Chapter 10: Muscle Tissue Flashcards
Functions of skeletal muscle
- move the body
- maintain posture
- protect and support
- regulate elimination of materials
- produce heat
Characteristics of skeletal muscle
- excitability
- conductivity
- contractility
- extensibility
- elasticity
Organ
two or more types of tissue that work together to perform a specific function
Skeletal muscle
is an organ composed of muscle fibers, connective tissue layers, blood vessels, and nerves
3 layers of connective tissue layers of wrapping of a skeletal muscle
1- epimysium
2- perimysium
3- endomysium
Epimysium
dense irregular connective tissue wraps whole muscle
Perimysium
dense irregular connective tissue wraps fascicle; many blood vessels/nerves
Endomysium
areolar connective tissue wraps individual fiber; electrical insulation, capillary support, binding of neighboring cells
Tendon
cordlike structure of dense regular connective tissue
Aponeurosis
flattened sheet of dense irregular connective tissue
Deep fascia
separates individual muscles
Superficial fascia
separates muscles from skin
Know the structural organization of skeletal muscle
Is skeletal muscle vascularized?
yes, highly
Is skeletal muscle innervated? If so, by what?
yes, by somatic motor neurons
Somatic motor neurons
extend from the brain and spinal cord to skeletal muscle fibers
Axon
nerve fiber
Sarcoplasm
cytoplasm in skeletal muscle fibers
Multinucleated
multiple nuclei
Myoblasts
groups of embryonic muscle cells that fuse to form single skeletal muscle fibers during development
Satellite cells
adult stem cells
Know the development of skeletal muscle
Structure and organization of a skeletal muscle fiber
Sarcolemma
plasma membrane of a skeletal muscle fiber
T-tubules (transverse tubules)
deep invaginations within the sarcolemma that extend into the skeletal muscle fiber as a network of narrow, membranous tubules to the sarcoplasmic reticulum
Myofibrils
protein myofilaments surrounded by sarcoplasmic reticulum and extend the length of muscle fiber
Sarcoplasmic reticulum
an internal membrane complex that is similar to smooth ER in other cells; contains calcium pumps that release Ca2+ into the sarcoplasm
Terminal cisternae
enlarged calcium ion reservoirs
Triad
2 cisternae with a T-tubule in between
Myofilaments
contractile proteins within myofibrils;
2 types:
1- thick filaments
2- thin filaments
Thick filaments
consist of bundles of ONLY myosin protein strands; each strand with a globular head and elongated tail
Thin filaments
twisted strands of actin protein; F-actin (filamentous) composed of G-actin (globular); G-actin has a myosin binding site; tropomyosin and troponin placed along F-actin strand
Tropomyosin
short, thin, twisted filament that is a “stringlike” protein
Troponin
globular, or “ball-like”, protein attached to tropomyosin; contains the binding site for Ca2+
Sarcomeres
myofilaments arranged in repeating units
Z discs
composed of specialized proteins that are positioned perpendicular to the myofilaments and serve as anchors for the thin filaments
I bands
light-appearing regions that contain only thin filaments and Z disc; get smaller when muscle contracts (can disappear with maximal contraction)
A band
a dark-appearing region that contains thick filaments and overlapping thin filaments; contains H zone and M line; makes up general region of sarcomere
H zone
central portion of A band; only thick filaments; disappears with maximal muscle contraction
M line
middle of H zone and centermost region of A band; attachment site for thick filaments
Molecular structure of thick and thin filaments
Structure of a sarcomere
Striations
repeating light and dark bands of the overlapping myofilaments that form unique striped patterns within the skeletal muscle fiber
Connectin
stabilizes thick filaments from Z disc to M line; has spring like properties (passive tension)
Dystrophin
links internal myofilament proteins to external proteins; anchors some myofibrils to sarcolemma proteins; abnormalities of this protein cause muscular dystrophy
Myoglobin
within cells allow storage of oxygen used for aerobic ATP production; unique to muscle tissue; binds oxygen when muscle is at rest
Glycogen
stored for when fuel is needed quickly (storage form of glucose)
Creatinine phosphate
can quickly give up its phosphate group to help replenish ATP supply; unique to skeletal muscle tissue; anaerobic
Motor unit
a motor neuron and all the muscle fibers it controls
Neuromuscular junction
location where motor neuron innervates muscle; site of communication between motor neuron and motor end plate of muscle
Structure of a motor unit
Structure and organization of a neuromuscular junction
Smaller motor units
have less than five muscle fibers and allow for precise control of smaller force output
Large motor units
have thousands of muscle fibers and allow for production of large amounts of force but not precise control
Synaptic knob
houses synaptic vesicles with acetylcholine (ACh); calcium pumps establish calcium gradient, with more outside the neuron
Motor end plate
specialized region of sarcolemma with numerous folds; has many ACh receptors which are opened by binding of ACh and allow Na+ entry and K+ exit
Synaptic cleft
separates the synaptic knob from the motor end plate; acetylcholinesterase (AChE) resides here and is an enzyme that breaks down ACh molecules
Muscle fibers exhibiting RMP
RMP inside the cell is -90mV compared to fluid outside the cell; threshold potential is -65mV
Skeletal muscle fiber at rest
End-plate potential (EPP)
the minimum voltage change (or threshold) in the motor end plate that can trigger opening of voltage-gated channels in the sarcolemma to initiate an action potential
Excitation of a skeletal muscle
1- binding of ACh at the motor end plate
2- excitation-contraction coupling
3- sarcomere: cross-bridge cycling
Events in skeletal muscle contraction
Neuromuscular junction: excitation of a skeletal muscle tissue
Sarcolemma, t-tubules, and sarcoplasmic reticulum: excitation-contraction coupling
Sarcomere: cross-bridge cycling
Depolarization
the reversal in polarity at the sarcolemma (- to +)
Repolarization
changes the membrane potential from positive to negative
Refractory period
the muscle cannot be stimulated
Crossbridge cycling
multiple repetitions to attach, pull, release, and reset lead to fully contracted sarcomere
Power stroke
when the myosin head swivels
Tetanus
overstimulation of a muscle that leads to spastic paralysis
Botulism
muscular paralysis caused by a toxin that’s ingested
Sarcomere shortening
3 ways to generate additional ATP in skeletal muscle
1- creatine phosphate
2- glycolysis
3- aerobic cellular respiration
Creatine phosphate
(Phosphagen System)
- unique to skeletal muscles
- high-energy bond found between creatine and phosphate
- phosphate can be transferred to ADP to form ATP
-catalyzed by creatine kinase
Glycolysis (Anaerobic Cellular Respiration)
- occurs in cytosol
- does not require oxygen
- glucose is converted to 2 pyruvate molecules
- 2 ATP released per glucose molecule
Aerobic Cellular Respiration
- makes the most ATP supply
- requires oxygen
- occurs within mitochondria
- pyruvate (from Glycolysis) broken down
- produces approximately 34 ATP
- triglycerides and amino acids can also be used as fuel to produce ATP
Metabolic processes for generating ATP
Lactate formation
pyruvate converted to lactate when O2 is low; lactate can be used as fuel by skeletal muscle fiber
Utilization of energy sources
Oxygen debt
amount of additional O2 needed after exercise to restore pre-exercise conditions
Additional oxygen required to
- replace O2 on hemoglobin and myoglobin
- replenish glycogen
- replenish ATP and creatine phosphate
- convert lactic acid back to glucose
Skeletal muscle fibers classified based on:
- type of contraction generated
- means for supplying ATP
Type of contraction generated
- power: related to the diameter of muscle fiber
- speed and duration
- fast-twitch fibers are more powerful and have quicker and briefer contractions than slow-twitch fibers
Speed and duration related to
- type of myosin ATPase
- quickness of action potential propagation
- quickness of Ca2+ reuptake by sarcoplasmic reticulum
Skeletal fibers classified based on means for supplying ATP
- oxidative fibers (fatigue resistant)
- glycolytic fibers (fatigable)
Oxidative fibers
use aerobic cellular respiration; have extensive capillaries, many mitochondria, lots of myoglobin
Glycolytic fibers
use anaerobic cellular respiration; have fewer capillaries, fewer mitochondria, fewer myoglobin, and large glycogen reserves
3 types of skeletal muscle fibers
1- slow oxidative (SO) fibers (type I)
2- fast oxidative (FO) fibers (type IIa, intermediate)
3- fast glycolytic (FG) fibers (type IIx, fast anaerobic)
Slow oxidative (SO) fibers
- contractions= slower and less powerful
- high endurance since ATP supplied aerobically
- slender, red in color due to myoglobin
Fast oxidative (FO) fibers
- contractions= fast and powerful
- primarily aerobic respiration
- intermediate size, light red color
Fast glycolytic (FG) fibers
- contractions= fast and powerful
- contractions are brief, as ATP production is primarily anaerobic
- thick, white in color due to lack of myoglobin
- most common type
Hand muscles
have high percentage of fast glycolytic fibers for quickness
Sprinters
have higher percentage of fast glycolytic fibers (fatigable)
Back muscles
have high percentage of slow oxidative fibers to continually maintain postural support
Long-distance runners
have higher proportion of slow-oxidative fibers (endurance) in legs
Muscle tension
force generated when a muscle is stimulated to contract (twitch)
Muscle twitch
a single, brief contraction from a single stimulus
Threshold
the minimum voltage needed to stimulate the skeletal muscle to generate a twitch
Latent period
time after stimulus, but before contraction begins; no change in tension
Contraction period
time when tension is increasing; begins during power strokes as thick pulls thin filaments
Relaxation period
time when tension is decreasing; begins with release of cross-bridges; generally, lasts a little longer than a contraction period
Muscle twitch
Recruitment (Multiple Motor Unit Summation)
- muscle is stimulated repeatedly
- as voltage increases, more units are recruited to contract
- muscles can exhibit varying degrees of force
- above a certain voltage, all units are recruited and maximum contraction occurs
- a muscle relaxes completely before the next contraction
Treppe
increase in contraction strength
Wave summation
occurs when stimulations are delivered to a muscle fiber faster than it is able to completely relax
if stimulus frequency is set at about 20 per second,
- relaxation is not completed between twitches
- contractile forces add up to produce higher tensions
Incomplete tetany
if frequency is increased further; tension increases and twitches overlap
Tetany
if frequency is increased further still; tension is a smooth line, without relaxation; high frequency stimuli lead to fatigue
Fatigue
no tension production
Skeletal muscle response to change in stimulus intensity
Skeletal muscle response to change in stimulus frequency
Muscle tone
the amount of tension in muscle
Resting muscle tone
random contraction of small numbers of motor units causes the skeletal muscle to develop tension
Isometric contraction
although tension increases (force), it’s still less than the resistance (weight); muscle length stays the same
Isotonic contraction
when skeletal muscle tension results in movement of the muscle; the tone of the muscle remains the same but the length changes
Isometric vs. Isotonic contraction
Fiber at shortened length (contracted) generates
weaker force; filament movement is limited (already close to Z disc)
Fiber at resting length generates
maximum contractile force; optimal overlap of thick and thin filaments
Fiber at extended length (stretched) generates
weaker force; minimal thick and thin filaments overlap for cross-bridge formation
Concentric contraction
the shortening of muscle length
Eccentric contraction
lengthening of muscle
Muscle length and tension relationship during muscle contraction
Length-tension curve
Maximizing force of contraction
Muscle fatigue
- reduced ability to produce muscle tension
- primarily caused by a decrease in glycogen stores during prolonged exercise
- insufficient Ca2+ to enter synaptic knob
- decreased number of synaptic vesicles
- altered ion concentrations impair action potential conduction and Ca2+ release from sarcoplasmic reticulum
- less Ca2+ available for troponin
Changes in muscle from a sustained exercise program
- endurance exercise leads to better ATP production
- resistance exercise leads to hypertrophy; limited amount of hyperplasia (increased number of fibers)
Changes in muscle from lack of exercise
atrophy= decrease in size due to lack of use
Fibrosis
muscle mass is often replaced by adipose connective tissue and dense regular connective tissue; decreased flexibility
Loss of muscle mass with age
- slow loss begins in a person’s mid-30s due to a decrease in activity
- decreased size, power, and endurance of skeletal muscle
- loss in fiber number and diameter
decreased oxygen storage capacity - decreased circulatory supply to muscles with exercise
Cardiac muscle tissue
- individual muscle cells arranged in thick bundles within the heart wall
- has one or two nuclei
- have large numbers of mitochondria and use aerobic respiration
- autorhythmic pacemaker that stimulates cardiac muscle cells
- branching cells
Intercalated discs
individual cells are joined to adjacent muscle cells at these specialized junctions
Smooth muscle tissue
found in organs of many body systems:
- cardiovascular system= blood vessels
- respiratory system= bronchioles
- digestive system= small & large intestine
- urinary system= ureters
- female reproductive system= uterus
- others= iris of the eye
Smooth muscle cell shape
- fusiform
- central nucleus
- small
Smooth muscle cell characteristics
- sarcolemma with various types of Ca2+ channels
- transverse tubules absent
- sarcoplasmic reticulum sparse
Smooth muscle arrangement of anchoring proteins and contractile proteins
- dense bodies
- dense plaques
