Lecture Outline - Chapter 12

12.1 Neuron Structure (p. 242, Figs. 12.1-12.3)
	1.	The brain and spinal cord comprise the central nervous system (CNS). The nerves leading to and from body parts to the CNS comprise the peripheral nervous system (PNS) (Fig. 12.1).
	2.	Neurons have a cell body, an axon, and one to many dendrites. There are three types of neurons (Fig. 12.2).
		a.	Sensory (afferent) neurons carry impulses to the CNS.
		b.	Motor (efferent) neurons carry impulses from the CNS.
		c.	Interneurons are found within the CNS and relay impulses to other portions of the CNS.
		d.	Neuroglial cells cover and protect the long axons on neurons. 
			i.	Schwann cells are found in the PNS and wrap axons, producing a myelin sheath. Gaps between Schwann cells are called nodes of Ranvier. 
			ii.	If the distant portion of the nerve fiber is damaged, it can regenerate with the aid of the Schwann cells.
12.2 Nerve Impulse (p. 244, Fig. 12.4)
	1.	Nerve impulses are generated in neurons because of electrical potential differences (voltage) across the plasma membrane. In long fibers, the speed of impulse conduction is rapid because the impulse jumps from one node of Ranvier to the next (saltatory conduction).
	2.	Resting Potential: Inside Is Negative (p. 244, Fig. 12.4)
		a.	The resting potential across a membrane is equal to -65mV. The membrane is said to be polarized in this condition.
		b.	The charge difference across the membrane is due to differences in ion distribution because of the action of the sodium-potassium pump. 
	3.	Action Potential: Upswing and Downswing (p. 244)
		a.	An action potential is reached when a threshold stimulus is received. 
		b.	Sodium Gates Open (p. 244)
			When a stimulus is received, the sodium channels open, allowing sodium to flow across the membrane, depolarizing it.
		c.	Potassium Gates Open (p. 244)
			The potassium gates open next, allowing potassium to leave the cell. This repolarizes the membrane.
	4.	Membrane Rests During a Refractory Period (p. 244)
		During the refractory period after a nervous impulse, the sodium gates are temporarily closed, and an impulse cannot be conducted.
12.3 Transmission Across a Synapse (p. 246, Fig. 12.5)
	1.	The junction between one neuron and the next is called a synapse, with the presynaptic neuron sending the impulse and the postsynaptic neuron receiving it. The presynaptic neuron has a synaptic bulb that releases neurotransmitters into the synaptic cleft. Receptors in the postsynaptic neuron receive the neurotransmitters.
	2.	Neurotransmitters Are Varied (p. 246)
		a.	At least 25 different neurotransmitters have been identified. Acetylcholine and norepinephrine can be either inhibitory or excitatory, depending on the nature of the receptor.
		b.	Once a neurotransmitter has been released, a specific enzyme in the postsynaptic neuron degrades it.
12.4 Peripheral Nervous System (p. 247, Fig. 12.6)
	1.	The peripheral nervous system consists of the nerves outside the CNS and has two divisions: the somatic and autonomic nervous systems.
	2.	Cranial and Spinal Nerves (p. 248, Fig. 12.7)
		a.	Nerves are bundles of nerve fibers, and their cell bodies are located within the CNS or in ganglia.
		b.	Sensory nerves contain only sensory fibers, motor nerves have only motor fibers, and mixed nerves contain both.
		c.	Humans have 12 pairs of cranial nerves that lead to the brain. Some are sensory, some are motor, and still others are mixed.
		d.	Humans has 31 pairs of spinal nerves emerging from the spinal cord. The dorsal root houses sensory nerve fibers; the ventral root contains motor fibers.
	3.	Somatic System Serves Skin and Muscles (p. 248)
		The somatic system is made up of mixed nerves that lead to the skeleton, muscles, and exterior sense organs of the skin.
	4.	Reflexes Are Automatic (p. 249, Fig. 12.8)
		a.	A reflex is an involuntary, automatic circuit designed to respond to external or internal changes in the body.
		b.	The automatic withdrawal of a hand from a hot flame is routed through the spinal cord in a reflex arc.
	5.	Autonomic System Serves Internal Organs (p. 251, Fig. 12.9, Table 12.1)
		a.	The autonomic branch of the motor nervous system serves the internal organs. It is involuntary and is divided into sympathetic and parasympathetic branches.
		b.	Sympathetic System: Fight or Flight (p. 251)
			i.	The short, preganglionic fibers of the sympathetic system are located in the thoracic- lumbar region of the back. Postganglionic fibers leading to an effector organ are long.
			ii.	Postganglionic fibers of this branch release the neurotransmitter norepinephrine.
			iii.	The sympathetic branch is associated with the "fight-or-flight" response.
		c.	Parasympathetic System: Relaxed State (p. 251)
			i.	Nerves for the parasympathetic branch arise from either the base of the cranium or from the sacrum. Postganglionic fibers are short because the ganglia lie close to an effector organ.
			ii.	Postganglionic fibers release the neurotransmitter acetylcholine.
			iii.	The parasympathetic branch brings about normal body conditions associated with a relaxed state.
12.5 Central Nervous System (p. 252)
	1.	The central nervous system consists of the brain and spinal cord.
		a.	Membranes called meninges cover, nourish, and protect the CNS. Cerebrospinal fluid circulates in spaces between meninges.
		b.	Ventricles in the brain produce and house larger amounts of cerebrospinal fluid.
	2.	Neuroglial Cells Are Versatile (p. 252, Fig. 12.10)
		a.	Oligodendrocytes form myelin, microglial cells are phagocytic, and astrocytes nourish neurons and produce a growth factor.
		b.	Recent evidence indicates that neuroglial cells communicate with each other and with neurons.
	3.	Spinal Cord Communicates (p. 252)
		a.	The spinal cord serves two functions: it is a center for reflexes and a highway for communication to and from the brain.
		b.	Unmyelinated cell bodies are located in the central gray matter of the cord. 
		c.	Myelinated nerve fibers make up tracts in the white outer portion of the cord.
		d.	Nerve tracts cross over at the top of the spinal cord or the base of the brain.
	4.	The Brain Commands (p. 253, Fig. 12.11)
		a.	The brain is divided into the sections that follow and has four major ventricles.
		b.	Brain Stem Is Closest to the Cord (p. 253)
			i.	The brain stem maintains basic life support. It consists of the medulla oblongata, pons, and midbrain.
			ii.	The medulla oblongata contains vital centers for regulating heartbeat, breathing, and blood pressure, and contains reflex centers. It relays impulses from the spinal cord to the higher centers of the brain.
			iii.	The pons houses axons traveling between the cerebellum and the rest of the CNS. It helps with breathing and also houses reflex centers.
			iv.	The midbrain is a relay station for tracts passing between the cerebrum and spinal cord, and houses numerous reflex centers.
	5.	Diencephalon Surrounds the Third Ventricle (p. 254)
		a.	The diencephalon consists of the hypothalamus and the thalamus.
		b.	The hypothalamus maintains many homeostatic mechanisms for the body, including hunger, thirst, sleep, blood pressure, and water balance. It also controls the pituitary gland.
		c.	The thalamus processes sensory input and relays it to appropriate places in the cerebrum.
 	6.	Cerebellum Coordinates Muscle Activity (p. 254)
		a.	The cerebellum lies at the back of the brain and functions in motor coordination to ensure smooth, graceful movement.
		b.	The cerebellum is made up of a core of white matter, with a gray matter cortex.
	7.	Cerebrum Is Paramount (p. 255, Fig. 12.12) 
		a.	The cerebrum is responsible for consciousness and higher mental processes, such as reasoning, the interpretation of sensory input, and the initiation voluntary muscle movements.
		b.	The cerebrum has been mapped, and certain areas are association areas, while others are responsible for sensory input from specific regions of the body.
	8.	The Limbic System Controls Memory and Emotions (p. 255, Fig. 12.13)
		The limbic system connects portions of the cerebrum, the basal nuclei, the thalamus, and the hypothalamus. This system is responsible for emotions and for learning and memory.
		HEALTH FOCUS: A Cure for Alzheimer and Parkinson Disease (p. 256, Fig. 12A)
		i.	Alzheimer disease (AD) is characterized by gradual loss of memory. A genetic defect may be the underlying cause, and acetylcholine may be in short supply in patients with AD.
		ii.	Parkinson is a disease of the basal nuclei in which the person shows tremors, slowness of movement, a shuffling gait, and rigidity of facial muscles. The problem seems to be in the release of the neurotransmitter dopamine.
		iii.	One day, treatments may include nerve growth factor for Alzheimer disease and glial-derived growth factor for Parkinson disease.
12.6 Drug Abuse (p. 257, Fig. 12.14)
	1.	Many drugs alter mood or emotional state. These have one of two general effects.
		a.	Mood-altering drugs can impact the limbic system.
		b.	Other drugs (stimulants or depressants) promote or decrease the action of a neurotransmitter.
		c.	Drug abuse occurs when a person takes more of a drug than is needed and also develops a psychological or physical dependence on the drug.
	2.	Alcohol (p. 257)
		a.	Alcohol may influence the action of several neurotransmitters.
		b.	Alcohol is first detoxified in the liver. Liver tissues are destroyed in the process and are replaced by fat. In cirrhosis, cells harden and die.
		c.	Extensive use of alcohol may impair the immune system and leads to muscle atrophy because protein digestion is upset.
		d.	Alcohol is the most abused drug in the United States and should never be consumed by pregnant women.
	3.	Nicotine (p. 258)
		a.	Nicotine from tobacco products causes neurons in the CNS to release dopamine. Users become psychologically and physically dependent.
		b.	Nicotine adversely affects the developing embryo and fetus. 
	4.	Marijuana (p. 258)
		a.	Marijuana, often called a gateway drug because it leads to the use of more potent drugs, is classified as a hallucinogen. It may have an effect on the action of serotonin.
		b.	Toxic compounds in leaves are released when marijuana is smoked.
		c.	Marijuana does not produce physical dependence but does induce psychological dependence in many users. 
	5.	Cocaine (p. 258, Fig. 12.15)
		a.	Cocaine increases the amount of dopamine in CNS synaptic clefts and also prevents the reuptake of this neurotransmitter, leading to the sensation of a rush.
		b.	The rush from cocaine lasts only a few seconds and then is replaced by a brief period of arousal. After these feelings pass, the person feels depressed, restless, and irritable. 
		c.	Cocaine is extremely addictive, and overdoses often lead to death.
	6.	Heroin (p. 259)
		a.	Heroin, a derivative of morphine, is usually injected intravenously.
		b.	Euphoria, in combination with pain relief, are the actions of this drug, which binds to endorphin receptors.
		c.	Heroin users become physically dependent on the drug and need to take increasing amounts over time.
		d.	A heroin overdose can cause death, since those who are excessively dependent may die upon withdrawal due to respiratory failure.
	7.	Methamphetamine (Ice) (p. 261)
		a.	Methamphetamine is related to the stimulant amphetamine.
		b.	A new form of methamphetamine, known as "ice," is used as an alternative to cocaine.
		c.	Ice can be illegally produced in laboratories locally, and does not need to be imported.
		d.	The stimulatory effects of ice are similar to those of cocaine with the exception that the effects of ice persist for hours compared to seconds for cocaine.
	8.	Designer Drugs (p. 261)
		a.	The so-called designer drugs are analogs of controlled substances, such as MPPP (1-methyl-4-phenylprionoxypiperidine) an analog of fentanyl.
		b.	Small doses of MPPP are highly toxic and can be deadly.
12.7 Working Together (p. 261)
	The Working Together box (p. 260) illustrates how the nervous system works with other body systems to maintain homeostasis.