ch10 Flashcards
muscle tissue
Muscle Tissue is A primary tissue type divided into..?
Skeletal muscle
Smooth muscle
Cardiac muscle
- Are attached to the skeletal system
- Allow us to move
Skeletal Muscle
Includes only skeletal muscles
muscular system
- Muscle tissue (muscle cells or fibers)
- Connective tissues
- Nerves
- Blood vessels
Skeletal muscle structures
- Produce skeletal movement
- Maintain body position
- Support soft tissues
- Guard body openings
- Maintain body temperature
Functions of skeletal muscles
Muscles have 3 layers of connective tissues …what are they?
o Epimysium
o Perimysium
o Endomysium
- Exterior collagen layer
- Connected to deep fascia
- Separates muscle from surrounding tissues
Epimysium
- Surrounds muscle fiber bundles (fascicles)
- Contains blood vessel and nerve supply to fascicles
Perimysium
- Surrounds individual muscle cells (muscle fibers)
- Contains capillaries and nerve fibers containing muscle cells
- Contains satellite cells (stem cells) that repair damage
Endomysium
o At ends of muscles
o To form connective tissue attachment to bone matrix
o i.e., tendon (bundle) or aponeurosis (sheet)
where/why endomysium, perimysium, and epimysium come together
Skeletal muscles are voluntary muscles, controlled by ____of the central nervous system
Nerves
(Blood vessels)
Muscles have extensive vascular systems that:
o Supply large amounts of oxygen
o Supply nutrients
o Carry away wastes
Skeletal muscle cells are called
fibers
Are very long
Develop through fusion of mesodermal cells (myoblasts)
Become very large
Contain hundreds of nuclei
Skeletal Muscle Fibers
- The cell membrane of a muscle cell
- Surrounds the sarcoplasm (cytoplasm of muscle fiber)
- A change in transmembrane potential begins contractions
The Sarcolemma
- Transmit action potential though cell
- Allow entire muscle fiber to contract simultaneously
- Have same properties as sarcolemma
Transverse Tubules (T tubules)
- Lengthwise subdivisions within muscle fiber
- Made up of bundles of protein filaments (myofilaments)
- Myofilaments are responsible for muscle contraction
Myofibrils
2 Types of Myofilaments are?
thin filiments and thick filiments
Made of the protein actin
thin filiments
Made of the protein myosin
thick filiments
- 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
Sarcoplasmic Reticulum
Is formed by 1 T tubule and 2 terminal cisternae
A Triad
- Concentrate Ca2+ (via ion pumps)
- Release Ca2+ into sarcomeres to begin muscle contraction
Cisternae
- The contractile units of muscle
- Structural units of myofibrils
- Form visible patterns within myofibrils
Sarcomeres
- Are strands of protein
- Reach from tips of thick filaments to the Z line
- Stabilize the filaments
Titin
- Transverse tubules encircle the sarcomere near zones of overlap
- Ca2+ released by SR causes thin and thick filaments to interact
Sarcomere Function
- Is caused by interactions of thick and thin filaments
- Structures of protein molecules determine interactions
Muscle Contraction
a. Is 2 twisted rows of globular G actin
b. The active sites on G actin strands bind to myosin
F actin:
Holds F actin strands together
Nebulin
a. Is a double strand
b. Prevents actin-myosin interaction
Tropomyosin
a. A globular protein
b. Binds tropomyosin to G actin
c. Controlled by Ca2+
Troponin
- Ca2+ binds to receptor on troponin molecules
- Troponin-tropomyosin complex changes
- Exposes active site of F actin
Initiating Contraction
- Contain twisted myosin subunits
- Contain titin strands that recoil after stretching
Thick Filaments
The Myosin Molecule has
a tail and a head
o Made of 2 globular protein subunits
o Reaches the nearest thin filament
the head (of the myosin molecule)
o Binds to other myosin molecules
the tail (of the myosin molecule)
(Myosin Action)
During Contraction, myosin heads:
o Interact with actin filaments, forming cross-bridges
o Pivot, producing motion
o Thin filaments of sarcomere slide toward M line
o Between thick filaments
o The width of A zone stays the same
o Z lines move closer together
Sliding filament theory
- Is the location of neural stimulation
- Action potential (electrical signal):
o Travels along nerve axon
o Ends at synaptic terminal
The Neuromuscular Junction
o Releases neurotransmitter (acetylcholine or ACh)
o Into the synaptic cleft (gap between synaptic terminal and motor end plate)
(Skeletal Muscle Innervation)
Synaptic Terminal
o 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 Neurotransmitter
- Generated by increase in sodium ions in sarcolemma
- Travels along the T-tubules
- Leads to excitation-contraction coupling
Action Potential
- Exposure of active sites
- Formation of cross-bridges
- Pivoting of myosin heads
- Detachment of cross-bridges
- Reactivation of myosin
5 Steps of the Contraction Cycle
As sarcomeres shorten, muscle pulls together, producing tension
Fiber Shortening
- Depends on: duration of neural stimulus
- Number of free calcium ions in sarcoplasm
- Availability of ATP
Contraction Duration
- Ca2+ concentrations fall
- Ca2+ detaches from troponin
- Active sites are recovered by tropomyosin
- Sarcomeres remain contracted until an outside force pulls muscle to original length
Relaxation
- A fixed muscular contraction after death
- Caused when:
o Ion pumps cease to function
o Calcium builds up in the sarcoplasm
Rigor Mortis
- 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
Key Concept
- Action potential reaches a triad
- Releasing Ca2+
- Triggering contraction
- Requires myosin heads to be in “cocked” position
- Loaded by ATP energy
Excitation–Contraction Coupling
-As a whole, a muscle fiber is either contracted or relaxed
Depends on:
-The number of pivoting cross-bridges
-The fiber’s resting length at the time of stimulation
-The frequency of stimulation
Tension Production by Muscles Fibers
Number of pivoting cross-bridges depends on:
Amount of overlap between thick and thin fibers
Optimum overlap produces greatest amount of tension
Length–Tension Relationships
A single neural stimulation produces:
A single contraction or twitch
Which lasts about 7–100 msec.
Require many repeated stimuli
Sustained muscular contractions
There are 3 twitches:
Latent period
Contraction phase
Relaxation phase
- The action potential moves through sarcolemma
- Causing Ca2+ release
Latent period
- Calcium ions bind
- Tension builds to peak
Contraction phase
- Ca2+ levels fall
- Active sites are covered and tension falls to resting levels
Relaxation phase
-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
Treppe
-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
Wave summation
- Twitches reach maximum tension
- If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension
Incomplete tetanus
If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction
Complete tetanus
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 by Skeletal Muscles
- Contain hundreds of muscle fibers
- That contract at the same time
- Controlled by a single motor neuron
Motor units in a skeletal muscle
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
Recruitment (multiple motor unit summation)
- Achieved when all motor units reach tetanus
- Can be sustained only a very short time
Maximum tension
- Less than maximum tension
- Allows motor units rest in rotation
Sustained tension
- 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
Muscle tone
Skeletal muscle develops tension, but is prevented from changing length
(same measure)
Isometric Contraction
The active energy molecule
Adenosine triphosphate (ATP)
The storage molecule for excess ATP energy in resting muscle
creatine phosphate (CP)
- Using the enzyme creatine kinase (CK)
- When CP is used up, other mechanisms generate ATP
Energy recharges ADP to ATP
- Is the primary energy source of resting muscles
- Breaks down fatty acids
- Produces 34 ATP molecules per glucose molecule
Aerobic Metabolism
- Is the primary energy source for peak muscular activity
- Produces two ATP molecules per molecule of glucose
- Breaks down glucose from glycogen stored in skeletal muscles
Glycolysis
When muscles can no longer perform a required activity
Muscle Fatigue
- Depletion of metabolic reserves
- Damage to sarcolemma and sarcoplasmic reticulum
- Low pH (lactic acid)
- Muscle exhaustion and pain
Results of Muscle Fatigue
- The time required after exertion for muscles to return to normal
- Oxygen becomes available
- Mitochondrial activity resumes
The Recovery Period
- The removal and recycling of lactic acid by the liver
- Liver converts lactate to pyruvate
- Glucose is released to recharge muscle glycogen reserves
The Cori Cycle
After exercise or other exertion:
- The body needs more oxygen than usual to normalize metabolic activities
- Resulting in heavy breathing
- Also called excess postexercise oxygen consumption (EPOC)
Oxygen Debt
- Active muscles produce heat
- Up to 70% of muscle energy can be lost as heat, raising body temperature
Heat Production and Loss
- Growth hormone
- Testosterone
- Thyroid hormones
- Epinephrine
Hormones and Muscle Metabolism
The maximum amount of tension produced
force
The amount of time an activity can be sustained
Endurance
Force and endurance depend on…
- The types of muscle fibers
- Physical conditioning
- Fast fibers
- Slow fibers
- Intermediate fibers
Three Major Types of Skeletal Muscle Fibers
-Contract very quickly
-Have large diameter, large glycogen reserves, few mitochondria
-Have strong contractions, fatigue quickly
~ weight lifting/muscle building
Fast Fibers
-Are slow to contract, slow to fatigue
-Have small diameter, more mitochondria
-Have high oxygen supply
-Contain myoglobin (red pigment, binds oxygen)
~ endurance/distance
Slow Fibers
- Are mid-sized
- Have low myoglobin
- Have more capillaries than fast fibers, slower to fatigue
Intermediate Fibers
- Mostly fast fibers
- Pale (e.g., chicken breast)
White muscles
- Mostly slow fibers
- Dark (e.g., chicken legs)
Red muscles
- Mixed fibers
- Pink
Most human muscles
- Muscle growth from heavy training
- Increases diameter of muscle fibers
- Increases number of myofibrils
- Increases mitochondria, glycogen reserves
Muscle Hypertrophy
- Lack of muscle activity
- Reduces muscle size, tone, and power
Muscle Atrophy
Improves both power and endurance
Physical Conditioning
-Use fast fibers
-Fatigue quickly with strenuous activity
Improved by:
-Frequent, brief, intensive workouts
-Causes hypertrophy
Anaerobic activities (e.g., 50-meter dash, weightlifting)
-Supported by mitochondria
-Require oxygen and nutrients
Improves:
-Endurance by training fast fibers to be more like intermediate fibers
-Cardiovascular performance
Aerobic activities (prolonged activity)
- Cardiac muscle cells are striated and found only in the heart
- Striations are similar to that of skeletal muscle because the internal arrangement of myofilaments is similar
Cardiac Muscle Tissue
- Are small
- Have a single nucleus
- Have short, wide T tubules
- Have no triads
- Have SR with no terminal cisternae
- Are aerobic (high in myoglobin, mitochondria)
- Have intercalated discs
Unlike skeletal muscle, cardiac muscle cells (cardiocytes):
- Are specialized contact points between cardiocytes
- Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes)
Intercalated Discs
-Coordination of cardiocytes
Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells
Intercalated Discs
Functions of :
Maintain structure
Enhance molecular and electrical connections
Conduct action potentials
Intercalated Discs
- Contraction without neural stimulation
- Controlled by pacemaker cells
Automaticity
reproductive and glandular systems
Produces movements
- Forms sphincters
- Produces contractions
digestive and urinary systems
- Non striated tissue
- Different internal organization of actin and myosin
- Different functional characteristics
Structural Characteristics of Smooth Muscle Tissue
Long, slender, and spindle shaped
Have a single, central nucleus
Have no T tubules, myofibrils, or sarcomeres
Have no tendons or aponeuroses
Have scattered myosin fibers
Myosin fibers have more heads per thick filament
Have thin filaments attached to dense bodies
Dense bodies transmit contractions from cell to cell
Characteristics of Smooth Muscle Cells
- Excitation–contraction coupling
- Length–tension relationships
- Control of contractions
- Smooth muscle tone
Functional Characteristics of Smooth Muscle Tissue
-Free Ca2+ in cytoplasm triggers contraction
-Ca2+ binds with calmodulin
In the sarcoplasm
-Activates myosin light–chain kinase
-Enzyme breaks down ATP, initiates contraction
Excitation–Contraction Coupling
- Thick and thin filaments are scattered
- Resting length not related to tension development
- Functions over a wide range of lengths (plasticity)
Length–Tension Relationships
Connected to motor neurons
Multiunit smooth muscle cells
- Not connected to motor neurons
- Rhythmic cycles of activity controlled by pacesetter cells
Visceral smooth muscle cells
- Maintains normal levels of activity
- Modified by neural, hormonal, or chemical factors
Smooth Muscle Tone
