Lecture 14 Flashcards
(31 cards)
Define:
Alpha motor neuron
A neuron innervating power producing extrafusal muscle fibers
Describe:
Alpha motor neurons
(4 points)
- Axons innervate extrafusal muscle fibers
- Axons are much bigger, have quicker conduction times
- Larger than gamma motor neurons
- Innervate numerous extrafusal muscle fibers
What is the difference between intrafusal and extrafusal muscle fibers?
Intrafusal muscle fibers lie inside extrafusal muscle fibres
What is the function of an intrafusal muscle fiber?
Detects stretching
What are intrafusal muscle fibers also known as?
Muscle spindle
Describe:
Gamma motor neurons
- Wraps around center of intrafusal muscle fiber
- Sends information back to central nervous system
- Synapse with alpha motor neuron to coordinate contractions
Where does information from the gamma motor neuron enter and exit?
Enter at the back of the spinal cord via the dorsal root - specifically the dorsal root ganglion
Leaves the central nervous system via the ventral root ganglion
What does the sensitivity of the intrafusal muscle fibers depend on?
Fusimotor neurons
What are fusimotor neurons also known as?
Gamma motor neurons
What is the result of increased fusimotor drive?
Any small stretch in the intrafusal muscle fibers can be controlled via contraction of extrafusal muscle fibres
Define:
Motor Unit
Alpha motor neurons and all the muscle fibers it innervates; a unit of force production within the CNS
True or False:
Motor units are smaller than gamma motor neurons
False, motor units are much larger than gamma motor neurons
What changes in motor units depending on the type of muscle that they are innervating?
Innervation ratio changes
What does innervation ratio depend on?
Dependent on the muscle and how precise the muscle has to be
True or False:
Higher innervation ratio allows for more precise motor control
False, low innervation ratio allows for more precise motor control
Define:
Gamma motor neuron
Small neurons innervating intrafusal muscle fibers
Describe:
Gamma motor neurons
- Determines sensitivity of intrafusal muscle fibers to stretch
- Smaller than alpha motor neurons
- Oriented in parallel to extrafusal muscle fibers
What type of connections do gamma motor neurons form?
Polar-to-polar connections
Define:
Polar-to-polar connections in gamma motor neurons
Connection to bone a and bone b along with its structure makes it optimally designed in order to detect stretch
List:
3 types of extrafusal muscle fibers
- Fast twitch, fatigable (FF) (Fast Motor Unit)
- Fast twitch, fatigue resistant (FR)
- Slow twitch, fatigue resistant (SR) (Slow Motor Unit)
Describe:
Fast twich, fatigable (FF) (Fast Motor Unit)
- Characterized by highest conduction velocity (100 m/s)
- Large fiber diameter
- Innervate fast twitch muscle fibers (Type II)
- Produce lots of force, uses anaerobic glycolysis
Describe:
Fast twitch, fatigue resistant (FR)
- Characterized by medium conduction velocity (60 m/s)
- Medium fiber diameter
- Innervate fast and/or slow twitch muscle fibers
Describe:
Slow twitch, fatigue resistant (SR) (Slow Motor Unit)
- Characterized by slow conduction velocity (40 m/s)
- Small fiber diameter
- Innervate slow twitch muscle fibers (Type I)
- Slow oxidative, uses aerobic glycolysis
- Creates sustained force over time
How do we read a muscle biopsy cross section?
Darkest colour is type I slow oxidative muscle type
Lightest colour is a fast twitch motor unit
