NOTES FOR QUIZ 1 CH 9 MUSCLE PHYSIOLOGY

Sarcoplasmic reticulum Tendon http://www.youtube.com/watch?v=GneonFlcZG8 Fascia Fascicle (Myofiber) Sarcoplasmic reticulum

Connective Tissue Wrappings Endomysium - each muscle fiber (cell) is wrapped in this thin, delicate layer of CT Fascicles- Many muscle fibers are bundled together into groups called fascicles Perimysium -Each fascicle is wrapped in a second layer of this CT made of collagen

Skeletal muscle - Many fascicles are bundled together to form a skeletal muscle Epimysium Each skeletal muscle is covered by a third layer of dense, fibrous CT called epimysium Fascia, Fascia is a soft connective tissue located just below the skin that wraps and connects the muscles, bones, nerves and blood vessels of the body .

* aponeurosis is a sheetlike and tendons are cordlike. . Tendon or Aponeuroses – structure that attaches muscle to a bone, cartilage or muscle. The deep fascia may extend past the length of the muscle and become a tendon or aponeurosis * aponeurosis is a sheetlike and tendons are cordlike.

Aponeurosis = A sheetlike fibrous membrane, resembling a flattened tendon, that serves as a fascia to bind muscles together or as a means of connecting muscle to bone

So why are there striations on skeletal muscle?????

INSIDE A MYOFIBER (MUSCLE CELL)

MICROSCOPIC ANATOMY A muscle fiber is a long, thin cell called a myofiber Each muscle fiber is composed of myofibrils Each myofibril is composed of two types of protein myofilaments (cytoskeletal elements): 1. Thick myofilaments primarily composed of the protein myosin 2. Thin myofilaments primarily composed of the protein actin

Striations are caused by the arrangement thick and thin filaments within the myofibrils 1. A-Band = dark area = overlapping of thick and thin filaments 2.I-Band = light area = thin filaments alone.

A bands I bands Myosin Actin

Thick filaments = protein myosin. rod-like tail (axis) that terminates in two globular heads or cross bridges Cross bridges interact with active sites on thin filaments

Thin filaments = protein actin . Thin filaments = protein actin coiled helical structure (resembles twisted strands of pearls)

TITIN It connects the Z line to the M line in the sarcomere .Titin protein contributes to force transmission at the Z line and resting tension in the I band region. It limits the range of motion of the sarcomere in tension

The length of each myofibril is divided into sarcomeres Sarcomeres meet one another at an area called the Z-line

A region containing only thick filaments is visible in the center of the A band--this region is called the H zone. Proteins connect adjacent thick filaments. These proteins form a line in the center of the H zone called the M line.

http://lessons.harveyproject.org/development/muscle/grsphysw.html http://lessons.harveyproject.org/development/muscle/qtpower.html http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html

Both tropomyosin and troponin help control actin's interaction with myosin during contraction

Tropomyosin = rod-shaped protein spiraling around actin backbone to stabilize it Troponin = complex of polypeptides 1. one binds to actin 2. one that binds to tropomyosin 3. one that binds to calcium ions

Within the sarcoplasm (cytoplasm) of a muscle fiber, there are two specialized membranous organelles: Sarcoplasmic reticulum (SR) Transverse tubules (TT)

Sarcoplasmic reticulum (SR) Network of membranous channels that surrounds each myofibril and runs parallel to it. Same as endoplasmic reticulum in other cells. SR has high concentrations of calcium ions compared to the sarcoplasm (maintained by active transport calcium pump). When stimulated by muscle impulse, membranes become more permeable to calcium ions and calcium diffuses out of SR and into sarcoplasm

Each TT runs between two enlarged portions of SR called cisternae.   Transverse tubules (TT)                  set of membranous channels that extend into the sarcoplasm as invaginations continuous with muscle cell membrane (sarcolemma). TTs are filled with extracellular fluid and extend deep into the cell. Each TT runs between two enlarged portions of SR called cisternae. These structures form a triad near the region where actin and myosin overlap.

"Sliding Filament Theory"  Skeletal Muscle Contraction called the "Sliding Filament Theory"

Sliding Filament Theory  Skeletal Muscle Contraction Sliding Filament Theory most popular theory concerning muscle contraction first proposed by Hugh Huxley in 1954 states that muscle contraction involves the sliding movement of the thin filaments (actin) past the thick filaments (myosin) Sliding continues until the overlapping between the thin & thick filaments is complete.

Sliding Filament Theory

Changes in muscle cell during contraction The distance between the Z-lines of the sarcomeres decreases; The I-Bands (light bands) shorten; The A-Bands move closer together, but do not diminish in length.

The Role of Calcium in Contraction Mechanism In a resting muscle cell (i.e. in the absence of calcium ions ) Tropomyosin blocks or inhibits the myosin binding sites on actin.

The Role of Calcium in Contraction Mechanism When calcium ions (Ca++) are present Ca++ binds to troponin causing a conformational change in the troponin-complex which causes Tropomyosin to move Which "opens" or exposes the myosin binding sites on actin; This results in interaction between the active sites on actin and the heads (or cross bridges) of myosin

In order for the myosin head to pull the actin (muscle contraction) 2 things are necessary:

Calcium ions (controlled by nervous system) In order for the myosin head to pull the actin (muscle contraction) 2 things are necessary: Calcium ions (controlled by nervous system) ATP (controlled by respiration)

Muscles, muscles, and more muscles!!                                                                                                                                                                                                                                                         Muscles, muscles, and more muscles!!

Give a function of each of the following when a muscle fiber contracts.  Cisternae of sarcoplasmic reticulum = enlarged portion of T tubule Mitochondria = provides energy Myofibrils = inside the muscle fiber, branches of the transverse tubules encircle cylindrical structures called myofibrils Myofilaments = individual actin and myosin Openings into transverse tubules = allows Ca+2 to exit

 Sarcoplasmic reticululm = storage of Ca+2 Sarcolemma = cell membrane of muscle cell Sarcoplasm = cytoplasm within muscle cell Transverse tubule = allows movement of Ca+2

Sequence of Events in Sliding of Actin filaments during Contraction

For a muscle to contract it must be stimulated by a nerve impulse coming from a motor neuron (we will discuss this in more detail later). The impulse causes the release of Ca+2 from the SR When Ca+2 is present, it binds with tropoinin and causes the tropomyosin to shift exposing the binding sites on actin are exposed: ATP breakdown provides energy to raise the myosin head. The crossbridges of myosin attaches to the exposed actin binding site

Cross-bridge (myosin head) springs from raised position and pulls on actin filament Cross bridges break ATP binds to cross-bridge (but is not yet broken down) Myosin heads are released from actin.   * As long as calcium ions and ATP are present, this walking continues until the muscle fiber is fully contracted.

Adenosine triphosphate ATP is the energy molecule needed for myosin’s heads to move.

ENERGY The energy is provided when ATP loses a Phoshate group and becomes ADP.

Important roles of ATP in muscle contraction: 1. ATP binds to myosin heads and upon hydrolysis into ADP and Pi, transfers its energy to the cross bridge, energizing it. 2. ATP is responsible for disconnecting the myosin cross bridge at the conclusion of a power stroke. 3. ATP provides the energy for the calcium ion pump, which actively transports calcium ions back into the sarcoplasmic reticulum

STEP 1 Calcium ions present Ca+ binds to troponin which makes tropomyosin move out of way for myosin head to attach

STEP 2 Cross-bridge attaches. ATP breakdown provides energy to ready the myosin head for a power stroke Myosin head attaches to exposed binding site on actin and the power stroke is accomplished

STEP 3 Cross-bridge (myosin head) springs from raised position and pulls on the actin filament.

STEP 4 Cross bridges break ATP binds to cross-bridge (but is not yet broken down) Myosin heads are released from actin

STEP 5 As long as calcium ions and ATP are present, this walking continues until the muscle fiber is fully contracted

NOW LET’S TIE IN THE NERVOUS SYSTEM WITH THE MUSCLES

Stimulation of Skeletal Muscle Cell

In order for a skeletal muscle to contract, its fibers must first be stimulated by a motor neuron.

A motor neuron can send impulses to move a muscle or a gland. Let’s move it! Mickey the Motor Neuron

Motor Unit = one motor neuron and all muscle cells it innervates

Motor Unit = one motor neuron and many skeletal muscle fibers

Motor units can vary in the amount of muscles cells they innervate.

Neuromuscular Junction (NMJ) = the site where a motor nerve fiber and a skeletal muscle fiber “meet” (also called a synapse or synaptic cleft)

Motor End Plate = the specific part of a skeletal muscle fiber's sarcolemma directly beneath the NMJ. It is a specialized portion of the muscle cell membrane that is extensively folded.

Neurotransmitter = chemical substance released from a motor end fiber, causing stimulation of the sarcolemma of muscle fiber; example is acetylcholine (ACh). Sarcolemma of myofiber

Sequence of Events in Skeletal Muscle Stimulation/Contraction

Sequence of Events in Skeletal Muscle Stimulation/Contraction 1. Acetylcholine is the neurotransmitter that motor neurons use to control skeletal muscle. 2. ACh is synthesized in the cytoplasm of the motor neuron and is stored in synaptic vesicles in axons. 3. When a nerve impulse reaches the end of an axon, acetylcholine is released into the synaptic cleft. 4. ACh combines with ACh receptors on the motor end plate, and stimulates the muscle fiber.

5. A muscle impulse is an electrical signal that is like a nerve impulse. 6. A muscle impulse changes the muscle cell membrane in a way that transmits the impulse in all directions along and around the muscle cell. Ultimately the muscle impulse reaches the sarcoplasmic reticulum and cisternae. The sarcoplasmic reticulum has a high concentration of calcium.

In response to a muscle impulse, the membranes become more permeable to calcium, and the calcium diffuses out of the cisternae into the cytosol of the muscle fiber. When a muscle fiber is at rest, the troponin-tropomyosin complexes block the binding sites on the actin molecules. Calcium ions bind to troponin, changing its shape and altering the position of the tropomyosin.

10. The movement of the tropomyosin molecule exposes the binding sites of the actin filaments, allowing linkages to form between myosin cross-bridges and actin. ***As long as ATP is available to operate the crossbridges, and Ca+2 allows the binding sites on actin to be exposed, the myosin is able to pull on the actin allowing the entire sarcomere to shorten.

Write the Sequence of Events in the Relaxation Mechanism of a myofiber

Sequence of Events in the Relaxation Mechanism of a Myofiber 1. In order for a muscle fiber to relax, acetylcholine must be decomposed by an enzyme called acetylcholinesterase. 2. The action of acetycholinesterase prevents a single nerve impulse from continuously stimulating a muscle fiber. 3. When acetylcholine is broken down, the stimulus to the sarcolemma and the membranes within the muscle fiber ceases.

4. The calcium pump moves calcium back into the sarcoplasmic reticulum. 5. When calcium is removed from the cytoplasm, the cross-bridge linkages break and tropomyosin rolls back into its groove, preventing any cross-bridge attachment. 6. Remember tht ATP is necessary for both muscle contraction and relaxation. http://www.blackwellpublishing.com/matthews/myosin.html

The Energy for a Muscle Contraction Introduction: The energy used to power the interaction between actin and myosin comes from ATP. ATP stored in skeletal muscle lasts only about six seconds. ATP must be regenerated continuously if contraction is to continue.

There are three pathways in which ATP is regenerated: 1. Coupled Reaction with Creatine Phosphate (CP) 2. Anaerobic Cellular Respiration 3. Aerobic Cellular Respiration

Coupled Reaction with Creatine Phosphate (CP)

Coupled Reaction with Creatine Phosphate (CP)   1. CP + ADP <------> creatine + ATP 2. Muscle stores a lot of CP 3. This coupling reaction allows for about 10 seconds worth of ATP.

Adenosine triphosphate ATP is the energy molecule needed for myosin’s heads to move.

ENERGY The energy is provided when ATP loses a Phoshate group and becomes ADP.

Anaerobic Respiration (NO OXYGEN) 1. Steps are called glycolysis. 2. Steps occur in the cytoplasm of the cell. 3. Results in production of pyruvic acid and 2 ATP. Begins with glucose and ends with pyruvate.

Aerobic Respiration (OXYGEN REQUIRED) 1. Steps are called citric acid cycle and electron transport chain 2. Oxygen is required 3. Steps occur in the mitochondrion of the cell. 4. Results in CO2, water and 36ATP. 5. Oxygen is transported on blood hemoglobin and transferred to myoglobin, an oxygen binding pigment found in muscle

CHEMICAL EQUATION FOR AEROBIC RESPIRATION – KNOW THIS!!! + 36 ATP