Muscular system part 1 Flashcards
How many muscles are there in the human body
600
what is the essential function of muscle
contraction or shortening
muscular contractions provide
body movement, propel body fluids and food, generate heartbeat, and distribute heat
What are the 3 types of muscle tissue that humans have
- Skeletal muscle
- cardiac muscle
- smooth muscle
Skeletal and smooth muscle cells are both
elongated; hence their cells are called muscle fibers
what are the functions of skeletal muscles
- support the body and maintains posture
- make bones and other body parts move
- help maintain a constant body temperature
- contractions assists in blood and lymphatic circulation
- help protect bones and internal organs and stabilize joints
- form sphincters to regulate the passage of substances
what are sphincters
specialized donut-shaped muscles that help to pinch shut openings
what are the properties of the skeletal muscles
- excitability
- contractility
- extensibility
- elasticity
What is Endomysium
a thin layer of areolar connective tissue that surrounds each individual muscle fiber (muscle cell)
What are muscle fibers grouped into bundles called
fascicles
what is perimysium
a sheath of connective tissue that covers the dascicles
what is epimysium
the connective tissue layer that closely surrounds the bulk of the entire skeletal muscle
collagen fibers of the epimysium continue as a strong
tendon that attaches the muscle to a bone that they will move
what is aponeurosis
connective tissue forms broad fibrous sheets that attach muscles indirectly to bones, cartilages, or connective tissue coverings
what is a skeletal muscle fiber
a single cells that contracts in response to stimulation and relaxes when the stimulation ends
what is the plasma membrane called in the skeletal muscle
sarcolemma
what is the cytoplasm called in the skeletal muscle
sarcoplasm
what is the smooth endoplasmic reticulum called in the skeletal muscle
sarcoplasmic reticulum
what is the storage site for calcium (Ca++)
sarcoplasmic reticulum
Nuclei are pushed aside by
the long ribbon-like organelles known as myofibrils
what does the sarcoplasmic reticulum do
encases hundreds or even thousands myofibrils which are bundles of myofilaments
the sarcoplasm contains
- mitochondria between myofibrils
- glycogen that provides stored energy for muscle contraction
- myoglobin that binds oxygen until it is needed for muscle contraction
Alternating Light (I) and Dark (A) bands along the length of the myofibrils give the muscle cell its
striated appearance
Each myofibril is composed of
numerous sarcomeres
Each sarcomere extends between two dark, vertical lines called
Z lines
The light (I) band has a midline interruption (darker area) called
Z discs
The dark (A) band has a lighter central area called the
H zone
The M Line is the
center of the H zone that contains tiny protein rods that hold the adjacent thick filaments together
a sarcomere contains two types of proteins called
myofilaments
Thick and dark (A band) are filaments composed of
a single protein called myosin
Thin and light (I band) are filaments composed of
3 proteins
- actin
- troponin
- tropomyosin
The thick filaments are located in the ___ while the thin filaments are located in the __
- center
- ends
When a sarcomere shortens
the actin filaments slide past the myosin filaments and approach one another, forming hundreds of cross-bridges
These cross-bridges then move like the oars of a boat to
pull the thin filaments toward the center of the sarcomere
this movement is called the
sliding filament theory of muscle contraction
The sliding filament theory of muscle contraction brings the
Z lines closer together and increases the zone of overlap between thin and thick filaments
The myosin filaments contain the
ATPase enzyme which breaks down ATP and release energy needed for muscle contraction
Troponin and tropomyosin are inhibitory proteins that prevent the
sliding of the actin and myosin filaments when the muscle fiber is relaxed
The nerve impulses for voluntary movement come from the
motor areas of the brain
the motor areas of the brain generate
motor impulses
what do the motor impulses travel along
motor nerves
after motor nerves
motor neurons in the spinal chord
motor neurons carry the impulses to the
muscles and cause them to contract
what is a motor unit
a single motor neuron and all the skeletal muscle cells it stimulates constitute a motor unit
each motor neuron has a long extension called an
axon
An axon reaches the muscle and branches into a number of
axon terminals
the axon terminals form
junctions with the sarcolemma of a different muscle cell
The junctions that contain vesicles filled with a chemical are called
Neuromuscular junctions
What is the chemical in the vesicles called
nuerotransmitter
What is the specific neurotransmitter that stimulates skeletal muscle cells
Acetylcholine
What is the point where the axon terminal of a motor neuron contacts the sarcolemma of a muscle cell
neuromuscular junction
The axon terminal contains presynaptic vesicles containing a chemical called
neurotransmitter acetylcholine
the sarcolemma of the muscle fibers contain
receptor sites for acetylcholine
At the synapse the synaptic cleft is
the tiny space between the axon terminal and the sarcolemma
events at the neuromuscular junctions
- motor impulse
- calcium channels open
- calcium stimulates the release of acetylcholine
- sarcolemma becomes more permeable to sodium ions
- generates a current called action potential
- a single nerve impulse produces only one contraction
what happens in event 1
contraction begins when a motor impulse arrives at the axon terminal
what happens in event 2
calcium channels open and the calcium enters the axon terminal
what happens in event 3
calcium stimulates the release of acetylcholine from presynaptic vesicles. Acetylcholine crosses the synaptic cleft and binds to receptors in the sarcolemma of the muscle fiber
what happens in event 4 (depolarization)
if enough acetylcholine is released, the sarcolemma becomes more permeable to sodium ions that rush into the muscle cells and diffuse potassium ions
- the imbalance gives the cell excessive positive sodium ions
what happens in event 5
action potential if generated and travels over the sarcolemma conducting electrical impulse resulting in the contraction of the muscle
when acetylcholine is broken down by acetylcholinesterase in event 5 what occurs
repolarization
what happens in event 6
a single nerve impulse produces only one contraction. Until one Is over the next one cannot start
depolarization is followed by repolarization which involves
the outflow of potassium ions that will restore positive charge to the outside of the sarcolemma
AcetylCholinesterase enzyme in the sarcolemma
inactivates acetylcholine and in the absence of further impulses, the muscle fiber will relax and return to its original length
Graded responses are produced in 2 ways
- by changing frequency
- by changing the number of muscle cells being stimulated
what is an example of changing the frequency of muscle stimulation
muscle twitches, Tetanus
what is an example of changing the number of muscle cells being stimulated at a time
stronger muscle contraction
ATP is the
primary source of energy and is not stored in large amounts in muscle fibers
Secondary sources of energy are
Creatin PO4 and Glycgoen
Creatine PO4
an energy-transferring molecule; the energy released by the break down of creatine is used to synthesize more ATP
Glycogen
the most abundant source of ATP
when energy is needed for sustained contractions it is first broken down to glucose and then ATP
aerobic metabolism
oxygen is present
anaerobic metabolism
oxygen is not present
muscles have 2 sources of oxygen
- hemoglobin
- myoglobin
Hemoglobin
circulating blood brings a continuous supply of oxygen carried by the protein hemoglobin present in the red blood cells
myoglobin
muscle fibers carry a protein called myoglobin which stores some oxygen
what are the 3 pathways for ATP generation
- aerobic respiration
- anaerobic glycolysis
- direct phosphorylation
aerobic respiration (Kreb’s cycle)
- occurs in mitochondria
- very efficient yields 32 ATP
- slow
- requires lots of oxygen during strenuous activty
Anaerobic glycolysis
- occurs in the cytoplasm
- glucose breaks down to pyruvic acid and produces 2 ATP molecules
- pyruvic acid is converted to lactic acid
- 2 1/2 times faster
lactic acid accumulation produces severe
muscle fatigue and soreness
direct phosphorylation
- it can regenerate ATP by transferring its phosphate to ADP
- generates ATP very rapidly but it supplies only for 8 seconds
creatine phosphate is rebuilt when a muscle is
resting by transferring a phosphate group from ATP to creatine
what is oxygen debt (deficit)
in spite of the increase in respiratory rate, muscle fibers literally run out of oxygen
the intermediate lactic acid produced in an anaerobic process
lowers the pH of the intracellular fluid within the muscle cell which contributes to muscle fatigue
muscle tone is a steady or
constant state of partial contraction in a resting muscle
hypertrophy
muscle increases in size due to exercise
atrophy
muscle decreases in size
what are the types of muscle contractions
- isotonic contractions
- isometric contractions
isotonic contraction
- muscle contracts and brings movement
- tone or tension remains the same
- examples include jogging, swimming, weight lifting etc
isometric contractions
- involves contraction without movement
- tension in muscles increases
- examples include pushing against the wall with bent elbows, both hands pushing equally
