10 Muscle Tissue

Question 1

How many muscles are there in the human body?

Answer 1

over 700

Question 2

What are the 5 functions of skeletal muscle?

Answer 2

1. move the body
   2.maintain posture
   3.protect and support
   4.regulate elimination of materials (spinchters)
   5.produce heat

Question 3

What are the 5 characteristics of skeletal muscle?

Answer 3

1. Excitability - respond to stimulus
2. Conductivity - electrical signals connect cell membrane (stimulus) to interior of cell
3. contractility - contractile proteins slide past one another
4. extensibility - lengthening of the muscle cell
5. elasticity - the ability of a muscle cell to return to its original length following shortening or lengthening

Question 4

epimysium

Answer 4

dense irregular CT surrounding the whole skeletal muscle

Question 5

perimysium

Answer 5

dense irregular CT surrounding each fascicle (bundle of muscle fibers

Question 6

endomysium

Answer 6

areolar CT surrounding each muscle fiber

Question 7

What is the cell membrane of a muscle cell called and why is it special?

Answer 7

sarcolemma
T(transverse)-tubules extend into muscle fiber’s sarcoplasmic reticulum so voltage gated Na+ and K+ channels in the sarcolemma extend into the cell interior, closely connected with sarcoplasmic reticulum

Question 8

Myofibril

Answer 8

a bundle of myofilaments, enclosed in portions of the sarcoplasmic reticulum, each skeletal muscle fiber contains hundreds to thousands of myofibrils

Question 9

sarcoplasmic reticulum

Answer 9

an internal membrane complex (similar to smooth ER), forms sleeves of membrane netting around myofibrils, at either end of sleeve are blind sacs called terminal cisternae which are closely associated with T-tubules (SR contains CA2+ pumps, calmodulin and calsequestrin)

Question 10

Thick filaments

Answer 10

bundles of mysoin
each protein contains two strands with a globular head (point toward middle) and elongated intertwined tail (point toward end of filament,) the head contains actin and ATP binding sites, also ATPase site where ATP attches and is split

Question 11

Thin filaments

Answer 11

bundles of actin
2 strands of actin protein twisted around each other to form a helical shape, G (globular)-actin is spherical and connects to form F (filamentous)-actin strands
associated regulatory proteins: tropomysin (short, thin twisted filament protein) and troponin (globular protein attached to tropomysin, contains Ca2+ binding site, covers myosin binding sites in non-contracting state)

Question 12

A band

Answer 12

-the central region of a sarcomere that contains the entire thick filament
-appears dark under a microscope
-does not change length during a contraction
-thin filaments partially overlap the thick filament on each end of the band

Question 13

H zone

Answer 13

-the central portion of the A band in a resting sarcomere
-does not have thin filament overlap
-during maximal muscle shortening this zone disappears when the thin filaments are pulled past thick filaments

Question 14

M line

Answer 14

-thin transverse protein meshwork structure in the center of the H zone
-attachment site for thick filaments, keeps them aligned

Question 15

Z discs

Answer 15

-at both ends of each sarcomere
-perpendicular to myofilaments and serve as anchors for the thin filaments
-appears zigzagged

Question 16

I bands

Answer 16

-extend form both directions of a Z disk and are bisected by the z disk
-contain only thin filaments
-appear light under a microscope
-at maximal muscle contraction, thin filaments are pulled parallel along thick filaments and I bands disappear

Question 17

synaptic knob

Answer 17

the expanded tip of an axon where it meets the sarcolemma
-cytosol houses synaptic vesicles filled with ACh (normally repelled from plasma membrane)
-Ca2+ pumps in plasma membrane establish a concentration gradient with Ca2+ outside of the cell
-when voltage-gated Ca2+ channels, also in plasma membrane, are opened Ca2+ flows down it’s concentration gradient, from interstitial fluid into the cell and triggers exocytosis of ACh from vesicles

Question 18

neuromuscular junction, definition and 3 parts

Answer 18

The specific location, usually mid-region of the skeletal muscle fiber, where it is innervated my a motor neuron
-synaptic knob
-synaptic cleft (houses AChE)
-motor end plate (of sarcolemma with folds/indentations to increase surface area)

Question 19

Describe a muscle fiber at rest

Answer 19

-the resting membrane potential of the sarcolemma is -90mV with more Na+ outside of the cell and K+ inside
-ACh receptors (chemically gated ion channels) within the motor end plate and the voltage gated Na+ channels and voltage gated K+ channels in the sarcolemma and T-tubules are closed
-Ca2+ ions are stored within the terminal cisternae of the sarcoplasmic reticulum
-contractile proteins of (myofilaments) within the sarcomeres are in their relaxed position

Question 20

myoglobin

Answer 20

molecule unique to muscle tissue
reddish globular protein similar to hemoglobin
binds oxygen when muscle at rest
releases it during muscular contraction
provides additional oxygen to enhance aerobic cellular respiration

Question 21

Three ways to generate ATP in skeletal muscle fiber

Answer 21

Immediate supply via phosphate transfer
Short-term supply via glycolysis (anaerobic energy production)
Long-term supply via aerobic cellular respiration

Question 22

creatine phosphate

Answer 22

molecule unique to muscle tissue
provides fibers means of supplying ATP anaerobically

Question 23

glycolysis

Answer 23

occurs in cytosol
does not require oxygen
glucose broken down into two pyruvate molecules
2 ATP released per glucose molecule
(pyruvate enters mitochondria for aerobic cellular respiration unless insufficient oxygen then converted to lactate)

Question 24

aerobic cellular respiration

Answer 24

Long-term supply of ATP
Fuel includes pyruvate, fatty acids and amino acids
Occurs within mitochondria
Requires oxygen
Pyruvate oxidized to carbon dioxide
Energy used to generate ATP
30 net ATP produced

Question 25

Oxygen debt

Answer 25

Amount of additional oxygen that must be inhaled following exercise Needed to restore pre-exercise conditions Additional oxygen required to -replace oxygen on hemoglobin and myoglobin -replenish glycogen -replenish ATP and creatine phosphate in phosphagen system -convert lactic acid back to glucose (in the liver)

Question 26

Slow oxidative fibers (type I fibers)

Answer 26

contains slow ATPase ATP supplied though aerobic cellular respiration can contract long periods of time without fatigue appear red due to large amounts of myoglobin (high percentage in postural muscles)

Question 27

Fast oxidative fibers (type II a fibers)

Answer 27

least numerous of types contain fast ATPase produce fast, powerful contraction primarily aerobic respiration, but delivery of oxygen lower

Question 28

Fast glycolytic fibers (type IIx, fast anaerobic fibers)

Answer 28

most common of types contain fast ATPase provide power and speed ATP primarily anaerobic (glycolysis) can contract only for short bursts appear white due to lack of myoglobin (high percentage in muscles of eye)

Question 29

Periods of a muscle twitch

Answer 29

Latent period (period after stimulus before contraction begins, time needed to initiate tension in fiber) Contraction period (begins as powerstrokes pull thin filaments, increasing muscle tension, shorter duration than relaxation period) Relaxation period (begins with release of crossbridges, decreasing muscle tension)

Question 30

Muscle Tension

Answer 30

Force generated when a skeletal muscle stimulated to contract

Question 31

Recruitment

Answer 31

Increase in number of motor units with increasing stimulus Helps explain how muscles can exert varying levels of force

Question 32

treppe

Answer 32

An increase in twitch tension when stimuli occur 10–20 times per second Voltage is the same for each stimulus and relaxation is complete for each twitch Twitches get stronger due to Insufficient time to remove all Ca2+ between twitches Increased heat improves enzyme efficiency

Question 33

wave summation

Answer 33

If stimulus frequency set at ~20 per/sec Relaxation is not completed between twitches Contractile forces add up to produce higher tensions

Question 34

Incomplete tetany

Answer 34

If frequency is increased further twitches partially fuse Sustained contraction in body

Question 35

Tetany

Answer 35

If frequency is increased further still (e.g., 40–50 per second) without relaxation leads to fatigue (decreased tension production)

Question 36

resting muscle tone

Answer 36

Resting tension in a muscle Generated by involuntary nervous stimulation of muscle Some motor units stimulated randomly at any time Change continuously so units not fatigued Tension called the resting muscle tone Do not generate enough tension for movement Decreases during deep sleep

Question 37

isometric contraction

Answer 37

Contraction of muscle and increased tension, but no movement Muscle length the same E.g., holding a weight while arm doesn’t move

Question 38

Isotonic contraction

Answer 38

Muscle movement Muscle length changes E.g., swinging a tennis racket

Question 39

concentric contraction

Answer 39

isontonic muscle shortens as it contracts e.g., in the biceps brachii when lifting a load

Question 40

eccentric contraction

Answer 40

concentric muscle lengthens as it contracts e.g., in the biceps brachii when lowering a load

Question 41

Hypertrophy

Answer 41

Increase in skeletal muscle size Results from repetitive stimulation of fibers Results in more mitochondria, larger glycogen reserves, increased ability to produce ATP, and more myofibrils that contain larger number of myofilaments

Question 42

Hyperplasia

Answer 42

increase in the number of muscle fibers may occur in a limited way with exercise

Question 43

Atrophy

Answer 43

decreasing muscle fiber size results from lack of exercise can arise from temporary reduction in muscle use e.g., individuals in a cast causes decrease in muscle tone and power initially reversible, but dead fibers not replaced with extreme atrophy, loss of muscle function permanent muscle replaced with connective tissue

Question 44

Cardiac Muscle Tissue

Answer 44

Cardiac muscle cells -arranged in thick bundles within heart wall -Short, thick, branching cells -one or two nuclei -striated and contain sarcomeres -have large numbers of mitochondria -use aerobic respiration -Intercalated discs-junctions joining cardiac cells, composed of desmosomes and gap junctions -Autorhythmic pacemaker-responsible for repetitious, rhymic heartbeat,stimulates cardiac muscle cells, rate and force of heartbeat controlled by autonomic nervous system

Question 45

Smooth Muscle Tissue -locations

Answer 45

Function by system,E.g., cardiovascular system,blood vessels regulating blood pressure and flow Respiratory system, bronchioles controlling amount of air in alveoli Digestive system, small and large intestines mixing and propelling materials Urinary system, ureters propelling urine from kidney to bladder Female reproductive system, uterus helping expel the baby And others, e.g., iris of the eye

Question 46

Smooth Muscle Tissue microscopic anatomy

Answer 46

Cell shape- Fusiform shaped,Central nucleus,Small (diameter up to 10 times smaller than skeletal muscle fiber, length thousands of times shorter) Endomysium wrapping around cell Cell characteristics: -Involuntary control by autonomic nervous system -Contracts in response to stretch -Transverse tubules absent -Sarcoplasmic reticulum sparse -Source of Ca2+ outside cell or from sarcoplasmic reticulum

Question 47

Smooth Muscle Tissue contraction

Answer 47

Contractile proteins actin and myosin oriented at oblique angles to longitudinal axis of cell, contraction causing a twisting motion No sarcomeres or Z discs contribute to “smooth” appearance Myofilaments have myosin heads along entire length can form additional crossbridges and can “latch on” to actin and remain attached without ATP termed latchbridge mechanism Have actin and tropomyosin, but no troponin Calcium from outside of cell and activates myosin heads through a calcium-calmodulin complex

Question 48

Controlling Smooth Muscle

Answer 48

Stimulated to contract by: stretch various hormones decreased pH lower oxygen concentration increased carbon dioxide levels certain drugs pacemaker cells in GI tract E.g., oxytocin causing contraction of smooth muscle cells in uterus