Chapter 7- Neurons and Synapses

Question 1

Describe the different parts of a neuron o

Answer 1

o Basic cell of the nervous system
o Structure
 Dendrites: hair like projections
 Cell body
 Axon hillock
 Axon
 Axonal transport
 Axon terminal

Question 2

Define afferent neuron, efferent neuron, and interneuron

Answer 2

o Afferent (sensory)
 Sends action potential INTO the CNS
o Efferent (motor)
 Somatic (out)
 Autonomic nervous system
o Interneurons
 Association

Question 3

describe the effects of myelination on a neuron

Answer 3

o Myelin= sheaths
 Allows “skipping”
o White matter
 Myelinated and can send signals faster
o Gray matter
 unmyelinated

Question 4

describe the different types of neurons and neuroglial cells, including their functions

Answer 4

o Neuron
 Conducts electrical signals
o Neuroglia
 Majority of all nerve tissue cells
 Supports neurons
 Nonconducting cells in PNS and CNS
 Types: myelinate
 Schwann Cells- PNS
 Oligodendrocytes- CNS
 Astrocytes
. Structural
 Microglia
 No toxicity
 Ependymal cells
 Conduct CSF

Question 5

compare neuron regeneration in PNS and CNS

Answer 5

o When an axon in the PNS is cut, the severed part degenerates
 Regeneration tube is formed by Schwann cells.
o The CNS does not regenerate

Question 6

compare and contrast action potential and graded potential

Answer 6

o Not all GP are AP
o All AP come from GP
o Electrical signals produced by changes in ion concentrations
 Changes brought about by triggering event
 Alter ion concentrations by altering ion permeability
* Describe the characteristics of graded potentials
o Magnitude varies with stimulus strength
o Graded potential decremental
o Depolarizing or hyperpolarizing
o Produced by some specific change in environment acting on specialized region

Question 7

describe the characteristics of action potentials and how they are conducted

Answer 7

o Brief, rapid, large (100 mV) changes in membrane potential
o Must reach threshold potential
o Not decremental
o Begins at axon hillock
 If there is a voltage change across the membrane at -50 mV, it will open Na+ voltage-gated channels.
 Sodium will rush in then we reach a + voltage
 At +30 mV, Na channels close and open up K+ channels and rush out of the cell
o Sequence
 Depolarization
 Voltage-sensitive Na+ channels open as the membrane depolarizes
 Reach threshold- induces more Na+ channels to open
 Peak
 Na+ channels close- inactivated
 Voltage-gated K+ channels open
 Repolarization
 K+ leaving neuron
 After hyperpolarization
 K+ still slowly leaving
 Return to resting membrane potential
 Sodium potassium ATP pump is always on

Question 8

describe the refractory period

Answer 8

o Absolute
 Cannot have another AP
o Relative
 Can generate another AP
 They are ready to be stimulated again

Question 9

define the terms depolarization, repolarization, overshoot, and hyperpolarization

Answer 9

o Polarization
 Membrane potential other than 0mV
o Depolarization
 Less negative than the resting membrane potential (closer to 0)
o Repolarization
 Membrane returns to resting potential after
o Hyperpolarization
 More negative than the resting membrane potential

Question 10

compare Na+ and K+ gating

Answer 10

o K+ has two types of channels
 Leaky: not gated, always open
 Voltage-gated K+ channels: open when a particular membrane potential is reached: closed at resting potential
 Open when we get to +30 mV
 Would rush out of the cell
o Na+ has only voltage-gated channels that are close at rest, open when a particular membrane potential is reached (55 mV)
 Would rush into the cell
 High to low

Question 11

describe the all or none principle of an action potential

Answer 11

o Amount of depolarization (amplitude) is always the same as long as depolarized to threshold
 AP don’t change size
o Differences in stimulus intensity are detected by the frequency of action potential generation
 Frequency of AP is how you differentiate

Question 12

describe saltatory conduction

Answer 12

o Action potential “jump” from one node to the next
o Up AP conduction speed by 50x

Question 13

describe electrical and chemical synapses

Answer 13

o Synapse: communication junction between a neuron and either another neuron or a muscle or gland cell
o Chemical and electrical
o Stimulates physiological change (usually change in membrane potential) in the recipient cell
o Anatomy of synapse
 Presynaptic neuron: before
 Synaptic cleft: space between
 Postsynaptic cell: after

Question 14

describe the sequence of events in neural communication across a synapse

Answer 14

o AP triggers opening of Ca2+ channels
o Ca2+ rushes in
o Ca2+ induced exocytosis of synaptic vesicles
o Neurotransmitter binds to receptors on postsynaptic cell membrane
o Opens ligand-gated ion channels
o Induces a synaptic potential (electrical signal) in postsynaptic cell
o Doesn’t depolarize to threshold=graded potential

Question 15

describe how a neurotransmitter is released from an axon terminal

Answer 15

o Presynaptic neuron stimulates postsynaptic neuron, if enough channels are open it will generate an action potential at the axon hillock.
o Goes down through the nodes of Ranvier and reach the terminal end
o AP stimulates Ca+ channels to open and rush into the cell
o Stimulates neurotransmitter vesicles to release the vesicles through exocytosis
o Neurotransmitters are released and bind to the next neuron

Question 16

describe excitatory and inhibitiory postsynpatic potentials

Answer 16

o Excitatory
 Opens Na+ channels
 Sodium rushes into cell
 Stimulates an action potential
 Acetylcholine binds to sodium ligated channel to open
 Na+ rushes in and K+ rushes out of the cell
o Inhibitory
 Opens Cl- channel
 GABA binds to ligand-gated Cl channel
 Opens and flows into cell making inside more negative causing hyperpolarization

Question 17

differentiate between temporal and spatial summation

Answer 17

o One synapse is not enough to get an effect-need to add the input together
o Spatial summation
 Many sources
o Temporal summation
 From 1 source

Question 18

define a ligand gated channel

Answer 18

o are a group of transmembrane ion-channel proteins which open to allow ions such as Na⁺, K⁺, Ca²⁺, and/or Cl⁻ to pass through the membrane in response to the binding of a chemical messenger, such as a neurotransmitter.
o Must bind to open

Question 19

compare the actions of an excitatory neurotransmitter and inhibitory neurotransmitter on the post synaptic neuron

Answer 19

o Acetylcholine- excitatory
o Gamma-aminobutyric acid (GABA)- inhibitory
o Glutamate-excitatory
 Main neurotransmitter in brain
o Glycine-Inhibitory
o Norepinephrine and epinephrine
 adrenaline

Question 20

describe the action of acetylcholinesterase

Answer 20

o Found in synaptic cleft
o Functions to breaks down Ach into component parts, which are taken back into the presynaptic cell for reuse.
o Tinman
o Must breakdown to finish movement

Question 21

explain how G-protein coupled signal pathways produce synaptic potentials

Answer 21

o Acetylcholine binds to the receptor on the membrane (polar)
o Stimulates the G-protein complex to disassociate
o Gamma units move across membrane to potassium channel
o Potassium channel opens and K+ moves out