Autonomic responses are coordinated with one another and with behavioral responses and emotions through the hypothalamus in the CNS.
between somatic motor neuron and ANS.
Autonomicfunctions are involuntaryFirst and second order axonsSynapse outside CNSEffectors include cardiac, smooth muscles and glands.
A nerve impulse in the ANS has to travel in along two(2) neurons in series to get from the CNS to effector.
muscarinetoxic alkaloid: a toxic substance, found in fly agaric and some other fungi, that affects the nervous system when ingested. Among other effects it dilates the blood vessels, slows the heart rate, constricts the airways, and stimulates the gut.
Splanchnic: intestinal: relating to the intestines (technical).
Autonomic nervous system
Chapter 4: physiology
Autonomic Nervous System
Out line presentation
Division of ANS
Sympathetic nervous system
Parasympathetic nervous system.
3. Adrenal medulla
4. Neurotransmitters and Receptors in ANS
The human internal environments is regulated in
large measure by the:
Endocrine glands and
N.B. Integrated activities of these two systems
The subdivision of the Peripheral NS that regulates body
activities independently (autonomously) and continuously
without conscious effort.
Smooth muscle, Cardiac muscle
Glands (eg, sweat glands, salivary glands)
mediates visceral reflex responses that are involuntary
and largely unconscious.
Although survival is possible without an ANS, the
ability to adapt to environmental stressors and other
challenges is severely compromised.
The ANS affects the following:
Heart rate, Respiration rate
Diameter of the pupils
Basic difference ANS VS SNS
operates under our conscious (voluntary) control.
Cell bodies of motor neurons reside in CNS
One motor neuron extends from the CNS to skeletal
Axons are well myelinated, conduct impulses rapidly.
chains of two motor neurons
1st = preganglionic neuron (in brain or spinal cord)
2nd = ganglionic neuron (cell body in ganglion
outside CNS) .
Slower because lightly or unmyelinated.
functions are involuntary
Preganglionic neurons :
the first neuron and its cell bodies in CNS
The second neuron
its cell bodies in the autonomic ganglion
The nerve impulse transmitted from pre-to-post ganglion
occur via Acetyl choline (ACH).
Ganglion: the collection of nerve cell bodies in the
peripheral nervous system.
Nuclei : collection of nerve cell bodies in CNS.
Divisions of Autonomic Nervous System
The ANS has two major divisions: the sympathetic and
parasympathetic nervous systems.
Sympathetic division (speeds up)
Prepares body for ‘fight or flight’ situations
Parasympathetic division (slows down)
Prepares body for ‘resting and digesting’ activities.
some target organs are innervated by both divisions
(Dual innervation), Opposing effects on the same
others are controlled by only one.
It has also Enteric division and has role in digestive
You come across a gangster with sharp materials @Gcmhs
campus at 8:00 pm on your walk to GCMHs library
………… what happens ???
Size of pupil
Bronchiole smooth muscle
Sympathetic nervous system
mobilization & increased metabolism “fight, flight or
Involves in activities of exercise, excitement,
emergency, and embarrassment.
Non-essential activities are dampened (GI/urinary).
Promotes adjustments during exercise – blood flow to
organs is reduced, flow to muscles is increased
Its activity is illustrated by a person who is threatened
HR increase and breathing is rapid and deep.
The skin is cold and sweaty, and the pupils dilate.
Bronchioles dilate which increasing
ventilation, delivering more oxygen to cells.
Constriction of visceral & cutaneous blood vessels
(blood is shunted to skeletal muscle ).
Liver releases more glucose into blood to provide
more readily avail energy
Targets adipocytes for lipolysis.
Issues from T1-L2 ( thoraco lumbar division )
Preganglionic fibers form the lateral gray horn.
Supplies visceral organs and structures of superficial body
Contains more ganglia than the parasympathetic division
Supplies the visceral structure in the head, neck and
face via the oculomotor, facial and glossophryngeal
Thorax and upper abdomen via vagus nerves.
Supplies pelvic organ via the pelvic branches of the
second to fourth sacral spinal nerves.
Preganglionic fibers run via:
Facial nerve (VII)
Glossopharyngeal nerve (IX)
Oculomotor nerve (III)
Vagus nerve (X)
Cell bodies located in cranial nerve nuclei in the brain
Ciliary muscle, accommodation for near vision
Pupillary constrictor of iris(sphincter), miosis
(contraction of pupil).
Submandibular and sublingual glands via
Lacrimal gland via Pterygopalatine ganglion .
Glands of nasal cavity, mouth, and palate
Parotid gland via otic ganglion
Outflow via the Vagus Nerve (X)
Fibers innervate visceral organs of the thorax and most of the
Stimulates - digestion, reduction in heart rate and blood pressure.
Preganglionic cell bodies
Located in dorsal motor nucleus in the medulla.
Confined within the walls of organs being innervated.
Emerges from S2-S4
Innervates organs of the pelvis and lower abdomen
Preganglionic cell bodies
Located in visceral motor region of spinal gray matter.
Form pelvic splanchnic nerves.
SNS VS PNS
2. Short preganglionic and long 2. Long preganglionic and short
post ganglionic neurons.
3. Sympathetic axons – highly
branched , Influences many
4. Location of Ganglia: Close to
3. Parasympathetic axons – few
branches , Localized effect.
4. Location of ganglia: In the
visceral effector organs
the spinal cord
SNS VS PNS cont’d…
Neurotransmitter released by preganglionic axons
Acetylcholine for both branches (cholinergic)
Neurotransmitter released by postganglionic axons
Sympathetic – most release norepinephrine (adrenergic).
Parasympathetic – release acetylcholine .
Neurotransmitters & Receptors in ANS
chemical messengers produced by the cell bodies of
neuron and have role in communication between neurons
and neuron, muscle coordination.
Neurotransmitters are released by the presynaptic cell.
Bind to specific receptors in the postsynaptic cell
Binding has either an excitatory or an inhibitory effect on
the effector, depending on the specific receptor.
Acethylcholine(ACh) and Norepinephrine( NE) are the
major neurotransmitters in autonomic nervous system.
Both the preganglionic and postganglionic axons in the
parasympathetic division release acetylcholine and thus
are called Cholinergic.
The preganglionic axon and a few postganglionic axons
in the sympathetic division are also cholinergic(blood
vessels of skeletal muscle and sweat gland).
C. Most of the postganglionic axons of the sympathetic
division release Norepinephrine and are called
D. The postganglionic chromaffin cells at the adrenal
medulla secrete Adrenaline(epinephrine).
ALL parasympathetic postganglionic neurons
ALL preganglionic neurons
Blood vessels of muscle and sweat gland.
ACH is rapidly hydrolyzed by a membrane-associated
Acetylcholinesterase in the synaptic cleft.
Effects are short and localized.
A. Cholinergic Receptors:
Receptor for Ach.
classified as nicotinic, muscarinic.
Muscarinic (M): at the target organ named after activation
by Muscarine (poison of Amanita muscaria).
Hetrotrimeric G protein-coupled
CNS, gastric mucosa: M1
Glandular/Smooth muscle: M3
The effect of ACh binding:
Can be either inhibitory or excitatory.
Depends on the receptor type of the target organ
Nicotinic (N) receptors
All ganglionic neurons of both sympathetic and
At the neuromuscular junction
The hormone-producing cells of the adrenal medulla
The effect of ACh binding to nicotinic receptors is always
named after activation by Nicotine.
The effect of ACh binding to nicotinic receptors is
always stimulatory (excitatory ).
Stimulation of muscarinic receptors produces a longer
lasting effect than does stimulation of nicotinic
The effects produced by the PS division center on
relaxation, food processing and energy absorption.
B. Adrenergic receptors: respond to norepinephrine/epinephrine
Subdivided in to α and β.
α Adrenergic receptors
α receptors are located postsynaptically at sympathetic
neuroeffector junctions of many organs.
In general, alpha receptors mediate excitation or increased
activity of the effector cells.
Vascular smooth muscle is an important site of alpha
They are subdivided into two types:
Located in the vascular smooth muscle of the skin and
splanchnic regions, the gastro intestinal(GI) and bladder
sphincters, and the radial muscle of the iris.
Produce excitation( e. g. contraction or constriction).
Are located in presynaptic nerve
terminals, platelets, fat cells and pancreatic islets.
inhibition of norepinephrine release and of insulin
Often produce inhibition ( e. g. relaxation or
β adrenergic receptors
are also located postsynaptically at sympathetic
neuroeffector junctions of many organs.
In general, beta receptors mediate relaxation or
Decreased activity of the effector cells. Thus, Blood
vessels dilate and Uterine smooth muscle relaxes in
response to activation of beta receptors.
A notable exception – NE binding to receptors of the heart
There are three known types of beta receptor, designated
β1, β2 and β3.
β1-Adrenergic receptors : are located mainly in the heart.
Produce excitation ( e. g. increased HR, increased
conduction velocity, increased contractility).
β2-Adrenergic receptors: are located on the vascular
smooth muscle of skeletal muscle, bronchial smooth
muscle, and in the wall of GI tracts and bladder.
Produce relaxation( e.g. dilation of vascular smooth
muscle, dilation of bronchioles, relaxation of the bladder
β3- adrenergic Receptors are located in fat cells.
Alpha receptor activation leads to smooth muscle
Activation of beta 1 leads to smooth muscle
contraction(especially in heart).
Activation of beta 2 receptors lead to smooth muscle
of viscera receive nerve fibers
parasympathetic and sympathetic divisions.
Both divisions do not normally innervate an organ equally.
oppose each other
Exerted through dual innervation of same effector
Heart rate decreases (parasympathetic)
Heart rate increases (sympathetic)
Exerted because each division innervates different cells
pupillary dilator muscle (sympathetic) dilates pupil
constrictor pupillae (parasympathetic) constricts pupil
Cooperative effects seen when 2 divisions act on different
effectors to produce a unified effect
parasympathetics increase salivary serous cell secretion
sympathetics increase salivary mucous cell secretion
ANS cooperation is best seen in control of the external
responsible for erection of the penis and clitoris.
Sympathetic fibers cause ejaculation of semen in males and
reflex peristalsis in females
Some effectors receive only sympathetic
adrenal medulla, arrector pili muscles, sweat glands and
many blood vessels.
Widespread, found in most
Inhibition of effector cell
Heart, kidneys, liver, adipose
Stimulation, increased energy
Smooth muscle in vessels of
heart and skeletal muscle;
smooth muscle layers in the
intestines, lungs, and bronchi
Inhibition of neurotransmitter
All autonomic synapses between
preganglionic and ganglionic
junctions of the SNS
Adrenergic and Cholinergic Receptors of the ANS
Describe the main functions of ANS.
Distinguish the division of the ANS
Appreciate the difference between the sympathetic
nervous and parasympathetic nervous system.
Identify the neurotransmitters and its receptors in ANS.
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