Lower Motor Neurons

Question 1

general reflex pathway

Answer 1

-afferent sensory input travels to the brainstem or spinal cord where it is integrated by local circuit neurons
-information travels from local circuit neurons to motor neuron pools (groups of lower motor neurons)

Question 2

reflex motion

Answer 2

mediated by a simple neural circuit which travels to the brainstem or the spinal cord

Question 3

rhythmic motion

Answer 3

requires an initial sensory input via the upper motor neurons to initiate motion. central pattern generators in the lower motor neuronal circuits allow for this input to create rhythmic motion by regulating oscillatory circuits in the brainstem/spinal cord

Question 4

voluntary

Answer 4

requires higher brain levels such as the basal ganglia or cerebellum to initiate movement (not just the initial push like in rhythmic motion)

Question 5

is there involuntary movement which requires cortical input

Answer 5

-idk but i do know that the cortex is generally always trying to suppress movement that it doesn’t want (ie the indirect basal ganglion pathway for example)
-this means that involuntary movement is generally going to be a reflexive behavior

Question 6

examples of involuntary movement

Answer 6

-spinal reflexes (ex. myotatic reflex, flexion reflex, knee-jerk reflex)

Question 7

examples of rhythmic movement

Answer 7

-posture, balance, walking, running, riding a bike, eye movement, breathing

Question 8

examples of voluntary movement

Answer 8

-reaching for something, speaking, dancing

Question 9

PQ: generally speaking, a reflex uses neurons located in _________ while voluntary movement uses neurons located in the _________

Answer 9

brainstem/spinal cord, cortex

Question 10

how are motor and sensory information related

Answer 10

-motion is generally always guided by sensory input via motivation, this makes the distinction between voluntary and involuntary a bit unclear

Question 11

feedforward information

Answer 11

-related to creating goal-oriented movement/ getting ready to respond to a perceived upcoming stimulus
-a shift from the natural resting position

Question 12

feedback information

Answer 12

-movement which occurs in response to some sort of change to the body
-motion to return to the initial state

Question 13

different methods of study

Answer 13

-anatomical connectome. in vitro neurophysiology, in vivo neurophysiology, energy use patterns of the brain, patterns of immediate early gene activation, and clinical correlations

Question 14

anatomical connectome

Answer 14

-understanding the anatomy of neural circuits
-ex. anterograde and retrograde dyes, viruses which can jump synapses and express fluorescent proteins,

Question 15

in vitro neurophysiology

Answer 15

-“in a dish”
-mimicking physiological conditions “in a dish” in order to determine synaptically coupled cells
-can also use dyes to do so

Question 16

in vivo neurophysiology

Answer 16

-determining synaptically coupled cells, see if the stimulation of certain cells changes behavior, observe the activity of cells during certain conditions

Question 17

in vivo neurophysiology

Answer 17

-determining synaptically coupled cells within a living organism
-can be accomplished using calcium imaging, optogenetics

Question 18

in vivo calcium imaging

Answer 18

-first, you inject the cells with a virus containging a fluorescent protein expressing gene which illuminates in response to calcium
-the miniscope will detect the illumination which signals for calcium
-calcium is used as a proxy for neural activity

Question 19

optogenetics

Answer 19

-allows for the stimulation of neurons using light. this is accomplished by the stimulation of light-sensitive ion channels within the cell GET A BETTER EXPLANATION

Question 20

immediate early gene expression

Answer 20

-use of a gene probe to identify the genes which were active before cell death
-“poor man’s fmri” DOES THE ORGANISM HAVE TO DIE IN THIS

Question 21

extrafusal fibers

Answer 21

-generate the mechanical force needed for movement

Question 22

do intrafusal fibers respond the feed forward or feed back information

Answer 22

feed back

Question 23

ventral horn of the spinal cord

Answer 23

location of alpha motor neurons which innervate the extrafusal fibers

Question 24

example of synergist muscles

Answer 24

-soleus and gastrocnemius (contract at the same time)

Question 25

how is somatotophy conserved in the spinal cord

Answer 25

-alpha motor neurons innervating similar regions (ex. gastrocnemius and soleus) are located near eachother in the spinal cord
-generally speaking, more medial alpha motor neurons correspond to muscles like the back shoulders etc (proximal muscles).
-lateral alpha motor neurons in the spinal cord control more distal muscles ex. the ones in your hands

Question 26

segmental orientation

Answer 26

UNSURE

Question 27

local circuit neurons

Answer 27

neurons whose entirety lies within the spinal cord

Question 28

interneurons

Answer 28

neurons whose axons and cell bodies lie within the same brain region

Question 29

projection neuron

Answer 29

neuron whose soma and axon terminal lie in different brain areas

Question 30

how do you increase muscle force

Answer 30

-stimulate an alpha motor neuron more
-stimulate more alpha motor neuron units
-stimulate more fast-fatiguable motor neuron units

Question 31

what are the three dif types of motor neurons

Answer 31

slow fatiguable, fast fatiguable resistant, slow fatiguable

Question 32

how does plasticity relate to muscle fiber type

Answer 32

alpha motor neurons determine the muscle fiber type. over time, depending on environmental need, fast fatiguable or slow fatiguable neurons can innervate muscles which were previously innervated by slow fatiguable neurons (ex. during marathon training)
-this is an example of how motor maps (of the spinal cord) are not rigid and can change over time

Question 33

what determines the type of motor neuron that develops

Answer 33

-stimulation frequency (lower stimulation frequencies will support the development of slow fatiguable and higher frequencies will support the development of fast fatiguable)

Question 34

size principle

Answer 34

-states that smaller motor neuron units will be recruited before larger ones. This is because smaller motor neurons have a smaller force output and therefore are more efficient and resistant to fatigue. It is not energetically efficient to recruit fast fatiguable neurons first unless you let the smaller more efficient motor neurons try first

Question 35

intrafusal muscle spindle anatomy

Answer 35

-there are 8-12 intrafusal fibers parallel in the spindle
-sensory afferents wrap around the fibers to send proprioceptive information
-intrafusal fibers in the spindle are innervated by gamma motor neurons

Question 36

where do alpha motor neurons terminate

Answer 36

in the ventral horn of the spinal cord

Question 37

walk through the myotatic reflex

Answer 37

-a passive stretch of the bicep elongates the extrafusal and intrafusal fibers of the muscle
-the mechanoion receptors in the intrafusal fibers open and cause a depolarization of the 1a afferents
-the 1a afferents which extend to the dorsal root ganglion directly excitatorily synapse with the alpha motor neurons that innervate the bicep
-the 1a afferents also synapse with an inhibitory motor neuron which releases GABA onto the alpha motor neuron innervating the tricep
-the alpha motor neurons release acetocholine onto the muscle causing contraction
-the second alpha motor neuron prevents acetocholine from being released onto the tricep causing relaxation
-the contraction of the bicep causes the mechanoionreceptors of the golgi tendon organ to open and 1b afferents depolarize
-1b afferents send proprioceptive information about the muscle contraction to the cns

Question 38

what causes 1a afferents to fire

Answer 38

-the stretch of a muscle

Question 39

what causes 1b afferents to fire

Answer 39

-the contraction of a muscle

Question 40

describe the tendon reflex

Answer 40

-a tap on the patellar tendon causes a stretch in the quadricep muscle
-1a afferents of the quadriceps fire to the dorsal root ganglion
-1a afferents synapse with an inhibitory interneuron which releases GABA onto the alpha motor neuron innervating the hamstring
-the synapse also directly releases glutamate onto the alpha motor neuron innervating the quadriceps
-the quadricep contracts and the hamstring relaxes
-golgi 1b afferents connected to the quadricep muscles fire

Question 41

what kind of muscles are the quadriceps

Answer 41

extensors (extend when contracted)

Question 42

what kind of muscle is the hamstring

Answer 42

flexor (flexed when contracted)

Question 43

The flexor/flexion reflex

Answer 43

-you step on a tack with leg A
-nociceptors from the sensory neurons of leg A synapse with a local circuit neuron in the dorsal root ganglion
-this interneuron synapses with the alpha motor neuron innervating the quadriceps of leg A(extensor). The interneuron releases GABA onto the interneuron here.
-another interneuron synapses with the hamstring on leg A (flexor). The interneuron releases glutamate and the leg A hamstring muscle is contracted.
-another interneuron synapses on the alpha motor neuron of leg B innervating the quadricep. The interneuron releases glutamate and the quad (extensor) contracts.
-The last interneuron finally synapses with the hamstring on leg B with GABA. The hamstring on leg B relaxes.

-the golgi tendon organ is firing 1b afferents for the leg B quadricep and the leg A hamstring.

Question 44

is the intrafusal muscle spindle series or in parallel with the extrafusal muscle

Answer 44

in series

Question 45

is the golgi tendon organ in series or in parallel with the extrafusal muscle

Answer 45

in series

Question 46

how did we determine that the flexion reflex is not a plausible explanation for locomotion without cortical input

Answer 46

we saw organisms which did not have sensory receptors/dorsal root ganglion doing locomotion

Question 47

what is escape from inhibition and how can that be accomplished

Answer 47

escape from inhibition can be accomplished through an autapse which we see during recipricol inhibition.
-could also result from the neurotransmitter diffusing out of the synapse