Week5- Study Guide for EXAM #2
Organization of the Nervous System
A. Central Nervous System (CNS)
1. Brain: This is the communication & control center of the body. It receives many kinds of input, processes & evaluates it, decides on the response or action to be taken and initiates the response, which includes both involuntary activity required to maintain homeostasis in the body (regulated by autonomic nervous system) and voluntary actions (controlled by the somatic nervous system . With both reflex and voluntary activities, person is often not aware of the amount & diversity of input received or integration or assessment of that input, but only of the response.
a) Brain is protected by the skull, 3 membranesof meninges and cerebral spinal fluid (CSF) which provides a cushion for the brain and spinal cord consisting of electrolytes & proteins which should be produced & absorbed at the same rate. CSF is an important diagnostic tool which normally should be clear but when it contains large numbers of RBCs, it indicates bleeding in the CNS.; consists of nerve cells & fibers. Forebrain- involved in emotional responses; consists of cerebral cortex, white matter, grey matter, basal ganglia; cerebrum - cortex responsible for some kinds of learning, thought, reasoning. Midbrain connects the forebrain and hindbrain; contains pleasure centers and the formation that keeps a person awake and alert ( works during lectures!); Hindbrain- cerebellum which is responsible for balance & complex muscle movements and rthe medulla oblongata which regulates involuntary functions such as breathing
b) Spinal cord - protected by bony vertebral column, the meninges, and CSF. Obtain sample of CSF here.
c) Meninges- continuous connective tissue membrane covering the brain & spinal cord
B. Peripheral Nervous System- peripheral nerves & sense organs
C. Nerve signal processing: a) sensory nerves detect stimulus; b) signal sent along peripheral nerves to brain; c) brain receives & processes signal; d) brain sends signal alongperipheral nerves to effector cells (muscle, gland); e) effector cells take some action as a result of receiving signal
III. Cells of the Nervous System: A. Neurons which are highly specialized, non-mitotic cells which require glucose and oxygen for metabolism; their structure varies according to its function. Sensory neurons - signal out towards the brain/CNS and Motor neurons - signal sent away from brain/CNS to effector organ. Synapse is the gap between neurons or neuron and effector cell.; Dendrite - receptor site which conducts impulses toward the cell body which contains the nucleus, and the Axon which conductts impulses away from the cell body toward an effector cell or connecting neuron, where it can release neurotransmmitter (nt) chemicals at its terminal point. Nerve fibers are covered with a myelin sheath, which insulates the fiber and wraps many layers of its membrane around axonwhich is formed by Schwann Cells. This keeps the nerve signal in the nerve. Multiple sclerosis (MS) has patches of myelin sheath destroyed, probably by an autoimmune resonse giving rise to symptoms of loss of coordination, bladder/bowel dysfunction, progressive weakness, and maybe some paralysis, sensory deficits in the upper body, face, legs and ultimately symptoms lead to respiratory infections and ulcers. Trigeminal neuralgia has loss of myelin sheath in the cheek leading to intense facial pain. Herpes simplex virus (HSV) 'hides' in the trigeminal ganglia and actually travels to the lip region when the individual is under stress, exposed to lots of UV. Once infected with HSV, this virus is a part of the body forever.
B. Neuroglia - non-neural cells of the nervous system; usually have cellular extensions from cell; astrocytes - wrap around blood vessels and carry nutrients from small blood vessels to neurons and provide some phagocytic activity.br>
C. Circulation: cell survival depends on availability of essential nutrients & removal of waste products; arteries & veins are only on the surface of the brain. Depend on blood brain barrier (BBB) no direct flow of blood to the CSF; nutients cross a thin membrane in the brain to the CSF. The BBB is a protective mechanism provided primarily by relatively impermeable cappilaries to the brain. It limits the passage of potentially damaging materials into the brain and controls the delicate but essential balance of electrolytes & proteins in the brain. BBB is poorly developed in the neonate so bilirubin ( as a result of Rh factor incompatibility) can easily pass into the infant's brain & cause damage. But when developed, unfortunately doesn't allow antibiotics, etc., in.
IV. Nerve Signals (simplified version - see our lecture outline drawings for details and figure 10.8) a) electrical impulses that travel along membranes of presynaptic neuron and postsynaptic neuron or other cell; b) passage of signal can be detected and measured, like in the famous squid axon studies (see text figure); c) synapse - junction between cells mentioned above, and 4) chemicals are required to transfer signal across synapse to post cell called neurotransmitters (nt)nt may stimulate or inhibit the conduction of the impulse. Knowing about nts helps us understand some of the effects on our nervous system when chemicals called stimulants or depressants are ingested. Stimulants increase the activity of the CNS by altering the effect of nt at synapses. Cocaine and amphetamines increase the normal stimulatory effect of the nt called norepinephrine (nep). Actually, amphetamines bind to the nt receptor and the post thinks it got another signal from the nt.also amphetamines inhibit monoamine oxidase (MAO) the enzyme that degrades certain nts. More nt remains in the synapse in the latter case and acts on the post longer In contrast to stimulants, depressants often inhibit signal transmission at synapses. Among the depressant drugs, barbituates, and the tranqulizers, Valium & Librium intensify the effect of the nt, GABA. Alcohol is a stron depressant; it seems to increase the inhibitory nt GABA also.So drugs can influence events at the synapse; medication may prevent stimulation and excessive heart activity while another increase heart rate & contraction.
Pesticides work by blocking the action of cholinesterases at the neuromuscular junctions. So any synapse stimulated by acetylcholine (Ach the nt involved here) remains continually on. The Ach is never broken down and the poor insect dies with its muscles in a state of rigid contractions.
B. Depression
1. Serotonin is a nt found in the brain. A decreased level of serotonin and nep in the synaptic cleft is associated with the disorder, depression. Serotonin does affect sleep, mood, attention, and learning. Depression symptoms include sleep disorders, attention problems, irritability, and lack of energy among others. Certain psycoactive drugs produce their hallucinatory effects (LSD & mescaline) by binding to serotonin receptors in the brain.
2. Treat depression by modulating the serotonin (and nep) level. We concentrated on serotonin. A widely prescribed class of drugs called selective serotonin reuptake inhibitors (SSRIs) are aimed at fighting depression . Prozac and Paxil reduce the reuptake of serotonin . MAO inhibitors such as Parnate block the destruction of nep and serotonin by the MAO enzyme at the synapse. These and other mechanisms allow the stimulation by excitatory nts to continue in the brain. Foods to be avoided - chocolate, old cheese, beer & wine. They interfere with the inhibition of MAO. Another method of treatment of depression involves electroconvulsive therapy (shock therapy) which increase nep activity.