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how is motor unit recruited
by the size principle -motor units are recruited from smallest to largest -higher levels of force require larger motor units
what are functional consequences to the size principle
-smooth increase in force production -minimizes fatigue as slow twitch, fatigue resistant muscle are activated first -negative: cannot selectively choose which MUs to recuit
can recruitment threshold change within a motor unit
yes threshold is amount of force necessary for motor units to turn on -order across motor units remain consistent
what is the relationship of rate coding
sigmoidal firing rate match contractile speed
how does the body increase control of strength
increase the number of motor units (recruitment)
increase the rate of firing of individual motor units (rate coding)
how does a motor unit keep force control at a steady contraction
each motor unit produces partially fused tetanus; because units fire asynchronously with each other, the net force is smooth.
what is a surface EMG
records the overall activity of all motor units in a muscle using electrodes
cant record single units
example of listening to a room full of people from the outside. cannot focus on one individual
EMG indwelling
focusing on singular units; single cells (sticking needle in part of body)
communication between neurons: divergence
a single neuron synapses on multiple neurons
communication between neurons: convergence
multiple neurons 'converge' on fewer neurons
extrafusal
skeletal muscle fiber
intrafusal
muscle spindle
afferent
targets information via CNS
efferent
targets information away from CNS (PNS)
what is the role of afferent/sensory inputs
-each projects centrally to the spinal cord -sending signals to CNS
How are afferent neurons classified?
based on diameter:
I (largest), II, III, IV (smallest) -larger diameter= faster conduction
where are spindle/fusiform-shaped receptors found
most in skeletal muscle
what is another word for muscle spindles
intrafusal muscle fibers
what are the two types of receptors
bag - based on shape (bag 1: dynamic ; bag 2: static)
chain: static
what are two types of afferents
type Ia (primary) - length and velocity -innervate bag 1, bag 2 and chain
type II (secondary) - length -innervate bag 2 and chain
how do we record muscle spindle receptors
microneurography -sticking needles into muscle -single unit action potentials
what is the monosynaptic reflex
tendon tap primaries (Ia) are very sensitive to taps and vibrations, and can stop firing on release
what does the gamma system do
prevents spindle from being unloaded during shortening contractions and keeps it sensitive to stretch
gamma dynamic: makes spindle more velocity sensitive gamma static: makes spindle more length sensitive
why does the body co-activate alpha and gamma during voluntary contraction
so the spindle maintains its sensitivity during shortening contraction
what is the function of a muscle spindle?
muscle receptors that provide feedback to the central nervous system about muscle length (stretch) and rate of length change
what is alpha-gamma co-activation
during a voluntary contraction, we activate both alpha and MNs and gamma MNs together so the spindle maintains its sensitivity during shortening
why does a tendon tap cause a reflexive kick?
spindles lengthen and la (primaries) sensitive to stretch activate MN via monosynaptic reflex
why are gamma motor neurons so important
regulate the gain of the stretch reflex by adjusting the level of tension in the intrafusal muscle fibers of the muscle spindle.
what technique allows experimenter to record action potentials from sensory afferents in awake humans
microneurography and electromyography
a _______ is the force output of a muscle in response to one stimulus
twitch
where are GTO located
at junction of tendon and the muscle fibers
spindles are spread throughout the muscle belly and lie in where
parallel with muscle fiber
GTO lie in ___ with the muscle fiber
series (at the end of the muscle fiber)
sensory innervation: the afferent fiber that innervates the GTO is the __ afferent
Ib
how is the Ib afferent activated
by collagen strands compressing down onto them
what is the function of GTO
tells the CNS how much force to regulate muscle control. ie. injury prevention
what does the level of force necessary to excite a GTO depend on
mode of activation
what are GTO most sensitive to (think eccentric, concentric and isometric movements)
active force (isometric)
how does the GTO inhibit agonist muscle
Ib sole function is to inhibit
feedback to spinal cord via Ib afferent
Ib inhibitory interneuron (disynaptic connection to motor neuron)
autogenic inhibition: inhibits agonist motor neuron which decreases force output)
what is the main function of GTO
inhibit the agonist motor neurons
protective mechanism
monitor and modulate force control
where is the location of joint receptors
within joint capsule, joint ligaments, and loose articular tissue
no receptors in cartilaginous surface of the joint or in synovial membranes
what do joint receptors respond to
respond primarily at the limits (ROM) of joint movements respond to joint pressure (ie. swelling) respond to both flexion and extension
what is the function of the GTO
inhibit agonist muscle -purpose: protective mechanism and modulates force control
what are the 2 sensory receptors in the inner ear
semicircular canals
otoliths
what do hair cells do
transform mechanical energy into neural activity (mechanoreceptors)
-kinocilium(long one) and stereocilia
when stereocilia are pushed towards the kinocilium the hair cell _______________
depolarizes
when the stereocilia are pushed away from the kinocilium the hair cells _________
hyperpolarize
where is the endolympth found and what is it
it is a fluid inside the semi-circular canal
what is cupula
house hair cells in the crista of the semi-circular canal
What can the semicircular canals detect?
detect angular accelerations
what are the responses to accelerations and decelerations in the 8th afferent nerve
accelerations: leads to increased firing rates
decelerations: leads to hyperpolarization (decreased firing rates)
constant velocity: hair cells return to normal leakiness and the 8th afferent nerve returns to baseline firing rates.
hair cells project into gelatinous material: utricle ______ linear acceleration
horizontal
hair cells project into gelatinous material: saccule ______ linear acceleration
vertical
otoliths
-small crystals allow them to deflect -linear acceleration sensitive
what causes stimulation in the otolith organ
gravity or linear shear due to movement causes stimulation
what are the 2 types of hair cells and how are they activated?
kinocilium and stereocilia depolarization/hyperpolarization - deflection by endolymph (canals) or movement of otoconia (otoliths)
why do people get the spins
-alcohol is a blood thinner which decreases the density of the blood
density between endolymph and cupula (hair cells) disrupted --> less density in cupula, hair cells move aritificially
what is BPPV
benign paroxysmal positional vertigo
what are the 4 types of BPPV
-benign - not life threatening -paroxysmal - sudden, brief epochs -positional - symptoms triggered by specific head positions or rotations -vertigo - false sense of rotational motion [mild to intense dizziness]
what is the cause of BPPV
idiopathic hit to the head
what is the pathophysiology of BPPV
otoliths (crystals) dislodged into semicircular canal especially when lying down canals become more sensitive
what is the treatment for BPPV
Epley maneuver -direct the crystal out of canal
Meniere's disease
cause: idiopathic pathophysiology: excess fluid in the labyrinth (canals). In turn increases endolymphatic pressure. Decreases firing in the affected side and increases firing on the intact side=sense of SPINNING
what is a part of the physiology in the neurons that increases the neurons sensory velocity
myelinated neurons
Benign Paroxysmal Positional Vertigo (BPPV) is a sudden non-life threatening false sensation of rotational motion when _________ becomes dislodged into semi-circular canal
otolithic cystals
what sensory receptors exist (4)
chemoreceptors (chemical concetrations) thermoreceptors (changes in temp) nociceptors (pain signals) mechanoreceptors (mechanical changes)
what are the 2 types of noiceceptors
A-fibres (sharp, localized pain) C-fibres (dull, burning, delayed pain)
what are 3 types of mechanoreceptors
-cutaneous (tactile) receptors -baroreceptors -proprioceptors
Name 4 types of cutaneous sensory receptors.Which is widest
widest in axon diameter to least 1.proprioceptions [muscle spindles] 2. touch 3. pain, temperature
how can firing rate increase
-increase in duration causes increase in firing rate which increase neurotransmitter release
what are 2 types of pain cutaneous receptors
tonic receptors slowly adapt to continual stimulation
phasic receptors rapidly adapt to continual stimulation, then reactivated when stimulus ends
what do cutaneous receptors under the skin provide
provide information about vibration, pressure, temperature
the _______ of a sensory neuron: encompasses the spatial extent of the receptor surface from which the sensory neuron recieves input
receptive field
what is the most sensitive spot called
hot spot
___________ has smaller receptive fields (type 1) than deep receptors (type 2)
superficial receptors
superficial receptors (type 1) receptive fields has __________ points of maximal sensitivity
multiple
deep receptors (type 2) have ________
one
polysynaptic pathways
mediate flexion and crossed-extension reflexes can cross and hit neurons across the body
the ________ of a sensory neuron, encompasses the spatial extend of the receptor surface from which the sensory neuron receives input
receptive field
for sensory neurons, intensity of the signal is influenced by ________ and __________ of the stimuli
amplitude duration
merkel cells (disks; superficial)
-25% innervation of hand -afferent: slowly adapting type 1 -pressure and texture -small, densely packed receptive fields; multiple hotspots -threshold: moderately low threshold
Meissner corpuscle (superficial)
-40% innervation of hand -afferent: fast adapting type 1 -stroking, velocity or motion across skin -small, densely packed receptive fields; multiple hotspots -low threshold
ruffini ending (deep)
-20% innervation of hand -slow adapting type II -skin stretch -large receptive field; only one hot spot -hightheshold to indentation
Pacinian corpuscle (deep)
-15% innervation of hand -fast adapting type II -vibration; feeling through objects -large receptive fields; only one hotspot -extremely low threshold
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