BIO 264 Lecture Notes - Lecture 18: Creatine Kinase, Myocyte, Motor Neuron
18 Jun 2018
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Muscle Contraction
● Need 2 ATP for muscles to contract
Muscle Relaxation
● Neurons do not release ACh
○ No action potential generated
● No more calcium released from SR and terminal cistae
○ Not much bonding
Motor unit- muscle fibers and motor neuron
Required ATP is generated by:
1. Cytosolic reaction inside cytoplasm with the help of enzyme creatine kinase
a. Gives you ATP for about 10 seconds
2. Glycolytic catabolism: in cytosol (Glucose → Pyruvate )
3. Aerobic respiration: biggest source of ATP, need O2 to happen in mitochondria
Creatine Phosphate
- No O2
- ATP for 10 secs
Glycolysis
- No O2
- ATP for 30-40 secs
Lactic Acid
- Can be converted back into glucose
Muscle Twitch: smallest muscle contraction, occurs in lab
- Tension produced during twitch movement varies with
- time/frequency
- Phase 1: Latent Period:
- Phase 2: Contraction Period, actomyosin sliding across each other
- Relaxation Period: Calcium pumped back in SR
- Length of fiber at rest
- Type of fiber
- Wave summation: increase tension due to repetitions of stimulation motor unit
- Stronger response
Muscle Fibers: Type I- Slow Twitch:
- Smaller diameter, slower contraction which produces less force but can stay contracted
for a longer period of time
Type II- Fast twitch:
- Large diameter, faster contraction
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- Fatigue quickly
- Eye muscles
All muscles are made of both Type I/II fibers, just one is in large quantity
Type I → only slow
Type II → only fast
Recruitment: greater force requiring more motor neurons to be stimulated
Muscle Tone: keeping posture, standing up right, baseline heat production, prepare for
movement
- Alternates motor units activated
Isotonic: tension is constant, muscle length changes
1. Concentric: force generated is greater than external force
2. Eccentric: constant tension, muscle lengthens, external force applied=greater
than force generated by muscles
Isometric: muscle length is same because external force is same as generated force
Muscle Tension is relative to:
1. Force which each muscle fiber is contracting
2. How many are contracting at once
Sarcomere A band is where tension is generated
Latent period, contraction period, relaxation period (SR pumping calcium)
Muscle twitch is smallest muscle contraction, produced in lab
Type I Slow Twitch- smaller diameter and stay contracted for a long time
● Slower, less myosin ATPase
● Type I fibers rely heavily on oxidative phosphorylation (cellular respiration) to produce
ATP, less force long contractions
● A lot of mitochondria
● A lot of blood vessels to deliver glucose
● Myoglobin molecules (storage form of oxygen in cytoplasm)
Type II Fast Twitch- eye muscles, sprinting, work hard and get tired easily
● Fast power strokes, high myosin
● Relies on Glycolysis (in cytoplasm)
● Few mitochondria
● Blood supply not as dense
● Less myoglobin
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Red vs. White Muscle
Length Tension Relationship: optimal length of a sarcomere is 100-120% of the natural length in
sarcomere
At optimal length a sarcomere can generate the greatest cross bridges that can form is maximal
● Need thick to pull thin toward M-line without running into Z discs
Myoplasticity- change in muscle structure as a result of function due to physical activity
● Change by packing more myofibrils, thus needing more mitochondria
● Amitotic- do not undergo mitosis
Endurance Training: more repetitions with lighter weight
● Type I/ slow twitch fibers
● Resist fatigue
● Increase oxidative enzymes and mitochondria
Strength Training: fewer reps, more weight
● Decreased proportion of mitochondria
Disuse- lose muscle mass
● Myofibrils break down
Skeletal Muscle: striated, sarcomeres defined by Z-lines
● actin/myosin in similar proportions
● Multinucleated
Smooth: no sarcomeres, thus no striations
● Changes shape
● Requires less ATP
1. The end plate potential is generated by the influx of sodium into the motor end plate
2. Ach is released in the synaptic terminus response to an action potential arriving at the
synaptic terminus
3. The term “synaptic cleft” refers to the gap between the neuron and
4. Sodium channels of the motor end plate are Ligand gated channels
5. End plate potential is a local depolarization
6. Hydrolysis of ATP is responsible for recocking of the myosin heads
7. Release of ADP and Pi from myosin occurs during power stroke
8. The power stroke pulls thin filaments towards the M lines
9. During muscle relaxation, calcium channels in the SR close because resting membrane
potential is restored
10. During muscle fiber relaxation Ca pumped back in SR
11. ACh in synaptic cleft degrades ACh, allowing ligand gated sodium channels close
12. Sarcolemma repolarization during relaxation restores the resting membrane potential
13. Pumping Ca requires ATP
14. Voltage gated K channels return sarcolemma towards resting membrane potential after
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Document Summary
Need 2 atp for muscles to contract. No more calcium released from sr and terminal cistae. Required atp is generated by: cytosolic reaction inside cytoplasm with the help of enzyme creatine kinase, gives you atp for about 10 seconds. Glycolytic catabolism: in cytosol (glucose pyruvate ) Aerobic respiration: biggest source of atp, need o2 to happen in mitochondria. Muscle twitch: smallest muscle contraction, occurs in lab. Tension produced during twitch movement varies with time/frequency. Phase 2: contraction period, actomyosin sliding across each other. Relaxation period: calcium pumped back in sr. Wave summation: increase tension due to repetitions of stimulation motor unit. Smaller diameter, slower contraction which produces less force but can stay contracted for a longer period of time. All muscles are made of both type i/ii fibers, just one is in large quantity. Recruitment: greater force requiring more motor neurons to be stimulated. Muscle tone: keeping posture, standing up right, baseline heat production, prepare for movement.
