Ch. 16: Review of Neurotransmitters and the Autonomic Nervous System

What are some effects of the parasympathetic nervous system?

- constricts pupil - stimulates salivation - slows heart - constricts breathing - stimulates digestion - stimulates gallbladder - contracts bladder - stimulates sex organs

What are some effects of the sympathetic nervous system?

- dilates pupils - inhibits salivation - accelerates heart - facilitates breathing - inhibits digestions - stimulates release of glucose - secretes epinephrine and norepinephrine - relaxes bladder - inhibits sex oragans

What are the functions of the nervous system?

- monitor the internal and external environment of the body and alert the brain of important changes - process and integrate the environmental changes that are perceived and determine an appropriate response - response to the environmental changes as needed by producing an action or response

How do autonomic drugs exert their effects?

1) By acting at synapses - some meds are identical to endogenous neurotransmitters and are able to directly activate a gland or muscle - others are used to stimulate or block the actions of natural neurotransmitters 2) By acting at the ganglia 3) By acting at the neuroeffector junction of the target organs

What are the four possible actions of ANS Drugs?

1) Stimulation of sympathetic nervous system - sympathomimetics - adrenergic-agonists 2) Stimulation of parasympathetic nervous system - parasympathomimetics - muscarinic agonists 3) inhibition of sympathetic nervous system - adrenergic antagonists or blockers 4) inhibition of parasympathetic nervous system - anticholinergics - parasympatholytics - muscarinic blockers

What are the two types of adrenergic receptors?

1) alpha: A1 and A2 2) beta: B1 and B2

structure and function of the ANS

1) contraction of smooth muscle of the bronchi, blood vessels, GI tract, eye, and GU tract 2) contraction of cardiac muscle 3) secretion of salivary, sweat, gastric, and bronchial glands

What are the 5 general mechanisms by which drugs affect synaptic transmission in the ANS?

1) medications may affect the SYNTHESIS of neurotransmitter in the preganglionic nerve 2) medications can prevent STORAGE of the neurotransmitter in vesicles within the preganglionic nerve 3) medications can influence RELEASE of the neurotransmitter from the preganglionic nerve 4) medications can bind to the NEUROTRANSMITTER RECEPTOR site on the postganglionic cell 5) medications can PREVENT THE DESTRUCTION OR REUPTAKE of the neurotransmitter

What are the two types of cholinergic receptors that bind Ach?

1) nicotinic 2) muscarinic

What is the PNS divided into?

1) somatic 2) autonomic - neurons in the peripheral nervous system either recognize changes to the environment (sensory) or respond to those changes by moving muscles or secreting chemicals (motor division)

What is the ANS divided into?

1) sympathetic 2) parasympathetic

What are the steps of synaptic transmission across the neuroeffector junction?

1) synthesis of the neurotransmitter: two primary neurotransmitters of ANS are norepinephrine (NE) and acetylcholine (Ach) 2) storage of neurotransmitter 3) release of neurotransmitter 4) binding to receptor: the more neurotransmitter released into the synapse the greater and longer lasting the response 5) termination of neurotransmitter action

alpha-adrenergic receptors

A1: excitatory effects A2: inhibitory effects

cholinergic transmission

Ach is the neurotransmitter released at cholinergic receptors, which may be nicotinic or muscarinic

beta-adrenergic receptors

B1: acts on heart and coronary vessels B2: act on smooth muscle in blood vessels, GI tract and lung

Why does activation of the sympathetic division produce longer lasting effects than those of parasympathetic activation?

Because NE acts indirectly through a second messenger mechanism. It's effects are produced more slowly than Ach, which acts directly at cholinergic sites. Additionally, the primary means of inactivation of NE is through reuptake, which is a slower process than the direct enzymatic destruction of Ach

Why is the conduction of AP in the ANS slower than in the somatic nervous system?

Because somatic nerves are myelinated and have no ganglia, impulses more quickly reach their target tissues

What happens after reuptake of NE?

NE is repackaged in vesicles for future use or destroyed enzymatically by MAO

synaptic transmission

allows information to be communicated between two nerves or from nerves to muscles or glands

synapse

a junction between two neurons or a neuron and a muscle; must be crossed before a message can be transferred

What is pseudocholinesterase?

a plasma cholinesterase (another enzyme that destroys Ach); found primarily in the liver

What is the adrenal medulla?

a specialized type of sympathetic nervous system tissue that secretes epinephrine an NE - preganglionic neurons from the spinal cord terminate in the adrenal medulla and release epinephrine and NE directly into the blood - these agents are distributed to target organs and elicit fight or flight symptoms - produces more diffuse and longer lasting effects than those produced by activation of sympathetic neurons in ANS

What is the neurotransmitter released at cholinergic receptors?

acetylcholine (Ach)

Why are dopaminergic receptors important?

action of certain antipsychotic medicines and in treatment of Parkinson's disease

How are autonomic drugs classified?

by which receptors they stimulate or block

fight-or-flight response

characteristic set of actions produced when the sympathetic nervous system is activated that prepares the body for heightened activity and for an immediate response to a threat

neurotransmitters

chemicals utilized in the communication of a message from one cell to another, or synaptic transmission

What occurs after the breakdown of Ach?

choline is re-formed and is taken up by the preganglionic neuron, where it is used to synthesize more Ach

catecholamines

class of endogenous hormones involved in neurotransmission that include epinephrine (adrenalin), norepinephrine (NE), and dopamine

ganglia

collection of neuron cell bodies located outside the central nervous system; contains neuron cell body of the postganglionic neuron, which is waiting to receive the action potential

What is biofeedback therapy?

controlling autonomic activity through conscious thought

catechol-O-methyltransferase

enzyme that destroys catecholamines such as NE in kidney and liver cells

monoamine oxidase (MAO)

enzyme that destroys catecholamines such as norepinephrine in the nerve terminal

acetylcholinesterase (AchE)

enzyme that resides in the synaptic cleft and catalyzes the destruction of Ach (breaks it down into acetate and choline)

What is the main integration center of the ANS?

hypothalamus - receives signals from the cerebrum and sensory input - interprets the info and responds by sending messages to various portions of ANS - messages travel along the medulla oblongata, the brainstem, and the spinal cord

Where is NE synthesized?

nerve terminal

somatic nervous system

nerves that provide for voluntary control of the skeletal muscle

adrenergic transmission

norepinephrine is the primary neurotransmitter released at adrenergic receptors, which may be alpha or beta

What is the goal of "autonomic drugs?"

not given to correct physiological defects in the ANS but to stimulate or inhibit target organs or glands (i.e. heart, lungs, digestive tract)...it corrects disorders of target organs through its effects on autonomic nerves

Where are cholinergic receptors located?

on postganglionic or neuroeffector cell membranes - cholinergic receptors bind Ach and either continue the impulse (at the ganglia) or cause the autonomic action (at the neureffector organ)

regulation of autonomic functions

the ANS is influenced by higher levels of control in the cerebral cortex and hypothalamus

parasympathetic nervous system

portion of the autonomic nervous system that is activated during non stressful conditions and produces a set of symptoms known as the rest-and-digest response

sympathetic nervous system

portion of the autonomic nervous system that is activated under emergency conditions or stress and produces a set of actions called the fight-or-flight response

autonomic nervous system (ANS)

portion of the peripheral nervous system that provides for the involuntary control of vital functions of the cardiovascular, digestive, respiratory, and genitourinary systems

Where is Ach synthesized?

preganglionic nerve terminal

acetylcholine (Ach)

primary neurotransmitter of the autonomic nervous system

norepinephrine (NE)

primary neurtransmitter in the sympathetic and autonomic nervous systems

nicotinic

receptor for acetylcholine in the ganglia of both the sympathetic AND parasympathetic nervous systems - when Ach binds to nicotinic receptors, the action is always stimulatory

adrenergic

receptors at the ends of postganglionic sympathetic neurons

cholinergic

relating to neurons that release acetylcholine (Ach)

rest-and-digest response

signs and symptoms produced when the parasympathetic nervous system is activated that promote relaxation and maintenance activities

synaptic cleft

space where neurotransmitters enter that must be crossed for the impulse to reach the postganglionic neuron or organ

neuroeffector junction

specialized synapse where the postganglionic neuron terminates on smooth muscle, cardiac muscle, or a gland

Basic structure of the nervous system

subdivided into: 1) central nervous system (CNS): brain and spinal cord 2) peripheral nervous system (PNS): nerves that carry messages to and from the CNS

Where is Ach stored?

synaptic vesicles

autonomic tone

the background level of autonomic activity that occurs even in the absence of stimuli Ex: 1) sympathetic nerves are constantly firing, keeping arterioles in a constant state of constriction; this sympathetic tone allows for faster changes in BP b/c vessels are in a constant state of readiness 2) parasympathetic tone on the smooth muscle of the alimentary and urinary tracts maintains continuous contractions and keeps intestinal peristalsis and urine flow steady

termination of norepinephrine action

the majority of NE is taken back into the nerve terminal, a process known as reuptake

termination of acetylcholine action

to produce an immediate, transient response, Ach must be removed from the synaptic cleft after producing its effect

What is the basic unit the ANS?

two-neuron chain first neuron: preganglionic neuron, originates in CNS second neuron: ganglia

muscarinic

type of cholinergic receptor found at postganglionic nerve endings in the parasympathetic nervous system that, when activated, result in stimulation - may be stimulatory or inhibitory depending on target organ

Where is NE stored?

vesicles