Midterm 1 Study Flashcards
Define a Motor Neuron Pool
- All motor neurons that innervate a specific muscle
- Motor Neurons that go down to muscle
Where do Cell bodies reside?
In ventral/anterior horn
How are Cell bodies grouped?
- in columns, by function
- for proximal muscles, found more medially
- for distal muscles found more laterally
What is a motor unit?
- motor neuron (cell body, axon, dendrites) and all muscle fibres it innervates
How many muscle fibres does a single motor neuron innervate?
- Many
- Varies depending on type of muscle
Muscle Unit
- All the muscle fibers innervated by 1 motor neuron
What are the 3 types of Skeletal Muscle?
- Slow Oxidative (SO)
- Fast oxidative glycolytic (FOG)
- Fast Glycolytic (FG)
What is the input resistance like for small MU? Why?
- Bigger, easier to elicit
- Due to high input resistance and slow conduction velocity
Twitch. What does it consist of?
- Physiological, quantal response of MU to stimulation
- key to starting movement
- change in force over time
- consists of rise in force, peak force and relaxation
Which motor neuron supplies fast twitch fibers?
- Large MN
Which motor neuron supplies slow twitch fibers?
Small MN
How are motor units grouped?
- Based on behaviour and function
Twitch characteristics of slow contracting, FR fibers?
- Slow to reach peak, slow to dissipitate
- long twitch
Twitch characteristics of fast contracting, FR fibers
-Quick to reach peak, quick to dissipitate
- Greater force at peak than slow contracting
What determines the physiological behaviour of the 3 types of MU (slow contracting FR, Fast contracting FR and Fast Contracting F)
- The neuron and muscle fibers they connect with
In what ways is muscle force controlled?
- frequency of motor units firing
- Number of motor units recruited
Why are motor units recruited in an orderly fashion?
- larger, more powerful MU recruited near end of contraction where increment will have effect on net force
- brain does not have to control hundreds of twitches, just adjust the level (think of a volume button)
- Con: unable to selectively activate MU out of order
Example when FG are activated
- Jumping
Receptors that transduce info from the environment?
- Exteroceptors
- Pick up info from the environment including rods and cones in the eyes
Role of efferent/sensory receptors?
- Carry info from periphery to spinal cord (centrally) to cell body in dorsal root ganglion
- Signal then goes to afferent fibers - relayed to SC if reflex and central projections move to superior structures
Subdivisions of I (largest) muscle fibers and characteristics?
- Ia = primary afferent fibers, greater number than Ib, connected to spindle *fastest conducting connected to spindle
- Ib = connected to golgi tendon, organ afferent, lower force production
Synaptic Potential
- inc AP = inc Ca2+ in synapse released from pre synaptic membrane = NT released from vesicles in synaptic cleft and bind to post synaptic membrane
(-40 to -70 mV)
Convergence of MN
- leads to greater spatial summation
- 3 excitatory neurons fire close to one another
- all individually are below threshold
- sum of all 3 = summate = reach threshold = AP generated
Primary Ia afferents?
- lots of myelin, conduct faster, greater current
- spiral bag1, Bag 2, and chain fibers
- spiral near center of spindle