The Muscular System
Muscles Produce Movement or Generate Tension
when resisting movement, muscles generate force that exactly opposes equal but opposite force being applied to a body part
maintenance of constant blood vessel even when blood pressure changes is another example of resistance
if you faint or collapse, you lose control over muscles that support upright posture
muscles generate heat
contraction of skeletal muscles account for over 3/4 of all heat made by the body
when too much heat is produce, the body sweats to release it
contributes to homeostasis
shivering when its cold outside
Muscle Contraction
muscles are EXCITABLE
contract in response to chemical or electrical signals from organ systems
have one basic mechanism (contraction)
in absence of contraction, muscles relax + return to their original length
Synergistic Muscle Groups
work together to create the same movement
Muscle Relaxation
occurs when nerve activity ends
means no Ca is released from sarcoplasmic reticulum
Ca released before end of impulses is transported back into the sarcoplasmic reticulum via active transport (requires ATP)
as Ca concentration in myofibrils falls, troponin tropomyosin complex shifts back into place + blocks binding sites
Antagonistic Muscle Groups
oppose each other
depends on simultaneous shortening of sarcomeres in its cells
IMPORTANT FACTORS
skeletal muscle must be activated by a nerve
nerve activation increases concentration of Ca in vicinity of contractile proteins
presence of calcium permits contraction
absence of calcium prevents contraction
when muscle is no longer stimulated, contraction ends
Isotonic Contractions
when a muscle contracts + maintains a constant force
lifting a weight
Isometric Contractions
force is generated, tension increases, but bones + objects don't move
sitting in a chair
help stabilize skeleton
muscle cells NEVER contract on their own
Muscle Composure
single muscle is a group of individual cells all with the same origin + insertion + same function
individual muscle cells are tube shaped + larger + longer than human cells
each cell contains more than 1 nucleus
located under cell membrane because entire cell is packed with myofibrils (long cylindrical parallel structures)
myofibrils packed with contractile proteins
Actin
thin filaments
structurally linked to Z-line
Myosin
thick filaments that are interspersed at regular intervals between paired actin
located near centre of sarcomeres + stretching between two actin filaments
myofibrils contract + cause muscle to shorten
contractile unit is sarcomere
segment of a myofibril is from one Z-line to a sarcomere
cross section of a muscle reveals it is arranged in fascicles (bundles) enclosed in fascia (sheath of fibrous tissue)
each fascicle contains a lot of muscle fibres
outer surface is also covered by fascia
end of a muscle forms together to make tendons that attach muscle to bone
Muscle Energy
Stored ATP
stored in small quantities
can be used for 10 seconds
only direct source of energy
must be replenished by other energy sources
Stored Creatine Phosphate
3-5x amount of ATP stored
can be used for about 30 seconds
converted quickly into ATP
reaction is reversible
if ATP is not needed, excess ATP is used to build fresh supply of creatine phosphate which is stored until needed
Stored Glycogen
only some muscles store this in large quantities
primarily used during heavy exercise within the first 3-5 mins
ATP yield depends on oxygen availability
one glucose can yield 2 ATP in absence of oxygen
36 can be produced in the presence of oxygen
Aerobic Metabolism
steady high yield because oxygen + nutrients (glucose + fatty acids) are constantly supplied by the blood
always present in the body
increases within several minutes of onset exercise, when blood flow + respiration increase
complete metabolism of 1 glucose yields 36 ATP
rapid breaths help reverse the body's oxygen debt
after exercise you still need oxygen to metabolize lactic acid by aerobic pathways to restore muscles stores of ATP + creatine phosphate to their resting levels
Muscle Fatigue
decline in muscle performance during exercise
most common cause is insufficient energy to meet metabolic demands due to the depletion of energy sources in the body
Slow-Twitch vs. Fast-Twitch Fibres
Slow-Twitch Fibres
break down ATP slowly
contract slowly
tend to make ATP as they need it by aerobic metabolism
contain many mitochondria + are well supplied with oxygen
store oxygen in myoglobin
ability to maintain temporary storage of oxygen, reduces need for oxygen from blood stream
store very little glycogen because they obtain glucose + fatty acids quickly from blood
red muscle
colour provided from myoglobin + blood vessels
offer more endurance
useful for jogging, swimming + biking
important for maintaining body posture
Fast-Twitch Fibres
contract quickly
break down ATP quickly
have fewer mitochondria + blood vessels
NO myoglobin
called white muscle
store large amounts of glycogen + rely heavily on creatine phosphate + anaerobic metabolism for quick bursts of high energy
depend on aerobic metabolisms for any activity sustained, but have capability of using anaerobic mechanisms for brief periods when bursts of power are needed
during anaerobic activities, lactic acid is made + causes fatigue
used for lifting weights or swinging a tennis raquet
Exercise Training
Strength Training
involves doing exercises that strengthen specific muscles usually by providing resistance that makes them work harder
short, intense exercises like weightlifting
builds more myofibrils in fast twitch fibres
causes fast twitch fibres to store more glycogen + creatine phosphate as quick energy sources
increases size of individual muscle cells + builds muscle mass + muscle strength
DOES NOT increase # of muscle cells
Aerobic Training
activities in which the body increases its oxygen intake to meet increased demands for oxygen by muscles
builds endurance
number of blood capillaries supplying muscle increases as well as mitochondria + myoglobin
Major Skeletal Muscle Groups
Anterior Muscle Groups
Masseter
closes the jaw
Pectoralis Major
draws arm forward + toward body
Orbicularis Oris
closes lips
kissing + whistling muscle
Serratus Anterior
helps raise arm
contributes to pushes
draws shoulder blade forward
Biceps Brachii
bends forearm at elbow
Rectus Abdominus
compresses abdomen
bends back bonde
compresses chest cavity
External Oblique
lateral rotation of trunk
compresses abdomen
Adductor Longus
flexes thight
rotates thigh laterally
draws thigh toward body
Sartorius
bends thigh at hip
bends lower leg at knee
rotates thigh outward
Quadriceps Group
flexes thigh at hips
extends leg at knee
Tibialis Anterior
flexes foot toward knee
Posterior Muscle Groups
Deltoid
raises arm
Trapezius
lifts shoulder blade
braces shoulder
draws head back
Triceps Brachii
straightents forearm at elbow
Latissimus Dorsi
rotates + draws arem backward + toward bodt
Gluteus Maximus
extends thight
rotates thigh laterally
Hamstring Group
draws thigh backward
bends knee
Gastrocnemius
bends lower leg at knee
bends foot away from knee
Achilles Tendon
connects gastrocnemius muscle to heel
Skeletal Muscles
attach to bones via tendons
few attach to other muscles or to skin (smile muscles)
Origin of A Muscle
one end of a skeletal muscle that joins to a bone that is relatively stationary
closer to the midline of the body
when a muscle contracts, the insertion is pulled toward the origin
Insertion of A Muscle
other end of a muscle that attaches to another bone across a joint
farther from the midline of the body
Nerve Activation + Ca Release
skeletal muscles stimulated to contract by motor neurons
motor neurons secrete acetylcholine
neurotransmitter that has either excitatory or inhibitory effects on cell
excites skeletal muscle cells
junction b/w motor neuron + skeletal muscle cell is a neuromuscular junction
1. electrical impulse arrives at junction, acetylcholine is released + diffuses across narrow spece b/w neuron + muscle cell + binds to receptor sites on muscle cell membrane
2. binding site causes cell membrane to generate electrical impulse that travels in all directions through T-Cells
function on T tubules is to get electrical impulse to all parts of cell as quickly as possible
3. arrival of impulses triggers release of calcium from sarcoplasmic reticulum
sarcoplasmic reticulum must fit into small amount of space in cell not occupied by myofibrils
function is to store Ca
4. calcium diffuses into cytoplasm + comes in contact w/ myofibrils + leads to contraction
Calcium Initiating Sliding Filament Mechanism
sarcomeres shorten when thick + thin filaments slide past each other
every thin filament consists of 2 actin molecules intertwined + myosin thick like a golf club head
troponin-tropomyosin complex is closely associated with actin filaments + are involved in initiating contraction
in the absence of Ca, it interferes w/ myosin binding sites on actin
in presence of Ca, Ca binds to troponin to shift the complex to expose myosin binding sites + permits the formation of cross bridges
Nerve Activation + Force
Muscle Tension
mechanical force that muscle generate when they contract
amount of tension depends on # of muscle cells in motor unit, # of motor units active + frequency of stimulation of individual motor units
Motor Unit
smallest functional unit of muscle contraction because as the motor neuron is activated, all muscle cells in that motor unit are activated together
larger units generate more force but offer less control
All Or None Principle
muscle cells are completely under the control of their motor neuron
mucle cells always respond with a complete cycle of contraction + relaxation (twitch) every time they are electrically stimulated by an action potential
Muscle Tone
intermediate level of force maintained in whole muscles
exists because at any one time, some muscles motor units are contracting while others are relaxed
increasing tone by activating more motor units is called recruitment
force generation by a muscle is the frequency of stimulation of individual motor units
Muscle Myogram
Latent Period
time delay b/w neural stimulation + start of contraction
time it takes for nerve impulse to travel to sarcoplasmic reticulum, calcium to be released + for myosin to bind to actin
Contraction
actin filaments are pulled toward centre of sarcomere by sliding filament mechanism (shortening)
Relaxation
calcium transported back into sarcoplasmic reticulum
troponin-tropomyosin complex shifts back to original position + sarcomere stretches passively to original length
Summation
if additional stimuli arrive at muscle cell before it has a chance to transport calcium back to sarcoplasmic reticulum, total force produced becomes greater than one twitch alone
force becomes greater because more calcium is present
increasing muscle cell force by increasing rate of stimulation of motor units
Tetanus
if stimulation becomes so frequent that muscle cannot relax, it will be in state of maximum contraction
Nerve Activation + Contraction
Motor Neuron Activation
brief electrical impulse (action potential) that travels down motor neuron from CNS
Neurotransmitter Release
acetylcholine released at neuromuscular junction
Muscle Cell Activation
release of acetylcholine causes electrical impulse in cell membrane of each muscle cell
Calcium Release
impulse in muscle cell membrane causes calcium to be released into cytoplasm from sarcoplasmic reticulum
Muscle Cell Contraction
presence of calcium allows thick + thin filaments to attach + slide past each other
ATP is required
Muscle Cell Relaxation
calcium pumped back into sarcoplasmic reticulum
requires ATP
thick + thin filaments detach from each other
muscle relaxes