Motor System Flashcards
What are lower motor neurons also known as
final common pathway
what does severing the LMN mean
that the motor unit cannot function (there is no other motor innervation besides the LMN serving that motor unit
What is the difference between striated, smooth, and cardiac muscle fibers
striated = voluntary control over (actively intended to do)
smooth = not under voluntary control (behave reflexively or below the level of consciousness), mainly internal (digestion, swallowing)
Cardiac = specialized for heart function
What are muscle fibers made up of
smaller structures called myofibrils
What are myofibrils and what do they do
filaments are really thin strands that are bound together to make up muscle fibers
made up of proteins called actin and myosin
has a particular structure of alternating myosin and actin layers
important to how myosin and actin interact with each other to cause the larger muscle fiber to contract
What is the neuromuscular junction
where the motor neuron (nerve fiber) meets the muscle fiber
How is an Action potential transduced for muscle contraction?
- AP reaches presynaptic terminal
- Causes depolarization of terminal which results in opening of voltage gated calcium channels
- Allows calcium to flow into the axon terminal
- Presence of calcium bathes to myofibril and causes the contraction
- Synaptic vesicles fuse to terminal membrane and release ACh into synaptic cleft
- Junctional folds keeps the neurotransmitter from diffusing away from the junction and stopping the process too quickly
- ACh binds to ligand-gated Na+ channels
- Depolarization of muscle fiber = motor end plate potential
- Causes opening of voltage-gated sodium channels
Initiates action potential in the muscle fiber sarcolemma - when the sarcomere is exposed to calcium it contracts
*ACh = acetylcholine
***action potential is transduced in a chemical signal and then transduced into an electrical signal in the muscle
What is the difference between an action potential in a muscle fiber and in a neuron
how it propagates down the axon
in an axon, the depolarization has to be regenerated at each segment
in muscle fibers we have unique anatomical features that allow for the flow of electrical charge in different ways than a neuron
What are T-tubules (transverse tubules)
tunnels that come into the muscle fiber and allows for electrical information to flow deep into the muscle fiber
depolarization occurs throughout the entire cell instead of just in specific segments
What are motor units
neuron and each of the fiber units it innervates
the smallest functional unit in the motor neuron
how does muscle innervation work?
each muscle fiber is innervated by a single motor neuron at the NMJ, but one motor neuron can innervate thousands of fibers
What is innervation ratio?
the number of fibers that are innervated by a particular motor unit
What are motor units that have large innervation ratio important for?
gross larger movements (flexing your hamstring)
require recruitment of more muscle fibers as well
what are motor units that have smaller innervation important for?
fine-grained motor behavior (moving your finger)
includes speech/writing
What is the size principle of motor unit recruitment
differences in motor unit size allows for varying levels of force in tension during real-world actions
smaller motor units need less activation to fire whereas larger motor units need more activation to fire
