Autonomic Nervous System

Sympathetic Nervous System - Overview & General Functions

"Fight or Flight" responses and the regulation of body responses to stress; characterized largely by episodic activity --> mediated by Norepinephrine/Epinephrine 1)↑ release of epinephrine from adrenal medulla --> adrenal medulla is essentially a de facto ganglion; it is innervated by a preganglionic SNS neuron that stimulates the adrenal medulla to release epinephrine as a hormone into the systemic circulation 2) ↑ Heart rate, conduction velocity, contractility, cardiac output 3) ↑ in systemic blood pressure (directly and indirectly) 4) Shift in blood flow away from skin/viscera and ↑ blood flow to skeletal muscle 5) ↑ bronchiolar dilation to more fully open airways and enhance oxygenation 6) Mydriasis (dilation of pupils) to allow more light to assist vision 7) Relaxation of bladder wall and tightening of sphincter to inhibit urination 8) ↓ GI motility/↓ digestion 9) ↑ blood glucose (via liver) to ↑ energy delivery to muscles 10) ↑ sweating to help regulate body temperature

Parasympathetic Nervous System - Overview & General Functions

"Rest and Digest" - the PSNS is tonically active and generally responsible for coordinating bodily functions such as digestion and excretion --> Acetylcholine signaling 1)↓ Heart rate, AV nodal conduction 2) Constricts the airways and increases bronchial secretions 3) Miosis (constriction of pupils) and rounding of the lens for accommodation for near vision 4) ↑ bladder tone and loosening of the sphincter to facilitate urination 5) ↑ GI motility, stimulates the release of bile to aid digestion 6) Stimulates salivation 7) Stimulates tear production (lacrimation)

Autonomic Nervous System Learning Objectives

- To describe the organization of autonomic system - To describe organization of sympathetic and parasympathetic system -Understand and describe co-transmission - Describe components of central autonomic network - Describe organization, transmitters and modulators of hypothalamus - Describe the hypothalamic control of pituitary gland

Three basic cell types of the autonomic pathways

1) Sympathetic 2) Parasympathetic 3) Enteric Preganglionic --> Acetylcholine Postganglionic

Characteristics of the Autonomic Nervous System

Consist of a 2 neuron chain First-neuron (Preganglionic fiber) - Arises from brainstem or spinal cord --> synapse on autonomic ganglia Second-neuron (Postganglionic fiber) - Arises from autonomic ganglia --> synapse at target/effector tissues

The function of the Hypothalamus in the Autonomic nervous system (6)

Hypothalamus - Principal integrative center for the entire autonomic nervous system Functions 1. Blood pressure and electrolyte composition. The hypothalamus regulates thirst, salt appetite, and drinking behavior, autonomic control of vasomotor tone, and the release of hormones like vasopressin (via the paraventricular nucleus). 2. Energy metabolism. The hypothalamus regulates hunger and feeding behavior, the autonomic control of digestion, and the release of hormones such as glucocorticoids, growth hormone, and thyroid-stimulating hormone (via the arcuate and paraventricular nuclei and the lateral hypothalamic area). 3. Reproductive (sexual and parental) behaviors. The hypothalamus controls autonomic modulation of the reproductive organs and endocrine regulation of the gonads (via the medial preoptic, ventromedial, and ventral premammillary nuclei). 4. Body temperature. The hypothalamus influences thermoregulatory behavior (seeking a warmer or cooler environment), controls autonomic body heat conservation/loss mechanisms, and controls secretion of hormones that influence metabolic rate (via the preoptic region). 5. Defensive behavior. The hypothalamus regulates the stress response and fight-or-flight response to threats in the environment such as predators (via the paraventricular, anterior hypothalamic, and dorsal premammillary nuclei, and the lateral hypothalamic area). 6. Sleep-wake cycle. The hypothalamus regulates the sleep-wake cycle (via a circadian clock in the suprachiasmatic nucleus) and levels of arousal when awake (via the lateral hypothalamic area and tuberomammillary nucleus).

Autonomic nervous system synapse

Known as Varicosities

Nucleus of the solitary tract

Sensory information transduced via this pathway serves either local reflex responses or more complex hormonal and behavioral responses via integration within a central autonomic network

Co-transmission of neurons

Some cells co-release different neuropeptides along with acetylcholine - CGRP [calcitonin gene-related peptide] - GIRK [G protein-coupled inward-rectifying K+ channel] - LHRH [Luteinizing hormone-releasing hormone] Neuropeptide release is greatly enhanced by high-frequency repetitive stimulation and produces a slow EPSP that is 60 times slower than the muscarinic IPSP Co-transmission involves the co-activation of more than one type of receptor by more than one transmitter. Parasympathetic postganglionic nerve terminals in the salivary glands release both ACh and vasoactive intestinal peptide (VIP) to control secretion. Autonomic synapses with end-organs sometimes employ more elaborate combinations, activating three or more receptor types.

Organs with exclusively SNS innervation

Sweat glands/piloerector muscles and blood vessels are exclusively innervated and regulated by the SNS Uses acetylcholine instead of usual SNSN Norepinephrine/Epinephrine signaling

Sympathetic vs Parasympathetic fibers

Sympathetic Nervous system - Vertebral column chain --> short pre-ganglionic fibers and long postganglionic fibers - SNS ganglia are interconnected --> pre-ganglionic fibers synapse on many (>20) post-ganglionic fibers --> SNS responses are ALL-OR-NONE Parasympathetic Nervous System - Located site distal from brain/spinal cord --> near target tissues/effectors --> long pre-ganglionic and short post-ganglionic fibers - Ganglia are set up as 1:1 ratio --> regulates discrete effector site INDEPENDENTLY of one another

Sympathetic vs Parasympathetic anatomic exit

Sympathetic Nervous system [Thoracolumbar] - Exit spinal cord between T1 and L2/L3 Parasympathetic Nervous System [Cranialsacral] - Exit spinal cord cranial nerves or sacral regions