Psych 255 midterm 2

what is embedded in semipermeable membranes?

ion channels used for communication

neuronal electrical acitivity

the movement of ions through channels across membranes

resting potential

unequal distribution of anions and cations which results in intracellular fluid at -70mV

3 ways the semipermeable membrane maintains resting potential

1. large, negatively charged protein molecules (anions) remain inside the cell (too big to transport)
2. gates keep out sodium ions and channels allow potassium and chloride to pass freely
3. sodium-potassium pumps extrude sodium from intracellular fluid and inject potassium

hyperpolarization

increase in electrical charge across a membrane (more negative)

depolarization

decrease in electrical charge across a membrane (more positive)

action potential

large, brief reversal of polarity of an axon, lasts 1ms

threshold potential

The minimum membrane potential that must be reached in order for an action potential to be generated. -50mV
-voltage on neural membrane
-opening of NA+ and K+ voltage-activated channels

nerve impulse

each action potential propogates another action potential on the adjacent axon membrane

refractory period

impulse moves in one direction

all-or-none law

size and shape of action potential remains constant

myelin

-produced by oligodendroglia in the CNS and Schwann cells in the PNS
-speeds up neural impulse

nodes of ranvier

uninsulated regions of an axon that enable saltatory conduction (leaping between nodes) -very fast

saltatory conduction

action potential jumps from node to node up to 120m/s

Multiple Sclerosis (MS)

-damaged myelin may cause a neuron to be unable to send any messages over its axons
-the myelin formed by oligodendroglia is damaged which disrupts the functioning of neurons whose axons encase it

how do neurons integrate information

- Through dendritic spines, a neuron can establish more than 50,000 connections to other neurons
- receiving neurons bombard with signals (excitatory and inhibitory)
- The cell body can receive inputs from many other neurons

two ways neurons integrate info

EPSP and IPSP

excitatory postsynaptic potential (EPSP)

-brief depolarization of a neuron membrane in response to stimulation
-depolarized neuron more likely to produce AP
-opens sodium channels allowing influx of NA+ into cell

inhibitory postsynaptic potential (IPSP)

-Brief hyperpolarization of a neuron membrane in response to stimulation,
-hyperpolarized neuron less likely to produce an action potential.
-opens potassium channels allowing reflux of K+ or opening chloride channels allowing influx of Cl-

summation of inputs

-A neuron sums all inputs close together in space and time
-neurons analyzed inputs to decide what to do
-the decision is made at in itial segment

neuron communication

communication between neurons occurs across synapse and is largely chemical, spurred by AP

neurotransmitter

chemical with excitatory or inhibitory effect when released by the neuron to a target
-similar to hormones but hormones are outside the CNS and are slower

chemical synapses

storage granules hold vesicles containing neurotransmitter that travel to the presynaptic membrane in prep for release
-neurotransmitter is expelled into the synaptic cleft by exocytosis, crosses the cleft, and binds to receptor proteins on the postsynaptic membrane

presynaptic membrane (axon terminal)

Where the action potential terminates to release the chemical message

postsynaptic membrane (dendritic spine)

the receiving side of the chemical message; EPSPs or IPSPs are generated

synaptic cleft (space between)

Small gap where the chemical travels from presynaptic to postsynaptic membrane

synaptic vesicle (presynaptic)

Small membrane-bound spheres that contain one or more neurotransmitters

storage granule (presynaptic)

membranous compartment that holds several vesicles containing neurotransmitters

postsynaptic receptor (postsynaptic)

site to which a neurotransmitter molecule binds

neurotransmission in 5 steps

1. neurotransmitter synthesis
2. neurotransmitter packaging and storage
3. neurotransmitter transportation and release into the cleft
4. neurotransmitter binding and activating receptors
5. neurotransmitter degradation

anterograde synaptic transmission

the five-step process of transmitting information across a chemical synapse from the presynaptic side to the postsynaptic neuron

step 1 and 2 (anterograde synaptic transmission)

neurotransmitters derived in two ways
-synthesized in axon terminal: building block from food pumped via transporters, protein molecule embedded in membrane
-synthesized in cell body: DNA peptide transmitters, transported on microtubules to axon terminal

step 3 (anterograde synaptic transmission)

at terminal, AP opens voltage sensitive CA2+ channels
-ca2+ enters the terminal, and binds to protein calmodulin forming a complex
-causes vesicles to empty contents into synapse

step 4 (anterograde synaptic transmission)

-after release, neurotransmitter diffuses across the synaptic cleft to activate receptors on postsynaptic membrane
-transmitter activated receptors: protein embedded in membrane with binding site for neurotransmitter

neurotransmitter may:
1. cause EPSP
2.cause IPSP
3. initiate other chemical reactions that modulate inhibitory or excitatory effect or influence functions

-may interact with receptors on presynaptic membrane
autoreceptor: self-receptor on presynaptic membrane that responds to the transmitter that neuron released

step 5 (anterograde synaptic transmission)

1. diffusion: some of neurotransmitter diffuse away from synaptic cleft and cannot bind to receptors
2. degradation: enzyme in synaptic cleft break down neurotransmitter
3. reuptake: transmitter brought back to presynaptic axon terminal, can be used again
4. astrocyte uptake: astrocytes take up neurotransmitter, can store for re-export to axon terminal

excitatory synapse

-located on dendrites
-round vesicles
-dense material on membranes
-wide cleft
-large active zone

inhibitory synapse

-located on cell body
-flat vesicles
-sparse material on membranes
-narrow cleft
-small active zone

gap junction

Fused presynaptic and postsynaptic membrane that allows an action potential to pass directly from one neuron to the next

evolution of complex neurotransmitter systems

-digestive juices secreted onto prey via exocytosis (release of neurotransmitter)
-prey is captured by endocytosis

4 criteria for identifying neurotransmitters

1) transmitter must be synthesized or present in a neuron
2) when released, transmitter must produce a response in target cell
3) the same receptor action must be obtained when transmitter is experimentally placed on the receptor
4) there must be a mechanism for removal after the transmitter's work is done

main functions of neurotrandmitters

1. carry a message from one neuron to another by influencing voltage on the postsynaptic membrane
2. changing the structure of the synapse
3. communicate by sending messages in the opposite direction. the retrograde messages influence the release or reuptake of transmitters on the presynaptic side

Five classes of neurotransmitters

1. small-molecule transmitters (ACh, DA, Glu)
2. peptide transmitters (oxytocin)
3. lipid transmitters (endocannabinoids)
4. gaseous transmitters (NO, CO)
5. ion transmitter (zinc)

1. Small-Molecule Transmitters

- quick acting
-synthesized from dietary nutrients and packaged ready for use in axon terminal
ex: acetylcholine synthesis: choline (egg yolk, salmon, avocado), acetate (lemon juice, vinegar)
-breakdown of acetylcholine by the enzyme acetylcholinesterase

amine synthesis

Enzyme Tyrosine synthesizes amines in L-dopa and then in dopamine, norepinephrine, and epinephrine
-tyrosine comes from food like cheese

three types of small molecule transmitters

serotonin, amino acid transmitters, purines

serotonin

-synthesized by amino acid L-tryptophan
-role in mood, aggression, appetite, arousal, respiration, pain perception

amino acid transmitters

Glutamate and GABA
Glutamate: main excitatory transmitter
GABA: main inhibitory transmitter, formed by a modification of glutamate molecule

purines

synthesized as nucleotides
ex: ATP: removing 3 phosphate groups leaves adenosine (promotes sleep, suppresses arousal, blood flow regulation)

2. Peptide Transmitters

act as hormone that responds to stress, enable a mother to pond with child, regulate eating and drinking, pleasure and pain, learning
such as neuropeptides

neuropeptides

Chains of amino acids that acts as neurotransmitters
-synthesized through translation of mRNA from instructions in the neurons DNA
-slowly and not replaced quickly

what can mimic the actions of natural brain peptides

Opioids such as morphine and heroin

types of peptide transmitters

opioids, neurohypophyseal, secretin, insulins, gastrin, somatostatins, tachykinins

3. Lipid transmitters

endocannabinoids like anadamide and 2-AG
-both derived from arachidonic acid and unsaturated fatty acid
-once synthesized it diffuses across the synaptic cleft and interacts with its receptor and the presynaptic membrane
-can reduce the amount of small-molecule transmitters being released

Endocannabinoids

synthesized at the postsynaptic membrane to act on receptors at the presynaptic membrane
-CB1 receptor is target of all cannabinoids

4. Gaseous transmitters

ex: nitric oxide, corbon monoxide, hydrogen sulfide
-neither stored in synaptic vesicles nor released from them
-synthesized in cell as needed; easily cross membranes

5. Ion transmitters

-ex: zinc
-actively transported, packaged into vesicles usually with another transmitter like glutamate and released into the synaptic cleft

two classes of receptors

ionotropic and metabotropic

ionotropic receptors

1. 1. binding site
2. pore or channel
-pore either opens or closes when neurotranmitter binds
-quicker, direct

metabotropic receptor

-slower, longer-lasting, widespread effects
-lack own pore for ions, indirectly producd changes in nearby ion channels or in cells metabolic activity
-linked to a guanyl nucleotide-binding protein, G protein, that can affect other receptors or act with second messengers to affect other cellular processes

G protein

a protein coupled to a metabotropic receptor; conveys messages to other molecules when a ligand binds with and activates the receptor
- consists of 3 subunits: alpha, beta, gamma

second messenger

chemical that initiates a biochemical process when activated
1. bind to channel and alter ion flow
2. form new ion channels
3. bind to DNA to alter protein production

receptor subtypes

-Each neurotransmitter may interact with a number of receptor subtypes specific to that neurotransmitter.

-Each subtype has slightly different properties, which confer different activities.

-Presence or absence of binding sites for other molecules, how long a channel remains open or closed, ability to interact with intracellular signaling molecules.

neurotransmission and behaviour

-many transmitters can coexist in one synapse
-more than one type of transmitter packaged within a single vesicle
-a neuron can either excite or inhibit but there is variation due to multiple combinations

somatic nervous system (SNS)

-motor or cholinergic, neurons send axons to muscles in the body
-Acetylcholine is main neurotransmitter
-transmitter-activated inotropic channel: nicotinic acetylcholine receptor (nAChr) - efflux of K+ and influx of Na+

autonomic nervous system (ANS)

CNS neurons synapse with parasympathetic neurons: Ach receptors on heart are inhibitory and excitatory on gut
CNS neurons synapse with sympathetic neurons: NE receptors on heart are excitatory on the heart and inhibitory on gut.

enteric nervous system (ENS)

- can act without input from CNS (second brain)
-uses main classes of neurotransmitters (30+)
-mainly serotonin and dopamine
-sensory neurons detect mechsnical and chemical conditions in GI system
-motor neurons control internal muscles for mixing intestinal contents and secreting digestive enzymes

Cholinergic system (acetylcholine)

- Active in maintaining attention and waking EEG pattern
- Thought to play a role in memory by maintaining neuron excitability
- Death of cholinergic neurons and decrease in ACh in the neocortex are thought to be related to Alzheimer's disease.

dopaminergic system (dopamine)

nigrostriatal pathways
-active in maintaining normal motor behaviour
-loss of DA is related to muscle rigidity and dyskinesia in parkinsons disease

mesolimbic pathways
-dopamine release causes repetition of behaviours
-thought to be the neurotransmitter system most affected by addictive drugs and behavioural addictions
-increases DA activity and may be related to schizophrenia
-decreased DA activity may be related to deficits of attention

noradrenergic system (norepinephrine)

-active in maintaining emotional tone
-decreases in NE activity are though to be related to depression
-increase in NE activity are thought to be related to mania
-decreased NE is associated with ADHD

serotonergic system (serotonin)

- Active in maintaining waking EEG pattern
- Changes in serotonin activity are related to obsessive compulsive disorder, tics, and schizophrenia
- decreases serotonin activity are related to depression
- abnormalities in brainstem 5-HT neurons are linked to disorders such as sleep apnea and SIDS