Human Anatomy and Physiology: U4 Exam

movement, maintenance of posture, joint stability, heat generation

What are the functions of muscle?

contractibility, excitability, extensibility, elasticity

What are the characteristics of muscle?

Skeletal muscle

type of muscle that produces voluntary movement; cells are striated and highly vascularized; amitotic (grow by protein synthesis)

Smooth Muscle

type of muscle that produces involuntary movement and lines the walls of hollow organs; cells are single nucleated, are not striated, and have gap junctions; regenerative throughout life

Cardiac muscle

type of muscle that produces involuntary movement and is only found in the walls of the heart; cells are striated, have intercalated disks, are single nucleated, and have gap junctions

Agonists

prime mover; the muscle that contracts/muscle group that does the most pulling (biceps brachii to triceps brachii)

Antagonists

opposite mover; the muscle that lengthens/produces the opposite action of the prime mover (triceps brachii to biceps brachii)

Synergists

muscles that assist the agonist and work together to perform similar function (rectus femoris, vastus lateralis, vastus medialis, vastis intermedius to quadriceps femoris)

Fixators

muscle that holds bone in a particular place to immobilize it (scapula)

Muscle fiber

another name for a muscle cell; long and cylindrical, have many mitochondria, multinucleate, huge cell (10-100 micrometers)

Sarcolemma

plasma membrane of a muscle cell

Sarcoplasm

cytoplasm of a muscle cell

Sarcoplasmic reticulum

specialized smooth ER of a muscle cell that can cause an impulse to be generated through the cell; contain calcium ions (released for contraction) and calsequestrin (for storage)

Myofibril

rod-like contractile element composed of sarcomeres

Sarcomeres

segment of a myofibril that is the smallest structural/functional component of a muscle fiber

Myofilaments

contractile proteins

Myosin

binding site for actin; thick filament

Actin

binding site for myosin; thin filament

Troponin

binding site for calcium; thin filament

Tropomyosin

covers myosin binding site on actin when muscle is at rest; thin filament

Elastic filament

extend from z-disc to thick filament

Dystrophin

protein that links thin filaments to integral proteins of sarcolemma

Transverse tubules

extends into sarcoplasm as invaginations continuous with sarcolemma

Epimysium

dense regular connective tissue layer of a muscle that surrounds the entire muscle

Perimysium

fibrous connective tissue layer of a muscle that surrounds each fascicle (bundle of fibers)

Endomysium

fine connective tissue sheath of a muscle that surrounds each individual muscle fiber

Fascia

fibrous connective tissue that blends with epimysium to cover entire muscle

Fascicle

bundle of muscle fibers

Tendon

attaches bone to muscle

Aponeurosis

attaches muscle to muscle

Ligament

attaches bone to bone

Origin

attachment on the nonmoving end of muscle (anchor)

Insertion

attachment on the moving end of muscle (inserted on the body part that moves when it contracts)

Direct attachment

when the muscle epimysium is fused to the bone periosteum

Indirect attachment

when the muscle forms a tendon that connects the muscle to the bone

Slide filament theory

myosin and actin overlap each other and slide past each other to cause a muscle contraction; muscle contraction causes muscle fibers to shorten

location, size, shape, number of origins, direction of fibers, points of attachment, action

What are the criteria for naming muscles?

Rectus

muscle direction parallel to the midline

Transverse

muscle direction perpendicular to the midline

Oblique

muscle direction diagonal to the midline

Neuron

electrically excitable cells that transmits electrical signals; specialized in producing and receiving action potential (conducting nerve impulses); have a high metabolic rate (require plenty of oxygen); amitotic and have long life-span

Sensory neuron

type of neuron that carry nerve impulses from peripheral body/internal organ to the brain/spinal cord

Motor neuron

type of neuron that carry nerve impulses out of the brain/spinal cord to effector organs (organs that respond)

Interneuron

type of neuron that lie within the brain/spinal cord; transmit impulses from one part of the brain/spinal cord to the other

Neuroglia

glial cells; support neurons (astrocytes, microglia, ependymal cells, oligodendrocytes)

Soma

cell body of a neuron; neurotransmitter synthesis

Dendrites

tree-like, highly branched extensions of sensory receptors that pick up signals that come into the cell

Axon hillock

decision maker of the cell (yes/no); controls the firing of neuron

Axon

send nerve impulses down the distal end to another cell; neuron only has one axon that transmits information away

Axon terminals

end of neuron; secrete neurotransmitters with will incite/inhibit adjacent neuron

Schwann cell

one internode; form myelin sheath around axon

Node of ranvier

gaps along axon; unmyelinated

Myelinated fibers

axon bearing a myelin sheath; conduct nerve impulses rapidly; myelination increases transmission speed down the axon; white colored

Unmyelinated fibers

axon bearing no myelin sheath; conduct nerve impulses slowly; gray colored

Action potential

momentary change in membrane potential on a neuron of muscle cell; motor neuron sends an electrical signal/impulse down its axon in order to send signals to muscle
1) Resting state: at resting potential; all voltage gated Na+ and K+ channels are closed; -70mV
2) Depolarization: membrane potential gets to threshold (-55 mV), Na+ channels open, Na+ enters the cell making it more positive (+30 mV)
3) Repolarization: Na+ channels close, extreme positivity (overshoot) opens voltage gated K+ channels and K+ exits making cell more negative
4) Hyperpolarization: some K+ channels remain open and Na+ channels reset; membrane potential may be more negative
5) Restoration of membrane potential: Na+/K+ channels restore membrane potential

All or none response

if a neuron responds at all, it must respond completely

Neuromuscular junction

site where the axon of a neuron is going to meet the muscle fiber; provide excitation for E-C coupling
1) Action potential arrives at terminal of motor neuron
2) Ca2+ channels open, Ca2+ enters axon terminal
3) Ca2+ entry causes synaptic vesicles to release acetylcholine
4) Acetylcholine diffuses across synaptic cleft and binds to receptors on sarcolemma
5) ACh binding allows Na+ to go in the cell and K+ to come out (end plate potential)
6) ACh is broke up by acetylcholinesterase

Excitation-contraction coupling

events that link action potential (excitation) to skeletal contraction
1) Action potential propagates along the sarcolemma and down t-tubules
2) Calcium ions are released; calcium flows into cytosol
3) Calcium bonds to troponin and removes blocking action of tropomyosin
4) Contraction begins (myosin and actin combine to form cross bridges)

Cross bridge cycle

cause of contraction/shortening of muscles; when myosin and actin for cross bridges and slide past each other
1) Muscle is relaxed
2) Exposed binding sites on actin allow muscle contraction to occur
3) Cross bridges bind actin to myosin
4) Cross bridges pull thin filament (power stroke); ADP and inorganic phosphate released from myosin
5) New ATP bind to myosin to release linkages
6) ATP splits which produce power to cock myosin bridges
7) Muscle relaxes because ATP takes calcium into SR and breaks myosin links

Muscle relaxation

happens when muscle returns to resting state after contraction; ATP dislodges myosin heads and pumps calcium out of the sarcoplasm and into the SR

Acetylcholine

triggers firing of motor neurons and control voluntary movement; synthesized in cytoplasm of motor neurons

Acetylcholinesterase

enzyme that breaks down acetylcholine into acetic acid and choline; stops excitation

Motor unit

one motor neuron and all the muscles it enervates

Subthreshold stimulus

less than necessary mV for contraction; not enough stimulus

Threshold stimulus

the mV needed to stimulate an individual muscle fiber; muscle will contract

Maximal stimulus

strongest stimulus; stimulates all motor units in an individual muscle

Twitch

refers to one cycle of muscle contraction in individual fiber/whole muscle followed by relaxation

Latent period

phase 1 of muscle twitch that follows stimulation where cross bridges cycle but no tension yet

Period of contraction

phase 2 of muscle twitch where cross bridges are active and tension increases

Period of relaxation

phase 3 of muscle twitch where calcium re-enters the SR and tension declines to zero

Isotonic contraction

causes movement when muscles contract

Concentric contraction

muscle shortens when it contracts with force greater than resistance (bringing up bicep curl, going up in a squat); isotonic

Eccentric contraction

muscle lengthens when it contracts with force less than resistance (lowering bicep curl, going down in a squat)

Isometric contraction

muscle contraction where no movement occurs (holding a wall-sit)

Hypertrophy

increase in muscle size due to regular physical activity; produces more contraction proteins and sarcomeres by stimulating protein synthesis

Atrophy

decrease in muscle size due to lack of physical activity; produces less contraction proteins and breaks down sarcomeres; fibrous connective tissue will replace lost muscle tissue in atrophy

Recruitment

when intensity of stimulus increases, the number of motor neurons that are fired increases; the activation of additional neurons increases strength on contraction

Summation

rapid stimulation of muscle fiber that does not have a full reset in between; sarcomeres have no time to relax; caused by release of stimulus before the first stimulus is over

Treppe

condition where muscles come to rest before contracting again but each contraction is stronger than the last

Tetanus

uncontrollable muscle spasms that are extremely painful and dangerous due to summated stimuli that prevent any relaxation between twitches; can be caused by bacterial infection from clostridium tetanus in a puncture wound (toxin inhibits regulation of motor neuron)

Muscle tone

constant, slightly contracted state of all muscles; keep muscles firm, healthy, and ready to respond; without tone, we would be paralyzed

ATP

- a major energy source for muscles; needed for the cocking and releasing of myosin heads
- in exercise, storage ATP is used 1st, second direct phosphorylation of ADP by creatine phosphate produces more ATP
-Once ATP and CP are used up, it is dependent on how much oxygen is available to replenish ATP

glycolysis (anaerobic)

What occurs when no oxygen is present to replenish ATP?

cellular respiration (aerobic)

What occurs when there is oxygen present to replenish ATP?

Creatine phosphate

regenerates ATP by transferring high energy phosphate to ADP; produced by enzyme creatine phosphokinase in kidneys and liver and is ingested in a high protein diet; muscles take up more water with they have more creatine in them which gives them more mass

Myoglobin

red pigment in muscles that store extra oxygen; like hemoglobin in blood

Muscle fatigue

happens when muscles are unable to contract; caused by ionic imbalances (disrupt E-C coupling) or from prolonged exercise

Oxygen debt

the amount of oxygen needed by liver cells to use accumulated lactic acid to produce glucose; in anaerobic conditions, glycolysis will continue but pyretic acid will be converted to lactic acid and the converted to glucose for energy

Lactic acid

organic acid produced by the body when glucose is broken down to generate ATP in the absence of oxygen; causes muscle soreness

Fast twitch fibers

muscle fibers that are well adapted for quick responses but not fatigue resistant; white colored, less blood supply, myoglobin, and mitochondria; anaerobic (used by baseball players sprinting to 1st)

Slow twitch fibers

muscle fibers that are well adapted for endurance movements because they are fatigue resistant; red colored, more blood supply, mitochondria, and myoglobin; use ATP slower; aerobic (XC runner)

Muscle cramp

sustained involuntary contraction; due to lack of ATP for calcium pump; calcium will stay attached to troponin

Rigor mortis

state of contraction after death; starts 3-4 hours after death and will continue for 72 hours until decomposition begins

Flaccid muscular paralysis

muscles go limp and cannot contract (botox paralyzes face muscles to get rid of wrinkles)

Sarcopenia

loss of muscle mass

Resistance exercise

form of high intensity exercise where muscles are pitted against high resistance/immovable forces; results in more mitochondria, myoglobin, myofilaments, myofibrils, and increased fiber size; lift for strength, run for endurance

Glucocorticoids

naturally produced by the adrenal cortex; steroids that counteract inflammatory responses and are prescribed to combat inflammatory disease (asthma, arthritis, etc); can cause sex hormone deficiencies and decrease in calcium absorption/excretion if taken in excess

Anabolic steroids

synthetic testosterone used to increase rate of recovery after a workout
- pros: help men with low testosterone to have a better sex life, more energy, and prevent osteoporosis
- cons: roid rage, clog arteries, damage kidneys and liver, too mush testosterone will be converted to estradiol, women develop very masculine features

Muscular dystrophy

progressive deterioration and weakness of skeletal muscles because of lack of dystrophin; X linked carried by the mother; most common and severe in males

Visceral smooth muscle

type of smooth muscle that occupies walls of most hollow organs; single-unit smooth muscle; exhibit rhythmicity and peristalsis; sheets of muscle fibers held together by gap junctions