Neural control Flashcards
major components of Neural system
central nervous system (CNS)
brain (integrative control centres) and spinal cord
-cerebellum is the motor control centre
analyze and organize information
motor system planning and commands
major components of Neural system
peripheral nervous system (PNS)
outputs CNS commands and sends sensory information to CNS
primarily motto movements (movement and motor control)
afferent neurons
-relay sensory information from peripheral to the CNS (brain) along posterior column
efferent neurons
-relay information from the CNS (brain) to the peripheral or away from the brain along the pyramidal tract
-somatic nerves
-autonomic nerves
20:1 ratio afferent to efferent nerves
efferent neurons
two types
somatic neurons
motor neurons
-make up somatic nervous system
-innervate skeletal muscle
efferent neurons
two types
autonomic neurons
visceral or involuntary neurons
-make up autonomic nervous system
-activate smooth muscle, cardiac muscle, sweat and salivary glands, and some endocrine glands
sympathetic (fight or flight) and parasympathetic
which brain region is associated with processing of sensory signals?
parietal lobe
which part of the brain is primary motor cortex
pre-central gyrus
which part of the brain connects each hemisphere via commissural fibres ?
corpus callosum
which part of the brain is known as the motor control centre?
cerebellum
the ____ roots of the spinal cord contain _______ neurons, and relay information back to the CNS
dorsal
afferent
control of movement: voluntary
-require integration at the cerebral cortex
-learned movements may become “reflexive” (for example walking)
-muscle memory
ex. throwing a javelin
control of movement: reflexive
-sensor input (vision, vestibular, muscle)
-can be modulated by higher brain centres
-involved in posture
ex. regaining your balance after tripping
control of movement: rhythmic movements
-voluntary and reflexive
-initiated by cerebral cortex
-can be sustained without input from the brain
ex. running
previous research for paralysis
-focused on stem research to repair damage in individuals with spinal cord damage
new research on paralysis
-we know voluntary and rhythmic movements such as walking can actually become reflexive (not requiring input from the brain)
-if stimulus is provided below the level of the injury we may be able to obtain a state of walking
central pattern generator (CPG)
the CPG is a neural network in the lower part of the spinal cord that is thought to control locomotion
it does not require input from higher brain centres or reflexes , but the CPG output can be modified by input from the brain or reflexes
reflex arc (order)
-basic mechanism to process “autonomic muscle action-involuntary
-peripheral stimulus causes afferent neuron impulses to enter spinal cord
-transmit sensory input from peripheral receptors
-afferent neurons interconnect (synapse) with interneurons in the spinal cord to relay info to CNS
-Efferent signals return via anterior motor neuron to the muscles
-muscle responses
the central pattern generator can control walking without input form the brain or reflexes…
however the activity of the central pattern generator can be modified by input from senses, reflexes and the brain
touching a hot iron
reflex
pain receptors in the fingers transmit sensory info to spinal cord (via afferent neurons)
Efferent neurons activate the appropriate muscular response reflex action and muscular response occurs can reach the brain and tell the body to feel pain
motor unit represents an
alpha-motor neuron and the fibers it innervates
motor neurons pool represents a
Collection of alpha-motor neurons that innervate one muscle
nerve supply to muscle
single nerve or motor neuron supplies multiple individual muscle fibres (each muscles function)
-the number of muscle fibers per motor neuron (motor unit size ) is related to a muscles function
-simple movements
-complex movements
small motor unit
-only have a few fibres/motor neuron (those involved in fine movements like finger actions, eye action)
-complex precise movement
large motor unit
-may have hundreds of muscle fibers/motor neuron (those involved in gross movements like walking)
-simple movement
all muscle fibers within a given motor unit are the same __________
Type (I, IIa,IIx)
if a motor unit is activated (by higher brain centres) __________ in that unit contract
all the muscle fibers
motor neurons may receive input from other neurons originating higher up in the ________
central nervous system (closer to the brain) or the brain itself (motor cortex)
they may also receive input form reflexes, originating in the limbs (periphery)
dendrites
recipes impulses and direct toward cell body
cell body
control center
axon
delivers impulse to body
Schwann cell
covers bare axon
myelin sheath
electrical insulator of the axon
neurilemma
membrane covering the myelin sheath
nodes of ranvier
permit depolarization of axon
action potential is ______ along the axon of the motor neuron
propagated
axon is covered by
myelin (lipid sheath)
at certain points along the axon, there is a space in the myelin _____________
nodes of ranvier
nodes of ranvier allow
reinforcement of the current strength, but the current flows slower in these sections
without myelin, current leaks out and the action potential becomes weaker
nerve fiber conduction speed ______ in direct proportion to fibers __________
increases
diameter. and myelin thickness
the more myelin or thicker the axon the faster the conduction velocity of the axon
____ motor neurons have thicker axons
fast
neuromuscular junction-NMJ (motor endplate)
interface/junction between the ______
end of a motor neuron and a muscle fiber
-transmits nerve impulses to imitate muscle action
anatomical features of NMJ
-presynaptic terminals
-synaptic cleft
-postsynaptic membrane
T/F
a motor neuron pool is 1 motor neuron and many muscle fibers
false
T/F
a motor unit innervates a variety of fiber types
false
T/F
small motor units are typically involved in complex movements
true
T/F
alpha motor neurons are afferent neurons
true
at rest inside the muscle fiber (cell)
sodium is ____ on the inside as compared to the cell (ie more Na+ ________)
low
outside
at rest inside the muscle fiber (cell)
potassium is _____ on inside compared to outside the cell (ie more K+________)
high
inside
at rest inside the muscle fiber (cell)
sodium and potassium controlled by
Membrane permeability (wether or not a stimulus changes this)
at rest inside the muscle fiber (cell)
although Na+ and K+ are both positively charged there are more Na+ ions outside compared to K+ ions inside
thus the fibre cell is
more negatively charged on the inside
resting membrane potential (RMP)
-70mV
-inside negative relative to outside the membrane
relative to the RMP (-70mV)
depolarization: membrane potential becomes more _______ (>-70mV, closer to 0 or above)
positive
need to increase positive charge inside
relative to the RMP (-70mV)
repolarization: membrane potential becomes more _______ (back towards _ ___)
negative
RMP
relative to the RMP (-70mV)
hyper-polarization: membrane potential becomes more_______ than resting membrane potential (________)
negative
less than -70mV
changes in membrane polarization are ____________
signals used to receive, transmit, and integrate info within or between cells
types of signals:
endpoint signal
Depolarization OR hyper-polarization of MP, but won’t cause AP
types of signals
action potential:
substantial depolarization of MP
voltage changes
changing from -70 to -50 is
depolarization
voltage changes
changing from -70 to -90 is
hyper-polarization
voltage changes
changing from -50 to -60
repolarization
end point potential vs. action potential
wether or not it is an endpoint potential or an action potential generated in a motor neuron (thus wether the muscle reacts) depends on the of sum excitatory and inhibitory post-synaptic potentials (EPSP or IPSP)
excitatory input
known as excitatory postsynaptic potential
EPSP
inhibitory
known as inhibitory postsynaptic potential
IPSP
EPSP
depolarization of postsynaptic membrane
- facilitates (may lead to) AP
IPSP
hyper-polarizations of post synaptic membrane
- inhibits AP (are endpoint potentials)
- hyper polarizations are EPPs
facilitation
threshold/ all or none
if EPSP reaches threshold for ______ then the action potential transmits to muscle fibre
excitation
-threshold: minimum change of 15-20mV in MP depolarization ie -70mV to -50mV
action potential can be generated by
temporal summation
one or few neutrons can delivers repetitive sub threshold stimulus over a short period of time
action potentials can be generated by
spatial summation
a bunch of excitatory post synaptic potentials can be delivered from different presynaptic terminals
what is resting membrane potential
-70mV
inside of cell membrane more negative as more Na+ outside than K+ inside
depolarization - influx or reflux of what
influx of sodium
repolarization - influx or reflux of what
efflux of potassium
hyper-polarization -influx or reflux of what
extra efflux of postman
action potential
substantial depolarization (threshold level) that will result in muscle contraction
end point potential
depolarization or hyper polarization that does not porduce AP in muscle
inhibitory post synaptic potentials
cause hyper polarization; therefore will result in an EPP (no contraction)
excitatory post synaptic potentials
cause depolarization; therefore will result in an EPP, or AP If at threshold
an action potential is
a rapid alternation in membrane potential whereby the polarity across the membrane becomes reversed
MP depolarizes from -70mV to +40 mV
the concentration of ___- and ____- on the inside and outside of the cell determine polarization of the MP
sodium
potassium
initiating the AP
-impulse travels down axon terminal
-calcium channel open and calcium diffuses into axon
-causes fusion of “synaptic vesicles” containing acetylcholine (ACh) with muscle membrane, excites membrane changing its permeably
-channels open to allow sodium in and potassium out
initial opening of sodium (and potassium channels) due to binding of _______- with muscle membrane
acetylcholine
opening of adjacent channels on the muscle membrane due to spread of electrical charge ________
voltage gated
in review: muscle fibre stimulation/excitation
1. Impulse (AP)- moves down axon of _______
motor neuron
in review: muscle fibre stimulation/excitation
2) calcium channels open and calcium _______
moves into terminal
in review: muscle fibre stimulation/excitation
3) ACh primes for ——
release
in review: muscle fibre stimulation/excitation
4) ACh transverses the synapse and binds to _____ on postsynaptic terminal (muscle membrane)
ACH receptors
in review: muscle fibre stimulation/excitation
5) changes permeability of membrane (_____________)
influx/efflux of Na+ and K+
in review: muscle fibre stimulation/excitation
6) depolarization generates an ______, if at threshold an ________
EPP
AP
in review: muscle fibre stimulation/excitation
7) AP depolarization wave spreads throughout the ______network into muscle fibre
T-tubule
ending excitation:
action potential
prepares muscle fibre for contraction by travelling down T-tubule
ending excitation:
ACh hydrolysis
-ACh is broken down by cholinesterase to depolarize postsynaptic membrane
-axon resynthesizes acetic acid to form ACh so that the enter process is ready to go again
complete muscle contraction
motor cortex
area in the brain where contraction originates
complete muscle contraction
motor neuron
innervates muscle fibers (“motor unit”)
complete muscle contraction
axons
branches of motor neuron; innervates muscle fibers
complete muscle contraction
Acetyl choline
released from axon terminal
complete muscle contraction
potassium and sodium
leaves
sodium enters muscle fiber
complete muscle contraction
action potential travels down
transverse tubules
complete muscle contraction
sarcoplasmic reticulum
releases calcium
complete muscle contraction
calcium binds to ________’ troponin lifts ________
troponin
tropomyosin
complete muscle contraction
_______ and ________ bind
actin and myosin
motor unit functional characteristics classified by
twitch characteristics
tension characteristics
fatiguability
twitch characteristics
3 general patterns
Type IIx
fast twitch, high force, fast fatigue
twitch characteristics
3 general patterns
Type IIa
fast twitch, moderate force, fatigue resistance
twitch characteristics
3 general patterns
Type IIa
slow twitch, low tension, fatigue resistant
SAG (titanic depression)
phenomenon where under repetitive stimulus a motor unit first increases int tension, but then decreases or sags in response to the same titanic stimulus
slow twitch
-slow contraction time
-slow relaxation time
- lower force output
-resitant to fatigue
fast twitch a
-intermediate contraction time
-intermediate relaxation time
- moderate force output
-moderately resistant to fatigue
-fats contraction
-fast relaxation time
- high force output
-fatiguable
=fast twitch x
gradation of force/force of contraction
influenced by:
number of motor units recruited
recruitment of more motor units increases force
gradation of force/force of contraction
influenced by:
discharge frequency
-increasing the rate (frequency) at which individual motor units
gradation of force/force of contraction
influenced by:
neuromuscular fatigue decrease
-CNS/PNS
-neuromuscular junction
-muscle fiber
Recruitment of fibres
recruitment order
Henneman’s size principle (small to large)
-ST to FT
- low to high activation
Type II fibres are innervated by larger neurons and take to recruit (_______) than their slow fibre (________) counterparts thus, _________ are typically recruited first
high threshold
small, low threshold
ST fibers
asynchronous and synchronous motor unit firing
skill vs. unskilled
-differences in degree of synchronic movement patterning
weightlifter vs. endurance runner
estimating motor unit activation
electromyography (EMG) measure electrical signals created by muscle
-surface electrodes
-needle electrodes
HD EMG electrode arrays
what is the importance of using EMG
-allows you to asses which muscles are activated during specific exercises
-allows you to asses the amount muscle are activated
-allows you to asses which muscles are under strain during work situations (important for injury prevention)
EMG terms
raw EMG
the actual electrical signal
EMG terms
rectified EMG
“negative” flipped to the “positive”
EMG terms
integrated EMG
area under the rectified EMG
Mean absolute value (MAP)
used to determine the amplitude of the signal
Median frequency -MDF
used to determine the frequency firing
-when frequency of EMG is measured the median frequency is often used instead of the mean frequency
-Median is the middle score in a group of scores. EMG can be quite variable and using the median instead of the mean corrects the extreme scores
median frequency of EMG
although it is affected by use of different fibre types, it is not accurate enough to determine muscle fibre types
-it is often used to asses fatigue
would you expect median frequency to be higher in slow twitch or fast twice muscles? or would there be no difference? why?
Fast twitch muscles should have a higher median frequency
FT fire faster, so the frequency content should be higher
would you expect median frequency to increase, decrease or stay the same with repeated muscle contractions? why?
decrease
they are fatiguing and then stop firing (FT)
what is the important of using EMG?
-allows you to assess which muscles are activated during specific exercises
-allows you to assess the amount muscles are activated
-allows you to assess which muscles are under strain during work situations(important for injury prevention)
force summation:
Before a muscle relaxes from a contraction, if ______ is applied force increases to a higher level
-this is due to _______ from the sarcoplasmic reticulum
-this calcium will bind more troponin, lifting tropomyosin allowing more_________
another electrical stimulus
increased release of calcium
myosin-actin cross bridges
is it easier to achieve force summation wit slow or fast twitch
slow twitch
les likely to fully relax before the next force
-Type I muscle does not have time to completely relax before another stimulus is applied
can still have summation in all fibres
tetanus
force will summate up to a maximal with repetitive stimulation
this maximal level is reached once ________________
all the sites for calcium on troponin have been occupied
definitions of fatigue
-any reduction in force producing capacity of the muscle
-a transient decrease in performance capacity of a muscle when they have been activated for a certain time
-failure to maintain the required or expected force leading to a reduced perforce of a given task
fatigue resistance
four components impact voluntary muscle action:
- central nervous system
- peripheral nervous system
- neuromuscular junction
- muscle fiber
fatigue occurs from disruption in the chain of events between cns and the muscle fibre
central v.s peripheral fatigue
central fatigue: failure of the neural drive or the initiation of the AP in the CNS
peripheral fatigue: fatigue occurring in the muscle cell
central fatigue
bigger factor in endurance exercise
motivational and psychological factors involved
hypoglycaemia impairs CNS function
peripheral fatigue
may occur due to mechanisms in
sarcolemma:
conductance of AP
T-tubules:
conductance of AP
sarcoplasmic reticulum
-release of calcium
nutriton/ metabolsim
kinaesthetic sense
is our body awareness
vestibular
Where our body is in space
-integrates with the visual system to enhance a sense of equilibrium and balance
proprioceptive
Where the body is relative to other parts of the body
-receptors in muscles, joints and tendons
proprioceptors relay information about muscular dynamics and limb movement (_________________)
kinaesthetic awareness
the proprioceptors: muscles joints and tendons
relay info about muscle dynamics and limb movement to conscious and subconscious areas within the CNS
proprioceptors monitor movement and allow for modification
specialized sensory receptors sensitive to stretch, tension and pressure
muscles spindles
golgi tendon organ
muscle spindles
receptor ( intrafusal fibers) in the muscle that is aligned parallel to muscle fibre ( extrafusal fibers)
-detects stretch in the muscle (muscle fiber length and tension)
-responsive to rate and amount of stretch
muscle spindle- stretch reflex
-MS repsonds to stretch, sends excitatory input to the motor neuron in the spinal cord
-initiate an equal or stronger action to reduce this stretch
- causes muscle contraction
-inhibitory input is sent to the opposite (antagonistic muscle typically counteracts movement)
Ex. Elbow flexor being stretched the spindle is activated, the elbow flexor gets activated. The extensor will be inhibited
activation of the muscle spindles relays _______ impulses through to the SC
afferent
SC sends ________ impulses to cause reflex activation of the motor neurons of the stretched muscle
efferent
myotatic reflex, aka the stretch reflex
stimulus: quadricep stretch
reciprocal inhibition
reaction: contraction of the quadriceps (knee extension)
polymeric exercise
stretch - shortening cycle
-muscle is stretched, then shortened
the concentric (shortening) contraction is enhanced by the previous stretch
how could you use stretch reflex to enhance strength and power performances during the push-up exercise?
Making the exercise more explosive, pushing yourself off the ground
true or false
dynamic stretching (heating up the muscle) training quick response
Golgi tendon organ
-receptors found at the junction between tendons and muscle fibres
-lie parallel to muscle fibre
-detect difference in tension generated by active muscles
Golgi tendon organs: detect difference in tension generated by active muscle
respond to tension (activated) generated by:
- muscle contraction
- passive stretch
Golgi tendon organs
protect muscle from excessive
load
golgi tendon organs
if activated, GT sends impulses to elicit ______ inhibition
reflex
-inhibits muscle contraction causing muscle relaxation (good for PNF stretching)
opposite muscle (antagonist) is excited
proprioceptive neuro-muscular facilitation (PNF)
-a type of stretching where the Golgi tendon organ is first activated of the Golgi tendon organ
-this causes inhibition of muscle concentration (causes muscle to relax)
-increases ability to stretch
muscle spindle vs. Golgi tendon
muscle spindle:
-activated by change in muscle length (stretch)
-causes agonist muscle contraction
inhibits agonist muscle
Golgi tendon:
-activated by tension in active muscle
-causes agonist muscle relaxation
-excites antagonist muscle
neural adaptation
-at the beginning of a training program, strength increases without and increase in muscle mass
-increased excitability of motor neurons (easier to recruit)
-enhanced nerve conduction
-alterations in motor unit recruitment (increased motor unit firing and synchronization)
bilateral deficit
the sum of unilateral strength is greater than bilateral strength
- sum of the strength of each individual limb is greater than the strength of both limbs put together
bilateral deficit
disappears with _______
increases with _______
bilateral training
unilateral training
implications for sport specific training:
-If your sport requires more unilateral movement, train unilaterally or the opposite
causes of the bilateral deficit
-sensory input from one limb causing inhibition on the motor neuron innervating muscle of the opposite limb
-possible inhibition of type II fibers/decreased recruitment
-interfercne between hemisphere (inhibition of one side of the motor cortex on the other) during bilateral contractions
-perceived exertion with bilateral effort
-biomechanical factors (stabilization)
how can we non invasively measure activation of the brain in humans?
fMRI
EEG
Trans-cranial magnetic stimulation
functional magnetic resonance imaging (fMRI)
detects changes in oxygenated hemoglobin
- indicates where there are increases or decreases in oxygen consumption in the brain
gives an indication of what areas of the brain are activated or de-activated
exercises that involve movement at more than one joint (leg press, lat pulldown) seem to be affected more by the ________ than exercises involving a single joint
why?
bilateral deficit
There is a lot more stabilization of the body than a knee extension (single joint)
a greater ______ was produced during leg exercise than hand grip exercise
bilateral deficit
activation of trunk stabilizers is the ______ for unilateral and bilateral exercises
same
with unilateral exercise all assistance from the stabilizers is directed to one limb, but with bilateral exercises, the assistance from the stabilizers has to be spread ___________
to two limbs
handgrip exercise does not involve much recruitment of the stabilizers in the trunk the _________
bilateral effect is less evident
cross-education
a neural phenomenon
def: a neuromuscular transfer effect from unilateral training to the untrained contralateral limb
def: the increase in strength of the untrained contralateral limb after unilateral training
caused by alters nervous system activation
strength gain 52% relative to trained limb
cross-education
magnitude related to strength increase of trained muscle
-52% of the strength observed in the trained limb
_________ effects shown with more novel (unfamiliar) tasks
greater
cross-education
candidate mechanisms
-higher order brain mechanisms
-changes brain activation on both sides have been shown
- ipsilateral brain activation during unilateral movements
what is the influence of handedness or limb dominance?
experiment: 3 groups- one trained only their right arm, one trained only left arm and one did no training
(measured brain activity before and after strength training)
appears to have a stronger effect when dominant limb is trained and transferred to non-dominant limb
theory why:
the dominant limb/hemisphere is more proficient at learning and mastering a task leading to better quality adaptations
-the non dominant limb has a greater capacity to improve (ceiling effect)
cross education
candidate mechanisms
changes in brain activation on both the trained and untrained side have been shown following unilateral strength training
how could you apply cross-education in a particle manner
what settings
with whom?
Injury on one side of the body (orthopaedic injury, one limb immobilized, offside the effects by training other limb)
Stroke rehabilitation
Brain activation in cross-education
after right handed training there was an increased activation during left hadn’t exercise
left temporal lobe
right sensorimotor
left temporal lobe- involved recital motion knowledge
right sensorimotor cortex- involved in motor learning
role of ipsilateral activation
increased ipsilateral brain activation in motor areas as grip contraction intensity increased
cross-education and immobilization
(cast)
healthy participants using wires cast
-immobilized for 3 weeks on non-dominant (left) arm
3 groups
cast - train
cast
control
measured strength and muscle size
summary of cast study
- when the left arm is casted, training of the right arm prevents loss of strength and perhaps loos of muslce mass in the left arm
- training of the non-broken wrist prevents loss of strength in the broken wrist
cross education summary
- magnitude related to strength increased of trained muscle
-effects normal shown in 4-6 week strength training program
-hypertrophy of trained, but not untrained limb
-effect shown for homologous muscle groups (quads on both sides)
-greater effects when task are novel (unknown)
-greater effect when dominant limb is trained and transferred to non-dominant limb
-can offset the effects of disuse during unilateral immobilization
-emerging that it can be useful in stroke rehabilitation (strength training less-affected limb to improve the more-affected)
bilateral deficit
sum of unilateral strengths greater than bilateral strength.
- decreases with bilateral training , force obtained using both limbs improves
- higher in activities that require grater levels of stabilization as same level of stabilization required for one or two limbs; however, unilateral at the advantage
cross education (basic def)
limb is trained; however opposite (untrained) shows improvement
