HTHS Mod 10

• Producing body movements
• stabilizing body positions
• storing and moving substances within the body
• generating heat

• digestive enzymes are kept in pancreas by specialized circular muscle called sphincter. When meal arrives and is detected by sphincter, it relaxes and releases it's cargo of digestive juices
• Lymph fluid is pushed around by muscular action, having no pump of it's own

• skeletal
• cardiac
• smooth
• *all depend on interactions btwn actin and myosin to change cell length

• also called voluntary muscle, under our voluntary control
• striated
• controlled by nervous system
• moves body at joints
• made up of long tubes formed from fusion of syncytium
• dozens or hundreds of nuclei, along outside of fused muscle cell
• *# of cells is set at birth. Cells can get bigger, but no more are created

• (mature skeletal muscle cells) are formed by fusion of many embryonic m. cells
• the resulting multinucleated, incredibly long cell of skeletal muscle
• nuclei remain along outside of long tube that is formed (called eccentrically placed nuclei)

nuclei which are away from the center of the tube in skeletal muscles

• in some ways resembles skeletal muscle
• striated
• single cells, branched, connected at intercalated discs
• single nucleus along outside of branched muscle cell
• *nuclei are in center of cell, the fusion of embryonic cells has produced a branched structure instead of long tubes
• not under voluntary control

the proteins of striated muscle are arranged in a regular, repeating pattern that gives it the appearance of tiger stripes

• not striated
• made up of single spindle-shaped cells, unbranched
• single nucleus in center of cell
• contractile proteins stick out in all directions
• Involuntary

• like all cells, muscle cells have thin filaments made up of globular shaped actin strung together like beads on a string to make long rods
• contain 3 proteins: contractile proteins, regulatory proteins and structural proteins

• contractile proteins, interact to contract
• Myosin = thick filament
• Actin = thin filament

• control how actin and myosin deal w each other
• Ex: one key regulatory protein keeps myosin away from actin until just the right moment, and then allows them to join together

• keep the actin filaments and myosin filaments in the correct orientation so they can interact when needed
• is the framework constructed by these proteins that give striated muscle it's appearance

• the basic functional unit of muscle cell necessary for contraction
• each strip is sarcomere
• The repeating sarcomeres give muscle it's striated appearance
• *When muscle is relaxed, sarcomeres are at maximum width
• *When sarcomeres collapse on themselves and become shorter, the entire muscle becomes shorter
• **If one shortens, they all do

by a nerve cell that makes synaptic (cell to cell) contact w the muscle fiber

• has sarcomeres; contracts due to combined action of millions of sarcomeres working together
• has it's own electrical signaling system
• *heart rate controlled for entire muscle, not for individual muscle fibers
• is involuntary

• the hearts own electrical signaling system
• sends an electrical spike every 0.8 seconds to cause the heart to contract 72 times a min.

• striated in appearance due to sarcomeres
• elaborate system of T tubules and sarcoplasmic reticulum to regulate contractility

Cardiac has branched fibers, single nucleus per cell, cells joined by intercalated discs, and not under voluntary control

• In response to stress, the nervous system can send a signal to increase the heart rate using epinephrine
• The nervous system can also slow the heart rate using acetylcholine

• All parts of muscle must fire together
• uses gap junctions to transmit electrical impulses btwn cells, through out the entire muscle simultaneously, to ensure coordinated firing of muscle contraction

• bind cells together and allow signals to move btwn cells
• are regions in cardiac muscle with multiple desmosomes holding muscle together
• insures that muscle isn't torn by force of contraction

• used in cardiac muscle
• allow rapid movement of ions (ions that tell heart to contract) from one cell to another so that all the muscle in that area of heart contracts (beats) at the same time
• *can also close off if one cell gets sick or dies. Ca⁺⁺ increases and seals door

• "spot-welds" that give tissue structural integrity and strength
• uses cadherin plus intermediate filament, hooking to cytoskeleton. Gives strength to physical connection btwn cardiac cells

lining blood vessels, lining airways, lining the gut tube throughout the digestive system, and in a number of there places

• doesn't have striations like cardiac and skeletal muscle
• have one nucleus per cell, spindle shaped
• does have gap junctions, but no desmosomes like skeletal & cardiac
• the actin and myosin filaments are there, but are arranged in a meshwork like a vegetable bac, and not in sarcomeres

• nerves that innervate smooth muscle are there to regulate contraction rather than control it
• the nerve cells release chemicals that increase or decrease the overall activity level, but don't control individual muscle cells

• uses actin and myosin for contraction
• actin: thin filaments
• myosin: thick filaments

• Organization of proteins in smooth muscle is a bit different
• smooth muscle is small cells, single nucleus per cell, spindle-shaped cells, not under voluntary control, no electrical or Ca⁺⁺ management

• Going from largest to smallest:
• muscle
• Fascicle
• muscle fiber (muscle cell)
• myofibril
• sacromere

sarcomere: a regular arrangement of interdigitated strands of actin (small filaments) and myosin (thick filaments) plus structural proteins to hold things in place

a long strand of (thousands) of sarcomeres arranged end to end

• also called muscle cell
• contains several dozen myofibrils bordered by sarcolemma
• is the syncytium that results when embryonic muscle cells fuse to form a long tube
• inside are sacs and tubules and dozens of myofibrils divided into sarcomeres

the plasma membrane of a muscle cell, surrounds & borders each muscle fiber

several dozen muscle fibers bounded together by a connective tissue sheath

• three connective tissue sheaths surround muscle cells, muscle fascicles, and entire muscle:
• epimysium, perimysium, endomysium
• *think of his shovel story, these would be the outer plastic coating of the wires

a dense irregular connective tissue which surrounds the entire muscle

connected to, and continuous with, tendon and then periosteum of bone

a dense irregular connective tissue which covers (surrounds) each fascicle

an areolar connective tissue sheath which surrounds each muscle fiber (muscle cell syncytium)

• a wave of electrical potential that arrives at the surface of the muscle cell
• releases Calcium ions

• also called T tubules
• help electrical potentials (voltage changes) rapidly penetrate into the center of the cell

• a specialized form of smooth endoplasmic reticulum which stores Ca⁺⁺ and releases them when needed
• "bags of calcium"

• formed by 1 transverse tubule spur plus 2 sacs of sarcoplasmic reticulum
• *T tubule brings electrical charge inside cell; SR releases Ca⁺⁺ in response to electrical signal
• *when action potential hits triad, calcium is released into cytoplasm of muscle cell

• wave of electrical potential on surface of muscle cell
• calcium ion concentration

membrane which covers the muscle fiber

• a special kind of light used before the invention of the electron microscope to see things better
• *some structures of myofibrils are named after there appearance in polarized light

• made up of many sarcomeres
• 1 sarcomere consists of Z disc, H zone, I band and A band
• nearest Z line: Only Actin (thin) filaments center of sarcomere: only myosin (thick) filaments
• *the actin and myosin are proteins within the filaments

• defines the borders of the sarcomere
• where actin filaments are held together

• isotropic band
• actin filaments ONLY
• by Z band
• does not bend polarized light (appears lighter)

• anisotropic: myosin and myosin + actin
• Includes H band
• part of sarcomere that bends polarized light

• myosin thick filaments only
• in middle of A band

• by releasing chemical substances (neurotransmitters)ONTO other cells 
• causes electrical change in the cell that receives the message

• the point of contact btwn the nervous system and muscular system
• neurons in the spinal cord send out a cable-like axon which ends at this junction
• the signal sent at the junction (which happens by the release of acetylcholine) triggers contraction of the entire muscle fiber

• chemical substances which allow neurons to work
• they transmit info from neurons, cause an electrical change in cell that receives message

Neurons (nerve cells), which are the thinking and info processing cells of the nervous system

• (ACh)
• the neurotransmitter which causes muscle cell contraction

• when it receives the proper stimulus, it releases acetylcholine onto the sarcolemma of muscle fiber
• there, specialized receptors turn chemical signal into electrical signal
• called nicotinic acetylcholine receptors

• specialized receptors which turn the chemical signal into an electrical signal which spreads over the entire surface of the muscle fiber, penetrating into T tubules where they meet the sarcoplasmic reticulum in triads. 
• This causes calcium release from it's stors in the SR
• best respond to nicotine, hence the name

• the way neurotransmitters are released from nerves
• understand that an electrical signal in both nerve and muscle is what triggers events in both cells

• brain cells (or nerve cell) that controls movement (muscle tissue)
• they receive input through the spinal cord
• generate an electrical impulse (action potential) which travels along a "cable" (axon) to its end (axon terminal)
• releases acetylcholine - receiving cell is skeletal muscle cell
• single motor neuron branches several times & contacts muscle fibers

the last neuron in the motor neuron chain, has it's cell body and dendrites (info receivers) INSIDE SPINAL CORD

• the electrical impulse generated by motor neurons, as long as a certain combination of events occur
• is a change in voltage that lasts for just a brief period of time and makes things happen (from neg to pos to neg.. as neg charge is normal)
• *remember scientists use the word "potential" to mean "voltage"
• *the motor neuron action potential releases acetylcholine from the end of the motor neuron

part of the nerve cell that takes signals away from the nerve body; therefore the action potential travels from the spinal cord to the muscle, using the axon of the cell for the journey

• the end of the axon, where action potential triggers the release of acetylcholine
• *attached to the synaptic end bulb 

• at the end of the axon terminal
• Where the exchange or signal, passing from neuron to the muscle cell to allow for a series of events to take place to get contraction

• after the ACh (acetylcholine) is released from the axon terminal, it diffuses across tiny gap btwn nerve and muscle and binds to receptors on muscle cell.
• these receptors allow the flow of Na⁺ (sodium) and K⁺ (potassium); which cause the voltage inside muscle cell to change from neg. to pos.
• This "flip" in voltage is the muscle cell action potential

• 1. motor neuron action potential arrives at neuromuscular junction, triggers release of acetylcholine in synapse btwn neuron & muscle
• 2. Acetylcholine binds up with acetylcholine receptors, which then sends that electrical impulse (action potential) along muscle surface (on plasma membrane of sarcomere)
• 3. When this impulse reaches T tubules, initiates release of Ca⁺⁺ from sarcoplasmic reticulum
• 4. Once acetylcholine is no longer needed (no need for constant contraction), cleared away by acetylcholinesterase

makes the ACh keep binding to receptors and opening ion channels; making the muscle stay w positive voltage forever

• Again, action potential travels along surface of muscle
• Penetrates into the interior muscle cell at transverse tubules (T tubules)
• The action potential in T Tubule initiates release of Ca⁺⁺ from sarcoplasmic reticulum
• Ca⁺⁺ interacts w proteins to help contraction btwn myosin and actin

• The Ca⁺⁺ released from SR then binds w troponin (a regulatory protein)
• troponin then changes it's shape, which causes the tropomyosin to move aside and expose binding site for myosin on the actin filament

• acetylcholinesterase ~ an enzyme used to stop the action of ACh
• breaks apart the ACh molecule at it's ester linkage, into acetate and choline - nether of these can bind to receptors
• the action potential ends and leftover pieces of ACh are taken up into the presynaptic axon terminal for recycling

• a special protein found only in muscle cells
• binds which calcium (which is released from the SR) and changes shape
• moves tropomyosin aside and exposes binding sites for myosin on the actin filament

• normally covers a myosin binding site on the actin molecule; keeps myosin (which wants to bind actin very much) from being able to reach it's binding site on actin
• therefore, when troponin shoves tropomyosin out of the way, myosin can grab actin

• series of events referring to the link btwn myosin and actin forming, then breaking, the forming, etc
• 1 - calcium binds to troponin, which shoves tropomyosin & exposes myosin binding site on actin
• 2 - as soon as sites are exposed, myosin heads bind to actin sites, creating "crossbridges"
• 3 - once attached, the myosin heads pull the actin fiber and Z disk inward (this motion is called the powerstroke)
• 4 - Myosin head then picks up fresh 
• ATP , which causes it to drop actin and reset to again form "crossbridges"

• After troponin shoves tropomyosin and exposes the myosin binding site on actin, myosin wants to bind - brings an ATP molecule
• As myosin binds to actin (requiring energy), the ATP is split into ADP & a loose P
• When myosin heads move to pull actin (powerstroke), releases ADP and open site for ATP to bind again
• Once ATP binds to myosin, it can let go of the actin, and start the cycle over by binding to a new site on actin, w it's ATP

• step in the cross-bridge cycle
• the movement of the myosin heads pulling the actin inward

• what happens when ATP is absent, 
• Myosin remains permanently bound to actin, muscles cannot move (they stay contracted) - they are locked in position
• When a person dies, they no longer make more ATP.  A  dead person uses up the rest of their ATP in a matter of mins or hours, depend on temp (usually 3-4 hrs after death)
• Later (again, depending on temp) enzymes and microbes destroy/break down muscle tissue (usually 24 hrs later) and corpse becomes "loose" again

• For RELAXATION, requires calcium clean-up
• Calcium pump proteins (found in the SR) sponge up the free calcium in muscle cell cytoplasm & stores it for next action potential
• When Ca is absent, troponin-tropomyosin slides back to original places and 
• No cross-bridges are formed, muscle relaxes

• The entire process of muscle contraction, from the brain sending first impulse to relaxation of muscle
• *action potentials are all-or-none, either happen or they don't
• if enough ACh is released, action potential which results always spreads over ENTIRE surface of muscle
• entire muscle cell contracts at once & always contracts "all the way"

• if actin and myosin filaments were not precisely aligned in skeletal and cardiac muscle
• because they are, excitation leads to contraction through shortening of the sarcomere

the protein that holds myosin molecules in a bundle, with the heads sticking out where they can interact with actin

protein that holds the actin filaments in place at the Z line (Z disc)

• as myosin heads flex (in cross-bridge cycle), they move actin filaments (sliding past the myosin thick filaments)
• as actin filaments move, the Z lines are brought together and the sarcomere shortens
• as thousands of sarcomeres shorten, the entire muscle fiber shortens
• As muscle fibers shorten, the muscle contracts

• refers to the location of the myosin & actin filaments and the strength of the contraction
• the amount of tension that muscles generate varies as a function of their length
• *Relaxed muscles can't generate much force
• *Partially contracted muscles generate max force
• *fully contracted muscles can't generate much force

• the overlap btwn myosin and actin
• At maximum stretch (relaxation) or maximum contraction, fewer actin-myosin interactions ↦ less force generated

• one motor neuron and all the muscle fibers that it's connected to (all the muscle fibers which the motor neuron forms neuromuscular junctions)
• *note that when one motor unit sends impulse for contraction, all the muscle fibers it innervates will contract

• recall muscle contraction is "all-or-none", that once muscle fiber contracts, it contracts as much as possible. But how can you have small movements?
• *While individual muscle fibers contract fully, not all the muscle fibers in a muscle contract.
• most of the time, very few contract at all. they take turns
• *other half of answer is existence of motor units

• important for the wide range of movements
• Precise control of muscles = small motor units
• More force from a single motor neuron = large motor units

• makes movements more smooth
• the small motor units are recruited first, than larger units, until finally largest motor units are recruited last
• *amount of force generated is directly proportional to the number of muscle fibers that contract

a graph showing the time it takes to move through the process of contraction to relaxation

the time it takes for an action potential to travel from the motor neuron to when action potentials spread over a few, or many, muscle fibers

time period from when the action potentials penetrates the T tubules & releases calcium; when troponin shoves tropomyosin, which results in more and more force generated by the muscle fiber until max. force is reached

• time period when calcium is packed back into sarcoplasmic reticulum, myosin releases actin, and muscle relaxes
• final segment of graph

• both muscle and nerve have this
• depending on type, it may take a few milliseconds up to a 2nd of a second for the muscle to be ready to contract again

roughly the same length of time

• force increases - up to a point
• when one action potential fires, the muscle starts to contract. If we receive another action potential before the muscle can relax from the first impulse, it increases the force

• referring to a graph of action potentials
• the process of firing multiple action potentials & having the small bumps begin adding together
• looks almost like a wave

• when the waves on the muscle graph increase in the frequency of the stimulation
• show discernable bumps or steps

• the name of the pattern you get on the graph
• when you get multiple action potentials firing, and the graph "waves" start looking like steps

• when the action potentials come so rapidly that the individual bumps fuse into one big ridge (on the myogram graph) - also called fused tetanus
• describes a muscle that is contracting as forcefully as possible

• greek word tonos means "tension"; "iso-" means equal
• those muscle contractions that use equal tension (or equal force, equal strength) to move objects
• 2 subcategories: concentric and eccentric contractions

• subcategory of isotonic contractions
• involves moving a muscle against gravity
• Ex: picking up a book

• subcategory of isotonic contractio
• think of lowering a dumbbell
• occur when gravity is stretching a muscle (increasing it's length) at the same time you are trying to shorten the muscle (to control the decent of the dumbbell)
• great for building muscle, but make muscle prone to injury

• associated w eccentric contractions
• happens about 24 to 72 hours after exercise
• Ex: running downhill means the muscle is in relaxed state when ur foot hits the ground

• involve holding things in place against gravity
• Position is being maintained
• no movement takes place; keep muscle at same length or measurement

• oxygen for glucose is in blood via hemoglobin or from myoglobin in muscle fibers
• Pyruvic acid from glycolysis (glucose breakdown)
• Fatty acids liberated from adipose cells
• Amino acids from protein breakdown

• blood glucose
• muscle stores glycogen, which can easily be converted to glucose
• *remember, it's important to have oxygen to use glucose

• blood oxygen
• myoglobin w/in muscles (an oxygen-binding protein similar to hemoglobin in blood)

• metabolism is anaerobic
• Prob 1. anaerobic glycolysis is inefficient
• Prob 2. anaerobic glycolysis produces lactic acid, which lowers blood pH (acidosis)

• bad choice; not easily utilized
• fatty acids produce acid (lowering blood pH) and ketones; cannot increase glucose rapidly
• Proteins can be used, but actin and myosin are proteins and muscle breakdown to operate muscle is counterproductive

• an additional energy source not used in other tissues
• when energy is plentiful, phosphate groups are stored on muscle creatine, creating creatine phosphate
• When energy it needed, these phosphates can be transferred to ADP to make ATP

• each with it's own metabolic strategy:
• slow oxidative, fast glycolytic, and fast oxidative-glycolytic
• *all muscles are a mix of all three fiber types, but dominated by one of the three types
• *each type tends to be innervated by different motor unit, so when one unit fires, only activates one type

• in postural muscles, like strong muscles of lower extremity
• comparatively weak, but have stamina
• aerobic glycolysis predominates
• slower to respond to activation
• use a steady supply of ATP
• tend to use oxidative metabolism, meaning they have lots of myoblobin

• muscles used for fine movement, like extraocular muscles moving eye of small muscles move fingers to thread needle
• anaerobic glycolysis predominates
• quick to respond to activation
• use ATP in brief bursts; very strong, but short endurance
• don't need to store glycogen or oxygen to work
• have little myoglobin
• since they only need to work for a few twitches, they don't need to rely on stored energy as much
• "white meat" in turkey

• those fibers that combine both strategies
• more common in muscles which need both endurance and speed
• mid level for both strength and endurance

• depletion of energy sources & a few metabolic factors
• *also can involve central fatigue

• when the nervous system "shuts down" and will not activate motor neurons (the person "quits")
• that point the your body says "no more" 
• Ex: doing pushups

• glucose and glycogen
• creatine phosphate and ATP
• blood oxygen and oxygen bound in myoglobin

• ADP & phosphate directly interfere w calcium release from sarcoplasmic reticulum
• lactic acid accumulation reduces pH and inhibits key muscle enzymes
• extracellular potassium builds up, reducing ability of muscle to fire an action potential
• glycogen is depleted
• *no one knows which of these, or something else, is the "most" important factor

consists of replenishing ATP, creatine, oxygen (bound to myoglobin), glycogen, Ca stores, and restoring pH to normal levels

• Cardiac muscle is adapted to be fatigue-resistant:
• higher number of mitochondria (energy producing factory)
• higher myoglobin content
• higher creatine phosphate (ready source of high-energy phosphate for ATP) content
• ample blood supply
• *w/o oxygenated blood, heart muscle can not work. if it is deprived of oxygen at all, it fails

• Effort/energy is the muscle force
• Fulcrum is the joint
• Load is the weight or object being moved

• arranged in the order Energy, Fulcrum, Load
• analogous to tee-ter-taw-ter
• Ex: neck muscles (E) are using the atlanto-occipital joint (F) as a fulcrum to support the weight of head (L) from falling forward

• order is Fulcrum, Load, Energy
• analogous to wheelbarrow
• Ex: metacarpophalangeal joints (F) are used as a fulcrum to support the weight of the body (L) through the contraction of the calf muscles (E)

• order is Fulcrum, Energy, Load
• analogy is to tweezers
• by far the most common levers in body but lack stability (hard to hold heavy weight w tweezers)
• Ex: elbow joint (F) is used as a fulcrum so that the arm muscles (E) can support a weigh in the hand (L)

origin, insertion, and action

• theoretically where it begins
• in general, origin is more proximal part

• place where the muscle "ends"
• theoretically attached to the part being moved
• usually the distal end of muscle

what it does when it contracts

• prime mover (agonist)
• antagonist
• synergist
• fixator

• agaonist
• the muscle that does most of the work

muscle opposes the agonist

muscle that helps the agonist muscle do it's job

muscles which stabilize the origin of the muscle to make the agonist more effective

• Location: Ex=extraocular
• Shape: deltoid, trapezius, rectus abdominis
• Number of origins: biceps brachii, triceps brachii
• Location and/or dirrection of fibers: transversus abdominis
• Origin and insertion: sternocleidomastoid
• Muscle action: adductor hallucis

• deltoid: after the greek letter delta (Δ)
• trapezius : cause it has 4 sides like a trapezoid
• rectus (straight) abdominis; rectus (straight) femoris

• six eye muscles
• Origin: skull (eye socket or orbit)
• Insertion: eyeball
• Action: eye movements

• in head & neck group
• "chewer" or closing of mouth. 
• origin: maxilla zygomatic arch
• insertion: mandible
• action: closes the mouth

• named after origins and insertion; head and neck group
• Origin: clavicle & sternum
• insertion: temporal bone (mastoid process)
• Action: tilt head towards ipsilateral shoulder
• **NOTICE origin is inferior to insertion point!

• part of the pectoral girdle and shoulder
• It's the big muscle on the upper back; when looking at both sides, forms a trapezoid
• Origin: occipital bone, cervical spine
• Insertion: clavicle & scapula
• Action: move scapula or shoulders (like shrugging shoulders)

• part of the pectoral girdle and shoulder
• it's the "big chest (boob) muscle"
• Origin: clavicle & upper ribs
• Insertion: humerus
• Action: adduct arm (some medial rotation of arm) *brings arms toward midline of body

• In the pectoral girdle/shoulder group
• "wide muscle of back" 
• Origin: thoracic vertebrae, lumbar vertebrae, and iliac bone of pelvis
• Insertion: humerus
• Action: pulls arm inferiorly & posteriorly (as in butterfly swim stroke) *notice origin is inferior to insertion

• In pectoral girdle and shoulder group
• "deltoid" = shaped like greek letter delta Δ
• the top shoulder muscle
• Origin: clavicle & scapula
• Insertion: humerus
• Action: abduct, flex, medially rotate upper arm

• upper extremity
• "two-headed muscle of arm"
• Origin: scapula
• Insertion: radius (radial tuberosity)
• Action: Flexes forearm at elbow

• upper extremity muscle
• "three-headed muscle of arm"
• Origin: scapula (long head); humerus (lateral/medial heads)
• Insertion: ulna (olecranon process - "funny bone")
• Action: extends arm and forearm

• upper extremity
• "arm muscle" on front
• Origin: humerus
• Insertion: ulna
• Action: flexes forearm at elbow

• upper extremity
• "rod in arm"
• Origin: humerus
• Insertion: radius
• Action: supinates foreman

• breathing muscle
• "partition wall"
• Origin: ribs 7 - 12, sternum, lumbar vertebra
• Insertion: central tendon
• Action: breathing (also separates thoracic & abdominal cavities

• btwn ribs
• internal and external intercostals aid in breathing:
• External elevate ribs - inhalation
• internal depress ribs - forced exhalation
• *normal exhalation is from elasticity of lungs
• Origin: lower surface of ribs
• Insertion: upper surface of ribs

• "straight abdominal muscle"
• Origin: pubic bone of pelvis
• Insertion: ribs 5-7 & sternum
• Action: flexes vertebral column and compresses abdomen

• "white line" 
• thin strip of connective tissue along the midline

• abdominal muscle
• Latin: "outside diagonal muscle"
• Origin: ribs 5-12
• Insertion: iliac crest of pelvis & linea alba
• Action: flexes vertebral column and compresses abdomen

• abdominal muscle
• "inside diagonal muscle"
• origin: iliac crest of pelvis
• Insertion: ribs 7-10, linea alba
• Action: flexes vertebral column and compresses abdomen

• abdominal muscle
• "perpendicular abdominal muscle"
• Origin: iliac crest of pelvis & ribs 5-10
• Insertion: rib 12, L1-L4
• Action: flexes vertebral column and compresses abdomen

• buttock large muscle
• Origin: iliac crest of pelvis, sacrum, coccyx
• insertion: femur, greater trochanter
• Action: extension of thigh, lateral rotation of thigh

• 3 compartments:
• anterior contains femur + quadriceps group
• posterior contains hamstring group
• medial compartment (don't need to know)
• blood vessels and nerves run in "seams' btwn compartments

• rectus femoris
• vastus lateralis
• vastus intermedius
• vastus medialis
• *recall that thigh is the proximal part of lower extremity, leg is distal

• Origin: iliac spine of pelvis, femur
• Insertion: quadriceps tendon, patella, patellar ligament, and tibia
• Action: flexes thigh, extends leg

• "calf muscle"
• Origin: femur
• Insertion: calcaneus (heel) via calcaneal tendon
• Action: flexes foot

• "sandal" - under Gastrocnemius 
• Origin: fibula & tibia
• Insertion: calcaneus via calcaneal tendon
• Action: flexes foot

• biceps femoris - 2 headed muscle of femur
• semitendinosus
• semimembranosus - 1/2 tendon/membrane muscle
• Origin: ischial tuberosity of pelvis
• insertion: fibula/tibia
• action: extends thigh/flexes leg