The endocrine system is the system of glands, each of which secretesdifferent types of hormones directly into the bloodstream (some of which are transported along nerve tracts to regulate the body.Blood-borne means able to be spread in the blood.
bowel?:The part of the alimentary canal below the stomach; the intestine
What is a muscarinic receptor? -ACh receptors-G-protein coupledWhat's the difference between muscarinic and nicotinic receptors? Both are ACh receptorsmuscarinic: G-protein couplednicotinic: ligand-gated ion channelWhat are the adrenergic receptors? beta, alpha1 and alpha2
Organization of ans
Topic: Organization , Subdivisions andInnervations of Autonomic Nervous System Zulcaif Ahmad
BRIEF INTRODUCTION TO NERVOUS SYSTEM• The nervous system is divided into anatomical divisions : CNS which is composed of composed of the brain and spinal cord, and PNS which includes neurons located outside the brain and spinal cord i.e. any nerve that enter or leaves the CNS• The peripheral nervous system is further subdivided into the efferent divisions , the neurons of which carry signals away from the brain and spinal cord to the peripheral tissues, and the afferent division, the neurons of which bring information from periphery to the CNS.
WHAT IS AUTONOMIC SYSTEM?• The autonomic nervous system (ANS) is largely autonomous (independent) in that its activities are not under direct conscious control .• It is concerned with visceral functions-cardiac output, blood flow to various organs, digestion, etc- that are necessary for life.
Autonomic nervous system and endocrine system• The autonomic nervous system, along with the endocrine system coordinates the regulation and integration of bodily functions.• The endocrine system sends signals to target tissues by varying the levels of blood borne hormones.• In contrast, the nervous system exerts its influence by the rapid transmission of electrical impulses over nerve fibers that terminate at effector cells, which specifically respond to the release of neuromediator substances
Autonomic drugs• Drugs that produce their primary therapeutic effect by mimicking or altering the functions of the autonomic nervous system are called autonomic drugs.• These autonomic agents act either by stimulating portions of the autonomic nervous system or by blocking the action of the autonomic nerves.
1.EFFERENT NEURONS• The ANS carries nerve impulses from the CNS to the effector organs by way of two types of efferent neurons• The first nerve cell is called a preganglionic neuron, and its cell body is located within the CNS . Preganglionic neurons emerge from the brainstem or spinal cord and make a synaptic connection in ganglia(an aggregation of nerve cell bodies located in the peripheral nervous system).• These ganglia function as relay stations between a preganglionic neuron and a second nerve cell, the postganglionic neuron . The latter neuron has a cell body originating in the ganglion .It is generally nonmyelinated and terminates on effector organs, such as smooth muscles of the viscera, cardiac muscle and the exocrine glands
AFFERENT NEURONS• The afferent neurons of the ANS are important in the reflex regulation of this system• For example:• By sensing pressure in the carotid sinus and aortic arch and in signaling the CNS to influence the efferent branch of the system to respond.
Sympathetic neurons• Anatomically, the sympathetic and parasympathetic neurons originate in the CNS and emerge from two different spinal cord regions.• The preganglionic neurons of the sympathetic system come from thoracic and lumbar regions (T1 and L2) of the spinal cord , and they synapse into two cord like chains of ganglia that run close to and parallel on each side of the spinal cord.• Axons of the postganglionic neuron extend from these ganglia to the tissues that they innervate and regulate.• The sympathetic nervous system is also called thoracolumbar division because of its origin.• In most cases, the preganglionic endings of sympathetic nervous system are highly branched enabling one preganglionic neuron to interact with many postganglionic neurons.• This arrangement enables them to activate numerous effector organs.
Parasympathetic nervous system• The parasympathetic preganglionic fibers arise from cranial nerves 3 (oculomotor), 7(facial), 9 (glossopharyngeal) and vagus as well as from the sacral regions (S2 and S4) of the spinal cord and synapse in ganglia near or on the effector organ.• They are also called as craniosacral division
Enteric neurons• The enteric nervous is the third division of the ANS.• It is a collection of nerve fibers that innervate the gastro intestinal (GI) tract, pancreas, gallbladder.• It constitutes the “BRAIN OF THE GUT”• This system functions independetly of the CNS and controls the motility ,exocrine and endocrine secretions, and microcirculation of the GI tract.
1.Dual innervations• Most organs in the body are innervated by both divisions of the ANS.• Thus , vagal parasympathetic innervation slows the heart rate, and sympathetic innervation increases the heart rate.• Despite this dual innervation, one system usually predominates in the controlling the activity of a given organ• For example• In the heart the vagus nerve is the predominant factor for controlling rate• This type of antagonism is considered to be dynamic and is fine-tuned at any given time to control homeostatic organ functions
2.Organ receiving only sympathetic innervation• Although most tissues receive dual innervation, some effector organs, such as the adrenal medulla, kidney , pillomotor muscles, and the sweat glands, receive innervation from the sympathetic system.• The control of blood pressure is also mainly sympathetic activity, with essentially no participation by the parasympathetic system.
Receptors ???• A receptor is a molecule most often found on the surface of a cell, which receives chemical signals originating externally from the cell. Through binding to a receptor, these signals direct a cell to do something—for example to divide or die, or to allow certain molecules to enter or exit.
Autonomic Nervous System Receptors• There are two types of autonomic neurons:• cholinergic• adrenergic.
Cholinergic Neurons and Receptors• They release Ach.• They are all the sympathetic and parasympathetic neurons, sympathetic postganglionic neurons that innervate most sweat glands, and all parasympathetic postganglionic neurons.• ACh from synaptic clefts in presynaptic neurons > binds specific cholinergic receptors in postsynaptic neurons.• There are two types of cholinergic receptors: nicotinic receptors and muscarinic receptors.
Adrenergic Receptors• Adrenergic receptors bind both hormones nor epinephrine and epinephrine.• There are two types of receptors: alpha and beta.• They are further classified as alpha1 (excitation), alpha2 (inhibition), beta1 (excitation), beta2 (inhibition), and beta3 (present on brown fat; activation causes heat production).
Agonists and Antagonists• Agonists activate receptors, mimicking the effect of a natural neurotransmitter or hormone.• Antagonists deactivate receptors.
SYMPATHETIC RECEPTORS• The major receptor types are alpha and beta• These are subdivided into alpha-1, alpha-2, beta-1 and beta-2• Alpha-1 type is found in the smooth muscle of most arterioles and in sphincter muscles of the GI tract and bladder. Alpha-2 type is found in presynaptic nerves and parts of the GI tract.• Beta-1 type is the dominant type in the heart. Beta-2 type is found in the bronchioles of the lung, the wall muscles of the bladder and other locations.
Parasympathetic receptors• Types of muscarinic receptors• The five main types of muscarinic receptors:• The M1 muscarinic receptors are located in the neural system.• The M2 muscarinic receptors are located in the heart• The M3 muscarinic receptors are located at many places in the body, such as the endothelial cells of blood vessels, as well as the lungs• The M4 muscarinic receptors: Postganglionic cholinergic nerves, possible CNS effects• The M5 muscarinic receptors: Possible effects on the CNS• Types of nicotinic receptors• In vertebrates, nicotinic receptors are broadly classified into two subtypes based on their primary sites of expression: muscle-type nicotinic receptors and neuronal-type nicotinic receptors.
Autonomicnerve endingsSympathetic Decrease NE M releaseParasympath Decrease Ach aetic release
Summary of differences SYMPATHETIC PARASYMPATHETICSites of origin Thoracic and lumbar brain and sacral areas region of the spinal cord of spinal cord (thoracolumbar) (craniosacral)Length of fibers Short preganglionic Long preganglionic Long postganglionic Short postganglionicLocation of ganglia Close to spinal cord Within or near effector organsPreganglionic fiber Extensive MinimalbranchingDistribution Wide LimitedType of response Diffuse Discrete