Motor System Flashcards
(40 cards)
Coordination and Posture: Major motor functions
Where does movement occur? How does it occur?
Most movement occurs at joints –> where 2 bones come together.
Movement occurs by muscles contracting and pulling. To get full range of motion around a joint, there must be at least one muscle attached on either side of joint. Smooth, useful movement requires coordination.
As muscles work there are changes in joint angle and changes in muscle length.
Two types of muscle: Flexors and Extensors
FLEX: decreases joint angle. Flexor contraction shortens the muscle, while it lengthens the extensor muscle.
EXTEND: Increases joint angle. Extensor contracts and shortens, while its contraction lengthens the flexor muscle.
Muscle Definitions: Agonist, Antagonist, Synergists
-Agonist: “actor” –> Which muscle is acting, flexor or extensor?
-Antagonist: the muscle with the opposite action at the joint
-Synergists: all muscles with the same action at the joint. Additive effect.
Posture: Definition, muscles involved
-2nd major function of the motor system
-posture definition = Resisting the force of gravity
-Antigravity muscles = Extensors
-Their antagonists = Flexors
Differences in descending control of flexors and extensors reflect the role of extensors in resisting gravity.
Postural fixation
Elimination of unwanted movement at a joint which is necessary for useful movement. For example when doing a root canal (fine motor movement skill) you need complete control.
4 Main Parameters of muscle action
Different muscles in the body vary in properties.
Parameters:
1) Force
2). Speed of contraction (how quickly muscle will respond)
3) Resistance to fatigue (how long muscle can work without getting weaker)
4) Fineness of control (small changes in force, small changes in joint angle) –> ex) important for hands and fingers fine motor control
What do the 4 parameters of muscle action each depend on?
1) Force: result from the structure of muscle
2) Speed of contraction: results from the structure of muscle
3) Resistance to fatigue: results from the structure of muscle
4) Fineness of control: results from both the structure of muscle as well as the pattern of innervation of muscle
The two Types of muscle fibers
Slow and fast twitch. Named for how quickly they respond.
Fast twitch muscle fibers
-White muscle
-FF fibers: fast, fatigable, large force, fast contraction time, fatigue readily. Most vulnerable to fatigue.
-FR fibers: also fast but more resistant to fatigue, also large force.
Slow twitch muscle fibers
-Red muscle
-S fibers: least force, slowest contraction time BUT most resistant to fatigue.
How does training effect muscle fibers?
CANNOT increase the number of muscle fibers or change the muscle fiber type with training; Properties of individual fibers are changed.
Muscle comoposition
Composition of different muscles reflect their function.
-Each muscle is composed of a mixture of these fiber types
-% different fiber types varies with different muscles, with how muscle is used.
-Composition of a particular muscle may vary among individuals, and may correlate with athletic ability
-% different types DO NOT change by training
Marathon runner vs. sprinter
Long distance runner likely has more S fibers (red muscle) where as a sprinter most likely has more F fibers (white muscle).
Efferent innervation of muscle
-done by Alpha motoneurons (located in ventral horn of spinal cord).
-Alpha MN cell bodies are in the ventral horn and axons leave in the ventral roots.
-The axons are large in diameter and myelinated. The Aalpha fibers have a known range of diameter and conduction velocity which is important because these numbers can change with various disorders
Each alpha MN branches and innervates muscle fibers, how many?
Number varies, 2-1000’s, depends on size od MN
Motoneuron pool
ALL MN’s innervating a particular muscle are the motoneuron pool; they are distributed over several cord segments (Not just at one level)
Motoneurons in a MN pool vary in size. How?
1) Size (diameter) of soma/ cell body
2) Diameter of axon (correlated with the cell body)
3) Number of branches of axons (Function of size, bigger MN’s more branches)
4) Number of muscle fibers innervated (function of number of branches and there for of size) {each mn pool contains a population of mn’ of a range of sizes}
Trophic factors
Motoneurons release chemicals called trophic factors which are essential for the health of muscles
-if motoneurons die their axons also die and the muscles die or ATROPHY therefore non of these trophic factors being released
Polio and ALS-lou Gehrigs disease
Both diseases that are caused by loss/ death of alpha motoneurons and therefore an absence of trophic factors for muscle.
-in ALS –> stands for amyotrophic lateral sclerosis
–> Amyotrophic= absence of trophic factors for muscles
–> Lateral sclerosis = pattern of scar tissue in the spinal cord and cortex
Poliomyelitis (aka polio)
Viral infection, highly contagious, human to human contact. Major health problem in the USA until vaccine. MN’s die, muscles atrophy (paralysis). It was gone in the usa since 1979 because of vaccine; still present in Afghanistan, Nigeria, and Pakistan
-look like skin and bones
Motoneurons and motor units
-Size of cell body (and axon diameter) is correlated with the number of branches the axon makes in muscle, therefore the number of muscle fibers innervated.
Motor unit: Single motoneuron and all muscle fibers it innervates
All muscle fibers in a motor unit are of the same type. (each muscle fiber receives innervation from one and only one motoneuron; mn fires, muscle fibers contract (all muscle fibers in that unit), unit of action of motor system).
Correlation between size of motor unit and muscle fiber type.
Motor Unit size and muscle fiber type
What are the largest motor units?
what are the smallest?
Largest: FF fibers
Smallest: S fibers
Muscle fibers in a single motor unit are scattered about the muscle
Relationship between motor unit size and muscle properties
All muscles are composed of a population of motor units of different sizes
The AVERAGE motor unit size varies among muscles
-Fine control: average motor unit size is smaller (activating a relatively small force which is necessary for control)
-Force, speed: average motor unit size is larger. (F twitch muscle fibers are found more in larger motor units)
Summary: properties of motor units
The larger to motoneuron the more muscle fibers it innervates; the larger the motor unit the more force it can produce, the more quickly it will respond AND the more quickly it will fatigue.
