lecture 23 - motor control Flashcards
What is a reflex movement?
A rapid, reproducible automatic motor response to external stimulus.
Are reflex movements reproducible or irreproducible?
Reproducible
What parts of the nervous system are involved in reflex movement?
A simple neural circuit involving peripheral nerves, motor neurons and the spinal cord (no higher brain centres)
What are the overall steps in a stretch reflex (5)?
Receptor stimulation, sensory neuron activation, information processing in spinal cord (CNS), motor neuron activation, response by peripheral effector.
What occurs at the receptor stimulation step of a stretch reflex?
Mechanically gated ion channels are activated when the muscle spindle is stretched.
What occurs at the sensory neuron activation step of a stretch reflex?
The mechanically gated ion channels trigger an action potential that travels via a sensory neuron to the dorsal root ganglia.
What occurs at the information processing step of a stretch reflex?
Sensory info received from sensory neuron and processed in lower structures of CNS (spinal cord) before a monosynaptic (single synapse) is initiated to active motor neuron.
What occurs at the motor neuron activation step of the stretch reflex?
Motor neuron activated by single synapse (MONOSYNAPTIC) and leaves ventral horn, reaching a peripheral effector muscle fibre.
What occurs at the effector response in a stretch reflex?
Neuro-muscular synapse occurs, generating muscle contraction, causing a stretch.
What are the afferent components of the stretch reflex?
Receptor stimulation, sensory neuron activation, CNS processing.
What are the efferent components of the stretch reflex?
Motor neuron activation, peripheral effector response (e.g. muscle contraction)
What type of neuron is the sensory neuron in reflex movements?
Unipolar.
What are the locations of the components of the sensory neuron in a reflex arc of a stretch reflex?
Input zone at muscle fibre, cell body in posterior/dorsal root ganglion, output in dorsal root
What are locations of the components of a motor neuron in stretch reflex?
Input/cell body in ventral horn, axon exits through ventral root to the periphery where output zone is at a neuro-muscular junction.
What are the overall steps in a withdrawal reflex (5)?
Receptor stimulation, sensory neuron activation, info processing in CNS (and transmission to higher centres), activation of motor neuron, peripheral effector response.
What occurs at the receptor stimulation step in withdrawal reflex?
A painful stimulus is detected by sensory receptors (e.g. in the skin).
What occurs at the sensory neuron activation step in the withdrawal reflex?
Signal from sensory receptor is received by sensory neuron and transmitted to posterior/dorsal root ganglion.
What occurs at the CNS information processing component of the withdrawal reflex?
Synapse between sensory neuron and excitatory interneuron in posterior root ganglia. Excitatory interneuron then transmits a signal both to higher levels of the CNS (brain) and to a a motor neuron.
What occurs at the motor neuron activation step of the withdrawal reflex?
Motor neuron transmits information from an excitatory interneuron to a peripheral effector.
What occurs at the peripheral effector activation step of the withdrawal reflex?
Motor neuron activates a a muscle fibre (effector) at a neuromuscular junction, causing the muscle to withdraw from the source of the painful stimulus.
What is the function of the cerebral cortex, in terms of movement planning and execution?
Plans and initiates voluntary motor activity
What is the function of the basal nuclei, in terms of movement planning and execution?
To modify voluntary and reflexive motor patterns at the subconscious level.
What is the function of the thalamus and midbrain, in terms of movement planning and execution?
Control reflexes on response to visual and auditory stimuli.
What is the function of the cerebellum, in terms of movement planning and execution?
Coordinates complex motor patterns through feedback loops.
What is the function of the brain stem and spinal cord, in terms of movement planning and execution?
Controls simple cranial and spinal reflexes
What is the function of the pons and medulla oblongata, in terms of movement planning and execution?
Controls balance reflexes and complex respiratory reflexes
What is the function of the hypothalamus, in terms of movement planning and execution?
Controls reflex motor patterns related to eating, drinking, sexual activity and respiratory reflexes.
What regions of the brain have the greatest level of motor complexity?
Cerebral cortex, cerebellum, basal nuclei
What regions of the brain have the least level of motor complexity?
Brain stem/ spinal cord, pons and medulla oblongata, hypothalamus.
What part of the brain is responsible for the learning of motor programmes?
Cerebellum.
What are motor programmes?
Learned patterns of complex neural activity associated with specific movements
What neurons allow the body to sense its own movement, action, position and location?
Proprioceptive sensory neurons
Where is information from proprioceptive sensory neurons received to coordinate movement?
The cerebellum
What part of the brain controls postural movements for balance and body position?
Cerebellum
What is ataxia?
Loss of bodily movement control
What do disorders of the cerebellum typically lead to?
Ataxia
What are the key types of ataxia (4)?
Drunken gait, tremor, dysarthria, dysmetria
What is dysarthria?
A form of ataxia, affecting speech
What is dysmetria?
A form of ataxia, resulting in an inability to judge distance
Where does the desire to initiate a voluntary movement typically arise?
The frontal cortex/frontal lobes
What information, which goes into planning movements, is processed in the frontal cortex?
Intentions, memories and experiences, risk, personality, emotion, environment.
What is the process in which movements are generated when the brain decides to initiate a voluntary movement?
Descending pathways (corticospinal tracts) are activated. The tracts cross at the medulla to opposite side of the body and terminate at interneurons and motorneurons, which activate skeletal muscle in the periphery.
How does the motor cortex control the amount of force generated by a muscle during voluntary movement?
By controlling the frequency of action potential firing (summation) and altering the number of motor units activated (recruitment)
