PHGY 213: CNS/Locomotion

what is the analogy to the human body's center of gravity?

an upside down pendulum

what does it mean that "muscles produce unpredictable force"?

the force muscle produces depends on the length of the muscle & the load and fatigue state

proprioception

physical sense of where the body is in space

feedback control

-comparison of actual & desired movements

-corrections for unanticipated disturbances

-accurate but slower

feed-forward control

-predictive; faster but assumes the prediction is correct

-based on previous experience

CPGs

central pattern generators

-circuitry at level of brain/spinal cord

-breathing, walking

example of how CPGs can be reset

1. walking on a turntable

2. marathon runners running in sync

what increases the EMG?

increasing strength of contractions (more motor units recruited, increased firing frequency of motor units) increases the amplitude of the EMG

if muscle is fatigued, what is the effect on the EMG?

smaller EMG (amplitude) for the same amount of work

2 types of EMG

1. surface

2. intramuscular

what does EMG measure?

input from multiple motor units

reflects underlying activity of MAPs (muscle action potentials)

motor unit

motor neuron + innervated muscle fibers

what do the electrodes do?

create an interface between the ionic solution (subject) & a metallic conductor (the electrode)

where are the electrodes placed?

2 on the gastrocnemius

1 elsewhere on the leg (ground electrode)

what coats the electrode & why?

silver chloride

to minimize polarization

what causes the noise on the EMG when the skin is moved?

DC currents between the layers of the skin

frequency range of the EMG recording

50-350 Hz

max amplitude of the EMG recording

1.5 mV

EMI

electromagnetic interference

60 Hz

how was EMI tested in the lab?

brining a power cord close to one of the electrodes

(if you bring it in between, effects will be lessened due to differential recording)

how were motion artifacts tested in the lab?

tapping on an electrode (transient deformation of the skin)

differential amplification

input from two different parts of the muscle; subtract the two to remove signals that are the same from each (noise)

amplify the difference

response latency

time of stimulus onset to time of response onset

monosynaptic stretch reflex

involves one synapse at the level of the spinal cord

stretching of the extensor muscles --> activation of stretch receptors --> leg kick

T wave

change in deflection characteristic of a monosynaptic stretch reflex

how was the monosynaptic stretch reflex elicited?

tapping on the Achilles tendon

FSR

functional stretch reflex

an anticipated/primed response

goes to the level of the brain stem

how was the FSR elicited?

tapping on the base of the foot after asking the subject if they're ready each time (so they anticipate it)

response was them pressing back

voluntary response

goes to the level of the cortex

no anticipation

what type of control was involved in the single step experiments?

feed forward control

what type of control was involved in the rhythmic hopping experiments?

feed forward, feedback, CPG

for the experiments, what is considered the "onset of stimulus"?

when the subject's foot (or feet) hit the floor

for the single step, why is there activity before the subject hits the floor?

feed forward: the subject knows what to expect

the muscle starts contracting before it hits the floor

what is the average hopping rate?

2.1 Hz

what is the up & down activity of the EMG during rhythmic hopping called?

spindle response

why is the digital filter set to 50-350 Hz?

because the desired frequencies for the EMG fall within this range (increasing the range would lead to more noise)

why is the computer set to sample signals at no less than 1000 Hz?

the bioamp is set to 500 Hz (so as to encompass the 350 Hz max of the data collected) so the Nyquist sampling rate has to be 2x this (1000 Hz)

avoid aliasing

does the EMG change as muscle contraction decreases & what is happening to the motor unit level to cause this change?

yes, the EMG amplitude decreases as muscle contraction decreases because the firing frequency is decreasing, resulting in fewer motor units being recruited

do the monosynaptic stretch reflex, FSR, and/or voluntary response contribute to the control of landing during the single step experiment?

all three contribute because the average response times for each reflex/response were smaller than the burst of EMG activity for the single step control

do the monosynaptic stretch reflex, FSR, and/or voluntary response contribute to the control of rhythmic hopping?

none of them make a significant contribution because the average values for the reflexes/responses tested were all higher than the rhythmic hopping EMG burst

calculation of the subject's normal preferred hopping rate

hops per cycle/avg time per cycle

why did the preferred hopping rate change after hopping faster than normal?

the metronome reset the CPG to a higher hop/minute rate