Lecture 15 - Control of movement Flashcards
Voluntary muscle control originates
Voluntary muscle control originates in the brain and must come down the spinal cord in order to activate motor neurons, for the most part the output from the motor cortex is activating interneurons which is the circuitry inside the spinal cord that is designed to remove the level of control down the spinal cord to free up the brain for other purpose
Basal ganglia
Basal ganglia = allows planning and intentional movement
Cerebellum
Cerebellum - monitor movement and ensures that it is the movement we desired
Spinal cord involved in
Processing commands from brain
Reflexes Stretch reflex (muscle spindle) Lab. 4
Rhythmic motor patterns, from ‘central pattern generators’:
Spinal cord & brainstem circuits generate basic patterns of rhythmic muscle activity for:
e.g. such as a snake moving where it undulates its whole body which originates from the spinal cord or a horse changing speed they might think about getting faster but not the movement actually required to do this i.e. they do not consciously change from all fours on the ground to two feet on the ground when going from walking to cantering
Locomotion (walking, running)
Breathing
Chewing
Swallowing
Do not have o think about each motion in these activities, they occur as a sequence of events that flow as a result of the rhythmic activity of the neural circuits
Voluntary commands and brains role
Commands from brain start/stop, and regulate speed, force, direction (this is the regulation that occurs for these activities)
Primary motor cortex
Ordered map of body (somatotopy) Regulates spinal cord motor systems Via Corticospinal (pyramidal) tract - Output from the primary motor cortex foes down the corticospinal tract
Somatotopy in primary motor cortex
Body parts represented roughly sequentially across cortex
Area devoted to each part is:
Dependent on level of fine control
Dependent on extent of use
i.e. representation is “plastic”
Damage causes problems with movement, particularly with fine voluntary control in specific parts of the body
Stimulation activates movements in specific parts of the body
Corticospinal pathway
Output from motor cortex controls spinal neurons, for fine, isolated movements (crosses to opposite side). [Note: most input is to interneurons]
Major one especially for direct control and more dextrous movements
Crosses over
Goes to larger groups of muscle that control the limbs
Brainstem pathway
Coordinated activity in large muscle groups, for posture, locomotion, routine activities (crossed and uncrossed)
Parts crossed and other parts are not crossed
Special roles of the primary motor cortex
Special role in controlling force of muscle contractions
Greater rate of neuronal activity, more input to motor units, greater force
Special role in controlling direction of movements
Relative activity of many cortical neurons, controlling muscles each side of a joint, control the direction of movement.
Most axons from motor cortex synapse on interneurons, not α-motor neurons
Special role of motor cortex neurons which synapse directly on α-motor neurons
Exception for higher primates
Have a particularly direct, fast and powerful effect
Mostly for control of distal limb (hand & fingers)
Most developed in higher primates
Claudia example
Think is not a good word as thinking about a movement does not necessarily cause movement
EMG activity in the muscle that is being used to operate the computerised motors in her arm
Brain is able to control what it thinks is the arm which is actually the chest muscle which is used to control the arm
(look at image in notes as well)
neural systems controlling movement - hierachal organisation
Highest level = higher centers like association cortex and prefrontal cortex
middle level = sensorimotor cortex, thalamus, basal nuclei, brainstem, cerebellum
Local level = brainstem and spinal cord
Flow chart of neural systems controlling movement
look at image in notes
Sensorimotor cortex
Sensorimotor cortex = primary sensory and primary motor cortex are mixed together here
Prefrontal cortex
Prefrontal cortex - form our intentions, make plans of what we want to achieve in the environment
Loop where the motor programming occurs
Basal nuclei to thalamus to sensorimotor cortex loop is the loop where the motor programming is occurring
Keeps going around until this release a dose of dopamine to the system and the dopamine release at the substantia nigra confirms that the proposed way of moving the body is actually going to be successful and at this point the inhibition is removed from the motor cortex and the motor neurons can then send output down the corticospinal pathway down to inter neurons and motor neurons directly to control muscle. So we have this planning stage where the information is going around and around a loop from the level of our intention down into deeper regions that are for programming and established programmes of muscle and the motor cortex then thinks it is an okay signal for the motor cortex to send out as an output to actually carry out that activity
Roles of the basal ganglia
Basal ganglia monitors and helps plan cortical activity involved in movement
Helps cortex select combinations/sequences of muscle activation
Cycle through loop (cortex – basal ganglia – cortex) occurs several times during preparation for movement
Positive feedback (withdrawal of inhibition) to cortex for selected motor output pathways Positive feedback in the form of dopamine released from the substantial nigra and once this occurs and the motor cortex is no longer prevented from giving output down the spinal cord and into the muscles then we need this in order to start doing things
Needed for initiation of movements
Dopamine input [from substantia nigra] vital to allow proper functioning
Death of dopamine neurons produces Parkinson’s disease
Death of dopamine neurons produces
parkinsons disease
parkinsons disease
Difficulty beginning movements, slowed movements, tremor
Cause uncertain, genetic + environmental, trauma
Treatments:
Dopamine replacing drugs (precursors for dopamine, taken up and released by surviving substantia nigra cells),
Deep Brain Stimulation
and (possibly) transplantation of dopamine cells
Cerebellum flow chart
look at notes
Loop of the cerebellum
Feedback loop where information is going back and forward and round and round, when we are forming a motor programme to design some muscle action which eventually gets given the ok signal from the substantial nigra in the basal ganglia through dopamine release to come out from the spinal cord and motor cortex we have to incorporate that into the motor programming where the body is to start with
Cerebellum circuitry
Basic circuit repeated millions of times
Resembles a massive “parallel processor”
Job is to compare one thing to another, compares what is actually happening to what the plans were
Roles of the cerebellum
Cerebellum helps plan, execute, and learn motor programs
Integrates sensory information with planned motor programs
Organizes timing of individual muscle contractions around joints
Compares the intended result of a planned movement with the actual result, and modifies ongoing activity, for smooth and accurate motor control
May also be used by other brain systems
[cognition, episodic memory, reading, emotion, dyslexia, schizophrenia, autism]
Cerebellar injury
= DRUNKEN GAIT
Cerebellar injury results in movements that are slow and uncoordinated. Individuals with cerebellar lesions tend to sway and stagger when walking (‘drunken gait’).
Damage to the cerebellum can lead to:
1) loss of coordination of motor movement (asynergia),
2) the inability to judge distance and when to stop (dysmetria),
3) the inability to perform rapid alternating movement (adiadochokinesia),
4) movement tremors (intention tremor),
5) staggering, wide based walking (ataxic gait),
6) tendency toward falling,
7) weak muscles (hypotonia),
8) slurred speech (ataxic dysarthria), and
9) abnormal eye movements (nystagmus).
Alcohol and cerebellum
Alcohol affects the cerebellum so drunk people often have problems with motor control
Chronic alcoholism will lead to degeneration of the cerebellum because of the long term messing with the GABA receptors
