PHYSIOL [B] motor Flashcards
role of cerebellum in voluntary movements:
compares planned action to actual action and helps correct disparity
- think touching your nose diagram!!
- drunk symptoms when it screws up
describe descending projection pathway:
primary motor cortex receives input from premotor areas
projects info to spinal cord through corticospinal tract
info goes to motor neurons and interneurons
what is the hierarchy of motor control?
premotor and non-motor cortical area basal ganglia cerebellum motor cortex brainstem spinal cord - execution
describe the path sensory info takes from skin to muscle:
receptors in the skin pick up sensory info -> dorsal ganglion(cell bodies) -> interneuron in spinal cord -> afferent pathway -> thalamus -> primary somatic sensory cortex -> primary motor cortex -> efferent pathway -> spinal cord -> muscle!
what info does the somatosensory cortex provide?
sensory info required for specific planning, initiation and ongoing movement
explain the concept of “plasticity” of the brain
brain can remodel itself in response to varying demands
eg. phantom limb, cortex normally dedicated to hand was dedicated instead to face
expansion due to training
2 main areas of sensory cortex?
primary somatosensory cortex
posterior parietal cortex
function of posterior parietal cortex(more towards back of brain):
encodes complex sensory info to ensure planned movement is matched to the external environment
guides movements of eyes, head, arms and hands
what areas does the posterior parietal cortex receive input from?
visual, auditory, somatosensory
3 mains areas of the motor cortex:
premotor cortex
supplementary motor area
primary motor cortex
function of premotor cortex:
involved with planning and coordination of movements in response to SENSORY MOVEMENTS
function of supplementary motor area:
active during planning and coordinating INTERNALLY-GUIDED movements
function of primary motor cortex:
controls simple features of movement
what does EMG stand for?
ElectroMyoGraphic
where do afferent fibres enter spinal cord?
through dorsal root
where do efferent fibres exit spinal cord?
ventral root
how are motor nuclei are interconnected across segments of the spinal cord?
by propriospinal neurons (interneurons?)
how are the motor nuclei of the spinal cord arranged?
along medial-lateral axis according to function
ie.
most medial nuclei => innervate proximal muscles
most lateral nuclei => innervate distal muscles
function of spinal cord?
integration of many basic reflexes, such as the withdrawl reflex
pathway of pain reflex:
pain receptor -> afferent pathway -> interneuron -> efferent pathway -> flexor/extensor muscles -> withdrawal response
where are voluntary movements organised?
cortex - primary motor cortex controls simple features of movement
what neurotransmitter is deficient in Parkinson’s disease?
dopamine
define voluntary movement:
continuous spectrum of movements ranging from most automatic to least automatic
what is muscle excitation-contraction coupling?
series of events linking muscle excitation to muscle contraction
what is the synapse between neuron and muscle called?
neuromuscular junction
what is the response in the muscle called?
EPSP = Excitatory Post-Synaptic Potential
or End Plate Potential
where is the end plate region?
plate of muscle fibre neuron attaches itself to
describe steps of “excitation” at NMJ:
1) AP propagation in motor neuron
2) Ca2+ voltage gated channel open
3) tiggers Ach to be released into synapse
4) binding of neurotransmitter to receptor
5) receptor opens, allows positively charged ions to enter(Na) and exit(small K) ..triggers post synaptic cell depolarisation => EPP
6) moves along postsynaptic cell until hits more Na+ channels
7) Na+ enters as wave of depolarisation hits
8) AP propagation in muscle fibre
9) enzyme destroys excess Ach (neurotransmitter)
As Ca+ enters axon terminal, what does it trigger the release of? and how?
triggers the release of Acetylcholine via EXOCYTOSIS (from vesicles into synapse)
What actually happens during an End Plate Potential?
local current flow occurs between the depolarised end plate and the adjacent membrane
why is excess Ach destroyed by enzymes in the synapse?
to terminate the response
what is a single muscle cell called?
muscle fiber
what is a sarcomere?
functional unit of skeletal muscle (2.5 um wide)
where is a sarcomere found?
between the Z lines(connects thin filaments of two adjoining sarcomeres)
describe and explain the appearance of sarcomeres:
displays alternating dark(thick filament-myosin) and light(thin filament-actin, troponin, tropomyosin) lines
giving appearance of striations
during contraction, what aspects of the sarcomere changes in length?
filaments remain the same length
slide over each other to a greater extent
dark band remains the same,
light band shortens,
H zone(middle of sarcomere, only think filaments) also shortens
what do thick filaments in muscle fibres consist of?
myosin
what do the thin filaments in muscle fibres consist of?
actin, troponin and tropomyosin
what is meant by the cross bridge interaction?
sliding filament mechanism by action of actin and myosin interactions
how is the cross-bridge link broken?
fresh ATP must attach itself to myosin in order for cross-bridge to be broken at the end of the cycle.
eg. when someone dies there is not fresh ATP to attach to myosin, so cross-bridge within muscles between actin and myosin cannot be broken, hence why stiffness occurs
what is Tropomyosin?
covers actin sites
allows muscle to contract with Ca2+ binding site
what is tropomyosin?
blocks myosin binding in resting
tropomyosin will move out of the way when Ca2+ binds to troponin
what is the source of Ca2+ in muscle?
sarcoplasmic reticulum
how does action potential enter muscle cell?
transverse tubule
what happens to CA2+ is released from sarcoplasmic reticulum following AP entering T-tubules?
Ca2+ bind to troponin on actin filaments, which makes tropomyosin move aside
this opens cross-bridge binding sites on actin
how is cross-bridge bending/pulling powered?
ATP
what happens after Ca2+ is no longer needed for binding?
its reused!
pumped back into sarcoplasmic reticulum using extra ATP
muscle enlargement is the result of:
increased diameter of muscle fibres
where does fibre thickening come from?
increased content of myosin and actin, which permits a greater opportunity for cross-bridge interaction and increases the muscles contractile strength
how are signals passed between the nerve terminal and the muscle?
by chemical messenger acetylcholine (ACh)
what element is the link between excitation and contraction?
calcium
what are the types of muscle contraction?
concentric
eccentric
isometric
how do different types of muscle contraction occur?
through altering amount of force produced in the muscle RELATIVE to the external load
what equation helps define the different muscle types?
muscle torque/load torque
> 1 = concentric(greater muscle torque eg. load LIFTED by arm)
< 1 = eccentric(greater load torque eg. load LOWERED by arm)
= 1 = isometric(equal)
what are the 2 main factors that affect force muscle can exert?
excitation (stimulated by nervous system)
properties of muscle (muscular + mechanical) eg. size, fiber type, velocity of shortening
what neural factors influence muscle force?
- number of muscle fibres contracting within a muscle(recruitment)
- twitch summation of each contracting fiber by increasing rate of APs (rate modulation)
what are the muscular and mechanical factors that influence muscle force?
size, fiber type/length velocity of muscle shortening muscle torque (torque produced at the joint)
what technique allows muscle fiber potentials to be recorded?
EMG - ElectroMyoGraphy
single motor unit refers to?
single motor neuron + all the muscle fibers it innervates
what is a motor neuron pool?
group of motor neurons that innervate one muscle
what is the innervation ratio?
number of muscle fibers per motor unit
for areas involved in small precise movements is the innervation ratio big or small?
small-er
as there are more motor neurons present, each motor neuron controls less muscle fibres creating more precise movements
eg. eye and hands
what is the “size” principle?
the orderly recruitment from smallest to largest motor units in increasing motor unit force
simple model explaining increasing force production? THINK OF
water tank with 4 exiting pipes at different levels
where water flow = excitatory drive!
what is the result of increasing frequency of APs?
allows twitch force to summate, due to higher availability of Ca2+ in cytosol
what is Tetanus?
it occurs if the muscle fiber is stimulated so rapidly that is doesnt have a chance to relax between stimuli
- fatigue follows this OR stimulation ceases
what does the max force a muscle can exert depend on?
its physiological cross-sectional area (PCSA)
wtf is the PCSA (Physiological Cross-Sectional Area)?
its a measure of the number of cross-bridges in parallel
what 3 physiological properties(of the muscle fibers they innervate) classify motor units?
twitch characteristics
tension characteristics
fatiguability
describe the likely classification of a greater exercise intensity motor unit:
more fast twitch fibers
high force
fast fatigue
what is “optimum length”?
length at which max number of cross bridges can be formed
sarcomere
state the relationship between velocity of contraction and force produced:
as speed goes up, amount of force produced goes down
what is the equation for calculating torque?
force (N) x moment arm (m)
..wtf is moment arm? ..the length of leaver
what does torque produce?
rotation about a joint
when is the feedforward control used?
during rapid movements and Anticipatory Postural Adjustments
What are Anticipatory Postural Adjustments?
any task that you do that involves changes in center of gravity
adjustment preformed by the CNS to compensate
eg. raising one arm, compensatory muscles activated to maintain balence
function of receptors in motor control?
take info from periphery and translate into neural code that CNS can use
which of our senses is the “dominant” one?
vision
where else does visual input go in the brain? and what do they control?
thalamus - visual perception
superior colliculus - saccades
midbrain - pupillary reflexes
what are saccades?
very fast eye movements to track different objects
what is the overall function of the superior colliculus?
- receives and maps sensory inputs from; visual, auditory, somatosensory and motor
- integrates all sensory info
what fibers do muscle spindles consist of?
2 sensory afferent
1 motor efferent
intrafusal muscle
function of muscle spindle:
- detects, responds to and modulates changes in the length of skeletal muscle fibers
- to provide an important regulatory function for movement and maintenance of posture
describe path of stretch reflex pathway:
afferent input from sensory endings of muscle spindle fiber ->
alpha motor neuron output connecting directly to regular skeletal muscle fiber
example of stretch reflex?
tendon tap reflex!
explain why the tendon tap results in knee jerk response:
tapping patellar tendon with a rubber mallet stretches muscle spindle(sensory afferent endings within muscle spindle connect with alpha motor neuron)
resulting in contraction of EXTENSOR muscle
what are articular receptors?
proprioceptors that reside in joints
what is the function of articular receptors?
signal potentially damaging states of the joints
eg. high joint capsule tension, joint angles close to anatomical limits, joint inflammation
function of mechanoreceptors in the skin?
respond to pressure, play particularly important role in motor control
what are the 2 superficial mechanoreceptors of the skin?
1) meissner corpuscles - rapidly conducts AP
2) merkel disks - slowly adapting to AP
name the 2 deep mechanoreceptors of the skin:
1) pacinian corpuscles (rapidly adapting)
2) ruffini endings
voluntary movements are ______ directed and improve with ______ as a result of ________ and ________ mechanisms
goal
practice
feedback AND feedforward
what receptors are important for motor control?
eyes muscle spindles golgi tendon organs joint receptors cutaneous receptors
what is the sensory receptor for the stretch reflex?
muscle spindle
what is the magnitude of muscle strength determined by?
muscular factors
mechanical factors
neural factors
describe mechanical factors that determine magnitude of muscle strength:
moment arms associated with the different forces
what evidence is there to suggest some differences in strength depend on the nervous system?
- strength can be increased WITHOUT activating the muscle
- dissociation between changes in muscle size and strength
name sites of potential neural adaption to training
1) cortical control
2) antagonist activity
3) descending drive
4) interlimb coupling
5) motor unit activity
6) motor neuron excitability
describe neural adaption in cortical control:
this is adaption of neurons in cortical map, which only occurs for NEW motor skills
eg. guitar playing - a new skill
describe neural adaption of descending drive with training:
increase in amount of drive through greater input from brain to motor neurons
increase in motor neurons - increase in force
describe what interlimb coupling is:
when one side is trained and there is a significant increase in muscle on the otherside
mechanism not yet completely understood
describe what neural adaption happens to motor unit activity with training:
increase in discharge rates
define fatigue:
a reduction of the force generating capacity of the neuromuscular system that occurs with muscle activity
any exercise-induced reduction in maximal voluntary force or power output
eg. increased effort needed to maintain submaximal contractile force
what are the possible sites for fatigue?
peripheral fatigue
central fatigue
describe peripheral fatigue:
due to sustained max contractor
-> change in muscle fibers themselves
describe central fatigue:
its the progressive reduction in voluntary activation of muscle
-> due to sustained weak contraction
name possible sites from brain to muscle where fatigue may occur:
1) input to motor cortex 5) excitation contraction coupling
2) CNS drive to lower motor neuron 6) availability metabolic substrates
3) activation of muscles and motor units 7) intracellular milieu
4) neuromuscular transmission 8) contractile apparatus
CENTRAL 9) muscle blood flow
PERIPHERAL
main effect of CNS fatigue:
decline in motor unit (motor neuron and muscle fibres) activity throughout a fatiguing task
describe muscle twitch after fatigue:
decrease in force
increase in duration
more chance for summation
repeated bout of the same eccentric exercise causes what(in terms of muscle damage)?
results in reduced symptoms of damage and soreness compared with initial bout
eg. footballers, first game is sore but after training games no longer make them sore
general mechanisms for the repeated-bout effect:
initial bout of eccentric exercise muscle damage adaption neural theory - connective tissue theory - cellular theory repeated bout of eccentric exercise less muscle damage
describe 3 locations within CNS that may adapt with strength training:
AND HOW:
cortical control -
antagonist activity - decrease in antagonist activity
descending drive - increase in amount(greater input from brain to motor neurons)
describe 4 potential sites of central fatigue:
1) input to motor cortex
2) CNS drive to lower motor neuron
3) activation of muscles and motor units
4) neuromuscular transmission
describe neural theory that is thought to contribute to the repeated bout effect:
increased motor unit activity
increased slow-twitch fiber recruitment
increased motor unit synchronisation
describe connective tissue theory that is thought to contribute to the repeated bout effect:
increased intramuscular connective tissue
intermediated filament remodelling
describe cellular theory that is thought to contribute to the repeated bout effect:
strengthening of cell membranes
removal of weak muscle fibres
longitudinal addition of sarcomeres
via WHAT does the basal ganglia influence the motor cortex to facilitate movement?
thalamus!
what is the corticospinal tract?
largest descending fibre tract
where does the corticospinal tract divide?
at the medullary pyramids -> into ventral and lateral tracts
what are direct corticospinal connections responsible for?
fine control of digits
what would be the effect of bilateral section of the corticospinal pathway?
instead of using small precise grip, entire hand is used
what is the leading cause of damage to the corticospinal pathway?
and what does this result in?
stroke!
results in paralysis of the contralateral upper and lower limbs and facial muscles
what does Parkinson’s disease result from?
loss of most of the neurons using dopamine as their neurotransmitter
how much of the total brain dopamine does the BG contain?
80%!
what characterises Parkinsons disease?
slowness
tremor(5-6 Hz)
rigidity (resistance to motion)
deficits in postural reactions
what are the current treatments for Parkinson’s disease?
Drugs (L-DOPA)
Deep brain stimulation
stem cell therapy?
what are the 3 functionally distinct parts of the cerebellum?
1) Vestibulocerebellum
2) spinocerebellum
3) cerebrocerebellum
function of Vestibulocerebellum:
important for maintaining balance(VESTIBULAR IN EAR!!) and controls eye movements
function of Spinocerebellum:
enhances muscle tone and coordinates skilled, voluntary movements
function of cerebrocerebellum:
plays role in planning and initiating voluntary activity by input to cortical motor areas
what are 3 typical defects observed in cerebellar diseases:
1) delay in movement initiation
2) inaccuracy in range/direction, decomposition of movement(shoulder first, elbow second), tremor increases on approaching nose
3) irregular pattern of alternating movements
how many pairs of spinal nerves are there?
31 pairs
what aspects of neural processing is limbic association cortex primarily responsible for?
motivation
emotion
memory
what aspects of neural processing is Broca’s area primarily responsible for?
speech formation
what aspects of neural processing is primary motor cortex primarily responsible for?
voluntary movements
what aspects of neural processing is posterior parietal cortex primarily responsible for?
integration of somatosensory and visual input; important for complex movements
what aspects of neural processing is Wernicke’s area primarily responsible for?
speech understanding
what is agnosia?
defect in the ability to recognise sensory stimuli without a defect in the sense
what is apraxia?
the inability to perform simple motor skills in the absence of paralysis
does the location of a spinal lesion matter?
YASSS
location will produce muscle weakness and atrophy based on spinal location and somatotopic organisation in the brain
what happens when the descending motor pathway is damaged?
can lead to spasticity, which is increased muscle tone cause by heightened stretch reflexes
what is ALS?
Amyotrophic Lateral Sclerosis
leads to the progressive death of alpha-motor neurons, resulting in muscle denervation and a loss of voluntary muscle control
true or false: Agnosia refers to the inability to perform simple motor skills in the absence of paralysis
FALSE!
thats Apraxia
true or false: the Spinocerebellum is a part of the cerebellum that plays a role in planning and initiating voluntary activity by input to cortical motor areas
FALSE
thats the cerebocerebellum
the spinocerebellum enhances muscle tone and coordinates skilled, voluntary movements
what is the condition of rigor mortis?
the locking in place of skeletal muscles that begins 3-4 hours after death
why does rigor mortis occur?
an increase in intracellular calcium creates cross-bridge binding, and there is no ATP avaliable for cross-bridge detachment
Nerve gas poison is known to inactivate acetylcholinesterase (AChE) so that the AChE normally in the neuromuscular junction no longer removes the ACh released at the end plate. The result of this poison is?
Large amounts of ACh can accumulate and repetitively stimulate the muscle fibre, causing muscle spasm
