Neuroanatomy & Electrochemical Activity (Test 1) G

Glia Cells

nonneuronal cells that support, protect, and nourish neurons of the nervous systems

Identify A

A: Dendrites

Identify B

B: Nucleus

Identify C

C: Soma/Cel Body

Identify D

D: Axon Hillock

Identify E

E: Axon

Identify F

F: Myelin

Identify G

G: Node of Ranvier

Identify H

H: Terminal Bouton

Name the space between the pre-and-post-synaptic neurons

synaptic cleft

What does the soma do?

the central region of the neuron or cell body, which integrates all the inhibitory and excitatory inputs the nerve receives to decide which one it is getting more of. Should it initiate an action potential/

What are dendrites?

neuronal process responsible for propagating received electrical messages towards the cell body

What is an axon?

the neuronal process responsible for propagating electrical messages away from the cell body towards synaptic terminals

How many axons can a neuron have?

every neuron has one axon, but they can branch a bunch of different ways

Collaterals

branches that come off the single axon on a neuron

Neurites

any neuronal processes: dendrites, axons, collaterals

Where does the axon start?

axon hillock

What are the three ways that a neuron can be classified?

1) Based on the number or neurites

2) Based on shape of dendritic trees

3) Based on neurotransmitter type

Three classifications for neurons based on number or neurites

1) Unipolar: single neurite (ex. DRG)

2) Bipolar: exhibits one axon and one dendrite, both of which may be highly branching (common in sensory pathways)

3) Multipolar: numerous processes; one axon and any number of dendrites (ex. ventral horn neurons

Inhibitory Neurotransmitters

GABA, Glycine, Serotonin

Examples of some neuron classifications based on dendritic trees

stellate (star-shaped), pyramidal, bushy, etc.

How to classify neuron based on neurotransmitter

neurotransmitter name (-ergic)

How many neurotransmitters does a neuron emit

every neurotransmitter can produce and release only a single neurotransmitter

Action Potential

Electrical event

Nerve impulse resulting from brief reversal of membrane potential due to movement of ions across the cell membrane

Neurotransmission

Chemical event

neurotransmitters are chemical messengers that propagate an electrical signal across a synapse (from pre- to posy-synaptic element)

Describe how a neurotransmitter is sent down the axon and the structures involved

1) Nucleus decides to make neurotransmitter, send mRNA to Ribosome

2) Ribosome transcribes proteins for neurotransmitter

3) sends these neurotransmitters to Golgi Apparatus where they are packaged into vesicles and sent down axon

4) arrive at terminal bouton where they can undergo exocytosis

Anterograde Axoplasmic Transport

Movement of molecules from soma, through axon, to terminal bouton

This is done via a kinesin that moves along microtubules

Retrograde Axoplasmic Transport

Movement of molecule from synaptic terminal, through axon, back to some

This is done via dynein that moves along microtubules

Sent back for a breakdown of waste products

Axodendritic Synapse

synapse where axon synapses with a dendrite

Axosomatic Synapse

synapse where axon synapses with the soma (bypass dentrites)

Axoaxonic synapse

Synapse is where an axon synapses with the axon of another neuron

Exocytosis

send something out of a cell

the processes of releasing a neurotransmitter

Endocytosis

take something into the cell

reuptake of unused neurotransmitter

Membrane Potential

uneven distribution of electrical charge across the membrane at a moment in time

What is membrane potential at rest

negative (-60 to -80 mV)

the inside of the neuron is negative compared to the outside

Charge of a cell is always referred to at ________ with respect to _________

inside with respect to the outside

Ion channels are an example of what kind of protein

transmembrane protein

What are the different ion channels

Conformational change happens in response to

Neurotransmitter-Gated (Ligand-Gated): Neurotransmitter (ligand)

Voltage-Gated: electrical activity

Mechanically-Gated: mechanical stress

Sodium-Potassium (ATPase) Pump

moves 3 sodium (NA+) outside while transporting 2 potassium (K+) into neuron

requires energy APT

Do Sodium-Potassium Pumps move ions along or against their concentration gradient

Against

that is why it requires ATP

Describe the ion distribution at the resting membrane potential for

Sodium (Na+)

Potassium (K+)

Calcium (Ca+)

Chloride (Cl+)

Sodium (Na+): more outside

Potassium (K+): more inside

Calcium (Ca2+): more outside

Chloride (Cl-): More outside

Depolarization

cations (positively charged ions) crossing the membrane into the neuron

makes membrane potential less negative

results in excitatory postsynaptic potential

Hyperpolarization

membrane less permeable to cations entry, or more permeable to anion (negatively charges ion) crossing the membrane into neuron

making membrane potential more negative

results in inhibitory postsynaptic potential

Describe the relationship between depolarization and action potential

you can have a depolarization that is not an action potential

Every action potential is a massive depolarization

Electrical Summation

Dendrites are constantly receiving inhibitory and excitatory potentials

These charges are summed to determine if the cell will become more positive (depolarizing it) or negative (inhibiting depolarization)

what is the first event of action potential generation

when net electrical integration results in the axon hillock reaching the threshold (10 to 20 mV above resting membrane) voltage-gated Na+ channels in the axon hillock open, resulting in an all-or-nothing action potential response

Threshold

critical level of depolarization that must be crossed in order to trigger an action potential (all-or-nothing response)

Phases of an Action Potential

1) Threshold

2) Rising Phase: rapid depolarization, influx Na+

3) Overshoot: inside of membrane flips to positive charge

4) Falling Phase: rapid repolarization, voltage-gated Na+ channels close & voltage-gated K+ channels open & K+ rushes out casing potential to become more negative

5) Undershoot: hyperpolarization relative to resting potential due to delated closing or K+ channels

Spatial Summation

Reaches threshold from one excitatory input or multiple excitatory inputs received at the same time

Temporal Summation

Teaches threshold from receiving excitatory input one right after another

Myelin

covering on axon that increases conductivity

Nodes of Ranvier

unmyelinated portion of axon rich in voltage-gated An+ channels

Action potentials skip down axon to these nodes to keep propagating action potential down axon

What causes exocytosis

action potential arrives at terminal bouton causing voltage-gates Ca+ channels to open and Ca+ rushes into neuron stimulating exocytosis

Three ways the excess neurotransmitters can be removed from synaptic cleft

1) reuptake: endocytosis

2: enzyme degradation: acetylcholine eats it all right up

3: passive diffusion: they just travel away

Examples of reuptake inhibors

SSRIs (serotonin) and Cocaine (dopamine & serotonin)

Neurotransmitter Types

Fast

Neuromodulators & Neuropeptides

Nontraditional WHa

Fast Neurotransmitters

can bind to isotropic and G-protein receptors to act in an excitatory and inhibitory manner that act within msec to seconds

Examples of Fast Neurotransmitters

acetylcholine

catecholamines (norepinephrine, epinephrine, dopamine)

GABA

Glycine

Glutamate

Aspartate

Neuromodulators & Neuropeptides

primary bond to G-protein receptors away from synaptic cleft over the course of minutes to days

They generally have a more widespread effect with a longer time course than fast neurotransmitters

Examples of Neuromodulators & Neuropeptides

Substance P (inflammation)

calcitonin (migraine)

endogenous opioids (endorphins, enkephalins, dynorphins)

Nontraditional Neurotransmitters

rapidly diffuse across cell membrane, no need to bind receptor to elicit a response

Examples of Nontraditional Neurotransmitters

Nitric Oxide & Prostaglandins

G-Protein Coupled (metabotropic)

conformational change is enacted via a g-protein on the inside of the phospholipid layer, which can then act on secondary messenger (g-protein gates ion channel & enzymes)

Agonist Drugs

drug binding to receptor & mimics effect of naturally occurring neurochemicals (endogenous)

Antagonist Drugs

drugs that competes/interferes with agonist binding site, thereby blocking receptor activation

Acetylcholine

What kind of neurotransmitter?

Where does it work?

Primary Function?

Fast neurotransmitter

in PNS at neuromuscular junction for contraction of voluntary muscle

What is the receptor for acetylcholine?

cholinergic receptor

Types of cholinergic receptors

Nicotinic: isotropic receptor at skeletal muscle, autonomic ganglia, and CNS

Muscarinic: G-coupled (metabotropic) at cardiac, smooth muscle, and glands

Nicotinic Receptor

type of receptor, Agonist, Antagonist

Cholinergic receptor

Agonist: Nicotinic

Antagonist: Curare

Muscarinic Receptor

type of receptor, Agonist, Antagonist

Cholinergic receptor

Agonist: Muscarine

Antagonist: Atropine

Glutamaterigic Receptors

AMPA: Isotropic receptor for Na+

Kainate: Isotropic receptor for Na+

NMDA: special case

Glutamate

principle fast excitatory transmitter of CNS

NMDA Receptor

What makes it special? Antagonist?

Required agonist binding (glutamate or NMDA) and depolarization

BOTH neurotransmitter and voltage-gated

Once activated lets in Na+ and Ca2+, and lets K+ out

Antagonist: PCP (“angel dust”)

Long Term Potentiation (LTP)

important and critical for learning and memory (making new memories) - induces changes in brain in response to experiences

long-lasting reaction

Excitotoxicity

too much glutamate, too much intracellular Ca+, activating enzymes that damage DNA, membrane, & cytoskeleton

Can cause seizure activity

(Enzymes: endonucleases, phospholipases, protases)

Gabaergic Receptors

isotropic neurotransmitter-gated receptor allowing chloride influx, having an inhibitory effect

Drugs act as agonists for these receptors (ex. alcohol, benzos) resulting in sedative effect

Too little GABA?

hyperexcitability

seizures

unwanted muscle contractions

anxiety

Catecholamines

dopamine, norepinephrine, epinephrine (adrenaline)

Act mainly on G-protein receptors

Tyrosine precursure

Dopamine

Catecholamine

cannot cross the blood-brain barrier

Norepinephrine

catecholamine

locally released in PNS from some sympathetic nerve fibers

Epinephrine

Catecholamine

released as a hormone by adrenal gland, eliciting widespread action

Serotonin

another important amine

Astrocytes

most numerous Glia cells

regulates chemical contents extracellular space & release neurotropic growth factor for functional regeneration

Oligodendrocytes

myelinator of the CNS

has many arms that can wrap around many neurons

Schwann Cells

myelinator of PNS

generally on myelinates a single axon

Microglia

neuronal macrophages

removes debris

primary immune defense of CNS important for pruning

Radial Glia

provides scaffolding for neuronal migration

Ependymal Glia

lines ventricular system and produces CSF

Hypothesis: not enough pruning in early development

could explain autism or schizophrenia

Neuroinflammation

response of CNS to infection, disease, & injury mediated by microglia & astrocytes

too much microglia and neurotropic factor can kill neurons and glia and lead to degeneration

Stem Cell Therapy

found in the hippocampus & lateral ventricles

While we can make stem cells into what we want, we don’t know how to make the brain accept them and make meaningful connections