CAS BI 315 Chapter Notes - Chapter 5: Skeletal Muscle, Myocyte, Motor Neuron
1 Jul 2018
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Lab 5: Characteristics of Skeletal Muscle (do you even lift bro?)
I. Myofibrils = repeating units of thicc and thin filaments in each muscle fiber (cell); one
repeat unit of filaments = sarcomere (functional unit of skeletal muscle contraction)
A. Thin Filament: actin with tropomyosin coiling around and troponin bound to coil
B. Thique Filament: myosin (long tail with globular heads containing actin and ATP
binding sites); myosin energized with hydrolyzed ATP (ADP+P)
C. Presence of Ca2+ causes a conformational change that exposes myosin binding
sites on actin → cross bridges → sarcomere shortens → ATP binds again which
causes release of the myosin head from actin
D. EMG=electromyogram= total electrical activity in muscle cell due to opening of
Na+ channels
II. Motor Units
A. Muscle mechanism dependent on the activation of motor units (single
motor/efferent neuron and all associated muscle fibers) → more fibers/motor unit
means less fine motor movement
B. Axon terminal of motor neuron and the synapse with a muscle fiber = NMJ
(neuromuscular junction)
C. ACh released in synaptic cleft → bind to nicotinic ACh receptors in the
postsynaptic muscle fibers
D. All or None Law: individual muscle fibers innervated by a stimulated motor
neuron will contract maximally
E. Raw EMG data is transformed by integration of the areas of the EMG spikes
(absolute integral of EMG = relative amount of electrical activity)
III. Skeletal Muscle Strength
A. To increase skeletal muscle strength:
A.1. Number of actin and myosin heads that bind should increase
A.2. Frequency of binding and unbinding per AP should increase
A.3. Optimal sarcomere length
B. Minimal Stimulus Voltage: The stimulus is strong enough to reach threshold of
one motor neuron to fire an action potential
C. A suprathreshold stimulus will reach threshold of multiple motor neurons
D. Maximal Stimulus Voltage: All the motor units of a muscle are activated
E. Increase the strength of muscle contraction by increasing the frequency of the
stimuli
F. More the skeletal muscle is stretched, the greater force it will contract with
IV. Skeletal Muscle Movement
A. Flexion: Bending of a Limb (Decreases joint angle) Extension: Straightening of a
limb (Increases Joint Angle)
B. Agonist: the contracting muscle. Antagonist: opposes the agonist to prevent
hyperextension
C. Agonist/Antagonist change per action, Flexor/Extensor cannot
D. If a neuron is communicating with two motor neurons, then to only stimulate one,
one must have a lower minimum stimulus voltage or threshold to fire by itself. If
the second is to fire, then both 1 and 2 will fire.
find more resources at oneclass.com
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Document Summary
Skeletal muscle strength: to increase skeletal muscle strength: Number of actin and myosin heads that bind should increase. Frequency of binding and unbinding per ap should increase. Increase the strength of muscle contraction by increasing the frequency of the stimuli: more the skeletal muscle is stretched, the greater force it will contract with. Skeletal muscle movement: flexion: bending of a limb (decreases joint angle) extension: straightening of a limb (increases joint angle, agonist: the contracting muscle. Antagonist: opposes the agonist to prevent hyperextension: agonist/antagonist change per action, flexor/extensor cannot. If a neuron is communicating with two motor neurons, then to only stimulate one, one must have a lower minimum stimulus voltage or threshold to fire by itself. If the second is to fire, then both 1 and 2 will fire. Rf: the inside of your forearm is the flexor (when pulling your wrist in)
