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Neuro > Unit 3: Neurobiology of Change > Flashcards

Unit 3: Neurobiology of Change Flashcards

1
Q

The forelimbs and hindlimbs

A

The forelimbs are the ones that are found in the front part of the body i.e arms. Hind limbs are those that are found in the back part of the body I.e legs.

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2
Q

How do muscles contract? How are muscles put together

A
  • The fundamental unit of contraction of a muscle –> a muscle fiber (single cell, many nuclei bc it results from the fusion of many cells, and it runs the entire length of the muscle)
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3
Q

What are muscle fibers?

A

Are bundled into fascicles, a bundle of fibers that are held together, connective tissue. Fascicles are held together in muscles connected by connective tissue.

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4
Q

Each muscle fiber:

A

Is a long series of sarcomeres, connected end-to-end.

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5
Q

What is a sarcomere?

A

Is a single contractile unit, and connected in series.

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6
Q

What is a sarcomere?

A

Is a single contractile unit, and connected in series. Functional unit of contraction

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7
Q

What will a skeletal muscle have?

A

It will have a stripy appearance (striated)

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8
Q

Myosin thick fibers, actin thin fibers –

A

Anchored at Z-bands. That thick myosin filament on either end interacts with actin filaments. Myosin heads when they pull on the actin filaments shorten the sarcomere and generate force.

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9
Q

How is force regulated?

A

Need ATP in order for myosin heads to move, and also need Ca in order for actin and myosin to interact.

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10
Q

The contraction is initiated by:

A

A flow of Ca from the sarcoplasmic reticulum.

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11
Q

Excitation-Contraction:

A

Exciting a muscle, causes it to contract.

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12
Q

What are the events:

A

What happens in the motor neuron: action potential arrives at the terminal –> opens the voltage-gated Ca channels –> causes Ach to be released.
Ach (need 2 bc you got 2 alpha subunits).
AchRs open and causes big depolarization, get a spike that rushes along the membrane of the muscle.

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13
Q

Muscle spike causes Ca efflux from SR

A

Causes the sarcoplasmic reticulum to release Ca through Ryanodine receptors (RyRs) which are located in the sarcoplasmic/endoplasmic reticulum membrane and are responsible for the release of Ca2+ from intracellular stores during excitation-contraction coupling in both cardiac and skeletal muscle.

Ca comes out of the SR and causes contraction –> you get a single twitch. Get one action potential in the motor neuron, one action potential in the muscle, and a twitch in the muscle fiber.

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14
Q

The Motor Unit

A
  • Each muscle has thousands to millions of fibers
    -Motoneurons in the spinal cord
    -Each motor neuron innervates many muscle fibers “motor unit”
  • Distributed throughout the muscle
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15
Q

“Motor Pool”

A

-Motoneurons innervating the whole muscle
-Forelimbs (arms) motor neurons in the cervical spinal cord
- Hindlimbs in lumbar SC
motor neuron innervates shoulder muscles are much more medial, and the ones innervating the fingers are much more distal and are much more lateral.

As you go from medial to lateral, you go from proximal to distal on your body. Proximal means close to the center of the body. Distal means the opposite: further away from the center of the body.

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16
Q

Where are the motor neurons located?

A
  • In the ventral horn of the spinal cord. The ventral horns contain the cell bodies of motor neurons that send axons via the ventral roots of the spinal nerves to terminate on striated muscles.
  • Sensory input comes through the dorsal root
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17
Q

Large neurons in the ventral horn of the spinal cord

A

Exit through the ventral root (big nerve)

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18
Q

Motor pool are made up of:

A

100 of thousands of motor neurons that innervate a particular muscle

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19
Q

Motor Neuron Pool Organization:

A

-Forelimbs (arms) motor neurons in the cervical spinal cord
-Hindlimbs in lumbar SC

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20
Q

Somatotopic map of limbs: Which controls fine movements?

A

Distal muscles –> the muscles that control our fingers

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21
Q

Motor neurons innervating fingers get:

A

Direct input from cortical neurons will make decisions about where to move.

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22
Q

How do you regulate force?

A
  • A motor neuron causes an action potential in the muscle fiber it innervates. Action potentials cause twitches

*Note: there are hundreds of motor neurons innervating a muscle, and not all of them fire/contract every time.
Not all muscle fibers produce the same amount of force, twitches are not all or none.

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23
Q

Different kinds of muscle fibers (vary in their fatigue resistance) from a single twitch.

In humans, muscle fatigue can be defined as an exercise-induced decrease in the ability to produce force.

A
  • Slow (S) fatigue resistant –> lower force
  • Fast fatigue resistant (FR) –> more force
  • Fast fatigable (FF) –> strongest
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24
Q

Response to Multiple Stimuli

A
  • Force evoked with multiple action potentials.
  • If the first twitch is 100% –> fast fatigable after not many twitches give out
  • Fast fatigue resistance can fire a lot more
  • Slow fibers can contract all day and don’t reduce the amount of force they generate
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25
Q

Experiment: Force II: Motor Unit Recruitment

A
  • If you stretch a muscle (removed from an animal), pull on the muscle which activates sensory neurons and will drive motor neurons to fire
  • Use an extracellular electrode –> look at spikes generated by motor neurons in the nerve.

The bigger the spike the bigger the motor neuron. big spike –> big axon.

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26
Q

Size principle

A

The first motor neuron unit to be recruited will generate a small force, and the last one will generate the most force. As the drive gets stronger it will produce more.

This is how muscle fibers are recruited –> if you start by generating a little bit of force, and if you pull something harder you will generate more force.

27
Q

What will happen if big units were recruited first?

A

If big units were recruited first, how coordinated would you really be?
- If you use big motor neurons first you will end up having big contractions and it will make you very clumsy.

28
Q

What happens if you recruit those fast fatigable muscles first?

A

They will fatigue and run out of juice, should save them last when you will really need them.

29
Q

Size vs threshold:

A

-Motor units are turned on (recruited) in order of size/force for some movements
- small motor neurons are innervated by small axons which come from small motor neuron

  • The cell body’s motor neurons are smaller for slow muscle fibers and bigger for fatigue resistance. S < FR < FF (size proportional to force)
30
Q

What is the relationship between size and membrane resistance Rm?

A
  • The bigger you are the more membrane you have, and the more channels you have in the membrane –> the leakier you are.
  • The bigger the resistance, the bigger the synaptic potential and the bigger depolarization (more likely for action potential threshold)
  • A little motor neuron with the same synaptic input is more likely to fire than a big motor neuron
    -If we want to generate more force, we can just recruit more motor units, and we can recruit bigger motor units, and fast fatigue motor units for a larger force.
31
Q

Increase force output of a muscle:

A
  1. Recruit more motor units –> thousands to work with, so you can keep activating motor neurons which will activate their motor units –> cause a stronger contraction
  2. Recruit stronger motor units –> Start with the little ones (produce small twitches) and then add motor units to generate more force, like the fast fatigue-resistant, or the fast fatigable
  3. Activate each motor unit more strongly: the higher the frequency the bigger the force you will get out of them
32
Q

Proprioceptors:

A

Information from:
-Ruffini corpuscles (involved in sensing the stretch of the skin
–> around a joint –> it will tell you what your joint angle is)
- Muscle spindles (will tell you about muscle length)
-Golgi tendon organs (tells you how much tension is on the muscle)

33
Q

Muscle spindles:

A

Specialized “intrafusal” muscle fibers (part of the sensory organ). Tucked inside a muscle you have special muscle fibers that make up the muscle spindle –> they are contractile.

  • Normal fibers are “extrafusal” –> generate the force
34
Q

Sensory neurons activated when muscle is stretched:

A
  • Group Ia reacts to change
  • Group II reacts to length
35
Q

Gamma motor neurons

A

Important for adjusting the length to optimize dynamic range.

36
Q

What are the adaptation properties of the two types?

A

Group Ia doesn’t care if something is going on all the time, they want to change (adapt quickly)
Group II will be more likely to adapt slowly, sending a constant signal about muscle length

37
Q

Spindle Reflex: local

A

-Afferents are going into the spinal cord and connect to motor neurons
-Excite homonymous muscle and synergists. The homonymous muscle is the same muscle that the sensor is in.

  • inhibit antagonists (red - inhibitory neurons) the muscle is going to try to oppose the activity of the homonymous muscle.
    The quadriceps is the homonymous muscle, the hamstring is the antagonist (opposite)
38
Q

Response to knee tap?

A

-If you tap the knee that stretches the tendons, if you stretch the muscle it will activate the muscle spindle, will cause an action potential to go into the spinal cord and cause contraction of the extensor muscle, and inhibit contraction of the flexor muscle.

39
Q

Stretch Reflex:

A

-Hold a mug at a particular angle, and stand there with a mug as drinking.
- The biceps muscle is going to bring that mug upwards –> this is the homonymous muscle that causes the mug to stay put.
-The antagonist is going to be the triceps –> extensor, which will make the mug go down.

40
Q

Synergist:

A

The synergist in a movement is the muscle(s) that stabilizes a joint around which movement is occurring, which in turn helps the agonist function effectively. Synergist muscles also help to create movement.

41
Q

Coming from the homonymous muscle is your muscle spindle afferent which will go into the spinal cord.

A

-It will excite synergists in the homonymous muscle and it will inhibit antagonist.

42
Q

What will happen is mug is empty and someone refills it?

A
  • Mug weight increases (gets heavier) –> pull on the homonymous muscle –> pull on the biceps. This will cause stretched limb muscles. This will excite the spindle afferent.
43
Q

Which muscles are activated? Which are inhibited?

A

The biceps will be excited, contract, and will cause the mug to go back up.

The triceps are inhibited, don’t want them in the way of bringing the mug back up

44
Q

Excited, inhibited, resistance

A

Biceps excited, triceps inhibited and you resist the passive change that happens when you change the way to the mug.

45
Q

What is the effect of this reflex on the position of the hand?

A

The hand will move back up. Maintaining stability in the phase of external change

46
Q

What does the gamma motoneuron do?

A

It can cause those intrafusal fibers to contract.

47
Q

Muscle spindle: Role of gamma MNs

A
  • when the alpha motoneurons tell the extrafusal fibers to contract, the force-generating muscle fibers are contracting
  • Gamma motoneurons are activated at the same time which causes those intrafusal fibers to contract, contracting at the same time. Maintaining the same length as the extrafusal fiber
48
Q

Output of afferent stays constant

A

Even though the length of the muscle changed.
-controlling the perceived length of the spindle by contracting, keeping tension constant
- feed-forward adjustment of dynamic range

49
Q

Stimulate alpha motoneurons:

A

We contract the muscle, not getting signals to contract so it goes limb. During the contraction of extrafusal fibers, the spindle afferent is not giving any signal and will reduce the amount of force that’s coming out of the alpha motor neuron.
-spindle afferent has a direct input to the alpha motor neuron

50
Q

Having the gamma motor neuron:

A
  • allows you to maintain a force in the face of environmental change
  • increase tonus during the difficult task
    -descending modulation of reflex gain
51
Q

Motorneurons and muscles are organized as motor units, with a single motoneuron innervating many fibers.

A

Muscle force depends on:
-The types of fibers activated
-Number of fibers recruited
-Motoneuron firing frequency

Force generating is regulated by:
-Muscle spindles
-Golgi tendon organs

52
Q

Golgi tendon organs

A

-consist of sensory neurons that are associated with the fibrous stuff at the end of the muscle. Associated with the tendons, and detect stretch.
-only react to the active force generated by the muscle
-no motor neuron
-the Golgi tendon organs inhibit the homonymous motor neurons (MN)
-innervated by type 1b afferent; no motor innervation –> signal to the CNS if there is tension on the muscle, the tendon doesn’t contract.

53
Q

Muscle fibers:

A

Muscle fibers consist of a single muscle cell. They help to control the physical forces within the body. When grouped together, they can facilitate organized movement of your limbs and tissues. There are several types of muscle fiber, each with different characteristics.

54
Q

Flexor vs Extensor Muscles

A

The muscles that decrease the angle between bones are called flexor muscles. The muscles that increase the angles between bones are called extensor muscles. These muscles decrease the angles between two body parts.

Extensor tendons present on top of the hand help with straightening the fingers. Whereas, flexor tendons that lie on the palm side of the hand help in bending the fingers.

So, your biceps is described as a “flexor” muscle. The opposing muscle of a flexor is called the “extensor” muscle. Your triceps is an extensor.

55
Q

Circuitry for Movements

A

Muscle & receptor properties allow us to build circuits that mediate reflexes and rhythmic movements

56
Q

The flexion reflex

A

Pain receptors in the body and skin. Ex: step on something painful –> going to excite some muscle

57
Q

Nociceptive stimulus leads to:

A
  • flexion on the stimulated side, inhibited the extensor and activated the flexor on the same side.
  • on the opposite side you got excitation of the extensor muscle and excitation of the inhibitory of the flexor muscle. The antagonist through the flexor muscle is inhibited.
58
Q

Spinal Interneurons

A

Spinal interneurons show a topography map
- medial interneurons found innervates axial muscles –> located in the medial ventral horn
-lateral interneurons innervate limb muscles –> distal parts of the body (foot muscles)

59
Q

Medial (trunk) vs lateral (limb) muscles

A
  • If you are trying to maintain an upright posture –> keep trunk muscles working together. Standing up want to make sure muscles along the spine are going to maintain an upright posture.
  • Which would be more local? The one controlling distal limbs
60
Q

Basic movements of limbs

A

-Movement of a limb is a cycle with two phases:
-stance when the foot is on the ground, leg extended to push forward
-swing when leg flexed to leave the ground and move forward to begin the next phase

61
Q

Flexors and extensors are going to be alternating

A

During flexion: flexors will be active during the swing when you are flexing the limb and moving it forward toward the body and moving it out.

When you are pushing, extending against the ground to move forward, your extensors will be active.

62
Q

Do you have to think about each muscle when you are going through locomotion?

A

No. Legs have lots of muscle and are used to provide a stable precise way of walking.

63
Q

What happens if you lose sensory input?

A
  • If your foot goes to sleep, you can still walk –> you’ll do it badly but without sensory input, you can still walk.

Neuro (7 decks)

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