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BIO -PHYSIOLOGY LECTUERS - PowerPoint PPT Presentation
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Chapter 10:Muscle Tissue
A&P Biology 141R.L. Brashear-Kaulfers
Muscle Tissue• One of 4 primary tissue types,
divided into:– skeletal muscle– cardiac muscle– smooth muscleWithout these muscles, nothing in the
body would move and no body movement would occur
Skeletal Muscles- Organs of skeletal muscle tissue
- are attached to the skeletal system and allow us to move
• Muscular System- Includes only skeletal muscles
Skeletal Muscle Structures• Muscle tissue (muscle cells or fibers)• Connective tissues• Nerves• Blood vessels
6 Functions of Skeletal Muscles
1. Produce skeletal movement2. Maintain body position and posture3. Support soft tissues4. Guard body openings
(entrance/exit)5. Maintain body temperature6. Store Nutrient reserves
How is muscle tissue organized at the tissue level?
Organization of Connective Tissues
Figure 10–1
Organization of Connective Tissues
• Muscles have 3 layers of connective tissues:
1. Epimysium-Exterior collagen layer• Connected to deep fascia• Separates muscle from surrounding
tissue2. perimysium- Surrounds muscle fiber
bundles (fascicles)• Contains blood vessel and nerve supply
to fascicles3. endomysium
3. Endomysium• Surrounds individual muscle cells
(muscle fibers)• Contains capillaries and nerve
fibers contacting muscle cells• Contains satellite cells (stem cells)
that repair damage
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)
NervesSkeletal muscles are voluntary
muscles, controlled by nerves of the central nervous system
Blood Vessels• Muscles have extensive vascular systems
that:– supply large amounts of oxygen– supply nutrients– carry away wastes
What are the characteristics of skeletal
muscle fibers? • Skeletal muscle cells are called
fibers
Figure 10–2
Skeletal Muscle Fibers• Are very long • Develop through fusion of mesodermal
cells (myoblasts- embryonic cells))• Become very large • Contain hundreds of nuclei –
multinucleate• Unfused cells are satellite cells- assist
in repair after injury
Organization of Skeletal Muscle Fibers
Figure 10–3
The Sarcolemma• The cell membrane of a muscle cell • Surrounds the sarcoplasm
(cytoplasm of muscle fiber)• A change in transmembrane
potential begins contractions• All regions of the cell must contract
simultaneously
Transverse Tubules (T tubules)
• Transmit action potential – impulses through cell
• Allow entire muscle fiber to contract simultaneously
• Have same properties as sarcolemma
• Filled with extracellular fluid
Myofibrils- 1-2um in diameter • Lengthwise subdivisions within muscle
fiber• Made up of bundles of protein filaments
(myofilaments)• Myofilaments - are responsible for
muscle contraction 2 Types of Myofilaments
• Thin filaments: – made of the protein actin
• Thick filaments: – made of the protein myosin
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
A Triad• Is formed by 1 T tubule and 2
terminal cisterna Cisternae
• Concentrate Ca2+ (via ion pumps) • Release Ca2+ into sarcomeres to
begin muscle contraction
Structural components of the Sarcomeres
Figure 10–4
-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)
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 2 ends of sarcomere Zone of Overlap
• The densest, darkest area on a light micrograph
• Where thick and thin filaments overlap
The H Zone• The area around the M line• Has thick filaments but no thin
filaments Titin• Are strands of protein • Reach from tips of thick filaments to
the Z line• Stabilize the filaments
Sarcomere Structure
Figure 10–5
Sarcomere Function• Transverse tubules encircle the
sarcomere near zones of overlap• Ca2+ released by SR causes thin
and thick filaments to interact
Figure 10–6 (1 of 5)
Level 1: Skeletal Muscle
Level 2: Muscle Fascicle
Level 3: Muscle Fiber
Figure 10–6 (3 of 5)
Level 4: Myofibril
Level 5: Sarcomere
Figure 10–6 (5 of 5)
Muscle Contraction• Is caused by interactions of thick
and thin filaments• Structures of protein molecules
detemine interactions
A Thin Filament
Figure 10–7a
4 Thin Filament Proteins1. F actin:
– is 2 twisted rows of globular G actin– the active sites on G actin strands bind to myosin
2. Nebulin:– holds F actin strands together
3. Tropomyosin:– is a double strand– prevents actin–myosin interaction
4. Troponin: - a globular protein
– binds tropomyosin to G actin– controlled by Ca2+
Troponin and Tropomyosin
Figure 10–7b
Ca2+ binds to receptor on troponin moleculeTroponin–tropomyosin complex changesExposes active site of F actin
Initiating Contraction
A Thick Filament
Contain twisted myosin subunits Contain titin strands that recoil after stretching
The Mysosin Molecule
• Tail:– binds to other myosin molecules
• Head:– made of 2 globular protein subunits– reaches the nearest thin filament
Mysosin Action• During contraction, myosin heads:
– interact with actin filaments, forming cross-bridges
– pivot, producing motion
Skeletal Muscle Contraction• Sliding filament
theory:– thin filaments of
sarcomere slide toward M line
– between thick filaments
– the width of A zone stays the same
– Z lines move closer together
Sliding Filaments
What are the components
of the neuromuscular junction, and the events
involved in the neural control of skeletal
muscles?
Skeletal Muscle Contraction
Figure 10–9 (Navigator)
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
Skeletal Muscle Innervation
Figure 10–10a, b (Navigator)
Skeletal Muscle Innervation
Figure 10–10c
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 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)
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
key steps involved in contraction
of a skeletal muscle fiber Exposing the Active Site
Figure 10–11
The Contraction Cycle
Figure 10–12 (1 of 4)
The Contraction Cycle
Figure 10–12 (2 of 4)
The Contraction Cycle
Figure 10–12 (3 of 4)
The Contraction Cycle
Figure 10–12 (Navigator) (4 of 4)
5 Steps of the Contraction Cycle
1. Exposure of active sites2. Formation of cross-bridges3. Pivoting of myosin heads4. Detachment of cross-bridges5. Reactivation of myosin
Fiber Shortening• As sarcomeres shorten, muscle
pulls together, producing tension
Figure 10–13
Contraction Duration• Depends on:
– duration of neural stimulus– number of free calcium ions in
sarcoplasm– availability of ATP
Relaxation• Ca2+ concentrations fall• Ca2+ detaches from troponin• Active sites are recovered by
tropomyosin• Sarcomeres remain contracted
Rigor Mortis• A fixed muscular contraction after
death• Caused when:
– ion pumps cease to function– calcium builds up in the sarcoplasm
A Review of Muscle Contraction
Table 10–1 (1 of 2)
A Review of Muscle Contraction
Table 10–1 (2 of 2)
KEY CONCEPT• Skeletal muscle fibers shorten as thin
filaments slide between thick filaments• Free Ca2+ in the sarcoplasm triggers
contraction• SR releases Ca2+ when a motor neuron
stimulates the muscle fiber • Contraction is an active process• Relaxation and return to resting length
is passive
What is the mechanism responsible for tension production in a muscle fiber, and what factors
determine the peak tension developed during
a contraction?
Tension Production • The all–or–none principal:
– 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
Tension and Sarcomere Length
Figure 10–14
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
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
Figure 10–15a (Navigator)
Tension in a Twitch• Length of twitch depends on type
of muscle
Myogram• A graph of twitch tension
development
Figure 10–15b (Navigator)
3 Phases of Twitch1. Latent period before contraction:
– the action potential moves through sarcolemma
– causing Ca2+ release 2. Contraction phase:
– calcium ions bind– tension builds to peak
3. Relaxation phase: – Ca2+ levels fall– active sites are covered– tension falls to resting levels
Treppe• A stair-step increase in twitch
tension
Figure 10–16a
Treppe• Repeated stimulations immediately
after relaxation phase:– stimulus frequency < 50/second
• Causes a series of contractions with increasing tension
Wave Summation• Increasing tension or summation of
twitches
Figure 10–16b
Wave Summation• Repeated stimulations before the
end of relaxation phase:– stimulus frequency > 50/second
• Causes increasing tension or summation of twitches
Incomplete Tetanus
• If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension
Twitches reach maximum tension
Complete Tetanus
• If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction
What factors affect peak tension production during
the contraction of an entire skeletal muscle,
and what is the significance of the motor
unit in this process?
InterActive Physiology: Contraction of Whole MusclePLAY
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
Motor Units in a Skeletal Muscle
Figure 10–17
Motor Units in a Skeletal Muscle
• Contain hundreds of muscle fibers • That contract at the same time• Controlled by a single motor
neuron
InterActive Physiology: Contraction of Motor UnitsPLAY
Recruitment (Multiple Motor Unit Summation)
• In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulated
Maximum Tension• Achieved when all motor units reach
tetanus• Can be sustained only a very short
time• Sustained Tension• Less than maximum tension• Allows motor units to rest in rotation
KEY CONCEPT
• Voluntary muscle contractions involve sustained, tetanic contractions of skeletal muscle fibers
• Force is increased by increasing the number of stimulated motor units (recruitment)
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
What are the types of muscle contractions,
and how do they differ? 2 Types of Skeletal Muscle Tension
• Isotonic contraction • Isometric contraction
Isotonic Contraction
Figure 10–18a, b
Isotonic Contraction• Skeletal muscle changes length:
– resulting in motion• If muscle tension > resistance:
– muscle shortens (concentric contraction)
• If muscle tension < resistance:– muscle lengthens (eccentric
contraction)
Isometric Contraction
Figure 10–18c, d
Isometric Contraction• Skeletal muscle develops tension,
but is prevented from changing length
Note: Iso = same, metric = measure
Resistance and Speed of Contraction
Figure 10–19
Resistance and Speed of Contraction
• Are inversely related• The heavier the 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
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
Gravity• Can take the place of opposing
muscle contraction to return a muscle to its resting state
What are the mechanisms by which muscle fibers obtain energy to power
contractions?
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 CP Reserves• Adenosine triphosphate (ATP):
– the active energy molecule• Creatine phosphate (CP):
– the storage molecule for excess ATP energy in resting muscle
Recharging ATP• Energy recharges ADP to ATP:
– using the enzyme creatine phosphokinase (CPK)
• When CP is used up, other mechanisms generate ATP
Energy Storage in Muscle Fiber
Table 10–2
ATP Generation• Cells produce ATP in 2 ways:
– aerobic metabolism of fatty acids in the mitochondria
– anaerobic glycolysis in the cytoplasm
Aerobic Metabolism • Is the primary energy source of
resting muscles• Breaks down fatty acids • Produces 34 ATP molecules per
glucose molecule
Anaerobic Glycolysis • Is the primary energy source for
peak muscular activity• Produces 2 ATP molecules per
molecule of glucose• Breaks down glucose from
glycogen stored in skeletal muscles
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
Muscle Metabolism
InterActive Physiology: Muscle MetabolismPLAY
Figure 10–20a
Muscle Metabolism
Figure 10–20c
What factors contribute to muscle fatigue, and
what are the stages and mechanisms involved in
muscle recovery?
Muscle Fatigue• When muscles can no longer perform a
required activity, they are fatigued
Results of Muscle Fatigue1. Depletion of metabolic reserves2. Damage to sarcolemma and
sarcoplasmic reticulum3. Low pH (lactic acid)4. Muscle exhaustion and pain
The Recovery Period• The time required after exertion
for muscles to return to normal • Oxygen becomes available• Mitochondrial activity resumes
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:
– the body needs more oxygen than usual to normalize metabolic activities
– resulting in heavy breathing
KEY CONCEPT
• 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
Heat Production and Loss• Active muscles produce heat• Up to 70% of muscle energy can be lost
as heat, raising body temperature Hormones and Muscle Metabolism• Growth hormone• Testosterone• Thyroid hormones• Epinephrine
How do the types of muscle fibers relate to muscle performance?
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
3 Types of Skeletal Muscle Fibers1. Fast fibers- Contract very quickly
• Have large diameter, large glycogen reserves, few mitochondria
• Have strong contractions, fatigue quickly2. Slow fibers-Are slow to contract, slow to fatigue• Have small diameter, more mitochondria• Have high oxygen supply• Contain myoglobin (red pigment, binds oxygen)3. Intermediate fibers-Are mid-sized• Have low myoglobin• Have more capillaries than fast fiber, slower to
fatigue
Fast versus Slow Fibers
Figure 10–21
Comparing Skeletal Muscle Fibers
Table 10–3
Muscles and Fiber Types• White muscle:
– mostly fast fibers– pale (e.g., chicken breast)
• Red muscle:– mostly slow fibers – dark (e.g., chicken legs)
• Most human muscles:– mixed fibers– pink
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
What is the difference between aerobic and
anaerobic endurance, and their effects on muscular
performance? Physical Conditioning –
Improves both power and endurance
Anaerobic Endurance • Anaerobic activities (e.g., 50-meter
dash, weightlifting):– use fast fibers– fatigue quickly with strenuous activity
• Improved by:– frequent, brief, intensive workouts – hypertrophy
Aerobic Endurance • Aerobic activities (prolonged
activity):– supported by mitochondria– require oxygen and nutrients
• Improved by:– repetitive training (neural responses)– cardiovascular training
KEY CONCEPT • What you don’t use, you loose • 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
What are the structural and functional differences between skeletal muscle fibers and cardiac muscle
cells?
Structure of Cardiac Tissue• Cardiac muscle is
striated, found only in the heart
Figure 10–22
7 Characteristics of Cardiocytes
• Unlike skeletal muscle, cardiac muscle cells (cardiocytes):– are small– have a single nucleus– have short, wide T tubules
7 Characteristics of Cardiocytes
– have no triads– have SR with no terminal cisternae– are aerobic (high in myoglobin,
mitochondria)– have intercalated discs
Intercalated Discs • Are specialized contact points between
cardiocytes• Join cell membranes of adjacent
cardiocytes (gap junctions, desmosomes) Functions of Intercalated Discs• Maintain structure• Enhance molecular and electrical
connections• Conduct action potentials
Coordination of Cardiocytes• Because intercalated discs link
heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells
4 Functions of Cardiac Tissue1. Automaticity:
– contraction without neural stimulation– controlled by pacemaker cells
2. Variable contraction tension:– controlled by nervous system
3. Extended contraction time4. Prevention of wave summation and
tetanic contractions by cell membranes
Role of Smooth Muscle in Body Systems
• Forms around other tissues • In blood vessels:
– regulates blood pressure and flow• In reproductive and glandular systems:
– produces movements • In digestive and urinary systems:
– forms sphincters– produces contractions
• In integumentary system:– arrector pili muscles cause goose bumps
What are the structural and functional differences between skeletal muscle fibers and smooth muscle
cells?
Structure of Smooth Muscle • Nonstriated tissue
Figure 10–23
Comparing Smooth and Striated Muscle
• Different internal organization of actin and myosin
• Different functional characteristics
8 Characteristics of Smooth Muscle Cells
1. Long, slender, and spindle shaped
2. Have a single, central nucleus3. Have no T tubules, myofibrils, or
sarcomeres4. Have no tendons or aponeuroses
8 Characteristics of Smooth Muscle Cells
5. Have scattered myosin fibers6. Myosin fibers have more heads
per thick filament7. Have thin filaments attached to
dense bodies8. Dense bodies transmit
contractions from cell to cell
Functional Characteristics of Smooth Muscle
1. Excitation–contraction coupling2. Length–tension relationships3. Control of contractions4. Smooth muscle tone
Excitation–Contraction Coupling
• Free Ca2+ in cytoplasm triggers contraction
• Ca2+ binds with calmodulin: – in the sarcoplasm– activates myosin light chain kinase
• Enzyme breaks down ATP, initiates contraction
Length–Tension Relationships• Thick and thin filaments are
scattered• Resting length not related to
tension development• Functions over a wide range of
lengths (plasticity)
Control of Contractions• Subdivisions:
– multiunit smooth muscle cells:• connected to motor neurons
– visceral smooth muscle cells:• not connected to motor neurons• rhythmic cycles of activity controlled by
pacesetter cells
Smooth Muscle Tone• Maintains normal levels of activity• Modified by neural, hormonal, or
chemical factors
Characteristics of Skeletal, Cardiac, and Smooth Muscle
Table 10–4
SUMMARY (1 of 3)• 3 types of muscle tissue:
– skeletal– cardiac– smooth
• Functions of skeletal muscles• Structure of skeletal muscle cells:
– endomysium– perimysium– epimysium
• Functional anatomy of skeletal muscle fiber:– actin and myosin
SUMMARY (2 of 3)• Nervous control of skeletal muscle fibers:
– neuromuscular junctions – action potentials
• Tension production in skeletal muscle fibers:– twitch, treppe, tetanus
• Tension production by skeletal muscles:– motor units and contractions
• Skeletal muscle activity and energy:– ATP and CP– aerobic and anaerobic energy
SUMMARY (3 of 3)• Skeletal muscle fatigue and recovery• 3 types of skeletal muscle fibers:
– fast, slow, and intermediate• Skeletal muscle performance:
– white and red muscles– physical conditioning
• Structures and functions of:– cardiac muscle tissue– smooth muscle tissue