A & P of Skeletal Muscles

Question 1

Skeletal muscles cells are usually called what?

Answer 1

Fibers

Question 2

Skeletal muscle cells are usually what size and shape?

Answer 2

small and long - up to several inches

Question 3

How many nuclei can one large fiber have?

Answer 3

100+

Question 4

Where are all nuclei located in a fiber?

Answer 4

on the outer edge of the cell, just under the cell membrane

Question 5

• Muscle cell membrane

Answer 5

Sarcolemma

Question 6

• 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

Answer 6

Myofibril

Question 7

o On the myofibrils, storage organelle for calcium ions

Answer 7

Sarcoplasmic reticulum

Question 8

o System of tubules that extend inward from the sarcolemma (muscle cell membrane)

Answer 8

• Transverse tubules or T-tubules

Question 9

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

Answer 9

I Bands

Question 10

o In the center of the I band
o Attachment site for actin filaments
o Disc on each end of the sarcomere

Answer 10

Z Line or Z Disc

Question 11

o Between the I bands
o Where myosin and actin overlap

Answer 11

A Bands

Question 12

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

Answer 12

H Bands

Question 13

• Series of protein filaments from the myofibril that make up the contractile units of muscle cells

Answer 13

Sarcomere

Question 14

Many sarcomeres laid end to end make up one what?

Answer 14

Myofibril

Question 15

o Sarcomeres share ______ so there is one common _______ between adjacent sarcomeres

Answer 15

Z disc

Question 16

o Thin protein filaments that connect to the Z lines and extend toward the center of the sarcomere, but don’t meet

Answer 16

Actin

Question 17

o Thick protein filaments that float in the middle of the sarcomere, between parallel actin fibers
o Don’t connect to Z lines

Answer 17

Myosin

Question 18

 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

Answer 18

Cross bridges

Question 19

o Sites where the ends of motor nerve fibers connect to muscle fibers

Answer 19

• Neuromuscular Junction

Question 20

 Exists between the end of the nerve fiber and the sarcolemma

Answer 20

o Synaptic space

Question 21

 Tiny sacs within the end of a nerve fiber in a neuromuscular junction

Answer 21

o Synaptic vesicles

Question 22

 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

Answer 22

o Acetylcholine

Question 23

 One nerve fiber and all the muscle fibers it innervates

Answer 23

motor unit

Question 24

 Muscles for very small, delicate movements (eye muscles) have how many muscle fibers per motor unit?

Answer 24

only a few

Question 25

 Large, powerful muscles (leg muscles) have how many muscle fibers per motor unit?

Answer 25

hundreds or more

Question 26

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

Answer 26

* Connective Tissue Layers

Question 27

 Surrounds each individual skeletal fiber  Composed of fine, reticular fibers

Answer 27

o Endomysium

Question 28

 Groups of skeletal muscle fibers

Answer 28

o Fascicles

Question 29

 Composed of reticular fibers and thick collagen fibers

Answer 29

o Perimysium

Question 30

 Fibrous connective tissue layer composed largely of tough collagen fibers  Outer covering of the entire muscle

Answer 30

o Epimysium

Question 31

What are the seven steps of muscle contraction?

Answer 31

1. Nerve impulse travels down a motor nerve fiber 2. Reaches the end of the bulb at the neuromuscular junction 3. Acetylcholine is released into the synaptic space 4. Acetylcholine molecules bind to receptors on the surface of the sarcolemma of the muscle cell fiber 5. Starts an impulse that travels along the sarcolemma and through the T tubules to the interior of the cell 6. When the impulse reaches the sarcoplasmic reticulum, it causes the release of stored calcium ions (Ca2+) into the sarcoplasm (cytoplasm) 7. Ca2+ diffuses into the myofibrils and turns on the contraction process, powered by ATP

Question 32

How does muscle relaxation happen?

Answer 32

1. 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. 2. 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.

Question 33

Muscle contraction and relaxation both require what?

Answer 33

ATP

Question 34

What is the ion released during muscle contraction?

Answer 34

Ca2+

Question 35

The amount of calcium in the muscle fiber is determined by what?

Answer 35

The level of calcium in the bloodstream

Question 36

Hypocalcemia or hypercalcemia is what? And either can cause what?

Answer 36

Too high or too low of calcium abnormalities in skeletal muscle function can result

Question 37

actin and myosin filaments overlap only a little when muscle fiber is what?

Answer 37

in a relaxed state

Question 38

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 _____________

Answer 38

tails of myosin actin center of the myosin

Question 39

The sliding of the filaments over each other does what to the sarcomere

Answer 39

shortens it

Question 40

The combined shortening of all end to end sarcomeres in a muscle fiber

Answer 40

 Muscle contraction

Question 41

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

Answer 41

All or Nothing Principle

Question 42

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

Answer 42

whole muscle movement

Question 43

 Single muscle fiber contraction

Answer 43

Twitch contraction

Question 44

What are the three phases of a twitch contraction?

Answer 44

o Latent phase o Contracting phase o Relaxation phase

Question 45

How long does the cycle of a twitch contraction take?

Answer 45

0.1 seconds

Question 46

Which phase of a twitch contraction is the brief hesitation between the nerve stimulus and the beginning of the actual contraction?

Answer 46

o Latent phase

Question 47

 Careful timing of the nerve impulses to the various motor units of the muscle  Happens when all the muscle fiber activity is averaged out

Answer 47

Smooth muscle contraction

Question 48

Visible muscle twitches during smooth muscle contraction means what?

Answer 48

contractions are out of sync

Question 49

What powers the sliding of actin and myosin?

Answer 49

ATP

Question 50

 Compound in muscle fiber that acts as a “Battery charger” to convert ADP back to ATP

Answer 50

o Creatine phosphate (CP)

Question 51

 Ultimate source of energy used to produce ATP and CP as well as keep the whole system operating

Answer 51

o Catabolism (breakdown) of nutrient molecules

Question 52

What are the two main components involved in the chemistry contraction?

Answer 52

glucose and oxygen

Question 53

 Stored in the fibers in the form of glycogen

Answer 53

Glucose

Question 54

 Stored attached to large protein molecules called myoglobin

Answer 54

Oxygen

Question 55

o Red like hemoglobin o Can store and release large quantities of oxygen

Answer 55

Myoglobin

Question 56

 Oxygen supply is adequate to keep up with the energy needs of the fiber  Maximum amount of energy is extracted from each glucose molecule

Answer 56

o Aerobic metabolism

Question 57

 Muscle fibers switch to this when oxygen need exceeds the available supply

Answer 57

o Anaerobic metabolism

Question 58

 Result of aerobic metabolism  Formation as a byproduct of incomplete glucose breakdown

Answer 58

Lactic acid

Question 59

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 ________

Answer 59

Liver Glucose Oxygen

Question 60

An animal may continue to breath heavy for a while as the body repays the ___________

Answer 60

An oxygen debt to the liver, to convert lactic acid back to glucose

Question 61

o Considerable amount of the energy produced in muscles is in the form of ______

Answer 61

heat

Question 62

What is one major heat generating mechanisms for the body?

Answer 62

Muscle activity

Question 63

o If heat production exceeds body needs, excess is eliminated by what?

Answer 63

Panting or sweating

Question 64

o Increased heat production by ________ can fight hypothermia

Answer 64

shivering