L23 - neurophysiology of motor control Flashcards
Why are movement injuries common?
Because a large portion of the brain is devoted to voluntary movement.
What is a reflex movement?
Rapid, reproducible, sterotypical, autonomic motor response to an external stimulus
What kind of circuit in a refex movement?
Simple neural circuit of spinal cord and peripheral nerves (sensory stimulus here –> info sent to SC locally and motor output from SC)
What is a voluntary movement?
Wide variety of movements of varying speed, duration and complexity
What kind of circuit in a voluntary movement?
Complex patterns of sensory and motor processing, centres involved in control is in the circuit i.e parts of the brain is required
What is a stretch reflex? Monosynapse at the SC
Stimulate a receptor (tendon) –> pull muscles i.e LENGTHENING stretch receptors present in muscle spindles –> opens mechanically gated ion channels leads to AP (receptor potential type of local potential - localised change in potential in the SENSORY APPARATUS of sensory nerve cell) –> info passed to posterior root ganglion unipolar cell body if AP occurs–>info processed in SC –> activation of motor neuron (sensory synapses with a motor neuron in the LATERAL horn - EXITATORY connection) –> ventral root –> changes length of muscle and muscle contraction in response to stretch
Which receptors give a sense of position?
Proprioceptors
Withdrawal reflex pathway (polysynaptic)
sensory receptor (Thermal - nociceptors in skin - free nerve endings) –> mechanically gated ion channels –> AP to dorsal root ganglion –> SC –> interneuron in dorsal horn to inhibit and excite motor neurons –> motor neuron in ventral horn
Also info sent through dorsal column pathway so brain is aware of sensation
What does the brain need to know
Position of muscles needed for an action so it uses proprioceptors eg muscle spindles to do that
What happens when there is movement of the joints and muscles
The proprioceptors are still at work so that brain knows the correct action is being carried out
What is the brainstem and SC responsible for?
*Simple cranial and spinal reflexes
*Group of neurons called central pattern generators control autonomic activity such as breathing and chewing so that thalamus is not overwhelmed with info input i.e rhythmic patterns
What is the Pons and Medulla Oblongata responsible for?
Balance replexes and more complex respiratory reflexes
What is the Hypothalamus responsible for?
Reflex motor patterns related to eating, drinking (osmotic pressure of ECM changes) , sexual activity, modifies respiratory reflexes
What is the Basal nuclei responsible for?
Basal ganglia modify motor and reflexive patterns at subconcious level, inititiation of voluntary movements
*Adjust output along corticospinal tract by altering pyrimydal cells sensitivity
*Change ex/in output of medial/lateral pathways
What is the motor cortex responsible for?
Initiates voluntary motor movement
What is the Thalamus and midbrain responsible for?
controls reflexes in response to auditory or visual stimuli
What is the Cerebellum responsible for?
complex motor patterns through feedback loops
What is the prefrontal cortex responsible for?
Making a decision of an action that is socially acceptable based on proprioception, memory
*emotion and personality
*Co-ordinates with basal ganglia and premotor cortex to carry out an action in their right order
What does the primary motor cortex form?
Latin for a small body homunculus
What do areas of the motor cortex mean?
Related to the complexity of the movement i.e more complex movements of the face have more neurons in the brain
Cerebellum
*motor programs - organises complex movements without having to “practice” everytime i.e a learned behaviour
*intergrates sensory info into planned events so voluntary movements can be modified
*Organises timing of of muscle contraction and comparing planned with actual movement with the pathways of the primary motor cortex –> correction mechanism
*Modify the output pathway and makes sure intentended action is carried out
*disorders of the cerebellum results in ataxia i.e movement disorders
Pathway of voluntary action
Prefrontal cortex –> premotor cortex –> basal nuclei and cerebellum to activate neurons that initiate movemnt and which sense the position of the required body parts and send info to the cortex? premotor cortex neurons activate appropriate neurons in primary motor cortex are picked and AP carried out to lower motor neurons –> change in position detected by sensory neurons and fed back to the cerebellum which then modifies pathways for the pri motor cortex and basal ganglia so that correct action is carried out i.e original plan
What kind of neuron is the unipolar cell body?
Somatic sensory neuron
Channels at the input end of the unipolar somatic sensory neuron
Mech GIC
What is a receptor potential
Localised change in voltage in the sensory apparatus of a sensory nerve cell
synapse between sensory and motor neuron is an?
Excitatory connection
The stretch synapse is what kind of neural circuit?
Monosynaptic, requires MGIC
What kind of neural circuit is the withdrawal reflex?
Polysynaptic
What is an interneuron?
Receives info from a neuron and gives out info to another neuron
What other neuron does the interneuron interact with?
The inhibitory interneuron
Motor activates the flexors and inhibitory removes excitation of the extensors eg triceps must not be active
*Inhibit neuron that would excite the muscle i.e IPSP (one muscle active at one)
Central pattern generators
Initiate response, take feedback and keep those activities going
What does the thalamus do
Major relay centre for sensory info to required parts of the brain
Frontal lobe
*Executive functions –> decision making on position of the body, memory on past experiences i.e is it risky
Desire to initiate a movement arises in?
Prefrontal cortex
Ataxia
*Slow feedback through circuit because correction mechanism not activating
Cerebellar disease
*Speech impediment
*Ataxia
*Tremor
*Dismetria - misjudge distances (a learned behaviour)
