PHT 5150 Peripheral Nervous System - Efferent Division PDF

PHT 5150 Peripheral Nervous System – Efferent Division Objectives 1. Describe the physiological role of the autonomic division and its branches. 2. Compare and contrast the anatomy and chemical communication of the SNS and PSNS branches. 3. Describe the synthesis and breakdown of the aut...

PHT 5150 Peripheral Nervous System – Efferent Division Objectives 1. Describe the physiological role of the autonomic division and its branches. 2. Compare and contrast the anatomy and chemical communication of the SNS and PSNS branches. 3. Describe the synthesis and breakdown of the autonomic neurotransmitters. 4. Describe the structure and secretions of the adrenal medulla 1 Peripheral Nervous System – Efferent Division The efferent division sends information from the CNS to target tissues through efferent neurons. The peripheral nervous system efferent division has two sub groups the autonomic neurons and the somatic motor neurons. Peripheral Nervous System – Efferent Division The autonomic division is further subdivided into the sympathetic nervous system (SNS) and parasympathetic nervous system (PSNS) branches. Autonomic neurons control internal organs, glands, some adipose tissue, cardiac and smooth muscle. Somatic motor neurons control skeletal muscles. 2 SNS vs PSNS The SNS dominates during stressful situations “Flight and Fight”. The PSNS dominates during quiet activities “Rest and Digest”. Homeostatsis is maintained as the two autonomic branches cooperate with each other. Autonomic Reflexes The ultimate goal is to maintain the body’s homeostasis. The ANS works with and influences the endocrine and behavioral state systems to maintain homeostasis. Sensory information goes to control centers in the hypothalamus, pons and medulla. 3 Autonomic Control Centers These control centers monitor and regulate involuntary body functions such as blood pressure, body temperature, respiration and water balance. Autonomic Pathways All autonomic pathways consist of two neurons in a series called preganglionic and postganglionic neurons with synapses in an autonomic ganglion and at a target tissue. 4 How are the SNS and PSNS different? The two autonomic pathways differ in their points origin in the CNS, in the location of their autonomic ganglia and in the lengths of their ganglionic axons. SNS and PSNS Responses The SNS and PSNS often innervate the same organs and tissues, but they are frequently antagonistic to each other. 5 SNS and PSNS Neurotransmitters and Receptors 1. The SNS and PSNS preganglionic neurons both release ACh onto postganglionic nicotinic cholinergic receptors. 2. Most postganglionic PSNS neurons release ACh onto muscarinic receptors on the target cell. 3. Most postganglionic SNS neurons release NE onto either α or β adrenergic receptors on the target cell. Neuroeffector Junction at the Target Tissue Autonomic postganglionic axons end with varicosities. The stringed bead like structure lies across the target tissue surface forming a different type of synapse model. 6 Neurotransmitter Release and Removal at a Neuroeffector Junction In this example, NE is synthesized, released and removed at this sympathetic neuroeffector junction between the varicosity and the target cell adrenergic membrane receptor. Autonomic Neurotransmitters The ANS has only a few neurotransmitters. However, there are multiple receptor subtypes with different second messenger pathways that allow many different actions to occur at the target tissue. 7 Adrenal Medulla The Adrenal Medulla is a modified sympathetic ganglion. The chromaffin cells, a modified postganglionic sympathetic neuron, secretes the neurohormone epinephrine directly into the blood. Excellent Review Table 8 Summary 1. The peripheral nervous system efferent division has two sub groups. The autonomic neurons control primarily glands, smooth muscle and cardiac muscle. While the somatic motor neurons control skeletal muscle. 2. The autonomic division is sub divided into the sympathetic and parasympathetic branches and is responsible for maintaining the body’s homeostasis. 3. All autonomic pathways are composed of preganglionic and postganglionic neurons that synapse at a neuroeffector junction of a target tissue. 4. The SNS and PSNS branches differ in their CNS point of origin, the lengths of the pre and postganglionic neurons and the location of the peripheral ganglia. Summary 5. All autonomic pathways are composed of preganglionic and postganglionic neurons that synapse at a neuroeffector junction of a target tissue. The SNS and PSNS are similar in that both secrete ACh onto postganglionic nicotinic receptors. They differ in that the SNS secretes NE onto adrenergic receptors of a target tissue, and most PSNS secrete ACh onto muscarinic receptors of a target tissue. 6. The adrenal medulla is a modified sympathetic ganglion. The chromaffin cells are modified postganglionic sympathetic neurons within the medulla. These cells secrete epinephrine, a neurohormone, directly into the blood. 9 References Silverthorn DU. Human Physiology: An Integrated Approach. 8th Edition. Pearson, 2018. Thanks for viewing the presentation 10