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PSB3002 Ch. 4 and 6 Exam 2 Review
Terms in this set (58)
. Describe the five stages of the life cycle of a neurotransmitter.
1.Synthesis: Precursors and enzymes
2.Storage/Packaging: In vesicles and Vesicular transporter
3.Release: In response to action potential (AP)
4.Binding: EPSP and IPSP, postsynaptic receptors (ionotropic and metabotropic), presynaptic autoreceptors (regulate amount of NT released), heteroreceptors (regulate amount of NT released by another neuron)
5.Inactivation: Enzymatic, Reuptake
Outline the synthesis of acetylcholine, including all substrates and enzymes.
Precursors: Choline, Acetyl Coenzyme A
Choline acetyltransferase (ChAT) creates ACh from precursors
Vesicular ACh transporter loads ACh into vesicles
. Name a drug that (a) blocks and (b) stimulates the release of ACh.
Botulinum toxin(Botox): prevents the release of ACh
Black widow spider venom: stimulates the release of ACh
Compare and contrast the two ACh receptor subtypes. What drugs (a) mimic and (b) block the effect of ACh at each receptor subtype? Where are the two subtypes found in the periphery? What type of receptor (ionotropic and metabotropic) do they bind to?
--Nicotinic (ionotropic), Agonist: nicotine
Found in CNS, ANS and skeletal muscle fibers
Found in smooth muscle fibers and cardiac muscle fibers
Blocks muscarinic receptors
Blocks nicotinic receptors
How is ACh inactivated? What drugs block this process? How is the action of hemicholinium-3 related to the inactivation of ACh?
--breaks down ACh
--Hemicholinium-3 blocks the choline transporter and slows
production of ACh
Outline the synthesis of catecholamines, including all substrates and enzymes.
Catecholamines: Dopamine, Epinephrine, Norepinephrine
Tyrosine (essential animo acid)→Tyrosine Hydroxylase→becomes L-DOPA→ decarboxylase→Dopamine...
Dopamine→ Dopamine β-Hydroxylase converts Dopamine to → Norepinephrine
Name a drug that (a) blocks the synthesis of the catecholamines. How does it work.
(AMPT) Tyrosine→Inactivates Tyrosine Hydroxylase (block synthesis)
Name a drug that blocks the storage of the catecholamines.
Storage via vesicular monoamine transporters
Blocked by reserpine
Blocks monoamine transporters
Compare & contrast the D1 and D2 families of dopamine receptors.
--Most common (+D2)
--Increases 2nd messenger cAMP (like D5)
--Presynaptic and postsynaptic
--Decreases 2nd messenger cAMP
--Chlorpromazine blocks antipsychotic receptors for schizophrenia treatment
D1 higher activity of dopamine
What effect does apomorphine (autoreceptor) have at low doses? At high doses?
Low doses: indirect antagonist to D2 receptors
High doses: direct agonist to D2 receptors
Explain the mechanism by which (a) amphetamine and (b) cocaine increase synaptic levels of dopamine.
Amphetamines reverse DA (dopamine) and NE (norepinephrine) transporters
Cocaine blocks the reuptake of dopamine
Name two enzymes that break down the catecholamines. How do they work?
-Monoamine oxidase (MAO)
--Destroys excess neurotransmitters
--DEPRENYL destroys MAO-B (agonist)
-Catechol-O-methyl transferase (COMT)
--Introduces a methyl group
What drug allows you to inhibit the synthesis of norepinephrine without interfering with the synthesis of dopamine?
This is important when you want to see what happens when you have dopamine but no NE
Explain the role of axonal varicosities in the release of norepinephrine
Release is usually at axonal varicosities, not through terminal buttons
Outline the synthesis of serotonin, including all substrates and enzymes
Tryptophan → Tryptophan hydroxylase → 5-HTP → decarboxylase 5-HTP → Serotonin (5-HT)
Name a drug that blocks the synthesis of serotonin. How does it work?
PCPA→ blocks Tyrosine hydroxylase
Which serotonin receptor subtypes are presynaptic autoreceptors?
5-HT1A (buspirone) treats anxiety
Which serotonin receptor subtype(s) is/are metabotropic? Ionotropic?
Metabotropic: 5-HT1b 1d, 1a
5-HT3 is a chloride ion channel
How is serotonin inactivated? What effect does (a) fluoxetine (Prozac) and (b) MDMA have on the inactivation of serotonin?
Serotonin transporter removes 5-HT from synapse
Fluoxetine(Prozac): directly blocks reuptake; to treat depression, anxiety, and obsessive-compulsive disorder
Reverse NE and serotonergic transporters
How is glutamate synthesized?
Synthesized from glutamine (precursor) by glutaminase (enzyme)
Name three ionotropic glutamate receptor subtypes. What ion channels are associated with each?
AMPA → Na+
NMDA → Cations
Kainate → Na+
What is unique about the NMDA receptor?
Multiple binding sites (6)
Glycine and magnesium
Explain the difference between competitive and noncompetitive antagonism of the NMDA receptor and cite one drug that does each.
A competitive antagonist binds to the same site as the agonist but does not activate it, thus blocks the agonist's action.
A non-competitive antagonist binds to an allosteric (non-agonist) site on the receptor to prevent activation of the receptor.
PCP and Ketamine are non-competitive as they block the Ca+ receptors
AP5 blocks the glutamate binding site: competitive
Explain how glutamate is inactivated. What is unique about the inactivation of glutamate?
Excitatory amino acid transporters remove glutamate from synapse
Glutamine synthase dismantles glutamate
Describe the synthesis of GABA.
Converted from glutamic acid to GABA by glutamic acid decarboxylase (GAD)
Universal inhibitory neurotransmitter
Explain the difference between GABAA and GABAB receptors. Name an agonist for each receptor subtype.
--5 binding sites
Benzodiazepines INDIRECT AGONIST
Barbiturates INDIRECT AGONIST
Baclofen AGONIST; muscle relaxant
Name an antagonist for the GABAA receptor. What behavioral effect does this drug have?
Bicuculline: light-sensitive competitive antagonist of GABAA receptors
Name a ligand for each of the five binding sites on the GABAA receptor.
Benzodiazepine, barbiturates, alcohol, gaba, steroids
How is GABA inactivated?
GABA removed from synapse by GABA transporters
Tiagabin blocks GABA transporter
Broken down by GABA amino-transferase (GABA-T)
Name three endogenous opioid peptides. How does their synthesis differ from that of conventional neurotransmitters?
b-endorphins, enkephalins and dynorphin
A peptide is two or more amino acids linked by peptide bonds
1.Produced when enzymes cleave large polypeptides in soma
2.Packaged into vesicles and transported to the terminal
3.Released from all parts of the terminal button, not just active zone
4.After release, peptides are destroyed by enzymes
5.No mechanism exists for reuptake
Name three opiate receptor subtypes. What is the natural ligand for each one? What drug blocks opiate receptors?
Mu - beta endorphins
Kappa - dynorphins
Delta - enkephalins
Naloxone (narcan) is an opiate blocker (antagonist)
Name two endocannabinoids. How and why is their synthesis different from that of other neurotransmitters?
Anandamide, 2-AG, and THC (tetrahydrocannabinol)
Synthesized on demand, can't be stored because of the lipid composition
Difficult to store lipids in lipid-soluble vesicles
What receptor subtypes mediate the effects of endocannabinoids? How does rimonabant work?
CB1 (in the brain)
CB2 (in PNS)
Rimonabant blocks the CB1 receptor (reduction in appetite) opposite of munchies
How are endocannabinoids inactivated?
Deactivated by enzyme FAAH (fatty acid amide hydrolase) in "presynaptic" cell
**MAFP: agonist that inhibits FAAH
Explain the concept of retrograde messengers. How does this concept apply to endocannabinoids? Nitric oxide?
-Retrograde messenger is a chemical substance that is released from postsynaptic neurons and acts on presynaptic neurons.
-Retrograde signaling increases action potential from the presynaptic neuron, which then increases the number of receptors at the postsynaptic neuron.
-This will then cause another increase of neurotransmission until a strong communication and higher resolution synapses are formed and plasticity is achieved.
--Gases are not stored and are produced on demand, and they are everywhere in the brain.
-Neurotransmitters released from the postsynaptic cell that is going to regulate presynaptic cells.
Describe in detail the anatomy of the visual system from the eye to the primary visual cortex.
-Conjunctiva - membrane that protects the eye
-Cornea - transparent layer covering the front of the eye
6 extraocular muscles - helps move the eye
-Sclera - white outer layer of the eyeball
-Pupil - hole allows light to enter
-Iris - pigmented muscles
-Lens - reverse the image (left and right)
-Ciliary muscles - loosen or tighten the lens
-Retina - (CNS) layer at the back of the eye containing sensitive to light ganglion cells that trigger nerve impulses
-Vitreous humor - transparent gelatinous tissue filling the eyeball behind the lens.
-Optic Nerve - nerves transmitting impulses to the brain
-Optic chiasm - is the part of the brain where the optic nerves partially cross
-Lateral geniculate nucleus - is a relay center in the thalamus for the visual pathway. It receives a major sensory input from the retina
-Primary Visual Cortex - sensations; receives visual input from the retina
What part of the spectrum of electromagnetic radiation is visible to the human eye?
380 -760 nm
What physical dimension of light waves is responsible for differences in perception of (a) hue (color) (b) saturation (purity) and (c) brightness (intensity)?
Very Far: red
Purity of light
Based on how many different wavelengths present
Same = pure/saturated
As increase different wavelengths = less pure
All visible = white, no sensation of hue
Height of light wave
What cells comprise the retina? How are they interconnected? How are they arranged within the retina?
The retina is the inner lining of the eye
Photoreceptor cells compromise the retina
Rods: used in dim light
Cones: color vision, high acuity, daytime vision
Photopigments, bipolar cells, retinal ganglion cells
Dark: light won't catch any pigments; continuous depolarization (release glutamate)
Light: light rays leave photopigments and continuous hyperpolarization
Define (a) photoreceptors (b) blind spot (c) photopigments (d) transduction (e) receptor potential.
Photoreceptors: cells that make up the retina
Blind spot: Optic disk; back of the eye where axons leave
Photopigments: light-sensitive molecules in the photoreceptors that are made up of a protein called opsin (bipolar cells)
Transduction: process by which environmental energy is converted to a change in neuronal membrane potential
Receptor potential: electrical changes in cell as a result of sensory transduction
Explain how electromagnetic radiation is converted into action potentials.
Dark: light won't catch any pigments; continuous depolarization (release glutamate)
Light: light rays leave photopigments and continuous hyperpolarization
In dark, photoreceptors constantly release transmitter; hyperpolarizes BP cell
Light hyperpolarizes photoreceptor and reduces the release of transmitter
ON center bipolar cells are hyperpolarized by glutamate
OFF center bipolar cells are depolarized by glutamate
The reason is that for light to be converted into nerve impulses, it must break down molecules of a protein called rhodopsin. When you come in from a very brightly lit setting, you therefore no longer have enough of these molecules left to see effectively in the dimmer light. Before you can see again, you must wait for your eyes' supply of rhodopsin molecules to be replenished, and this is a relatively slow process. During this transitional period, your eyes are described as adapting to the darkness.
Define "receptive field." How do receptive fields for cones differ from those of rods? Why are receptive fields for cones well-suited for detecting small differences in visual stimuli (e.g., the letters in a word) while rods are better suited for detecting dim stars in the night sky.
Receptive Field: visual field that an individual neuron "sees" (i.e., the place the stimulus must be
located to produce a response in that neuron).
BASICALLY: the area a neuron (ganglion cells) see
Rods are located in the center of the retina (larger general receptive field)
Cones are located around the boundary of the retina (small and specific receptive field)
Describe the receptive field properties of retinal ganglion cells in cats.
Cat retina: Receptive field is a circular center surrounded by a ring
ON cells: respond when center is light, but ring is dark
OFF cells: respond when center is dark, but ring is light
ON/OFF cells: respond when light turns on and when it turns off
On cells respond when there is light
Off cells responds when light is off
neurons whose firing is inhibited while the light is on show increase firing after light is turned off (OFF cells)
neurons whose firing increases while light is on show decreased firing
after light is turned off (ON cells)
Explain how the visual field "maps" onto the retina of each eye and how the retina of each eye "maps" onto the lateral geniculate nuclei in the thalamus. Using this answer, explain why a stroke affecting the right striate cortex would result in a loss of vision from the left visual field.
The left side of the visual field is going to project to the right side
The right side of the visual field is going to project to the left side
What is "blindsight"?
The ability to respond to visual stimuli without consciously perceiving them
Cortical regions involved in conscious perception of vision are damaged
Other visual pathways are undamaged
Non-image forming pathways can guide behavior
Person perceives him/herself to be blind
Describe the cellular organization of the lateral geniculate nucleus. Where do inputs from the two eyes go? Explain the differences between the magnocellular and parvocellular layers. Where are the koniocellular sublayers located?
6 layers: recieve info from only 1 eye
Layers 1, 4, 6: contralateral eye
Layers 2, 3, 5: ipsilateral
The lateral geniculate nucleus of the thalamus is a layered structure that receives segregated input from the two eyes and projects to the primary visual cortex
sensitive to movement
Two inner layers (1,2)
Project to layer 4Ca in striate cortex
Outer layers ( 3,4,5,6)
Sensitive to color and detail
Projects to later 4CB (beta) in striate cortex
Layers 2 and 3
In between M and P layers
How many cellular layers are there in the striate cortex? How are they labeled? Which layers receives inputs from the lateral geniculate nucleus? What is meant by "columnar organization" regarding the receptive field properties of visual cortical cells?
Six layers: 1, 2, 3, (4a, 4b, 4ca, 4cbeta), 5, 6
Columnar organization: vertical columns perpendicular to layers
Input from layers of LGN goes to a different layer in striate cortex
What is cytochrome oxidase? What does staining for this enzyme reveal about the functional organization of the primary (V1) and secondary (V2) visual cortex? (Your answer should refer to the receptive field properties of cells that make up the blobs and various stripes.)
Cytochrome oxidase: is the terminal, or final, enzyme of the electron transport system, mitochondrial enzyme
The energy of the areas that have stripes and blobs
Thin - process color info
Pale - orientation, movement, retinal disparities, and spatial frequencies
Thick - orientation, movement, retinal disparities, and spatial frequencies
Describe the organization of a module in the striate cortex. How do the receptive fields for cells within CO blobs differ from those outside the CO blobs?
Each module analyzes information from a small portion of visual field; collectively get
information from the entire visual field
Each half of the module gets info from one eye
Circuity combines both info together
2 segments to module:
Within CO blob
Cells are sensitive to color
Outside CO blob
Cells are sensitive to orientation, movement, spatial frequency, retinal disparity
Explain receptive fields
Each receptive field is arranged into a central disk, the "center", and a concentric ring, the "surround", each region responding oppositely to light. For example, light in the centre might increase the firing of a particular ganglion cell, whereas light in the surround would decrease the firing of that cell.
Explain the difference between the dorsal stream and the ventral stream. Where do they originate from? Where do they terminate? What role do they play in perception?
What pathway: object info processing
Size, shape, color, texture
BEGINS in pale and thin stripes of V2 (M and P pathways)
Passes through V4 and TERMINATES in inferior temporal cortex
Where pathway: location and speed of movement
Begins in the thick stripes of V2 (M pathways)
TERMINATES in the posterior parietal cortex
Movement + vision
Define lateral inhibition. How does lateral inhibition explain Mach bands?
Lateral inhibition: adjacent cells inhibit their neighbors; amount of inhibition is proportional to the
amount of excitation.
Mach Bands: picture that exaggerates the contrast between edges of the slightly differing shades of gray,
as soon as they contact one another, by triggering edge-detection in the human visual system.
Lateral inhibition plays an important role in visual perception by increasing the contrast and resolution
of visual stimuli.
How do the photoreceptors code color? How do the ganglion cells code color? Explain what effect red, green, blue and yellow have on cones and ganglion cells.
Absorbance properties of opsin defines type of cone
Three types of cones in humans: blue, green, red
Two kinds of color sensitive ganglion cells: yellow-blue, red-green
Other ganglion cells encode relative brightness in the center and surround
Serve as "black and white detectors"
Responses are determined by circuits connecting three types of cones with
two types of ganglion cells
Color is determined by relative excitation and inhibition of cones
I.e.: red color stimulates red cone, which stimulates red sensitive ganglion cells
I.e.: yellow color would point to multiple cones, since it does not have a specific cone
Which layers in the LGN receive information from red and green cones? Blue cones?
Parvocellular: red and green cones
Koniocellular: blue cones
Explain the connectivity between inputs from the LGN, blobs in the primary visual cortex and stripes in the visual association cortex?
Information is first processed in LGN
Striate cortex performs additional processing of color information
Receives info from konio and parvo pathways
P cells go to thin and pale stripes then to ventral streams
M cells go to thick stripes then to dorsal stream
Konio cells go to thin pale stripes and then to the ventral stream
Blobs are sections of the visual cortex where groups of neurons that are sensitive to color assemble in cylindrical shapes
respond strongly to bars of light in their favorite orientation
respond strongly to moving bars of light in their favorite orientation
respond strongly to moving bars of light in a particular length or angle