CH12 Review of Neurotransmitters and the Autonomic Nervous System

Components of the PNS (motor division)

1.) somatic nervous system 2.) autonomic nervous system (ANS) (p.137)

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 threat (p.138)

neurotransmitters

Chemicals utilized in the communication of a message from one cell to another, or synaptic transmission. (p.140)

norepinephrine (NE)

Primary neurotransmitter in the sympathetic and autonomic nervous systems (p.140)

acetylcholine (ACH)

Primary transmitter of the ANS. (one of 2) -Primary location: Synapses throughout the CNS; preganglionic neurons ending in the ganglia in both the symathetic and parasympathetic nercous systems (nicotonic); postganglionic neurons ending in neuroeffector target tissues in the parasympathetic nervous system (muscarinic) (p.140-142)

neuroeffector junction

Specialized synapse where the postganglionic neuron terminates on smooth muscle, cardiac muscle, or a gland (p.140)

Motor division of the PNS

carries nerve impulses from the CNS to muscles and glands. -contains the somatic and autonomic nervous system (ANS)

somatic nervous system

part of the motor division of the peripheral nervous system (PNS) that controls the voluntary movements of skeletal muscle. (p.138)

adrenal medulla

-The adrenal medulla is a specialized type of sympathetic nervous system tissue that secretes epinephrine and norephinephrine -Located in the inner portion of each adrenal gland

Classifying Autonomic Drugs

-Autonomic drugs are classified by which receptors they block -Autonomic drugs are classified based on one of four possible actions:

Norepinephrine (NE)

-Norepinephrine is the primary neurotransmitter released at adrenic receptors, which may be alpha or beta -In the sympathetic nervous system, NE is the neurotransmitter that is releasted at almost all postganglionic nerves. -NE belongs to a class called CATECHOLAMINES, all of which are involved in neurotransmission.

Termination of Acetylcholine Action

-The goal of nerve transmission is to produce an immediately, though transient, response. -To accomplish this, Ach must be rapidly removed from the synaptic cleft after producing its effect -The enzyme that resides in the synaptic cleft and catalyzes the destruction of Ach is called ACETYLCHOLINERASE (AchE). -It is estimated that over half the Ach molecules released from the vesicles are destroyed before they have a chance to reach their receptors. (p.144)

Termination of Norepinephrine Action

-The majority of the NE (50%-80%) is taken back in to the nerve terminal, a process known as reuptake. -Following its reuptake, NE is repackaged in vesicles for future use or destroyed enzymatically by MONOAMINE OXIDASE (MAO). -NE entering the circulation, such as that secreted by the adrenal glands or given as medication, is destroyed, by the enzyme CATECHOL-O-METHYLTRANSFERASE (COMT) in kidney and liver cells -The primary means of inactivation of NE is through reuptake, which is a slower process than the direct enzymatic destruction of Ach. (p.145)

Autonomic drugs

-These medications are used to stimulate or inhibit target organs or glands of the ANS, such as the heart, lungs, or digestive tract. Thus, when an autonomic drug is administered, the goal is to correct disorders of target organs through its effects on the autonomic nerves -exert their effects by acting at synapses

Alpha-adrenic receptors

-when alpha receptors are stimulated, enzymes on the inside of the plasma membrane are activates and cascade of changes occurs within the cell. -In alpha1 receptors intracellular calcium stores are released , causing excitatory effects such as smooth muscle contraction or sphincter closure. -Drugs affecting alpha1 receptors are primarily used for their effects on vascular smooth muscle in treatment of hypertension . -Drugs that block the alpha1receptor are used to treat benign prostatic hyperplasia -Simulation of alpha2 receptors causes different effects due to the activation of a seperate cascade of events in the target cells. -By increasing cyclic adenosime monophosphate (cAMP) within the cell, activation of alpha2 receptors inhibits NE release from sympathetic nerve endings, causing inhibitory actions. -In addition, activation of alpha2 receptors in the CNS can suppress the outflow of sympathetic activity from the brain (p. 145)

Life cycle of acetylcholine (Ach)

1. Ach is released into the synaptic cleft 2.Ach binds to receptors on the postsynaptic membrane 3. Ach is broken down ito acetate and choline 4. Choline is returned to the presynaptic neuron and recycled to make additional Ach

Two basic types of nerve terminals where norpinephrine is synthesized

1.) Alpha 2.) Beta

Process of synapric transmission

1.) An action potential is illustrated 2.) Action potential reaches the synapse 3.) Neurotransmitter released for the synaptic vesicles 4.) Neurotransmitter binds to receptor and opens ion channel 5) Action potential continues

The five general mechanisms by which drugs affect synaptic transmission in the ANS

1.) Medications may affect the SYNTHESIS of the neurotransmitter in the preganglionic nerve. Drugs that decrease neurotransmitter synthesis inhibit autonomic responses. Those that increase neurotransmitter synthesis have the opposite effect. 2.) Medications can prevent the STORAGE of the neurotransmitter in vesicles within the preganglionic nerve. Prevention of neurotransmitter storage inhibits autonomic actions. 3.) Medications can influence the RELEASE of the neurotransmitter from the preganglionic nerve. Promoting neurotransmitter release stimulates autonomic responses, whereas preventing neurotransmitter release has the opposite effect. 4.) Medications can bind to the NEUROTRANSMITTER RECEPTORS on the postganglionic cell. Drugs that bind to receptors and stimulate the cel will increase autonomic responses. Those that attach to the postganglionic cell and preent the natural neurotransmitter from reaching its receptors will inhibit autonomic actions. 5.) Medications can PREVENT THE DESTRUCTION OR REUPTAKE of the neurotransmitter. These drugs cause the neurotransmitter to remain in the synapse for a longer time and will stimulate the autonomic actions. (p.142)

Basic functions of the nervous system

1.) Monitor the internal and external environment of the body and alert the brain of important changes. 2.) Process and integrate the environmental changes that are perceived and determine an appropriate response. 3.) Respond to environmental changes by producing an action or response. (p.137)

Life cycle of norephinephrine (NE)

1.) NE is synthesized from the amino acid tyrosine 2.) NE is released into the synaptic cleft 3.) NE binds to receptors on the postsynaptic membrane 4.) NE is taken back into the presynaptic neuron 5.) NE is degraded by MAO 6.) Small amounts of NE are degraded by COMT (p.145)

Two types of cholinergic receptors that bind to Ach

1.) NICOTINIC RECEPTORS 2.) MUSCARINE RECEPTORS

Synaptic transmission accross the neuroeffector junction

1.) SYNTHESIS OF THE NEUROTRANSMITTER- the neurotransmitter is synthesized in the ell body of the neuron or in the terminal where the synapse is located (the two primary neurotransmitters of the ANS are neropinephrine and acetylcholine). 2.) STORAGE OF THE NEUROTRANSMITTER- because nerve impulses travel rapidly from neuron to neuron, there must be an ample and continuous supply of the neurotransmitter. At the terminal ends of each axon lie millions of granules or vesicles loaded with neurotransmitters, waiting for action potential to release them. 3.) RELEASE OF THE NEUROTRANSMITTER- when the nerve impulse reaches the end of the axon, it stimulates some of the vesicles to release their stored neurotransmitter into the synapse. The neurotransmitter enters the synaptic cleft, which must be bridged for the impulse to reach the post ganglionic neuron or organ. 4.) BINDING RECEPTOR- The neurotransmitter diffuses across the synaptic cleft to reach receptors waiting on the surface of the postsynaptic cell. There is a brief delay in impulse conduction of about 0.2 to 0.5 msec for the neurotransmitter to cross the synapse. Once the neurotransmitter binds to its receptor, the message is conveyed to the postsynaptic cell.The neurotransmitter induces the target muscle cell, glandular cell, or another neuron tissue to elicit its characteristic response. Generally, the more neurotransmitter released into the synapse, the more intense and longer lasting response. 5.) TERMINATION OF NEUROTRANSMITTER ACTION- Once the message is transmitted, the neuron and the effector cell must return to baseline conditions and ready themselves for future messages. This is accomplished by removal of the neurotransmitter. The neurotransmitter is either degraded in the synaptic cleft by enzymes, or diffuses back into the pregagnlionic neuron, thus stopping the action of the muscle of gland. (P.141-142)

Four possible actions of autonomic drugs

1.) Stimulation of the sympathetic nervous system (these drugs are called sympathomimetics or adrenic agonists and they produce the classic symptoms of the fight-or flight response) 2.) Stimulation of parasympathetic nervous system (These drugs are called parasympathomimetics or muscarinic agonists and they produce the characteristic symptoms of the rest-and-digest response) 3.) Inhibition of the sympathetic nervous system (These drugs are called adrenic antagonists or adrenic blockers and they produce actions opposite to those of sympathomimetics) 4.) Inhibition of the parasympathetic nervous system (these drugs are called anticholinergics, parasympatholytics, or muscarinic blockers and they produce actions opposite to those of the parasympathomimetics) (p.147)

two distinct (mostly opposing) components of the ANS

1.) Sympathetic nervous system 2.) Parasympathetic nervous system -The ultimate action of the cardiac muscle, smooth muscle, or gland depends on which branch is sending the most signals at any given time -Under most conditions, the two branches of the ANS cooperate to achieve a balance of readiness and relaxation

THREE MAIN ACTIVITIES OF THE ANS

1.) contraction of smooth muscle of the bronchi, blood vessels, GI tract, eye, and genitourinary tract 2.) contraction of cardiac muscle 3.) secretion of salivary, sweat, gastric, and bronchial glands (p.137)

Two major subdivisions of the nervous system

1.) the central nervous system (CNS) 2.) the peripheral nervous system (p.137)

Higher centers influencing autonomic function

1.)Cerbral Cortex- Thoughts 2.) Limbic System- Emotions 3) Hypothalamus- ANS integration 4.) Pons and Medulla- Cardiac, respiratory, BP, swallowing centers 5.) Spinal Cord- Reflexes for defacation, urination, erection, and ejaculation

Peripheral Nervous system (PNS)

=Carries nerve impulses between the CNS and the rest of the body -Neurons in the peripheral nervous system RECOGNIZE changes to the environment (sensory division) and RESPOND to those changes by moving muscles or secreting chemicals (motor division)

Dopamine

Another type of adrenergic receptor -Although the functional role of dopamine was one thought to be only a chemical precursor to NE, research has determined that this agent servers a larger role as a neurotransmitter. -5 dopaminergic receptors (D1-D5) have been discovered in the CNS -Dopaminergic receptors are important to the action of certain antipsychotic medicines and in the treatment of Parkinson's disease -Dopamine receptors in the peripheral nervous system are located in the arterioles of the kidney and other viscera -Therapeutic importance has yet to be discovered

catecholamines

Class of endogenous hormones involved in neurotransmission that include epinephrine (adrenaline), nonepinepharine, and dopamine. (p.144)

ganglia

Collection of neuron cell bodies located outside the central nervous system (p.140)

monoamine oxidase (MAO)

Enzyme that destroys catcholamines such as norepinephrine in the nerve terminal. (p.145)

catechol-O-methyltransferase (COMT)

Enzyme that destroys catecholamines such as norepinephrine in kidney and liver cells. (p.145)

acetylcholinesterase (AchE)

Enzyme that resides in the synaptic cleft and catalyzes the destruction of Ach. [**The suffix "erase" can be thought of as "wiping out" the Ach] (p.143-143)

autonomic nervous system (ANS)

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

parasympathetic nervous system

Portion of the autonomic nervous system in the PNS that is activated during non stressful conditions and produces a set of symptoms known as the rest-and-digest response. -These nerves promote relaxation and body maintenance activities. -Digestive secretions INCREASE, peristalsis propels substances along the alimentary canal, and defecation is PROMOTES. -Heart rate and blood pressure DECLINE -Because less air is needed, the bronchi CONSTRICTS and respiration SLOWS **Notice that that the actions of the parasympathetic nervous system are OPPOSITE of the sympathetic nervous system

nicotonic

Receptor for acetylcholine in the ganglia of both the sympathetic and parasympathetic nervous system. (p.142)

Adrenergic

Receptors at the ends of postganglionic sympathetic neurons. (p.144)

cholinergic

Relating to neurons that release acetylcholine (p.142)

Synaptic transmissions

allows information to be communicated between two nerves or form nerves to muscles or glands.

autonomic tone

The background level of autonomic activity that occurs even in the absence of stimuli. Ex. sympathetic nerves are constantly firing, keeping arterioles in a constant state of constriction. This sympathetic tone allows for faster changes in blood pressure because the vessels are in a constant state of readiness. On the other hand, parasympathetic tone on the smooth muscle of the alimentary and urinary tracts maintains continuous contractions and keeps (p.138-139)

Beta-adrenic receptors

Three subtypes of beta-adrenic receptors have been identified (although only beta1 and beta 2 have pharmacological importance) 1.) Beta1receptors -The primary tissues served by beta 1 receptors are the heart, coronary vessels, and kidneys. -Activation of these receptors increases the heart rate and strength of contraction and dilates the coronary arteries, thus preparing the heart for fight or flight. -Beta1 receptors in the kidney respond by releasing renin, which helps to maintain (increase) bloodpressure. 2.)Beta 2 receptors -More widely distributed than beta1 receptors -Locations in smooth muscle or arterioles, the GI tract, and the lungs. -Activation will dilate arteries to skeletal muscles, dilate bronchioles, slow peristalsis, and decrease urine production

muscarine

Type of cholinergic receptor found at postganglionic nerve endings in the parasympathetic nervous system that, when activated, result in stimulation. (p.143)

synapase

a junction between to neurons or a neuron and a muscle.

pseudocholinesterase (plasma cholineserase)

another enzyme that destroys Ach. -Found primarily in the liver, it rapidly inactivates Ach and drugs with a structure similar to Ach as they circulate in the plasma. (p.144)

Sensory division of the PNS

caries nerve impulses to the CNS from sensory organs. - Consists of specialized nerves that recognize touch, pain, heat, body position, light, or specific chemicals in the body fluids -The sensory neurons send their messages to the spinal cord; based on this info, the brain determines what messages are important, determines whether an action is needed, and plans an appropriate response.

Neuropharmacology

nervous system drugs used to treat a large and diverse set of conditions including pain, anxiety, depression, schizophrenia, insomnia, and seizures. -through their action on nerves, these medications are used to treat disorders affecting other body systems such as abnormalities in the heart rate and rhythm, hypertension, glaucoma, asthma, and even a runny nose. -represents one of the largest, most complicated, and least understood branches of pharmacology. (p.137)

sympathetic nervous system

portion of the autonomic nervous system in the PNS that is activated under emergency conditions of stress and produces a set of actions called the fight-or-flight response. -Activation of this branch prepares the body for heightened activity and for an immediate response to threat: *the BRAIN experiences an INCREASE in alertness and readiness, *heart rate and blood pressure INCREASE and blood is shunted to skeletal muscles, thus preparing the body for intense physical activity. *the liver immediately produces more glucose for energy *the bronchi DILATE to allow maximum airflow into the lungs, and breathing becomes faster and deeper *the pupils DILATE to provide better vision for dealing with emergency *the body warms and perspiration INCREASES -At the same time the body is preparing for the threat, non-emergency maintenance functions such as peristalsis and urine formation are temporarily suspended (p.138)

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.