B$B Exam2

EPSP (excitatory postsynaptic potential)

• associated with the opening of sodium channels

• allows influx of Na+; depolarization

• depolarized neuron more likely to produce action potential

IPSP (inhibitory postsynaptic potential)

• associated with the opening of potassium channels

• allows efflux of K+ or with opening of chloride channels allows influx of Cl-

Temporal Summation

• pulses that occur approx. the same time on a membrane are summed

• summing of potentials in a specific time period

Spatial Summation

• pulses that occur approx the same place on a membrane are summed

• summing of potentials in specific area

• EPSPs produced at the same time close together sum to form a larger EPSP

• EPSPs produced at the same time on separate parts of the membrane do not influence each other

EEG

graph that records electrical activity through the skull or from the brain & represents the graded potentials of many neurons 

Microelectrodes

• set of electrodes small enough to place on or in the axon

• can be used to:

  • measure a neurons electrical activity 

  • deliver a current to a single neuron (stimulation)

Oscilloscope

• made Huxley & Hodgkin experiments possible

• device that serves as a sensitive voltmeter

• used to record voltage on an axon 

Optogenetics

• rather than responding to voltage some ion channels respond to light by opening & allowing ions to pass 

Jules Bernstein

• its not the ions themselves that travel along the axon its a wave of charge 

• neuronal chemistry based on ions produces an electrical potential that could change + act as a signal 

• movement of ions constitutes the message conveyed by the neuron 

• voltmeter detects the waves passage (wave of ionic potential)

3 factors that influence the movement of anions & cations into + out of the cell

1. diffusion: something with more substance flows to something with less substance 

2. Concentration Gradient: someone of higher concentration moves to something of lower concentration (ink dropped into water diffuses from initial point of contact until it is equally distributed) 

3. voltage gradient: something negative flows to something positive 

The difference in the relative abundance of a substance among regions of a container is called the _____

concentration gradient 

Equilibrium is achieved when the concentration Gradient is equal to the _____

voltage gradient

resting potential

• electrical charge across the membrane in the absence of stimulation

• store of negative energy on the intracellular side relative to the extra cellular side 

• the inside of the membrane at rest is -70 mV relative to the extracellular side 

ion distribution across the resting membrane

• more protein anions & potassium ions are found in the intracellular fluid (inside cell)

• more sodium & chloride ions are present in the extracellular fluid (outside cell)

cations

positively charged ions (Sodium, potassium)

anions

negatively charged anions (Chloride, protein molecules (A))

what 3 features contribute to the cell membranes resting charge

1. negatively charged proteins remain inside the cell (bc membrane is relatively impermeable)

2. ungated potassium & chloride channels allow potassium & chloride ions to pass freely BUT gates on sodium channels keep out positively charged sodium ions 

3. Na+ & K+ umps extrude Na+ from the intracellular fluid & inject K+

depolarization

• decrease in electrical charge across a membrane (more positive)

• usually due to the inward flow of sodium 

hyper polarization

• increase in electrical charge across a membrane (more negative)

• usually due to the inward flow of chloride ions or outward flow of potassium ions 

EPSP (excitatory postsynaptic potential)

• depolarization (+)

• associated with the opening of sodium channels: allows influx of Na+

• depolarized neuron more likely to produce action potential

IPSPs (inhibitory postsynaptic potential)

• Hyperpolarization (-)

• associated with he opening of potassium channels: allows an efflux of K+ or with with the opening of chloride channels: allows influx of Cl- 

• hyper polarized neuron is less likely to produce an action potential 

when do action potentials occur

when EPSPs & IPSPs are summed to produce it or inhibit it

sequence of action of the voltage-activated ion channels

1. both sodium sodium & potassium voltage activated channels are attended to the threshold of about -40 mV

2. the voltage activated sodium channels respond more quickly than the potassium channels

3. sodium channels have 2 gates, once the membrane depolarizes to +30mV one gate closes

4. the potassium channels open more slowly than sodium channels and they remain open longer

where are the voltage gated canals located

at the axon hillock, where the action potential starts

what must happen in order to produce an action potential

summed graded potentials (IPSPs & EPSPs) on cell body membrane must depolarize the membrane at the initial segment to -50mV

all or none law

shape and size of action potential remain constant along the axon

2 practical uses of the refractory periods

• action potential prevented from reversing direction& returning to point of origin 

• the time & frequency of action potentials, not size, conveys variations in infos 

• sensitivity of voltage activated channels affect firing frequency 

myelin

• produced by oligodenrioglia in the CNS & Schwann cells in PNS

• speeds up neural impulse, energetically cheaper 

node of ranvier

• part of the axon that is not covered by myelin 

• tine gap in myelin sheath

• enables saltatory conduction

what are responsible for frequency of action potential occurrence (refractory periods)

sodium & potassium channels

absolute refractory period

• state of an axon in depolarizing period, during which a new action potential cannot (usually) be elicited because gate 2 of sodium channels, which is not voltage activated, is closed

relative refractory period

• the state of an axon in the later phase of an action potential, during which stronger electrical current is required to produce another action potential 

• potassium channels still open

chemical synapse

junction where messenger molecules (neurotransmitters) are released from one neuron to excite or inhibit the next neuron 

exocytosis

vesicles empty their contents into the synapse

Transmitter Activated Receptors (Ligand Gated Channel)

• when activated by a neurotransmitter, the receptors on neurons may change shape (inotropic) or alter chemical reactions in the target cell (metabotropic receptors)

up regulation

an increase in the number of receptors

down regulation

decrease in number of receptors

small molecule neurotransmitters

• class of quick acting neurotransmitters 

• synethized at axon terminal from dietary nutrients & packaged ready for use in axon terminal 

• Acetylcholine 

• amines

• amino acids 

acetylcholine

• synthesis = acetate choline 

• receptors: nicotinic vs muscarinic 

amines

• dopamine → norepinephrine (NE)

  • tyrosine → dopamine → norepinephrine

  • dopamine receptors (D1-like, D2-like)

• NE → epinephrine

• serotonin (5-HT): L-Tryptophan

• Melatonin & Histamine (no synthesis)

amino acids

• glutamate

  • receptors: NMDA, AMPA< Kainate (ionotropic)

  • mGluRs (metabotropic)

• GABA

  • receptors: GABA A & C (inotropic)

  • GABA B (metabotropic)

• peptide transmitters (synethesis at soma)

• Opioids

Lipid Transmitters

• synthesis at postsynaptic neurons

• endocannabinoids (2-AG, Anandamide) (no syntheses) 

endocannabinoids (2-AG, Anandamide)

• cannabinoid receptors CB1 & CB2

• retrograde signaling 

Gaseous Transmitters

• nitric oxide (NO) + carbon monoxide (CO): diffusion from blood/inhalation

• retrograde signaling 

barriers for drugs

• BBB

• endothelial cells of vascular system

Cholinergic System

• acetylcholine 

• basal forebrain 7 brainstem nuclei 

• alzheimers disease 

dopaminergic system

• dopamine 

• mesotriatal pathway (motor control) - Parkinson’s disease (L-dopa, substantial nigra)

• mesolimbocortical pathway (reward, addiction) - schizophrenia vs ADHD

Noradrenergic system

• norepinephrine 

• locus ceruleus 

• mood, arousal, sexual behavior 

• depression/mania

serotonergic system

• serotonin 

• raphe nuclei 

• SSRIs, MAO inhibitors, tricyclics

• depression, OCD, schizophrenia 

GABAergic system

• GABA

• benzodiazepines, alcohol

• sedation continuum, fetal alcohol spectrum disorder 

glutamatergic system

• glutamate 

• NMDA, AMPA, Kainate receptors 

• Ketamine, PCP, memantine

opioidergic system

• endorphins, enkephalins, etc

• morphine, heroine, fentanyl 

• naloxone (Narcan)

Cannabinergic system

• endocannabinoids, THC, CBD

• cannabis, anandamide, 2-AG

Adenosinergic system

• caffeine (adenosine antagonist) 

Parkinsons Disease

• substantial nigra had degenerated on the side opposite to that showing symptoms 

• symptoms appeared when he level of dopamine was reduced to less than 10% of normal in the basal ganglia 

• selectively destroyed dopamine containing neurons produced symptoms of Parkinson disease & confirmed the role of dopamine in a neural pathway connecting the substantia nigra to the basal ganglia