem and spinal cord capable of driving rhythmic behaviour (eg. breathing, chewing, walking) without input from higher centres
Breathing:
- need to balance respiration to metabolic demand
- need smooth muscle rendition between inspiration and expiration
- involves stretch receptors and chemoreceptors
- opioid medicines can inhibit inspiratory signals
describe orofacial motor control (diagram on slides)
Chewing:
- central pattern generators allow for continued cycling until food is ready for swallowing
- continually modified based on feedback from sensory receptors
