better study guide 2 Flashcards
What did Volta (Alessandro Volta) invent?
He invented the electric battery. He proved electricity could be generated chemically.
What is a cell’s resting membrane potential?
-70mV
What do Na+/K+ pumps do?
Helps to maintain osmotic equilibrium and membrane potential in cells.
What about K+ leak channels?
allow K+ to diffuse out of cells (passive transport)
What are fixed intracellular anions
negatively charged organic ions (anions) that cannot leave the cell
what role do they play?
help with the transport of gases, nutrients, and other molecules.
Why does the thickness of the plasma membrane matter? (Think about fixed intracellular
anions and what they attract)
it plays a key role in protein function
How much of the cell’s total K+ ions are needed to establish the resting membrane
potential?
-90mV
Do you know the concentrations for Na+ and K+ ions inside vs. outside the
cell?
The sodium and chloride ion concentrations are lower inside the cell than outside, and the potassium concentration is greater inside the cell (salty banana)
What can you calculate with the Nernst equation?
calculates the equilibrium potential (also referred to as the Nernst potential) for an ion based on the charge on the ion (i.e., its valence) and its concentration gradient across the membrane
Which cells are the main excitable cells in the body?
Neurons and muscle cells
What are some key features of action potentials?
-local events (occur in specific place)
-transmitted in one direction
-all or nothing (do not vary in size)
What are the three states of voltage gated sodium channels? Which of the states are ions
able to pass through?
resting, activated, inactivated
How can ion channels be selective?
They surround a central pore, guarded by the selectivity filter made up of the P-loops from each of the subunits. This filter determines the permeability of the pore to different ions.
Sphere of hydration
when a polar water molecule surrounds charged or polar molecules thus keeping them dissolved and in solution
selectivity filter?
a region of ion-channel proteins that determines the specificity of a particular channel
What is Loligo? What about this organism made it ideal to study action potentials?
Marine squid that led to understanding the ionic basic of action potentials
What is the action potential threshold?
enough Na+ leaks in for any potion of inner membrane to be + = spontaneous depolarization (“All or nothing principle”)
If threshold is met what is the probability an action potential will be triggered?
15 milivolts
Do all voltage-gated sodium channels have to open to trigger an action potential?
all of the gated sodium and potassium channels are closed. These gated channels are different from the leakage channels, and only open once an action potential has been triggered.
What happens 1-2ms after voltage-gated sodium channels open? Why would this be
important?
the voltage-gated sodium channels will inactivate, stopping the flow of sodium, even in the presence of persistent stimulation.
What is repolarization?
the membrane returns to its resting membrane potential
How do local anesthetics work?
They prevent sodium channels from opening, thus blocking action potentials
What does tetrodotoxin (TTX) do?
inhibits voltage gated sodium channel opening
Where does TTX come from?
puffer fish
What is myelin?
Myelin is a fatty, insulating sheath that surrounds nerves in the brain and spinal cord
What does myelination do for a neuron?
Insulate the axon to conduct the signal faster
What are nodes of Ranvier
Gaps in the myelin sheath
what ion channels are found in the nodes of ranvier?
Voltage gated sodium channels (VGNCs)
What is saltatoryconduction?
the rapid method by which nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier
What is a synapse?
A synapse is a point of very close physical contact between a neuron and another cell.
Are there different kinds of synapses?
could be another neuron, a muscle cell, an endocrine
cell, an exocrine cell, or other cell type
Where would you find a gap junction?
In virtually all solid tissues. They are different from chemical synapses.
What are connexins and connexons made of? What do these structures do?
Six connexins (the individual proteins) form one connexon. Two connexons form one gap junction.
What is a synaptic cleft? What happens here? Is it a really big space? How big is a
synaptic cleft?
A 20-40nm gap between the presynaptic axon terminal and the postsynaptic dendrite. It is very small.
Skeletal muscle fibers are encased in extracellular material that provide a covering,
protection, and support. What is this covering?
Connective tissue. The periosteum, tendon, fascia, epimysium, perimysium and endomysium are all part of it.
Each skeletal muscle fiber in an adult human is innervated by how many presynaptic
terminals of a somatic motor neuron?
A single presynaptic terminal of a somatic motor neuron.
What is a motor unit? Why wouldn’t all of the muscle fibers in a muscle be innervated by just one motor neuron?
Motor units are the basic functional units of skeletal muscle. Because if there was just one motor neuron it would severly limit the muscles ability to produce graded movements.
Why study the neuromuscular junction (NMJ)?
Skeletal muscle fibers are very large which makes recording the postsynaptic response relatively easy. Explanted skeletal muscle is extremely hardy. Easy to find with a microscope.
What are some unique features? (think about the extensive folding).
Presynaptic terminal secretes a threefold excess of neurotransmitters (100-300 synaptic vesicles containing both acetylcholine and ATP.)
What neurotransmitter is released at the NMJ?
Acetylcholine
At the neuromuscular junction, the presynaptic terminal secretes an excess amount of
neurotransmitter. How much excess is released and why would this be necessary?
To ensure a strong and reliable muscle contraction.
Once a neurotransmitter like acetylcholine is released what happens to it?
Sodium ions flow into the muscle cells and induce muscle contraction.
What special enzyme is present in the synaptic cleft at the neuromuscular junction?
acetylcholinesterase (AChE)
What are myofibrils?
Bundles of myofilaments
What filaments are found in myofibrils?
Actin and myosin
What are thick filaments made of?
myosin
What are thin filaments made of?
actin, troponin, tropomyosin
What is a sarcomere?
contractile unit of a muscle fiber
There are two binding sites on the head of myosin II molecules. What binds here?
One allows it to bind with the actin filament, and one binds to ATP
What are Z disks?
coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another
Does anything attach to these Z disks?
F-actin filaments, titin, and the nebulin/nebulette system directly attach to the Z-disc
What are I bands or A bands?
isotropic bands (better known as I bands) are the lighter bands of skeletal muscle cells Isotropic bands contain only actin-containing thin filaments. The darker bands are called anisotropic bands (A bands)
What is an M line?
anchor for thick filaments
What shortens during contraction?
sarcomeres shorten therefore muscle cells shorten, therefore the whole muscle shortens
Do the filaments shorten?
yes
Do you understand the cross-bridge cycle?
As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP.
How does the head of myosin move?
moves its head groups along the actin filament in the direction of the plus end.
Why is the release of calcium so important for contraction?
Calcium triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin.
What is troponin
a regulatory protein that moves tropomyosin aside & exposes myosin binding sites when Ca+ is released during muscle contraction
tropomyosin?
It is a long, fibrous protein that winds around the actin polymer, blocking all the myosin-binding sites.
Role of troponin 1
prevents myosin from binding to actin in relaxed muscle
Role of troponin C
responsible for binding calcium to activate muscle contraction
Role of troponin T
transducing Ca2+ signals in the regulation of contraction.
Why are t-tubules so important?
permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
What is a triad?
T-tubule plus 2 terminal cisternae.
RYR1 and Cav1.1 have important roles to play during excitation-contraction coupling.
What do each of these channels do? How are they gated?
RYR1 is the gatekeeper of calcium in the muscle cell. A voltage-gated Ca2+ channel.
Cav1 provides instructions for making a protein called caveolin-1. Voltage gated.
Where does most of the calcium that plays a role in contraction come from?
Sarcoplasmic reticulum
What happens to calcium once it is released?
it binds to and alters the shape of troponin as well as removes tropomyosin from the binding sites.
When is ATP used?
When is ATP used?
used during quick movements; a short burst of energy; anerobic
Is ATP only needed during contraction? What about relaxation?
ATP is required for both muscle contraction and muscle relaxation.
Why is SERCA important?
key regulator of cellular calcium homeostasis
What is SERCA
Sarcoplasmic Endoplasmic Reticulum Calcium ATPase
What toxin causes spastic paralysis
tetanus toxin
What toxin causes flaccid paralysis
botulinum toxin
