Download NotesSkeletalMuscleActivity

Anatomy
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Skeletal Muscle Activity
Neuromuscular Junction
Motor Unit
Neuron
Axon
Axon Terminals
Dendrites
Muscle Fiber
Synaptic Cleft
Acetylcholine (ACh) – neurotransmitter that stimulates skeletal muscle cells; leads to
an influx of Na+ ions, generating an action potential; triggers release of Ca+2
ions from sarcoplasmic reticulum
http://www.neuroanatomy.wisc.edu/SClinic/Weakness/Nmj.JPG
Sliding Filament Theory
1. Influx of calcium triggers the exposure of binding sites on actin. Action potential  release of
Ca+2  Ca+2 binds to troponin  troponin moves tropomyosin exposing active site of actin.
2. Myosin binds to actin.
3. The power stroke of the cross bridge causes the sliding of thin filaments.
4. Binding of ATP causes cross bridge to disconnect from actin.
5. Hydrolysis of ATP leads to re-energizing and repositioning of the cross bridge.
6. Active transport of calcium ions into the sarcoplasmic reticulum.
Energy for Muscle Contraction
Muscles require ATP for muscle contraction. Muscles contain only 4-6 seconds worth of ATP. ATP
must continuously be regenerated. A lack of ATP such as in death leads to rigor mortis.
Three ways ATP is generated:
 Direct Phosphorylation of ADP by Creatine Phosphate
CP + ADP  creatine + ATP
No Oxygen Required
1 ATP per Creatine Phosphate
Provides 15 seconds of energy
Fastest source of energy

Aerobic Respiration (also called Oxidative Phosphorylation)
Glucose  Pyruvic Acid  CO2 + H2O
Requires Oxygen
36 ATP per molecule of glucose (38 Total = Glycolysis, Krebs & ETC)
Provides energy for hours
Energy comes from glucose, pyruvic acid, fatty acids & amino acids
Occurs in mitochondria

Anaerobic Respiration
Glycogen  Glucose  ATP + Pyruvic Acid  Lactic Acid
No Oxygen Required
2 ATP per molecule of glucose
Provides 30-60 seconds of energy
Faster than aerobic respiration but very inefficient
Lactic acid build up in muscles and leads to muscle soreness & fatigue
Types of Muscle Contractions
Isotonic – same tone; muscles shorten in size
Ex. bending knee, curling arm
Isometric – same length; muscles do not shorten in size; tension increases
Ex. holding a heavy object
Graded Responses
“All or none” law applies to muscle cells not whole muscles
1. Changing the frequency of muscle stimulation
2. Changing the number of muscle cells being stimulated