(Smooth Muscle) Should be at bottom.
Skeletal Muscle Fiber Structure and Functions
(Should be placed two pics down... oops!)
Neuromuscular Junction
Mechanism of Muscle Control
Parts of Muscle Cell
Anatomy of Skeletal Muscles
Skeletal Muscles Work in Pairs
Skeletal Muscle
Cardiac Muscle
I. Overview of the Muscular System
II. Skeletal Muscle Fiber Contraction
III. Whole Muscle Contraction
I. Overview of the Muscular System
A. All muscles contract, and when they do, some part of the body moves.
B. Types of Muscles: Three types. Cells of these tissues are called muscle fibers.
1b. Smooth Muscle: These fibers are spindle-shaped cells, each with a single nucleus.
- Usually arranged in parallel lines, forming sheets.
- No striations.
- Found in walls of hollow internal organs, and it makes these walls contract.
- Contraction is involuntary.
- Slower to contract than skeletal muscle, but can sustain prolonged contractions and does not tire easily.
(Insert Smooth Muscle picture / http://www.east-haven.k12.ct.us/ / http://www.east-haven.k12.ct.us/eha/grade6/system6/smoothcardiacmusclekc/indexkc.htm)
2b. Cardiac Muscle: Forms heart walls.
- Fibers are generically without nuclues, striated, tubular, and branched.
- Branching allows fibers to interlock at intercalated disks.
- Plasma membranes at intercalated disks have gap junctions allowing contractions to spread quickly throughout wall of heart.
- Fibers relax completely between contractions.
- Involuntary contractions.
(Insert Cardiac Muscle picture / http://www.east-haven.k12.ct.us/ / http://www.east-haven.k12.ct.us/eha/grade6/system6/smoothcardiacmusclekc/indexkc.htm)
3b. Skeletal Muscle: Skeletal muscles that attach to the skeleton.
- Fibers are tubular, multinucleated, and striated.
- Run the length of the muscle and can be very long.
- Voluntary: we decide when to move a particular body part, like arms and legs.
- Contraction causes movement of bones at joint.
(Insert Skeletal Muscle picture / oregonstate.edu / http://rds.yahoo.com/_ylt=A0S020qgTXBIJTIB1K6jzbkF/SIG=1367v0nr2/EXP=1215405856/**http%3A//oregonstate.edu/~peila/Pharmstuff/Projector%2520Slides/Projector%2520Slides"
C. Functions of Skeletal Muscles
1c. Support the body. Allows us to remain upright.
2c. Make bones move: Contractions move arms, legs, eyes, facial expressions, and breathing.
- Rigor Mortis: Muscle contractions at death.
3c. Help maintain a constant body temp.
- Muscle contractions causes ATP to break down, releasing heat to spread throughout the body.
3c. Assists movement in cardiovascular and lymphatic vessels.
- Pressure of contraction keeps blood moving in cardiovascular veins and lymph moving in lymphatic vessles.
4c. Help protect internal organs and stabilize joints- Muscles pad bones.
- Muscular wall in abdominal region protects internal organs.
- Muscle tendons help hold bones and joints together.
D. Skeletal Muscles of Body:
- Humans are vertebrates: skeletal muscles lie outside an internal skeleton that has jointed appendages.
1d. Basic Structure of Skeletal Muscles:
- Well-orgnized.
- Contains fascicles: Bundles of skeletal muscle fibers in whole muscle.
- Each fascicle is surrounded by connective tissue, and so are the fibers within the fascicles.
- Fascia: Covers muscles. Type of connective tissue that extends beyond the muscle and becomes a tendon.
2d. Work in pairs:
- Origin of a muscle is on a stationary bone, and the insertion of a muscle is on a bone that moves.
- Muscle contracts, it pulls on tendons at its insertion, and bone moves.
- Function in groups. So, nervous system stimulates a group of muscles, not a single.
- However, one muscle does most of work and is called a prime mover.
- Synergists: Muscles that assist the prime mover.
- Muscles shorten when they contract. They can only pull, not push.
- So, they work in opposite pairs. Antagonist: the muscle that acts opposite to a prime mover.
- Smooth muscle movements depend on an antagonist relaxing when a prime mover contracts. (Mader 228-229)
(Insert Skeletal Muscle Work in Pairs picture / Frolich PowerPoint Slide 11)
E. Names and Actions of Skeletal Muscles:
1e. Names of Skeletal Muscles are often cominations of the following terms:
- Size: Minimus, Maximus, Vastus (huge), Longus, and Brevis (short).
- Shape: Deltoid, Trapezius, Latissimus (wide), and Terres (round).
- Location: External, Internal, Frontalis, Pectoralis (chest), Gluteus (buttock), Brachii (arm), and Sub (beneath).
- Direction of Muscle Fibers: Rectus (straight), Orbicularis (circular), Transverse ( across), and Oblique (diagonal).
- Attachment: Where and / or to what the muscle attaches. Ex. Brachioradialis: Attached to the brachium (arm) and the radius.
- Number of Attachments: Ex. Biceps (two attachments), or origi- Action: Ex. Extensor digitorum extends the fingers. Adduction- movement of a body part toward the midline. Other terms: Flexor, Masseter (chew), and levator (lift). (Mader 230-231)
(Insert Anatomy of Skeletal Muscles picture / http://www.doereport.com/ / http://rds.yahoo.com/_ylt=A0S0207GV3BIQBQACPGjzbkF/SIG=12aro790h/EXP=1215408454/**http%3A//www.doereport.com/generateexhibit.php%3FID=8106 )
II. Skeletal Muscle Fiber Contraction
A. Muscle Fibers and How They Slide
- "Muscle cells are large—visible with naked eye as “fibers of meat/chicken/fish". (Frolich PowerPoint Slide 5)
1a. Muscle Fiber: Cell containing the usual cellular components, with different names given to some of the combonents.
- Sarcolemma: Plasma Membrane.
- Sarcoplasm: Cytoplasm.
- Sarcoplasmic Reticulum: Endoplasmic reticulum.
(Insert Parts of Muscle Cell picture / Frolich PowerPoint Slide 6)
2a. Unique Anatomical Characteristics:
- T (for transverse) System: Sarcolemma forms T tubules that penetrate, or dip down into, the cell so that they come into contact but do not fuse with expanded portions of the sarcoplasmic reticulum.
- These expanded portions of the sarcoplasmic reticulum are calcium storage sites, and calcium is essentail for muscle contraction.
3a. Myofibrils: Hundreds and sometimes thousands of these, found in the sarcoplasmic reticulum, are the contractile portions of the muscle fibers.
- All other organelles are found in the sarcoplasm between the myofibrils.
- Sarcoplasm also contains glycogen, which provides stored energy for muscle contraction.
- Also contains red pigment myoglobin, which binds oxygen until it is needed for muscle contraction.
B. Myofibrils and Sarcomeres:
1b. Myofibrils: Cylindrical. Along the length of muscle fiber.
- Striations: light and dark bands, formed by placement of myofilaments within myofibrils called sarcomeres.
2b. Sarcomeres: Extends between two dark lines called Z lines.
- Contains two types of protein myofilaments.
- Thick filaments: Composed of a protein called Myosin.
- Thin filaments: Composed of a protein called Actin.
C. Myofilaments: The thick and thin filaments differ in the following ways:
1c. Thick Filaments: Composed of several hundred molecules of protein myosin.
- Myosin molecules are shaped like golf clubs. "Head" is called "Crossbridge", which occurs on each side of a sarcomere but not the middle.
2c. Thin Filaments: Made up of two intertwining strands of the protein actin.
- Tropomyosin and Troponin are two other proteins involved.
3c. Sliding Filaments:
- Muscles are stimulated, impulses travel down a T tubule, and calcium is realeased from sarcoplasmic reticulum.
- Muscle fiber contracts as the sarcomeres in the myofibrils shorten.
- When a sarcomere shortens, the actin (thin filaments) slide past the myosin (thick filaments) and approach one another.
- This makes the I band shorten, the Z line move inward, and the H zone disappear.
- Sliding Filament Model: This movement of actin filaments in relation to myosin filaments during muscle contraction.
(Insert Skeletal Muscle Fiber Structure and Functions picture / Frolich Powerpoint Slide 5)
- During the sliding process, the sarcomere shortens, though the filaments themselves remain the same length. ATP supplies energy, and the myosin filaments break down ATP, and their cross-bridges pull the actin filaments toward the center of the sarcomere. (Mader 232)
(Insert Mechanism of Muscle Contraction picture / courses.cm.utexas.edu / http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-1.htm)
D. Control of Muscle Fiber Contraction:
1d. "Neuron brings impulse to synapse with muscle." (Frolich PowerPoint Slide 4).
- Motor Neurons stimulate muscle fibers to contract. Their axons are in nerves.
- This axon can stimulate a few to several muscle fibers because each axon has several branches.
- Each branch ends in an axon terminal that is close to the sarcolemma of a muscle fiber.
- Synaptic cleft: small gap separating the axon terminal from the sarcolemma.
- Neuromuscular Junction: Name for this entire region.
(Insert Neuromuscular Junction picture / Frolich PowerPoint Slide 4)
2d. Axon terminals have synaptic vesicles filled with neurotransmitter acetylcholine (ACh).
- When a nerve impulses, (traveling down a motor neuron), it arrives at an axon terminal, where the synaptic vesicles release ACh into the synaptic cleft.
- When ACh is released, it diffuses across the cleft and binds to receptors in the sarcolemma.
- Sarcolemma gives impulses that spread over the sarcolemma and down T tubules to the sarcoplasmic reticulum. (Mader 234)
- Ca2+ is released from the sarcoplasmic reticulum and leads to sarcomere contraction.
- Muscle relaxes when Ca2+ returns to sarcoplasmic reticulum. (Mader 232)
- Sooo, in a nutshell: Calcium release occurs in the following manner:
- Motor neuron impulse arrives to axonal terminus.
- Neuro-muscular junction synapse passes message on to muscle cell.
- Sarcolemma (muscle cell membrane) undergoes action potential all along length of cell membrane and into T-tubule system.
- Voltage change causes release of Ca+2 ions into muscle cell.
- Calcium causes actin-myosin units (sarcomeres) to shorten. (Frolich PowerPoint Slide 7)
- " Muscle cells shorten by sliding protein filaments (actin-myosin units)" (Frolich PowerPoint Slide 4)
- "Movements at protein level cause whole muscle to rapidly shorten or contract." (Frolich PowerPoint Slide 4)
- The protein Tropomysin wraps around an actin filament, and troponin occurs at intervals along the threads.
- Myosin can then bind with actin.
III. Whole Muscle Contraction
A. Dependent on muscle fiber contraction.
1a. Muscles Have Motor Units:
- Motor Unit: A nerve fiber and all of the muscle fibers it innervates.
- All-or-None Law: All muscle fibers in a motor unit are stimulated at once, and they either ALL contract, or none contract.
- Variable of Interest: Number of muscle fibers within a motor unit.
2a. Muscle Twitch: Occurs when a motor unit is stimulated by infrequent electrical imulses, and a single contraction occurs that lasts a fraction of a second. Divided into three periods:
- Latent period: Time between stimulation and initiation of a contraction.
- Contraction period: Muscle shortens.
- Relaxation period: Muscle returns to former length.
3a. Summation: Increased muscle contraction until maximal sustained contraction (tetanus) is achieved.
- Muscles fatigue due to use of energy reserves.
- Recruitment: When the intensity of nervous stimulation increases, more and more motor units in a muscle are activated.
- Maximum contraction of a muscle occurs when all motor units undergo tetanic contraction. (Rare, to avoid all of the fatiguing at the same time.)
- Muscle Tone: Firm and solid muscle.
B. Energy for Muscle Contraction: Various fuel sources for energy, various ways of producing ATP. 4 possible energy sources:
1b. Fuel Sources for Exercise:
- Glycogen and fat (triglycerides), stored in muscles.
- Blood glucose and plasma fatty acids in blood.
* Adipose Tissue: Source of plasma fatty acids that muscle burns as energy source.
* Both delivered to muscles through circulating blood.
C. Sources of ATP for Muscle Contraction:
1c. Muscle cells can acquire more ATP needed for contraction once stored ATP has been used up in three ways:
1. Formation of ATP by the creatine phosphate pathway.
- Simplest and fastest, only one reaction.
- Occurs in the midst of sliding filaments.
- Creatine phosphate is formed when a muscle cell is resting.
(Mader 236-237)
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