Flashcards in BIOL 0800 Reading- Chapter 6 Deck (278):
1
Why are neurons said to serve as integrators?
Because their output reflects the balance of inputs they receive from up to hundreds of thousand of other neurons
2
What are processes, referring to neurons?
Long extensions, which connect neurons to each other and perform the neuron's input and output functions
3
What are dendrites and dendritic spines?
Highly branched outgrowths that receive most of the inputs from other neurons; and knoblike outgrowths that increase the surface area of dendrites even more, and often contain ribosomes
4
What is contained in dendritic spines that generally isn't contained in dendrites? Why?
Ribosomes that allow dendritic spines to remodel their shape in responses to variation in synaptic activity
5
What is the axon?
Also called a nerve fiber; long process that extends from the cell body and carries output to its target cells
6
What is the initial segment or axon hillock?
The region of the axon that arises from the cell body; the "trigger zone" where electrical signals are usually generated
7
What are collaterals?
Branches of the axons that increase the cell's sphere of influence
8
What is the axon terminal?
The end of each axon branch that is responsible for releasing neurotransmitters from the axon
9
What are varicosities?
A series of bulging areas along the axon that can also release chemical messengers from the neuron
10
What is myelin?
The layers of highly modified plasma membrane wrapped around the axon by a nearby supporting cell called an oligodendrocyte; shields the axon from excess electrical signal and prevents loss of the axon's own electrical signal
11
What is an oligodendrocyte?
In the brain and spinal cord, supporting cell that branches to for myelin on axons; can support up to 40 different axons
12
What is a Schwann cell?
In the PNS, cells that form individual myelin sheaths surrounding small segments of the axons at regular intervals; don't cover the nodes of Ranvier
13
What are the nodes of Ranvier?
The spaces between adjacent sections of myelin where the axon's plasma membrane is exposed to extracellular fluid
14
What is the purpose of the myelin sheath?
To speed up conduction of the electrical signals along the axon and to conserve energy
15
What is axonal transport?
The movement of various organelles and other materials as far as a meter between the cell body and the axon terminals; depends on scaffolding of microtubule rails running along the axon and motor proteins called kinesins and dyneins
16
What are kinesins and dyneins?
Motor proteins that facilitate axonal transport along the microtubule "rails"
17
What is the difference in kinesin and dynein movement?
Kinesins usually undergo anterograde movement (from cell body to axon terminals) and dyneins usually undergo retrograde movement (from axon terminals to cell body)
18
What is anterograde movement with kinesins useful for?
Moving nutrient molecules, enzymes, mitochondria, neurotransmitter-filled vesicles, growth factors, and other organelles
19
What is retrograde movement with dyneins useful for?
Carrying recycles membrane vesicles, growth factors, and other chemical signals that can affect the neuron's morphology, biochemistry, and connectivity; also for harmful agents can invade the central nervous system
20
What are afferent neurons?
Convey info from the tissues and organs of the body toward the central nervous system
21
What are efferent neurons?
Convey info away from the CNS to effector cells like muscle, gland, or other nerve cells
22
What are interneurons?
Connect neurons within CNS
23
What are sensory receptors?
At the peripheral ends of afferent neurons, to respond to various physical or chemical changes in their environment by generating electrical signals in the neuron
24
How do sensory receptors work?
Generating electrical signals in the neurons; propagate electrical signals from their receptors into the brain or spinal cord
25
Why are afferent neurons unusual?
Only have a single process, usually considered an axon; after the cell body, the axon divides into the peripheral (begins where dendritic branches converge from receptor endings) and central (enters the CNS to form junctions with other neurons) processes
26
What parts of the afferent neurons are in the CNS?
Only a little bit of the central process; NOT the cell body or rest of the axon
27
What parts of the efferent neurons are in the CNS?
The cell bodies and dendrites, but usually not the axons
28
What is the different between nerve and nerve fiber?
Nerve fiber is generally referring to a single axon, but nerve is a bundle of axons (fiber) bound together by connective tissue
29
What parts of interneurons are in the CNS?
All of it! They're 99% of all neurons
30
What is an example of a process that requires no interneurons?
Knee-tap reflex: the afferent neuron interacts directly with efferent neurons
31
What are the two characteristics of afferent neurons?
Transmit info into CNS from receptors' peripheral endings; cell body and long peripheral process of the axon in the PNS, but short bit of central process of the axon in the CNS
32
What are the two characteristics of efferent neurons?
Transmit info out of CNS to effector cells like muscle/gland/neurons; cell body, dendrites and part of axon in CNS< most of axon in the PNS
33
What are the four characteristics of interneurons?
Function as integrators and signal changers; integrate groups of afferent/efferent neurons into reflex circuits; lie entirely within CNS; more than 99% of all neurons
34
What is a synapse?
The anatomically specialized junction between two neurons where one alters the electrical and chemical activity of the other
35
What transmits the signal across synapses, usually?
Neurotransmitters
36
What are glial cells?
The other ~90% of the nervous system; surround the soma, axon, and dendrites of neurons and provide physical and metabolic support
37
What are the types of glial cells?
Oligodendrocytes (and Schwann cells), astrocytes, microglia, and ependymal
38
What is an astrocyte?
Glial cell: regulates the composition of the ECF in the CNS by removing potassium ions and neurotransmitters around synapses; stimulates formation of tight junctions between the cells that make up the walls of capillaries found in the CNS to form the blood-brain barrier (prevents toxins and other substances from other substances from entering the brain)
39
What is the blood-brain barrier?
Prevents toxins and other substances from entering the brain
40
How do astrocytes function in developing embryos?
Guide the neurons to their final destinations and stimulate neuronal growth by secreting growth factors
41
What are microglia?
Glial cells: specialized macrophage-like cells that perform immune functions in the CNS
42
What are ependymal cells?
Glial cells: line the fluid-filled cavities within the brain and spinal cord and regulate the production and flow of cerebrospinal fluid
43
How does development of the nervous system begin?
In embryo: division of stem cells develops into neurons or glia; differentiate and migrate and send out processes that will become axons/dendrites
44
What is the growth cone?
A specialized enlargement that forms the tip of each extending axon and is involved in finding the correct route and final target for the process
45
What are neurotrophic factors?
Growth factors for neural tissues that help guide the axon along the surfaces of other cells; along with cell adhesion molecules that reside on the surface of glia and embryonic neurons
46
What are two types of substances that help guide the developing axons along the surfaces of other cells, usually glial cells?
Cell adhesion molecules and soluble neurotrophic factors
47
What happens once the target of the advancing growth cone is reached?
Synapses form; BUT they're active even before they get there
48
What strange phenomenon occurs with the majority of developing neurons?
Apoptosis! Probably to refine and fine-tune the connectivity in the nervous system
49
What factor affects the final function of neurons?
The neuron's early activity before they're done maturing
50
Axon regeneration depends on what?
If the damage occurs outside the CNS and doesn’t affect the neuron's cell body
51
Does neuron function restoration occur quickly or slowly?
VERY slowly: 1 mm per day, approximately
52
What happens when electrical resistance is high?
Current flow will be low
53
What is Ohm's Law?
I = V/R
54
What is the effect of high electrical resistance on current flow?
Lower flow; characteristic of insulators
55
What is the effect of low electrical resistance on current flow?
Higher flow; characteristic of conductors
56
What is water that contains dissolved ions, and what are lipids, in terms of conductivity? Why?
Water with ions is a conductor because ions can carry current; Lipids are insulators because they have few charged groups
57
What is the resting membrane potential?
The potential difference across the plasma membranes from in to out, negative
58
What is the convention when defining membrane potential?
The ECF is set at 0 mV, and the polarity of the membrane potential is in terms of the sign of the excess charge on the inside of the cell
59
How is the resting membrane potential defined?
From inside to outside
60
What can cause the resting membrane potential to change?
An electrical current that alters the potential
61
Why does the resting membrane potential exist?
Tiny excess of negative ions in the cell and an excess of positive ions outside; excess neg inside are electrically attracted to the excess pos outside, and the excess charges collect in a thin shell tight against the inner and outer plasma surfaces
62
For each of these three (Na+, K+, Cl-), determine whether they're more concentrated in or out of typical neuron.
Out, In, Out
63
Why is Na+ concentrated outside of the cell, but K+ concentrated inside the cell?
Because of the sodium potassium pump that pumps Na+ out and K+ in
64
What two factors does the magnitude of the Respo depend on?
Difference in specific ion concentrations in the intra and extra cellular fluids, and difference in membrane permeabilities to the different ions, which reflect the number of open channels for the different ions in the plasma membrane
65
What is the equilibrium potential?
The membrane potential at which the two fluxes (ions down their concentration gradient, and ions back against their concentration gradient due to electrical gradient) become equal in magnitude but opposite in direction
66
What is characteristic of the equilibrium potential for different ion species?
Can be different in magnitude and direction among ion species, depending on the concentration gradients between intracellular and extracellular compartments for each ion
67
What is the Nernst equation?
Describes the equilibrium potential for any ion species: aka the electrical potential necessary to balance a given ionic concentration gradient across a membrane so that net flux of that ion is 0; Eion = (61/Z)log(Cout/Cin) where Z is the valence of the ion and C out and C in are the extra/intracellular concentrations of the ion
68
For a given concentration gradient, how does membrane permeability to an ion species affect that ion species' contribution to the membrane potential?
The greater the membrane permeability to an ion species, the greater the contribution that ion species will make to the membrane potential
69
What is the Goldman Hodgkin Kats equation?
V= 61log{ ([PsubK*Kout] + [PsubNa*Naout] + [PsubCl*Clin])/([PsubK*Kin] + [PsubNa*Nain] + [PsubCl*Clout])}
70
What do the Ps stand for in the GHK equation?
Permeabilities; essentially creates a weighted average
71
What is largely the reason for the resting membrane potential across the plasma membrane?
The movement of K+ out of the cell down its concentration gradient through open K+ "leak" channels, so that the inside of the cell becomes negative with respect to the outside; BUT the resting membrane potential isn't equal to the K+ concentration, because a small number of Na+ channels are open in resting state
72
What isn’t the Respo equal to the K+ equilibrium potential if the K+ is the primary reason for the negative charge inside the cell?
Because there are some Na+ channels open in resting state, so some sodium ions continually move into the cell, canceling the effect of an equivalent number of potassium ions simultaneously moving out
73
Why doesn't the concentration of intracellular sodium and potassium ions change over time if the ions are constantly moving to create the resting potential?
Because the sodium potassium pump maintain the concentrations at stable levels
74
How does the NaK pump work?
Moves 3 Na+ out, and 2 K+ in: makes the inside of the cell more negative than it would be from ion diffusion alone
75
What is an electrogenic pump?
A pump that moves net charge across the membrane and contributes directly to the membrane potential
76
How does the NaK pump indirectly contribute to the membrane potential, since its electrogenic contribution is small?
It creates the concentration gradients down which the ions diffuse to produce most of the charge separation that makes up the potential
77
How is Cl ion concentration affected by the difference in Na and K concentration?
The membrane has Cl channels, but not pumps. So, Cl concentrations shift until the equilibrium potential is equal to the resting membrane potential: moves it out of the cell
78
What are the two ways neurons process and transmit information?
Graded potential and action potentials
79
What are graded potentials import for, vs action potentials?
Graded for signaling over short distances, but action for long-distance signals of neuronal and muscle membranes
80
What is depolarization?
When the membrane potential becomes less negative, closer to zero
81
What is overshoot?
A reversal of the membrane potential polarity, that is when the inside of a cell becomes positive relative to the outside
82
What is repolarization?
When the membrane potential that has been depolarized returns toward the resting value
83
What is hyperpolarization?
When the membrane potential gets more negative than at resting level
84
What are graded potentials?
Changes in membrane potential that are confined to a relatively small region of the plasma membrane; usually produced when some specific change in the environment acts on a specialized region o the membrane
85
True of False, graded potentials are always depolarizing and aren't related to the magnitude of the initiating event.
FALSE! They can be depolarizing OR hyperpolarizing, and are related to the magnitude of the initiating event
86
What does it mean that local current is decremental, and why?
That the flow of change decreases as the distance from the site of origin of the graded potential increases, because the plasma membranes are leaky to ions so the currents die out
87
What is summation?
When additional stimuli occur before the graded potential has died away and they're added to the depolarization from the first stimulus; particularly important for sensation
88
What are action potentials?
Large alternations in the membrane potential; generally very rapid and may repeat at frequencies of several hundred per second; used often in neurons and muscle cells, as well as of some endocrine, immune, and reproductive cells; are also all-or-none, in that superthreshold stimuli elicit the same effect as threshold stimuli
89
What are excitable membranes?
Membranes that are capable of producing action potentials
90
What is the mechanism that the nervous system uses to communicate over long distances?
Propagation of action potentials
91
How are ligand-gated, mechanically-gated, and voltage-gated channels involved in propagation of action potentials?
Ligand and mechanical are usually the initial stimulus for an action potential, but voltage-gated channels give a membrane the ability to undergo action potentials
92
What kind of channel enables a membrane to propagate action potentials?
Voltage-gated
93
How do voltage-gated Na+ and K+ channels operate for action potential propagation?
Depolarization of the membrane causes Na+ channels to open, and then are inactivated by the opening of K+ channels; when the membrane repolarizes to negative voltages, both channels return to the closed state
94
What are the two key differences that allow Na+ and K+ channels to play different roles in the production of action potentials?
1) Na+ channels are faster to respond to changes in voltage; they open before K+ channels do; 2) Na+ channels have an inactivation gate that limits the flux of sodium ions by blocking a channel shortly after depolarization opens it and allows the channel to return to the closed state after repolarization
95
What are the steps that occur in an action potential?
1) resting membrane potential is close to K+ equilibrium potential because there are more open K+ than Na+ channels; 2) depolarizing stimulus occurs; 3) depolarization opens some voltage-gated Na+ channels and Na+ enters to add to local depolarization; 4) when the threshold potential is reached, depolarization becomes positive feedback: Na+ causes depolarization, which opens more Na+ channels to cause more depolarization; 5) when membrane potential approached peak value, Na+ permeability declines when inactivation gates step in to block Na+; sluggish K+ gates have started to open up; 6) once the K+ gates are opened, K+ rushes in and repolarizes the membrane and allows the Na+ channels to close again; 7) slowly closing K+ channels allow a little too much positive charge back in, resulting in afterhyperpolarization
96
How are anesthetics related to action potentials?
Prevent action potentials from occurring because they block voltage-gated Na+ channels so that they can't open in response to depolarization
97
What is the absolute refractory period?
Occurs during the period when the voltage-gated Na+ channels are either already open or have proceeded to the inactivated state; when the second stimulus can't produce a second action potential
98
What is the relative refractory period?
The interval during which a second action potential can e produced but only if the stimulus strength is considerably greater than usual, after the absolute refractory period
99
Why is the only direction that propagation can occur away from the region of membrane that has recently been active?
Because a membrane area that has just undergone an action potential is refractory and can't immediately undergo another
100
What happens when membrane after action potentials aren't refractory?
Then the action potential can be conducted both ways, like when action potentials in skeletal muscle cells are initiated in the middle and propagate towards both ends
101
What affects the velocity with which an action potential propagates?
Fiber diameters and whether the fiber is myelinated or note (larger fiber diameter, faster propagation)
102
Why do larger fibers propagate action potentials faster?
Because they offer less resistance to local current, more ions flow in a given time, bringing adjacent regions of the membrane to threshold faster
103
Where do action potentials occur?
Only at the nodes of Ranvier, because there are fewer voltage-gated Na+ channels in the myelinated regions of axons
104
What is saltatory conduction?
The way action potentials appear to jump from one node to another as they propagate across a myelinated fiber
105
Which is faster, saltatory conduction or propagation in nonmyelinated fibers of the same axon diameter?
In saltatory conduction, because less charge leaks out through the myelin-covered sections of the membrane and more charge arrives at the node adjavent to the active node, to generate the action potential there sooner than if the myelin wasn't present
106
How is initial depolarization achieved in afferent neurons?
By graded potential: receptor potential, generated in the sensory receptors at the peripheral ends of the neurons
107
What is receptor potential?
The graded potential that starts in the sensory receptors at the peripheral ends of the neurons for start action potentials from afferent neurons
108
What is synaptic potential?
The graded potential generated by synaptic input to the neuron that starts action potentials from neurons other than afferent neurons
109
What s pacemaker potential?
The spontaneous change in neuron's membrane potential that starts action potentials from neurons other than afferent neurons
110
Why is there no stable, resting membrane potential in cells that can trigger action potentials with pacemaker potentials? What kinds of cells are they?
Cells like smooth muscle and cardiac muscle cells; because of the continuous change in membrane permeability
111
Where are pacemaker potentials usually seen?
In rhythmic activity, like breathing, heartbeat, and peristalsis
112
What is convergence/divergence?
When many presynaptic neurons affect one post, or one pre affects many post; convergence allows multiple influences, and divergence allows influence of multiple pathways
113
What are the two types of synapses?
Chemical and electrical
114
How are the pre and post synaptic cells joined for electrical synapses?
Gap junctions
115
What is the basic structure of the chemical synapse?
The presynaptic cell has the axon terminal with synaptic vesicles, and the postsynaptic cell has all different kinds of receptors to make up the postsynaptic density
116
What is the synaptic cleft for?
Preventing direct propagation of current, and forces use of neurotransmitters instead
117
What is a cotransmitter?
When more than one neurotransmitter is released from an axon
118
What are active zones?
Presynaptic membrane release regions where neurotransmitter vesicles are docked
119
How does calcium influence neuron terminals?
The neuron terminals in the presynaptic membrane have voltage-gated Ca ion channels, which open to allow Ca during depolarization; also activates processes that lead to the fusion of docked vesicles with the synaptic terminal membrane
120
What are SNARE proteins?
Proteins that loosely dock the vesicles in the active zones (can be in vesicle membrane and in terminal membrane)
121
What are synaptotagmins?
The family of proteins that bind to calcium ions during depolarization, to activate the SNARE complex that induces neurotransmitter release
122
What is kiss-and-run fusion?
When the vesicles fuse briefly with the membrane but then go on their merry way after releasing their neurotransmitter.
123
What are ionotropic receptors?
The activated receptors on the postsynaptic membrane which are ion channels
124
What are metabotropic receptors?
The activated receptors on the postsynaptic membrane that act indirectly or use G proteins or second messengers
125
What happens to neurotransmitter molecules that do not bind to receptors?
They're actively transported into the presynaptic axon terminal (reuptake), OR into glial cells, OR they diffuse away OR they're enzymatically inactivated and sent back to the axon terminal
126
What is EPSP?
Excitatory postysynaptic potential: the potential change due to a slight depolarization when the neurotransmitter opens up Na+ and K+ channels
127
Is the EPSP a graded of action potential?
Graded
128
What effect do excitatory neurotransmitters have on the membrane potential?
They depolarize it, which allows a small eflux of K+ and a large influx of Na+ in and leads to the EPSP
129
What effect do inhibitory neurotransmitters have on the membrane potential?
The hyperpolarize it, which allows an influx of Cl- or an eflux of K+
130
Why is IPSP sometimes called stabilization? What happens to chloride ions?
With cells that can't transport Cl- actively, a rise in chloride ion permeability doesn't change the membrane potential, but can increase chloride's influence on the membrane potential (makes it more difficult for other ions to change the potential, thus stabilizing the membrane at the resting level)
131
What is temporal summation?
When input signals arrive from the same presynaptic cell at different times, but summate because there is a greater number of open ion channels and a greater flow of positive ions into the cell
132
What is spatial summation?
When the two inputs occur at different locations on the same cell, and are summated that way
133
How does the threshold of the initial segment of the neuron compare to the rest of the neuron?
It's more negative/lower: much closer to resting potential than the cell body and dendrites, because there are more voltage-gated Na+ channels, so it's very responsive to small changes in membrane potential
134
Which lasts longer, postsynaptic potentials, or action potentials. Why?
Postsynaptic potentials, because as long as the membrane is depolarized to threshold, action potentials will arise and neuronal response will occur in bursts of action potentials
135
What affects synapse strength, pre or post synaptic mechanisms?
Both!
136
What happens when calcium ions aren't absorbed into organelles or transported out of the cell before entry of neurotransmitters, once the Ca ions have entered the terminal during previous action potentials?
There's a greater calcium concentration, and thus a greater amount of neurotransmitter release upon subsequent stimulation, leading to a greater EPSP or IPSP in the postsynaptic cell
137
What is an axo-axonic synapse? How does axon A then affect axon C, if A and B are axo-axonic synapses and B and C are regular synapses?
When an axon terminal of one neuron ends on an axon terminal of another; A affects C indirectly by affecting how much neurotransmitter B releases to C, usually by affecting Ca concentration in the presynaptic cell
138
What are autoreceptors?
When there are receptors on the presynaptic cell that are activated by chemical messengers released by the axon itself
139
What is receptor desensitization?
When a receptor that responds once temporarily fails to response, despite the continued presence of a receptor's neurotransmitter
140
What are neuromodulators?
Messengers that cause modulation, which is a complex response that isn't just EPSP/IPSP, and alter the effectiveness of the synapse
141
What is the distinction in speed of neurotransmitters/modulators?
Neurotransmitters work much faster, because neuromodulators often rely on G proteins couple to second-messenger systems
142
How does Ach work in cholinergic neurons?
Released and then broken down by acetylcholinesterase into choline and acetate; choline is transported back into presynaptic axon to be reused
143
What are the two general types of ACh receptors?
Nicotinic and muscarinic
144
What is a nicotinic receptor?
Respond to ACh and to nicotine; often present at neuromuscular junction
145
What are nicotinic receptors useful for?
Attention, learning, and memory, especially in reward circuits (why tobacco is so addictive)
146
What is a muscarinic receptor?
Respond to ACh and poisonous mushroom, muscarine; couples with G proteins to alter enzyme/ion channel activity; prevalent at peripheral glands and organs
147
What is atropine?
An antagonist of muscarinic receptors, so can be used to dilate eye muscles for exams
148
What neurotransmitter malfunction is associated with Alzheimer's?
Acetylcholine: degeneration of cholinergic neurons: decreased ACh in certain areas, so loss of postsynaptic neurons
149
What are beta-amyloid proteins' role in Alzheimer's?
And increase is associated with neuronal cell death, for extreme cases
150
What are biogenic amines?
Small, charged molecules synthesized from amine acids that contain an amino group
151
What are the most common biogenic amines?
Dopamine, norepinephrine, serotonin, and histamine (and epinephrine, but in the adrenal medulla, not the central nervous system)
152
What are three catecholamines?
Dopamine, norepinephrine, and epinephrine
153
How is a catecholamine formed?
Amine acid tyrosine taken up by axon, converted into L-dopa by tyrosine hydroxylase, then modulated and released by autoreceptors
154
What is MAO?
Monoamine oxidase: enzyme that breaks down catecholamine neurotransmitters
155
How do MAOIs work?
Inhibit breakdown of catecholamines, so leave more dop/epi/NE in the synapse for absorption
156
Where are the cell bodies for catecholamine-releasing neurons?
The brainstem and hypothalamus: but the axons go AAAALLLLLL over the CNS
157
What is "adrenergic?"
Neurons that release NE or Epi, or their receptors
158
What are the two major receptor classes for norepi/epi?
Alpha-adrenergic and beta-adrenergic
159
Are catecholamine receptors ionotropic or metabotropic?
Metabotropic: use second messengers to transfer a signal from the surface to the cytoplasm
160
What are beta-adrenergic receptors?
For norepi/epi: act via stimulatory G proteins to increase cAMP in postsynaptic cells; three subclasses are beta 1, 2, and 3
161
What are alpha-adrenergic receptors?
For norepi/epi: act presynaptically to inhibit norepi release (alpha 2) or postsynaptically to stimulate OR inhibit different K+ channel activity (alpha 1)
162
What is a biogenic amine, but not a catecholamine?
Serotonin
163
What amino acid is serotonin from? How does that affect its effects?
Tryptophan: acts slowly, so more of a neuromodulator
164
What effect does serotonin have on muscle vs sensation pathways?
Excites muscle pathways, but inhibits sensation pathways
165
Is the majority of serotonin in the CNS or outside of it?
Outside of it
166
What is the most prevalent class of neurotransmitter?
Amino acid neurotransmitters! Affect virtually all CNS neurons
167
What is the most common excitatory amino acid neurotransmitter?
Glutamate
168
Are most glutamate receptors metabotropic or ionotropic?
Ionotropic
169
What are the two important ionotropic receptors for glutamate?
AMPA and NMDA receptors
170
What happens with cooperation between the AMPA and NMDA ionotropic receptors for glutamate?
Creates a long-term potential, which couples frequent activity across a synapse with lasting changes in signaling strength; probably underlies learning and memory
171
How does long-term potential work?
Glutamate is release when the neuron fires action potentials, and its binds to AMPA and NMDA receptors on the postsynaptic membranes; the AMPA functions is a regular excitatory postsyn receptor (permeable to Na+ and K+, but since Na+ has a greater driving force, more Na+ comes in for a depolarizing EPSP) BUT the NMDA channels open for Ca influx (but required a significant depolarization to drive the magnesium ion from out of the way), which activates a second messenger cascade to activate two protein kinases to increase sensitivity of the postsyn neuron to glutamate
172
What is excitotoxicity?
When the injury or death of some brain cells rapidly spread to adjacent regions, mediated sometimes by NMDA receptors for glutamate
173
How does excitotoxicity work with NMDA for glutamate?
When the glutamate-containing cells die, glutamate floods the nearby AMPA and NMDA receptors, causing toxic accumulated Ca iona, which kills those cells too
174
What is the major inhibitory neurotransmitter in the brain?
GABA: gamma aminobutyric acid; modified form of glutamate
175
Typically, what are GABA neurons?
Small interneurons that dampen activity within neural circuits
176
What kind of receptors does GABA bind to?
Both ionotropic and metabotropic receptors (for iono, increases Cl flux, for hyperpolarization)
177
What common substance targets GABA synapses?
Ethanol (alcohol)
178
What is the major inhibitory neurotransmitter in the spinal cord/brainstem?
Glycine: binds to ionotropic receptors on postsynaptic cells to allow Cl- to enter, causing hyperpolarization
179
What are neuropeptides?
Composed of two or more amino acids linked by peptide bonds; many also function in nonneural tissue as hormones or [paracrine substances
180
How does synthesis of neuropeptides differ from synthesis of other neurotransmitters?
Not synthesized in axon with few enzyme steps; INSTEAD: derived from large precursor proteins tat have little inherent biological activity, and occurs on ribosomes from cell body and large dendrites
181
What are endogenous opioids?
A group of neuropeptides including beta-endorphin, dynorphins, and enkephalins
182
What is substance P?
Another neuropeptide; released by afferent neurons, involved in pain sensation
183
Which short-lived gases can be neurotransmitters? (Name three.)
Nitric oxide, carbon monoxide, hydrogen sulfide
184
How do gases as act neurotransmitters?
Produced by enzymes in axon terminals in response to Ca 2+ entry, and diffuse from one cell into the other to bind to and activate proteins
185
Do ATP and adenosine act as neurotransmitters or neuromodulators?
Neuromodulators
186
How do neurons regulate effector cell activity?
Through neurotransmitters at neuroeffector junctions: diffuse from efferent neuron to effector cell and bind to receptors there (ionotropic OR metabotropic)
187
What does it mean that there are no nerves in the CNS? Why is that definition confusing?
The bundles of nerve fibers/axons are referred to as either pathways/tracts (in the CNS) or commissures (linking the right and left halves of the CNS)
188
What's the difference between pathways/tracts and commissures?
One is within the CNS, and the other links the right/left of the CNS
189
What are ganglia?
Groups of neuron cell bodies in the PNS
190
What are nuclei?
Groups of neuron cell bodies in the CNS
191
What's the different between ganglia and nuclei?
In the PNS vs CNS
192
What are the four subdivisions of the brain?
Cerebrum, diencephalon, brainstem, and cerebellum
193
What is the forebrain?
The cerebrum and diencephalon
194
What structure do the cerebrum and diencephalon make up?
The forebrain
195
What three structures make up the brainstem?
Midbrain, pons, and medulla oblongata
196
What are the four interconnected cavities in the brain called?
Cerebral ventricles
197
What is the larger component of the forebrain?
The cerebrum
198
What is the cerebral cortex?
The outer shell of gray matter and inner layer of white matter of the cerebral hemispheres of the forebrain
199
What is overlayed by the cerebral cortex? What kind of matter is it?
The subcortical nuclei, which are made of gray matter
200
What are the four lobes of the brain?
Frontal, parietal, occipital, and temporal
201
What are gyri?
The sinuous ridges of the brain, separated by sulci
202
What are sulci?
The grooves in the brain between the gyri
203
What are the two basic types of brain cells?
Pyramidal cells, and nonpyramidal cells
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What are pyramidal cells?
The major output cells to the cortex; send axons to other parts of the cortex and to CNS
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What are nonpyramidal cells?
Mostly involved in receiving inputs to the cortex and in local info processing
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How does number of cortex layers correlate to number and integration of neurons for signal processing?
Positively: we have six, reptiles have three
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What happens in the cerebral cortex?
Info Is collected/processes, and control over movement is refined
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What is the basal ganglia (aka basal nuclei)?
A subcortical nucleus; important role in movement/posture/complex behavior aspects
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What is the diencephalon?
Contains the thalamus, hypothalamus, and epithalamus; divided into two by the narrow third cerebral ventricle
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What are the three parts of the diencephalon?
Thalamus, hypothalamus, epithalamus
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What is the thalamus?
Collection of several large nuclei that serve as synaptic relay stations and important integrating centers for most inputs to cortex; general arousal and focusing attention
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What is the hypothalamus?
Master command center for neural and endocrine coordination; homeostatic regulation; appetite behaviors; connected to pituitary gland for endocrine regulation
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What gland is connected to the hypothalamus?
Pituitary gland
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What is the epithalamus?
Includes pineal gland, regulation of biological rhythms
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What gland is included in the epithalamus?
Pineal gland
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What is the limbic system?
An alternate classification of some forebrain areas: parts of frontal love cortex, temporal lobe, thalamus, hypothalamus, and the fiber pathways that connect them
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What is the limbic system for?
Learning, emotional experience and behavior, and visceral/endocrine functions
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What is the cerebellum?
Outer layer of cells (cerebellar cortex) and deeper clusters; center for coordinating movements, controlling posture and balance; implicated in some learning
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What is the brainstem?
Where all the nerve fibers that relay signals from forebrain/cerebellum/spinal cord pass through; contains the reticular formation; also nuclei for processing 10 of 12 cranial nerve info
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What is the reticular formation?
Part of the brainstem: absolutely essential for life; receives/integrates info from everywhere, involved in motor functions, cardiovascular and respiratory control, and regulations of sleep/wake/attention; releases most of the biogenic amine neurotransmitters
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Where are most biogenic amine neurotransmitters released from?
The reticular formation in the brainstem
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What brain structure is the only one absolutely essential for life?
The reticular formation
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What are cranial nerves?
The peripheral nerves that connect directly with the brain and innervate the muscles, glands, and sensory receptors of the head, and organs in the thoracic and abdominal cavities
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What are the dorsal vs ventral horns?
Part of the spinal cord: dorsal is back, ventral is front; the regions of gray matter in the butterfly shape in the spinal cord
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What is the spinal cord composed of?
Interneurons, cell bodies and dendrites of efferent neurons, entering axons of afferent neurons, and glial cells
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How do afferent nerve fibers enter the spinal cord?
Through the dorsal roots; their cell bodies are contained in the dorsal root ganglia
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How do efferent neuron axons leave the spinal cord?
Through the ventral roots
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What is the spinal nerve?
Where the dorsal and ventral roots from the same level combine, one on each side of the spinal cord
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How many pairs of nerves are there in the PNS?
43: 12 are cranial and 31 are spinal
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How many cervical nerves are there and what do they control?
Eight, and the muscles/glands/sensation of neck, shoulders, arms, and hands
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How many thoracic nerves are there, and what do they control?
Twelve, and the chest and upper abdomen
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How many pairs of lumbar nerves are there, and what do they control?
Five, and lower abdomen, hips, and legs
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How many sacral nerves are there, and what do they control?
Five, and the genitals and lower digestive tract
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What kind of nerve only has one nerve? For what?
Coccyngeal nerve, for the tailbone
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What does it mean that nerves are classified into afferent or efferent divisions of the PNS?
They convey info to the body from the brain, or vice versa
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What do afferent neurons do?
Carry info from sensory receptors at their peripheral endings to the central nervous system; first cells entering the CNS in the synaptically linked chains of neurons that handle incoming info
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What do efferent neurons do?
Carry signals from the CNS to muscles/glands; subdivided in somatic and autonomic nervous system
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What is the difference between somatic/automatic nervous system of the PNS?
Somatic is skeletal muscles, and autonomic is smooth/cardiac muscle or glands/neurons in GI tract
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What are somatic or autonomic nerves for, excitation or inhibition?
Excitation for somatic, but either for autonomic
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What kind of activity do somatic neurons lead to, and how does that influence their name?
Lead to muscle stimulation and movement, so they're called motor neurons
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What is the enteric nervous system?
The subdivision of the autonomic nervous system of the PNS that controls the GI tract; includes sensory and interneurons
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How are the neurons formations of somatic/autonomic NS different?
For somatic, it's just one long neuron, but for autonomic, it's interrupted into two neurons by an autonomic ganglion, which is outside of the CNS
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Where is the autonomic ganglion?
Between the two neurons in an autonomic nervous system nerve (preganglionic and postganglionic), outside of the CNS
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What are the two subdivisions of the autonomic nervous system, besides the enteric?
Sympathetic and parasympathetic
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At which levels do the neurons of the sympathetic and parasympathetic divisions leave the CNS?
Sympathetic fibers leave from the thoracic and lumbar regions, and parasympathetic fibers leave from the brainstem and sacral portion of the spinal cord
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Which autonomic division leaves the CNS at the thoracic/lumbar region?
Sympathetic
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Which autonomic division leaves the CNS at the brainstem or sacral region?
Parasympathetic
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What are the sympathetic trunks?
The two chains of ganglia that lie on each side of the spinal cord, from the different levels of ganglia from sympathetic/parasympathetic
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What are collateral ganglia, and where are they?
Other sympathetic ganglia that are in the abdominal cavity to control the organs there
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What is the difference in location between sympathetic ganglia (collateral, too) and parasympathetic ganglia?
For sympathetic, they're located kind of away but nearish to the organs they innervate, but for parasympathetic, they're super duper closer.
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What is the difference in departure from the spinal cord for preganglionic sympathetic neurons and the sympathetic trunk?
Only the thoracic/lumbar preganglionic neurons disconnect from the spinal cord, but the trunk spans the entire spine: it's just that the lower preganglionic sympathetic neurons gather together later before branching to the postganglionic neurons
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Why is the sympathetic nervous system more likely to activate body-wide?
Because of the close anatomical association of the sympathetic ganglia, as well as the divergence of presynaptic sympathetic neurons
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What neurotransmitter is responsible for both sympathetic and parasympathetic ganglia interaction?
Acetylcholine
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What is the difference in neurotransmitters between postganglionic cells and effector cells of sympathetic/parasympathetic?
Parasympathetic uses acetylcholine, and sympathetic uses norepinephrine
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What are the majority of acetylcholine receptors in autonomic ganglia vs in smooth muscle/cardiac/gland cells, nicotinic or muscarinic?
Nicotinic; muscarinic
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What are the majority of acetylcholine receptors in somatic motor neurons, nicotinic or muscarinic?
Nicotinic
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What does the adrenal medulla do?
Releases 80% epinephrine, 20% norepinephrine (catecholamines as hormones, not neurotransmitters) to effector cells
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What is the adrenal medulla?
An endocrine gland formed by postganglionic sympathetic neurons that never develops axons
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What happens to the group of postganglionic sympathetic neurons that never develops axons?
Turns into the adrenal medulla that releases epinephrine and norepinephrine into the blood stream to reach effector cells
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What is dual innervation?
When the effector cells are innervated by both sympathetic and parasympathetic nerves; like the heart and glands and smooth muscles
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How does dual innervation work?
Both sympathetic and parasympathetic influences are opposite, usually, and are activated reciprocally (if the activity of one increases, the activity of the other decreases)
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How does the sympathetic/parasympathetic nervous system affect the iris muscle?
Contracts radial muscle (widens pupil) vs contract sphincter muscle (makes pupil smaller)
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How does the sympathetic/parasympathetic nervous system affect the SA node, atria, AV node, and ventricles of the heart?
Increase of heart rate/contractility/conduction velocity/contractility, vs decreases the same processes
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How does the sympathetic/parasympathetic nervous system affect the bronchial muscle?
Relaxes vs contracts
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How does the sympathetic/parasympathetic nervous system affect stomach or intestinal secretion? Stomach of intestine sphincters?
Inhibits vs stimulates secretion, and contracts vs releases sphincters
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How does the sympathetic nervous system affect the coronary arteriole with alpha vs beta receptors?
Constricts it (alpha), but dilates (beta)
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How does the sympathetic nervous system affect the skin arterioles?
Constricts, with alpha receptors
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How does the sympathetic nervous system affect skeletal muscle arterioles, with alpha vs beta receptors?
Constricts (alpha) vs dilates (beta)
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How does the sympathetic nervous system affect the abdominal viscera, kidney, and salivary gland arterioles?
Constricts, with alpha receptors
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For arterioles, how does the sympathetic nervous system affect behavior? What are the exceptions based on receptor type?
Constricts, EXCEPT for dilates with beta receptors for the coronary/skeletal muscle
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What are the meninges?
The three membrane coverings between the neural tissues and bones of the skull/spine and brain/spinal cord
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What are the three meninges?
Dura mater, arachnoid mater, and pia mater
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What is the subarachnoid space?
The space between the arachnoid and the pia; filled with cerebrospinal fluid
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Where are the three meninges?
Dura mater is next to the bone, arachnoid mater is in the middle, and the pia mater is next to the nervous tissue
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What is the choroid plexus?
Produces CSF hella fast (thrice replaced per day), made of ependymal cells in a special epithelial structure
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Why does the brain depend on continuous blood flow?
For oxygen and glucose, since it has no glycogen stored up and it really only ever uses glucose to get ATP to survive
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What is the blood-brain barrier?
The cells that line the smallest blood vessels in the brain to minimize the ability of harmful substance to reach the neurons
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