history
hippocrates, aristotle
brain is seat of sensation though action
descartes
clockword motors responding to stimuli with predetermined motor outputs
galvani & volta
involving electricity
flourens, goltz
lesion studies - brainstem and spinal cord can generate motor acts.
sechenov, pavloc
innate and conditioned reflexes
eccles
intracellular recording
- synaptic transmission involved NT
neher & sakkman =
patch clamping
muscle
- how many neurons to muscle fibers
how many sensory axons signal force, how many signal pressure, temp rate
- 200 axons of 1 -MN activate msucle fibers
200 sensory signal force
200 sensory signal pressure, temp rate
what is motor unit
one nerve and all the muscle fibers it innervates
innervation ratio
smaller?
smaller = finer gradation of control
muscle force controlled by?
varying number of active motor units and varying their individuals firing rates
define passive force
active force
p: due to stretching of elastic
a: myosin cross-bridge attach to actin and swivel, generating “power stroke”
sliding filament theory
cross-bridge attachs, swivel, release, swivel back and re-attach
AKA cross-bridge cycle
isometric
eccentric
concentric
I: force produced without muscle length change
E: force produced during muscle lengthening
C: force producd during muscle sortening
total force
elastic elements
T: sum of active and passive forces
E: force produced by elastic resistance of connectin and tendon
force depends non-linearly on muscle length
- experiments
- slow stretch from shortest length = produce passive length-force curve.
- stimulating muscles nerve, activate muscle & measure force.
= after certain force, cross bridges too far extended. cant produce force.
force depends non-linearly on velocity
stimulate muscle via nerve and measure force at given length.
- repeat for different lengthening and shortening velocities.
= force highest during rapid lengthenin and lowest during rapid shortening.
* velocity = time for crossbridge to attach, detach swing.
- shorter cycle = larger relative duration of unattached phase (consistent)
length-force depends on level of muscle activation
experiment
- larger sitmulation amplitude = MN’s =?
- MU?
force vs length at different amplitudes of stimulation of muscle nerve.
larger stimulation amplitude, the more MNs are recruited, so the greater the active force. slope increase
- depends on MU, recruited in order of size.
force depends non-linearly on MN firing rates
- muscular wisdom
isometric - stimulated with increasing pulse rate. ratte increases = twitch force becomes smooth = tetanic contraction
- CNS matches MN firing rates to musce properties
force and its many relationships
A force depends non-linearly on muslce length
B non-linearly on velocity
C length-force depends on level of muscle activation
D force depends non-linearly on MN firing rates.
3 types of neurons
S = small, slow, fatigue-resistant FFR= fast, fatigue-resistant FF = fast, fatiguable
% MUS recruited & force
90% of MUS recruited generate first 50% of force.
remaining 10% of force = 2nd 50% of force.
fatigue of muscle,
rate of decline depends on?
muscle activated by long train to its nerve, force declines.
- rate of decline depends on muscle fibre types.
muscle order of stimulation in voluntary contractiong
- vs how nerves stimulated electrically
- voluntary = S, FFR, FF
electrically = FF FFR, S
this is why electrically-evoked fatigue more rapidly than voluntary contractions.
