Nervous System ANS PDF

The Nervous System Part 3 www.psychlopedia.wikispaces.com Outline Compare the structural and functional differences of the sympathetic and parasympathetic divisions of the ANS. ANS Comparison Autonomic nervous system (ANS). – Regulates smooth muscle, cardiac muscle, and certa...

The Nervous System Part 3 www.psychlopedia.wikispaces.com Outline Compare the structural and functional differences of the sympathetic and parasympathetic divisions of the ANS. ANS Comparison Autonomic nervous system (ANS). – Regulates smooth muscle, cardiac muscle, and certain glands – Usually operates without conscious control from the cerebral cortex, but other brain regions, mainly the hypothalamus and brain stem, regulate it. Somatic motor neurons – Axon extend from the CNS and synapse directly with an effector (skeletal muscle). – Consist of two motor neurons that synapse in an autonomic ganglion. Autonomic Motor Two divisions: 1. the sympathetic division and the 2. parasympathetic division. Most body organs receive dual innervation; usually one ANS division causes excitation and the other causes inhibition. Somatic motor neurons release acetylcholine (ACh), and autonomic motor neurons release either acetylcholine or norepinephrine (NE). Copyright © 2016 by Nelson Education Ltd. Comparison of SNS and ANS Somatic motor neurons release acetylcholine (ACh) Autonomic motor neurons release either acetylcholine or norepinephrine (NE). i. Pre-ganglionic neurons release ACh ii. Postganglionic neurons release: Sympathetic: NE Parasympathetic: ACh Recall: what is a ganglion??? ANS The neurons of the sympathetic and parasympathetic divisions leave the central nervous system at different levels: – Sympathetic fibres from the thoracic (chest) and lumbar regions of the spinal cord, and – Parasympathetic fibres from the brainstem and the sacral portion of the spinal cord. ANS Sympathetic Division Also called the thoracolumbar division Has short preganglionic and long postganglionic synapses This is the “flight or fight” response system Parasympathetic Division Also called the craniosacral division It has long preganglionic and short postganglionic synapses This is the “rest and digest” system ANS The heart and many glands and smooth muscles are innervated by both sympathetic and parasympathetic fibres; that is, they receive dual innervation. Whatever effect one division has on the effector cells, the other division usually has the opposite effect. Moreover, the two divisions are usually activated reciprocally; that is, as the activity of one division increases, the activity of the other decreases. Activities of the ANS Balance between sympathetic and parasympathetic activity – Known as “tone” – Regulated by hypothalamus Typically: – Turns up sympathetic tone at same time turns down parasympathetic tone Sympathetic Activities Sympathetic division stimulated by: – “E” situations: exercise, emergency, excitement, embarrassment Fight-or-flight response – Activation of the sympathetic division and release of hormones by the adrenal medullae  Body’s Response to Fight-or-Flight Pupils dilate Heart rate, force of heart contraction and blood pressure increase Airways dilate, allowing faster movement of air into and out of lungs Blood vessels supplying nonessential organs constrict – Kidneys – GI tract – Slowing of urine formation and digestive activities Blood vessels supplying organs involved in exercise or fighting off danger dilate allowing greater blood flow – Skeletal muscles – Cardiac muscle – Liver – Adipose tissue Parasympathetic Activities Parasympathetic division enhances “rest-and- digest” activities – Support body functions that conserve and restore body energy In quiet intervals between periods of exercise: – Parasympathetic impulses predominate Impulses to digestive glands and smooth muscle of GI tract Parasympathetic responses also reduce body functions that support physical activity Parasympathetic Activities SLUDD – five parasympathetic responses: (S) Salivation (L) lacrimation (U) urination (D) digestion (D) defecation Three decreases: Decreased heart rate Decreased diameter of airways Decreased diameter (constriction) of pupils Dealing with Stress One of the best ways to deal with stress is to engage in regular, vigorous exercise. Here are the benefits of exercise with respect to stress: – Brain releases endorphins that make you feel good (e.g. runner’s high) – Dopamine levels have been shown to increase, which in turn helps you concentrate – Increases other molecules involved in elevating mood (serotonin and oxytocin) THE END