Physio Chapter 4: NS 2 Nervous System: Neurotransmitters

Excitatory

Acetycholine is _ at the nicotinic receptors causing skeletal muscles to contract

mACh receptors in the heart

Acetycholine is inhibitory at these receptors causing postsynaptic hyperpolarization and the heart slows down

Alpha receptors and beta receptors

Two families of receptors for norepinephrine

indirectly, slow EPSPs

Acetycholine acts _ with mACh to produce _

Bound to the G protein

At rest GDP is

Acetycholine and epinephrine

Act indirectly on the effector organs of the autonomic nervous system and their action is slow

Direct, fast and excitatory

Action of acetylcholine on skeletal muscle and ganlionic neurons

What glutamate does

Acts directly on ion channels that permit passage of both sodium and potassium, producing fast excitatory postsynaptic potentials

GABA (gamma-aminobutyric acid)

An important CNS neurotransitter that binds directly to ligand-gated Cl- channels causing Cl- to flow into cells and induces IPSPs

Acetycholine for mACh

Are excitatory causing neurons to fire action potentials and smooth muscles to contract

Glycine

BLike GABA it inds to receptors which directly open chloride channels, producing fast inhibitory postsynaptic potentials

Norepinephrine

Binds to the G coupled receptor to activate G proteins to release GDP and bind to GTP

Where alpha-one receptors are found

Blood vessels, which supply the skin, mucosae and abdominal viscera

Indirectly-acting neurotransmitters

Can change effector organs of the peripheral ANS, CNS states, learning and memory

When ACh binds to Nicotinic ACh receptors

Channels open, Na+ flows into the cell quickly and K+ flows out of the cell slowly to induce EPSPs

A less negative membrane potential and deplarization of the cell

Closing the potassium channel results in

Epinephrine

Comes from the adrenal medulla it is more potent than norepinephrine and inhibits beta 2 receptors

Generate EPSPs or IPSPs

Depending on the particular mechanism activated by the binding of acetycholine it can

Types of Monoamine Neurotransmitters

Dopamine, norepinephrine, epinephrine, serotonin

Acetylcholinesterase

Enzyme that breaks down acetylcholine embedded in the postsynaptic membrane or in the synaptic cleft

Where the cholinergic nicotinic receptor is

Found at the neuromuscular junction

Monoamine neurotransmitters

Function though G-Protein linked receptors Leads to the activation of enzymes and production of second messengers (cAMP) inside cell 2nd messenger activates additional enzymes (protein kinases) that induces metabolic changes or changes in membrane potential

When ACh binds muscarinic receptors

G-protein is activated and it dissociates into alpha and beta-gamma subunits which soon become inactivated and link back together

IPSPs (inhibitory postsynaptic potentials)

G-proteins in the cardiac muscle generate

EPSPs (excitatory postsynaptic potentials)

G-proteins in the smooth muscle in the digestive tract generate

Directly-acting neurotransmitters

Important for sensory-motor coordination, communication, and many other higher functions (playing music)

Second neurons (ganglionic neurons)

In both the sympathetic and parasympathetic chains has nACh receptors on these neurons

Where nicotinic receptors are found

In certain brain regions, skeletal muscle cells and cell bodies of autonomic motor neurons in ganglia

Where muscarinic receptors are found

In some CNS neurons, smooth muscle, glands and cardiac muscle (autonomics)

Where adrenergic receptors are found

In the central nervous system and on effector organs of the sympathetic nervous system

Where muscarinic ACh receptors are found

In the central nervous system and on most effector organs of the parasympathetic branch of the nervous system

Movement of K+ out of the cell

In the resting neuron this acts to hyperpolarize the cell

Nicotinic ACh receptors

Ligand-gated ion channels that open by direct binding of ACh

A second messenger

Part of the G protein travels in the membrane and activates an enzyme that induces the production of

GABA and glycine

Major inhibitory neurotransmitters in the central nervous system

Adrenergic receptors

Norepinephrine acts indirectly when it binds to these receptors

Where beta-two receptors are found

On the respiratory airways and blood vessels that supply skeletal muscles and heart

Phosphorylates a K+ ion channel and closes it

The 2nd messenger activates an intracellular enzyme that

Seperate from the ion channel (G-protein linked receptors)

Receptors for ACh for Muscarinic ACh receptors are

Cholinergic receptors

Receptors that bind to acetylcholine

Motor neurons of the somatic nervous system

Release acetycholine and are cholinergic

Parasympathetic ganglionic neurons

Release acetycholine and are cholinergic

Sympathetic ganglionic neurons

Release norepinephrine and are adrenergic

How monoamines are taken up

Taken back up by presynaptic cells

Cholinergic

The first 2 neuwons of the sympathetic and parasympathetic chain preganglionic neuron are

Glutamate

The most common and most potent excitatory neurotransmitter in the CNS

A fast excitatory postsynaptic potential

When acetycholine acts directly to open the nACh channels it produces

mACh receptors in the central nervous system and heart

When acetycholine acts indirectly at these receptors they produce slow inhibition of the postsynaptic cells

Intracellular second messengers

When neurotrasnmitters bind to receptors that are seperate from the ion channel which leads to the production of

Alpha 1 receptors

When norepinephrine acts indirectly on these receptors it causes smooth muscle to contract Norepinephrine= excitatory

Beta-two receptors

When norepinephrine binds slow inhibition is produces and smooth muscle dilates

Beta-one receptors in the heart

When norepinephrine binds to these receptors slow excitation Heart rate and strength of contraction increase

Catecholamines

dopamine, norepinephrine, epinephrine