Movement Flashcards
What is the motor hierarchy (most important to least important)?
Cerebral cortex, basal ganglia, cerebellum, spinal cord
How does the spinal cord connect to muscles?
Spinal cords has hundreds of specialised nerve cells called motor neurons which increase their rate of firing. The axons of these neurons project out to muscles where they activate contractile muscle fibres. The terminal branches of the axons of each motor neuron form specialised neuromuscular junctions on to a limited number of muscle fibres within one muscle
What happens after motor neurons are connected to produce movement?
Each action potential in a motor neuron causes the release of neurotransmitter from nerve endings and generates a corresponding action potential in the muscle fibres. This causes Ca2+ ions to be released from the intracellular stores inside each muscle fibre which triggers contraction of muscle fibre, producing movement
What is used to measure the level of electrical activity produced by muscles?
Electro-myographic recordings (EMGs)
What important part does the spinal cord play?
It plays an important part in the control of muscles through several reflex pathways such as withdrawal reflex and stretch reflex
What kind of reflex is knee-jerk?
Stretch reflex
What type of nerve cell does knee-jerk involve?
Sensory neurons that signal muscle length, connected through synapses to motor neurons that cause movement
How are complete behaviours formed?
Reflexes combine together with more complex ones in spinal circuits that organise behaviours
What is the final common path to muscles that move your bones?
Motor neurons
What happens in the cerebral cortex?
An large number of calculations have to be made by cells for each element of movement to ensure that movements are carried out smoothly and successfully
What happen between the cerebral cortex and motor neuron of the spinal cord?
Critical areas in the brain stem combine information about the limbs and muscles ascending from spinal cord with descending information from the cerebral cortex
Where is the motor cortex?
Thin strip of tissue running across the surface of the brain, directly in front of the somatosensory cortex
What happens in the motor cortex?
There is a complete map of the body: nerve cells that cause movement in different limbs are topographically arranged, neurons may be found in any part of this map that are active about 100ms before activity in the appropriate muscles
What is used to specify the actions by firing of an ensemble of neurons?
Population code
What does the pre-motor cortex do?
It is involved in planning actions, preparing spinal circuits for movement and in processes that establish links between seeing movements and understanding gestures
What are mirror neurons used for?
Imitating and understanding actions
What happens in the parietal cortex?
A number of different cortical areas are concerned with the spatial representation of the body and of visual and auditory targets around us and where interesting targets are with respect to us
What is parietal neglect?
Failure to notice objects (often on left side) or even ignore the left side of own body
What happens if you damage right parietal lobe?
There is hemispatial neglect where the left side is ignored
What is the basal ganglia?
A cluster of interconnected areas located beneath the cortex in the depths of the cerebral hemispheres
What do basal ganglia do?
They are crucial in the initiation of movements
How does basal ganglia act?
Like a complex filter, selecting information from amongst the enormous numbers of diverse inputs they receive from the anterior half of the cortex and the output feeds back to the motor cortical areas
What regions are considered the anterior half of the cortex?
Sensory, motor, prefrontal and limbic regions
What is Parkinson’s disease characterised by?
Tremor and difficulty in initiating movements
What causes Parkinson’s disease?
Degeneration of neurons in the substantia nigra whose axons release dopamine into the basal ganglia, there is a precise arrangement of dopamine axons onto their target neurons in the basal ganglia
What is the treatment for Parkinson’s disease?
Treatment with drug L-Dopa which is converted into dopamine in brain, restores dopamine levels and movement
What else is basal ganglia important for besides the initiation of movement?
It is important in learning, allowing the selection of actions that lead to rewards
What is the cerebellum important for?
It is crucial for skilful smooth movements
What does damage to the cerebellum cause?
Poorly coordinated movements, loss of balance, slurred speech and cognitive difficulties
What substance has a powerful effect on cerebellum?
Alcohol
What else is cerebellum important for besides skilful smooth movements?
Motor learning and adaptation, almost all voluntary actions rely on fine control of motor circuits and cerebellum is important in their optimal adjustment
How does the cerebellum work?
It has a very regular cortical arrangement and seems to have evolved to bring together vast amounts of information from the sensory systems, cortical motor areas, spinal cord and the brain stem. It generates a model fo how motor systems work and builds this model using synaptic plasticity that is embedded into this network
What does the acquisition of skilled movements depend on?
Cellular learning mechanism called long-term depression which reduces that strength of some synaptic connections
What does the Purkinje cell of the cerebellum look like and do?
It has an extensive branching of its dendritic tree which serves to receive the myriad of inputs required for the precise timing of skilled movements we learn
What is the chemistry underlying actions and habits?
Neurotransmitter dopamine is released on to neurons in the basal ganglia where it acts at metrabotropic receptors
What does dopamine serve as?
An incentive to act and a reward signal for acting appropriately
When is the release of dopamine the highest?
When the reward is unexpected
When do dopamine neurons fire the most strongly?
Dopamine neurons fire most strongly at a stage of learning when it really helps to give a strong reinforcement to motor system for having produced the right output
How does movement get strung together?
They get strung together in a sequence through release of successive burst of dopamine
What happens when complex movements become habitual?
System free-runs without dopamine reward
What plays a role if movements have to be accurately timed?
Cerebellum
