HES 202 - Human motor behaviour - Midterm 1 - 2023

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

1. increase the number of motor units (recruitment)
2. 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

1. bag - based on shape (bag 1: dynamic ; bag 2: static)
2. chain: static

what are two types of afferents

1. type Ia (primary) - length and velocity
-innervate bag 1, bag 2 and chain

2. 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

1. feedback to spinal cord via Ib afferent
2. Ib inhibitory interneuron (disynaptic connection to motor neuron)
3. autogenic inhibition: inhibits agonist motor neuron which decreases force output)

what is the main function of GTO

inhibit the agonist motor neurons
1. protective mechanism
2. 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

1. semicircular canals
2. 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