motor systems Flashcards
motor behaviour
refers to the movements of the body produced as a consequence of contractions of skeletal muscles
first view of spinal reflexes
were highly specific, repeatable, unchangeable, unlearned movement patterns present in the spinal cord
this gave rise o the view of a reflex as a basic unit of behaviour, and that all behaviours were simply a long string of reflexes, with each reflex providing the stimulus to start the next
motor plan
hiearchial system
calling on lower units as needed
a plan for a series of muscle contractions
complex set of commands before an act occurs - feedback informs and fine tunes
EMG
records moment to moment positions of the body
labeled lines
each nerve input to the brain reports only a specific type of information
recognizes each modality as separate and distinct
ie/ one line signals smell, another touch and another taste
convey spatial info ie/ knowing where a mosquito is biting
what are the 6 categories in the motor behaviour hierarchy
simple reflexes, postural adjustments, locomotion, sensory orientation, species typical behaviours and acquired behaviours
simple reflexes
usually spinal but not always
ie/ knee jerk, pupillary constriction
usually involve only a few synapses
at any given level of the cord these reflect local processing and integration of corresponding sensory info from that level
usually involve only one or a couple of synapses between input side (sensory) and output side (motor)
postural adjustments
standing, head tilt, balancing
locomotion
walking, running, flying
within own species unique motor system
sensory orientation
aiming sensors at stimulus sources (turning eyes toward light)
moving body to align with environement
species typical behaviours
complex movements, but usually executed according to a pre wired plan
acquired behaviours
motor skills acquired and/or tuned through interaction with the environment
ie/ speech, tool use, fishing by bears, riding a bike
susceptible to change through experience
speed-accuracy tradeoff
for any muscle, increased speed can only come at a cost of decreased accuracy
sensory adaptation
progressed decrease in receptor’s response to sustained stimulation
allows us to ignore unimportant events
phasic receptors
a receptor in which frequency of action potentials drop rapidly as stimulation is maintained
tonic receptors
a receptor in which frequency of AP declines slowly or not at all as stimulation is maintained
closed-loop movement
accuracy is provided by the neural mechanism of using feedback from the sensory system
as a movement is executed, visual, proprioceptive or other sensory info is used to determine the accuracy of a movements
deviations from the intended movement, once detected, can be corrected “on the fly”
you can correct a movement if you felt that it was off
open-loop movemetns
some movements require maximal speed, such as a predatory attack, or an escape or grabbing for the keys that you just dropped
in these movements, the entire sequence is pre-programmed and then executed all at once (ballistic movement)
disconnection between systems and feedback, aiming for optimal speed - no time for feedback
ballistic movemetn
not subject to feedback and thus no on the fly correction
sequence of a movement is preprogrammed, and executed all at once
combinations of movements
many human movements, especially of the upper limbs combine both open loop and closed loop
ie/ visually guided reaching, the first phase is ballistic, and then the arm shoots out in the desired direction. as the hand nears the target, a closed-loop component guides the hand to the target and prepares the hand to grasp it
implicit memory
memory you can not describe - you have learned how to do it
motor ability is learned and retained through a non-conscious mechanism (bottom - up processing), as a consequence of simply doing it over again
ie/ riding a bike
cognitive stage
effortul - direct control over it
conscious guidance of the behaviour
ie/ hunting and pecking for each piano or computer key (when first learning)
what are the three stages in learning a new motor skill
cognitive stage
association stage
automatic stage
association stage
links are formed between certain actions and sucessful outcomes (and between other actions and unsuccessful outcomes)
this in the tuning phase
with enough practice, a certain pattern of movement is associated with being successful
automatic stage
once the skull has been acquired it can be rattled off as a single unit, produces smooth seamless behaviour
ie/ accomplished pianist, balance corrections in riding a bike
transcranial magnetic stimulation mapping
directly activate neurons on cortical surface which can cause a movement
has revealed that while motor skills are being learned, the cortical representation for the muscles being used actually enlarges and then shrinks down again after the skill is acquired
it is thought that this corresponds to an automatic stage, and that the learned skill is stored elsewhere in supplementary motor cortex
lowest to highest level of the motor control system
muscle
spinal cord
brainstem
motor cortex
subcortical regions - basal ganglia and thalamus
cerebellum
dorsal column system
delievers most touch stimuli to brain via dorsal columns of spinal white matter - then to thalamus
spinal cord
contains the motor neurons innervating the muscle
ventral horn motor neurons
contains skeletal muscles in response to motor commands from the brain
brainstem
nuclei project (transmit) to the spinal cord
integrates motor commands from higher levels
motor cortex
primary and supplementary areas - executive control
precentral gyrus
1/3 of axons in this tract originate from cells within here
organized via somatosensory map
major source of pyramidal tract
synergist
muscle that acts together with another muscle
antagonist
muscle that counteracts the effect of another muscle
primary motor cortex
also the precentral gyrus
executive region for initiation of movement
axons form pyrimydal tract
nonprimary motor cortex
contributes to the programming of movement
primary motor cortex to spinal cortex
main pathway for orientation of movement
skeleton
bodily movements constrained by joints
muscles use bones as levers around joints
degrees of freedom
number of directions possible in an articulation
tendons
connect muscle to bone
ligaments
connect bone to bone
flexor
muscle that flexes (bends joint)
usually toward body
extensor
muscle that straightens joint
usually away from body
myofibrils
each muscle fibers consists of
made up of myofilaments
myofiliments
where contraction occurs
make up myofibrils
consists of regularly arranged overlapping molecules of myosin and actin
myosin and actin
make up a molecular motor, runs on calcium
need calcium to make the binding sites available
contraction increases the overlap of myosin and actin - muscle shorten as they slide past each other
specialized to do fast or slow twitch
myosin
thick filament
actin
thin filament
myosin head
forms a mechanical bridge between actin and myosin
fast twitch
explosive movement
fatigues quickly
slow twitch
puts out less force, but can be sustained for a long time
fatigues slowly.
through training athletes enhance slow twitch properties
proprioception
body sense; info about the position and movement of the body
golgi tendon organ
load
receptor found in tendons that sends impulses to CNS when a muscle contracts
concerned with tension as muscle shortens
load is strong enough to stretch the tough tendon are sense by the nerve endings of this organ
monitors force of muscle contraction
2nd source of muscle contraction
muscle spindle
stretch
respond to length muscle and sends impulses to CNS when muscle is lengthened
contains: intrafusal fiber
intrafusal fiber
any of the small muscle fibers that lie within each muscle spindle
neuromuscular junction
basically a highly specialized synapse
large
action potentials arriving from the axon trigger Ach release, in the usual fashion
Ach binds to receptors on the motor endplate - the postsynaptic membrane, located on the muscle fibre
- typically large release of Ach
Ach produces a large depolarization, called an endplate potential as sodium and calcium ions rush in (channels open)
basically an AP that runs along the muscle fiber
respond to Ach release by triggering actin and myosin to produce a contraction
fasciculation
misfiring of a facial motor unit
ie/ twitch of an eyelid
ACh receptors
during developmet, and prior to formation of innervation, ACh receptors are found all along fibers
axon growth cone contacts fibre and as synapses develop, a signal of some sort causes receptors to migrate to the patches of membrane opposite to growth cone tips
thereafter, ACh receptors insert into the fibre membrane only at the endplate
the signaling between the neuron and fiber is complex and subject to various forms of regulation
receptor potentials
a local change in resing potential of a receptor cell in response to a stimuli
neuromuscular synapse elimination
early on, each fibre receives innervation from a number of different motor neuros
these synapses are weeded out, until each fibre receives innervation from one and only one motor neuron
this platicity is mantained into adulthood - if a motor neuron dies, its corresponding muscle fibres may recruit innervation from other neurons
motor unit
one motor neuron, plus all of the fibres which which it innervates, constitutes a motor unit
basic unit of movemetn
motor pool
motor nucleus
conversely, all of the neurons that innervate a single muscle are that muscles motor pool
usually closely aggregated in the spinal cord, sometimes as distinct nuclei
integration
as final common pathway, the motor neuron must integrate information from a large variety of sources
ie/ descending control from the cortex, modulation from other brain regions, direct input from sensory systems, actions of antagonist muscles
consequently, motor neurons have large cell bodies, and have large and complicated dendritic arbors
patellar tendon reflex
knee jerk
knee tap stretches quadriceps, as if knee had flexed
spindles are stimulated, signal via sensory nerve
excitatory impulse from spindle fires motor nerve
quadriceps contract, producing jerk
central pattern generators
these are networks of spinal motor and sensory neurons that coordinate to produce complex acts
in cats, the rhythmic stepping movements also imply that the central pattern generators acts as oscillators
chunking hypothesis
simple motor circuits may also become closely associated with one another through the effects of practice
happens at all levels of the nervous system
what are the two major divisions of motor projections
pyramidal system and extrapyramidal system
pyramidal system
most important
projection from the cortical motor neurons whose axons pass through the ‘pyramids of the medulla”
have betz cells
also called the corticospinal system
neuronal cell bodies in frontal cortex, pass through the brainstem forming pyramidal tract to spinal cord
betz cells
extra large, very fast cortical motor neurons
especially important for lower limbs and thus locomotion
extrapyramidal system
as name implies are axons from cells other than the pyramidal cells
axons pass into spinal cord
especially from subcortical regions. may play a special role in movement initiation, gait, error correction
include basal ganglia
lesions affect spinal reflexes
outside pyramids of medulla
pass through spinal cord via specialized motor regions
precentral gyrus
strip of frontal cortex in front of central sulcus
important for motor control
innervation ratio
muscle fibres/neuron
supplementary motor and premotor areas
neurons in these regions receive very complex inputs from basal ganglia and cerebellum, and from sensory regions of the parietal lobes
some neurons in these regions are polymodal
integration of info across sensory modalities
extensions implicated and in initiating behaviours at appropriate times
cortico-basal-ganglia-cortex-loops
projection to spinal cord
inputs received from substantia nigra and thalamus
the wiring exists for info to pass from cortex to basal ganglia, be modified by inputs from lower down, and pass back to cortex
substantia nigra
source of dopamine containing neurons
caudate basal ganglia
integrates info from frontal lobes
lesion affect complex behaviour, especially dealing with spatial relations - such as where to move to, coordinating gaze with location
programming movement with space in the environment
putamen basal ganglia
integrates inputs from sensorimotor cortical areas
lesions have straightforward motor effects - problems with strength, rate of responses
what are the 3 layers of the cerebellum
molecular, purkinje, granule layers
compare inputs and outputs
motor inputs cerebellum
efference copy of the planned motor behaviour.
this is also termed a corollary discharge
what is intended? what do you want to do?
extra copy of the plan to the cerebellum
sensory inputs from cerebellum
inputs from a variety of senses
especially reafference from proprioceptive systems
in essence what happened?
cerebellum output
all output via gigantic purkinje cells and all output is inhibitory
mahor function is to calculate mismatches between intended and actual movement and coordinate corrections, either by altering the motor plan, or by directly modulating spinal neurons
muscular dystrophy
x-linked gene -codes for dystrophin protein
faulty regulation of calcium stores, consequently contractile properties of muscles are abnormal
mostly a disease of men - b/c on every x chromosome, and men only have one
eventually lethal as more and more muscles malfunction
earlier canidate for gene therapy
myasthenia gravis
immune malfunction - produce antibodies that attack own acetylcholine receptors
maybe from having a sickness and it being an immune system attack
characterized by rapid fatigue after normal start of movements - dont have enought ach for muscle contractions
treatable with immune surpressants
spinal cord injury
transection with extensive damage - leads to flaccid paralysis, complete loss of movement including reflexes below level of back
with less damage - some reflexes persist
brown-sequard syndrome
hemitransection (one side) of cord
motor tracts cross in brain, but sensory fibres cross in the spinal cord - right side contains right motor fibres and left sensory fibres
thus hemitransection severs motor tracts for one side of the body and sensory fibres for the other side
paresis
weakness
often result to damage to motor cortex
plegia
paralysis
spasticity
hyperreflexia
due to loss of inhibition from brain on ventral horn motor neurons
babinski’s sign
upgoing toe when sole is strokes
lesions to non-primary motor areas
apraxia
ideomotor
apraxia
associated with parietal damage
problem with movements in the absense of weakness
paralysis
can’t carry out complex movement
ideomotor
can not do things to verbal command and ideational - can not sequence movements smoothly
ataxia
loss of coordination
epilepsy
area of seizure speads adjacent aresa
tonic clonic movements appear in more and more of the body
parkinson’s disease
loss of dopamine containing projection from the substantia nigra to the striatum
tremor, flat affect, trouble initiating movements, shuffling gait, dementia
treatable, at least for a while, by replacing the lost dopamine
exercise can slow progression
huntingtons disease
genetic deterioration of the lenticular nuclease
gives rise to chorea, dementia
no treatment
jerky aimless movement
subtele behaviour changes, clumsy, twitches
hemiballismus
violent uncontrollable flinging of the limbs
due to lesion of subthalamic nucleus
may cause death through exhaustion
mirror neuron
a neuron both active when an individual makes a specific movement and when they see an individual make the same movement
pacinian corpuscle
a skin receptor cell that detects vibration and pressure
acts as a filter only letting vibrations of 200 cycles/sec to stimulate
stimulation created when we feel a texture against our skin
messner’s corpuscle
skin receptor that detects light touch, responding especially to changes in stimuli
detecting locatlized movement between skin and a surface
merkel’s disc
a skin receptor cell that detects light touch
responds best to edges and isolated points on a surface
ruffini corpuscle
a skin receptor cell that detects stretching of the skin
sparsely distributed in the skin
free nerve endings
pain, itch, heat and cold stimulate
primary sensory cortex
one for each modality
receive info mostly from thalamus
primary somatosensory cortex
mostly the postcentral gyrus of the parietal lobe
receives touch info from opposite side of the body
polymodal neuron
a neuron upon which info from more than one sensory system converges
allows different sensory systems to interact
synesthesia
a condition where stimuli in one modality evoke the involuntary experience of an additional sensation in another modality
pain
body’s emergency signaling system
unpleasant sensory and emotional experiences
guides our behaviour to minimize risk to body
nocieptors
a receptor that responds to stimuli that produce tissure damage or pose the threat of damage
when tissues get injured the affected cells release chemicals that activate nearby pain receptors
specialized to detect damage - chemicals cause inflammation
