Textbook notes-Chapter 11-Efferent Division-Autonomic and Somatic Motor Control

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University of Toronto Scarborough
Biological Sciences
Ingrid L.Stefanovic

Chapter 11- Efferent Division: Autonomic and Somatic Motor Control The Autonomic Division N It is subdivided into sympathetic and parasympathetic branches - The sympathetic branch is dominant in stressful situations like threat from a snake and one of the most dramatic examples of this action is the fight-or-flight response, in which the brain triggers massive simultaneous sympathetic discharge throughout the body; mediated through the hypothalamus Autonomic Reflexes Are Important for Homeostasis N The autonomic nervous system works closely w the endocrine system and the behavioural state system N Sensory info from somatosensory and visceral receptors goes to homeostatic control centres in the hypothalamus, pons, and medulla - These centres monitor and regulate important functions like blood pressure, temp regulation, and water balance - The hypothalamus also contains neurons that act as sensors which monitor osmolarity, and thermoreceptors, which monitor body temp - Motor output from the hypothalamus and brain stem creates autonomic responses, endocrine responses, and behavioural responses - The behavioural responses are integrated in brain centres responsible for motivated behaviour and control of movement N Sensory info integrated in the cerebral cortex and limbic system can create emotions that influence autonomic output Antagonistic Control Is A Hallmark of the Autonomic Division N The sympathetic and parasympathetL.-7,3.K08419K0,:94342L.307;4:888902L85O,,OO14:741:,O907,33438 properties of homeostasis: (1) preservation of the fitness of the internal environment, (2) up-down regulation by tonic control, (3) antagonistic control, and (4) chemical signals w different effects in different tissues N Most internal organs are under antagonistic control, on which one autonomic branch is excitatory and the other branch is inhibitory N Although the two autonomic branches are usually antagonistic in their control for a given target tissue, they sometimes work cooperatively on different tissues to achieve a common goal N In some autonomic pathways, the neurotransmitter receptor determines the response of the target tissue; e.g. most blood vessels contain one type of adrenergic receptor that causes smooth muscle contraction (vasoconstriction) - Some blood vessels also contain a 2 type of adrenergic receptor that causes smooth muscle to relax (vasodilation) Autonomic Pathways Have Two Efferent Neurons in Series N All autonomic (sympathetic and parasympathetic) consist of two neuron in series 1. Preganglionic neuron originates in the CNS and projects to an autonomic ganglion outside the CNS. There the preganglionic neurons synapses w the 2 neuron in the pathway 2. Postganglionic neuron has its cell body in the ganglion and projects its axon to the target tissue N Divergence is an important feature of autonomic pathways as on avg, one preganglionic neuron entering ganglion synapses w 8 or 9 postganglionic neuron. - Each postganglionic neuron may then innervate a different target, meaning that a single signal from the CNS can affect a large # of target cells simultaneously N Ganglia are more than a simple collection of axon terminals and nerve cell bodies: they also contain interneurons that lie completely within them - These interneurons enable the autonomic ganglia to act as mini-integrating centres, receiving sensory input from the periphery of the body and modulating outgoing autonomic signals to target tissues. Sympathetic and Parasympathetic Branches Exit the Spinal Cord in Different Regions N The main anatomical differences are (1) where the pathways originate in the CNS and (2) the location of the autonomic ganglia N Fig 11-5 shows, most sympathetic pathways (red) originate in the thoracic and lumbar regions of the spinal cord; parasympathetic pathways (shown in blue) originate in the brain stem, and their axons leave the brain in several cranial nerves N Sympathetic ganglia are found primarily in two chains that run along either side of the spinal column, w additional ganglia along the descending aorta 1 www.notesolution.com
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