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Neuroscience 🧠 > Chapter 13: Spinal Control of Movement > Flashcards

Chapter 13: Spinal Control of Movement Flashcards

1
Q

Intro

What is the motor system?

A

Muscles and neurons that control muscles.
* coordinated movements are produced by spatial and temporal patterns of muscle contractions orchestrated by the brain and spinal cord.

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2
Q

Intro

What is the role of the spinal cord and the brain?

A

Spinal cord —> Contains motor programs necessary for generating coordinated movements
Brain—> Controls motor programs in spinal cord

Majority of into is descending. Starts in upper neurons then goes down

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3
Q

Intro

What are the two types of muscles and their purposes?

A
  1. Smooth: digestive tract, arteries, viscera
    - innervated by automic nervous system fiber
  2. Striated:
    * Cardiac (heart)
    * Skeletal (bulk of body muscle mass)
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4
Q

Intro

What are flexors and extensors?

A

Flexors and extensors pull on the joint in opposite directions

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5
Q

Intro

What are the 3 locations joints act on and fucntions?

A
  • Axial Muscles: trunk movement (maintains posture)
  • Proximal Muscles: Shoulder, elbow, pelvis, kneww movement
  • Distal Muscles: Hands, feet, digits (fingers and toes) movement
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6
Q

Upper and lower motor neurons

What are lower motor neurons and their function?

A

Somatic muscles are innervated by somatic motor neurons in the ventral horn of the spinal cord
**Lower motor neurons are the “final common pathway”
* directly command muscle contraction
* When LMNs are activated, we get muscle contractions and they’re two types: alpha and gamma. **

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7
Q

Upper and lower motor neurons

What are upper motor neurons and their function?

A

Soma is in the cerebral cortex or brainstem
* **Provides input to LMNs
* Only LMNs command muscles **

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8
Q

Upper and lower motor neurons

How can scientists tell if their is damage to lower or upper motor neurons?

A
  • Upper motor neurons when damaged cannot provide input which leads to a muscle constantly contracting.
  • Lower motor neuros when damaged leads to a range of diseases including ALS, not producing muscle contraction at all.
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9
Q

Upper and lower motor neurons

Are skeletal muscles evenly distributed throughout the body?

A

Naur!
* Limb enlargements
* regions of the cord where innervation of the muscles of the arms and legs occur
* dorsal and ventral horns are swollen

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10
Q

Upper and lower motor neurons

How are lower motor neurons mapped?

A
  • Motor neurons controlling flexors lie dorsal to extensors
  • Motor neurons controlling axial muscles lie medial to those controlling distal muscles.
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11
Q

Alpha Motor Neurons & Motor Units

What are the two categories of LMNs in the spinal cord and their purpose?

A
  1. Alpha: innervated extrafusal muscle fibers (triggers the generation of force by muscles)
  2. Gamma: Innervate intrafusal muscle fibers
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12
Q

Alpha Motor Neurons & Motor Units

What is a motor unit?

A

One alpha motor neuron and all the muscles fibers it innervates
* Muscle contraction is due to the combined action of motor units

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13
Q

Alpha Motor Neurons & Motor Units

What is a motor neuron pool?

A

All alpha motor neurons that innervate a single muscle

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14
Q

Alpha Motor Neurons & Motor Units

What are the two types of muscle fibers and their characteristics?

A
  1. Red muscle fibers
    * Large # of mitochondrias, rich in myoglobin, rich in capillary beds
    * SLOW to contract
    * SLOW twitch
  2. White muscle fibers
    * Sparse mitochondria, anaerobic metabolism, contract and fatigue repidly
    * FAST twitch
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15
Q

Alpha Motor Neurons & Motor Units

What are the 3 different types of motor units and describe them

A

1. Slow motor units (s)
* Innervated by small alpha motor neurons
* “red” muscles that contracts slowly and generates small forces.
* Resistant to fatigue
* ex. Marathon

2. Fast fatigue - resistant motor units (FR)
* Intermediate in size - innervated by intermediate size alpha motor neurons
* Generate twice the force of slow motor units

3. Fast Fatigue motor units (FF)
* Large motor neurons - innervated by large aplha motor neurons
* Pale muscle fibers
* Brief exertions that require large forces
* Ex. spinters

All 3 exists in all muscles each motor unit has muscle fiber of one type

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16
Q

Alpha Motor Neurons & Motor Units

What are the two mechanism used to control the force of muscle contraction?

A

**1. Varying the firing rate of AMNs **
* A single AP in an AMN causes a muscle twitch
* Sustained contraction requires contrinuous stimulation since APs are being contrinuously fired.
* # of and frequency of APd increases

2. Motor neurons are recruited from smallest to largest: Size principle **
**Small motor units have small AMNs, large motor units have large AMNs
* Small motor units have a lower threshold for activation

increas. # of active motor units changes the amt. of force produced.

17
Q

Alpha Motor Neurons & Motor Units

What are the contractile properties of motor units?

A
  • Single AP triggers contraction strength of differing force & time course in each of the different motor units.
  • When the different muscle units experience repeated APs over a longer time period, they show different rates of fatigue.
18
Q

Alpha Motor Neurons & Motor Units

What did the crossed-innervation experiment tell us?

A

Muscle phentotype switch can occur by changing the activity in the input motor neuron.

19
Q

Alpha Motor Neurons & Motor Units

What are the three major sources of input for Alpha motor neurons?

A
  1. DRG neurons with axns innervate the muscle spindle
  2. Upper motor neurons in the motor cortex and brainstem
  3. Interneurons in the spinal cord - largest input.
20
Q

Muscle Spindles and the Stretch Reflex

How is the activity of the motor neuron regulated?

A
  • Muscle Spindles (stretch receptors)
  • Group 1a sensory axons wrap around the muscle fibers
  • contain mechanosensitive ion channels –sensitive to stretch.
21
Q

Muscle Spindles and the Stretch Reflex

What are the characteristics of muscle spindles?

A
  • Situated in parallel with extrafusal muscle fibers
  • 1a sensory afferents wrap around intrafusal muscle fibers and inform CNS about muscle length.
22
Q

Muscle Spindles and the Stretch Reflex

What is the stretch reflex?

A

Tapping on the knee lengthens quad - this tests if muscle spindles are reporting
* When a muscle is pulled it tends to contract
- Requires sensory feedback from the muscle
- Stretching a muscle spindle leads to increased activity in 1a afferents
- increase in. activity of alpha motor neurons that innervate same muscle to contract it.

23
Q

Gamma Motor Neurons

What are gamma motor neurons?

A
  • LMNs that innervate intrafusal inside muscle spindle
  • Intrafusal fibers- skeletal muscle within the fibrous capsule
24
Q

Muscle Spindles and the Stretch Reflex

What would happen without GMNs?

A

Spindle no longer sensitive to stetch

25
Q

Golgi Tendon Organs

What are golgi tendon organs?

A
  • Strain gauges
  • innervated by 1b sensory axons
  • protects muscle from being overloaded
  • decreases activation of the muscle when large forces are generated
26
Q

Golgi Tendon Organs

What is the main difference between muscle spindles and golgi tendon organs?

A

Muscle spindles: 1a axons encode info abt muscle length
Golgi tendon organs: 1b axons encode info about muscle tension

27
Q

Golgi Tendon Organs

What is passive stretch?

A
  • Both afferents discharge in response
  • golgi tendon organ discharge is less than that of the spindle
28
Q

Golgi Tendon Organs

What is active contraction?

A
  • The spindle is unloaded&raquo_space; falls silent
  • Rate of golgi tendon organ firing increasess
29
Q

Spinal interneurons, flexor withdrawal reflex, and spinal walking

What are spinal interneurons?

A
  • inhibirtory interneurons plays an essential role in execution of simple reflexes
  • Involved in reciprocal inhibition – contraction of one muscle get accompanied by relaxation of the antagonist muscle.
30
Q

Spinal interneurons, flexor withdrawal reflex, and spinal walking

What do excitatory neurons do?

A

Excitatory interneurons mediate the flexor withdrawal reflex
- Used to withdrawal a limb from an aversive stimulus
- Slower than the stretch reflex
- Process begins with pain signal from delta A nociceptive axons

31
Q

Spinal interneurons, flexor withdrawal reflex, and spinal walking

What is the crossed-extensor reflex?

A
  • Used to compensate for extra load imposed by limb withdrawal on the opposite side
  • Reciprocal inhibition - activation of flexors on one side is accompanied by inhibition of flexors in opposite side

Neuroscience 🧠 (14 decks)

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