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