Midterm 1

Question 1

Define a motor neuron pool

Question 2

Where do cell bodies reside?

Question 3

Afferents =

Answer 3

action potentials going into the nervous system

Question 4

the bulk of connections of neurons are _____

Answer 4

interneurons

Question 5

afferent neurons always come in through the ____ ____, and send axons out through the ____ ____

Answer 5

dorsal root, ventral root

Question 6

efferent axons exit from the ____ ____ via the ____ ____

Answer 6

anterior horn via the ventral root

Question 7

the ___ ___ carries sensory or afferent axons

Answer 7

dorsal root

Question 8

motor neuron pool =

Answer 8

all the motor neurons innervating a particular muscle

Question 9

the motor unit =

Answer 9

the cell body and dendrites of a motor neuron, the multiple branches of its axon, and the muscle fibers that it innervates

Question 10

the muscle unit =

Answer 10

all the muscle fibers belonging to a motor unit

Question 11

innervation ratio =

Answer 11

number of muscle fibers innervated by a single motor neuron (varies for different muscles)

Question 12

gastroc innervation ratio

Answer 12

1:1900

Question 13

eye muscle innervation ratio

Answer 13

1:15

Question 14

innervation ratio changes with aging

Answer 14

of motor units declines, but size increases

Question 15

3 types of skeletal muscle fibers

Answer 15

1. SO - slow oxidative
2. FOG - fast oxidative-glycolytic
3. FG - fast glycolytic

Question 16

S type motor units =
FR type motor units =
FF type motor units =

Answer 16

slow contracting type
fast contracting, fatigue resistant
fast contracting, fatigable

Question 17

S motoneurons innervate ___ type muscle fibers forming ___ type motor units

Answer 17

slow oxidative, slow

Question 18

FR motoneurons innervate ___ type muscle fibers forming ___ type motor units

Answer 18

fast oxidative-glycolytic, fast fatigue resistant

Question 19

FF motoneurons innervate ___ type muscle fibers forming ___ type motor units

Answer 19

fast glycolytic, fast fatigable

Question 20

Large motoneurons supply ___-twitch muscle fibers, small motoneurons supply ___-twitch

Answer 20

fast, slow

Question 21

Characteristics of type S motor units

Answer 21

Small, slow contracting, fatigue resistant, small innervation ratio

Question 22

Characteristics of type FR motor units

Answer 22

Fast contracting, fatigue resistant. Reach peak force sooner (peak is not much bigger than SO)

Question 23

Characteristics of type FF motor units

Answer 23

Fast contracting, fast to fatigue. quick rise to peak, quick decline to half, large peak force. Bad blood supply, and glycogen gets used up.

Question 24

What happens if you re-attach a slow motoneuron to fast muscle fibers?

Answer 24

it will change behavior, but the changes are not dramatic and there will only be a minor transition in behavior. ex: Trying to turn a bodybuilder into a marathon runner or vice versa - will not 100% turn into the other type => training effects. You dont change the number of sarcomeres w weight training, just make them bigger.

Question 25

Methods for recording single motor units:

Answer 25

Metal micro electrodes and fine wires

Question 26

2 ways to control muscle force

Answer 26

1. recruit more motor units 2. make the ones that are active fire more often

Question 27

Performance of a particular movement always appeared to be accomplished by....

Answer 27

the activation of motor units in a set sequence - orderly recruitment. Motor unit #1 is activated and remains active so as long as force doesnt decrease. Increases in force by adding more motor units.

Question 28

Henneman's size principle =

Answer 28

the orderly recruitment of motor units is due to variations in motor neuron size, w smaller motor units w the smaller MN being recruited first.

Question 29

Derecruitment =

Answer 29

sequential inactivation

Question 30

Why recruit in an orderly fashion? positives and negatives?

Answer 30

- Add the larger, bigger, more powerful motor units near the end of a contraction when increment of increase will have an effect on net force. Better control of force. - Positive effect: sequence is predetermined, and the brain doesnt have to contend with 445 switches, but instead with just the control of the level of the input (drive) to the motor pool. - Negative effect: inability to selectively activate motor units, out of order.

Question 31

All motor units are recruited when force reaches _% of max

Answer 31

50%

Question 32

why are motor units not synchronous?

Answer 32

they would not be able to do a smooth contraction

Question 33

motor unit recruitment continues until about _% of maximum

Answer 33

85_

Question 34

Each motor unit produces a partially ___ ___; because units fire ____ with each other, the ____ ____ is smooth

Answer 34

partially fused tetanus, asynchronously, net force

Question 35

a compartment =

Answer 35

a unique population of motor units, being confined to a certain region of the muscle - several groups of motoneurons being controlled at the same time

Question 36

How do compartments work?

Answer 36

They come on at different times - only relevant compartments are turned on to do a specific movement.

Question 37

evidence for neuromuscular compartmentalization:

Answer 37

In biceps brachii there are two functional components in the human - idea or concept of “task groups”. Some MUs active during supination, others active during elbow flexion. 2 physiological muscles! Extensor digitorum in humans - 4 compartments.

Question 38

interoceptors =

Answer 38

transduce info from within the body - pain, temp, pressure, receptors in gut and bladder

Question 39

exteroceptors =

Answer 39

transduce info from the environment - rods and cones in retina pick up light coming in

Question 40

proprioceptors =

Answer 40

transduce info about the relative configuration of body segments - knowing where a limb is with closed eyes

Question 41

receptors can be stimulated by ___ or ___ stimuli (or sometimes both)

Answer 41

chemical, mechanical

Question 42

receptors in the __ project ___ to the spinal cord

Answer 42

periphery, centrally

Question 43

cell bodies are located in the ___ ____ ____

Answer 43

dorsal root ganglion

Question 44

central receptors project to ___ ___

Answer 44

superior structures

Question 45

Afferents are labeled based on ___-___ ____. 4 numbers: which is smallest?

Answer 45

cross-sectional diameter I - IV IV is smallest

Question 46

Subdivisions of I afferents

Answer 46

Ia and Ib

Question 47

Conduction velocity of afferents depends on ____. larger ___ = ____ conduction.

Answer 47

diameter. larger diameter = faster

Question 48

Where to the Ix and Ix afferents go? What are IIb afferents?

Answer 48

I's go to muscle. Ia: primary endings, go to specific receptors. Ib: go to different muscle things like golgi tendon organ. IIb: secondary endings, secondary spindle afferents

Question 49

synaptic potential =

Answer 49

the way that a presynaptic neuron influences a postsynaptic neuron's susceptibility to generate an AP

Question 50

how many synapses are on a dendritic tree of a motoneuron?

Answer 50

10-20k

Question 51

types of post synaptic potentials: What does the interplay between them determine?

Answer 51

excitatory and inhibitory whether or not the neuron will fire an AP

Question 52

What are excitatory post-synaptic potentials and their characteristics?

Answer 52

1. EPSP is local and graded (not propagated, not all or none) - magnitude of the EPSP is proportional to the amount of neurotransmitter released. 2. EPSP is not followed by a refractory period - they can summate.

Question 53

Divergence = Convergence =

Answer 53

divergence = a single neuron synapses on multiple neurons convergence = multiple neurons "converge" on fewer neurons

Question 54

steps of spatial summation:

Answer 54

1. Three excitatory neurons fire. Their graded potentials separately are all below threshold. Each cause a small dimple but cant get neuron to threshold. Critical area doesnt see big enough membrane shift, unless theyre all at the same time. 2. Graded potentials arrive at the trigger zone together and sum to create a suprathreshold signal. 3. An action potential is generated.

Question 55

reasons for APs not being fired from spatial summation?

Answer 55

If enough negativity at the same time, it does not result in an AP. Two excitatory potentials are diminished by summation with an inhibitory potential. The summed potentials are below threshold, so no action potential is generated

Question 56

difference between spatial and temporal summation:

Answer 56

Temporal summation occurs when a single pre-synaptic neuron fires many times in succession, causing the post-synaptic neuron to reach its threshold and fire. Spatial summation occurs when excitatory potentials from many different pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire.

Question 57

Characteristics of muscle spindle receptors:

Answer 57

Fusiform or spindle shaped receptors found in most skeletal muscle (ie football). Lie in parallel with large force producing skeletal (extrafusal) muscle. Different muscles have different numbers of spindles = density.

Question 58

Proximal and distal muscles have a (lower/higher) density of muscle spindles?

Answer 58

proximal - lower distal - higher

Question 59

Describe the muscle spindle (anatomy)

Answer 59

1 cm in length, middle (equatorial) region covered by a connective tissue capsule, while polar (end) regions have myofilament contractile components.

Question 60

Bag and chain fibers are two types of ____ fibers?

Answer 60

intrafusal

Question 61

What are bag and chain fibers?

Answer 61

Bag and chain fibers are defined based on their distribution of the nuclei. Bag fibers are usually longer than chain fibers. They are subdivided into Bag1 and Bag2. 2-20 intrafusal fibers per spindle, with about 2-3 bag fibers and 3 or more chain fibers.

Question 62

Two types of sensory afferent innervation:

Answer 62

Primary or Ia afferents, spiral around the central area of Bag1, Bag2 and all chain fibers. Secondary or II afferents innervate Bag2 and chain fibers, but never, if ever Bag1 afferents.

Question 63

rapidly vs slowly adapting receptor behavior:

Answer 63

Rapidly adapting: provides dynamic info about the stimulus = info about to change. Slowly adapting: provides static info about the stimulus = info about persistence. Slowly adapting can also code for rate of application of probe.

Question 64

Ia afferents are sensitive to the ___/___ of the muscle stretch, as well as the ____ of stretch. II afferents are sensitive to the ____ of change.

Answer 64

Ia afferents are sensitive to the speed/velocity of the muscle stretch, as well as the length of stretch. II afferents are sensitive to the length of change.