Cellular neurobiology

Question 1

Name the differentiated classes of Glia Cells and their function

Answer 1

Astrocyte

Oligodendrocyte

Microglial cell

Question 2

What are the passive properties of nerve cells

Answer 2

Passive properties refer to the capacitative and resistive aspects inherent in neuronal membranes, along with the resistivity inherent in the cytoplasm and the extracellular milieu.

Question 3

What determines the resting membrane potential?

Answer 3

The RMP is set by a combined flux of Na and K ions

The RMP influences the direction of ion flux through ion channels

All neurons have a RMP around -65 mV.

Question 4

Name the classes of ion channels and their properties

Answer 4

Non-gated ion channels

• Always open
• Leak channels
• Maintain the resting membrane potential

Gated ion channels

• Open and close in response to a specific stimulus
• Transition between closed and open states = Gating
• Synaptic potentials, Action potentials

Question 5

What is a Ligand-gated ion channel?

Answer 5

Responds to transmitter substance and directly affects gated synaptic transmission

Question 6

What is a phosphorylation-gated ion channel?

Answer 6

Responds to phosphorylation and affects 2nd messenger mediated synaptic transmission

Question 7

what characterizes voltage-gated ion channels?

Answer 7

Responds to change in membrane potential and generates action potential

Question 8

Describe the membrane time constant

Answer 8

Membrane time constant is the time for the potential to fall from the resting to a fraction (1-l/e), or 63%, of its final value in the charging curve during the application of a small negative current pulse. Negative voltage shift from the resting potential hardly activates any voltage-dependent ion channel, resulting in nominal changes in cell membrane resistance.

Question 9

What determines the decay time of the action potential?

Answer 9

The time constant of the neuron.

Short time constant = fast decay

Long time constant = slow decay

Question 10

Summation

Answer 10

The addition in space and time of sequential synaptic potentials to generate a postsynaptic response larger than that produced by a single synaptic potential.

Question 11

How can synapses transmit information if their PSPs are subthreshold?

Answer 11

The answer is that neurons in the central nervous system are typically innervated by thousands of synapses, and the PSPs produced by each active synapse can sum together—in space and in time—to determine the behaviour of the postsynaptic neuron.

Question 12

Describe the space constant

Answer 12

The space constant depends on the ratio of the membrane resistance to the axial resistance (resistance of the axoplasm). You can change the membrane’s passive resistance by changing leakage conductance in this panel to determine how such changes affect passive decay.

Question 13

glia cell

Answer 13

most numerous type of cell in the nervous system, 3:1 ratio to neurons, responsible for supporting neurons

Question 14

dendrite

Answer 14

extension of a neuron that receives input from axons of other cells and conducts signal towards cell body

Question 15

interneurons

Answer 15

neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs

Question 16

action potential

Answer 16

electrical signal that is carried down the axon

Question 17

chemical synapse

Answer 17

synapses where information is transmitted via the secretion of signaling molecules (neurotransmitters)

Question 18

synaptic vessicles

Answer 18

small sacs containing neurotransmitters at presynaptic terminal

Question 19

dorsal root ganglia

Answer 19

contain cell bodies of sensory neurons

Question 20

cranial nerve ganglia

Answer 20

The sensory ganglia associated with the cranial nerves; these correspond to the dorsal root ganglia of the segmental nerves of the spinal cord.

Question 21

extracellular recording

Answer 21

Method of taking measurements of cell firing by inserting a fine-tipped electrode into the extracellular fluid surrounding the cell…good for temporal resolution of action potentials

Question 22

intracellular recording

Answer 22

Method of taking measurements of cell firing by inserting a fine-tipped electrode into the cell…good for resolution of receptor potentials or synaptic potentials

Question 23

receptor potential

Answer 23

A slow, graded electrical potential produced by a receptor cell in response to a physical stimulus

Question 24

synaptic potential

Answer 24

Graded potentials produced in the post-synaptic cell in response to neurotransmitters binding to receptors

Question 25

Visceral or autonomic motor division

Answer 25

sympathetic, parasympathetic, and enteric divisions...innervate smooth muscles, cardiac muscle, and glands

Question 26

sympathetic division

Answer 26

The part of the autonomic nervous system that arouses the body to deal with perceived threats.

Question 27

parasympathetic nervous system

Answer 27

the division of the autonomic nervous system that calms the body, conserving its energy

Question 28

enteric system

Answer 28

A subsystem of the visceral motor system, made up of small ganglia and individual neurons scattered throughout the wall of the gut; influences gastric motility and secretion.

Question 29

active transporters

Answer 29

Transmembrane proteins that actively move ions into or out of cells against their concentration gradients. Their source of energy may be ATP or the electrochemical gradients of various ions.

Question 30

depolarization

Answer 30

Displacement of a cell's membrane potential toward a less negative value.

Question 31

electrochemical equilibrium

Answer 31

The condition in which no net ionic flux occurs across a membrane because ion concentration gradients and opposing transmembrane potentials are in exact balance.

Question 32

equilibrium potential

Answer 32

The membrane potential at which a given ion is in electrochemical equilibrium.

Question 33

hyperpolarization

Answer 33

The displacement of a cell's membrane potential toward a more negative value.

Question 34

ion channels

Answer 34

Integral membrane proteins possessing pores that allow only certain ions to diffuse across cell membranes, thereby conferring selective ionic permeability.

Question 35

Nernst equation

Answer 35

A mathematical formula that predicts the electrical potential generated ionically across a membrane at electrochemical equilibrium.

Question 36

overshoot phase

Answer 36

The peak, positive-going phase of an action potential, caused by high membrane permeability to a cation such as Na+ or Ca2+.

Question 37

passive flow

Answer 37

The flow of electrical current across neuronal membranes that does not entail the action potential mechanism.

Question 38

receptor potential

Answer 38

The membrane potential change elicited in receptor neurons during sensory transduction. Also called generator potential.

Question 39

rising phase

Answer 39

The initial, depolarizing, phase of an action potential, caused by the regenerative, voltage-dependent influx of a cation such as Na+ or Ca2+.

Question 40

threshold potential

Answer 40

The level of membrane potential at which an action potential is generated.

Question 41

undershoot

Answer 41

The final, hyperpolarizing phase of an action potential, typically caused by the voltage-dependent efflux of a cation such as K+.

Question 42

active transporters

Answer 42

Transmembrane proteins that actively move ions into or out of cells against their concentration gradients. Their source of energy may be ATP or the electrochemical gradients of various ions.

Question 43

ATPase pumps

Answer 43

Membrane pumps that use the hydrolysis of ATP to translocate ions against their electrochemical gradients.

Question 44

co-transporters

Answer 44

Active transporters that use the energy from ionic gradients to carry multiple ions across the membrane in the same direction.

Question 45

electrogenic

Answer 45

Capable of generating an electrical current; usually applied to membrane transporters that create electrical currents while translocating ions.

Question 46

ion exchangers

Answer 46

Membrane transporters that exchange intracellular and extracellular ions against their concentration gradient by using the electrochemical gradient of other ions as an energy source.

Question 47

ligand-gated ion channels

Answer 47

Ion channels that respond to chemical signals rather than to the changes in membrane potential generated by ionic gradients. The term covers a large group of neurotransmitter receptors that combine receptor and ion channel functions into a single molecule.

Question 48

macroscopic currents

Answer 48

Ionic currents flowing through large numbers of ion channels distributed over a substantial area of membrane.

Question 49

microscopic currents

Answer 49

Ionic currents flowing through single ion channels.

Question 50

patch clamp

Answer 50

An extraordinarily sensitive voltage clamp method that permits the measurement of ionic currents flowing through individual ion channels.

Question 51

pore

Answer 51

Structural feature of an ion channel that allows ions to diffuse through the channel.

Question 52

pore loop

Answer 52

An extracellular domain of amino acids, found in certain ion channels, that lines the channel pore and allows only certain ions to pass.

Question 53

voltage-gated

Answer 53

Term used to describe ion channels whose opening and closing is sensitive to membrane potential.

Question 54

acetylcholine

Answer 54

Neurotransmitter at motor neuron synapses, in autonomic ganglia, and in a variety of central synapses. Binds to two types of acetylcholine receptors (AChRs), either ligand-gated ion channels (nicotinic receptors) and G-protein-coupled receptors (muscarinic receptors).

Question 55

clathrin

Answer 55

The most important protein for endocytotic budding of vesicles from the plasma membrane; its three-pronged "triskelia" attach to the vesicular membrane to be retrieved.

Question 56

co-transmitters

Answer 56

Two or more types of neurotransmitters within a single synapse; may be packaged into separate populations of synaptic vesicles or co-localized within the same synaptic vesicles.

Question 57

connexons

Answer 57

Precisely aligned, paired transmembrane channels that form gap junctions between cells. They are formed from connexins, members of a specialized family of channel proteins.

Question 58

end plate current (EPC)

Answer 58

A macroscopic postsynaptic current resulting from the summed opening of many ion channels; produced by neurotransmitter release and binding at the motor end plate.

Question 59

end plate potential (EPP)

Answer 59

Depolarization of the membrane potential of skeletal muscle fiber, caused by the action of the transmitter acetylcholine at the neuromuscular synapse.

Question 60

end plate

Answer 60

The complex postsynaptic specialization at the site of nerve contact on skeletal muscle fibers.

Question 61

excitatory postsynaptic potential (EPSP)

Answer 61

Neurotransmitter-induced postsynaptic potential change that depolarizes the cell, and hence increases the likelihood of initiating an action potential.

Question 62

G-protein-coupled receptors

Answer 62

A large family of neurotransmitter or hormone receptors, characterized by seven transmembrane domains; the binding of these receptors by agonists leads to the activation of intracellular G-proteins.

Question 63

G-proteins

Answer 63

Proteins that are activated by exchanging bound GDP for bound GTP (and thus also known as GTP-binding proteins).

Question 64

gap junction

Answer 64

A specialized intercellular contact formed by channels that directly connect the cytoplasm of two cells.

Question 65

inhibitory postsynaptic potential (IPSP)

Answer 65

Neurotransmitter-induced postsynaptic potential change that tends to decrease the likelihood of a postsynaptic action potential.

Question 66

ionotropic receptors

Answer 66

Receptors in which the ligand binding site is an integral part of the receptor molecule.

Question 67

ligand-gated ion channels

Answer 67

Ion channels that respond to chemical signals rather than to the changes in membrane potential generated by ionic gradients. The term covers a large group of neurotransmitter receptors that combine receptor and ion channel functions into a single molecule.

Question 68

miniature end plate potential (MEPP)

Answer 68

Small, spontaneous depolarization of the membrane potential of skeletal muscle cells, caused by the release of a single quantum of acetylcholine.

Question 69

metabotropic receptors

Answer 69

Receptors that are indirectly activated by the action of neurotransmitters or other extracellular signals, typically through the aegis of G-protein activation. Also called G-protein-coupled receptors.

Question 70

neurotransmitter

Answer 70

Substance released by synaptic terminals for the purpose of transmitting information from one cell (the presynaptic cell) to another (the postsynaptic cell).

Question 71

postsynaptic

Answer 71

Referring to the component of a synapse specialized for transmitter reception; downstream at a synapse.

Question 72

postsynaptic current (PSC)

Answer 72

The current produced in a postsynaptic neuron by the binding of neurotransmitter released from a presynaptic neuron.

Question 73

postsynaptic potential (PSP)

Answer 73

The potential change produced in a postsynaptic neuron by the binding of neurotransmitter released from a presynaptic neuron.

Question 74

presynaptic

Answer 74

Referring to the component of a synapse specialized for transmitter release; upstream at a synapse.

Question 75

reversal potential

Answer 75

Membrane potential of a postsynaptic neuron (or other target cell) at which the action of a given neurotransmitter causes no net current flow.

Question 76

summation

Answer 76

The addition in space and time of sequential synaptic potentials to generate a larger than normal postsynaptic response.

Question 77

synaptic cleft

Answer 77

The space that separates pre- and postsynaptic neurons at chemical synapses.

Question 78

synaptic vesicle cycling

Answer 78

Sequence of budding and fusion reactions that occurs in presynaptic terminals to maintain the supply of synaptic vesicles.

Question 79

saltatory conduction

Answer 79

Mechanism of action potential propagation in myelinated axons; so named because action potentials "jump" from one node of Ranvier to the next due to generation of action potentials only at these sites.

Question 80

The relative refractory period is dependent on..

Answer 80

K+ channels

Question 81

What is true about the resting membrane potential?

Answer 81

It depends on the intracellular and extracellular K+ concentration

Question 82

What is true about the action potential?

Answer 82

The early afterhyperpolarization regulates the frequency of action potentials

Question 83

What is true about the neuron´s electrical properties?

Answer 83

1. Synaptic summation depends on the time constant 2. Synaptic summation depends on the space constant

Question 84

What is true about the neuron´s electrical properties?

Answer 84

Inhibitory synapses occur frequently on the soma and proximal dendrites Excitatory synapses occur frequently on distal dendrites

Question 85

What is true about excitability?

Answer 85

Excitability depends on voltage-gated ion channels

Question 86

What is true about ion channels?

Answer 86

Ligand-gated channels occur in cell bodies Leak channels determine the resting membrane potential

Question 87

What is true about electrical synapses?

Answer 87

They contain connexin

Question 88

What is true about synaptic vesicles?

Answer 88

Large dense cored vesicles are not recycled in nerve terminals

Question 89

channel selectivity

Answer 89

This is the principle that only certain ions will pass a channel. This can be due to charge of the ion, size of the molecule, or whether the ion gathers water molecules around itself (hydration, making it bigger).

Question 90

Voltage across the membrane is a form of energy that cells use to move things. What is the ultimate source of that energy?

Answer 90

Metabolism that generates ATP molecules that run the sodium/potassium ATPase pump.

Question 91

What is the mechanism for selectivity in voltage-gated ion channels?

Answer 91

Selectivity in most ion channels is based on interaction between the ions to which the channel is permeable and amino acids in the channel pore. Factors that are important include size and charge of the ion, and whether the ion is strongly attracted to water molecules (hydrated). If the hydrated diameter is too large for the pore, it must interact with molecules in the channel to break the connection with water molecules if it is to pass. Many channels have loops of amino acids that extend into the channel that provide the selectivity filter.

Question 92

How are some voltage-gated ion channels inactivated?

Answer 92

Several voltage-gated channels inactivate after being activated. A classic example of this is the voltage gated fast sodium channel. There is a segment of the amino acid chain of the channel protein that enters the pore and blocks further ion movement after the initial activation of the channel. This inactivation "gate" will be reopened once the cell has repolarized.

Question 93

What is responsible for the rising (depolarizing) phase of the action potential?

Answer 93

nce the neuron reaches threshold, the rising (depolarizing) phase of the action potential is due to the conformation change in the fast sodium channel once threshold is reached, with the rapid influx of some sodium ions.

Question 94

What are the two processes that contribute to the falling (repolarizing) phase of the action potential?

Answer 94

The rapid repolarization of a neuron once an action potential has been generated is due to the very rapid inactivation of fast sodium channels along with activation of the slower responding voltage-gated potassium channels.