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Muscles and Bones - eternity vasquez period 6 - Coggle Diagram
Muscles and Bones - eternity vasquez period 6
Types of Muscle Tissue
Three types of Muscle tissue
Skeletal
(muscle cells elongated and referred to as muscle fibers)
Cardiac
Smooth
( muscle cells elongated and referred to as muscle fibers)
Skeletal
Body Location
attach to bones o facial muscles to skin
Cell shape and appearance
single, long cylindrical, mutlinucleate cells with striations
Cardiac
Body Location
walls of heart
Cell Shape and appearance
branching chains of cells, one or two striations
Smooth
Body Location
Unitary ,muscle in walls of hollow
Cell shape and appearance
single, spindle shaped, uninucleate, no striations
Characteristics of Muscle Tissue
Excitability
: ability to receive and respond to stimuli
Contractility
: ability to shorten forcibly when stimulated
Extensibility:
ability to be stretched
Elasticity:
ability to recoil to resting length ( bounce back to normal size )
Muscle Functions
Produce Movement:
responsible for all locomotion and manipulation
2 Maintain posture and body position
3. Stabilize joints
4. Generates heat as they contract
Skeletal Muscle ( made up of 3 features )
Nerve and Blood Supply
muscles receive a nerve, artery, and veins
contracting muscle fibers require a huge amount of oxygen and nutrients
Connective Tissue Sheaths
- Epimysium
:
dense irregular connective tissue surrounds entire muscle ( can blend with fascia )
- Perimysium:
fibrous CT surrounding fascicles ( fasicicles are a group of muscle fibers)
- Endomysium:
fine areolar CT surrounding each muscle fiber
Attachments
muscles span joints and attach to bones ( muscles attach bone in 2 places )
*- Insertion:
* attachment to movable bones
-
Origin
: attachment to immovable or less movable bone
Muscle Fiber Microanatomy & Sliding Filament Model
skeletal muscle fibers are long, cylindrical cells that contain multiple nuclei
- SarcoLEMMA:
muscle fiber plasma membrane
- SarcoPLASM:
muscle fiber cytoplasm
contains glycosomes for glycogen storage and for myogoblin for 02 storage
Myofibrils ( modified organelles )
myofibrils are densely packed, rodlike elements
Myofibril Features:
-
Striations
: strips
A bands:
dark regions
- H zone:
lighter region in middle of dark A band
-
M Line
: line of protein (myomesin) that bisects H zone vertically
- I bands:
lighter regions
- Z disc (line)
: coin shaped sheet of proteins on midline of light I bands
Sarcomere:
the smallest contractile unit ( functional unit ) of muscle fiber
contains A band with half of an I band at each end
are between Z discs
Myofilaments:
smaller than sarcomere
an arrangement of actin and myosin myofilaments within sarcomere
- Actin
: thin filaments. Extends length of A band and anchored to z discs
- Myosin
: thick filaments. Extend length of A band and connected at M line
Thick Filaments:
composed of protein
MYOSIN
that contains two heavy and four light polypepticle chains; heavt chains intertwine and form myosin tail
During contraction, myosin globular heads link thick and thin filaments together. It forms cross bridges
Thin Filaments:
composed of fibrous protein
ACTIN
; actin is polypeptide made up of kidney shaped G actin globular subunits
G actin subunits link together to form long, fibrous F actin filaments
The two F actin strands twist together to form a thin filaments.
Tropomyosin and troponin
: regulatory proteins bound to actin
Proteins that help form structure of myofibril
- Elastic Filament:
composed of protein titin; it holds thick filaments in place and helps recoil after stretch, resists excessive stretching
-Dystrophin:
links thin filaments to protein of sarcolemma
Nebulin, myomesin, C proteins
bind filaments or sarcomeres together; this maintains alignment of sarcomere
Sarcoplasmic Reticulum
smooth endoplasmic reticulum tubules surrounding each myofibril
; most run LONGtidudinally, terminal cisterns form perpendicular cross channels at the A - I band junction
stores and releases Ca^2+
T- Tubules
tube formed by protrusion of sarcolemma deep into cell interior
it increases muscle fiber's surface area greatly
allows electrical nerve transmissions to reach deep into interior of each muscle fiber
tube penetrate cells interior at each A - I band junction between terminal cisterns
Triad: formed from terminal cistern of one sarcomere, T tubule, and terminal cistern of neighboring sarcomere
Triad Relationships:
t tubule contains integral membrane proteins that protude into intermembrane space; it acts as voltage sensors that change shape in response to an electrical current
SR cistern membranes also have integral membrane protein that protrude into intermembrane space ; SR integrals proteins control opening of calcium channels in SR cisterns
Sliding Filament Model of Contraction
Contraction
: activation of cross bridges to generate force
there is shortening when tension generated by cross bridges on thin filaments exceeds forces opposing shortening
contraction ends when cross bridges become inactive
at a relaxed state thin and thick filaments overlap only slightly at ends of A band
Sliding Filament model of contraction: states that during contraction, thin filaments slide past thick, causes actin and myosin to overlap more
Causes of shortening of muscle fiber
Z discs are pulled toward the M line
I bands shorten
Z discs become closer
H zones dissapear
A bands move closer to each other
Ion Channels
Chemically gated ion channels (class of ion channels)
Voltage gated ion channels (class of ion channels)
role in changing of membrane potentials
Anatomy of Motor Neuron and the neuromuscular Junction
axon: (long extensions of motor neurons) travel from central nervous system to skeletal muscle
axon terminal: (end of axon) and muscle fiber are seperated by gel filled space called synaptic cleft
stored within axon terminals are membrane bound synaptic vesicles
NMJ ( neuromuscular junction) consists of axon terminals, synaptic cleft and junctional folds.
4 steps must occur for skeletal muscle to contract
1: Events at Neuromuscualr Junction
2: Muscle Fiber Excitation
3: Excitation Contraction Coupling
4: Cross Bridges Cycling
Events at the Neuromuscular Junction
1- AP arrives at axon terminal ( the end of an axon)
2- Voltage gated calcium channels open, calcium enters motor neuron
3- Calcium entry cause release of ACh neurotransmitter into synaptic cleft
4- ACh diffuses across to ACh receptors on sarcolemma
5- ACh binding to receptors, open gates, allows Na^+ to enter results in end plate potential
6- Acetylcholinesterase degrades ACh
Generation of an Action Potential Across the Sarcoloemma
resting sarcolemma is polarized; voltage exists across membrane
Occurs in 3 steps
Generation of end plate potential
cause chemically gated ion channels (ligands) on sarcolemma to open
Na^+ diffuses into muscle fibers; sarcolemma becomes less negative ( which means more positive )
Ka^+ diffuses outward
Depolarization
generation and propagation of an action potential (AP)
large influx of Na^+ through channels into cell triggers AP that is unstoppable and will lead to muscle fiber contraction
AP spreads across sarcolemma from one voltage gated Na^+ channel to next one in adjacent areas, cause that area to depolarize
Repolarization
Na^+ voltage gated channels close and voltage gated K^+ channels open
K^+ efflux out of cell rapidly brings cell back to initial resting membrane voltage
Refractory Period: muscle fiber cannot be stimulated for a specific amount of time until repolarization is complete
Muscle Fiber Contraction: cross bridge cycling
Cross Bridge formation high energy myosin head attaches to actin thin filament active site
Working (power) stroke: myosin head pivots and pulls thin filament toward M line
Cross Bridge detachment: ATP attaches to myosin head, causing cross bridge to detach
Cocking of myosin head: energy from hydrolysis of ATP " cocks" myosin head into high energy state
Rigor Mortis
3 to 4 hours after death, muscle will begin to stiffen
intracellular calcium levels increase due to ATP no longer being synthesized. calcium cannot be pumped back into SR
ATP is needed for cross bridge detachment
muscles stay contracted until muscle proteins break down, causing myosin to release
Whole Muscle Contraction
- Isometric contraction
: NO shortening; muscle tension increases but does NOT exceed load
muscle changes in length and moves load
-
Isotonic contraction
: shortens when muscle tension exceed load; load is greater than the max tension can generate. muscle neither shortens nor lengthens
each muscle is served by at least one motor nerve
The motor unit, muscle twitch, and muscle tone
Muscle Twitch:
simplest contraction resulting from a muscle fiber's response to a single AP from motor neuron
Motor unit:
consists of the motor neuron and all muscle fibers it supplies
the smaller the fiber #, the greater the fine control
Muscle tone:
constant, slightly contracted state of all muscles
due to spinal reflexes
Muscle Fatigue
inability to contract despite continued stimulation
causes include :
ionic imbalances can cause fatigue
decrease ATP and increase magnesium
decrease glycogen
lack of ATP is rarely a reason for fatigue, except in severely stressed muscles
Factors of Muscle Contraction
number of muscle fibers stimulated
the more motor units recruited, the greater the force
Relative size of fibers
the bulkier the muscle, the more tension it can develop
Frequency of stimulation:
the higher the frequency, the greater the force
Degree of Muscle stretch
muscle fibers with saromere that are 80% - 120% their normal resting length generate more force
Adaption to Exercise
- Aerobic (endurance) exercise
: jogging, swimming, biking leads to increase
: muscle capillaries
: number of mitochondria
: Myoglobin synthesis
results in greater endurance, strength and resistance to fatigue
Resistance Exercise
weights, lifting, or isometric exercises. can lead to muscle hypertrophy
due primarily to increase in fiber size; it increases mitochomndria, myofilaments, glycon stores and ct