Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
40 Cards in this Set
- Front
- Back
|
What are the components of a motor unit?
|
-a single alpha motor neuron
-all its axon terminals -the skeletal muscle fibers it innervates |
|
|
Define motor unit.
|
-contractile group
-the smallest sub-unit of muscle that can individually and willfully be controlled |
|
|
True or false: Motor neurons do not innervate intrafusal fibers.
|
True (intrafusal fibers are not part of the motor unit)
|
|
|
True or false: A motorneuron may have a hundred or more axons that innervate different muscle fibers.
|
True
|
|
|
The smaller the motor unit,:
|
-the less force it produces
-the more graded the force production of the entire muscle (fine motor control) -small motor units innervate fewer muscle fibers |
|
|
The number of muscle fibers served by a single axons varies. What are the 2 types of controls?
|
-fine control
-gross control |
|
|
Describe course control.
|
-gross motor
-1 motor neuron to 300 fibers (leg) -simplifies motor programming |
|
|
Describe fine control.
|
-1 motor neuron to 3 fibers (eye)
-more independent control |
|
|
How does muscle power increase?
|
-recruitment of more motor units (population code)
-increased frequency of discharge in each unit (frequency code) |
|
|
During a "maximal voluntary contraction" all motor units are activated?
|
-No, some reserve is left
|
|
|
What are the types of muscle action? AND tell what they do.
|
-phasic (causes movement)
-tonic (causes tension rather than movement) |
|
|
What is the problem of motor control?
|
-degrees of freedom in the neuromotor system (each level has a level of control)
-How do we ever achieve control over all these elements to perform simple motor tasks? (we don't know) |
|
|
True or false: Muscles move.
|
False: Muscles can only pull bone or change shape.
|
|
|
What are antagonist muscles?
|
joints must have a pair of muscle with opposite actions, because muscle cannot push the bones but only pull them
|
|
|
What are agonist muscles?
|
-muscles that help each other
-result of a group of muscles (synergies) |
|
|
Describe skeletal muscle.
|
-striated
-voluntary control -contractions fast -composed of chains of sarcomeres |
|
|
Describe smooth muscle.
|
-slow and sustained contractions
-contracts in waves across entire muscle -stomach, intestines, blood vessels -innervated by autonomic nervous system -responds to neural or hormonal stimulation |
|
|
What two fiber types are skeletal muscles composed of?
|
-extrafusal
-intrafusal |
|
|
What are extrafusal fibers?
|
-part of skeletal muscle
-innervated by alpha motorneurons from spinal cord -exert force |
|
|
What are intrafusal fibers?
|
-part of skeletal muscles
-muscle spindle -sensory organ even though its a muscle -sensory fibers and motor fibers that do not generate force |
|
|
What do the afferent fibers of intrafusal fibers (muscle spindle) do?
|
-report length of intrafusal
-when stretched, the fibers stimulates the alpha-neuron that innervates the muscle fiber -maintains muscle tone |
|
|
What do the efferent fibers of intrafusal fibers (muscle spindle) do?
|
contraction adjusts sensitivity of afferent fibers
|
|
|
What are extrafusal muscle fibers made up of?
|
thousands of myobibrils
|
|
|
What are myofibrils? AND what are myofibrils made up of?
|
-the contractile apparatus
-made up of strands of sarcomeres, longitudinal array of protein filaments (actin and myosin) |
|
|
What is a sarcomere?
|
-a repeating unit of the muscle cell's contraction machine (make up myofibrils)
-chains of sarcomeres give the striated appearance |
|
|
What is the sarcolemma?
|
-the covering of muscle fiber (muscle cell membrane)
-conducts the electrical signal that initiates muscle contraction -includes 'Transverse tubules' or 'T-tubules' that penetrate deep into the interior of the fiber |
|
|
Describe the sarcoplasmic reticulum.
|
-smooth endoplasmic reticulum of muscle fibers
-stores calcium -comes into contact with the T-tubules -surronds the myofibrils -upon activation by an electrical signal (by ACh)--releases Ca++ to activate the contractile apparatus |
|
|
What cause the myofibrils to contract?
|
the presence of Ca++
|
|
|
What is actin?
|
-part of a myofibril
-thin protein filament that extends from wall of sarcomere |
|
|
What is myosin?
|
-part of myofibril
-thick filament in the middle of the sarcomere |
|
|
What are transverse tubules?
|
-carry the AP into the interior of the cell
|
|
|
What does anticholinesterases nerve gas do?
|
-affects NMJ
-paralyzing drug -nerve agent binds to part of the AChE molecule -thus, ACh hangs around and keeps the endplate polarized |
|
|
What does botulinum toxin do? AND how is it used therapeutically?
|
-affects NMJ
-blocks release of ACh from the presynaptic terminal (ACh antagonist) -Therapeutic use: injected into muscles of people with uncontrolled muscle spasms |
|
|
What is myasthenia gravis? AND how can it be controlled?
|
-caused by a loss of ACh receptors in the motor endplates of all muscles in the body
-patients become very weak, but can be helped by controlled doses of anti-cholinesterases (allows the ACh to act longer. maximizing the use of the few receptors that are left) |
|
|
What drugs affect NMJ?
|
-curare
-anticholinesterases -botulinum toxin |
|
|
What is curare?
|
-affects NMJ
-paralyzing drug -blocks ACh from binding with receptor -muscle cell can no longer be depolarized |
|
|
True or false: ACh's binding with its receptor is not permanent.
|
True
|
|
|
What destroys ACh when it is released? AND where is it present?
|
it is destroyed by an enzyme, AChE (AChase), which is present in the synaptic cleft
|
|
|
Why is it essential for AChE to destroy ACh?
|
-so that the muscle cell membrane can repolarize to its resting potential
-if a muscle cell cannot repolarize (get rid of the e.p.p.), then it cannot generate another AP |
|
|
What does the bond between actin and myosin create?
|
muscle tension
|
