Week 8 A&P
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.