Midterm #1 Main Topics (also look at diagrams on D2L) Flashcards

Question

Membrane Structure

Answer 1

Phospholipids are the molecules that make up the cell membrane. They have three sections. 2 hydrophobic tails: will not dissolve in water 1 hydrophilic head: will dissolve in water Phospholipid Bilayer Cell membrane is semi-permeable

Answer 2

DNA→ mRNA: Transcription RNA→ Protein: Translation Amino acids are the building blocks of proteins

Answer 3

Ions, charged particles, are unevenly distributed 4 Ions Contributing: - Sodium (Na+) - Chloride (Cl- ) - Potassium (K+) - Negatively charged proteins: synthesized within the neuron found primarily within the neuron

Answer 4

Particles move down their concentration gradient From areas of high concentration to area of low concentration Even distribution

Answer 5

Like forces repel, opposites attract Even distribution

Answer 6

Some ions can pass through others cannot Uneven distribution

Answer 7

Moves 3 Na+ out for every 2K+ in Uneven distribution

Answer 8

To calculate the equilibrium of one ion -> Nerst equation All relevant ions -> Goldman equation Resting membrane potential: -70mV

Answer 9

"All or nothing" Mechanical or chemical (neurotransmitter) input causes depolarization of the cytoplasm when sodium enters the cell (stretching of ion channels, or gated ion channels) Lots of sodium outside, not as much inside – it floods in and makes the inside more positive in charge If the potential reaches –55mV, an AP is triggered Na+ is concentrated outside the cell Depolarization caused by Na+ influx when channels open (voltage-gated) K+ is concentrated inside the cell, so moves outward. It takes longer for K+ channels to open compared to Na+ channels! Refractory period caused by efflux of K+ (because delay in channel opening) - cell becomes temporarily hyperpolarized

Answer 10

Absolute refractory period: sodium channels inactivate when the membrane becomes strongly depolarized. They cannot be activated again, and another action potential cannot be generated until the polarization becomes low enough Relative refractory period: the membrane potential stays hyperpolarized until the voltage-gated potassium channels close. An action potential can be generated but requires a stronger depolarization to do so

Answer 11

Ions cannot flow in and out of the cell across fatty tissues, and so they flow directly towards the next node without activating ion channels until they reach an "open space" (which takes time) Myelin allows current to spread further between nodes, and speeds up AP conduction

Answer 12

Electrical and chemical synapses Neurotransmitter families - Cholinergic, catecholaminergic, serotonergic, amino acids Receptor families - G-proteins, transmitter-gated channels Pharmaceuticals - Agonists, antagonists

Answer 13

Electrical - Occur at specialized sites called gap junctions - Membranes of two cells are very close together (3nm); the gap contains proteins called connexins - Allow direct transfer of ionic current from one cell to the other (very fast) Chemical - Presynaptic and postsynaptic membranes are separated by a 20- 50nm cleft (10x the width of gap junctions) - Many specialized components on both sides help to convert chemicals (i.e., neurotransmitters) from the presynaptic neuron into electrical signals on the postsynaptic side (a much slower process)

Answer 14

6 connexins = 1 connexon 2 connexons = 1 gap junction channel Each gap junction channel bridges the cytoplasm of two cells. Ions and small molecules can travel in both directions. Many gap junction channels create one "gap junction" Fast and reliable! Cells connected this way are "electrically coupled" PSPs generated at a single gap junction are very small, but neurons form gap junctions with many cells – many PSPs generated at the same time can add together to generate an AP

Answer 15

The cleft is filled with fibrous proteins that act as a "glue" to hold the two cells together Presynaptic side: - Site of release is called an active zone - Contains many synaptic vesicles that hold neurotransmitters (produced in the cell body and then transported to the presynaptic site) - Contains voltage-gated calcium channels Postsynaptic side: - Protein clusters known as postsynaptic density contain neurotransmitter receptors - This is where the chemicals (neurotransmitters) bind and become translated into a change in membrane potential (electricity) - The postsynaptic response varies depending on what kind of receptor is activated (ionotropic vs metabotropic)

Answer 16

Action potential arrives at the presynaptic terminal Voltage-gated calcium channels are opened in response to changing cell potential – calcium enters the presynaptic cell rapidly Calcium influx triggers synaptic vesicle exocytosis Vesicles are recycled back into the cell via endocytosis

Answer 17

Neurotransmitters are like a "key in a lock" - you need the right key to activate each receptor Transmitter-Gated Ion Channels: - Transmitters trigger conformational change that opens a pore between subunits - Consequences depend on which ions can pass through the channel - Not as selective as voltage-gated channels (e.g., ACh activated channels allow passage of both Na+ and K+) G-protein Coupled Receptors: - Slower and longer-lasting effects than transmitter-gated ion channels - More steps involved - Receptors activate g-proteins - G-proteins activate effector proteins (ion channels or enzymes)

Answer 18

Excitatory Postsynaptic Potential (EPSP): - If the open channels are permeable to Na+ then the net effect is to depolarize the postsynaptic cell (i.e., take the cell closer to triggering an action potential) Examples: ACh-hated and glutamate-gated ion channels Inhibitory Postsynaptic Action Potential (IPSP): - If the open channels are permeable to Cl then the net effect is to hyperpolarize the postsynaptic cell (i.e., take the cell further from triggering an action potential) Examples: GABA and glycine-gated ion channels

Answer 19

Not every EPSP triggers an action potential. Most EPSPs are very small (A) Spatial summation (B) occurs when many nearby synapses each generate an EPSP to generate a larger depolarization when added together Temporal summation (C) occurs when a synapse fires multiple times in short succession (before the cell has time to repolarize)

Answer 20

If the resting membrane potential is already - 65mV, no IPSP will be visible (membrane potential already = reversal potential for Cl) So what effect is the IPSP having on cell signaling? When an EPSP depolarizes the cell membrane and the current flows towards the soma, the current may pass by an active inhibitory synapse Positive current here will flow out of the cell, redirecting the excitatory potential away from the soma The inhibitory synapse acts as a "shunt" and prevents an action potential from being generated

Answer 21

Cholinergic: - Present at neuromuscular junction - Produced by all motor neurons in the spine and brainstem - Examples: Acetylcholine Catecholaminergic: - Tyrosine is the precursor of all catecholaminergic neurotransmitters - Regulate movement, mood, attention, and visceral function - Examples: dopamine, norepinephrine, epinephrine Serotonergic: - Tryptophan is the precursor of serotonergic neurotransmitters - Plays a role in regulating mood, emotional behaviour, and sleep - Examples: serotonin Amino Acid: - Literally amino acids (building blocks of proteins) - Very small - Examples: glutamate (excitatory), glycine, GABA (inhibitory Other: ATP - excitatory Endocannabinoids - retrograde messengers Nitric Oxide - gaseous, membrane permeable

Answer 22

Like neurotransmitters, many drugs bind to receptors to exert an effect on the nervous system Agonists - Bind to receptors and imitate the actions of neurotransmitters - Effect looks similar to response to naturally-occurring neurotransmitter release - Example: nicotine (binds to ACh receptors, mimics ACh function – muscle activation) Antagonists - Binds to receptors and inhibits (antagonizes) their function - Blocks the action of naturally-occurring neurotransmitters - Example: curare (binds to ACh receptors, prevents ACh function at the neuromuscular junction – paralysis)