The Motor System Flashcards
Give examples of voluntary motor activities
Walking, talking and running.
Goal-directed is
Conscious, explicit and controlled.
Habits are
unconscious, implicit and automatic.
Name involuntary actions:
eye movement, facial expressions, jaw, tongue, postural muscles throughout trunk.
Name a sophisticated system developed throughout evolution
Defence
Different levels of sensory input have different effects on ..
motor output
Give an overview of the sensorimotor system
Primary motor cortex - command to move leg/arm
Brain stem motor nuclei
Spinal motor circuits
M2 - motor planning e.g planning to move your arm is in your secondary motor cortex
Association cortex - higher level planning- perceptual context for movement.
What systems make up perceptual context and what is the sequence
Visual system
Auditory system -> motor plan (M2) -> M1 primary
Memory system motor cortex
Final stage: Movement implementation
What other brain part is associated with perceptual context?
Basal ganglia
What is the function of the basal ganglia?
Circuit of structures decides what your going to do and stick to those decisions.
What is the function of the cerebellum?
How to do it- fine tuning action to make precise adjustments in a movement.
What is motor control governed by?
Upper and lower motor neurons.
The lower motor neuron has…
a cell body in brainstem (or spine) and projects to the muscle that you want to switch on or off.
How are the upper motor neurons and lower motor neurons connected?
The upper motor neurons originate in higher centres and project down to meet the lower motor neurons, synapse and goes to muscle.
How much body weight do muscles make up?
40%
What are the three types of muscles?
Cardiac
Smooth (blood flow/ gut)
Skeletal (attached to skeleton does movement)
Where is the smallest skeletal muscle found?
stapediv in the inner ear that alters volume and dampens loud sound.
Where is the largest skeletal muscle?
In bum
Where is the strongest skeletal muscle?
in jaw
Where is the hardest working skeletal muscle?
heart
eye muscles
neck
What happens to muscles over time and after training?
Number of muscle fibres vary, seems genetically determined.
In two people where one person is skinny and one is muscly what difference would this be of the muscle fibre?
Type of muscle fibre could be different.
Muscle size and strength refers to what?
Cross sectional area of individual muscle fibres and different proportions of different types of fibre.
Muscle can only
contract or relax
The activation of muscle fibres is
all or none.
What arrangement are muscles in?
Antagonistic arrangement combined co-ordinated action.
Recruitment of muscle fibres-
fast/slow twitch, small and large motor units.
State the process of muscle contraction
Thick filament myosin heads attach to thin filaments then bends releases, touches it extends the neck. Involves magnesium/calcium ions and ATP energy.
Descibe the function of the motor unit…
Switches on activates all muscle fibres at only single alpha motor neuron and all muscle fibres it innervates. Controls small number of muscle fibres deliver small amount of force. Different motor neurons innervate different numbers of muscle fibres- fewer fibres means greater movement resolution - those innervating finger tips and tongue.
The motor unit is the final common pathway for motor control.
What happens when alpha motor neuron activates?
Depolarizes and causes contraction of all fibres in that unit.
Muscle fibres innervated by each unit are…
the same type of fibre and often distributed through the muscle to provide evenly distributed force and may help reduce effect of damage.
What does it mean for more motor units that fire?
More fibres contract more power.
State the features of a motor pool..
All the lower motor neurons that innervate single muscle
The motor pool contains both the alpha and gamma motor neurons
Motor pools are often arranged in a rod like shape within the central horn of the spinal column.
Where is white matter?
Fibre tracts by axons
Where is grey matter?
Cell bodies
Where does sensory input go?
Through dorsal root.
Where does motor output go?
Through ventral root.
Where are alpha motor neurons arranged?
Innervate mid line parts of body are arranged near centre
Outer part for cell bodies
What is the process of sensing in muscles?
Cell bodies project out of ventral horn go to muscle, sensory information coming in from dorsal horn synapse onto the motor neurons. Central neurons also project up to the brain, the project to lower motor neurons. Motor command going down sensory information going up.
What two things do you need to know about muscles in relation to the CNS?
Golgi tendon organs sense tension
1) How much tension is on the muscle; muscle spindles sense stretch.
2) What is the length (stretch) of the muscle.
What does the Golgi tendon organ do?
It’s within the tendon and links the muscle to the bone. Mostly just sending ascending sensory information to the brain via the spinal cord about how much force there is in the muscle
What happens to Golgi tendon organs under extreme tension?
Inhibit muscle fibres to prevent damage.
What do muscle spindles do?
Muscle spindles - Muscle length (stretch)
Muscle spindles sense the length of muscle ie the amount of stretch. Heavily involved in the reflux circuit.
What is a reflux circuit?
Multiple fibres - four muscle fibres - motor pool
Extrafusal muscle fibres
Intrafusal muscle fibres
Muscle spindles stretched - message sent to the spinal columns through sensory/dorsal root to alpha motor neurons then signal extrafusal muscle fibres to contract.
A system that detects stretch is needed…
regardless of the current muscle length.
If intrafusal muscle fibre is controlled by same motor neurons as extrafusals…
when muscles is slack or taught the system won’t be sensitive to slight changes.
Intrafusal fibres are…
innervated separately by motor neurons
What is muscle spindle feedback?
Efficient motor control system needs to know how much each muscle is stretching - information provided by muscle spindles.
Embedded within most muscles composed of intrafusal fibres, detect strength regardless of the current muscle length.
how are sensory fibres arranged around the intrafusal fibres?
They are coiled.
What is the interaction between intrafusal fibres and gamma motor neurons?
Intrafusal fibres are innervated separately. They keep the intrafused fibres set at a length that optimizes muscle stretch direction.
What does stretched muscle do to muscle spindle>
Activates a lot of muscle spindle firing.
What does relaxed muscle do to intrafusal fibres?
Intrafusal fibres slack - tighten intrafusal fibres so can detect stretch in muscle
What does stretch reflex do?
Signals muscle spindle counteracts it to put limb I the right position.
What is the withdrawal reflex?
E.g step on sharp object -through dorsal root take foot off and extend other leg to put weight on it.
What is reciprocal innervation?
Sherrington’s law of reciprocal innervation. Explains why the contraction of one muscle induces the relaxation of the other.
Control of gross movement patterns can be..
devolved to simple spinal circuitry, but constant modulation regained to account for the unexpected.
In higher CNS centres …
constant adjust ongoing activity resolve conflicting demands on the motor system and direct it towards goals.
What does average number of muscle fibres in a motor unit depend on?
Level of control
Strength
Units are recruited in order of
size.
Fine control typically require..
lower forces.
What are the three types of muscle fibre?
Slow - strong endurance
Fast fatigue resistant - long period of exercise
Fast fatigable - Jump/ burst out of power.
What does the primary motor cortex do?
Issues a command to move particular muscles or motor units in a particular way.
Voluntary movement-
wider association
What initiates voluntary control and what regulates it?
Initiated by primary motor cortex and basal ganglia nd cerebellum regulate this.
What happens without cortical movement?
Balance and control.
What happens when the vagus nerve projects to the larynx?
There is a control of speech.
What is the circuit of the vagus nerve and larynx connected with?
The cerebellum and other brainstem sensorimotor systems.
How has speech changed over time?
Believed to have started with a series of grunts.
Cortex under the influence of speech sculpts the circuits that gained control to refine speech sounds through and evolutionary adaptive process increased capacity to which they can be refined.
Descending projections from cortical motor areas state what happens
Primary motor cortex project down through spinal column into spinal segment that it reads to get to synapse with lower motor neurons to get to muscles and control motor units.
Lots of circuits in the brain - only one synapse for this process, the original medial premotor cortex or upper motor neuron straight out of motor cortex straight down the spine. Until you get to the spinal segment where it controls your limbs and arms there’s a synapse there onto lower motor neuron, sometimes interneurons are involved. Only one synapse two neurons involved - direct control over other motion and behaviour.
Where does motor command originate?
In the motor cortex pyramidal cell.
Where are cell body located?
In grey matter of cortex
What can pyramidal cell axon do?
It can project directly to the spinal cord and onto lower brainstem motor neurons.
What do most cortical projections innervate?
Contralateral motor units.
Pyramidal cortical control may…
operate in co-operation with brainstem control.
What is the motor cortex: the homunculus?
A motor homunculus represents a map of brain areas dedicated to motor processing for different anatomical divisions of the body. The primary motor cortex is located in the precentral gyrus, and handles signals coming from the premotor area of the frontal lobes.
Few motor command require…
isolated activation of a single motor unit.
What is the primary descending white matter pathway that control for the motor system? When does information descend in them?
Ventromedial tracts
When it gets to part of the spinal cord it wants to exit from - lower motor neurons control those muscles axons pop out of the pathway go into grey matter where has synapses with an interneuron or lower motor neuron come out to control the muscles.
Large parts of motor representation –>
Where muscles are controlled. Down then through medulla pyramid - (bulge on brain stem) white matter pathway.
What is the dorsolateral corticospinal tract involved in?
Mainly involved in contralateral distal (distant) limb muscles arms, finger, hands –> fine motor control.
Which parts of the spinal cord does the dorsolateral corticospinal tract descend in?
Red nucleus - involved in contralateral distal limb muscles - facial muscles and distal limb muscles.
Say a bit about the ventromedial corticospinal tract
Ventromedial corticospinal tract - stays ipsilateral on one side - where the white matter is. But the axons project bilaterally. More about limb muscles near the centre of your body.
The ventromedial cortico brainstem- spinal tract state a bit about this
Synapses in a bunch of different brains stem nuclei: controlling trunk - shoulder/elbow/hips/knees and proximal limb muscles
Talk about the tectum
Low level visual processing - salient images of the visual world –> appearing - disappearing.
State the similarities and differences of the dorsolateral tracts and the ventromedial tracts
Both contain a direct corticospinal route
Both contain an indirect route via brainstem nuclei but in ventromedial tracts its via tectum, vesticular nuclei, reticular formation and cranial nerve nuclei. In dorsolateral tract its via the red nucleus.
Dorsolateral tract differences:
Innervate contralateral side of one segment of spinal cord.
Sometimes project directly to alpha motor neuron.
Project to distal muscles eg fingers.
Ventromedial tract differences:
Project to proximal muscles of trunk and limbs
Diffuse innervation projecting to both sides and multiple segments of the spinal cord.
What is the basal ganglia?
Its a group of nuclei living deep within cerebral hemispheres. Receives excitatory input from many areas of the cortex. sends inhibitory projections back to the cortex via the thalamus.
What does neurotransmitter does inhibitory projections?
GABA
What five nuclei are involved in inhibitory?
Substantia nigra (pars compact & pars reticula)
Caudate and Putamen (together - striatum)
Globus Pallidus (internal & external segments
Subthalmic nucleus
Basal ganglia
What diseases are caused by the disruption of GABA?
Huntingtons Parkinson's Hemiballisimus Tourettes Tardive dyskinesia
What is the selection problem?
There is multiple command systems
spatially distributed
Processing in parallel
All act through final common motor path
What are predisposing conditions?
Energy balance
Fluid balance -> Motor resources -> behavioural output
Threat
Increasing numbers of competitor
Centralised selection
Selection system sticks to something to satisfy need -> basal ganglia sits at the heart of this - output inhibit. Inhibits less important needs one need is allowed through.
The cerebellum
No direct projection to lower motor neurons - instead modulate activity of upper motor neurons 10% brain weight. half of all neurons. Projects to almost all motor neurons. When damage movement becomes jerky erratic and poorly coordinated. Voluntary movement loss fluidity and appears mechanical and robot like. Intention tremor
What is dysarthria?
Disruption of the control of speech, slurring some people born without one and show little impairment.
SPINAL CORD
Cerebral cortex -> - Thalamus -> Motor cortex
copy of motor command
First arrow should state pons.
State features of cortical
Mainly from motor cortex
Also somatosensory and visual areas
Parietal cortex
State features of spinal
Sensory touch from muscle joints
Propiriocephine info about limb position and movement.
Vestibular
Rotational and accelatory head movement.
State key points of the cerebellum
1) Knows what current motor command is
2) knows about actual body position and movement
3) It projects bulk to motor cortex - computes motor error and adjusts cortical motor commands accordingly.
Argued that the cerebellum ..
Not just motor control, motor learning too inn collaboration with basal ganglia and cortical circuits
Functional brain imaging studies have demonstrated that the cerebellum is involved in a wide variety of non-motor tasks.
