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AUTONOMIC NERVOUS SYSTEM The ANS is part of the efferent portion of the peripheral nervous system Functions Regulation of heartbeat Smooth muscle contraction Secretions of glands ***It is controlled by the hypothalamus with input from the cerebral cortex and limbic system Comparing the Somatic and Autonomic Nervous System Somatic Nervous System Receptors (sensory neurons) are sensitive to external enviroment and transmit signals to the CNS Causes stimulation of reflexes or conscious sensation Information from efferent fibers sent to skeletal muscle Cell bodies located in CNS; only one motor neuron involved Autonomic Nervous System Internal enviroment monitored by interoceptors Stimulation of ANS rarely results in conscious sensations Visceral Effectors: smooth,cardiac muscle and glands Pathway involves TWO motor neurons in sequence – Preganglionic neuron cell body is in CNS; Postganglionic cell body is outside CNS Axon fibers of 2nd neuron not myelinated and release ACh or NE Divisions of the Autonmic Nervous System Sympathetic Division - Flight or Fight Parasympathetic Division - Rest or Repose Differ in location of preganglionic cell body Sympathetic Division (Thoracolumbar) cell bodies located in lateral gray horns of thoracic & lumbar regions of spinal cord Parasympathetic Division (Craniosacral) cell bodies found in cranial & sacral regions of the cord Differ in location of ganglionic synapse Sympathetic – – – Division - Paravertebral ganglia - Chain ganglia Prevertebral ganglia - Collateral ganglia Postganglionic axon fiber is very long Parasympathetic – – – Division- Terminal ganglia – close to effectors Preganglionic axon fiber is long Postganglionic axon fiber is very short Neurotransmitters Sympathetic Division - ACh is released at preganglionic axon terminal; NE or adrenalin is released at the postganglionic axon Parasympathetic division - ACh is released at both synapses * Effect: inhibitory/excitatory depending on receptors on effectors Length of influence Sympathetic - is more widespread, more intense and response is of longer duration Parasympathetic - a more controlled reaction with local effect and shorter duration Types of Autonomic Neurons Cholinergic – All preganglionic neurons & all parasympathetic postgangionic neurons Adrenergic – neurons - release ACh neurons - release NE Most sympathetic postganglionic neurons Sympathetic Responses Pupils and bronchioles dilate Heart and respiration rate increases Dilation of blood vessels to skeletal muscles Constriction of vessels to nonessential organsBLOOD PRESSURE ZOOMS UP Secretion and motility to digestive structures inhibited Parasympathetic Responses Constriction of pupils and bronchioles Decreases respiration rate; slows down the heart Increases blood flow to GI tract Decreases blood flow to skeletal muscle Kidneys begin to function - urination Erection on both male and female