EXSC 490 Unit 1 Definitions

myofibrils

• composed of sarcomeres, the smallest functional unit of a muscle

• long and rod like; helps muscle contract

• structures: sarcomeres, thick/thin/elastic filaments

• sliding action: myosin heads grab onto actin and pull inward

myosin

• a thick filament, folded into a globular head at one end

• ATP dependent motor proteins; generates force and movement in muscles

action potential

• travels along the sarcolemma, then through the tubule system, eventually causes stored Ca to be released from the SR

• resting: NaK pump keeps Na out of K

• threshold: stimulus makes cell less negative, all or nothing response if cell hits trigger level

• depolarization: Na channels open and rushes in the make inside positive

• repolarization: Na channels close, K channels open; K rushes out, inside cell is now negative

Ca

• Ca binds with troponin, then moves the tropomyosin molecules off the active sites on actin filaments, opening the sites for binding with myosin heads

• myosin head tilts, pulling actin filament to the side; tilting is the power strike

• for energy, myosin head binds to ATP, ATPase found on heads spilts ATP = ADP+Pi, releases energy

• action ends when Ca is pumped out of sarcoplasm and into SR for storage

slow-twitch muscle

• skeletal muscle

• ATPase acts slower, providing energy much slower than FT

• has less fibers, producing less force

• has higher aerobic endurance, well suited to low intensity endurance activity

fast-twitch muscle

• ATPase act faster, providing energy for muscle action quickly

• more developed SR = enhanced Ca delivery

• motor units have more fibers to contract and can produce more force

• better for anaerobic activity

hypertrophy

• the increase in size, or the cross sectional area of muscle fibers

• myofibrillar hypertrophy focuses on increasing size and number of myofibrils

• sarcoplasmic hypertrophy focuses on increased volume of sarcoplasm and glycogen in muscle cell

muscle spindle

• the main muscle receptor

• continually allows neural information to be relayed back to CNS of muscle stretch, length, and rate of change in length

• functions are results of arraignment between afferent, efferent nerves, and components of the muscle spindle

hyperplasia

• the increase in the number of muscle fibers

isometric contraction

• muscle contraction causing no change in muscle length

isotonic contraction

• contractions causing a change in muscle length

isokinetic contraction

• concentric contraction where velocity of muscle shortening remains constant

synapse

• the junction site between two different nerves

• all synapses release chemical substance from the pre-synaptic membrane, and diffuses into space between nerves, called neurotransmitters

• synapses function unidirectly

• involves axon terminals, post synaptic receptor, and the synaptic cleft

cerebellum

• structure located at the base of the skull behind the brainstem

• functions in movement coordination, balance and posture, motor learning, and cognitive roles

basal ganglia

• group of structures located deep in the brain

• starts and stops action, habits, rewards, and moods

• parkinson’s and huntington’s disease

mechanical work

• energy transferred when a force moves an object over a distance

• work = (force)(distance)(cos(0))

temporal summation

• a single presynaptic neuron fires signals in rapid succession at a single synapse

• one neuron firing repeatedly overtime at a single location

spatial summation

• process where multiple presynaptic neurons release neurotransmitters simultaneously on a single post synaptic neuron

• can trigger action potential as voltage changes mix together

• multiple neurons firing simultaneously at separate locations on the same cell

joint receptors

• sensory nerves ending in joint capsules, ligaments, and menisci

• detect mechanical changes and protects joints

• type 1: slow, signal stretch, position, and slow movement

• type 2: rapid, respond to movement and acceleration

• type 3: slow, in ligaments, detects tension

• type 4: unmyelinated nociceptors that signal pain, inflammation, and extreme stress

golgi tendon organ

• small sensory receptor located at junction where skeletal muscle connects to its tendon

• made of collagen fibers surrounded by a capsule

• senses tension, fires a signal, relaxes the muscle, and protects the cell body

monosynaptic reflex

• automatic nerve pathway with only one connection point (synapse) between a sensory nerve and motor nerve

• action happens within spinal cord

• helps with posture

proprioceptor

• specialized sensory receptor located in muscles, tendons, and joints

• muscle spindles measures rate and length the muscle changes

• golgi tendon organs measures force on tendon

• joint receptors detect joint angles, pressure, and movement

motor unit

• single lower motor neuron, skeletal muscle fibers control it

• key parts: motor neuron, muscle fibers, and neuromuscular junction

• all or none response

myoneural junction

• specialized chemical synapse between a motor neuron and a skeletal muscle fiber

• key parts: presynaptic terminal, synaptic cleft, motor end plate

• triggers muscle contraction

motor endplate

• specialized area of skeletal muscle fiber’s membrane (sarcolemma) and forms the post synaptic region of the neuromuscular junction

• structures: junctional folds, ACh receptors, and synaptic cleft

atrophy

• partial or complete wasting away or reduction in size of cell, tissue, organ, body part

• common causes: disuse, nerve damage, poor blood supply/nutrition, hormonal/aging changes

muscle biopsy

• medical test where a piece of muscle tissue is taken and examined under a microscope

• done to find muscle and nerve disorders, check for myositis, diagnose inherited muscle conditions, and check for metabolic problems in tissue

dendrites

• tree-like branch structure that extends from the cell body of a neuron

• filled with cytoplasm to make proteins

• receives input, processes information, and passes it on

axon

• the long, thin part of a nerve cell/neuron

• carries electrical signals away

motor neurons

• never cells that transmit electrical signals to muscles and glads to control (in)voluntary movements

• soma (cell body), dendrites, axon

sarcomere

• composed of filaments of two proteins responsible for muscle contraction

• the basic working unit of a striated muscle

• key parts: z-line, m-line, a-band, I-band, h-zone

• sliding filament theory: muscles get shorter when actin fibers slide over myosin fibers

transverse tubules

• an extension of the muscle cell membrane (sarcolemma)

• allows electrical signals to travel into the cell to release Ca to trigger muscle contraction

synaptic vesicles

• small, membrane-bound sac found inside a neuron’s axon terminal

• released with Ca ions enter cell during action potential

sarcoplasmic reticulum

• smooth type of endoplasmic reticulum found in striated muscle cells

• stores, releases, and receives Ca during muscle contraction and relaxations

tropomyosin

• helps control muscle contraction and cell

• wraps around actin filaments to block myosin from binding, keeping muscle relaxed

troponin

• proteins to help muscle contract

• connects to tropomyosin and controls

• binds to Ca to move tropomyosin during muscle contraction

actin

• protein that forms microfilaments inside cells

• slides through myosin to shorten and pull muscle fibers

• supports cell shapes

z-line

• zigzag border that defines outer edges of sarcomere

• anchors actin filaments

• moves closer to the center as muscle contracts

endomysium

• thin layer of loose areolar connective tissue that wraps around every muscle fiber

perimysium

• strong layer of connective tissue that wraps around groups of muscle cells to form bundle called fascicles

epimysium

• tough layer of dense irregular connective tissue that surrounds the entire muscle

sarcoplasm

• jelly-like fluid (cytoplasm) found inside a muscle cell

• contains SR, withholding Ca

• holds glycogen, myoglobin, mitochondria, and myofibrils

sarcolemma

• specialized cell membrane that surrounds striated muscle cells

cross-bridges

• link formed when thick myosin head attaches to a binding site on a thin actin filament

• actin, myosin, Ca, ATP

type 2 muscle fibers

• fast twitch fibers

• contract quickly, generate high power, tire fast

• rely on aerobic energy (glycolysis) instead of o2

• ideal for short, explosive movements

type 1 muscle fibers

• slow twitch fibers

• rely on o2 and aerobic metabolism to generate energy

• ideal for endurance activities

force velocity relationship

• as the force (load) on the contracting muscle increases, contraction velocity (speed of shortening) decreases during concentric movements

length tension relationship

• the rule that a muscle’s ability to produce force depends on its length when it starts to contract

automatic nervous system

• the body’s network that controls hidden, automatic jobs

• sympathetic: fight or flight

• parasympathetic: rest and digest

• controls HR, breathing, digesting, body fluids

somatic nervous system

• part of the peripheral nervous system

• sensory neurons (afferent)

• motor neurons (efferent)

• spinal and cranial nerves

• voluntary movements, sensory perception, reflex actions

inhibition

• ongoing reflex in the nervous system that stops a muscle from fully flexing