MSN - FNP 590 CHAPTER 11 NEUROLOGICAL DISORDERS.

MSN - FNP 590 CHAPTER 11 NEUROLOGICAL DISORDERS. NEURAL FUNCTION Anatomy and physiology: Brain: CNS Spinal cord: CNS Nerves: PNS (cranial and spinal nerves) 1. CNS – Meninges encase the cns, dura mater is the outer and toughest layer, arachnoid is middle, and pia is innermost that rests directly on brain and spinal cord. CSF fills space between arachnoid and pia mater (produced by choroid plexus cells in brain’s ventricles). 600 ml in adults and 50ml in newborns produced daily. -CSF: electrolytes, glucose, proteins, and red and white blood cells. Flow through cavities, foramens, and aqueducts of the brain. 150mls of it circulates within the ventricles and excess CSF drains into the bloodstream. -Neural tissue: neuroglia and neurons *Neuroglia: more numerous, scaffold neural tissue and isolate and protect neuron cell membranes, regulate interstitial fluid, defend neurons against pathogens, assist with neural repair. Consist of: astrocytes, oligodendrocytes, Schwann cells, microglia, and ependymal cells. Astrocytes form the framework of the brain and spinal cord (central nervous system) and form the blood–brain barrier. Ependymal cells form the epithelial lining of the central nervous system and produce cerebrospinal fluid. The oligodendrocytes are responsible for the development of myelin in the central nervous system. Schwann (neurilemma) cells produce myelin in the peripheral nervous system. Schwann cells also provide metabolic support. Schwann cell transplantation for therapeutic purposes is in a preclinical trial phase. Microglia have phagocytic activities. *Neurons: fundamental unit of the nervous system, generate bioelectrical impulses and transmit signals, do not have the ability to divide (unless they’re olfactory neurons). Neurons can take responsibility of other neurons if some were to die. In pns, severed nerves can regenerate and reestablish connections but in brain or spinal cord severed axons cannot be repaired leading to paralysis. Require constant oxygen and glucose. Have axons (transmit impulses away from cell body) and dendrites (transmit impulses toward cell body). When the axon reaches its destination, it often branches into several small fibers that terminate into miniscule bulges, called terminal boutons. These terminal boutons communicate with neurons, muscle fibers, or glands. Axons can communicate with several different neurons or influence one single neuron. Axons may be surrounded by a myelin sheath made of lipids, which increases the rate of impulse transmission to approximately 400 times faster than is possible in unmyelinated nerves (FIGURE 11-3). Schwann cells produce the myelin sheath in the PNS, and oligodendrocytes produce myelin in the CNS; these cells are separated by nodes of Ranvier. Nutrient exchange can occur at the nodes but not where there is myelin. Because of the myelin, impulses move at greater speeds down the axon, jumping from one node to the next, much like stones skipping across water. Bundles of these myelinated nerves are referred to as white matter. Impulses move in a slow, wavelike pattern in unmyelinated nerves. The larger the axon, the faster the impulse transmission. Gaps between the neurons are referred to as synapses. Each of these gaps includes a presynaptic terminal (e.g., a terminal bouton or some similar structure), a synaptic cleft (the space between neurons), and a postsynaptic cell membrane (FIGURE 11-4). The presynaptic and postsynaptic terminals are opposite ends of the nerve. Presynaptic neurons relay impulses toward the synapse, while postsynaptic neurons relay impulses away from the synapse. Throughout life, brain synapse numbers and strength can change, and the ability to do so is termed neuroplasticity or synaptic plasticity. Instead, small ionic changes such as potassium, sodium, and calcium moving across cell membranes generate neural impulses (action potential) (FIGURE 11-5). Usually several potentials, whether excitatory or inhibitory, are necessary for impulse transmission; this concept is known as summation. The plasma side of the neuron membrane has a slight charge at rest, or resting potential, because of the sodium ions concentrated on the outside of the cell. When the neuron is stimulated, protein gates open and sodium flows into the cell. The rapid inflow of positively charged sodium ions increases the charge—a process called depolarization. This is the same process that occurs in the cardiac cells. Immediately following depolarization, the cell membrane returns to its resting state through the rapid outflow of the positively charged potassium ions. When generated, these impulses travel down the nerve to trigger the release of neurotransmitters from vesicles in the presynaptic terminal. The neurotransmitters cross the synaptic cleft, albeit only in one direction, to stimulate an electrical reaction in nearby neurons. The neurotransmitters bind to a receptor on the postsynaptic membrane. Synaptic transmission of the impulse takes a mere millisecond. This electrical reaction passes through those neurons to the next synapse, where the process is repeated. At each synaptic transmission, a small burst of neurotransmitters is released and then removed. Neurotransmitters are either destroyed by enzymes or reabsorbed by the postsynaptic membrane to be recycled for the next transmission. Whereas some neurotransmitters stimulate the action potentials of neurons, other neurotransmitters inhibit action potentials (see TABLE 11-1). Some common neurotransmitters include acetylcholine, norepinephrine, dopamine, and serotonin. -Brain: cerebrum and cerebral cortex, diencephalon (thalamus and hypothalamus), brainstem (midbrain, pons, and medulla) and cerebellum. *Cerebrum: largest, controls higher though processes, cerebral cortex is thin layer of gray mater surround cerebrum (info is stores, received, transmitted here). Left and right hemispheres and control opposite sides of the body. Divided into lobes – frontal: motor activity and personality traits, parietal: sensory input except smell, hearing, and vision, occipital: visual, temporal: hearing, smell, memory