Download KPC Notes

General Biology Lecture BIO 211 Regis University Spg 1992 B. Rife
1
II.
Vertebrate Muscle Organization
Muscles perform three functions. Along with the skeleton they give support and structure to the body. When they contract, they account
for movement of both the limbs and internal organs. Contraction also
releases heat that serves to warm the body. Vertebrates
have three types of muscle:
Smooth muscle is found in the walls of hollow internal organs like the stomach, intestine, and urinary bladder.
Cardiac muscle have structures called intercalated disks where the individual fibers meet. These permit contractions to spread
throughout the wall of the heart, the only place where cardiac muscle is found.
Skeletal muscle fibers are long and striated. Skeletal muscles are attached to and move the bones of the skeleton.
Smooth muscle and cardiac muscle are said to be involuntary muscles because their contraction is most often controlled by the
autonomic nervous system without conscious thought.
Skeletal muscle is called voluntary muscle, and we often consciously control its contraction by way of the somatic nervous system.
Skeletal Muscle Contraction
Skeletal muscles, which make up over 40% of the body’s weight, are attached to the skeleton by tendons, tough, fibrous bands of cords.
When muscles contract, they shorten. Therefore, muscles can only pull. Because of this, skeletal muscles must work in antagonistic
pairs.
The muscle can be stimulated electrically, and when it contracts, its graphed contraction pattern called a myogram is recorded.
III
Muscle Fiber Anatomy and Physiology
A. Muscle Fiber Structure
A muscle fiber has some unique anatomical characteristics. For one thing, it has a T (for tubule) system. The sarcolemma, or plasma
membrane, forms these tubules that penetrate or dip down into the cell, so that they come into contact with, but not fuse with, expanded
portions of modified endoplasmic reticulum, termed the sarcoplasmic reticulum. The sarcoplasmic reticulum encases hundreds, and
sometimes even thousands of myofibrils, which are the contractile portions of the fibers.
1. Myofibrils
Myofibrils are cylindrical in shape and run the length of the muscle fiber. A myofibril has light and dark bands called striations.
The striations of myofibrils are dependent on the placement of protein filaments that contain units called sarcomeres.
2. Filaments
A sarcomere contains two types of filaments, thin filaments and thick filaments.
Sarcomere contraction is dependent on the action of two proteins, actin and myosin, that make up the thin filaments and
the thick filaments respectively.
The movement of actin in relation to myosin is called the sliding filament theory of muscle contraction.
During the sliding process, the sarcomere shortens, even though the filaments themselves remain the same length.
In the presence of Ca++, portions of the myosin filaments, called cross bridges, reach out and attach to the actin filaments,
pulling them along. (myosin pull the actin filaments inward)
If more ATP molecules are not available, detachment cannot occur. This explains rigor mortis, permanent muscle contraction
just after death.
ATP provides the energy for muscle contraction. In order to assure a ready supply, muscle fibers contain creatin phosphate
(phosphocreatine), a storage form of high-energy phosphate.
B. Oxygen Debt from Fermentation
When all of the creatine phosphate has been depleted and there is no oxygen available for aerobic respiration, a muscle fiber can generate
ATP by using fermentation. Fermentation, which is apt to occur during strenuous exercise, can supply ATP for only a short time because
lactic acid buildup produces muscular aches and fatigue.
The continued deep breathing following strenuous exercise is required to complete the metabolism of lactic acid that has accumulated
during exercise and represents an oxygen debt that the body must pay to rid itself of lactic acid.
The lactic acid is transported to the liver, where one-fifth of it is completely broken down to carbon dioxide and water by means of the
Krebs cycle and respiration chain. The ATP gained by this respiration is then used to convert the remaining four-fifths of the lactic acid
back to glucose.
General Biology Lecture BIO 211 Regis University Spg 1992 B. Rife
2
C. Contraction and Relaxation Process
Nerves innervate muscles, and nerve impulses cause muscle to contract.
A motor axon within a nerve has branches that go to several muscle fibers, which collectively are termed a motor unit. Each branch has
terminal end knobs that contain synaptic vesicles filled with the neuromuscular transmitter ACh (acetylcholine). A terminal end knob lies in
close proximity to the sarcolemma of the muscle fiber.
This region, called a neuromuscular junction has the same components as a synapse: a presynaptic membrane, a synaptic cleft, and
a postsynaptic membrane.
Nerve impulse cause synaptic vesicles to fuse with the presynaptic membrane and release ACh into the synaptic cleft.
When ACh reaches the sarcolemma, the sarcolemma is depolarized.
The result is a muscle action potential that spreads over the sarcolemma and down the
T system to the calcium-storage sacs of the sarcoplasmic reticulum.
KPC Notes
Muscle Types
-skeletal muscle (striated, voluntary)
-Cardiac
-Smooth (visceral, involuntary)
-Skeletal
-makes up 40% of body weight
-outer membrane can conduct a wave of deplorization
-outer membrane called sacrolemma
-600 differn’t muscles (about)
-muscle can only contract and shorten
-muscle cells = muscle fibers
-muscle cells are multinucleated
-skeletal muscle
-individual muscle cell has myofibrils
-epimiysuim outside cell, surrounds
-endomysium
-muscle cells are surrounded by a connective tissue layer, endomysium
-groups of bundles are surrounded by connective tissue layers
-dense connective tissue
-forms the tendons or apanererosis
-tendons connect to periosteum of the bone and the bone itself by special fibers
-perimysium
-bundles of muscle cells are formed into packets and surrrounded by connective tissue
Muscle Contraction
-protiens
-myosin, actin, tropomyosin, troponin
-sacromere
-one piece of repetive pattern
-tropomyosin
-a small globular protien
-it likes to be bonded to three things
-tropomyosin
-actin
-calcium ions
-when bonded to all three, shape changes
General Biology Lecture BIO 211 Regis University Spg 1992 B. Rife
Inside the cell
-sacroplasmic reticulum
-membranous sac, surrounds each myofibril
-contain high concentrations of Ca+
-release Ca+ when stimulated by T-Tubles
-T-tubles
-invagenation of the sacrolemma
-surround each myofibril, nestled in between the sacroplasmic reticulum sections
-carry wave of depolarization into the myofibril’s
-found at the places corresponding to the two-disks (pg 286)
Chemical Transmittor
-Acetylcholine
-contraction
-wave of deplorization that travels along the axon to nueromuscular junction
-axon terminal releases transmitter substance, causes deplorarization of sacrolemma (acetylcholine)
-deplorization wave travels along sarcolemma, enters cell via t-tubles
-sarcoplasmic reticulum is stimulated to release calcium ions
-Ca+ are bound to troponin, causes troponin to change its shape
-changing shape(troponin) causes a pull on tropomyosin
-the active sites on Actin are then exposed
-myosin heads attach to the active sites on actin (crossbridge formation)
-on attachment of myosin to actin the myosin head tilts or shifts to the side
( pulling actin over top of myosin filaments)
-tilting of the myosin head exposes one ATPase in the myosin
-ATP is broken down (releasing energy)
-the ATP causes the myosin to release it’s hold on the active & return to it’s upright shape
-if another active site is exposed, it binds to it
-when head binds to another active site, it tilts again pulling one filament over the top of the other again
-as long as there are active sites and ATP to breakdown the myosin head will attach again and again causing a
contraction
-contractions will continue until
-ATP is depleted
-Ca+ is removed ( by sacroplasmic reticulum)
-excess resistence exists fatigue
-a drop of tension after prolonged stimulation
-deplorization waves continue, less response
-less ATP is available(inadequate blood supply and less sugars to make ATP)
-buildup of lactic acid (from anerobic ATP production)
rigor mortis
-rigidity of muscles after death ( no ATP )
-muscles retain their position until protiens begin to breakdown (12-24 hrs.)
energy
-no O
-glucose
(2 ATP)
-pyruvate -> lactic acid
-krebs cycle
-electron transport(citric acid cycle) (34 ATP)
(relatively slow & O needed)
-muscle contractions require large amounts of energy
3
General Biology Lecture BIO 211 Regis University Spg 1992 B. Rife
-additional phosphates come from adp combining with phosphates form Creatine Phosphate
-Motor unit
-a motor nueron and all the muscle cells it innervates
-when the nueron is depolarizes, all of its muscle cells contract
-calf muscle, 1000/1700 cells per neuron
-eye muscles 1-2 muscle cells per nueron
-when additional tension (strength) is needed more motor units needed
-for extended tension maintence “alternate motor units”
- firing all motor units at one time
4