Cellular & Molecular Neuroscience Flashcards
Neuroanatomy terminology review
nuclei Vs ganglia
nuclei (pleural) = CNS
ganglia (pleural) = PNS
reticular theory
- connected through protoplasmic links
- neurons linked together = “reticulum”
- info can flow in any direction
5 Principles of “Contact theory”
1) neuron = elementary structural and signaling unit
2) law of dynamic polarization (dendrite –> terminal)
3) synapse
4) connection specificity
5) synaptic or neural plasticity
Electrophysiology - population recording
- Utilizes macro-electrodes
- Measures voltage
- EEG (cortex) & EMG & ERP (specific sensory p/way)
- Whole nerve (peripheral nerves)
- Excellent temporal resolution, poor spatial resolution *
- Clinical assessment
Electrophysiology - Single Cell Recording
-Utilizes micro-electrodes
-Measures ion current & voltage
-Resting membrane potential (RMP) & Graded potentials (IPSPs, EPSPs) & Action potentials (APs)
-Intracellular (in vivo/ in vitro) & Extracellular (in vivo)
& Patch clamp (in vitro)
-Experimental method
Neural Communication Properties
- Electrical
- Unique to “excitable” cells: neurons and muscle cells
- Very fast (
Single-unit Electrophysiology : Extracellular unit recording
-in vivo
all-or-none action potentials (APs)
Single-unit Electrophysiology : Intracellular unit recording
-in vivo or vitro
resting membrane potential (RMP)
graded potentials (EPSPs, IPSPs)
APs
Single-unit Electrophysiology : Patch clamp
-in vitro
ionic current
Leak/leakage channels
-Open even in a resting state
• Selective for a single ion species
• Contribute to the RMP
Gated ion channels (active)
-Closed until opened by stimulus (voltage, ligand, sensory
stimuli)
• Can be selective for one or multiple ion species
• Necessary for graded and all-or-none action potentials
(APs) and neurosecretion
• Depolarizing & hyperpolarizing effects
Location of Leak channels
plasma membrane on cell body
dendrites
along the axon (nodes of ranvier)
Location of Ligand-gated channels
cell body & dendrites
Location of Voltage-gated channels
- axon hillock
- all along unmyelinated axons
- nodes of Ranvier in myelinated axons
2 general classes of Synaptic Transmission
electrical and chemical.
Electrical synaptic transmission
- intercellular region = gap junction
- center pore = subunits called connexins = hexameric complex “connexon”
- Transmission = bidirectional & very rapid
- *Allows Synchronized electrical activity of a population
- Minority of synapses*
Chemical synapses direct Vs non-direct
- Directed: neurotransmitter release site and reception site are in close proximity
- Non-directed: release site is at some distance from the site of reception
Gray type 1 Vs gray type 2
Axodendritic synapses = Gray type I -Larger synaptic cleft -Often excitatory Axosomatic synapses = Gray type II -Smaller synaptic cleft -Often inhibitory
Neuromuscular Junction (NMJ) -definition
chemical synapse that connects a motor neuron with the motor end-plates of multiple muscle fibers
NMJ
- Activity = muscle fibers to contract.
- Single motor neuron & all of the individual skeletal muscle fibers that it innervates = motor unit.
- **All NMJs use acetylcholine (ACh).
- r/c for ACh on sarcolemma = nicotinic r/c (nAChR)
Nicotinic ACh receptor
- large protein consisting of 5 subunits (2α, 1β, 1γ, 1δ)
- α subunits contain an ACh-binding region
- Center pore = ion channel for Na+ ions
Electrical & then Chemical Synapses - compare
Size of synaptic cleft & delay -3.5 nm & 10-100 μsec -20-40 nm & 1-5 msec  Functional attributes -electrical = Synchronized firing of interconnected cells -chemical = -Provides spatially & temporally focused transmission -alterations in synaptic strength efficiency  Synaptic plasticity & amplification? somewhat & no (all-or-none) yes & yes
Properties of EPSPs/IPSPs
- Depolarization = EPSP
- Hyperpolarization = IPSP
- Graded potentials (have varying amplitudes)
- Travel passively & rapidly
- Decremental (decrease in amplitude as they travel)
Features of an AP
- Generated in axon hillock
- Momentary reversals = negative to positive
- all-or-none responses =magnitude =consistent
- Voltage-gated channels mediate APs via membrane potential
Summation
- majority of postsynaptic potentials (PSPs) = sub threshold
- Spatial summation = PSPs from different synapses
- Temporal summation = PSPs rapidly from same synapse
Stages of an action potential (AP)
1) Resting State: Na+ and K+ ion channels are closed = -70
2) Threshold: Na+ ion channels will open = AP
(3) Depolarization Phase:
Na+ ions = rush into the cell = alters membrane potential (less negative/more positive). ***K+ ion channels are still closed
(4) Repolarization Phase:
K+ ion channels begin to open while Na+ ion channels close. K+ ions rush out of the cell, which changes the membrane potential (making it more negative/less positive).
5) Undershoot: Na+ ion channels are closed and K+ ion channels are closing but slowly. = more (-) /less (+)
6) Refractory Period: In the wake of the AP, Na+ ion channels are deactivated and K+ ion channels are activated for a brief time. = harder to produce APs at this time.
Absolute Vs. Relative Refractory Period
**Absolute Refractory Period: Initiation of AP to immediately after the peak. ~1-2 ms.
**Relative Refractory Period: Following the absolute refractory period, Na+ channels begin to recover from inactivation. requires a stronger stimulation than normal.
AP Vs. postsynaptic potentials
- APs are nondecremental
- APs can travel in either direction
- APs are conducted slower than post-synaptic potentials
Neurotransmitters (NTs)- defining criteria
1) Presynaptic Presence
2) Release -in response to presynaptic depolarization
- must be Ca2+ dependent
3) Postsynaptic R/c
Properties of NTs
- contained in spherical vesicles in presynap
- secreted via presynap –> synaptic cleft –> post synap
- produce inhibitory effects, excitatory effects, or both
Categories of NTs (small)
- slow. - ionotropic OR metabotropic r/c
1) amino acids
2) monoamines
3) acetylcholine
4) unconventional NTs
amino acids NTs
- Glutamate
- Aspartate
- Glycine
- Gamma-aminobutyric acid (GABA) inhib
Monoamine NTs
Slightly larger than AA NTs & more diffuse effects
- Dopamine
- Epinephrine
- Norepinephrine
- Serotonin (5-HTP, 5-HT)
Acetylcholine (Ach)
- = add acetyl group to a choline molecule
- Ach is the main NT at neuromuscular junctions (NMJs)
- Also found at synapses in the ANS & CNS
Unconventional NTs
soluble-gases: nitric oxide & carbon monoxide
- Produced in cytoplasm = diffuse cell membrane = (+) 2nd messenger cascades
- Some = ~ few seconds!
Categories of NTs (large)
Neuropeptides (NP) -Many act as NTs & hormones 5 loose categories: Pituitary peptides Hypothalamic peptides Brain-gut peptides Opioid peptides Misc. peptides 
Axonal Transport, Synthesis, & Packaging of Small-molecule NTs
- synthesized = terminal button
- Enzymes needed for synthesis = slow axonal transport
- Packaged = small, clear core synaptic vesicles by Golgi in terminal button
Axonal Transport, Synthesis, & Packaging of Large-molecule/ Neuropeptides
-Synthesized = cell body on ribosomes
-Packaged into large, dense core synaptic vesicles by the Golgi in cell body
-Vesicles transported = fast axonal transport

Co-existence
- neurons synthesize &release two or more different NTs
- (not necessarily released simultaneously)
- low frequency (+) = releases only small-molecule NTs
- high frequency (+) = release of neuropeptides
Dale’s Rule (goes with co-existence)
A single neuron produces, packages, & releases the same chemical transmitter(s) at ALL of its synapses.
Synaptic Vesicle Cycle
1) NTs = into synaptic vesicles @ PREsynaptic terminal
2) Vesicles–>‘active zones’ w/ voltage-gated Ca2+ channels
- synapsins = anchor vesicles
3) AP = depolarized = ion channels to open = more Ca2+ into the terminal
4) This Ca2+ influx = phosphorylation of synapsin proteins
5) Phosphorylation of synapsins = docking facing the synaptic cleft, fuse with it, and release their transmitters into the synaptic cleft (exocytosis)
6) Synaptic vesicles and/or membrane components are then rapidly retrieved (endocytosis)
- -Proposed mechanisms: “clathrin-mediated” endocytosis and/or “kiss-and-run”
7) Vesicles are recycled and re-filled with NT
- entire vesicle cycle lasts ~1 minute!>
of vesicles released by a neuron?
directly related to the level of Ca2+ at terminal
- low frequency (+) = releases only small-molecule NTs
- high frequency (+) = release of neuropeptides
importance of voltage-gated Ca2+ channels in neurotransmitter release:
-tetrodotoxin (blocks NA+ channels) still produced APs
-NT released is very sensitive to the exact amount of Ca2+
-Block voltage-dependent Ca2+ (via cadmium) = no NT
release or postsynaptic response
-Micro-injec of Ca2+ to presynaptic=NT release w/o AP
postsynaptic basic r/c properties
-transmembrane protein with extracellular binding sites
-r/c are specific for NTs based on binding sites (ligand-
specific)
- most NTs can bind to >1 receptor type
- different brain regions
- Often respond differently to the same NT
postsynaptic Receptor subtypes
- Ionotropic = ligand- or voltage-activated ion channels
- Metabotropic (aka G-protein coupled)
Ionotropic Receptors
- (+) via small molecule NTs
- Binding = conformational change opening the ion channel
- A postsynaptic potential will be immediately produced (an IPSP or an EPSP) Direct action leads to fast activation (~10 ms)
Metabotropic Receptors
- (+) both small NT or neuropeptides
- (+) of a G-protein to the receptor –> intracellular r/n
- longer lasting effects
Autoreceptors
- Metabotropic r/c located on the PREsynaptic:
- Bind to their own neuron’s NT
- homeostatic feedback system
Agonist r/c binding
- binds same receptor site & mimics the action of the endogenous ligand
- Results in either full or partial response
competitive antagonist r/c binding
- binds to the same receptor site as the natural ligand (agonist)
- Fully prevents activation by an agonist
Non-competitive antagonist r/c binding
binds to a different binding site as the natural ligand
-Fully or partially prevents activation by an agonist
Termination of Synaptic Messages
- Enzymatic degradation
- Reuptake
- Passive diffusion
Molecular Signaling
mediates and modulates all brain functions
Signaling cell–> Signal –> R/c –> Target cell –> Response
signal transduction pathway (STP)
-immediate and temporary changes in the physiological
state of the target cell
-or longer lasting and more permanent changes by
altering the transcription of genes, which affects the protein composition of the target cell
**allows for amplification of the signal as well as control of cell behavior
Signal Amplification
- Intracellular signal transduction is signal amplification
- An individual signaling rxn can cause a greater response by generating a large number of molecular products
- Similar amplification occurs in all signal transduction pathways
Control of cell behavior
-Every signaling molecule’s concentration must return to baseline before the next stimulus arrives
-Keeping the intermediates activated is critical for sustained responses

signalling molecule (3 classes)
1) Cell-impermeant molecules
2) Cell-permeant molecules
3) Cell-associated molecules
1) Cell-impermeant molecules
- extracellular receptors // short-lived
- includes: all NTs, other proteins, and peptide hormones
2) Cell-permeant molecules
- intracellular r/c in cytoplasm or nucleus
- includes: steroid and thyroid hormones)
- Tend to be insoluble and are often transported in the blood or other extracellular fluid by binding to specific carrier proteins
- Unlike cell-impermeable molecules, these may persist in the bloodstream for hours or even days
*Cell-associated molecules
bound to the extracellular surface of the plasma membrane of the signaling cell, bind to extracellular receptors
on target cells that they come into physical contact with (includes: integrins and neural cell adhesion molecules)
Cell-impermeant molecule receptors
proteins that span the entire membrane
-Signal binding portion is extracellular & intracellular portion activates the signaling cascade
ex: ligand-gated ion channels, enzyme-linked receptors, and G-protein-coupled receptors
Cell-permeant molecule receptors
- intracellular proteins = cytoplasm or nucleus
- Often bound to an inhibitory complex
- Once activated, the complex is removed and a DNA-binding domain is exposed
- Often activate signaling cascades that produce new mRNA and proteins within the target cell
Two general classes of GTP-binding proteins:
Heterotrimeric & Monomeric
Monomeric
G-proteins: made up of a single subunit
Often small GTPases involved in growth & development. not neurotransmitters
Heterotrimeric
-Ligand binds to G-protein-coupled receptor
R/c = conformational change = G-protein activated = GDP bound to the G-protein complex is exchanged for GTP
-α subunit dissociates from β and γ subunits
-2nd messengers in the intracellular cascade
are activated by either the α subunit bound to
GTP or the βγ subunits
*Hydrolysis of GTP to GDP terminates the
signal
Second Messengers =
cAMP, Ca2+, IP3, and nitric oxide (NO).
Second Messenger Targets
2nd messengers can regulate neuronal function by modulating the phosphorylation state
- Phosphorylation occurs via a wide variety of protein kinases
- Dephosphorylation occurs via protein phosphatases
basic brain connections are established
- Formation of distinct brain regions
- Neurogenesis: generation of neurons
- Axogenesis: axon tract formation
- Synaptogenesis: synapse formation
Neuroplasticity- Critical periods
temporal windows = activity-mediated (environmentally-driven) influences on the brain are essential for development
Neuroplasticity - Sensitive periods
temporal windows in which environmental activity influences brain circuitry however, to a lesser degree than during the critical period
** Majority of developmental = sensitive>critical periods *
Evolutionary Perspective of Neuroplasticity
General principle: Once formed, neuronal circuits must be used. If not, they will often not survive or function normally.
**advantage = opportunities for experience
Neuroplasticity: Early Studies
- Sensory deprivation (Rats raised in total darkness)
- Environmental enrichment (rats in groups/complex cages)
Competitive Nature of Experience and Neurodevelopment
Neural pathways that receive the most input form stronger connections and can potentially even ‘take over’ cortical regions
ex: Monocular deprivation
Neurogenesis found where in humans?
hippocampal neurons (via: dentate gyrus of hippocampus) olfactory bulb (via: adult neural stem cells)
Ischemia-induced Neural Injury Consequences
- Limited or eliminated oxygen & glucose supply
* Prevention of removal of metabolic waste products
Ischemia-induced Neural Injury Mechanisms:
1) Ionic imbalances
- no oxygen & glucose = no ATP = no [ion] gradients = depolarize = release NT = hinders re-uptake
2) Excitotoxicity (**main mechanism)
- prolonged exposure to excitatory NTs (e.g. glutamate)
- Deterioration cell structure & signaling capability
The Role of Glutamate in Excitotoxicity
-Postsynaptic glutamate r/c (NMDA) over-(+) = excessive depolarization at postsynaptic = flood of Na+ and Ca2+
-overload of Ca2+ =
-Free radicals
-Mitochondrial dysfunction
-Disruption of the cell membrane
-Fragmentation of DNA
-Cell death via apoptosis, necrosis, or both
Anterograde degeneration
- degeneration = distal portion of the axon
- rapid
- Early regenerative changes do not guarantee that the neuron will survive- it must re-establish appropriate synaptic contacts or else it will die *
Retrograde degeneration
- degeneration = proximal segment
- gradual
- Early regenerative changes do not guarantee that the neuron will survive- it must re-establish appropriate synaptic contacts or else it will die *
Conditions necessary for axonal regeneration:
1) gene expression
2) supportive environment:
CNS & axonal regeneration
-unfavorable environment = Glia, astrocytes & other produce inhibitory signals
-protein called Nogo = block axon elongation by
interacting with the growth cone
-Macrophages do NOT promptly arrive
PNS & axonal regeneration
favorable environment = Schwann cells & other non-neuronal cells produce cell adhesion molecules, extracellular matrix, neurotrophins = promote growth
-macrophages come rapidly
Wallerian Degeneration & Repair
- degeneration of the distal axon portion
- cascade of cellular responses = clearing inhibitory debris & production of a supportive environment for axonal regrowth
enhance the quality of life for CNS injuries
Blocking inhibitory molecules
Enhancing axon regeneration
Providing trophic (nutrition) support to surviving neurons
Mechanisms of Neural Reorganization
- Strengthening of existing connections
- new connections by collateral sprouting
Treatment of Nervous System Damage
- Blocking neurodegeneration
- Promoting Regeneration
- Neurotransplantation
- Rehabilitative Training
Blocking Neurodegeneration
- apoptosis inhibitor protein
- Estrogens = neuroprotective = limiting neuron death
** Also, may explain why several brain diseases are more prevalent in males (e.g. Parkinson’s disease)
Promoting Regeneration
Segments of myelinated peripheral nerves were transplanted
Neurotransplantation
1) fetal tissue (Fetal substantia nigra cells implanted = released dopamine)
2) stem cells (Cells migrated to damage, matured & regained some motor function BUT uncoordinated
Rehabilitative Training
importance of experience in brain development and organization.
Hebbian Dynamics/Plasticity
consistent and coordinated activation of one neuron by another neuron should strengthen their synaptic connection
Short-term Facilitation (3 steps)
1) facilitation
2) augmentation (increase in efficacy)
3) potentiation (increase PSP)
causes of Short-term Facilitation
-Transient increase in synaptic strength
-Necessary pattern of stimulation: high-frequency, APs arrive close together in time
-Ca2+ ion removal processes are overloaded
-Elevated concentration of Ca2+ ions in the presynaptic terminal
-Increased numbers of synaptic vesicles containing NT are released following an AP
-Increased amplitude of PSPs at the postsynaptic neuron
Short-term Depression
- Depletion of synaptic vesicles in the readily releasable
- Inhibitory feedback from presynaptic autoreceptors
- Ca2+ ion channel inactivation
Long-term Potentiation (LTP)
=structural changes of the synapse=
1) Addition of AMPA receptors on the postsynaptic neuronal membrane
2) Recruitment of “silent” synapses
3) Increases in size and/or density of dendritic spines
4) Increased arborization of dendritic “trees”
Long-term Potentiation Phases
Induction, Expression, and Maintenance
NMDA receptors are activated when:
- Glutamate is bound to the receptor
2. The postsynaptic neuron is highly depolarized (removing the Mg2+ block)
NT nitric oxide (NO)
coordinates recycling mechanism- (NO) therefore increases vesicle release
LTP vs. LTD
LTP relies on the activities of protein kinases
LTD relies on protein phosphatases
