Electrical Signaling and Synaptic Transmission

how do neurons communicate within a neuron

using electrical signals

how do neurons communicate between neurons

using chemical signals

what encases neurons

cell membrane

what causes electrial signals in a neuron 

ions moving across the membrane 

ions def 

particles with either a positive or negative electric charge 

two types of potentials created by ions

graded potentials and propogated potentials

graded potential def

added up as ions enter the neuron and restricted ot one place in the neuron

what does a propogated potential do

travel down the neuron’s axon 

what encases a neuron

cell membrane

significance of neuronal membrane

has special properites that contribute to electrical signaling 

neuronal membrane composition

double layer of lipids in which proteins are embedded 

what does the neuronal membrane separate

intracellular and extracellular fluids, each with their own ionic composition

structure of neuronal membrane- lipid component

double layer of phospholipids which have 2 ends, a polar head and fatty acid chain tail

properties of polar head 

hydrophilic toward the intracellular and extracellular fluid 

non-polar tail properties

hydrophobic, faces away from the fluid; tails face each other in the center of the membrane 

2 functions of lipid part of neuronal membrane 

1. bilayer isolates the cytoplasm of the nuron from the extracellular fluid 

2. asle serves as a capacitator in that it is able to store charges of opposite signs that are attracted to each other but unable to cross the membrane 

diffusion barrier 

not permeable to ions 

protein component of neuronal membrane structure 

some proteins are exposed mostly on the outer or inner surface and some span the membrane 

primary function protein componenet

regulate movement of ions across the membrane

active movement of ions

pumping ions across memebrane; this occurs through proteins called ion pumps 

passive movement of ions across the membrane

allows ions to flow down concentration or electrical grandients (diffusion); this occurs through proteins called ion channels

ion channel def

neuronal membrane proteins with a central aqueous pore 

3 main characteristics of ion channels

1. mutliple states

2. gating 

3. selectivity 

multiple states of ion channels

open or closed

ion channels gating

mechanism by which ion channel switches states

voltage gated ion channel 

gate opens/closes based on chagnes in electrical membrane potential 

ligand gated ion channel 

gate opens/closes based on the binding of a neurotransmitter or hormone called a ligand 

thermally gated ion channel

gate opens/closes based on temperature of neuron 

mechanically gated ion channel 

gate opens/closes based on movement 

selectivity

ion channel’s ability to allow only certain ions through 

channelopathies

disease caused by defective ion channels

resting membrane potentials

cellective difference in electrical potential between the inside and outside of a neuron

inside of a neuron charge at rest

negative

outside of a neuron charge at rest

positive

draw out the phospholipid bilayer

draw out the 5 steps of synaptic transmission

what is the normal resting membrane potential

-65 mV

what does the neuron imbalance at rest result in

polarization of neuron- it is ready to be fired at any second

what causes the difference in electrical potential on either side of the neuronal membrane 

differences in ion concentration 

where is there more Na+

extracellular

where is there more K+

intracellular

where is there more Ca²⁺

extracellular 

where is there more Cl-

extracellular

factors that keeps resting potential at -65 mV

1. intracellular fluid contains many fixed anions

2. membrane proteins called ion pumps use active transport to maintain intracellular negativity 

anions 

negatively charged ions taht always stay inside the cell 

active transport

energy is needed to move ions across cell membrane

classic example of ion pump using active transport

sodium potassium pump

overall concept of sodium potassium pump 

pumps out Na+ from the intracellular space to the extracellular space and pumps in K+ from the extracellular space to the intracellular space 

what form of energy does the sodium-potassium pump use 

ATP

specifics on how sodium-potassium pump keeps the inside of the cell negative 

for every 3 Na+ that go out of the cell, only 2 k+ come into the cell

temporal summation

the adding up of postsynaptic potentials generated in the same neuron at slightly different times

spatial summation

the adding up of postsynaptic potentials generated at spatially separate sites on aneurons

electronic spread (summation)

electrical inputs come at varying places in the neuron and passively spread

what happens if inputs travel too far

the electrical current leaks out of the neuron, thus it is decremental

what is the way in which neurons deal with the decremental electronic spread

action potentials

sequence of events in action potentials

1. resting membrane potential 

2. local excitatory state 

3. threshold

4. rising phase 

5. peak

6. falling phase

7. hyperpolarization

8. resting membrane potential 

Robinsons lost their retriever pray for her recovery 

what is resting membrane potential

-65 mV

2 steps of local excitatory state

• neuron receives and excitatory input and cell membrane depolarizes

• this change in voltage in the cell cuases voltage-gated Na+ ion channels to open so Na_ start to flow into the cell 

in which way do concentration gradients move ions 

from areas of high concentration to low concentration 

how do electrical gradients move ions

from areas of positive charge to negative charge 

why does the movement of sodium change the electrical gradient 

more positive ions are coming into the cell 

threshold def

level of depolarization that results in an action potential 50% of the time OR the point of no return 

at what mV does sufficient depolarization occur

about -55mV

what does sufficient depolarization lead to in the threshold stage 

mass opening of voltage-gated sodium channels 

what two things happen during the rising phase

• sodium channels are in open state

• sodium flows in rapidly 

what is the spike peak mV

+35mV

what happens to sodium channels during peak 

they close 

what happens to potasium channels at peak 

they open 

what happens in the falling phase 

potassium begins to flow out of the neuron down its concentration and electrical gradient 

what happens during hyperpolarization

outward flow of K+ causes the membrane potential to dip below (and be even more neg than) resting membrane potential 

what happens during resting membrane potential 

APs happen rapidly in an all or none fashion 

propogation of action potentials

APs propogate with full amplitude

amplitude AP

positive voltage to adjacent areas of axon causes Na+ gates to open

APs propogate with constant velocity (larger axons) 

have increased velocity and less resistance 

APs propogate with constant velocity (myelinated  axons) 

have increased velocity due to more insulation 

insulated conduction

myelinated axons have bare regions called nodes of ranvier that contain many voltage-gated na+ channles 

movement of voltage in axon

spreads passively down myelinated axons until it reaches a node 

what happens at the node once the voltage reaches it 

sodium channels opena nd another AP is produced 

what is chemical communciation called

synaptic transmission

what are the chemicals used to pass along the message

neurotransmitters

5 steps of conventional chemical synaptic transmission

1. neurotransmitter symthesis

2. NT are concentrated and packaged in synaptic vesicles which are found in the presynaptic element or travel there by anterograde axonal transport

3. NT are released into synaptic cleft

4. NTs bind to ion channels in postsynaptic membrane

5. NT action is terminated in several ways 

what happens when NTs are released into the synaptic cleft

• AP traveling down axon depolarizes the presnaptic nerve terminal

• volatage-gated Ca²⁺ causes NT-filled vesicles to bind to active zones on neuronal membrane

• exocytosis- NT are released into the synaptic cleft

what happens when NTs bind to ion channels in the postsynaptic membrane

ligand-gated ion channels either open or close, thus changing the permeability of the postsynaptic cell membrane

postsynaptic potential 

when ligated gated channels open or close, changing the permeabiity of the postsynaptic membrane 

3 ways a NT action is termiated 

1. NT in synaptic cleft can diffuse away

2. NT can be reabsorbed by presynaptic ending or by glial cells 

3. NTs can be degraded by enzymes in the synaptic cleft

what two types of potential changes occur in the postsynaptic membrane 

either a depolarizing or hyperpolarizing 

depolarizing

inside of a neuron becomes more pos

hyperpolarizing

inside of a neuron becomes more negative

what is a depolarizing potential change called

excitatory postsynaptic potential (EPSP)

what happens in an EPSP

1. NTs bind to ion channel on postsynaptic membrane

2. ion channels open cuasing an influx of positively charged ions

3. membrane is depolarized 

process of EPSP at Neuromuscular Junction 

AP is produced → influx of Ca+ → acetylcholine is released → acetylcholine binds to ion channels called acetylcholine receptors → EPSP produced (end plate potential) → muscle contraction → extra acetylcholine in synaptic cleft is removed by acetylcholinesterase 

what is a hyperpolarizing potential change called 

inhibitory postsynaptic potentiual 

what happens in an IPSP

• NTs bind to ion channel on postsynaptic membrane

• ion channels open causing an influx of negatively charged ions or an efflux of pos charged ions

• memebrane is hyperpolarized 

• IPSP inhibits generation of AP by postsynaptic cell

what determines if an IPSP or EPSP happens

postynaptic ion channels

what do postsynaptic neurons do

compare and summate all inputs to determine how to respond 

what does the probability of a response depend on 

• amount of NT released

• number of postsynaptic ion channels present. 

• distance from ion channel to axon hillock in postsynaptic neuron 

what does it mean that neurons that fire together wire together 

strength of a synapse is influenced by history of activity at the synapse 

agonists 

drug that promotes effects of NT 

antagonists 

drug that impedes the effects of the NT

Myastenia Gravis def

autoimmune disease in which body produces antibodies that bind with the ion channels in motor end plates, preventing acetylcholine from binding to these receptors