THE AUTONOMIC THE AUTONOMIC NERVOUS SYSTEM (ANS)NERVOUS SYSTEM (ANS)

What is the autonomic What is the autonomic nervous system?nervous system?

The autonomic nervous system The autonomic nervous system (ANS) is the motor division of the (ANS) is the motor division of the

peripheral nervous system that peripheral nervous system that controls visceral activities, with the controls visceral activities, with the

goal of maintaining internal goal of maintaining internal homeostasis.homeostasis.

What does the autonomic What does the autonomic nervous system do?nervous system do?

It provides motor fibers to smooth and cardiac It provides motor fibers to smooth and cardiac muscles and glandsmuscles and glands

It operates subconsciouslyIt operates subconsciously

It causes excitation and inhibitionIt causes excitation and inhibition

It makes adjustments to support body activitiesIt makes adjustments to support body activities

It has an efferent pathway made up of a two-It has an efferent pathway made up of a two-neuron chain: preganglionic and ganglionicneuron chain: preganglionic and ganglionic

Two divisions of the ANSTwo divisions of the ANS

1) Parasympathetic division1) Parasympathetic division

2) Sympathetic2) Sympathetic

Although they have different roles, they Although they have different roles, they have effects on many of the same organs of have effects on many of the same organs of the bodythe body

Organs affected by both divisionsOrgans affected by both divisions

Roles of the two different Roles of the two different divisionsdivisions

1. 1. The parasympathetic division…The parasympathetic division…

_conserves body energy and maintains body _conserves body energy and maintains body activities at basal levelsactivities at basal levels

_is involved in digestion, diuresis, and _is involved in digestion, diuresis, and defecationdefecation

_causes heart rate and blood pressure to be _causes heart rate and blood pressure to be low, the skin to be warm and the pupils to low, the skin to be warm and the pupils to be constrictedbe constricted

2. 2. The sympathetic division…The sympathetic division…

_activates the body under conditions of emergency _activates the body under conditions of emergency which is why it is often called the “fight or flight which is why it is often called the “fight or flight system”system”

_is involved in emergency, exercise, and excitement_is involved in emergency, exercise, and excitement

_causes blood flow to organs to reduce and blood flow _causes blood flow to organs to reduce and blood flow to muscles to increaseto muscles to increase

_also causes skin to be cold, heart rate to increase, and _also causes skin to be cold, heart rate to increase, and rapid breathingrapid breathing

Parasympathetic division Parasympathetic division outflowoutflow

Neurons of the cranial and sacral Neurons of the cranial and sacral outflows of the parasympathetic outflows of the parasympathetic

division are located in the following division are located in the following nerves and create an effect on the nerves and create an effect on the

organs mentioned in the table below.organs mentioned in the table below.

Table of parasympathetic outflowTable of parasympathetic outflow

Cranial OutflowCranial Outflow Cranial NerveCranial Nerve Effector Organ(s)Effector Organ(s)

Occulomotor (III)Occulomotor (III) EyeEye

Facial (VII)Facial (VII) Salivary, nasal, and Salivary, nasal, and lacrimal glandslacrimal glands

Glosso-pharyngeal Glosso-pharyngeal (IX)(IX)

Parotid salivary glandsParotid salivary glands

Vagus (X)Vagus (X) Heart, lungs, and most Heart, lungs, and most visceral organsvisceral organs

Sacral OutflowSacral Outflow SS22-S-S44Large intestine, urinary Large intestine, urinary bladder, ureters, and bladder, ureters, and reproductive organsreproductive organs

Parasympathetic division outflowParasympathetic division outflow

Sympathetic division Sympathetic division outflowoutflow

Sympathetic division outflow is different from parasympathetic Sympathetic division outflow is different from parasympathetic division outflow because…division outflow because…

It arises from spinal cord segments TIt arises from spinal cord segments T11 through L through L22

Preganglionic fibers pass through the white rami Preganglionic fibers pass through the white rami communicantes and synapse in the chain (paravertebral) communicantes and synapse in the chain (paravertebral) gangliagangliaFibers from TFibers from T55-L-L22 form splanchnic nerves and synapse with form splanchnic nerves and synapse with collateral ganglia collateral ganglia Postganglionic fibers innervate the numerous organs of the Postganglionic fibers innervate the numerous organs of the bodybodySympathetic neurons produce the lateral horns of the spinal Sympathetic neurons produce the lateral horns of the spinal cordcord

Sympathetic division outflowSympathetic division outflow

ANS PhysiologyANS PhysiologyNeurotransmitters and Neurotransmitters and

ReceptorsReceptorsThe two major neurotransmitter involved in the ANS are:The two major neurotransmitter involved in the ANS are:

Acetylcholine (ACh)Acetylcholine (ACh)Norepinephrine (NE)Norepinephrine (NE)

ACh is the same neurotransmitter that is found in the somatic ACh is the same neurotransmitter that is found in the somatic motor neurons and is released in the ANS:motor neurons and is released in the ANS:

All ANS preganglionic axonsAll ANS preganglionic axonsAll parasympathetic postganglionic axons at synapses All parasympathetic postganglionic axons at synapses with their effectorswith their effectors

ACh releasing fibers are called Cholinergic FibersACh releasing fibers are called Cholinergic FibersNE is released by most sympathetic postganglionic axonsNE is released by most sympathetic postganglionic axonsNE releasing fibers are called Adrenergic FibersNE releasing fibers are called Adrenergic FibersThe effects of ACh and NE are either excitation or inhibition The effects of ACh and NE are either excitation or inhibition which is dependant on the receptor type allowing them to exert which is dependant on the receptor type allowing them to exert these different effects at different areas in the bodythese different effects at different areas in the body

ReceptorsReceptorsACh binds to two types of receptors:ACh binds to two types of receptors:

NicotinicNicotinicMuscarineMuscarine

Nicotinic Receptors are located on:Nicotinic Receptors are located on:Motor end plates of skeletal muscles (somatic targets)Motor end plates of skeletal muscles (somatic targets)All ganglionic neurons (sypathetic and parasympathetic)All ganglionic neurons (sypathetic and parasympathetic)The hormone-producing cells of the adrenal medullaThe hormone-producing cells of the adrenal medulla

ACh always produces a stimulatory effect when it binds with nicotinic ACh always produces a stimulatory effect when it binds with nicotinic receptorsreceptorsMuscarine Receptors occur on all effector cells stimulated by Muscarine Receptors occur on all effector cells stimulated by postganglionic cholinergic fibers (parasympathetic targets like the eccrine postganglionic cholinergic fibers (parasympathetic targets like the eccrine sweat glands and some blood vessels of skeletal muscle)sweat glands and some blood vessels of skeletal muscle)ACh binding produces a inhibitory or excitatory depending on the receptor ACh binding produces a inhibitory or excitatory depending on the receptor type of the target organ type of the target organ

ReceptorsReceptors

There are also receptors know as Adrenergic There are also receptors know as Adrenergic Receptors (two types):Receptors (two types):

Alpha with two subtypes (A1,A2)Alpha with two subtypes (A1,A2) Beta with three subtypes (B1,B2,B3)Beta with three subtypes (B1,B2,B3)

The general effects of NE binding are:The general effects of NE binding are: Alpha receptors are mostly stimulatoryAlpha receptors are mostly stimulatory Beta receptors are mostly inhibitoryBeta receptors are mostly inhibitory

However, an exception to this is when NE binds to However, an exception to this is when NE binds to the Beta receptors of cardiac muscle and the result is the Beta receptors of cardiac muscle and the result is stimulatory stimulatory

Overview of the location and Overview of the location and effects of receptor subclasseseffects of receptor subclasses

Drugs and the ANSDrugs and the ANS

Knowing the locations of the cholinergic and adrenergic Knowing the locations of the cholinergic and adrenergic receptors subtypes allows specific drugs to be prescribed receptors subtypes allows specific drugs to be prescribed to obtain the desired inhibitory or stimulatory effect on to obtain the desired inhibitory or stimulatory effect on selected organsselected organsAn example of this is Atropine (blocks parasympathetic An example of this is Atropine (blocks parasympathetic effects):effects):

administered during surgery to prevent salivation administered during surgery to prevent salivation and dry up respiratory secretionsand dry up respiratory secretionsOphthalmologists use it to dilate the pupils for an Ophthalmologists use it to dilate the pupils for an eye exameye exam

There are several examples of drugs in Table 14.4 that There are several examples of drugs in Table 14.4 that influence the Activity of the ANS on page 544influence the Activity of the ANS on page 544

Interactions of the Autonomic Interactions of the Autonomic DivisionsDivisions

Most visceral organs receive innervation by both Most visceral organs receive innervation by both sympathetic and parasympathtic fiberssympathetic and parasympathtic fibers

This dual innervation produces a dynamic This dual innervation produces a dynamic antagonism that allows visceral activity to be antagonism that allows visceral activity to be precisely controlledprecisely controlled

Sympathetic fibers increase heart and respiratory Sympathetic fibers increase heart and respiratory rates. They also inhibit digestion and eliminationrates. They also inhibit digestion and elimination

Parasympathetic fibers allow for digestion and Parasympathetic fibers allow for digestion and elimination and decrease respiratory and heart rates elimination and decrease respiratory and heart rates

Parasympathetic & Parasympathetic & SympatheticSympathetic

The parasympathetic division is know as the “resting and The parasympathetic division is know as the “resting and digesting” divisiondigesting” divisionThe sympathetic division controls blood pressure and The sympathetic division controls blood pressure and keeps the blood vessels in a continual state of partial keeps the blood vessels in a continual state of partial constrictionconstrictionFlight or Fright response – the sympathetic can override Flight or Fright response – the sympathetic can override the parasympathetic in an emergency to increase heart the parasympathetic in an emergency to increase heart and respiratory rates while inhibiting digestion.and respiratory rates while inhibiting digestion.Parasympathetic division restores the heart and Parasympathetic division restores the heart and respiratory rates back to resting levels when the respiratory rates back to resting levels when the emergency is over and then returns back to it’s functions emergency is over and then returns back to it’s functions of digestion and eliminationof digestion and elimination

Sympathetic ToneSympathetic Tone& Parasympathetic Tone& Parasympathetic Tone

The Sympathetic Tone:The Sympathetic Tone:Constricts blood vessels & controls blood pressure to rise in Constricts blood vessels & controls blood pressure to rise in response to the body’s needsresponse to the body’s needsPrompts vessels to dilate if blood pressure needs to be Prompts vessels to dilate if blood pressure needs to be decreaseddecreased

The Parasympathetic Tone:The Parasympathetic Tone:Slows the heartSlows the heartControls Digestion and EliminationControls Digestion and Elimination

ANS control is best seen in the external ANS control is best seen in the external genitalia:genitalia:

Parasympathetic fibers cause vasodilation resulting in the Parasympathetic fibers cause vasodilation resulting in the erection of the penis and clitoriserection of the penis and clitorisSympathetic fibers cause ejaculation of sperm and reflex Sympathetic fibers cause ejaculation of sperm and reflex peristalsis in femalesperistalsis in females

Sympathetic DivisionSympathetic Division

The adrenal medulla, sweat glands and the The adrenal medulla, sweat glands and the arrector pili muscles of the skin, the kidneys, and arrector pili muscles of the skin, the kidneys, and most blood vessels receive only sympathetic most blood vessels receive only sympathetic fibers.fibers.

The Sympathetic Division controls:The Sympathetic Division controls:

Thermoregulatory Responses to heatThermoregulatory Responses to heat

Release of Renin from the kidneysRelease of Renin from the kidneys

Metabolic Effects Metabolic Effects

Control of Autonomic Control of Autonomic FunctionsFunctions

Autonomic functions are controlled by several factors:Autonomic functions are controlled by several factors:1.1. Reflex Activities mediated by the Spinal Cord and Reflex Activities mediated by the Spinal Cord and

Brain Stem (Medullary Center)Brain Stem (Medullary Center)2.2. Hypothalamic integration centers interact with both Hypothalamic integration centers interact with both

higher and lower centers of autonomic, somatic, higher and lower centers of autonomic, somatic, and endocrine responseand endocrine response

3.3. Cortical centers influence autonomic functioning Cortical centers influence autonomic functioning via connections with the limbic system; conscious via connections with the limbic system; conscious controls are rare but maybe learned via biofeedback controls are rare but maybe learned via biofeedback trainingtraining