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Chapter 8
Neurons: Cellular & Network Properties
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Undergraduate 3
09/11/2015

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Term
nervous system
Definition
a network of billions of nerve cells linked together in a highly organized manner to form the rapid control system of the body; controlled by the brain & spinal cord
Term
neurons
Definition
nerve cells that carry electrical signals rapidly & sometimes over long distances
Term
processes
Definition
long, thin extensions that most neurons have that can extend up to a meter in length; give neurons their unique shapes
Term
neurotransmitters
Definition
chemical signals released by neurons in most pathways into the ECF to communicate with neighboring cells
Term
emergent properties
Definition
complex processes (consciousness, intelligence, & emotion) that cannot be predicted from what we know about the properties of individual nerve cells & their specific connections
Term
2 things that make up the central nervous system (CNS)
Definition
1. brain
2. spinal cord
Term
2 things that make up the peripheral nervous system (PNS)
Definition
1. sensory (afferent) neurons
2. efferent neurons
Term
2 divisions of the efferent neurons
Definition
1. somatic motor division (controls skeletal muscles)
2. autonomic division (controls smooth & cardiac muscles, exocrine glands, some endocrine glands, & some types of adipose tissue)
Term
2 branches of the autonomic neurons
Definition
1. sympathetic branch
2. parasympathetic branch

*can be distinguished by their anatomical organization & by the chemicals they use to communicate with their target cells*
Term
enteric nervous system
Definition
a network of neurons in the walls of the digestive tract
Term
2 types of processes that extend from the nerve cell body
Definition
1. dendrites (receive incoming signals)
2. axons (carry outgoing information)
Term
interneurons
Definition
neurons that lie entirely within the CNS
Term
collaterals
Definition
branches into with axons may divide several times
Term
axon terminals
Definition
enlarged endings of efferent neurons
Term
varicosities
Definition
enlarged regions along the axon of many autonomic neurons
Term
nerves
Definition
cordlike fibers into which the long axons of both afferent & efferent peripheral neurons are bundled with connective tissue that extend from the CNS to the targets of the component neurons
Term
3 types of nerves
Definition
1. sensory nerves (nerves that carry only afferent signals)
2. motor nerves (carry only efferent signals)
3. mixed nerves (nerves that carry signals in both directions)
Term
Does the cell body of a neuron resemble a typical cell with a nucleus & all organelles needed to direct cellular activity?
Definition
yes!
Term
How can a dendrite's surface area by expanded?
Definition
by the presence of dendritic spines that vary from thin spikes to mushroom-shaped knobs
Term
axon hillock
Definition
the specialized region of the cell body from which a single axon originates in most peripheral neurons
Term
axonal transport
Definition
the process by which proteins are moved down the axon
Term
How does slow axonal transport move material from the cell body to the axon terminal?
Definition
axoplasmic or cytoplasmic flow
Term
How fast can fast axonal transport move organelles?
Definition
up to 400mm per day
Term
synapse
Definition
the region where an axon terminal meets its target cell
Term
2 types of neurons involved in a synapse
Definition
1. presynaptic cell (the neuron that delivers a signal to the synapse)
2. postsynaptic cell (the cell that receives the signal)
Term
synaptic cleft
Definition
the narrow space between two cells
Term
The human CNS also contains _____, where the presynaptic & postsynaptic cells are connected by gap junction channels
Definition
electrical synapses
Term
growth cones
Definition
special tips put out by the axons of embryonic nerve cells that extend through the extracellular compartment until they find their target cell
Term
The survival of neuronal pathways depends on _____ secreted by neurons & glial cells
Definition
neurotrophic factors
Term
Are there more glial cells or neurons in the nervous system?
Definition
glial cells (outnumber neurons by 10-50 to 1)
Term
_____ in the PNS & _____ in the CNS support & insulate axons by forming myelin, a substance composed of multiple concentric layers of phospholipid membrane
Definition
Schwann cells; oligodendrocytes
Term
nodes of Ranvier
Definition
tiny gaps left between the myelin-insulated areas of each axon because each Schwann cell wraps around a 1-1.5mm segment of an axon
Term
satellite cell
Definition
the second type of PNS glial cell; a nonmyelinating Schwann cell
Term
astrocytes
Definition
highly branched glial cells that by some estimates make up about half of all cells in the brain
Term
Are microglia cells actually neural tissue?
Definition
no!
Term
ependymal cells
Definition
the final class of glial cells; specialized cells that create a selectively permeable epithelial layer (the ependyma) that separates the fluid compartments of the CNS
Term
neural stem cells
Definition
immature cells that can differentiate into neurons & glial cells (ex. ependyma)
Term
2 factors that influence the membrane potential
Definition
1. the uneven distribution of ions across the cell membrane
2. differing membrane permeability to those ions
Term
What does the Goldman-Hodgkin-Katz (GHK) equation calculate?
Definition
the membrane potential that results from the contribution of al lions that can cross the membrane
Term
conductance
Definition
the ease with which ions flow through a channel
Term
3 categories of gated channels
Definition
1. mechanically gated ion channels
2. chemically gated ion channels
3. voltage-gated ion channels
Term
current (Iion)
Definition
the flow of electrical charge carried by an ion
Term
Current flow, whether across a membrane or inside a cell, obeys a rule known as _____
Definition
Ohm's Law
Term
resistance
Definition
a force that opposes flow
Term
graded potentials
Definition
variable-strength signals that travel over short distances & lose strength as they travel through the cell
Term
action potentials
Definition
very brief, large depolarizations that travel for long distances through a neuron without losing strength
Term
local current flow
Definition
a wave of depolarization that moves through the cell
Term
2 reasons why graded potentials lose strength as they move through the cytoplasm
Definition
1. current leak
2. cytoplasmic resistance
Term
Graded potentials that are strong enough eventually reach the region of the neuron known as the _____
Definition
trigger zone
Term
initial segment
Definition
the very first part of the axon; along with the axon hillock, it is the trigger zone for efferent neurons & interneurons
Term
conduction
Definition
the high-speed movement of an action potential along the axon
Term
Why are action potentials sometimes called all-or-none phenomena?
Definition
they either occur as a maximal depolarization or do not occur at all
Term
9 steps in the changing ion permeability along the axon during an action potential
Definition
1. resting membrane potential
2. depolarizing stimulus
3. membrane depolarizes to threshold
4. rapid Na+ entry depolarizes the cell
5. Na+ channels close & slower K+ channels open
6. K+ moves from cell to ECF
7. K+ channels remain open & additional K+ leaves cell, hyperpolarizing it
8. voltage-gated K+ channels close, less K+ leaks out of the cell
9. cell returns to resting ion permeability & resting membrane potential
Term
The double gating of Na+ channels plays a major role in the phenomenon known as the _____
Definition
refractory period
Term
absolute refractory period
Definition
the delay where a second action potential cannot be triggered once an action potential has begun; represents the time required for the Na+ channel gate to reset to their resting positions
Term
Which comes first: absolute refractory period or relative refractory period?
Definition
absolute refractory period
Term
5 steps for the conduction of an action potential
Definition
1. a graded potential above threshold reaches the trigger zone
2. voltage-gated Na+ channels open & Na+ enters the axon
3. positive charge flows into adjacent sections of the axon by local current flow
4. local current flow from the active region causes new sections of the membrane to depolarize
5. the refractory period prevents backward conduction
Term
2 physical parameters that influence the speed of action potential conduction
Definition
1. diameter of the axon
2. resistance of the axon membrane to ion leakage out of the cell
Term
saltatory conduction
Definition
the apparent jump of the action potential from node to node

*"saltare" means "to leap" in Latin*
Term
What is the most common & best-known de-myelinating disease?
Definition
multiple sclerosis
Term
hyperkalemia
Definition
an increase in blood K+ concentration; shifts the resting membrane potential of a neuron closer to threshold & causes the cells to fire action potentials in response to smaller graded potentials
Term
hypokalemia
Definition
when blood K+ concentration is too low; the resting membrane potential of the cells hyperpolarizes, moving farther from treshold
Term
2 parts of a synapse
Definition
1. the axon terminal of the presynaptic cell
2. the membrane of the postsynaptic cell
Term
electrical synapses
Definition
pass an electrical signal (current) directly from the cytoplasm of one cell to another through the pores of gap junction proteins
Term
chemical synapses
Definition
use neurocrine molecules to carry information from one cell to the next; make up the vast majority of synapses in the nervous system
Term
ionotropic receptors
Definition
receptor-channels that mediate rapid responses by altering ion flow across the membrane
Term
metabotropic receptors
Definition
GPCRs for neuromodulators
Term
7 classes of neurocrine molecules (according to their structure)
Definition
1. acetylcholine
2. amines
3. amino acids
4. peptides
5. purines
6. gases
7. lipids
Term
From what 2 things is acetylcholine (ACh) synthesized?

*it is a chemical class by itself
Definition
1. choline
2. acetyl coenzyme A
Term
cholinergic
Definition
neurons that secrete ACh & receptors that bind ACh
Term
2 main subtypes of cholinergic receptors
Definition
1. nicotinic (nicotine is an agonist)
2. muscarinic (muscarine, a compound found in fungi, is an agonist)
Term
From what is serotonin (5-hydroxytryptamine or 5-HT) made?
Definition
the amino acid tryptophan
Term
3 things that the amino acid tyrosine is converted into
Definition
1. dopamine
2. norepinephrine
3. epinephrine
Term
adrenergic neurons (noradrenergic neurons)
Definition
neurons that secret norepinephrine
Term
2 classes of adrenergic receptors (there are multiple subtypes of each)
Definition
1. alpha
2. beta
Term
_____ is the primary excitatory neurotransmitter of the CNS, and _____ is an excitatory neurotransmitter in selected regions of the brain
Definition
glutamate; aspartate
Term
gamma-aminobutyric acid (GABA)
Definition
the main inhibitory neurotransmitter in the brain
Term
What are AMPA receptors (ligand-gated monovalent cation channels) similar to?
Definition
nicotinic acetylcholine channels
Term
Where do NMDA receptors get their name from?
Definition
the glutamate agonist N-methyl-D-aspartate
Term
2 peptides involved in pain sensation
Definition
1. substance P (involved in some pain pathways)
2. opioid peptides (enkephalines & endorphins)(mediate pain relief or analgesia)
Term
synaptic vesicles
Definition
filled with neurotransmitter that is released on demand; can be seen under an electron microscope when looking at the axon terminal of a presynaptic cell
Term
5 steps in neurotransmitter release
Definition
1. an action potential depolarizes the axon terminal
2. the depolarization opens voltage-gated Ca2+ channels & Ca2+ enters the cell
3. calcium entry triggers exocytosis of synaptic vesicle contents
4. neurotransmitter diffuses across the synaptic clef & binds with receptors on the postsynaptic cell
5. neurotransmitter binding initiates a response in the postsynaptic cell
Term
kiss-and-run pathway
Definition
a model of secretion where synaptic vesicles fuse to the presynaptic membrane at a complex called the fusion pore just long enough to diffuse its neurotransmitters before releasing itself back into the cell as an intact vesicle
Term
acetylcholin-esterase (AChE)
Definition
an enzyme that rapidly breaks acetylcholine down into choline & acetyl CoA in the ECF; exists in the extracellular matrix & the membrane of the postsynaptic cell
Term
convergence
Definition
the pattern when a group of presynaptic neurons provide input to a smaller number of postsynaptic neurons
Term
synaptic plasticity
Definition
the ability of the nervous system to change activity at synapses
Term
slow synaptic potentials
Definition
changes in membrane potential resulting from alterations in ion flow; the response of the second messenger pathway takes longer than the direct opening or closing of a channel
Term
Why is the change in membrane potential called fast synaptic potential named "fast"?
Definition
it begins quickly & lasts only a few milliseconds
Term
excitatory postsynaptic potential (EPSP)
Definition
if the synaptic potential is depolarizing; makes the cell more likely to fire an action potential
Term
inhibitory postsynaptic potential (IPSP)
Definition
if the synaptic potential is hyperpolarizing; hyperpolarization moves the membrane potential away from threshold & makes the cell less likely to fire an action potential
Term
spatial summation
Definition
the combination of several nearly simultaneous graded potentials
Term
postsynaptic inhibition
Definition
the type of summation if summation prevents an action potential in the postsynaptic cell
Term
temporal summation
Definition
summation that occurs from graded potentials overlapping in time
Term
long-term potentiation
Definition
process in which activity at a synapse brings about sustained changes in the quality or quantity of synaptic connections; opposite of long-term depression; one of the "hot topics" in neurobiology today
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