neurotransmitters and receptors in autonomic responses

Cholinergic neuron

-A neuron that releases acetylcholine as its neurotransmitter. -ACh is stored in synaptic vesicles and released by exocytosis. -diffuses across the synaptic cleft and binds with specific cholinergic receptors, integral membrane proteins in the postsynaptic plasma membrane.

What are the 2 types of cholinergic receptors?

-The two types of cholinergic receptors, both of which bind ACh, are nicotinic receptors and muscarinic receptors

agonist

-a substance that binds to and activates a receptor, in the process mimicking the effect of a natural neurotransmitter or hormone.

The two main types of adrenergic receptors for norepinephrine?

-alpha (α) receptors. -beta (β) receptors. -found on visceral effectors innervated by most sympathetic postganglionic axons.

agonist: Phenylephrine

-an adrenergic agonist at alpha1 receptors, is a common ingredient in cold and sinus medications. Because it constricts blood vessels in the nasal mucosa, phenylephrine reduces production of mucus, thus relieving nasal congestion.

antagonist: atrophine

-blocks muscarinic ACh receptors, dilates the pupils, reduces glandular secretions, and relaxes smooth muscle in the gastrointestinal tract. -used to dilate the pupils during eye examinations, in the treatment of smooth muscle disorders such as iritis and intestinal hypermotility, and as an antidote for chemical warfare agents that inactivate acetylcholinesterase.

what are receptors for neurotransmitters?

-integral membrane proteins located in the plasma membrane of the postsynaptic neuron or effector cell.

norepinephrine can be released as a hormone: Chromaffin cells

-located in the adrenal medullae. -release norepinephrine as a hormone into the blood.

Muscarinic receptor

-may excite (depolarize) or inhibit (hyperpolarize) a cell when activated. Receptor for the neurotransmitter acetylcholine found on all effectors innervated by parasympathetic postganglionic axons and on sweat glands innervated by cholinergic sympathetic postganglionic axons. -named because muscarine activates these receptors but does not activate nicotinic receptors for acetylcholine.

norepinephrine can be released as a neurotransmitter: adrenergic neurons

-neurons that release norepinephrine as a neurotransmitter. -stored in synaptic vesicles and released by exocytosis -located at most sympathetic post ganglionic neurons -binds with receptor on the post synaptic cell membrane and is either excited (depolarized) or inhibited (hyper polarized).

monoamine oxidase (MAO)

-slowly inactivates norepinephrine.

antagonist

-substance that binds to and blocks a receptor, thereby preventing a natural neurotransmitter or hormone from exerting its effect.

Sub types of alpha (α) and beta (β) receptors:

-subtypes: a1, a2, b1, b2, b3. -subtypes based on the specific responses they elicit and by their selective binding of drugs that activate or block them. -Cells of most effectors contain either alpha or beta receptors; some visceral effector cells contain both. -activation of a1 and b1 receptors produces excitation. -activation of a2, b2 receptors causes inhibition of effector tissues. -b3 receptors are present only on cells of brown adipose tissue, where their activation causes thermogenesis (heat production).

Nicotinic receptor

-when activated, always excite (depolarize) the cell. -Receptor for the neurotransmitter acetylcholine found on both sympathetic and parasympathetic postganglionic neurons and on skeletal muscle in the motor end plate.

In the ANS, the cholinergic neurons (neurons that release ACh) include:

1. all sympathetic and parasympathetic preganglionic neurons. 2. sympathetic postganglionic neurons that innervate most sweat glands. 3. all parasympathetic postganglionic neurons.

What are the 2 classifications of autonomic neurons:

1. cholinergic. 2. adrenergic. -This is based on the neurotransmitter they produce and release.

actylcholine is quickly removed from the synapse by:

Acetylcholine is quickly removed from the synapse by achtylcholinesterase

Acetylcholinesterase

An enzyme found in neuromuscular junctions and in neuron synapses that quickly breaks down acetylcholine, preventing continuous stimulation of the postsynaptic cell.

Which ANS neurons are adrenergic? What types of effector tissues contain muscarinic receptors?

Most (but not all) sympathetic postganglionic neurons are adrenergic. Muscarinic receptors are present in the plasma membranes of all effectors (smooth muscle, cardiac muscle, and glands) innervated by parasympathetic postganglionic neurons and in sweat glands innervated by cholinergic sympathetic postganglionic neurons.

norepinephrine stimultes ________ receptors more strongly than _______.

Norepinephrine stimulates alpha receptors more strongly than beta receptors; epinephrine is a potent stimulator of both alpha and beta receptors.

norepinephrine can be released in 2 ways:

norepinephrine can be either released as a neurotransmitter (by sympathetic postganglionic neurons) -or released as a hormone into the blood by chromaffin cells of the adrenal medullae.