Download Lecture #7 Muscles 10/31/12

Muscle
 Lecture #10 Ch 10 Muscle
Muse 10/31/12
An Introduction to Muscle Tissue
 Muscle Tissue
 A primary tissue type, divided into
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
Functions of Skeletal Muscles
 Produce skeletal movement
 Maintain body position
 Support soft tissues
 Guard openings
 Maintain body temperature
 Store nutrient reserves
Skeletal Muscle Structures
 Muscle tissue (muscle cells or fibers)
 Connective tissues
 Nerves
 Blood vessels
Skeletal Muscle Structures
 Organization of Connective Tissues
 Muscles have three layers of connective tissues
 Epimysium:
– exterior collagen layer
– connected to deep fascia
– Separates muscle from surrounding tissues
 Perimysium: (not to be confused with paramecium)
– surrounds muscle fiber bundles (fascicles)
– contains blood vessel and nerve supply to fascicles
 Endomysium:
– surrounds individual muscle cells (muscle fibers)
– contains capillaries and nerve fibers contacting muscle cells
– contains myosatellite cells (stem cells) that repair damage
Skeletal Muscle Structures
Figure 10–1 The Organization of Skeletal Muscles.
Epimysium
Bone
Epimysium
Perimysium
Endomysium
Tendon
Muscle fiber
in middle of
a fascicle
(b)
Blood vessel
Fascicle
(wrapped by perimysium)
Endomysium
(between individual
muscle fibers)
(a)
Perimysium
Fascicle
Muscle fiber
Figure 9.1
Skeletal Muscle Structures
 Organization of Connective Tissues
 Muscle attachments
 Endomysium, perimysium, and epimysium come
together:
– at ends of muscles
– to form connective tissue attachment to bone matrix
– i.e., tendon (bundle) or aponeurosis (sheet)
Skeletal Muscle Structures
 Nerves
 Skeletal muscles are voluntary muscles, controlled by
nerves of the central nervous system (brain and
spinal cord)
 Blood Vessels
 Muscles have extensive vascular systems that
 Supply large amounts of oxygen
 Supply nutrients
 Carry away wastes
Skeletal Muscle: Attachments
 Muscles attach:
 Directly—epimysium of muscle is fused to the
periosteum of bone or perichondrium of
cartilage
 Indirectly—connective tissue wrappings
extend beyond the muscle as a ropelike
tendon or sheetlike aponeurosis
Skeletal Muscle Fibers
 Are very long
 Develop through fusion of mesodermal
cells (myoblasts)
 Become very large
 Contain hundreds of nuclei
Skeletal Muscle Fibers
Figure 10–2 The Formation of a Multinucleate Skeletal Muscle Fiber.
Skeletal Muscle Fibers
Figure 10–2a The Formation of a Multinucleate Skeletal Muscle Fiber.
Skeletal Muscle Fibers
Figure 10–2b The Formation of a Multinucleate Skeletal Muscle Fiber.
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 The sarcolemma
 The cell membrane of a muscle fiber (cell)
 Surrounds the sarcoplasm (cytoplasm of muscle
fiber)
 A change in transmembrane potential begins
contractions
Sarcolemma
Mitochondrion
Myofibril
Dark A band
Light I band
Nucleus
(b) Diagram of part of a muscle fiber showing the myofibrils. One
myofibril is extended afrom the cut end of the fiber.
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Transverse tubules (T tubules)
 Transmit action potential through cell
 Allow entire muscle fiber to contract
simultaneously
 Have same properties as sarcolemma
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Myofibrils
 Lengthwise subdivisions within muscle fiber
 Made up of bundles of protein filaments
(myofilaments)
 Myofilaments are responsible for muscle
contraction
 Types of myofilaments:
– thin filaments:
» made of the protein actin
– thick filaments:
» made of the protein myosin
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcoplasmic reticulum (SR)
 A membranous structure surrounding each
myofibril
 Helps transmit action potential to myofibril
 Similar in structure to smooth endoplasmic
reticulum
 Forms chambers (terminal cisternae) attached to
T tubules
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Triad
 Is formed by one T tubule and two terminal
cisternae
 Cisternae:
– concentrate Ca2+ (via ion pumps)
– release Ca2+ into sarcomeres to begin muscle
contraction
Skeletal Muscle Fibers
Figure 10–3 The Structure of a Skeletal Muscle Fiber.
Show video excitation coupling
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 The contractile units of muscle
 Structural units of myofibrils
 Form visible patterns within myofibrils
 Muscle striations
 A striped or striated pattern within myofibrils:
– alternating dark, thick filaments (A bands) and light, thin
filaments (I bands)
Sarcomere
 Smallest contractile unit (functional unit) of
a muscle fiber
 The region of a myofibril between two
successive Z discs
 Composed of thick and thin myofilaments
made of contractile proteins
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 M Lines and Z Lines:
– M line:
» the center of the A band
» at midline of sarcomere
– Z lines:
» the centers of the I bands
» at two ends of sarcomere
Thin (actin)
filament
Thick (myosin)
filament
Z disc
I band
H zone
A band
Sarcomere
Z disc
I band
M line
(c) Small part of one myofibril enlarged to show the myofilaments
responsible for the banding pattern. Each sarcomere extends from
one Z disc to the next.
Sarcomere
Z disc
M line
Z disc
Thin (actin)
filament
Elastic (titin)
filaments
Thick
(myosin)
filament
(d) Enlargement of one sarcomere (sectioned lengthwise). Notice the
myosin heads on the thick filaments.
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 Zone of overlap:
– the densest, darkest area on a light micrograph
– where thick and thin filaments overlap
 The H Band:
– the area around the M line
– has thick filaments but no thin filaments
Skeletal Muscle Fibers
 Internal Organization of Muscle Fibers
 Sarcomeres
 Titin:
– are strands of protein- quite elastic, like
springs
– reach from tips of thick filaments to the Z line
– stabilize the filaments
Skeletal Muscle Fibers
Figure 10–4a Sarcomere Structure.
Skeletal Muscle Fibers
Figure 10–4b Sarcomere Structure.
Skeletal Muscle Fibers
Figure 10–5 Sarcomere Structure.
Skeletal Muscle Fibers
Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.
Skeletal Muscle Fibers
Figure 10–6 Levels of Functional Organization in a Skeletal Muscle.
Skeletal Muscle Fibers
 Sarcomere Function
 Transverse tubules encircle the sarcomere
near zones of overlap
 Ca2+ released by SR causes thin and thick
filaments to interact
Skeletal Muscle Fibers
 Muscle Contraction
 Is caused by interactions of thick and thin
filaments
 Structures of protein molecules determine
interactions
Skeletal Muscle Fibers
 Four Thin Filament Proteins
 F-actin (Filamentous actin)
 Is two twisted rows of globular G-actin
 The active sites on G-actin strands bind to myosin
 Nebulin
 Holds F-actin strands together
 Tropomyosin
 Is a double strand
 Prevents actin–myosin interaction
 Troponin
 A globular protein
 Binds tropomyosin to G-actin
 Controlled by Ca2+
Skeletal Muscle Fibers
Figure 10–7a, b Thick and Thin Filaments.
Skeletal Muscle Fibers
 Initiating Contraction
 Ca2+ binds to receptor on troponin molecule
 Troponin–tropomyosin complex changes
 Exposes active site of F-actin
Skeletal Muscle Fibers
 Thick Filaments
 Contain twisted myosin subunits
 Contain titin strands that recoil after
stretching
 The mysosin molecule
 Tail:
– binds to other myosin molecules
 Head:
– made of two globular protein subunits
– reaches the nearest thin filament
Skeletal Muscle Fibers
Figure 10–7c, d Thick and Thin Filaments.
Skeletal Muscle Fibers
 Myosin Action
 During contraction, myosin heads
 Interact with actin filaments, forming cross-bridges
 Pivot, producing motion
Skeletal Muscle Fibers
 Skeletal Muscle Contraction
 Sliding filament theory
 Thin filaments of sarcomere slide toward M line,
alongside thick filaments
 The width of A zone stays the same
 Z lines move closer together
Skeletal Muscle Fibers
Figure 10–8a Changes in the Appearance of a Sarcomere during the
Contraction of a Skeletal Muscle Fiber.
Skeletal Muscle Fibers
Figure 10–8b Changes in the Appearance of a Sarcomere during the
Contraction of a Skeletal Muscle Fiber.
Skeletal Muscle Fibers
 Skeletal Muscle Contraction
 The process of contraction
 Neural stimulation of sarcolemma:
– causes excitation–contraction coupling
 Cisternae of SR release Ca2+:
– which triggers interaction of thick and thin filaments
– consuming ATP and producing tension
The Neuromuscular Junction
 Is the location of neural stimulation
 Action potential (electrical signal)
 Travels along nerve axon
 Ends at synaptic terminal
 Synaptic terminal:
– releases neurotransmitter (acetylcholine or
ACh)
– into the synaptic cleft (gap between synaptic
terminal and motor end plate)
The Neuromuscular Junction
Figure 10–10a, b Skeletal Muscle Innervation.
The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.
The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.
The Neuromuscular Junction
 The Neurotransmitter
 Acetylcholine or ACh
 Travels across the synaptic cleft
 Binds to membrane receptors on sarcolemma
(motor end plate)
 Causes sodium–ion rush into sarcoplasm
 Is quickly broken down by enzyme
(acetylcholinesterase or AChE)
The Neuromuscular Junction
Figure 10–10c Skeletal Muscle Innervation.
The Neuromuscular Junction
 Action Potential
 Generated by increase in sodium ions in
sarcolemma
 Travels along the T tubules
 Leads to excitation–contraction coupling
 Excitation–contraction coupling:
– action potential reaches a triad:
» releasing Ca2+
» triggering contraction
– requires myosin heads to be in “cocked” position:
» loaded by ATP energy
Show video neuromuscular junction
The Neuromuscular Junction
Figure 10–11 The Exposure of Active Sites.
The Contraction Cycle
 Five Steps of the Contraction Cycle
 Exposure of active sites
 Formation of cross-bridges
 Pivoting of myosin heads
 Detachment of cross-bridges
 Reactivation of myosin
The Contraction Cycle
Figure 10–12 The Contraction Cycle.
The Contraction Cycle
[INSERT FIG. 10.12, step 1]
Figure 10–12 The Contraction Cycle.
The Contraction Cycle
Figure 10–12 The Contraction Cycle.
The Contraction Cycle
Figure 10–12 The Contraction Cycle.
The Contraction Cycle
Figure 10–12 The Contraction Cycle.
The Contraction Cycle
Figure 10–12 The Contraction Cycle.
The Contraction Cycle
 Fiber Shortening
 As sarcomeres shorten, muscle pulls together,
producing tension
 Contraction Duration
 Depends on
 Duration of neural stimulus
 Number of free calcium ions in sarcoplasm
 Availability of ATP
The Contraction Cycle
Figure 10–13 Shortening during a Contraction.
The Contraction Cycle
 Relaxation
 Ca2+ concentrations fall
 Ca2+ detaches from troponin
 Active sites are re-covered by tropomyosin
 Sarcomeres remain contracted
 Rigor Mortis
 A fixed muscular contraction after death
 Caused when
 Ion pumps cease to function; ran out of ATP
 Calcium builds up in the sarcoplasm
The Contraction Cycle
Tension Production
 The all–or–none principle
 As a whole, a muscle fiber is either contracted or
relaxed
 Tension of a Single Muscle Fiber
 Depends on
 The number of pivoting cross-bridges
 The fiber’s resting length at the time of stimulation
 The frequency of stimulation
 Need more force? Recruit more fibers
Tension Production
 Tension of a Single Muscle Fiber
 Length–tension relationship
 Number of pivoting cross-bridges depends on:
– amount of overlap between thick and thin fibers
 Optimum overlap produces greatest amount of tension:
– too much or too little reduces efficiency
 Normal resting sarcomere length:
– is 75% to 130% of optimal length
Tension Production
Figure 10–14 The Effect of Sarcomere Length on Active Tension.
Tension Production
 Tension of a Single Muscle Fiber
 Frequency of stimulation
 A single neural stimulation produces:
– a single contraction or twitch
– which lasts about 7–100 msec.
 Sustained muscular contractions:
– require many repeated stimuli
Tension Production
 Three Phases of Twitch
 Latent period before contraction
 The action potential moves through sarcolemma
 Causing Ca2+ release
 Contraction phase
 Calcium ions bind
 Tension builds to peak
 Relaxation phase
 Ca2+ levels fall
 Active sites are covered
 Tension falls to resting levels
Control of Muscle Tension
Tension Production
Figure 10–15 The Development of Tension in a Twitch.
Tension Production
Figure 10–15 The Development of Tension in a Twitch.
Tension Production
 Treppe
 A stair-step increase in twitch tension
 Repeated stimulations immediately after relaxation
phase
 Stimulus frequency <50/second
 Causes a series of contractions with increasing
tension
Tension Production
 Tension of a Single Muscle Fiber
 Wave summation
 Increasing tension or summation of twitches
 Repeated stimulations before the end of relaxation
phase:
– stimulus frequency >50/second
 Causes increasing tension or summation of
twitches
Tension Production
 Tension of a Single Muscle Fiber
 Incomplete tetanus
 Twitches reach maximum tension
 If rapid stimulation continues and muscle is not
allowed to relax, twitches reach maximum level of
tension
 Complete Tetanus
 If stimulation frequency is high enough, muscle
never begins to relax, and is in continuous
contraction
Tension Production
Figure 10–16 Effects of Repeated Stimulations.
Tension Production
Figure 10–16 Effects of Repeated Stimulations.
Tension Production
 Tension Produced by Whole Skeletal
Muscles
 Depends on
 Internal tension produced by muscle fibers
 External tension exerted by muscle fibers on
elastic extracellular fibers
 Total number of muscle fibers stimulated
Tension Production
 Tension Produced by Whole Skeletal Muscles
 Motor units in a skeletal muscle
 Contain hundreds of muscle fibers
 That contract at the same time
 Controlled by a single motor neuron
Tension Production
 Tension Produced by Whole Skeletal Muscles
 Recruitment (multiple motor unit summation)
 In a whole muscle or group of muscles, smooth motion and
increasing tension are produced by slowly increasing the size or
number of motor units stimulated
 Maximum tension
 Achieved when all motor units reach tetanus
 Can be sustained only a very short time
Tension Production
Figure 10–17 The Arrangement and Activity of Motor Units in a Skeletal
Muscle.
Tension Production
Figure 10–17 The Arrangement and Activity of Motor Units in a Skeletal
Muscle.
Tension Production
 Tension Produced by Whole Skeletal Muscles
 Sustained tension
 Less than maximum tension
 Allows motor units rest in rotation
 Muscle tone
 The normal tension and firmness of a muscle at rest
 Muscle units actively maintain body position, without motion
 Increasing muscle tone increases metabolic energy used,
even at rest
Tension Production
 Two Types of Skeletal Muscle Tension
 Isotonic contraction
 Isometric contraction
Tension Production
 Two Types of Skeletal Muscle Tension
 Isotonic Contraction
 Skeletal muscle changes length:
– resulting in motion
 If muscle tension > load (resistance):
– muscle shortens (concentric contraction)
 If muscle tension < load (resistance):
– muscle lengthens (eccentric contraction)
Tension Production
 Two Types of Skeletal Muscle Tension
 Isometric contraction
 Skeletal muscle develops tension, but is prevented
from changing length
Note: iso- = same, metric = measure
Tension Production
Figure 10–18a, b Isotonic and Isometric Contractions.
Tension Production
Figure 10–18c, d Isotonic and Isometric Contractions.
Tension Production
 Resistance and Speed of Contraction
 Are inversely related
 The heavier the load (resistance) on a muscle
 The longer it takes for shortening to begin
 And the less the muscle will shorten
 Muscle Relaxation
 After contraction, a muscle fiber returns to resting
length by
 Elastic forces
 Opposing muscle contractions
 Gravity
Tension Production
Figure 10–19 Load and Speed of Contraction.
Tension Production
 Elastic Forces
 The pull of elastic elements (tendons and ligaments)
 Expands the sarcomeres to resting length
 Opposing Muscle Contractions
 Reverse the direction of the original motion
 Are the work of opposing skeletal muscle pairs
Tension Production
 Gravity
 Can take the place of opposing muscle
contraction to return a muscle to its resting
state
ATP and Muscle Contraction
 Sustained muscle contraction uses a lot of
ATP energy
 Muscles store enough energy to start
contraction
 Muscle fibers must manufacture more ATP
as needed
ATP and Muscle Contraction
 ATP and CP Reserves
 Adenosine triphosphate (ATP)
 The active energy molecule
 Creatine phosphate (CP)
 The storage molecule for excess ATP energy in resting
muscle
 Energy recharges ADP to ATP
 Using the enzyme creatine phosphokinase (CPK or
CK)
 When CP is used up, other mechanisms generate
ATP
ATP and Muscle Contraction
 Energy Use and Muscle Activity
 At peak exertion
 Muscles lack oxygen to support mitochondria
 Muscles rely on glycolysis for ATP
 Pyruvic acid builds up, is converted to lactic acid
ATP and Muscle Contraction
Figure 10–20 Muscle Metabolism.
ATP and Muscle Contraction
Figure 10–20a Muscle Metabolism.
ATP and Muscle Contraction
Figure 10–20c Muscle Metabolism.
ATP and Muscle Contraction
 Muscle Fatigue
 When muscles can no longer perform a required
activity, they are fatigued
 Results of Muscle Fatigue
 Depletion of metabolic reserves
 Damage to sarcolemma and sarcoplasmic reticulum
 Low pH (lactic acid)
 Muscle exhaustion and pain
ATP and Muscle Contraction
 The Cori Cycle
 The removal and recycling of lactic acid by the liver
 Liver converts lactic acid to pyruvic acid
 Glucose is released to recharge muscle glycogen
reserves
 Oxygen Debt
 After exercise or other exertion
 The body needs more oxygen than usual to normalize
metabolic activities
 Resulting in heavy breathing
ATP and Muscle Contraction
 Skeletal muscles at rest metabolize fatty acids
and store glycogen
 During light activity, muscles generate ATP
through anaerobic breakdown of carbohydrates,
lipids, or amino acids
 At peak activity, energy is provided by anaerobic
reactions that generate lactic acid as a
byproduct
ATP and Muscle Contraction
 Muscle Performance
 Power
 The maximum amount of tension produced
 Endurance
 The amount of time an activity can be sustained
 Power and endurance depend on
 The types of muscle fibers
 Physical conditioning
Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Fast fibers
 Slow fibers
 Intermediate fibers
Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Fast fibers
 Contract very quickly
 Have large diameter, large glycogen reserves, few
mitochondria
 Have strong contractions, fatigue quickly
Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Slow fibers
 Are slow to contract, slow to fatigue
 Have small diameter, more mitochondria
 Have high oxygen supply
 Contain myoglobin (red pigment, binds oxygen)
Muscle Fiber Types
 Three Types of Skeletal Muscle Fibers
 Intermediate fibers
 Are mid-sized
 Have low myoglobin
 Have more capillaries than fast fibers, slower to
fatigue
Muscle Fiber Types
Figure 10–21 Fast versus Slow Fibers.
Muscle Fiber Types
 Muscles and Fiber Types
 White muscle
 Mostly fast fibers (aka Fast twitch)
 Pale (e.g., chicken breast)
 Red muscle
 Mostly slow fibers
(aka slow twitch)
 Dark (e.g., chicken legs)
 Most human muscles
 Mixed fibers
 Pink
(General proportions determined by genetics)
Muscle Fiber Types
 Muscle Hypertrophy
 Muscle growth from heavy training
 Increases diameter of muscle fibers
 Increases number of myofibrils
 Increases mitochondria, glycogen reserves
 Muscle Atrophy
 Lack of muscle activity
 Reduces muscle size, tone, and power
Muscle Fiber Types
 What you don’t use, you lose
 Muscle tone indicates base activity in motor
units of skeletal muscles
 Muscles become flaccid when inactive for days
or weeks
 Muscle fibers break down proteins, become
smaller and weaker
 With prolonged inactivity, fibrous tissue may
replace muscle fibers