Types of Receptors

Types of receptors

ionotropic

metabotropic

receptors

proteins embedded in the postsynaptic membrane which recognize a specific NT (lets bind to it)

Ionotropic receptors

aka ligand gated, when NT bind to this receptor it causes an ion channel to open

Metabotropic receptors

aka G-protein coupled receptors:
when NT binds to this receptor a chain of reactions are set off, sometimes involving a 2nd messenger

Ionotropic receptor structure (+open, +closed) and function

• 4 or 5 subunits forming a “pore”

• this pore is closed when no NT is bonded

• when NT binds it slightly twists the pore opening it

• opening it allows ions to come through, which helps cause Post synaptic potential

Nicotinic Acetylcholine Receptor (ACh)

structure, how it functions

• an ionotropic receptor

• nicotinic ACh receptor has 5 subunits with two ligand binding sites that like to take in Acetylcholine but will take in agonists from outside body too (exogenous) like nicotine

• two acetylcholine molecules must bind to the receptor to open and allow Na+ inside the cell

Properties of Ionotropic Receptors

these ligand gated channels usually get help from amino acid NTs like (G.G.G.)

and a couple non-amino acid NT (nicotine ACH)\

need to take into account

• Pharmacology

• Kinetics

• Selectivity

Pharmacology (property of ionotropic receptor)

which neurotransmitters and drugs bind to receptor

(interact with receptor)

Kinetics (property of ionotropic receptor)

(how long channels open after NT molecule binds to receptor)

how it affects the duration of opening

Selectivity of ion channels

what type of ions are able to pass through ion channels. it determines whether there is an excitatory or inhibitory effect

Transmitter gated channels vs Voltage gated channels selectivity

Voltage gated channels are more selective about which ion molecules can go through

compared to Transmitter gated channels (ex. Na+, K+ both can go through Nicotinic ACh channels)

Excitatory PSP by  Na+

a recorded excitatory membrane potential

when Na+ positive comes through the open channels into cell, it membranes depolarizes

causing an excitatory membrane potential (mV increased)

How Metabotropic receptors work

1. the NT binds to the g coupled receptors

2. this activates a g protein which splits into a alpha and beta subunits

3. these subunits go to their own effector proteins. subunits open an ion channel or activate second messengers (enzymes)

Shortcut pathway of Metabotropic receptors

receptor → G protein → ion channel

no 2nd messenger, it is fast and localized

(ex. musacarnic ACh receptors in heart: NT binds to receptor, acitiving G protein, Beta subunit opens ion channel, K+ flows thru, causing hyperpolzarization that slows the heart)

Second messenger cascades (metabotropic recpetor long route)

1. NT binds to receptor

2. receptor activates G protein

3. G protein spitls into subunits

4. activating effector enzyme

5. effector enzyme creates 2nd messengers

6. the 2nd messengers activate other enzymes

7. signal stops eventually

Second messenger function

they are the intermediary between first effector enzyme and last enzymes that cause a cellular response (ex. opening ion channel, gene expression, etc)

when you have the same NT causing different effects in two neurons, what is happening

one receptors could be excitatory like when NT binds it opens to Na+ and receptor is inhibitory since when NT binds it opens to Ka+ causing hyperpolarization

Different receptor subtypes can cause very different responses in the target cells

same NT affecting cells in very different ways

different areas of the brains different receptor subtypes importance

the distribution of receptors subtypes also varies across the NS, so the same NT when binding to diff receptor can have completely different effect

Divergence

when one single NT can affect multiple receptor subtypes, causing different postsynaptic responses

can happen not just to different neurons but different parts of the same neuron

divergance can happen at any step of metabotropic cascading reaction

Convergence

when multiple diff NTs bind to their specifc receptor type and they affect the same effector system (ex. both NT A and B cause hyperpolzation)