Neurons, Synapses, and Signalling

Question 1

What are neurons?

Answer 1

Nerve cells that act as the main information processing units in the body that communicate via electrical (long-distance, intracellular) and chemical signals (short-distance, intercellular)

Question 2

Where does the processing of information that takes place?

Answer 2

Ganglia: Simple clusters of neurons

Brain: complex organization of neurons

Question 3

What are the parts of a neuron?

Answer 3

Soma: cell body that stores organelles

Dendrites: Highly branched extensions that receive signals from other neurons

Axon: longer extension that transmits signals to other cells from other neurons

Axon hillock: Cone shaped base of axon

Question 4

What is the synapse?

Answer 4

Junction between an axon and another cell

Question 5

What is a synaptic terminal?

Answer 5

End of the axon where information is passed across the synapse via neurotransmitters

Question 6

What is the difference between a presynaptic cell and a postsynaptic cell?

Answer 6

Presynaptic: Neuron that transmits information

Postsynaptic: Cell (that may or may not be a neuron) that receives the signal.

Question 7

What are glia?

Answer 7

Cells around the neurons that nourish and insulate the glia.

Question 8

What are the three stages in which nervous system processes information?

Answer 8

1. Sensory input: detect external stimuli and transmit info along sensory neurons
2. Integration: sensory info is sent to the brain and interneurons integrate the information
3. Motor output: motor output leaves the brain or ganglia via motor neurons which trigger muscle or gland activity.

Question 9

What are the two parts of the animal nervous system?

Answer 9

Central nervous system (CNS): where integration takes place; brain + nerve cord

Peripheral nervous system (PNS): bunldes of neurons called nerves carries information into and out of CNS

Question 10

What is membrane potential?

Answer 10

The voltage (difference in electrical charge) across its plasma membrane. Changes in this potential acts as the signal, transmitting and processing information.

Question 11

What is resting potential?

Answer 11

The membrane potential of a neuron (not sending signals). Concentration of K+ is highest inside cell, while concentration of Na+ and CL- are highest outside the cell.

Question 12

What maintains the K+ and Na+ gradients across the plasma membrane?

Answer 12

1. Many potassium channels let potassium out of the cell
2. Few sodium channels that let sodium into the cell
3. Sodium/Potassium pump that lets more K out of the cell than Na into the cell.

Question 13

What is equilibrium potential?

Answer 13

membrane voltage for a particular ion at equilibrium. for K it is -90mV, and for Na it is +62mV

Question 14

What is depolarization? What is hyperpolarization?

Answer 14

Depolarization: When positive ions move into the cell/negative ions moving out as the charge approaches zero

Hyperpolarization: positive ions move out of the cell/negative ions move into the cell, increasing the charge of the

Question 15

What are graded potentials?

Answer 15

Changes in polarization where the magnitude of the change varies with the strength of stimulus. If depolarization shifts the membrane potential sufficiently, it results in an action potential.

Question 16

What is a voltage gated ion channel?

Answer 16

membrane channels that open or close when the membrane potential passes a certain level

Question 17

What are the steps of an action potential?

Answer 17

1. resting potential: sodium and potassium channels are closed. inside of the cell is negatively charged (2 K+ goes in) and outside of the cell is positively charged (3 Na+ goes out)
2. When a threshold of excitation is reached, sodium channels open, allowing sodium to flow into the cell and increase membrane potential (depolarization)
3. At peak action potential, sodium channels close, potassium channels open and potassium floods out of the cell (repolarization)
4. Membrane becomes hyperpolarized due to potassium going into cell which triggers the closing of potassium channels.
5. Refractory period caused by the temporary inactivation of Na+ channels allows return to resting membrane potential

Question 18

What causes action potentials to travel in one direction?

Answer 18

Inactivated Na+ channels behind the zone of depolarization prevents the action potential from travelling backwards.

Question 19

what is myelin?

Answer 19

Fatty tissue made by oligodendrocytes (CNS) and Schwann cells (PNS) that insulate segments of the axon.

Question 20

What are the nodes of ranvier?

Answer 20

Gaps in the myelin sheath where voltage gated channels are found.

Question 21

What is saltatory conduction?

Answer 21

Process of action potentials jumping between nodes of ranvier.

Question 22

Difference between electrical and chemical synapses?

Answer 22

Electrical synapse: electrical current flows from one neuron to another via gap junctions

chemical synapse: chemical neurotransmitter carries information between neurons

Question 23

How does calcium play a role at chemical synapses?

Answer 23

1. Influx of calcium opens voltage gated calcium channels
2. calcium goes into the axon terminal which stimulates release of neurotransmitters in vesicles
3. vesicles open to release neurotransmitters alowing it to diffuse across the synaptic cleft
4. neurotransmitters act as ligands to open ligand gated ion channels on the post-synaptic cell causing postsynaptic potential

Question 24

What are synaptic vesicles?

Answer 24

Vesicles in the synaptic terminal that hold neurotransmitters. Vesicles are made by the presynaptic neuron.

Question 25

What are the two categories of postsynaptic potential?

Answer 25

excitatory postsynaptic potential: depolarization that brings membrane potential towards threshold (bringing in sodium)

inhibitory postsynaptic potential: hyperpolarization that move the membrane potential farther from threshold (bringing in potassium)

Question 26

What is temporal summation?

Answer 26

Two excitatory post synaptic potentials produced in rapid succession which causes an action potential

Question 27

What is spatial summation?

Answer 27

post synaptic potentials produced nearly simultaneously by different synapses on the same neuron. May generate an action potential, but may also be countered by the effect of an IPSP

Question 28

How are neurotransmitters cleared from the synaptic cleft?

Answer 28

inactivation via enzyme hydrolysis or recapture by presynaptic neuron

Question 29

what is a metabotropic receptor?

Answer 29

a receptor that activates a G protein to activate an ion channel, rather than the receptor being the channel itself

Question 30

What are the four classes of neurotransmitters?

Answer 30

amino acids: glutamate, GABA, glycine

biogenic amines: epinephrine, norepinephrine, dopamine, serotonin

neuropeptides (short polypeptides): substance P, endorphins

gases: nitric oxide, carbon monoxide