A & P of Skeletal Muscles Flashcards
Skeletal muscles cells are usually called what?
Fibers
Skeletal muscle cells are usually what size and shape?
small and long - up to several inches
How many nuclei can one large fiber have?
100+
Where are all nuclei located in a fiber?
on the outer edge of the cell, just under the cell membrane
- Muscle cell membrane
Sarcolemma
- Hundreds or thousands make up most of the volume of skeletal muscle fiber
- Packed together lengthwise
- Composed of thousands of even tinier protein filaments
- Mitochondria between produce energy
Myofibril
o On the myofibrils, storage organelle for calcium ions
Sarcoplasmic reticulum
o System of tubules that extend inward from the sarcolemma (muscle cell membrane)
- Transverse tubules or T-tubules
o Large light-colored bands made up of the thin actin filaments
o Extends from one end of myosin filaments in one sarcomere across the Z line to the beginning of the myosin fibers in the next sarcomere
I Bands
o In the center of the I band
o Attachment site for actin filaments
o Disc on each end of the sarcomere
Z Line or Z Disc
o Between the I bands
o Where myosin and actin overlap
A Bands
o In the middle of the A band
o Made of all myosin, no overlapping actin
o Doesn’t always cover the entire width of the myosin
H Bands
- Series of protein filaments from the myofibril that make up the contractile units of muscle cells
Sarcomere
Many sarcomeres laid end to end make up one what?
Myofibril
o Sarcomeres share ______ so there is one common _______ between adjacent sarcomeres
Z disc
o Thin protein filaments that connect to the Z lines and extend toward the center of the sarcomere, but don’t meet
Actin
o Thick protein filaments that float in the middle of the sarcomere, between parallel actin fibers
o Don’t connect to Z lines
Myosin
Twisted tail on the end of the myosin molecule that is attached to two globular heads
Interact with actin to shorten the sarcomere during muscle contraction
Cross bridges
o Sites where the ends of motor nerve fibers connect to muscle fibers
- Neuromuscular Junction
Exists between the end of the nerve fiber and the sarcolemma
o Synaptic space
Tiny sacs within the end of a nerve fiber in a neuromuscular junction
o Synaptic vesicles
Chemical neurotransmitter
Released when a nerve impulse comes down the motor nerve fiber
Quickly diffuses across the synaptic space and binds to receptors on the sarcolemma
Effect on receptor is very short
o Acetylcholine
One nerve fiber and all the muscle fibers it innervates
motor unit
Muscles for very small, delicate movements (eye muscles) have how many muscle fibers per motor unit?
only a few
Large, powerful muscles (leg muscles) have how many muscle fibers per motor unit?
hundreds or more
What kind of tissue layers -
o Skeletal muscle fibers must be securely fastened together and to the structures (usually bones) that they move
o Contain the blood vessels and nerve fibers that supply the muscle fibers
- Connective Tissue Layers
Surrounds each individual skeletal fiber
Composed of fine, reticular fibers
o Endomysium
Groups of skeletal muscle fibers
o Fascicles
Composed of reticular fibers and thick collagen fibers
o Perimysium
Fibrous connective tissue layer composed largely of tough collagen fibers
Outer covering of the entire muscle
o Epimysium
What are the seven steps of muscle contraction?
- Nerve impulse travels down a motor nerve fiber
- Reaches the end of the bulb at the neuromuscular junction
- Acetylcholine is released into the synaptic space
- Acetylcholine molecules bind to receptors on the surface of the sarcolemma of the muscle cell fiber
- Starts an impulse that travels along the sarcolemma and through the T tubules to the interior of the cell
- When the impulse reaches the sarcoplasmic reticulum, it causes the release of stored calcium ions (Ca2+) into the sarcoplasm (cytoplasm)
- Ca2+ diffuses into the myofibrils and turns on the contraction process, powered by ATP
How does muscle relaxation happen?
- Almost as soon as the sarcoplasmic reticulum releases its Ca2+ into the sarcoplasm, it beings pumping it back in again. This pulls the Ca2+ out of the myofibrils and the contraction shuts down.
- The elasticity of the muscle fiber then restores it to its original length, relaxing the fiber. Pumping the Ca2+ back into the sarcoplasmic reticulum requires energy which is also supported by ATP molecules.
Muscle contraction and relaxation both require what?
ATP
What is the ion released during muscle contraction?
Ca2+
The amount of calcium in the muscle fiber is determined by what?
The level of calcium in the bloodstream
Hypocalcemia or hypercalcemia is what? And either can cause what?
Too high or too low of calcium
abnormalities in skeletal muscle function can result
actin and myosin filaments overlap only a little when muscle fiber is what?
in a relaxed state
When fiber is stimulated to contract, the globular heads attach to the _______ and ratchet back and forth and pull the ______ on both sides toward the _____________
tails of myosin
actin
center of the myosin
The sliding of the filaments over each other does what to the sarcomere
shortens it
The combined shortening of all end to end sarcomeres in a muscle fiber
Muscle contraction
What principle states that an individual muscle fiber (not a whole muscle) either contracts completely when it receives a nerve impulse or it does not contract at all
All or Nothing Principle
What is it called when the body controls how many muscle fibers it stimulates for a particular movement
* Small, fine movements require only a few muscle fibers to contract
* Larger, more powerful movements require the contraction of many muscle fibers
whole muscle movement
Single muscle fiber contraction
Twitch contraction
What are the three phases of a twitch contraction?
o Latent phase
o Contracting phase
o Relaxation phase
How long does the cycle of a twitch contraction take?
0.1 seconds
Which phase of a twitch contraction is the brief hesitation between the nerve stimulus and the beginning of the actual contraction?
o Latent phase
Careful timing of the nerve impulses to the various motor units of the muscle
Happens when all the muscle fiber activity is averaged out
Smooth muscle contraction
Visible muscle twitches during smooth muscle contraction means what?
contractions are out of sync
What powers the sliding of actin and myosin?
ATP
Compound in muscle fiber that acts as a “Battery charger” to convert ADP back to ATP
o Creatine phosphate (CP)
Ultimate source of energy used to produce ATP and CP as well as keep the whole system operating
o Catabolism (breakdown) of nutrient molecules
What are the two main components involved in the chemistry contraction?
glucose and oxygen
Stored in the fibers in the form of glycogen
Glucose
Stored attached to large protein molecules called myoglobin
Oxygen
o Red like hemoglobin
o Can store and release large quantities of oxygen
Myoglobin
Oxygen supply is adequate to keep up with the energy needs of the fiber
Maximum amount of energy is extracted from each glucose molecule
o Aerobic metabolism
Muscle fibers switch to this when oxygen need exceeds the available supply
o Anaerobic metabolism
Result of aerobic metabolism
Formation as a byproduct of incomplete glucose breakdown
Lactic acid
After burst of energy is over, some lactic acid diffuses into the bloodstream and goes to the ________, where it is converted back to _______ by a process that requires ________
Liver
Glucose
Oxygen
An animal may continue to breath heavy for a while as the body repays the ___________
An oxygen debt to the liver, to convert lactic acid back to glucose
o Considerable amount of the energy produced in muscles is in the form of ______
heat
What is one major heat generating mechanisms for the body?
Muscle activity
o If heat production exceeds body needs, excess is eliminated by what?
Panting or sweating
o Increased heat production by ________ can fight hypothermia
shivering
