8 The Physiology of Muscle Flashcards
Classification of the Muscle According to the structure:
Striated Muscle
Smooth Muscle
Classification of the Muscle According to nerve innervation:
Voluntary Muscle
Involuntary Muscle
Classification of the Muscle According to the function:
Skeletal Muscle
Cardiac Muscle
Smooth Muscle
-makes up the great mass of somatic musculature
-It is striated and voluntary.
-Microstructures of this muscle, particularly the light and dark bands, give the it its striated appearance
-It is also the only muscle that can be controlled consciously, thus the term “voluntary”.
-Its muscle fibers are also multinucleated. Except for about 2 percent of the fibers, each fiber is usually innervated by only one nerve ending, located near the middle of the fiber.
-consist of muscle fibers bound by connective tissue.
Skeletal muscle
Functions of the skeletal muscle include
production of force for locomotion and breathing
the production of force for posture, and heat production during cold stress.
Skeletal muscles consist of muscle fibers bound by connective tissue. Individual fibers are covered by ____. These fibers are then arranged into bundles called ____ and are covered by perimysium. The fascicles are then encased by the ____.
endomysium
fascicles
epimysium
The plasma membrane of the fiber is called sarcolemma. Each fiber contains a long threadlike cylindrical structure called ____. These make up almost the entire fiber pushing the nuclei to the outer edge.
myofibrils
Each myofibril has a light and dark bands. The light bands are called ____, and the dark bands are called ____.
I bands
A bands
The line in the middle of the I band is called the _____ or ____ and the light zone in the middle of the A band is called the ____.
Z line or Z disc
H zone
-precise arrangement of the features of myofibrils
-the basic contractile unit of the muscle fiber.
-An individual of this extends from one Z line to another.
-consists of protein elements and some of these are thread-like proteins called myofilaments.
sarcomere
two major types of filaments
thick myosin myofilaments
thin actin myofilaments
what are the filaments that are made up of proteins called myosin
Thick myofilaments
The myosin molecules are shaped like
golf clubs with long shafts.
are arranged to a point toward the center of the sarcomere
Myosin tails (long shaft)
-points to the sides of the myofilament band
-form attachment to the thin actin myofilament and are called cross bridges.
-are also the places on the thick myofilaments that use the energy in the ATP molecule to power muscle contraction.
Myosin heads (golf club)
-are composed of the protein actin.
-have the binding sites to which the heads of the thick myofilaments attach.
-are made up of proteins called actin, troponin, and tropomyosin.
thin myofilaments
The backbone of the actin filament is made up of ____ that wound up in a helix.
double-stranded F-actin molecules
-Attached to each one of the actin molecules is one molecule of ___
-are the active sites on the actin filaments with which the cross bridges of the myosin filaments interact to cause muscle contraction.
ADP
The ____ molecules are wrapped spirally around the actin helix. During the resting state, these molecules lie on top of the active sites of actin.
tropomyosin
-is a protein complex made up of three loosely bound protein subunits.
-have a strong affinity for actin, troponin T for tropomyosin, and troponin C for calcium ions.
Troponin
-it is within the sarcoplasm
-serves as the storage site for calcium.
-Other structures include the transverse tubules and terminal cisternae.
sarcoplasmic reticulum
What are the Molecular Mechanism of Muscle Contraction
- Sliding Filament Mechanism
- The “Walk-Along” Theory of Contraction
*what mechanism
In a relaxed state, the actin filaments from the successive Z discs barely begin to overlap one another while in a contracted state, actin filaments are pulled and overlap the myosin filament. This slide inward movement is caused by the interaction of cross-bridges of the myosin filament with the actin filament as initiated by the release of calcium ions as well as the presence of ATP.
Sliding Filament Mechanism
Before contraction begins, ATP binds with the myosin head and the myosin head subsequently cleaves the ATP into ADP and Pi. This leads to a conformational change in the cross-bridges causing the perpendicular extension of the cross-bridges. When the troponin-tropomyosin complex binds with calcium, the active site of the actin filament is uncovered. The bond between the bridges and the actin filament will then cause a conformational change in the head, prompting the head to tilt toward the arm of the cross- bridges pulling the actin filament. This is called the power stroke. AP and Pi attached in the head will then be released and another molecule of ATP will bind in the head. A new cycle will once again occur.
The “Walk-Along” Theory of Contraction
Factors that Affect the Efficiency of Muscle Contraction
Tension
Load
what is the force exerted on an object by a contracting muscle
Tension
what is the force exerted on the muscle by an object (usually its weight), it is divided into preload and afterload.
Load
Types of Contractions
twitch
tetanus
what is the type of contraction that is a brief mechanical contraction of a single fiber produced by a single action potential at low-frequency stimulation
twitch or single twitch
what is the type of contraction that is a summation of twitches that occurs at high-frequency stimulation.
tetanus
-Smaller fibers
-Innervated by smaller nerve fibers
-Extensive blood vessel system and capillaries to supply extra amounts of oxygen
-Greater numbers of mitochondria
-Large amounts of myoglobin, an iron- containing protein similar to hemoglobin in red blood cells
Slow Fibers/Type 1/Red Muscle
-Large fibers
-Extensive sarcoplasmic reticulum
-Large amounts of glycolytic enzymes
-Less extensive blood supply
-Fewer mitochondria
Fast Fibers /Type II/White Muscle
It is composed of an alpha motor neuron and all the myofibers innervated by that neuron.
Motor Unit
-It is the site where motor neuron meets the muscle fiber.
-It is the site for the transmission of action potential from the nerve to the muscle.
The Neuromuscular Junction (NMJ)
NMJ is divided into three main parts:
presynaptic part (nerve terminal)
postsynaptic part (motor endplate)
the area between these two parts (synaptic cleft).
-A myelinated motor neuron will branch out into multiple nerve endings called
nerve terminals
Thickened areas in the nerve terminal membrane called ____ have voltage-gated Ca channels and synaptic vesicles containing Acetylcholine (Ach), the neurotransmitter in the NMJ.
active zones
When an action potential travels through the nerve terminals, ____ will open to cause influx. Increased Ca inside the nerve terminal causes docking of synaptic vesicles and the exocytosis of Ach into the synaptic cleft.
Ca channels
-is the space between the nerve terminal and motor endplate.
-It is where the Ach is released before its interaction with the nicotinic Ach receptor in the motor endplate.
-Within this cleft is also the presence of acetylcholinesterase that catabolize acetylcholine into acetyl and choline.
-AChE resides in the this cleft, breaking down ACh so that it does not remain bound to ACh receptors, which would cause unwanted extended muscle contraction
Synaptic cleft
-It is the region of the myofiber directly under the terminal axon branches.
-are thickened portions of the sarcolemma that are called junctional folds. These folds have nicotinic Ach receptors.
motor endplate.
The binding of Ach in the nicotinic Ach receptors opens what channels
sodium channels
-The influx of Na ions will create endplate potential and generate and transmit action potential to the muscle membrane. There is also the occurrence of ____
-It is where the stimulation of the nerve fiber at rates greater than 100 times per second for several minutes diminishes the number of acetylcholine vesicles so much that impulses fail to pass into the muscle fiber.
fatigue of the junction
Drugs That Stimulate the Muscle Fiber by Acetylcholine-Like Action
methacholine
carbachol
nicotine
Drugs That Block Transmission at the NMJ
curariform drugs
It is a condition of muscle paralysis due to the inability of the NMJ to transmit enough signals antibodies that attack the acetylcholine-gated sodium ion transport proteins autoimmune disease patient dies of paralysis (respiratory muscles). This can be ameliorated by neostigmine or some other anticholinesterase drug.
Myasthenia gravis
-is the physiological process of converting an electrical stimulus to a mechanical response.
-It is the link (transduction) between the action potential generated in the sarcolemma and the start of a muscle contraction.
Excitation–contraction coupling
-is named so because cells do not have striations and are present on the walls of hollow organs, blood vessels, in the eye (iris), and skin (erector pili muscle).
-non-striated, involuntary, and are triggered by hormones, the autonomic nervous system (ANS).
-spindle-shaped and have a single nucleus.
-has a lack of striation
Smooth muscle
what is the counterpart of z discs in the smooth muscle
dense bodies
what is the counterpart of t-tubules in the smooth muscle
-are small indentations in the sarcolemma where there is a high density of calcium channels.
calveoli
what is the counterpart of troponin in the smooth muscle
calmodulin
The ____ is present in the smooth muscle but not as developed compared to skeletal muscle.
sarcoplasmic reticulum
In the smooth muscle, Troponin is not present. Cross-bridge formation is instead regulated by what protein
calmodulin
-is found in the walls of hollow organs
It’s cells contract synchronously, are coupled by gap junctions and exhibit spontaneous action potential.
Single-unit smooth muscle
Because most smooth muscles must function for long periods without rest, their
power output is relatively ____ to minimize energy needs. Some smooth muscles can also
maintain contractions even as Ca++ is removed and myosin kinase is
inactivated/dephosphorylated.
low
-is found in airways to the lungs and large arteries.
-It’s cells lack gap junctions, and their contractions are not synchronous.
multiunit smooth muscle
-a subset of cross-bridges between myosin heads and actin
-keep the thick and thin filaments linked together for a prolonged period, without the need for ATP.
-allows for the maintenance
of muscle “tone” in smooth muscle that lines arterioles and other visceral organs with very
little energy expenditure.
latch bridges
-is a series of neurotransmitter filled bulges in the smooth muscle
-along the axon of the neuron feeding the smooth muscle that release neurotransmitters over a wide synaptic cleft.
varicosities
-visceral muscle in the walls of the
hollow organs (except the heart) contains this cell
-It can spontaneously trigger action potentials and contractions in the muscle.
pacesetter cell
