Notes Ch. 11g Nervous System II
Autonomic Nervous System This is the part of the nervous system that works without thought or control and continuously. This regulates activities of smooth muscle (like the linings of organs and blood vessels), cardiac muscles, and various glands. It oversees heart rate, blood pressure, breathing rate, body temperature, and any activity that aids in maintaining homeostasis.
General Characteristics There are 2 divisions – Parasympathetic and sympathetic divisions. Sometimes one will activate an organ while another will inhibit it. Sympathetic will speed up the heart but slow down digestive system. It will also be most active during stressful, energy-expending, emergency situations. Parasympathetic will slow heart rate, activate digestion. It will be most active under ordinary, restful conditions.
Autonomic Nerve Fibers Motor pathways have 2 neurons. The cell body of one neuron is in the brain or spinal cord, the axon is called the preganglionic fiber. The axon of the second neuron is called the postganglionic fiber and it goes into the effector.
Sympathetic Division The nerve fibers all extend from the spinal cord. The sympathetic chain ganglia (chains on the side of the vertebral column) run signals to effectors. There are special ganglia fibers that extend into adrenal glands and secrete norepinephrine (20%) and epinephrine (80%) when stimulated.
Parasympathetic Division These fibers come from the midbrain, pons, and medulla oblongata and the sacral area of the spinal cord. These then move to ganglia that are by specific muscles or glands. The vagus nerve is a big part of this system.
Autonomic Neurotransmitters They all secrete acetylcholine. Most sympathetic postganglionic neurons secrete norepinephrine (they are called adrenergic).
Actions of the Autonomic Neurotransmitters Look at page 436
Control of Autonomic Activity Control of the autonomic nervous system is in the hypothalamus. There are also reflex centers in the medulla oblongata and the spinal cord.
Life-Span Changes From birth we have death of neurons throughout life. They have found in young adults with schizophrenia that they have the same number of neurons as newborns. By 30, the die-off of neurons accelerates Over an average lifetime the brain shrinks about 10%, with more loss in gray matter than white. By 90 the frontal cortex has lost about ½ its neurons. The number of dendritic branches in the cerebral cortex decreases as you age. Nervous system disorder that happen on older adults are stroke, depression, Alzheimer disease, Parkinson disease, and multi-infarct dementia. Other signs of an aging nervous system are fading memory and slowed responses and reflexes. Also possibly drops in blood pressure. Sleep pattern change, less sleep is required and insomnia may be a problem. Also poor balance can occur.