Muscles Pt. 1 Flashcards
Muscle has 4 common characteristics
-Excitability
-Contractibility
-Extensibility
-Elasticity
Excitability
Respond to a stimulus
Contractility
Shorten in length when stimulated
Extensibility
will stretch when pulled
Elasticity
return to normal shape and length
3 types of muscle
skeletal, cardiac, and smooth
Skeletal muscle
-controlled by the conscious mind
-Moves bones of the skeleton
-is usually what we think of when we hear the word muscle
Cardiac muscle
-found only in the heart
-starts the entire heart beating before an animal is born and keeps it going until it dies
Smooth Muscle is found where?
Found all over the body - eyes, air passageways, lungs, stomach/intestines
Skeletal Muscle - Gross Anatomy
Skeletal muscle is a group of muscle cells surrounded by a fibrous connective sheath called Epimysium (means upon muscle)
Most skeletal muscles are attached to bones at both ends by
Tendons - Tough, fibrous connective tissue - they are a continuation of the epimysium
Some muscles are attached to bones or other muscles by sheets of fibrous CT called
Aponeuroses
What is the most prominent aponeuroses??
Linea alba (white line) - Runs lengthwise between abdominal muscles on the ventral midline (where you cut during a spay)
Which site of attachment is the most stable?
origin of the muscle - does not move much when the muscle contracts
Which site of attachment undergoes the most movement?
insertion of the muscle
What happens to the muscle when a nerve impulse hits a muscle?
it contracts - pulls on its attachment - the contraction produces movement of bones and other structures
Skeletal muscles rarely act alone - they work in groups - One group _________ and the other _________
One group makes the movement - this group is known as the agonist (prime mover) - other groups stabilize nearby joints
Antagonist
muscles the directly opposed the action of an agonist
- partial contraction - antagonists can smooth out the movements of the agonist
-Can contract forcefully - results in rigidity and lack motion
Synergist
The skeletal muscle that contracts at the same time as an agonist and assists it in carrying out its action
- Ex: deep flexor muscle flexes the digit at the same time the superficial digital flexor flexes to aid in movement
Fixator
Stabilizes joint to allow other movements to take place
Skeletal muscle cells are large (not wide, but long), these are called
fibers rather than cells
Skeletal fibers can have up to 100 or more per fiber. All are located just beneath __________
the sarcolemma - muscle cell membrane
Muscle fibers are made up of hundreds or thousands of smaller _______ packed together lengthwise
myofibrils - these fibrils are made of thousands of even tinier protein filaments
Organelles between the myofibrils in a muscle fiber include:
-many energy producing mitochondria
-extensive network of sarcoplasmic reticulum - storage organelle for Ca ions
-A system of tubules called transverse tubules or T-tubules - extend in from the sarcolemma
One myofibril is made up of a series of protein filaments. Together they form the contractile units of a myofibril. Each contractile unit is known as _________
sarcomere - the basic contracting unity of skeletal muscle
Sarcomeres lay end to end in one myofibril. Each sarcomere has a disc on each end
these are know as the Z line or Z disc
-Sarcomeres share these discs - there is one common disc between adjacent sarcomeres
Inside each sarcomere, there are two primary protein filaments responsible for contraction
Actin filaments
Myosin filaments
Actin filaments
thin protein filaments
Attach to the Z lines and extend toward the center of the sarcomere - actin filaments don’t meet
Myosin filaments
thick protein filaments
Appear to float in the middle of the sarcomere between the parallel actin fibers - THEY DO NOT CONNECT TO Z LINES
Looking at the myofibril under the microscope, there will be large light-colored bands
-These are I-bands - made of thin actin filaments
-Extend from one end of thick myosin in one sarcomere across the Z-line to the beginning of the myosin fibers of the next sarcomere
-In the center of the band is the dark Z disc/line - this is the attachment site for actin filaments
-From one z-line to the next is one sarcomere
Between the light I-bands are darker bands called
A-bands and H-bands
A-bands
are areas where the thick myosin and thin actin filaments overlap
H-bands
The light-colored area located in the middle of the A-band
Made up of myosin filaments only - no overlapping actin filaments
-Does not cover the entire width of the myosin filament
Actin fibers are actually ……..
Two strands of protein twisted together - In a helical structure like DNA
-The myosin molecule has a twisted tail attached to two globular heads - They form cross-bridges to actin and interact with the actin to shorten the sarcomere during contraction
Sites where the ends of the motor never fibers connect to muscle fibers are called
Neuromuscular junctions - there is a small space between the end of the nerve fiber and sarcolemma called the synaptic space
In the end of a nerve fiber in a neuromuscular junction are tiny sacs called
synaptic vesicles
synaptic vesicles contain a chemical neurotransmitter called
Acetylcholine (ACh)
When an impulse comes down the motor neuron It causes ACh release
Quickly diffuses across the synaptic space - Binds to the sarcolemma receptors - This starts contraction of the muscle fiber
The effect of ACh on the receptor is very short
ACh found in the synaptic space - quickly removes ACh from the receptor and splits it apart - this ends the effect of the nerve impulse
Each nerve fiber innervates more than one fiber
the number of muscle fibers per nerve fiber determines how small a movement will result from the stimulus
motor unit
used to describe one nerve fiber an all the muscle fibers it innervates
endomysium
a delicate CT layer that surrounds the individual skeletal muscle fiber - composed of fine reticular fibers
Groups of skeletal muscle fibers are known as ____
fascicles
these fascicles are bound together by a tougher CT layer called
perimysium - composed of reticular fibers an thick collagen fibers
Groups of fascicles are surrounded by
epimysium
-a fibrous connective tissue layer composed of largely of tough collagen fibers
- this is the outer covering of the entire muscle
these 3 layers (fascicles, perimysium, and epimysium) are continuous with ____
tendons or aponeuroses
when a muscle is relaxed
actin and myosin are barely overlapped
when the fiber is stimulated
-Globular heads of the myosin tails - rachet back and forth and pull actin filaments on both sides towards the center of the myosin filaments
-Sliding of filaments over each other shortens the sarcomere
- all sarcomeres moving together causes entire muscle contractions
An individual muscle fiber works on the all-or-nothing principle
it either moves or it doesn’t
The nervous system controls movement by controlling the number of muscle fibers it stimulates
-Small fine movements only require a few fibers to contract
-Larger movements require many fibers to contract
-This is how we develop muscle memory
Muscle contraction requires much energy
Immediate energy source that powers the sliding of actin and myosin filaments is adenosine triphosphate (ATP) - Produced by mitochondria
ATP can release energy, recharge, and release it again
-ATP has 3 phosphate groups attached to an adenosine core - when one phosphate is split off- ATP -> ADP - a lot of energy is released
-Actin and myosin filaments slide
ADP has to be charged back to ATP
Creatine phosphate (CP) does this
-When CP splits, the released energy adds a phosphate group to ADP - Making it turn into ATP
Ultimate source of energy used to make ATP and CP to keep the whole system going
Catabolism = the breakdown of nutrient molecules
- The main compounds used are glucose and oxygen
Glucose
a sugar molecule that is the primary energy source of most body cells
- muscles have a large blood supply that constantly bring new supplies of glucose and oxygen to muscle fibers
When glucose and oxygen supplies are plenty, muscles store energy
Glucose is stored as glycogen
Oxygen is stored in a large protein molecules called myoglobin
When strenuous muscle activity depletes the O2 supply
Myoglobin can release stored O2 supply and resupply the fiber
As long as there is enough oxygen to keep up with demand, myoglobin can continue to release O2 - This is known as
aerobic (oxygen consuming) metabolim
- max amount of energy is extracted from each glucose molecule
Sometimes O2 demand exceeds available supply and the muscle fiber shifts to …
anaerobic metabolism
- this is not as efficient as aerobic
- Incomplete glucose breakdown - Lactic acid is a byproduct
Why do we breath heavy after strenuous activity?
Lactic acid in the blood stream diffuses to liver to be turned into glucose
-this process requires O2
- Heavy breathing is a way to recover the O2 debt
Muscles are less than 100% efficient at converting energy to an activity. A lot of energy is converted to _______
heat
muscle activity is one of the main heat producers in the body
If too much heat is made
heat dissipation takes plave
If hypothermia is present
Muscles generate heat by small, spasmodic contractions - Shivering
