Lecture 10 Review

Question 1

Where are lower motor neurons located and what are their function?

Answer 1

they are located in the ventral horn of the spinal cord and have axons that innervate the muscle fibers
directly command muscle contraction

Question 2

Describe the anatomy of a muscle fiber

Answer 2

Sarcolemma - surrounds the myofibril bundle, excitable membrane
T-tubules - connects the sarcolemma to the sarcoplasmic reticulum
Sarcoplasmic reticulum - myofibril fibers encased inside, controls proteins in charge of muscle contraction, causes release of Ca
Myofibrils - contract in response to an AP

Question 3

What is the structure of the myofibril

Answer 3

Thin filaments attached to z line
Thick filaments are attached to thin filaments
all come together to form a sacromere

Question 4

Describe the structure of a thin filament

Answer 4

actin - binds to myosin for contraction
tropomyosin - blocks myosin-actin binding
troponin - binds Ca to remove tropomyosin

Question 5

describe the structure of thick filaments

Answer 5

comprised of myosin proteins

they can bind ATP, link to thin filaments, move and bend

Question 6

Describe muscle contraction

Answer 6

1. Ca binds to troponin to change tropomyosin to allow myosin and actin to bind
2. they bind
3. myosin bend, pulls the actin filaments, shortens the sacromere

Question 7

Describe the relationship the sarcoplasmic reticulum and calcium hvae

Answer 7

the sarcoplasmic reticulum contains stores of Ca which is released in response to muscle depolarization
depolarization around T-tubules - last control of Ca

Question 8

What is the function of the neuromuscular junction?

Answer 8

The motor neuron releases Ach on muscle to active nAchR (Na/K channel), depolarization and contraction
it is a large synapse that has one input. strong and reliable

Question 9

What is a motor unit and a motor pool?

Answer 9

Unit = single motor neuron and the muscle fiber it innervates. each fiber gets on neuronal output
Pool = all the motor neurons that innervate a single muscle

Question 10

What is the spinal organization of the lower motor neurons?

Answer 10

The size of the ventral horn is proportional to the number of lower motor neurons
The number of lower motor neurons are determined by the number of muscles

Question 11

What is the difference between slow and fast motor units?

Answer 11

slow fibers = slow activation, prolonged contraction, lots of mitochondria
fast fibers = fast activation, fatigue, few mitochondria
these activation properties are determined by innervation

Question 12

What are the input to alpha motor neurons?

Answer 12

sensory = input from spinal interneurons
muscle = sensory input from muscle spindles
brain commands = input from motor neurons of the brain

Question 13

What is a muscle spindle?

Answer 13

proprioreceptors that provide information about muscle length
intrafusal fibers are sensitive to their own length

Question 14

What is the spindle sensory neuron (Ia afferent)?

Answer 14

a neuron whose firing is proportional to muscle length. it activates the alpha motor neuron, contracts muscle, and produces negative feedback to muscle

Question 15

What is the myotatic reflex?

Answer 15

muscle feels stretched and activates the muscle spindle

Ia afferent and motor neuron activated, contracts muscle

Question 16

What does the gamma motor neuron do?

Answer 16

stimulate contraction of fibers within the spindle (intrafusal fibers)
makes intrafusal fibers contract when the extrafusal muscle fibers contract, makes up for lost tension

Question 17

When does the golgi tendon organ do?

Answer 17

monitors muscle tension

responds to contraction of extrafusal fibers by increasing firing of Ib fibers

Question 18

what is the reverse myotatic reflex?

Answer 18

activation of the golgi tendon organ increases firing Ib afferents, inhibits via interneurons to alpha motor cortex. prevents contraction

Question 19

What is reciprocal inhibition?

Answer 19

Ia afferents synapses on inhibitory interneurons that connect to opposing alpha neurons, preventing them from working against each other

Question 20

What is the flexor withdrawal reflex?

Answer 20

Pain afferents stimulate excitatory interneurons, synergistic activation of multiple flexor muscles
also have inhibition of extension muscles (reciprocal inhibition)
goes opposite direction of pain stimulus

Question 21

What is the crossed extensor reflex?

Answer 21

synergistic activation of muscles in one limb is couples with opposing muscle control of opposing limb
flexor coupled with opposing extensor to prevent falling

Question 22

How does the spine control walking?

Answer 22

rhythmic spinal interneurons use reflex arcs to produce coordinated muscle movement in the legs
this is produced by dual channel coupling