Autonomic Nervous System Flashcards
The _____ nervous system is under conscious control and innervates skeletal muscle
somatic
The _____ nervous system is under involuntary control and innervates visceral organs
autonomic
Each pathway in the autonomic nervous system consists of what 2 neurons?
preganglionic and postganglionic neurons
Where does the cell body of each preganglionic neuron reside?
In the CNS
Where do the axons of preganglionic neurons synapse with the bodies of postganglionic neurons?
In the autonomic ganglia located outside the CNS
All preganglionic neurons of the ANS release what NT?
ACh
All postganglionic neurons of the ANS release one of what 2 NTs?
ACh or norepinephrine
What are the 3 divisions of the ANS?
- Sympathetic
- Parasympathetic
- Enteric
What NT do adrenergic receptors release?
norepinephrine
What are receptors for norepinephrine on the effector organs called?
Adrenoreceptors
What NT do cholinergic receptors release?
ACh
What are receptors for ACh on the effector organs called?
Cholinoreceptors
What type of receptors describes some postganglionic parasympathetic neurons of the GI tract that release peptides or other substances as their NT rather than ACh?
Non-adrenergic, non-cholinergic receptors
Because all preganglionic neurons release ACh they are called what?
cholinergic
Most postganglionic parasympathetic neurons release ACh therefore they are called what?
cholinergic
Postganglionic sympathetic neurons release ACh and norepinephrine therefore they are called what?
cholinergic OR adrenergic
What is the junction between postganglionic neurons and their effector organs called?
the neuroeffector junction
Describe neuroeffector junctions
They are diffuse, branching networks in which the receptors are not concentrated in one region
What is the overall function of the sympathetic nervous system?
mobilize the body for activity
Where do the preganglionic neurons of the sympathetic division arise from?
In spinal cord segments T1 - L3 (thoracolumbar)
Where are the ganglia of the sympathetic nervous system found?
Near the spinal cord, either in the paravertebral ganglia (sympathetic chain) or in the prevertebral ganglia
Because sympathetic ganglia are located near the spinal cord, the preganglionic nerve axons are ____ and the postganglionic nerve axons are _____.
short
long
Preganglionic neurons of the sympathetic division are always _____ because they release ACh
cholinergic
Postganglionic neurons of the sympathetic division are _____ in all of the effector organs, except for the thermoregulatory sweat glands.
adrenergic
thermoregulatory sweat glands of the sympathetic division are innervated by what?
sympathetic cholinergic neurons, and therefore have muscarinic cholinorecpetors
What are the 4 types of adrenoreceptors of the sympathetic division?
- alpha1
- alpha2
- beta1
- beta2
Sympathetic adrenergic varicosities contain both the classic neurotransmitter and non-classic transmitters. What are they?
Classic: norepinephrine
Non-classic: ATP and neuropeptide Y
Describe the roles of norepinephrine, ATP, and neuropeptide Y play in contraction via the sympathetic nervous system
1) ATP binds to purinergic receptors on the target tissue causing contraction of the vascular smooth tissue
2) Norepinephrine binds to its receptors on vascular smooth muscle and causes a second, more prolonged contraction
3) With more intense stimulation, the large dense-core vesicles release neuropeptide Y which binds to its receptors on the target tissue causing a third, slower phase of contraction
What is considered a specialized sympathetic ganglion whose preganglionic neurons originate in the thoracic spinal cord (T5-T9), pass through the sympathetic chain and the celiac ganglion without synapsing, and travel in the greater splanchnic nerve to the adrenal gland?
the adrenal medulla
Once the axons from the adrenal medulla reach the adrenal gland what do they do?
They synapse on chromaffin cells and release ACh, which activates nicotinic receptors
When activated the chromaffin cells of the adrenal medulla secrete __% epinephrine and __% norepinephrine
80
20
Why does the adrenal medulla secrete both epinephrine and norepinephrine?
Because of the presence of phenylethanolamine-N-methyltransferase (PNMT) which catalyzes the conversion of norepinephrine to epinephrine
What is a pheochromocytoma?
a tumor of the adrenal medulla
A pheochromocytoma releases what primarily?
norepinephrine
The fight or flight system of the sympathetic nervous system includes what?
- Increases in HR, CO, BP, ventilation, and blood glucose
- Redistribution of blood flow away from the skin and splanchnic regions toward the skeletal muscle
- Decreases in GI motility and secretions
What is the overall function of the parasympathetic nervous system?
Restorative, to conserve energy
Where do the preganglionic neurons of the parasympathetic division arise from?
nuclei of cranial nerves III, VII, IX and X or from sacral spinal cord segments S2-S4 (craniosacral)
Where are the ganglia of the parasympathetic nervous system found?
near, on, or in the effector organs
Because parasympathetic ganglia are located near or in the effector organs, the preganglionic nerve axons are ____ and the postganglionic nerve axons are _____.
long
short
Preganglionic neurons of the parasympathetic division are always _____ because they release ACh
cholinergic
Most of the postganglionic neurons of the parasympathetic division are _____.
cholinergic
ACh released from preganglionic neurons of the parasympathetic division activates _____ receptors, whereas ACh released from postganglionic neurons of the parasympathetic division activates _____.
nicotinic
muscarinic
Parasympathetic cholinergic varicosities contain both the classic neurotransmitter and non-classic transmitters. What are they?
Classic: ACh
Non-classic: Vasoactive intestinal peptide (VIP) and nitric oxide (NO)
Describe the roles of ACh, VIP, and neuropeptide NO play in contraction via the parasympathetic nervous system
1) ACh is released from the varicosities and binds to muscarinic receptors on the target tissue which direct its physiological action
2) With intense stimulation the large dense-core vesicles release VIP or NO which binds to receptors on the target tissues and augments the actions of ACh
Because most organs have both sympathetic and parasympathetic innervation they are said to work ____ to produce coordinated movement
reciprocally or synergistically
An increase in sympathetic activity and a decrease in parasympathetic activity ____ heart rate via beta1 and muscarinic receptors of the SA and AV nodes
decreases
When the urinary bladder is filling _____ control predominates which produces a relaxation of the detrusor muscle, via ___ receptors and contraction of the internal sphincter via ____ receptors
sympathetic
beta2
alpha1
During micturition (emptying of the bladder) _____ control predominates which produces a contraction of the detrusor muscle and relaxation of the internal sphincter, both via ____ receptors
parasympathetic
muscarinic
What are the 2 muscles of the iris?
- pupillary dilator (radial) muscles
- pupillary constrictor (circular) muscles
The pupillary dilator (radial) muscles are controlled by ______ innervation through ___ receptors
sympathetic
alpha1
Activation of alpha1 receptors causes constriction of the radial muscles which causes ____ of the pupil
dilation
The pupillary constrictor (circular) muscles are controlled by ______ innervation through ___ receptors
parasympathetic
muscarinic
Activation of muscarinic receptors causes constriction of the circular muscles which causes ____ of the pupil
constriction
What are the 6 organs that have only sympathetic innervation?
- sweat glands
- vascular smooth muscle
- pilomotor muscles of the skin
- liver
- adipose tissue
- kidney
In the parasympathetic division, effector organs have what type of receptor?
muscarinic receptors only
In the sympathetic division, effector organs have what type of receptor?
- 4 adrenoreceptors (alpha1, alpha2, beta1, and beta2)
- muscarinic receptors
Because there is more than one receptor type in the sympathetic division, what does the receptor type depend on?
function
What do alpha1 and alpha2 receptors cause?
contraction of smooth muscle such as vascular smooth muscle, GI and bladder sphincters, pilomotor muscles, and the radial muscles of the iris
What are beta1 receptors involved in?
metabolic functions such as glucogenesis, lipolysis, renin secretion, and all functions in the heart
What doe beta2 receptors cause?
relaxation of smooth muscle in bronchioles, wall of the bladder and wall of the GI tract
What center of the hypothalamus is responsible for temperature regulation, thirst, food intake, and micturition?
the midbrain
What center of the hypothalamus is considered the pneumotaxic center?
the pons
What center of the hypothalamus is responsible for breathing, cardiovascular function, swallowing, coughing, and vomiting?
the medulla
Describe the difference between beta1 receptors in the SA node and ventricular muscle
The beta1 receptor in the SA node is coupled to mechanisms that increase the spontaneous rate of depolarization and increase heart rate
- binding of an agonist such as norepinephrine to this B1 receptor increases the heart rate
The beta1 receptor in ventricular muscle is coupled to mechanisms that increase intracellular Ca2+ concentration and contractility
- binding of an agonist such as norepinephrine to this B1 receptor increases contractility, but does has no direct effect on the HR
Drugs that are B1 agonists are expected to cause _____ HR and contractility
increased
Drugs that are B1 antagonists are expected to cause _____ HR and contractility
decreased
Agonists _____ their receptors and antagonists _____ their receptors
activate
block
What are G-protein-linked receptors?
Autonomic receptors that are coupled to GTP-binding proteins (G proteins)
Describe the structure G-protein-linked receptors
They are composed of a single polypeptide chain that winds back and forth across the cell membrane 7 times.
What do the 2 ends of the
The ligand binds to the extracellular domain of its G-protein linked receptor. The intracellular domain of the receptor binds to a G protein
G proteins are heterotrimeric , meaning that have 3 different subunits, what are these subunits?
- α
- β
- γ
What does the α subunit of a G protein bind to?
Either guanosine diphosphate (GDP) or guanosine triphosphate (GTP)
What a G protein is bound to guanosine triphosphate (GTP) it is in its _____ state. When it is bound to guanosine diphosphate (GDP) it is in its ______ state.
active
inactive
Activated G proteins activate enzymes (e.g. adenylyl cyclase, phospholipase C) that produce what?
A second messenger (e.g. cyclic adenosine monophosphate [cAMP] or inositol triphosphate [IP3]) that amplifies the message and executes the final physiological action
In some cases can a G protein directly alter the function of an ion channel without the mediation of a second messenger?
Yes
Where are adrenoreceptors found?
In target tissue of the sympathetic nervous system
What 2 hormones activate adrenoreceptors?
norepinephrine and epinephrine
What are the 2 types of adrenoreceptors and the 4 subtypes?
α and β
- α1 - α2 - β1 - β2
Where are α1 receptors found?
In vascular smooth muscle of the skin, skeletal muscle, and the splanchnic region, in the sphincters of the GI tract and bladder, and in the radial muscle of the iris
Activation of α1 receptors leads to what?
The contraction of the tissues in which it is found
Describe the mechanism of action of α1 adrenoreceptors
IP3 is catalyzed and causes a release of Ca2+ from intracellular stores in the endoplasmic reticulum
Where are α2 receptors found?
On presynaptic adrenergic and cholinergic nerve terminals and in the GI tract
Describe the mechanism of action of α2 adrenoreceptors
They inhibit adenylyl cyclase which results in cAMP levels decreasing
Where are β1 receptors found?
In the heart, salivary glands, adipose tissue, and in the kidneys
When β1 are activated in the SA node what happens?
heart rate increase
When β1 are activated in ventricular muscle what happens?
contractility increases
When β1 are activated in the salivary gland what happens?
secretion increases
When β1 are activated in in the kidney what happens?
renin is secreted
Where are β2 receptors found?
In the vascular smooth muscle of skeletal muscle, in the walls of the GI tract and bladder, and in the bronchioles
Activation of β2 receptors leads to what?
Relaxation or dilation of the tissues in which they are found
Describe the mechanism of action of β1 and β2 adrenoreceptors
They activate the stimulation of adenylyl cyclase which results in the increase of cAMP levels
_______ is the primary catecholamine released from postganglionic sympathetic adrenergic nerve fibers
Norepinephrine
_______ is the primary catecholamine released from the adrenal medulla
Epinephrine
Where are nicotinic receptors found?
- on the motor end plate of skeletal muscle
- on all postganglionic neurons of both sympathetic and parasympathetic nervous systems
- on the chromaffin cells of the adrenal medulla
Describe the mechanism of action of nicotinic receptors
When rhw nicotinic receptor is activated by ACh, then channel opens and both Na+ and K+ flow through the channel leading to depolarization
Where are muscarinic receptors found?
- In all effector organs of the parasympathetic nervous system heart, GI tract, bronchioles, bladder, and male sex organs)
- In the sweat glands of the sympathetic nervous system
Describe the mechanism of action of muscarinic receptors
IP3 is generated which causes a release of Ca2+ from intracellular stores
