Ch 10 study guide
2 minutes
Anaerobic glycolysis supplies enough ATP for muscles for two minutes of maximal activity.
Skeletal muscle
voluntarily controlled
Cross-bridges
when cross-bridges bind to the active site of actin thin filaments (myosin binding site), the thick filaments pivot toward the M line
Fascia
Fascia lines the body wall and limbs that surround and support muscles
15 seconds
In skeletal muscles, the combined amounts of creatine phosphate and ATP provide enough energy for the muscle to contract maximally for approximately 15 seconds.
Smooth muscle contraction
Smooth muscle contracts when calcium ions Ca2+ interact with calmodulin which activate the enzyme myosin light chain kinase, enabling myosin heads to attach to actin
Contraction Cycle
Step 1: Myosin head hydrolyses ATP and become energized and oriented
Transverse tubules (T-tubules)
T tubules are tunnels in from the surface toward the center of each muscle fiber
Triad
a T-tubule and two terminal cisterns on either side form a triad
Twitch
a brief contraction of all muscle fibers in a motor unit in response to a single action potential moving down the somatic motor neuron.
Rigor mortis
a condition in which muscles are in a state of rigidity 3-4 hour after death and last about 24 hours
Cori cycle
a cycle in the liver in which the lactic acid is converted to pyruvic acid and glucose
Zone of Overlap
a dark region where thin and thick filaments lie side by side
Perimysium
a fibrous connective tissue that covers each fascicle of muscle and contains nerves and blood vessels that service the muscle fibers
Nebulin
a long, non-elastic protein wrapped around the entire length of each thin filament
Incomplete tetanus (unfused tetanus)
a muscle producing peak tension with rapid cycles of contraction and relaxation
Complete tetanus (fused tetanus)
a muscle that is stimulated so frequently that the relaxation phase is completely eliminated
Refractory Period
a period that the muscle fiber loses its excitability and cannot response to a second stimulus
A myogram
a record of muscle contraction
Muscle tone
a small amount of tension in the muscle at rest due to weak, involuntary contractions of its motor units
Flaccid
a state of limpness in which muscle tone is lost.
Aponeurosis
a wide and flat tendon
Myasthenia Gravis
an autoimmune disorder that targets the ACh receptors at the NMJ and ultimately reduces the number of available receptors. Treat the patient with a drug that inhibits the activity of acetylcholinesterase will increase contraction
Spasticity
an increased muscle tone associated with an increase in tendon reflexes
Rigidity
an increased muscle tone in which tendon reflexes are not affected (tetanus)
tropomyosin
at rest, active sites of actin (myosin-binding site) thin filament are blocked (covered) by tropomyosin molecules
tropomyosin
at rest, the tropomyosin molecule is held in place by troponin
Overlapping
The overlapping of thick and thin filaments and the prominent striations of the myofibrils make the entire skeletal muscle fiber appear striated
Titin
The part of the titin that extends from the Z disc is very elastic. Thus, titin accounts for much of the elasticity and extensibility of myofibrils
Action potentials
conducted into a skeletal muscle fiber by transverse tubules (T-tubules)
The cytoplasm of the synaptic terminal
contains mitochondria and vesicles filled with neurotransmitter acetylcholine
Myofibrils
contractile organelles of muscle cell
Excitation-contraction coupling
The sequence of events that links excitation (generation an action potential) to the contraction
receptors for Ach
There are approximately 40 million receptors for Ach that are found in the motor-end -plate
Actin and myosin
contractile proteins of the muscle fiber
Acetylcholine (Ach)
To generate an action potential, acetylcholine (Ach), a neurotransmitter must be released at the neuromuscular junction (NMJ)
Contraction of myofibrils
contraction of myofibrils within a muscle fiber begins when calciumion is released from the terminal cistern of sarcoplasmic reticulum
calcium release
When a muscle fiber is relaxed, the concentration of Ca++in the sarcoplasm is very slow, but the concentration of Ca++ in the sarcoplasm reticulum (SR) is very high. As a result, to trigger muscle contraction, Ca++ must be released from SR
Acetylcholine
When acetylcholine binds to receptors at the motor-end plate, the muscle membrane becomes more permeable to sodium ions ( Voltage-gated Na+ channel opens to allow Na+ ions entering inside the sarcolemma)
Terminal cisterns
dilated end sac of the SR
Rigor mortis
disappears as proteolytic enzymes from lysosomes digest the cross-bridges)
thin filament
each thin filament consists of a pair of protein actin strands wound together into a helix
Myoblast
embryonic cell (stem cell) that forms muscle fiber
ATP hydrolysis reaction
energizes the myosin head
Energy Reserves in a Muscle
When energy reserves in a muscle are exhausted and lactic acid levels increase, muscle fatigue occurs
Single-unit smooth muscle tissue
found in the skin and in tubular arrangements that form part of the walls of small arteries and veins and of hollow organs such as the stomach, intestines, uterus, and urinary bladder.
Multi-unit smooth muscle tissue
found in the walls of large arteries, in airways to the lungs, in the arrector pili muscles that attach to hair follicles, in the muscles of the iris that adjust pupil diameter, and in the ciliary body that adjusts focus of the lens in the eye
Muscle fibers
have many nuclei in order to produce large amounts of the enzymes and structural proteins needed for contraction
Skeletal muscle cells
have more than one nucleus, are large and run parallel to each other
A myogram of twitch contraction
includes the latent period, the contraction period, and the relaxation period
Cardiac & Smooth muscle tissue
involuntary and auto-rhythmic
Skeletal muscle fiber
is controlled by a neuron at a single neuromuscular junction
Tetanus
is due to a toxin that makes the muscle cell membrane more permeable to calcium ions (Ca2+), causing powerful tetanic contraction
The mechanisms of rigor mortis
is due to calcium ions leak out of the SR (allowing myosin heads to bind to actin) and muscle fibers run out of ATP (causing the cross-bridges cannot detach from actin)
action potential or a (depolarization) or a (nerve impulse)
is required for the SR releases Ca2+ into sarcoplasm because when an action potential travels along the T. Tubule to open the voltage-gated Ca2+ channel allows a large amount of calcium flow out of the SR
Recruitment
is the increase in muscle tension that is produced by increasing the number of active motor units.
Neuromuscular Junction (NMJ)
is the synapse between the terminal end of a somatic motor (axon terminal) neuron and a portion sarcolemma (called Motor-End-Plate) of a skeletal muscle fiber
smooth muscle cells
like cardiac muscle cells, some smooth muscle cells communicate via gap junctions
Receptors for acetylcholine
located on the motor-end plate (the region of the sarcolemma opposite the synaptic end)
Levels of Exertion
mitochondria can provide only one-third (33%) of the ATP needed. The remainder comes from glycolysis
Multi-unit smooth muscle tissue
muscle cells have few gap junctions with neighboring cells and thus must be excited by their own motor neuron terminal
Z line or Z disk
narrow, plate-shaped region of dense protein material that separates one sarcomere to another
Cramp
occurs because the relaxation phase of a muscle contraction is often prolonged in a fatigued muscle, raising the likelihood of fused summation of action potentials causing painful disturbances to a skeletal muscle
Sarcolemma
plasma membrane of a muscle fiber (muscle cell)
Dystrophin
protein used to reinforce the sarcolemma and help transmit the tension generated by the sarcomeres to the tendons
Somatic motor neurons (voluntary control)
provide nerve impulses that stimulate skeletal muscle to contract
Hypotonia
refers to decreased or lost muscle tone
Hypertonia
refers to increased muscle tone
Tropomyosin and troponin
regulatory proteins of the muscle fibers
SR (sarcoplasmic reticulum)
releases calcium in response to an arrival of action potential
Mitochondrial activity
skeletal muscle cells are usually efficient, but can have limited ATP production if there is limited O2 availability
Smooth muscle cells
small but form thick layers of hollow organs
Microfilaments
smaller proteins within myofibrils
SR
stores calcium ions (Ca2+)
Sarcoplasm
stores glycogen and myoglobin, a red-colored protein that binds O2
Titin, myomesin, nebulin, α-Actinin, & dystrophin
structural proteins of the muscle fibers
Aerobic respiration
supplies enough ATP for muscles during periods of rest or moderate exercises (running, jogging, swimming, and walking)
Sarcomere
the basic functional unit of a myofibril of a skeletal muscle fiber
Sarcoplasm
the cytoplasm of a muscle fiber
A band
the darker middle area of sarcomere that contains thick & thin filament
Endomysium
the delicate connective tissue that surrounds the individual muscle fiber and contains a large capillary network
Epimysium
the dense irregular connective tissue that surrounds the entire muscle
Treppe (stair case)
the increased strength of a contraction that occurs when a second stimulus arrives after the muscle fiber has relaxed completely following the previous stimulus
Wave summation
the increased strength of a contraction that occurs when a second stimulus arrives before the muscle fiber has relaxed completely.
Titin
the largest size protein in the muscle fiber that extends from the Z disk to M line
I band
the light area of the sarcomere that contains thin filament only
Myosin
the main component of the thick filament and functions as a motor protein of muscle tissue
Actin
the main protein of the thin filament
Eccentric isotonic contraction
the muscle fiber lengthens. (object is dropped)
Concentric isotonic contraction
the muscle fiber shortens. (object is lifted)
H zone
the narrow area in the center of the A band that contains thick filament only
Synaptic cleft
the narrow space between the neuron and the muscle fiber
Myomesin
the protein of M line
Sarcoplasmic reticulum (SR)
the series of membranous channels that surround each myofibril.
Isometric contraction
the type of contraction in which the muscle fibers produce tension but do not shorten nor lengthen. (Object cannot be moved)
Isotonic contraction
the type of contraction in which the muscle fibers produce tension while muscle length is changed
(sarcomere)M line
thick and thin filaments are linked laterally
Microfilaments
thin and thick filaments
Sarcomere
thin and thick filaments do not extend the entire length of muscle fiber. Instead, they are arranged in compartment
Thin filaments
thin filaments at either end of sarcomere are attached to the Z line (Z disc)
Cardiac muscle cells
usually have only one, sometimes two, centrally located nuclei and are branched
Cross bridges
- are portions of thick filament (myosin head) - act as (an enzymes) ATPase during the contraction cycle of muscle - generate force
Motor unit
-A term describes a somatic motor neuron and all the skeletal muscle fibers it stimulates -The ratio of motor neurons to muscle fiber is the greatest in muscles that control the eye and the tongue
Form crossbridges
-ATP must be broken down by enzyme ATPase -Calcium ions must be present in the sarcoplasm -Myosin binding sites (actin active site) must be exposed
Functions of Smooth Muscle
-Altering the diameter of the respiratory passageways -Moving food materials along the digestive tract -Moving sperms in the male reproductive tract and oocytes in the uterine tract Expelling fetus by contraction of the wall of the uterus -Acting as a sphincter
Slow fibers: Slow oxidative fiber (SO)
-Small diameter -MOST resistant to fatigue -Oxidative fibers have many mitochondria. That is a reason why they use aerobic respiration. -high concentration of myoglobin (Red meat) -Produce slow contraction
Major characteristics of smooth muscle cells
-Smooth muscle cells are uninucleate -Smooth muscles lack sarcomeres -Thin filaments are attached to dense bodies -Transmitting the contractile forces from cell to cells throughout the muscle tissue. -Involuntary control (pacesetter cells)
skeletal muscle fiber contracts in the sliding filament mechanism
-Z line (Z disk) moves closer together -the H zones and I bands get smaller -the width of the A band remains constant -the zone of overlap gets larger (more zone of overlaps between thin & thick filament)
Provide the oxygen after exercise
-convert the lactic acid produced during exercise back into glycogen -resynthesize creatine phosphate -replace oxygen displaced from muscle myoglobin
A Troponin molecule consists three globular subunits
-unit 1 binds to tropomyosin -unit 2 binds to G-actin -unit 3 binds to calcium ions
Muscle has 3 ways to produce ATP
-Producing ATP from creatine phosphate by direct phosphorylation -Producing ATP from anaerobic glycolysis -Producing aerobic respiration
4 major functions of skeletal muscle
-Producing body movement and storing nutrients as glycogen, proteins -Maintaining posture (upright position) -Generating heat d. Controlling entrance and exit
4 properties of muscle tissues
-Electrical excitability -Contractility -Extensibility [property of muscle gives it the ability to stretch without damage] -Elasticity [property of muscle gives it the ability to recoil]
Factors that lead to Muscle Fatigue
-Inadequate release of calcium ions from the SR -Deletion of creatine phosphate -Insufficient oxygen -Depletion of glycogen and other nutrients -Buildup lactic acid -Failure of action potentials in the motor neurons to release enough Ach
Fast fibers: Fast glycolytic fibers (FG)
-Large diameter -Produces powerful contraction -Less resistant to fatigue -Glycolytic fiber: fast fibers have fewer mitochondria and large of glycogen reserves and that why it uses anaerobic respiration -Low concentration of myoglobin (White meat)
Anaerobic endurance
-Most of the muscle's energy is produced in cytoplasm by glycolysis -Glycolysis is a main source of ATP (2ATPs) -Oxygen debts are common -Dependent on fast glycolytic fibers -Oxygen is NOT required -Muscle fatigue quickly (not able to have sustained contraction for hours)
Aerobic endurance
-Most of the muscle's energy is produced in mitochondria -Krebs cycle is a main source of ATP (36 ATPs) -No oxygen debt d. Oxygen is required -Dependent on slow oxidative fibers -Fatigue resistant (sustained contraction for hours)
Length-Tension Relationship
A muscle fiber develops its greatest tension when there is an optimal zone of overlap (sarcomere length is 2.0- 2.4 μm) between thick and thin filament. This dependency is the length-tension relationship
Steps in Generation an Action Potential
Step 1: the arrival of a nerve impulse at a motor neuron opens voltage-gated calcium Ca2+ channel in the sarcolemma, allowing Ca2+ enter to the synaptic terminal to trigger the releasing of acetylcholine.
Steps in Generation an Action Potential
Step 2: Ach diffuses across the synaptic cleft by exocytosis and binds to receptors in the motor-end-plate. The binding opens voltage-gated sodium Na+ channel in the sarcolemma, allowing Na+ enters to the sarcoplasm.
Contraction Cycle
Step 2: Myosin head binds to actin , forming the cross bridge
Contraction Cycle
Step 3: Myosin head pivots, pulling the thin filament past the thick filament toward center of the sarcomere (power stroke)
Steps in Generation an Action Potential
Step 3: The influx of Na+ produces a depolarization of the sarcolemma called "muscle action potential"
Contraction Cycle
Step 4 : Another ATP binds attaches to the cross bridge, myosin head detaches from actin. Then the cycle repeats
Steps in Generation an Action Potential
Step 4: The muscle action potential that propagates along the T. Tubules triggers the opening of voltage-gated Ca channel in the sarcoplasmic reticulum (SR). SR releases Ca into sarcoplasm
Steps in Generation an Action Potential
Step 5: Termination of Ach by enzyme Acetylcholinesterase (AChE)
Steps in Generation an Action Potential
Step 6: Ca2+ binds to troponin on the thin filament, exposing the active site or myosin-binding site of actin.
Steps in Generation an Action Potential
Step 7: Crossbridges are formed and contraction cycle begins
Steps in Generation an Action Potential
Step 8: When the generation of action potential ends, Ca2+ is pumped back to the SR by an active transport
Single-unit smooth muscle tissue
action potentials are initiated in response to neurotransmitters, hormones, or an auto-rhythmic signal. The action potential spreads throughout the tissue by moving through gap junctions that connect all the muscle cells together within the tissue
Active sites
active sites on the actin thin filament become available (exposed) for binding when calcium ion binds to troponin subunit. Once calcium ion binds to troponin, troponin then moves tropomyosin away from the myosin-binding sites of thin filament
Creatine phosphate
acts as an energy reserves in muscle tissue
Refractory Period
additional oxygen is required to metabolize the lactic acid produced during exercise
epimysium, perimysium, & endomysium
all continuous with the connective tissue to form a rope like tendon that attaches a muscle to the periosteum of the bone
Cardiac muscle cells
also are connected to each other via gap junctions
Plasticity
an ability of the smooth muscle to function over a wide range of lengths
Cardia muscle & Smooth muscle
both cardiac and skeletal muscle tissues are striated and smooth muscle is not.
Muscle tissue
capable of undergoing the stress-relaxation response when stretched is single-unit smooth muscle fibers