Week 8 A&P

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exocytosis, action potential

ACh is released from axon terminal via _________ when an ______ ______ arrives.

titin

"molecular spring," a thick filament's elastic core made up of a protein called ______, which extends across the I band to the Z line.

Nebulin

(B) a giant protein that coextends with F-actin strand between G-actin rows, helps hold structure together

rigor mortis

______ ______ is stiffness of the body that sets in several hours after death, it occurs as membranes break and calcium releases into myofibrils, causing contraction of muscles.

calcium, actin, actin,

_________ ions bind to troponin, weakening its bond with ________. This causes tropomyosin to roll away from the active sites of ________.

tropomyosin

a double stranded protein, bound to a troponin midway along its length, which covers myosin binding sites on the G-actin molecules

troponin

a molecule which consists of three globular subunits: - one binds to tropomyosin, -one binds to G-actin -one binds two calcium ions

negative, attracted

a resting cell has a slightly _______ inner inner plasma membrane surface compared to the outer surface. the membrane itself keeps these ________ charges separated.

propagated

action potential is _________ along the plasma membrane, in one direction, in muscle cells

close, open, repolarization

after depolarization peaks (+30mV), the voltage-gated channels Na+ channels ______ and voltage-gated K+ channels ______, this is called ________, and it occurs until the resting potential (-70mV) is reached.

reverse

changes in the ion membrane potential can temporarily _____ the electrical charge across the membrane

voltage-gated ion channels

channels that open or close in response to a change in the membrane potential.

increase, into

charge reversal begins with small _______ in sodium ion permeability to a set threshold (-55mV in neurons). once threshold is reached, voltage-gated Na+ channels open and positively charged sodium ions rush ______ the cell - it becomes depolarized

G-actin (globular actin)

contains an active site to which myosin can bind (like a substrate)

axon (synaptic) terminal

contains vesicles filled with acetylcholine (ACh)

polarized

due to the unequal distribution of positive and negative charges across the plasma membrane, all cells in the body are _______.

1

each muscle fiber has ____ NMJ.

F-actin, nebulin, tropomyosin, troponin

each thin filament is composed of four main proteins:

action potential

electrical impulse that is created by depolarization and repolarization in skeletal muscle membranes, "blip in voltage"

Acetylcholinesterase (AChE)

enzyme that degrades acetylcholine

skeletal muscle fibers have electrically _________ membranes

excitable

muscle tension

force created by muscle contraction

myosin, away

in a resting sarcomere, each ________ uses ATP to "cock" its head _______ from the M line, becoming energized like a spring. ADP and P remain bound to it.

botulinum toxin

inhibits exocytosis of ACh, paralyzing muscle

sodium-potassium pump

ion pump which export 3 Na+ from the cell and import 2 K+ to maintain the cell's resting membrane potential.

millivolts (mV)

measurement which compares inner membrane charge with outer membrane charge

motor neuron

nerve cell that propagates an electrical impulse to muscle fiber.

acetylcholine (ACh)

neurotransmitter that is released by neuron at the NMJ to change permeability of muxcle cell's plasma membrane.

released, power stroke

once a cross-bridge is formed, the energy stored in the myosin head is __________ as it pivots towards the M-line. The bound ADP and P are released. This process is called the _________ _________.

close, terminal cisternae, actin

once action potential stimulus is removed: - calcium channels in SR _______, - calcium ion pumps pull calcium from cytosol for storage in the __________ __________. - tropomyosin shifts to cover the active sites of ________.

actin, cross-bridges

once tropomyosin is removed from the active sites of _____, the energized myosin heads bind to the sites forming ________ ________.

motor end plate

pocket formed around motor neuron by sarcolemma, has ACh receptors and junction folds (deep creases)

membrane potential

potential energy across the plasma membrane of a cell - measured in millivolts (mV)

actinin

protein that interconnects thin filaments at the Z line

NMJ (neuromuscular junction)

special site, located midway along muscle fiber, where nervous system controls muscle fiber

motor neuron, ACh, calcium, contraction, shorten, tension

steps of excitation-contraction coupling: 1. muscle fiber is stimulated by a _______ _______ at a NMJ (action potential) 2. ______ is released into synaptic cleft, creating action potential in sarcolemma and down T tubules. 3. this triggers the release of ________ ions from terminal cisternae. 4. ________ cycles begin when calcium binds to troponin, exposing active sites and forming cross bridges. 5. sarcomeres ________ as filaments interact. 6. muscle ______ is produced.

action potential, removed

sudden intake of sodium into the sarcoplasm generates an ________ _________ in the sarcolemma, sweeping across the membrane. ACh is then _________ from site and broken down by Acetylcholinase.

axon terminal, motor end plate,

the NMJ is made up of an _______ of a motor neuron, a ________ (specialized region of sarcolemma), and a synaptic cleft (intervening space)

free head

the _____ _______ of a myosin molecule is composed of two globular protein subunits which interact with thin filaments during contraction.

hinge

the connection between the myosin head and tail acts like a ______.

elevated, T tubules,

the contraction cycle only continues if Ca2+ (calcium) concentrations remain __________. This will only occur as long as action potentials move along __ ___________.

ATPase

the enzyme that catalyzes the hydrolysis of ATP, located on the head of a myosin molecule

synaptic cleft

the gap between the axon terminal and motor end plate into which neurotransmitters are released

charge separation

the imbalance of charges between two locations - potential energy

ATP

the link between an actin molecule and myosin head is broken when another ______ molecule binds to the myosin head and "recocks" it.

excitation-contraction coupling

the link between the generation of an action potential in the sarcolemma and the start of a muscle contraction

proteins

the main contributors of negative charges within the cell are ________ which cannot cross the membrane.

troponin complex

the regulatory proteins that control the position of tropomyosin on the thin filament

contraction cycle

the repeating sequence of events, beginning with the arrival of calcium ions, that causes the filaments to slide

diffusion, leak

there is a constant low rate of _________ of Na+ and K+ down their concentration gradients. They require "_______" channel proteins to do this.

chloride (Cl-)

there is an excess of negatively charged ________ ions outside the cell. Little diffusion of these ions occurs.

Na+, K+

there is more ______ outside the cell, and more ______ inside the cell. These are the main contributors to positive charges

myosin, subunits

thick filaments are composed of about 300 _______ molecules, each made up of a pair of _______ twisted around each other.

refractory period

time when the membrane cannot respond to another stimulus, sodium potassium concentrations are restored.

F-actin (filamentous actin)

twisted strand composed of two G-actin rows

smaller, wider, closer, change

when a skeletal muscle fiber contracts: - the H and I bands get ______, - the zones of overlap get_________. - the Z lines move ________. - the width of the A band does not ________.

channels, permeability, sarcoplasm

when in the synaptic cleft, ACh binds to an ACh receptor which is also an Na+ ________, altering the cell membrane's ______________. Sodium (Na+) ions rush into the ___________.

shortens

when myofibrils shorten during contraction, the muscle fiber _________.

depolarized cell

when the membrane potential of a cell is positive, peaking at +30mV

thin, thick

Sliding Filament Theory: when a skeletal muscle fiber contracts, _____ filaments slide past _______ filaments.


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