L5: Spinal Cord: Reflexes, Muscle tone, and the CPG for locomotion Flashcards
What is a motor unit?
A single motor neuron and all of the muscle fibers it innervates
What is a motor neuron pool?
All motor neurons innervating a given muscle.
Eg. all neurons that innervate the bicep
Describe the following characteristics for a large motor nueron
1. Force
2. contraction velocity
3. rate of fatigue
4. ATP source
5. Myoglobin content
6. recruitment order
- Great force
- Fast
- Fast
- glycolysis
- low
- 3rd
Describe the following characteristics for a Intermediate motor nueron
1. Force
2. contraction velocity
3. rate of fatigue
4. ATP source
5. Myoglobin content
6. recruitment order
- Intermediate
- Fast
- Intermediate
- fast-oxidative
- High
- 2nd
Describe the following characteristics for a small motor nueron
1. Force
2. contraction velocity
3. rate of fatigue
4. ATP source
5. Myoglobin content
6. recruitment order
- Small
- Slow
- Slow
- Slow-oxidative
- High
- 1st
What is size principle?
The order of motor neuron recruitment: smaller untis recruited 1st and get tired last
What is the anatomy of a muscle spindle?
A connective tissue sheath that contains interfusal fibers that are arranged in parallel with extrafusal fibers with a sensory nerve on the interfusal fibers going to the **dorsal root **of the spinal cord.
What type of afferent neurons detect stretch in muscle spindles?
Ia and II
What is the function of the muscle spindle?
To detect stretch in the muscles
What is the difference between Ia and II afferent neurons?
**Ia: **Fire APs rapildly but dont last long (initiation of movement)
* Measures muscle length and rate of length change
II: fire APs slower but last longer (maintainence of movement)
* measures muscle length
Name the steps of the patellar stretch reflex in order:
- Hammer hits patellar tendon
- Sensory neuron (Ia or II) is activated by spindle feeling stretched
- Sensory neuron (Ia or II) enters dorsal horn and synapses with an alpha motor neuron which activates the extensor (monosynaptic stretch reflex)
- The same sensory (Ia or II) neuron also synapses with a inhibitory interneuron which inhibits the alpha motor neuron to the flexor (disynaptic reflex) this is called reciprocal inenervation
What is proprioception?
The sense of relative position to neighboring body parts.
How does the body know when something in your hand gets heavier and how does it keep holding the item?
Muscle spindles will feel the increased stretch from adding weight and send Ia afferent signals to the psinal cord and the alpha motor nueron will activate the bicep and inhibit the tricep via the same pathway as the patellar stretch reflex.
How can vibration selectively change perception of joint angle?
Ia afferents also have proprioceptive function and if vibration selectively activates only some of the spindles, the perception of the joint angle will change.
What is the purpose of gamma-motor neurons?
Gamma motor neurons innervate intrafusal fibers and contract both ends during stretching to keep the spindle taught so they can detect another signal.
What are the two decsending routes of apha motorneuron activation?
- Direct activation: direct signal through monosynaptic or interneurons
- Indirect activation via the gamma loop where signals excite gamma which strethces the spindle and activates Ia and proceeds from there. (alpha-gamma coactivation)
What is responsible for load compensation?
Alpha-gamma coactivation
What is responsible for load compensation?
Alpha-gamma coactivation
Describe the inverse myotactic reflex
Golgi-tendon reflex
- The golgi tendon organ detects tension produced by muscle contraction
- Ib afferent sensory neurons are activated
- The Ib affarent neuron synapses with an inhibitory interneuron and inhibits the contracted muscle
- The Ib afferent neuron also synapses on the opposing muscle’s alpha motor neuron and activates it.
What is the equation describing muscle stiffness and the associated relationships?
Muscle stiffness=Change in force/change in length
* increased length decreases stiffness
* Increased force increases stiffness
What is the relationship of the stretch reflex on stiffness?
Increases stiffness
What is the tendon organ reflexs’ effect on stiffness?
Decreases stiffness
Describe the spinal flexor reflex
- A cutaneous nociceptor detects pain in the toe and the afferent fiber inters the dorsal horn
- The afferent fiber stimulates the leg in pain to withdraw (activate flexor and inhibit extensor) and at the same time stimulates the other leg to provide support (activate the extensor and inhibit the flexor)
Polysynaptic reflex
Describe the spinal flexor reflex
- A cutaneous nociceptor detects pain in the toe and the afferent fiber inters the dorsal horn
- The afferent fiber stimulates the leg in pain to withdraw (activate flexor and inhibit extensor) and at the same time stimulates the other leg to provide support (activate the extensor and inhibit the flexor)
