Chapter 10 Flashcards
Primary function of muscle?
- Transformation of chemical energy into mechanical energy to generate force perform work and produce movement
- Stabilizes body position
- Regulates organ volume
- Generates heat
- Propels food and fluid matter through various body systems
What are the three types of muscular tissue?
- Skeletal
- Cardiac
- Smooth
Myology
Scientific study of muscles
Skeletal muscle tissue
- Move bones of the skeleton
- Striated, seen under a microscope
- Works voluntarily
Cardiac muscle tissue
- Forms most of the heart wall
- Striated
- Involuntary
Autorhythmicity
Natural pacemaker/Built-in rhythm of the heart, Controlled by hormones and neurotransmitters
Smooth muscle tissues
- Walls of hollow internal structures and skin attached to hair follicles
- Non striated
- Involuntary
- Controlled by neurons and hormones
Functions of the muscular tissue
- Producing body movements
- Stabilizing body positions
- Storing and moving substances within the body
- Generating heat
Thermogenesis
When muscular tissue contracts it produces heat
What are the four special properties of muscular tissue?
- Electrical excitability
- Contractility
- Extensibility
- Elasticity
Action potentials
The ability to respond to certain stimuli by producing electrical signals
What are the two main types of stimuli triggers for action potential in muscle cells?
- Electrical signals, arises in the muscle tissue itself
- Chemical stimuli, such as neurotransmitters, hormones, and local changes in pH
Muscle fibers
Hundreds to thousands of cells that make up the separate organs of the skeletal muscles
Subcutaneous layer or hypodermis
Separates muscle from skin
Fascia
- dense sheet or broadband of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body
- holds muscles with similar functions together
- allows free movements of muscles 4. carries nerves, blood vessels, and lymphatic vessels
- fill spaces between muscles
The three layers of connective tissue?
- Epimysium
- Perimysium
- Endomysium
Epimysium
The outer layer in circling the entire muscle
consists of dense irregular connective tissue
Perimysium
Also a layer of dense irregular connective tissue but surrounds groups of 10 to 100 or more muscle fibres separating them into bundles called fascicles
Fascicles
Little bundles
large enough to be seen with the naked eye
give a cut of meat its characteristic “grain”
Endomysium
Penetrates the interior of each fascicle and separates into individual muscle fibres from one another
mostly reticular fibres
Tendon
All three connective tissue layers may extend beyond the muscle fibres to form a rope like tendon the attaches of muscle to the periosteum of a bone
Aponeurosis
Connective tissue elements that extend as a broad, flat sheet
Nerves and blood supply of the skeletal muscles
1.Well supplied With nerves and blood vessels
2. neurons that stimulates skeletal muscles to contract are somatic motor neurons
3.
Plasma membrane of a muscle cell?
Sarcolemma
Thousands of tiny invaginations of the sarcolemma ?
Transverse (T) tubules
Transverse tubules
Tunnel in from the surface towards the centre of each muscle fibre
open to the outside of the fibre they are filled with interstitial fluid
muscle action potentials travel along the sarcolemma and through the T tubules quickly spreading throughout the muscle fibre
Sarcoplasm
Within the sarcolemma the cytoplasm of a muscle fibre includes a substantial amount of glycogen and includes a red coloured protein called myoglobin found only in muscle
Myoglobin
A red coloured protein found only in muscle that binds oxygen molecules that diffuse into muscle fibres from interstitial fluid
releases oxygen when it is needed by the mitochondria for ATP production
Myofibrils
It small structures that appear in the sarcoplasm like it’s stuffed with little threads
the contractile organelles of skeletal muscle extending the entire length of a muscle fibre
giving it the striated look
Sarcoplasmic reticulum (SR)
A fluid filled system of membraneous sacs that in circles each myofibril similar to smooth endoplasmic reticulum and non-muscular cells
Terminal cisterns
Dilated Sarco plasmic reticulum
butt against the T tubule from both sides
Triad
Is formed by a transverse tubules and the two terminal cisterns on either side of it
Filaments
Smaller structures within the myofibrils consisting of thin filaments and thick filaments
Directly involved in the contract I’ll process
Arranged in compartment called sacral mirrors
Thin filaments
8nm in diameter and 1-2 um long, Composed of the protein Actin
Too thin filaments for every thick filament in the region of filament overlap
Thick filaments
16 nm in diameter and 1-2 um long, Composed of the protein myosin
Sacromeres
Basic functional units of a myofibril
Z discs
Are narrow plate shaped regions of dense protein material that separate one sarcomere from the next
Organization of a sarcomere
A band - darker middle portion
Zone of overlap - toward each end of the A band, where thick and thin filaments lie side by side
I band - Lighter less dense area that contains the rest of the thin filaments but no thick filaments and a Z disc passes through the centre of each I band
Alternating dark A bands and light I-band create the striation look
H zone - narrow, centre of each A band contains thick filaments
M line - supporting proteins that hold the thick filaments together at the centre of the H zone
The three kinds of proteins the build myofibrils
- Contractile proteins
- Regulatory proteins
- Structural proteins
Contractile proteins
Generate force during contraction
Consists of myosin and actin proteins and other components of thick and thin filaments
Myosin
Main component of thick filaments and functions as a motor proteins in all three types of muscle tissue
Motor protein
Pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion which is the production of force
Shaped like to golf clubs twisted together
Myosin tail
Points toward the end line in the centre of the circle mirror tales of neighbouring myosin molecules lie parallel to one another forming the shaft of the thick filament
Myosin heads
Two projections of each meion molecule that has two binding sites
1. active binding site
2. ATP binding site
Actin
Main component of thin filament individual actin molecules join to form an actin filament that is twisted into a helix
on each actin molecule is a myosin binding site where a myosin head can attach
Tropomyosin and troponin
Part of the thin filament in smaller amounts than actin
Tropomyosin blocks myosin from binding to actin in relaxed muscles tropomyosin strands are held in place by troponin molecules
What do structural proteins contribute to
Alignment, stability, elasticities, extensibility of myofibrils
Titin
A key structural protein the third most plentiful protein in skeletal muscle after actin and myosin and span half a sacromere from a Z disk to an M line help stabilize the position of thin filament
Key structural proteins
Titin
Actin
Myomesin
Nebulin
Dystrophin
Sliding filament mechanism
As the thin filaments slide inward the I-band and H zones narrow and eventually disappear all together when the muscle is maximally contracted
Contraction cycle
The repeating sequence of events that causes the filament to slide
What are the four steps in the contraction cycle
- ATP hydrolysis
- Attachment of myosin to actin
- Power stroke
- Detachment of myosin from actin
Cross-bridge
When a myosin head attaches to the Myosin binding site during the contraction cycle the Myosin head is referred to as a crossbridge
Power stroke
As the myosin head changes to its new position it pulls the thin filament past the thick filament toward the centre of the Sarcomere generating tension in the process
Excitation-contraction coupling
The sequence of events that links excitation (a muscle action potential) to contraction (sliding of the filaments)
Voltage gated calcium channels
Are located in the T tubule membrane they are arranged in clusters of four known as tetrad with the main role been excitation-contraction coupling the service voltage sensors, the trigger, opening of calcium release channels
Calcium release channels
Present in the terminal sisternal membrane of the SR when a skeletal muscle fibre is at rest the part of the calcium release channel that extends into the sarcoplasm is blocked by a given cluster of voltage gated calcium channels preventing calcium from leaving the SR
Calcium ATPase pumps
Found in the terminal cisternal membrane of the sarcoplasmic reticulum
Use ATP to constantly transport calcium from the sarcoplasm into the SR
Calsequestrin
Molecules of a protein found inside the SR bind to calcium allowing even more calcium to be sequestered within the SR
Length-tension relationship
Indicates how the forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins
Somatic motor neurons
Stimulates skeletal muscle fibres to contract has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibres
Neuromuscular junction (NMJ)
Where muscle action potential arises
The synapse between a somatic motor neuron and a skeletal muscle fibre
Synapse
A region where communication occurs between two neurons or between a neuron and a target cell
in this case between a somatic motor neuron and a muscle fibre
Synaptic cleft
A small gap at the synapse that separates the two cells because the cells are not touching the action potential cannot “jump the gap” from one cell to another
Neurotransmitter
Used for cell communication due to the synaptic cleft
How does a nerve impulse elicit a muscle action potential?
- Release of acetylcholine
- Activation of ACh receptors
- Production of muscle action potential
- Termination of ACh activity
Curare
A poison used by South American Indian on arrows and blow gun darts causes muscle paralysis by binding to and blocking ACh receptors in the presence of curare the ion channels do not open
What are the three ways muscle fibres have to produce ATP
- From creatine phosphate
- By anaerobic glycolysis
- By aerobic respiration
Creatine phosphate
 An energy rich molecule that is found in muscle fibres synthesized from excess ATP that was produced when the muscle fibres were relaxed
First form of energy when muscle contraction begins
Creatine
Small amino acid like molecule does synthesized in the liver kidneys and pancreas and then transported to muscle fibres
Glycolysis
Quickly breaks down each glucose molecule into two molecules of pyruvic acid
occurs in the cytosol and produces a net gain of two molecules of ATP
Does not require oxygen
Anaerobic glycolysis
The entire process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration
Aerobic respirations
If sufficient oxygen is present the pyruvic acid formed by glycolysis enters mitochondria where it undergoes aerobic respiration a series of oxygen requiring reactions (the Krebs cycle and the electron transport chain) that produces ATP, carbon dioxide, water, and heat
when oxygen is present glycolysis the Krebs cycle and electron transport chain occur
What are the two sources of oxygen for muscular tissue
- Oxygen that diffuses into muscle fibres from the blood
- Oxygen released by myoglobin within muscle fibres
Muscle fatigue
The inability of a muscle to maintain force of contraction after prolonged activity
Oxygen debt
Refers to the added oxygen over and above the resting oxygen consumption that is taken into the body after exercise
What are the three ways that extra oxygen is used to pay back or restore metabolic conditions?
- Convert lactic acid back into glycogen stores in the liver
- To resynthesized creatine phosphate and ATP in muscle fibres
- To replace the oxygen removed from myoglobin
Recovery oxygen uptake
Is a better term than oxygen debt for the elevated use of oxygen after exercise
Motor unit
Consists of a somatic motor neuron plus all of the skeletal muscle fibres it stimulates
a single somatic motor neuron makes contact with an average of 150 skeletal muscle fibres
in one motor unit contract in unison
Twitch contraction
Is the brief contraction of all muscle fibres in a motor unit in response to a single action potential in its motor neuron
Myogram
The record of a muscle contraction
Latent period
The brief delay that occurs between application of the stimulus in the beginning of the contraction
Contraction period
Calcium binds to troponin, myosin-binding sites on actin are exposed, and cross bridges form. peak tension develops in the muscle fibre
Relaxation period
Is actively transported back into the sarcoplasmic reticulum, myosin binding sites are covered by a tropomyosin, myosin heads detach from actin, and tension in the muscle fibre decreases
Refractory period
The period of lost excitability and is a characteristic of all muscle and nerve cells
Wave summation
Stimuli arriving at different times causing larger contractions
Unfused (incomplete) tetanus
Sustainable wavering contraction caused by partially relax muscles between stimuli
Fused (complete) tetanus
Is the stain contraction in which individual twitches cannot be detected caused by a stimulated muscle fibre that does not relax at all
Motor unit recruitment
The process in which the number of active motor unit increases
Muscle tone
A small amount of tauntness or tension in the muscle due to week in voluntary contractions of its motor units muscle tone is established by neurons in the brain and spinal cord that excite the muscles motor neurons
Why is a muscle flaccid
When the motor neuron serving a skeletal muscle or damaged or cut the muscle becomes flaccid the state of lymph nodes in which muscle tone is lost
Isotonic contraction
The tension developed in the muscle remains almost constant while the muscle changes in length
isotonic contractions are used for body movements and for moving objects
the two types of isotonic contractions are concentric and eccentric
Concentric isotonic contraction
If the tension generated is great enough to overcome the resistance of the object to be moved the muscle shortens and pulls on another structure such as a tendon to produce movement and to reduce the angle at a joint
Eccentric isotonic contraction
When the length of a muscle increases during a contraction the tension exerted by the myosin cross bridges resist movement of a load process this type of contraction produce more muscle damage then concentric isotonic contractions
Isometric contraction
The tension generated is not enough to exceed the resistance of the object to be moved in the muscle does not change its length
important for maintaining posture and for supporting objects in a fixed position
even though the body is not moving energy is still expended
Red muscle fibres
Skeletal muscle fibres that have a high myoglobin content and appear darker
Contain more mitochondria in our supplied by more blood capillaries
White muscle fibres
Those that have a low content of myoglobin and appear lighter
The three main types of skeletal muscle fibres classification
- Slow oxidative fibres
- Fast oxidative glycolytic fibres
- Fast glycolytic fibres
Slow oxidative (SO) fibers
Appear dark red because they contain large amounts of myoglobin and many blood capillaries because they have large amounts of mitochondria SO fibres generate ATP mainly by aerobic respiration
Fast oxidative-glycolysis (FOG) fibers
Typically the largest fibres
contain large amounts of myoglobin in many blood capillaries
dark red appearance
generate considerable ATP by aerobic respiration which give them a moderately high resistance to fatigue
Fast glycolytic (FG) fibers
Have low myoglobin content relatively few blood capillaries and few mitochondria and appear white in colour
contain large amounts of glycogen and generate ATP mainly by glycolysis contract strong and quickly due to the rapid ability to produce hydrolyze ATP
Cardiac muscle tissue
The principal tissue in the heart wall are sheets of connective tissue that contain blood vessels, nerves, and the conduction system of the heart
cardiac muscle fibres have the same arrangement of actin and myosin in the same band zones and Z discs of skeletal muscle fibres with unique inter-collated discs
Intercalated discs
Unique to cardiac muscle fibres and are structures with irregular transverse thickening of the sarcolemma that connect the ends of the cardiac muscle fibres to one another
Containing desmosomes which hold the fibres together and gap junctions which allow muscle action potentials to spread from one cardiac muscle fibre to another
Visceral smooth muscle tissue
Found in the skin in tubular arrangements that form part of the walls of small arteries and veins and of Hall of organs it is the more common type of smooth muscle tissue
Multiunit smooth muscle tissue
Consists of individual fibres each with its own motor neuron terminals and with few gap junctions between neighbouring fibres
stimulation of one visceral muscle fibre causes contractions of many adjacent fibres but stimulation of one multiunit fibre causes contractions of that fibre only
Microscopic anatomy of smooth muscle
Sarcoplasm is smooth muscle fibres contains both thick and thin filaments not arranged in orderly sarcomeres
Also contains intermediate Filaments
Smooth muscle has small pouch like invaginations of the plasma membrane called caveolae that contain extracellular calcium
In smooth muscle fibres the thin filaments attached to structures called dance bodies with your functionally similar to Z discs in striated muscles
Physiology of smooth muscle
Contraction in a smooth muscle fibre starts more slowly and last much longer than skeletal muscle fibre contractions
smooth muscle fibers shorten and stretch to a greater extent than the other muscle types
Calmoudin
After binding to calcium in the Sarcoplasm, calmodulin activates an enzyme called myosin light change kinase, this enzyme uses ATP to add a phosphate group to a portion of the myosin head once the phosphate group is attached, the myosin head can bind to actin and contraction can occur
Smooth muscle tone
Slow moving calcium in and out of the muscle fibre delays relaxation
this prolonged presence of calcium in the cytosol provides for smooth muscle tone
Stress relaxation response
Is the phenomenon from which tension decreases after smooth muscle fibres are stretched developing increase tension
Hypertrophy
The enlargement of existing cells
how mature skeletal muscle fibres grow after birth
Hyperplasia
An increase in the number of fibres
Pericytes
Cells that new smooth muscle fibres can arise from these are stem cells found in association with blood capillaries and small veins
