Pharmacology: Pharmacology: The Autonomic Nervous System Flashcards

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Endocrine System

Sends signals to target tissues by varying the levels of bloodborne hormones


Nervous System

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Exert its influence by the rapid transmission of electrical impulses over nerve fibers that terminate at effector cells


Effector cells

respond to the release of neuromediator substances.


What are autonomic drugs

Drugs that produce their primary therapeutic effects by mimicking or altering the function of the autonomic nervous system.

Either stimulate ANS or Block ANS


Nervous system is divided into how many anatomical divisions?

2; CNS (Central Nervous System) & PNS (Peripheral Nervous System)


What is the CNS

Composed of brain and spinal cords


What is the PNS

Its subdivided into:

efferent division- neurons of which carry signals away from brain and spinal cord of peripheral tissues

afferent- bring information from peripheral to CNS
It provides sensory imput to modulate function of efferent division through reflex arcs, or neural pathways that mediate a reflex action


Efferent portion of PNS is divided into 2 major functional subdivisions. What are they?

Somatic & Autonomic System


What is the Somatic system

thee somatic efferent neurons are involved in voluntary control of functions such as contraction of skeletal muscles essential for locomotion


What is the Autonomic system

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regulates everyday requirements of vital bodily functions without the conscious participation of the mind


Because of the involuntary nature of the ANS, as well as its function, its also known as?

Visceral, Vegetative, or Involuntary Nervous System


ANS is composed of?

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efferent neurons that innervate smooth muscle of the viscera, cardiac muscle, vasculature, and the exocrine glands; controlling digestion, cardiac output, blood flow, and glandular secretions


Anatomy of the ANS:
What are Efferent Neurons

ANS carries nerve impulses fromt he CNS to effector organs by 2 types of efferent neurons:
Preganglionic & Postganglionic


What are Preganglionic neurons?

Cell body located within CNS
Emerge from brainstem (spinal cord) and make a synaptic connection in ganglia (collection of nerve cell bodies located in PNS)


What are the functions of the ganglia

its a relay station between a preganglionic neuron and second nerve cell called Postganglionic
Collection of nerve cell bodies located in PNS)


What are Postganglionic neurons?

Cell body originating in Ganglion
Nonmyelinated & terminates on effector organs; ex. smooth muscles of viscera, cardiac muscle and exocrine glands


Anatomy of the ANS:
What are Afferent Neurons

They are important in the reflex regulation.
Ex: Sensing pressure in carotid sinus and aortic arch

Signals CNS to influence the efferent branch of the system to respond


Efferent ANS is divided into what 3 Nervous systems?



Anatomy of the Efferent ANS:
Sympathetic Neurons

Originate in CNS and emerge from 2 different spinal cord regions

Pregangionic neurons (short in comparison to Post) of Sympathetic system come from the thoracic & Lumbar region (T1-L2)

Synapse into 3 cord like chains of ganglia that run close to and in parallel on each side of the spinal cord.

Post gangionic nuerons extend from ganglia to tissues that innervate and regulate


Anatomy of the Efferent ANS:
The Sympathetic nervous system is also called the?

Thoracolumbar division (because of its location)


Anatomy of the Efferent ANS:
Describe the Preganglionic nerves ending of SNS

highly branched, enabling one pregangionic neuron to interact with many postganglionic neurons

Enables to activate numerous effector organs at the same time

(Adrenal medulla): receive preganglionic fibers from Sympathetic.

The adrenal medulla, in response to stimulation by ganglionic neurotransmitter acetylcholine, influences other organs by secreting the hormone epinphrine

lesser amounts of norepinpherine into the blood

Adrenal Medulla --> acetylcholine ---> epinephrine


Anatomy of the PNS:
Parasympathetic Neurons; where do they arise?

Arise from Cranial nerves:

III- oculomotor
VI- Facial
IX- Glossopharyngeal
X- Vagus
Sacral region (S2-S4)
Synapse in ganglia near or on the effector organ


Anatomy of the PNS:
Parasympathetic Neurons; Vagus Nerves

Accounts of 90% of preganglionic parasympathetic fibers in the body

Postgangionic from Vagus innervate most organs in thoracic & Abdominal Cavity


Anatomy of the Efferent ANS:
The Parasympathetic nervous system is also called the?

Craniosacral Division

Preganglionic fibers are longer and post gangionic are short with the ganglia close to or within the organ innervate


So Difference between Parasympathetic and Sympathetic Pre & Post ganglionic nerves?

Sympathetic: Pre = Short
Post = Longer as it extend from
ganglia to tissues that innervate and

Para: Pre = Long
Post = Short with ganglia close to or
within organ innervate


Anatomy of the PNS:
Enteric Neurons

3rd division of ANS

Collection of nerve fibers that innervate the GI tract, pancreas, & gallbladder

"Brain of the gut"


Anatomy of the PNS:
Enteric Neurons function

functions independently of CNS & controls motility, exocrine and endocrine secretions, and microcirculation of GI tract.

Modulated (adapted) by both sympathetic & parasympathetic


Function of SNS

Adjust in response to stressful situation; fear, trauma, hypoglycemia, cold, & exercise


Sympathetic actions of SNS

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Eye: Contract of Iris radial muscle (Pupil dilates)

Trachea & Bronchioles: Dilation

Adrenal Medulla: Secrete epinepherine & norepinephrine

Kidney: secrete renin (Beta increases Alpha decreases)

Ureters & Bladder: Relaxation of detrusor
Contract Trigone & Sphincter

Genitalia: Stimulate ejaculation

Salivary Glands: Thick, viscous secretion

Heart: Increase rate; increase contractility

GI: Decreased muscle motility and tone; contraction of sphincter

Genitalia (Female): Relax of uterus

Blood Vessel (Skeletal muscle): Dilation

Blood Vessels (Skin, mucous membranes, and splanchnic area): Constrict


Parasympathetic action of SNS

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Eye: Contraction of Iris sphincter muscle (pupil contract) Contract of ciliary muscle (lens accomodate for near vision)

Trachea & Bronchioles: Constriction, increased secretions

Ureters & Bladder: Contraction of detrusor; relaxation of trigon sphincters

Genitalia (Male): Stimulate erection

Lacrimal Glands: Stimulate tears

Salivary glands: Copious, watery secretion

Heart: Decrease rate; decrease contractility

Gastrointestinal: Increase muscle motor & Tone:


Different Stimulations of Sympathetic & Parasympathetic

Sympathetic: "Fight or Flight" with sympathetic output (diffuses because postganglionic neurons may innervate more than one organ)

Parasympathetic: "Rest & Digest Stimulus" with parasympathetic output (discrete because postganglionic neurons are not branched, but are directed to a specific organ



Effects of stimulation of the sympathetic division

Output = increase HR & BP
mobilize energy stores of the body

increase blood flow to skeletal
muscles & heart while diverting
flow from skin & internal organs


Symapthetic "Flight or Flight"

Changes experienced by the body during emergencies:

triggered: direct sympathetic activation of effector by stimulation of adrenal medulla to release epinephrine & less norepinephrine

Function as a unit & often discharges as complete system; (ex. severe exercise/increase reaction to fear)

Helps body handle uncertain situations and unexpected stimuli

not essential for survival



stimulation of the parasympathetic division

Maintains homeostasis of body
maintains essential bodily functions; digestive process and elimination of wastes

required for life

acts to OPPOSE or balance actions of sympathetic division and is DOMINATE over sympathetic in "rest & digest situations"

not a functional entity and never discharges as a complete system. If did, massive, undesirable, and unpleasant symptoms (ex; involuntary urination & defecation

activated SEPARATE and system functions to affect specific organs; stomach or eye


Role of CNS in control of autonomic functions

does not require sensory input from peripheral structures to provide info on state of affairs in body

feedbacks are from afferent impulses, originating in viscera & other autonomic innervates that travel to CNS (hypothalamus, medulla oblongata, and spinal cord)

sends Efferent reflex impulses via Autonomic nervous system


Role of CNS: Reflex arcs

most afferent impulses are translated into reflex response w/o involving consciousness

Ex: Fall in blood pressure causes pressure-sensitive neurons (baroreceptors in heart, vena cava, aortic arch, and carotid sinus) to send fewer impulses to cardiovascular center in brain
It prompts a reflex response of icnrease sympathetic output to heart and vasculature and decrease parasympathetic output to the heart, results in rise in BP and tachcardia

Ex: An example would be a pinprick of the finger. The reflex arcs consist of an afferent (sensory) arm and an efferent (motor) arm


Emotions from ANS

Stimuli evokes strong feelings; rage, fear, pleasure, and can modify the activities of ANS


Innervations by ANS

Dual: most innervated by both divisions of ANS
Ex: Vagal parasympathetic = slows heart rate
Vagal Sympathetic = increase heart rate

one system usually predominates in controlling the activity of a given organ
Ex: heart, the vagus nerve is predominant factor for controlling rate


What organs ONLY receive sympathetic innervation?

adrenal medulla
pilomotor muscle
sweat glands


Somatic Nervous system

efferent somatic nervous system difference from autonomic in that single myelinated motor neuron from cns travels directly to skeletal w.o mediation of ganglia

Somatic nervous system is under voluntary control.
Autonomic nervous system is under involuntary control

Response in somatic are generally faster than ANS


Summary of differences between Sympathetic & Parasympathetic

Sympathetic Parasympathetic
widely distributed limited distrib
innervate all effectors circumscribed (1-1
broader influence interaction
synapse large number of anatomical arrangement
postganglionic fibers


Somatic Nervous system innervates:

skeletal muscles.
one somatic motor neuron axon is highly branched
each branch innervates a single muscle fiber (1 may intervate 100)
leads to formation of motor unit
when lack of ganglia and myelination of motor nerves, somatic nervous system enables a fast response


What are some Chemical Signalling between cells

Nuerotransmission in ANS
local Mediators


Chemical Signalling between cells

Specialized endocrine cells secrete hormones into bloodstream where they travel throughout body

exert effects to target cells in body


Chemical Signalling between cells
Local Mediators

most cells secrete chemicals that act locally; on cells in their immediate environment

these chemical signals are rapidly destroyed or removed, they do not enter blood and are not distributed throughout body

Histamine & Prostiglandins



Distinct anatomic units with no structual continuity

communications between nerve cells and effector organs occur through release of specific chemical signals


How is release of neurotransmitters triggered?

Release of neurotransmitters is triggered by arrival of the action potential which
leads to depolarization.

An increase in calcium ion leads to fusion of synaptic vesicles with presynaptic membranes that release their content

It Rapidly defuses across cleft or space (synapse) moving cleft and expel neurotransmitters which
combine with specific receptors on postsynaptic


Membrane receptors of Nuerotransmitters

too hydrophilic to penetrate the lipid bilayers of target cell plasma membranes
signal than is mediated by binding to specific receptors on the cells surface of a target organ


what are the types of neurotransmitters (6)

gama aminobutyric acid (GABA)


What 2 neurotransmitters are the primary chemical signals in ANS?

Acetylcholine & Norepinephrine


What are the neurotransmitters that are primary chemical signals of the CNS

gama aminobutyric acid (GABA)



ANS fibers can be divided into 2 groups based on chemical nature of neurotransmitter released

Its a ganglionic transmitter

If transmission by acetylcholine, the neuron is cholinergic

Cholinergic – autonomic nerve fibers which
transmission is mediated by acetylcholine. It mediates transmission of nerve impulses across autonomic ganglia in both sympathetic and
parasympathetic nervous systems


Acetylcholine continued

is the neurotransmitter for Adrenal medulla

Transmission from autonomic
postganglionic nerves to effector organs via

Somatic nervous system is cholinergic


Norepinephrine & Epinephrine

when transmitted its adrenergic (another name for epinephrine)
Sympathetic system- norepinephrine mediates nerve impulses from autonomic postganglionic nerves to effector organs


Transmitters and Receptors:
Sympathetic innervation of adrenal medulla

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Preganglionic transmitter: Acetylcholine

Ganglionic transmitter: Acetylcholine

Ganglionic receptor: Nicotrinic

Postganglionic transmission: Epinephrine
& Norepinephrine released in blood

Receptors in Postganglionic
Effector Organ: Adrenergic receptors


Transmitters and Receptors:
Sympathetic Nervous System

Preganglionic transmitter: Acetylcholine

Ganglionic transmitter: Acetylcholine

Ganglionic receptor: Nicotrinic

Postganglionic transmission: Norepinephrine

Receptors in Postganglionic
Effector Organ: Adrenergic receptors


Transmitters and Receptors:
Parasympathetic Nervous System

Preganglionic transmitter: Acetylcholine

Ganglionic transmitter: Acetylcholine

Ganglionic receptor: Nicotrinic

Postganglionic transmission: Acetylcholine

Receptors in Postganglionic
Effector Organ:
Muscarinic or Nicotinic receptors


Transmitters and Receptors:
Somatic Nervous System

No Ganglia

Acetylcholine dominated

Receptors in Postganglionic Effector Organ
Nicotinic receptor in striated muscle


All preganglionic fibers of the autonomic nervous system use the neurotransmitter ______________.



The major neurotransmitter for sympathetic
postganglionic fibers is __________________.



Stimulation of sympathetic innervation to the eye causes contraction of the ____________ muscle and, therefore, __________ of the pupil



The rate-limiting step in the synthesis of norepinephrine is ___________.

formation of DOPA by tyrosine b-hydroxylase


The major pathway for the termination of the action of norepinephrine is ______________

Its reuptake


The actions of acetylcholine released from parasympathetic fibers in viscera are mediated by _______ receptors.



Adrenergic receptors in the heart are predominantly

beta 1


Stimulation of alpha 1 receptors causes predominantly ____________ of blood vessels.



Stimulation of the sympathetic nervous system causes ___________ in gluconeogenesis and glycogenolysis.

An increase


Stimulation of the b2
receptor in the pregnant uterus causes ______________ of the smooth muscle.



Baroreceptors maintain what?

Baroreceptors maintain normal blood pressure
by influencing SN and/or PSN