1. Muscular System: Chapter 8

2. Functions of Muscles 1) Movement 2) Heat Production Move the skeleton
Move food and body fluids
Create heartbeat
2) Heat Production
Used to regulate body temperature

3. Types of Muscle Tissue 1) Skeletal 2) Cardiac 3) Smooth
Striated, Voluntary
Multiple nuclei/cell
Ex: Quadriceps, triceps
2) Cardiac
Striated, Involuntary
1 nucleus/cell
Ex: heart
3) Smooth
Unstriated, Involuntary
Ex: stomach wall, espophagus

4. Structure of a Muscle Fascia Epimysium Perimysium
Outer layer of fibrous connective tissue
Continuous with tendon and/or bone
Epimysium
Layer under the fascia
Perimysium
Layer under epimysium
Wraps around bundles called fascicles

5. Structure of a Muscle (cont)
Endomysium
Layer under perimysium
Wraps around muscle fiber
Sarcolemma
Layer under endomysium
Cell membrane of a muscle cell (fiber)
Surrounds bundles of myofibrils

7. Structure of a Muscle Fiber
Sarcolemma- cell membrane
Sarcoplasm- cytoplasm
Sarcoplasmic reticulum- endoplasmic reticulum
Multiple nuclei/cell
Many mitochondria
Transverse tubules- membrane-bound canals through the fiber;
surrounded by cisternae of sarcoplasmic reticulum
Filled with bundles of myofibrils

10. Structure of the Myofibril
Composed of myosin (thick) filaments and actin (thin) filaments
Filaments overlap creating striations
Z-line- attachment for actin filaments
M-line- attachment for myosin filaments
I-band- zone containing only actin filaments
A-band- zone containing myosin filaments
H-zone- zone containing only myosin filaments
Sarcomere- unit stretching from one Z- line to the next

11. Neuromuscular Junction
Motor neuron - nerve that connects to muscle fiber
Neuromuscular junction - connection between nerve and muscle fiber
Motor end plate - specialized area of the sarcolemma modified to connect with the nerve
Neurotransmitters - messengers that are stored in synaptic vesicles in the neuron and released across synaptic cleft

12. Motor Units A fiber usually has 1 neuromuscular junction
A motor neuron can be connected to many fibers
Motor unit - a motor neuron and all of its connected fibers
Fibers will contract as a unit

13. Quick Review
If your muscle cells were not producing enough ATP, which part of the cell is dysfunctional?
A) Sarcoplasmic reticulum
B) Sarcolemma
C) Mitochondria
D) Nucleus

14. Quick Review
If you were diagnosed with a disease that affected your ability for your muscles to communicate (connect) to your nervous tissue, which part of your muscle would this affect?
A) Motor unit
B) Motor neuron
C) Neuromuscular junction
D) All of the above

15. Sliding Filament Model
Structure animation
Muscle shortens as filaments slide past each other
This means that the I-band will get smaller during a contraction

17. Timeline of a Contraction
Step 1- Release of Acetylcholine
Acetylcholine is a neurotransmitter made and stored in the neuron
Release with nerve impulse into synaptic cleft
Crosses cleft and binds with receptors on motor plate
Step 2- Muscle Impulse
Binding of acetylcholine at motor plate stimulates muscle impulse
Impulse spreads across sarcolemma and down into T-tubules

18. Timeline of a Contraction (cont)
Step 3- Movement of Calcium
Cisternae of sarcoplasmic reticulum become more permeable to Ca+ ions
Ca moves out of reticulum into sarcoplasm
Step 4- Exposing Binding Sites of Actin
High Ca+ in sarcoplasm cause a change in the actin filaments
Troponin and tropomyosin
Thin filaments attached to actin; act together to expose the binding site

20. Timeline of a Contraction (cont)
Step 5- Contraction
Readied myosin heads attach to exposed actin binding sites and pull
A new ATP must bind with the myosin ATPase before myosin will release binding site
Readied myosin head then binds with a new actin binding site
I-band gets smaller
This will continue as long as acetylcholine is present

22. Timeline of a Contraction (cont)
Step 6- Relaxation
Two steps lead to relaxation:
1) Acetylcholinesterase breaks down acetylcholine
2) Once acetylcholine is low, Ca+ is actively pumped back into sarcoplasmic reticulum
Low Ca+ levels in sarcoplasm stop linkage of actin and myosin and muscle fiber relaxes to it normal length
Muscle Contraction Animation: Myofibril
Muscle Contraction Animation: Sarcomere

23. Quick Review
Which protein filaments are involved in muscle contraction?
A. Actin
B. Myosin
C. ATPase
D. More than one answer is correct

24. Quick Review
Which muscle fiber structures are involved in contraction?
A. I-band
B. Sarcomere
C. Active site
D. More than one answer is correct

25. Quick Review
Acetycholine is a neurotransmitter whose amount will increase during contraction (to a point); the amount then decreases to stimulate relaxation.
True
False

26. Energy Sources for Contraction
1st source- available ATP’s (very small amount)
2nd source- Creatine phosphate breaks down to produce more ATP
3rd source- Cellular respiration to create new ATP’s
Extra oxygen stored in myoglobin in muscles
4th source- Anarobic respiration
Creates a build-up of lactic acid

27. Oxygen Debt
Lactic Acid is moved to the liver to be converted back to glucose
Oxygen debt
Amount of oxygen needed for liver to convert the lactic acid
How much is needed by the muscle to reset the other sources
Debt may take hours to repay after strenuous activity

28. Muscle Fatigue Occurs because: Blood supply interrupted
Acetylcholine used up
Build-up of lactic acid which lower pH of muscle which lowers muscles response to stimulation

29. Muscle Fiber Responses
Threshold stimulus - intensity of stimulation needed to make a contraction occur
All-or-none response - muscle fiber responds fully or not at all

31. Recording Muscle Fiber Contractions
Recording is a myogram
Latent period- period of time between stimulus and response
Period of Contraction
Period of Relaxation
Making a muscle fiber go through a single contraction is called a twitch

33. Quick Review Muscles could take hours to recover from oxygen debt.
True
False

34. Quick Review
Which of the following is a reason why a muscle could become fatigued?
A. Blood supply increases
B. Acetylcholine is present
C. Build-up of lactic acid which lowers pH of muscle
D. None of the above

35. Summation and Tetany
Summation - strength of muscle fiber response increases if another stimulus is applied before relaxation is finished
Tetany - a sustained maximum muscle fiber response produced by a high frequency of stimuli that don’t allow the muscle to relax

36. Recruitment Muscles do NOT have all-or-none contractions
Muscles are made of many motor units
Respond to a variety of stimulus strengths
Muscle used for strength normally have more bigger motor units
Muscles used for fine movements have more smaller motor units

37. Muscle Tone A few motor units go through sustained contractions
Help keep posture and support

38. Skeletal Muscle Action
Origin - muscle attachment on bone that is immobile during movement
Insertion- muscle attachment on bone that will move
For any body movement:
Prime mover (agonist)- major muscle creating movement
Synergist- help with movement
Antagonist – create movement in the opposite direction

39. Smooth Muscle
Contains myosin and actin filaments but more randomly arranged (no striations)
Multiunit- stimulus is through nerves or hormones (iris or walls of blood vessels)
Visceral- cells can stimulate each other (walls of intestine, uterus, urinary tract)
Peristalsis- wave-like contraction

40. Cardiac Muscle Cells form interconnecting network
Cells are connected at intercalated disks
Impulses can rapidly transmit from cell to cell
Network response is all-or-none

41. Inherited Diseases of Muscle
Disease name
Description
Muscular Dystrophy
Missing proteins (specifically dystrophin – which attaches skeletal muscles together), weakened muscles, degenerate over time, specific type: Duchenne’s – only affects boys, die by early adulthood
Charcot-Marie-Tooth Disease
Caused by duplicate gene (impairs insulating sheath around nerve cells – so nerves can’t stimulate muscles), causes slowly progressing weakness in muscles of hand and feed, symptoms can resemble AIDS, diabetes, vitamin deficiency

42. Inherited Diseases of Muscle
Disease name
Description
Myotonic Dystrophy
Delays muscle relaxation following contraction, causes facial/limb weakness and irregular heartbeat, caused by “expanding gene” – gets worse with subsequent generations
Hereditary Idiopathic Dilated Cardiomyopathy
Very rare, heart failure – doesn’t begin until person’s 40s, lethal in 50% of cases within 5 yrs of diagnosis, caused by tiny genetic error in form of protein actin –cannot anchor to Z lines in heart muscles, causes heart chambers to enlarge and not function

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Animation with Quiz: ent/chp47/ html