lemastm/Teaching/BI234/Chapter 09... · Muscle Tissue Muscle – “little ... Involuntary...
Transcript of lemastm/Teaching/BI234/Chapter 09... · Muscle Tissue Muscle – “little ... Involuntary...
1
Page 1
Chapter 9:
Muscle Tissue
Muscle – “little mouse”
Types of Muscle Tissue:
Chapter 9: Muscular System
Characteristics:
Composes heart wall
Involuntary control
Striated / uni-nucleated
Characteristics:
Attaches to skeleton
Voluntary control
Striated / multi-nucleated
Characteristics:
Lines visceral organs
Involuntary control
Non-striated / uni-nucleated
Skeletal Muscle Cardiac Muscle Smooth Muscle
Characteristics of Muscle:
1) Excitability: Ability to respond to stimulation
2) Contractility: Ability to shorten forcefully
3) Extensibility: Ability to stretch and still contract
4) Elasticity: Ability to resume resting length after contraction
Function of Muscle:
Prune Belly
Syndrome
4) Guard entrance / exit (e.g., lips / anus)
3) Support soft tissue (e.g., abdominal wall)
2) Maintain posture / body position
• Locomotion / manipulation (skeletal)
• Blood pressure (cardiac)
• Propulsion (smooth)
1) Produce movement
6) Store nutrients (e.g., glycogen)
5) Maintain body temperature (e.g., shivering)
Chapter 9: Muscular System
2
Page 2
Gross Anatomy of Muscle: Connective Tissue Layers:
• Outside muscle covering
• Form tendons
1) Epimysium:
• Divides muscle into fascicles
Compartments
• Contains blood vessels / nerves
2) Perimysium:
• Surrounds individual muscle fibers
and ties them together
3) Endomysium:
Connective Components:
A) Tendons (cords)
B) Aponeuroses (sheets)
C) Fascia (wrap / bind body)
• Satellite cells (stem cells)
Endomysium
Perimysium
Epimysium
Marieb & Hoehn – Figure 9.1
Chapter 9: Muscular System
Similar to Marieb & Hoehn – Figure 9.5
Microanatomy of Muscle:
Sarcolemma: Cell membrane
Transverse Tubules: Network of passageways through fiber
• Continuous with outside of cell
Sacroplasmic Reticulum: Specialized endoplasmic reticulum
• Contain calcium ions (Ca++) – [40,000x] compared to cytoplasm
Muscle Fiber (cell):
Functional Unit of Muscle
Sarcoplasma: Cytoplasm
Triad
Chapter 9: Muscular System
Myofibrils: Cylindrical structures containing contractile fibers
3
Page 3
Microanatomy of Muscle:
Myofibrils contain myofilaments (protein):
1) Actin (Thin filament)
2) Myosin (Thick filament)
Sarcomere: Repeating units of myofilaments
Myosin Actin
Sarcomere
Z line M line I Band
A Band
(~ 10,000 / myfilament)
Chapter 9: Muscular System
Similar to Marieb & Hoehn – Figure 9.6
Microanatomy of Muscle:
Chapter 9: Muscular System
Interactions between the thick and thin filaments of sarcomeres are
responsible for muscle contraction
Microanatomy of Muscle:
Sliding Filament
Theory
Thick filaments:
• Composed of many myosin molecules
Tails: Attach molecules together
Heads: Bind with thin filament
Hinge
Chapter 9: Muscular System
4
Page 4
Interactions between the thick and thin filaments of sarcomeres are
responsible for muscle contraction
Microanatomy of Muscle:
Sliding Filament
Theory
Thick filaments:
• Composed of many myosin molecules
Tails: Attach molecules together
Heads: Bind with thin filament
Thin filaments:
• Composed of interwoven actin molecules
Tropomyosin: Cover active sites
Troponin: Bind tropomyosin to actin
Chapter 9: Muscular System
Interactions between the thick and thin filaments of sarcomeres are
responsible for muscle contraction
Microanatomy of Muscle:
Sliding Filament
Theory
Chapter 9: Muscular System
Sarcoplasmic Reticulum
Ca++ Ca++ Ca++
Ca++ Ca++ Ca++ Ca++ Ca++
Ca++ Ca++ Ca++ Ca++
Neuromuscular Junction:
• Neuron Muscle fiber
• 1 connection / muscle fiber
Sarcolemma
Sarcoplasm
T-tubule
Synaptic
Knob
Neuron
Motor End Plate
Muscle Contraction Events:
1) Acetylcholine (ACh - neurotransmitter)
released from synaptic knob
ACh ACh ACh
2) ACh binds to receptors on motor end
plate; generates action potential
3) Action potential (AP - electrical impulse)
conducted along sarcolemma
Sarcomere of
myofibril
Chapter 9: Muscular System
5
Page 5
Sarcoplasmic Reticulum
Ca++ Ca++ Ca++
Ca++ Ca++ Ca++ Ca++ Ca++
Ca++ Ca++ Ca++ Ca++
Neuromuscular Junction:
• Neuron Muscle fiber
• 1 connection / muscle fiber
Sarcolemma
Sarcoplasm
T-tubule
Synaptic
Knob
Neuron
Motor End Plate
ACh ACh ACh
4) AP descends into muscle fiber via
T-tubules
Ca++ Ca++ Ca++ Ca++ Ca++
5) AP triggers release of Ca++ from
sarcoplasmic reticulum
6) Ca++ initiates cross-bridging (actin / myosin) Sarcomere of
myofibril
Chapter 9: Muscular System
Muscle Contraction Events:
1) Ca++ binds with troponin; exposes
active sites on actin
Cross-Bridging in Action:
Chapter 9: Muscular System
Cross-bridging Events:
Troponin
Actin
Tropomyosin
Myosin
Head
Ca++
6
Page 6
Cross-bridging Events:
1) Ca++ binds with troponin; exposes
active sites on actin
2) Myosin head (cocked) binds with
active site
3) Myosin head pivots – pulls actin
forward
Cross-Bridging in Action:
Chapter 9: Muscular System
1) Ca++ binds with troponin; exposes
active sites on actin
2) Myosin head (cocked) binds with
active site
3) Myosin head pivots – pulls actin
forward
4) ATP binds to myosin head; head
detaches and re-cocks
Cross-Bridging in Action:
Chapter 9: Muscular System
Cross-bridging Events:
7
Page 7
ATP
ATP ATP
ADP
P
Re-cock
1) Ca++ binds with troponin; exposes
active sites on actin
2) Myosin head (cocked) binds with
active site
3) Myosin head pivots – pulls actin
forward
4) ATP binds to myosin head; head
detaches and re-cocks
5) Myosin head binds to active site;
Process repeated
Cross-Bridging in Action:
Chapter 9: Muscular System
Cross-bridging Events:
ATP
ATP
ADP
P
Re-cock
ATP
ADP
P
Re-cock ATP
8
Page 8
1) Ca++ binds with troponin; exposes
active sites on actin
2) Myosin head (cocked) binds with
active site
3) Myosin head pivots – pulls actin
forward
4) ATP binds to myosin head; head
detaches and re-cocks
5) Myosin head binds to active site;
Process repeated
6) Process ends when APs cease
• Ca++ returned to sarcoplasmic
reticulum (active transport)
• ACh broken down by
acetylcholinesterase (AChE)
Cross-Bridging in Action:
Chapter 9: Muscular System
Cross-bridging Events:
Martini & Nath – Table 10.1
• Rigor Mortis • Tetanus
Chapter 9: Muscular System
What Regulates Muscle Tension Production?
A) Single Fiber:
• Tension Production = # of cross-bridge attachments
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
• All-or-none response (muscle “on” or “off”)
Too contracted = no room for movement; poor
cross-bridge formation
Too stretched = no cross-bridge
formation
Resting length = # of cross-bridges;
distance to slide
(maximal muscle force;
normal resting length)
Chapter 9: Muscular System
9
Page 9
What Regulates Muscle Tension Production?
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
B) Whole Muscle:
• Tension Production = 1) Frequency of stimulation
2) # of muscle fibers activated
Chapter 9: Muscular System
What Regulates Muscle Tension Production?
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
B) Whole Muscle – Frequency of stimulation:
Twitch = Single stimulus-contraction-relaxation sequence
Ten
sio
n
Time
Stim
ulu
s
Latent Period:
Time between stimulus
and tension development
LP
Ca++ release;
cross-bridge formation
Ca++ uptake;
cross-bridge detachment
CP
Contraction Phase:
Period where tension
rises to peak level
RP
Relaxation Phase:
Period where tension
falls to resting level
Chapter 9: Muscular System
What Regulates Muscle Tension Production?
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
B) Whole Muscle – Frequency of stimulation:
Twitch = Single stimulus-contraction-relaxation sequence
Martini & Nath – Figure 10.15
Twitches alone are not
a useful contraction
Variation exists in the
duration of twitches
among muscles
Chapter 9: Muscular System
10
Page 10
What Regulates Muscle Tension Production?
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
B) Whole Muscle – Frequency of stimulation:
Incomplete Tetanus: Rapid cycles of contraction & relaxation Ten
sio
n
Time
Stim
ulu
s
Maximum
Tension
Summation:
Addition of twitches to
produce a more powerful
contraction
Chapter 9: Muscular System
What Regulates Muscle Tension Production?
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
B) Whole Muscle – Frequency of stimulation:
Ten
sio
n
Time
Complete Tetanus: Rapid stimulation erases relaxation phase
Stim
ulu
s
Maximum
Tension
SR can not reclaim Ca++
(stimulation too rapid)
Most normal muscle contraction
involves complete tetanus
Chapter 9: Muscular System
What Regulates Muscle Tension Production?
Muscle Tension: Force exerted on an object by a contacting muscle
Muscle Mechanics:
B) Whole Muscle – Number of muscle fibers activated:
Motor Unit: A single motor neuron and all the muscle fibers innervated by it
All-or-none
response
Recruitment:
Addition of motor units to produce
smooth, steady muscle tension (small large motor units)
Muscle Tone:
Resting tension maintained in muscle
Motor unit size dictates control:
• Fine Control = 1-5 fibers / MU (e.g., eye)
• Gross Control = 1000’s fibers / MU (e.g., leg)
Chapter 9: Muscular System
Similar to Marieb & Hoehn – Figure 9.13
11
Page 11
Types of Muscle Contractions:
Isometric Contraction:
(e.g., pushing against wall / standing)
Tension maximized; no muscle shortening
Isotonic Contraction:
Tension stabilized; muscle shortens
(e.g., lifting / walking)
Similar to Marieb & Hoehn – Figure 9.18
Muscle Elongation (following contraction):
• Passive process:
1) Elastic rebound (fibers / organelles)
2) Antagonistic muscles (e.g., biceps brachii vs. triceps brachii)
Chapter 9: Muscular System
• Muscle fibers use ATP for contraction (~ 600 trillion / second)
How does a fiber replenish ATP?
1) Creatine phosphate (CP) reserves: high energy
• Nitrogen-containing compound bound to phosphate
ATP
ADP CP ADP
ATP
Converted to
creatine
Creatine
kinase
• Limited supply
• Replaced by aerobic / anaerobic respiration
• Only enough reserve to sustain short contraction periods (~ 5 sec)
• Must be replenished to sustain contraction
Muscle Energetics:
Chapter 9: Muscular System
ATP ADP + P
Creatine
Phosphate
15 seconds
Chapter 9: Muscular System
12
Page 12
• Muscle fibers use ATP for contraction (~ 600 trillion / second)
How does a fiber replenish ATP?
ATP
ADP ADP
ATP
• Only enough reserve to sustain short contraction (~ 2 sec)
• Must be replenished to sustain contraction
Muscle Energetics:
2) Anaerobic Metabolism (Glycolysis):
Glucose
Pyruvate
Lactate
(Glycogen) • Primary source of ATP during times of peak activity
• Inefficient (2 ATP / glucose)
• Acid buildup leads rapidly to muscle fatigue
Chapter 9: Muscular System
ATP ADP + P
Creatine
Phosphate
15 seconds
Anaerobic
Respiration
1 - 2 minutes
Chapter 9: Muscular System
• Muscle fibers use ATP for contraction (~ 600 trillion / second)
How does a fiber replenish ATP?
ATP
ADP ADP
ATP
• Only enough reserve to sustain short contraction (~ 2 sec)
• Must be replenished to sustain contraction
Muscle Energetics:
Glucose
Pyruvate
CO2 + H2O
(Glycogen)
3) Aerobic Metabolism (Aerobic Respiration):
• Primary source of ATP during periods of rest (95% of ATP)
• Efficient (36 ATP / glucose)
• Can use multiple energy sources (carbohydrates, lipids, proteins)
Chapter 9: Muscular System
13
Page 13
ATP ADP + P
Creatine
Phosphate
15 seconds
Anaerobic
Respiration
1 - 2 minutes Weeks
Aerobic
Respiration
Chapter 9: Muscular System
Energy Use at Different Levels of Activity:
• Aerobic metabolism predominates
• Fuel = Fatty acids
• ATP surplus: 1) Glycogen reserves
2) Recharge CP
At Rest:
Chapter 9: Muscular System
Energy Use at Different Levels of Activity:
• Aerobic metabolism predominates
• Fuel = Glycogen
• ATP required for muscle contraction
At Moderate Activity:
Chapter 9: Muscular System
14
Page 14
Energy Use at Different Levels of Activity:
• Anaerobic metabolism predominates
• Fuel = Glycogen
• ATP required for muscle contraction
• ATP acquired from CP (initially)
At Peak Activity:
Chapter 9: Muscular System
Muscle Fatigue: Fibers lose ability to contract despite neural stimulation
Decoupling of electrical
signaling and muscle contraction
Low Intensity Activity:
Fatigue = Energy reserves depleted
Energy reserves include
glycogen, lipids, proteins
Muscle Recovery: Return of fibers to pre-activity conditions
A) Lactate removed (blood liver) or recycled (glycogen)
B) Aerobic respiration replenishes energy reserves
• Oxygen debt: Amount of oxygen needed to restore body to
pre-activity conditions
• Muscle fibers, liver, sweat glands
C) Excess heat is lost via blood flow to skin
Process can take days to weeks…
High Intensity Activity:
Fatigue = Ionic imbalances
Chapter 9: Muscular System
Muscle Performance: Power:
Maximum amount of tension
produced by a muscle
Endurance: Amount of time a muscle
can perform an activity
Factors Determining Muscle Performance:
1) Muscle Fiber Type:
vs.
• Contract in 0.01 s or less (after stimulation)
• Large diameter (densely packed myofibrils)
• Rely on anaerobic respiration
• Large glycogen reserves
• Fatigue rapidly
A) Fast Fibers (most common)
• 3x slower contract; ½ the diameter
• Powerful ( sarcomere # = tension)
• Sustained contractions ( endurance)
• Rely on aerobic metabolism:
• Extensive capillaries ( O2 supply)
• Myoglobin: Binds O2 ( O2 storage)
• Large # of mitochondria ( O2 usage)
B) Slow Fibers
Chapter 9: Muscular System
15
Page 15
The distribution of muscle fibers impacts muscle performance:
White Muscle:
Muscle dominated by fast fibers (e.g., turkey breast)
Red Muscle:
Muscle dominated by slow fibers (e.g., turkey leg)
(Genetically determined)
Human muscles a mixture of the
two fiber types
Fast Fibers Slow Fibers
Marathoners 18% 82%
Avg. Human 55% 45%
Sprinters 64% 37%
Chapter 9: Muscular System
Physical Conditioning:
1) Anaerobic Endurance
• Sustained, powerful muscle contractions (e.g., weight lifting)
• Training = Frequent, brief, intense workouts
• Muscle Hypertrophy: Enlargement of muscle
2) Aerobic Endurance
• Continual contraction of muscle over time (e.g., jogging)
• Training = Sustained low levels of muscle activity
• muscle fiber size, not overall #
• mitochondria; capillaries
Chapter 9: Muscular System
Cardiac Muscle: Skeletal Muscle: Smooth Muscle: Property
Filament
Organization
Control
Mechanism
Calcium
Source
Contraction
Energy Source
Sarcomeres along
myofibrils
Sarcomeres along
myofibrils Scattered in
sarcoplasm
Neural Automaticity (pacemaker cells)
Automaticity,
neural, hormonal
Sarcoplasmic
reticulum
SR / across
sarcolemma
Across
sarcolemma
Rapid onset;
tetanus can occur;
rapid fatigue
Slower onset;
no tetanus;
fatigue-resistant
Slow onset;
tetanus can occur;
fatigue-resistant
Aerobic / Anaerobic
metabolism
Aerobic
metabolism
Aerobic
metabolism