9A.3 Flashcards
Motor Neuron=
- uses a process called an axon to conduct nerve impulses
- allows for contraction of muscle
- FUNCTIONALLY connects to the muscle fiber, but not physically
- can attach to many muscle fibers(avg. 150)
Synapse
- space that info can pass across-> synaptic cleft
- communication occurs using neurotransmitters
The point at which the muscle fiber and motor neuron meet is…
neuromuscular junction
Motor End Plate=
-usually one for each muscle fiber
-abundant nuclei and mitochondria
Motor Unit=
-all muscle fibers of motor unit will contract and relax together
Neuromuscular Junction (NMJ)
- where nerves meet
Motor Neuron (def)=
-neurons that stimulate effectors (muscle/ glands)
Synapse (def)=
site of functional connection between a motor neuron and muscle fiber
Motor end plate (def)=
are of sarcolemma that receive neurotransmitters from motor neuron
Motor unit (def)=
combination of the motor neuron and muscle fibers it controls
Acetylcholine (ACh)
- during a skeletal muscle contraction, motor neurons will release it across the synaptic cleft
-synthesized in the cytoplasm and stored in vesicles
-nerve impulse forces release of vesicles- attaches to ACh receptors on the motor end plate, stimulating the muscle fiber (30-40 million)
- fiber creates an electrical signal called a “muscle impulse”
Muscle impulse
-changes sarcolemma and transmits impulse in all directions
- most important change will be at the use of Ca^2+
where is the NMJ usually found
the middle of a fiber
ATP is necessary for both contraction and relaxation
- muscle fibers only have enough ATP for brief contraction
- must be regenerated
Creatine phosphate (Def)=
much more abundant than ATP in muscle fibers
Creatine phosphate
-transfers stored energy to ADP to form ATP again
after about 10 sec of contraction, begins to break down glycogen
- approx. 15-20 min of energy than fat
Oxygen debt and fatigue
- many ATP molecules are made during cellular respiration, thus requiring high amounts of glucose
- muscles also have myoglobin
- function of respiratory and cardiovascular systems
Myoglobin=
made in muscle cells and binds oxygen
- gives skeletal muscle reddish color
- can store oxygen temporarily for tissue (more attractive than hemoglobin)
- reduces a muscles requirement for constant blood supply
Oxygen debt
- after a few minutes of strenuous activity, oxygen is not supplied fast enough for aerobic respiration
- anaerobic reactions begin, building up lactic acid
- diffuses out and is carried to liver
- liver begins to use ATP and O2 to react with the lactic acid
- creates oxygen debt
- athletic training increases ones ability to do aerobic reactions
Fatigue=
prolonged oxygen debt can lead to the inability of a muscle to control contraction
Fatigue
- mostly due to accumulation of the lactic acid
- lowers pH level, inhibiting muscle response
Causes of Fatigue
- decreased blood flow
- ion imbalances
- (psychological loss of desire to continue usually counters this)
- Can also cause CRAMPS :(
Cramps=
- sustained painful, involuntary muscle contractions
- decreased electrolyte concentration leads to uncontrolled stimulation
Sarcomeres
- the functional unit of contractions
Sliding Filament Theory
- these are the parts within fibers that will shorten
- Thick and thin filaments will not change shape, but rather slide past each other
- the Z- line will therefore move closer together, shortening the sarcomere
what occurs in 2 parts
Contraction and Relaxation
Contraction
- ACh arrives at sarcolemma forming a electrical muscle impulse
- Ca^2+ are released thru T-tubules flooding the sarcoplasm
- attach to troponin of actin filaments
- “opens up” their binding sites
- shape change that occurs produces the “power stroke” of contraction
- once complete, ATP binds to myosin again releasing actin
- these steps can repeat as long as ATP is available and Ca^2+ is present in high levels (fully contracted)
Contraction
- ACh arrives at sarcolemma forming a electrical muscle impulse
- Ca^2+ are released thru T-tubules flooding the sarcoplasm
- attach to troponin of actin filaments
- “opens up” their binding sites
- shape change that occurs produces the “power stroke” of contraction
- once complete, ATP binds to myosin again releasing actin
- these steps can repeat as long as ATP is available and Ca^2+ is present in high levels (fully contracted)
Relaxation
- Acetylcholmesterase (AChE) decomposes any ACh left in the synapse and at the motor end plate
- as muscle impulse stops, Ca^2+ is reabsorbed into the sarcoplasmic reticulum (no more ACh)
- Cross- bridge linkages break
- muscle fiber relaxes (titin
