Exam 1 ANS Flashcards
How is the nervous system organized?
- CNS
2. PNS → SMS and ANS → sympathetic and parasympathetic
What is the somatic motor pathway in the PNS?
- contains a single neuron that releases ACh as the neurotransmitter and the receptor is a nicotinic receptor
- target is the skeletal muscles, mostly voluntary
What are the three pathways within the autonomic pathways of the PNS?
- parasympathetic
- sympathetic
- adrenal sympathetic
What is the parasympathetic pathway?
- long preganglionic neuron that releases ACh to a nicotinic receptor
- short postganglionic neuron that releases ACh to a muscarinic receptor
- ganglia is close to the post-ganglionic
What is the sympathetic pathway?
- short preganglionic neuron that releases ACh to a nicotinic receptor
- long postganglionic neuron that releases NE to alpha and beta1 receptors
- ganglia is close to CNS
What is the adrenal sympathetic pathway?
- ganglia synapses in the adrenal medulla and the release of epinephrine has to go into the circulation to go to the target organ and can interact with beta1 and beta2 receptors
What are some autonomic targets?
- smooth and cardiac muscles
- some endocrine and exocrine glands
- some adipose tissue
What are some things to know about autonomic neurons?
- regulation of the activity of smooth and cardiac muscle, glands, lymphoid and some adipose tissue
- concept of autonomic tone (involuntary) which means that the pathways tend to be active to some degree at rest
- sympathetic and parasympathetic actions are often (but not always) opposing
What are the important things to know about somatic motor neurons?
- controls skeletal muscles
2. mostly voluntary
What is the ganglia?
group of cell bodies outside of CNS
What is the first neuron in the ANS?
- termed the preganglionic neuron
- located in the CNS
- projects to the autonomic ganglia
What is the second neuron in the ANS?
- termed the postganglionic neuron
- located outside of the CNS in the autonomic ganglia
- projects to the target organ
What is the anatomy of the sympathetic nervous system?
- the preganglionic neuron is located in the middle regions of the spinal cord (thoracolumbar)
- the postganglionic neuron is long and projects to the target organ
- the sympathetic ganglia located near the spinal cord
What is the anatomy of the parasympathetic system in the ANS?
- the preganglionic neuron is located in the brainstem or outer regions of spinal cord (craniosacral)
- the postganglionic neuron is short and projects to the target organ
- parasympathetic ganglia is located in or near the target organs
What are the preganglionic neurons like in the parasympathetic system?
- long
- synapses with postganglionic neurons at or near the target organ
- releases ACh to activate nicotinic receptors on the postganglionic neurons
What are the postganglionic neurons like in the parasympathetic system?
- short
- synapses on the target organ
- releases ACh to activate muscarinic receptors on the target organ
What are the preganglionic neurons like in the sympathetic system?
- short
- synapses with postganglionic neurons near the spinal cord
- releases ACh to activate nicotinic receptors on the postganglionic neurons
What are the postganglionic neurons like in the sympathetic pathway?
- long
- synapses on the target organ
- releases NE to activate adrenergic receptors on target organs
What are the exceptions in the sympathetic nervous system?
- sweat glands
- adrenal glands
- kidneys
How are sweat glands an exception?
- postganglionic neurons involved with stress related excretion release NE → sweaty palms
- postganglionic neurons involved with thermoregulation release ACh
How are adrenal glands an exception?
- preganglionic neurons do not synapse in the paravertebral sympathetic ganglion → they synapse directly on the adrenal gland to release ACh and activate nicotinic receptors on the adrenal gland
- adrenal glands release epinephrine into systemic circulation → then to target organ
How are kidneys an exception?
- they are also affected by dopamine (endogenous) → mainly synthesized locally and not in the ANS
Most postganglionic sympathetic neurons release what neurotransmitter?
norepinephrine (NE)
What are the major points of the autonomic nervous system?
- primary transmitter of all preganglionic neurons is ACh
- the transmitter in all PSNS (parasympathetic) neurons is ACh
- transmitter in most SNS postganglionic neurons is norepinephrine (NE) → BUT sweat glands have ACh, adrenal medulla has epinephrine, and renal vasculature has dopamine
What are cholinoceptors?
- acetylcholine receptors
2. has two types: nicotinic (Nm, Nn) and muscarinic (M1, M2, M3)
What are adrenoceptors?
- norepinephrine and epinephrine receptors
2. has two types: alpha (a1, a2) and beta (beta1, beta2, beta3)
Why do we study the ANS?
- many drugs exhibit anticholinergic effects → important for treating the elderly
- ANs plays a major role in regulating BP and heart function
- there are many adrenergic drugs for BP and cardiovascular diseases
- ANS plays a large role in bronchoconstriction/dilation
- cholinergics play a role in pesticides and chemical weapons
- is the basis for the discipline of pharmacology → medication therapy management!
What is adrenergic pharmacology?
the pharmacology of sympathetic mechanisms involving norepinephrine and epinephrine and their receptors
What is cholinergic pharmacology?
the pharmacology of parasympathetic mechanisms involving acetylcholine and its receptors
What are the neurotransmitters of the parasympathetic system (cholinergic)?
acetylcholine (endogenous), muscarine (exogenous), and nicotine (exogenous)
What are the neurotransmitters in the sympathetic system (adrenergic)?
norepinephrine (endogenous) and epinephrine (endogenous)
What is acetylcholinesterase?
membrane bound enzyme that is specific for the cholinergic receptor in which acetylcholine can bind to
What are nicotinic receptors?
- has 5 subunits and is an ionotropic open ligand gated Na channel
- acetylcholine is the ion which leads to the depolarization of the membrane → leads to the opening of the voltage gated sodium channels to produce an action potential
- selectively activated by nicotine
What are muscarinic receptors?
- 7 transmembrane domain G-protein coupled receptors (GPCRs)
What pathway does the M1, M3, and M5 muscarinic receptors signal through?
Gq pathway → IP3 mobilizes Ca2+ from intracellular stores and DAG activates PKC (protein kinase C)
What pathway does the M2 and M4 muscarinic receptors signal through?
Gi pathway → K+ channel opening causes hyperpolarization and counteract beta1 receptors which result in reduced cAMP dependent protein kinase activity
What are the agonists for muscarinic receptors?
endogenous acetylcholine or muscarine (exogenous)
What pathway do alpha1 adrenergic receptors signal through?
Gq pathway → IP3 mobilizes Ca2+ from intracellular stores and DAG activates PKC (protein kinase C)
Alpha1 adrenergic receptors are found where?
- vascular smooth muscle
- genitourinary smooth muscle
- intestinal smooth muscle
- heart
- liver