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The Nervous System Overview of the Nervous System Nervous System Overview organization of the nervous system two major divisions central nervous system (CNS) peripheral nervous system (PNS) sensory receptors afferent (sensory) nerves efferent (motor) nerves The Efferent Nerves somatic nervous system voluntary autonomic nervous system involuntary sympathetic parasympathetic Nervous Tissues neuroglia also known as glial cells support the neurons protect the neurons neurons transmit nerve impulses Two Major Divisions Funtions of the Nervous System 1. Sensory Functions derive from sensory receptors at the end of peripheral neurons. Receptors gather information by detecting changes inside and outside the body and then convert the info into nerve impulses, which are transmitted over peripheral nerves to the CNS. Funtions of the Nervous System 2. Integrative functions are receiving signals and bringing them together, creating sensations, adding to memory, or helping to produce thoughts that translate sensations into perceptions. Funtions of the Nervous System 3. Motor functions employ peripheral neurons, which carry impulses from the CNS to responsive structures called effectors (muscles and glands that secrete when stimulated). Neurons: Basic Unit of the Nervous System Neuron Structure Cell Body (Soma)– consists of granular cytoplasm, cell membrane, organelles, and a network of fine threads called neurofibrils, which extend into nerve fibers Neuron Structure Nerve Fibers – extend from the cell body Neuron Structure Dendrites – one neuron may have many dendrites; short and highly branched; together with the membrane, dendrites are the neuron’s main receptive surfaces with which fibers from other neurons communicate Neuron Structure Axons – one neuron has only one axon; arises from slight elevations of the cell body; begins as a single fiber but may give off side branches; near its end it may have fine extensions that contact the receptive surfaces of other cells Neuron Structure Schwann cells – neuroglial cells that enclose large axons forming myelin sheaths that wind tightly around the axon; portions of the Schwann cells that contain most of the cytoplasm and the nuclei remain outside the myelin sheath and make up the nuerilemma (neurilemmal sheath); narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier Neuron Structure CNS – myelinated nerve fibers are also found in the central nervous system; myelinated fibers appear white, and masses of such fibers form white matter in the CNS; unmyelinted nerve fibers and neuron cell bodies form gray matter within the CNS Types of Neuron and Neuroglial Cells Neuron Structures bipolar one axon and one dendrite • unipolar – one axon • multipolar – one axon and many dendrites Classification of Neurons: Structural Differences Bipolar Neurons – cell body has two nerve fibers one arising from each end; one is an axon and the other is a dendrite; located within specialized parts of the eye, nose and ears Classification of Neurons: Structural Differences Unipolar Neurons – single nerve fiber that extends from the cell body then divides into two branches; one connecting to a peripheral body part and functioning as a dendrite, and the other entering the brain or spinal cord and functioning as an axon; some cell bodies gather in specialized masses of nervous tissue called ganglia(located outside the brain or spinal cord) Classification of Neurons: Structural Differences Multipolar Neurons – have many nerve fibers arising from their cell bodies; only one fiber is an axon and the rest are dendrites; neurons which lie within the brain or spinal cord Classification of Neurons: Functional Differences Sensory Neurons (afferent neurons) – carry impulses from peripheral body parts into the brain or spinal cord; most are unipolar, but some are bipolar Classification of Neurons: Functional Differences Interneurons (internuncial or association neurons) – lie within the brain and spinal cord; multipolar and link other neurons; transmit impulses from one part of the brain or spinal cord to another; direct incoming sensory impulses to appropriate parts for processing and interpreting Classification of Neurons: Functional Differences Motor Neurons (efferent neurons) – multipolar and carry impulses out of the brain or spinal cord to effectors; stimulate muscles to contract or glands to secrete Classification of Neuroglial Cells: Neuroglial cells fill spaces, provide structural frameworks, produce myelin, and carry on phagocytosis. Within the PNS neuroglial cells include Schwann cells and satellite cells In the CNS they greatly outnumber neurons and are of the following types: Neuroglia peripheral nervous system Schwann cells satellite cells Neuroglia central nervous system astrocytes microglia ependymal oligodendrocytes Classification of Neuroglial Cells: Microglial Cells – scattered throughout; support neurons and phagocytize bacterial cells and cellular debris Classification of Neuroglial Cells: Astrocytes – found between neurons and blood vessels; provide structural support, join parts by numerous cellular processes, help regulate the concentrations of nutrients within tissue; form scar tissue that fills spaces following injury to the CNS Classification of Neuroglial Cells: Ependymal Cells – form an epithelial like membrane that covers specialized brain parts and forms the linings that enclose spaces within the brain and spinal cord Classification of Neuroglial Cells: Oligodendrocytes: provide support and insulation to axons in the CNS; equivalent to the function performed by Schwann cells in the PNS Review and Assessment Match these words with 1–4 below: sympathetic nervous system, myelin, synapse, axon. 1. high alert 2. transmits impulses away from cell body 3. fatty insulating material 4. gap between neurons Transmission of Nerve Impulses Cell Membrane Potential A cell membrane is usually polarized as a result of unequal ion distribution. Cell Membrane Potential Distribution of Ions a. Ion distribution is due to pores and channels in the membranes that allow passages of some ions but not others b. Potassium ions (K+) pass more easily through cell membranes than do Sodium ions (Na+) Cell Membrane Potential Resting Potential a. a high concentration of sodium ions is on the outside of a membrane, and a high concentration of potassium ions is on the inside of the cell. b. Many negatively charged ions are inside a cell. c. In a resting cell, more positive ions leave than enter, so the outside of the cell membrane develops a positive charge, while the inside develops a negative charge. Cell Membrane Potential Potential Changes a. Stimulation of a membrane affects the membrane’s resting potential. b. When its resting potential becomes more positive, a membrane becomes depolarized. c. Potential changes are subject to summation. d. Achieving threshold potential triggers an action potential. Cell Membrane Potential Action Potential a. At threshold, sodium channels open, and sodium ions diffuse inward, depolarizing the membrane. b. About the same time, potassium channels open, and potassium ions diffuse outward, repolarizing the membrane c. This rapid change in potential is an action potential. d. Many action potentials can occur before active transport re-establishes the resting potential. Nerve Impulses: A wave of action potentials is a nerve impulse. Impulse Conduction 1. Unmyelinated fibers conduct impulses over the entire surface of the nerve. 2. Myelinated fibers conduct impulses more rapidly because the impulse jumps between the nodes of Ranvier. 3. Nerves with large diameters conduct impulses faster than those with small diameters. Nerve Impulses All-or-None Response 1. A nerve impulse is conducted in an all-ornone manner when a stimulus of threshold intensity is applied to a fiber. 2. All the impulses conducted on a fiber are of the same strength. The Synapse – A synapse is the junction between two neurons. Synaptic Transmission 1. Impulses usually travel from a dendrite to a cell body, then along the axon to a synapse. 2. Axons have synaptic knobs at their ends, which secrete neurotransmitters. 3. A neurotransmitter is released when a nerve impulse reaches the end of an axon. 4. A neurotransmitter reaching the nerve fiber on the distal side of the synaptic cleft triggers a nerve impulse. The Synapse The Synapse Excitatory and Inhibitory Actions 1. Neurotransmitters that trigger nerve impulses are excitatory. Those that inhibit impulses are inhibitory. 2. The net effect of synaptic knobs communicating with a neuron depends on which knobs are activated from moment to moment. The Synapse Neurotransmitters 1. The nervous system produces many different neurotransmitters, such as acetylcholine, monoamines, amino acids, and peptides. 2. A synaptic knob releases neurotransmitters when an action potential increases membrane permeability to calcium ions. 3. After being released, neurotransmitters are decomposed or removed from synaptic clefts. Neurotransmitters Review and Assessment Fill in the blanks with: reflexes, saltatory conduction, neurotransmitter, or action potential. 1. A(n) _______________ is an all or none response. 2. _______________ occurs only in myelinated axons. 3. _______________ are rapid, involuntary responses. 4. The axon terminal has tiny vesicles filled with _______________. Types of Nerves Nerves are cordlike bundles of nerve fibers held together by layers of connective tissue. Types of Nerves 1. Sensory Nerves – conduct impulses into the brain or spinal cord 2. Motor Nerves – carry impulses to muscles or glands 3. Mixed nerves – include both sensory and motor fibers Nerve Pathways A nerve pathway is a route an impulse follows through the nervous sytem. Nerve Pathways Reflex arc – usually includes a sensory neuron, a reflex center composed of an interneuron, and a motor neuron Reflex Behavior 1. Reflexes are autonomic, subconscious responses to changes (stimuli) within or outside the body. 2. Reflexes help maintain homeostasis by controlling may involuntary processes. 3. Reflexes carry out autonomic actions of swallowing, sneezing, coughing, and vomiting. 4. The knee-jerk reflex (patellar tendon reflex) employs two neurons (sensory and motor). 5. Withdrawal reflexes are protective. Employs all three types of nerves. Functional Anatomy of the Central Nervous System The Brain: An Overview Weight – between 2.25 and 3.25 pounds 100 billion neurons (approximately); even more neuroglial cells About 6.7% of individual variation in intelligence is attributed to brain size. 4 major anatomic regions: cerebrum diencephalon brain stem cerebellum Meninges Meninges are membranes that lie between the bones and soft tissues of the cranial cavity and vertebral canal. They protect the brain and spinal cord Meninges They consists of three layers: 1. Dura Mater – outermost layer 2. Arachnoid Mater – located between the dura and pia mater a. Subarachnoid space – lies between the arachnoid and pia mater and contains the clear watery cerebrospinal fluid (CFS) 3. Pia Mater – very thin and contains nerves and blood vessels that nourish underlying cells of the brain and spinal cord; hugs the surface of these organs following their irregular contours, passing over high areas and dipping into depressions The Brain Structures of the Cerebrum Cerebral Hemisphere – 2 large masses which are essentially mirror images of each other connected by a deep bridge of nerve fibers called the corpus callosum; the surface has many convolutions (ridges) separated by grooves (shallow groove is called a sulcus and a deep groove is called a fissure) Cerebrum The lobes of the cerebral hemisphere are named after the skull bones they underlie: Frontal Lobe Parietal Lobe Temporal Lobe Occipital Lobe Structures of the Cerebrum Cerebral Cortex thin layer of gray matter that forms the outermost portion of the cerebrum; contains nearly 75% of all the neuron cell bodies in the nervous system Mass of White Matter lies just beneath the cerebral cortex and makes up the bulk of the cerebrum; bundles of myelinated fibers Functions of the Cerebrum Functional Regions of the Cerebral Cortex Primary Motor Areas – lie in the frontal lobes; fibers cross over in the brain stem from one side of the brain to the other (right CH motor area generally controls skeletal muscles on the left side of the body and vise versa) motor speech area frontal eye field Primary Motor Areas Functional Regions of the Cerebral Cortex Sensory Areas – located in several lobes a. cutaneous senses – sensations of the skin b. visual area c. auditory area d. taste area e. smell area Functional Regions of the Cerebral Cortex Association Area – neither primarily sensory or motor; analyzes and interprets sensory experiences and oversees memory, reasoning, verbalizing, judgment, and emotion Functional Regions of the Cerebral Cortex General Interpretive Area – complex thought processing Hemisphere Dominance Although both cerebral hemispheres participate in basic functions, in most people, one side of the cerebrum is the dominant hemisphere, controlling other functions. Hemisphere Dominance In over 90% of the population, the left hemisphere is dominant for language-related activities of speech, writing, reading, and for complex intellectual functions requiring verbal, analytical, and computational skills. Hemisphere Dominance In addition to carrying on basic functions, the non-dominant hemisphere specializes in nonverbal functions, such as motor tasks that require orientation of body in space, understanding, and interpreting musical patterns, and nonverbal visual experiences, as well as emotional and intuitive thinking. Cerebrospinal Fluid Cerebrospinal Fluid is secreted by capillaries from the pia mater. It completely surrounds the brain and spinal cord. These organs float in the fluid, which supports and protects them. It also provides a pathway to the blood for waste Diencephalon The diencephalon is located between the cerebral hemispheres and above the midbrain. It is largely composed of gray matter Parts of the Diencephalon Thalamus – relay station for sensory impulses (except smell); produces a general awareness of certain sensations, such as pain, touch, and temperature Parts of the Diencephalon Hypothalamus – below thalamus; maintains homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine systems; regulates: heart rate and arterial blood pressure body temperature water and electrolyte balance control of hunger and body weight control of movements and glandular secretions of stomach and intestines production of neurosecretory substances that stimulate the pituitary gland to secrete hormones sleep and wakefulness Hypothalamus Diencephalon Epithalamus: act as a connection between the limbic system to other parts of the brain. Some functions of its components include the secretion of melatonin by the pineal gland (involved in circadian rhythms) and regulation of motor pathways and emotions. Diencephalon Limbic System – controls emotional experiences and expression - can modify the way a person acts by producing such feelings as fear, anger, pleasure, and sorrow - recognizes upsets in a person’s physical and psychological condition that might threaten life - guides a person into behavior that is likely to increase the chance of survival Limbic System Other Structures of the Diencephalon 1. Optic Tract Optic Chiasma - vision 2. infundibulum – structures in which the pituitary gland is attached 3. pituitary gland – master gland 4. olfactory bulbs - smell 5. pineal gland – structure that secretes melatonin, which affects the sleep cycle; the darker it is the more melatonin is released, the lighter it is the less melatonin is released optic tracts and optic chiasma optic tracts and optic chiasma infundibulum – structures in which the pituitary gland is attached pituitary gland olfactory bulbs pineal gland structure that secretes melatonin, which affects the sleep cycle; the darker it is the more melatonin is released, the lighter it is the less melatonin is released Brain Stem a bundle of nerve tissue that connects the cerebrum to the spinal cord Midbrain joins lower parts of the brain stem and spinal cord with higher parts of the brain contains centers for certain visual and auditory reflexes Reticular Formation (reticular activating system) – in the midbrain The reticular formation extends from the upper portion of the spinal cord into the diencephalon and is connected to all ascending and descending fiber tracts. When sensory impulses are received it activates the cerebral cortex into wakefulness. Without this arousal, the cortex remains unaware of stimulation and cannot interpret information or carry out thought processes. Decreased activity results in sleep. Injury to it causes a person to be unconscious and cannot be aroused, even with strong stimulation (comatose state). Pons rounded bulges on the underside of the brain stem transmits impulses to and from the cerebrum and medulla oblongata and the cerebrum and cerebellum relays messages from the PNS to high brain centers functions with the medulla oblongata in regulating the rate and depth of breathing Medulla Oblongata All descending and ascending nerve fibers pass through the medulla oblongata. It is composed of gray matter surrounded by white matter and contains centers for controlling visceral activities: a. cardiac center – alters heart rate b. vasomotor center - certain cells initiate impulses which stimulate blood vessels to contract (vasoconstriction) elevating blood pressure - other cells have the opposite affect – dilating blood vessels (vasodilation) dropping blood pressure c. respiratory center – acts with centers in the pons to regulate the rate, rhythm, and depth of breathing Medulla Oblongata Cerebellum large mass located below the occipital lobes and posterior to the pons and medulla oblongata; two hemispheres composed largely of white matter surrounded by a thin layer of gray matter; Cerebellum communicates with other parts of the CNS by means of three pairs of nerve tracts called cerebellar peduncles: inferior peduncle – brings sensory information concerning the position of the limbs, joints, and other body parts to the cerebellum middle peduncle – transmits signals from the cerebral cortex to the cerebellum concerning the desired positions of the above mentioned parts after integrating and analyzing this information the cerebellum sends correcting information via the superior peduncle Cerebellum Cerebellum The cerebellum is a reflex center for integrating sensory information concerning position of the body parts and for coordinating complex skeletal muscle movements. Damage is likely to result in tremors, inaccurate movements of voluntary muscles, loss of muscle tone, a reeling walk, and loss of equilibrium. Spinal Cord The spinal cord is a nerve column that extends from the brain into the vertebral canal. Functions of the Spinal Cord Conduction of Nerve Impulses – provides a two-way communication system between the brain and body parts. Ascending tracts carry sensory information to the brain and descending tracts conduct motor impulses from the brain to muscles and glands. Center for Spinal Reflexes Structure of the Spinal Cord The spinal cord is composed of thirty-one segments, each of which gives rise to a pair of spinal nerves. The spinal cord has a cervical enlargement, which gives off nerves to the upper limbs, and a lumbar enlargement, which gives off nerves to the lower limbs. Spinal Nerves Spinal Cord Structure of the Spinal Cord Two grooves, a deep anterior fissure and a shallow posterior median sulcus, extend the length of the spinal cord, dividing it into right and left halves. It has a central core of gray matter within white matter. The white matter is composed of bundles of myelinated nerve fibers that comprise major nerve pathways called nerve tracts. Peripheral Nervous System Somatic Nervous System The somatic nervous system consists of the cranial and spinal nerve fibers that connect the CNS to the skin and skeletal muscles. It oversees conscious activities (voluntary). Autonomic Nervous System The autonomic nervous system consists of sensory neurons and motor neurons that run between the central nervous system (especially the hypothalamus and medulla oblongata) and various internal organs such as the: heart lungs viscera glands (both exocrine and endocrine) Autonomic Nervous System The autonomic nervous system is the portion of the PNS that functions independently (autonomously/involuntary) and continuously without conscious effort. 1. It controls visceral functions by regulating the actions of smooth muscles, cardiac muscles, and glands. 2. It regulates heart rate, blood pressure, breathing rate, body temperature, and other visceral activities that maintain homeostasis. 3. Portions respond to emotional stress and prepare the body to meet demands of strenuous physical activity Autonomic Nervous System General Characteristics: 1. regulated by reflexes 2. typically, peripheral nerve fibers lead to ganglia outside the CNS where they are integrated and relayed back to viscera (muscles and glands) that respond by contracting, releasing secretions, or being inhibited 3. provides the autonomic system with a degree of independence from the brain and spinal cord includes two divisions: Autonomic Nervous System The autonomic nervous system includes two divisions: Sympathetic division – prepares the body for energy-expending, stressful, or emergency situations (fight-or-flight) Parasympathetic division – most active during ordinary, restful conditions; counterbalances the effects of the sympathetic division and restores the body to a resting state following a stressful experience Sympathetic division The preganglionic motor neurons of the sympathetic system (shown in black) arise in the spinal cord. They pass into sympathetic ganglia which are organized into two chains that run parallel to and on either side of the spinal cord. Sympathetic division The preganglionic neuron may do one of three things in the sympathetic ganglion: 1. synapse with postganglionic neurons (shown in white) which then reenter the spinal nerve and ultimately pass out to the sweat glands and the walls of blood vessels near the surface of the body. 2. pass up or down the sympathetic chain and finally synapse with postganglionic neurons in a higher or lower ganglion Sympathetic division 3. leave the ganglion by way of a cord leading to special ganglia (e.g. the solar plexus) in the viscera. Here it may synapse with postganglionic sympathetic neurons running to the smooth muscular walls of the viscera. However, some of these preganglionic neurons pass right on through this second ganglion and into the adrenal medulla (endocrine gland on top of the kidney). Here they synapse with the highly-modified postganglionic cells that make up the secretory portion of the adrenal medulla. Sympathetic division The neurotransmitter of the preganglionic sympathetic neurons is acetylcholine (ACh). It stimulates action potentials in the postganglionic neurons. The neurotransmitter released by the postganglionic neurons is noradrenaline (also called norepinephrine). The action of noradrenaline on a particular gland or muscle is excitatory in some cases, inhibitory in others. (At excitatory terminals, ATP may be released along with noradrenaline.) Sympathetic division The release of noradrenaline stimulates heartbeat raises blood pressure dilates the pupils dilates the trachea and bronchi stimulates glycogenolysis — the conversion of liver glycogen into glucose shunts blood away from the skin and viscera to the skeletal muscles, brain, and heart inhibits peristalsis in the gastrointestinal (GI) tract inhibits contraction of the bladder and rectum Sympathetic division Stimulation of the sympathetic branch of the autonomic nervous system prepares the body for emergencies: for "fight or flight" (and, perhaps, enhances the memory of the event that triggered the response). Activation of the sympathetic system is quite general because a single preganglionic neuron usually synapses with many postganglionic neurons; the release of adrenaline from the adrenal medulla into the blood ensures that all the cells of the body will be exposed to sympathetic stimulation even if no postganglionic neurons reach them directly. Parasympathetic Nervous System The main nerves of the parasympathetic system are the tenth cranial nerves, the vagus nerves. They originate in the medulla oblongata. Other preganglionic parasympathetic neurons also extend from the brain as well as from the lower tip of the spinal cord. Parasympathetic Nervous System Each preganglionic parasympathetic neuron synapses with just a few postganglionic neurons, which are located near — or in — the effector organ, a muscle or gland. Acetylcholine (ACh) is the neurotransmitter at all the pre- and many of the postganglionic neurons of the parasympathetic system. However, some of the postganglionic neurons release nitric oxide (NO) as their neurotransmitter. Parasympathetic Nervous System Parasympathetic stimulation causes: slowing down of the heartbeat lowering of blood pressure constriction of the pupils increased blood flow to the skin and viscera peristalsis of the GI tract Parasympathetic Nervous System The parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation. In times of danger, the sympathetic system prepares the body for violent activity. The parasympathetic system reverses these changes when the danger is over. Parasympathetic Nervous System The vagus nerves also help keep inflammation under control. Inflammation stimulates nearby sensory neurons of the vagus. When these nerve impulses reach the medulla oblongata, they are relayed back along motor fibers to the inflamed area. The acetylcholine from the motor neurons suppresses the release of inflammatory cytokines, e.g., tumor necrosis factor (TNF), from macrophages in the inflamed tissue. Parasympathetic Nervous System Although the autonomic nervous system is considered to be involuntary, this is not entirely true. A certain amount of conscious control can be exerted over it as has long been demonstrated by practitioners of Yoga and Zen Buddhism. During their periods of meditation, these people are clearly able to alter a number of autonomic functions including heart rate and the rate of oxygen consumption. These changes are not simply a reflection of decreased physical activity because they exceed the amount of change occurring during sleep or hypnosis. Autonomic Nervous System Functional Anatomy of the Peripheral Nervous System Nerve Structure endoneurium covers axons perineurium bundles fascicles epineurium wraps nerves Cranial Nerves 1. 12 pairs 2. arise from the underside of the brain; except for the first pair, which begins within the cerebrum 3. lead to parts of the head, neck, and trunk 4. most are mixed nerves, but some associated with smell and vision contain only sensory fibers 5. some that control muscles and glands in this area are primarily motor fibers Cranial Nerves Cranial Nerves Spinal Nerves 1. 31 pairs 2. originate from the spinal cord 3. All of the spinal nerves are "mixed"; that is, they contain both sensory and motor neurons. They provide two way communication between the spinal cord and parts of the upper and lower limbs, neck, and trunk. Spinal Nerves Spinal nerves are grouped according to the level in which they arise: cervical nerves (C1-C8) – 8 pairs thoracic nerves (T1-T12) – 12 pairs lumbar nerves (L1-L5) – 5 pairs sacral nerves (S1-S5) – 5 pairs coccygeal nerve (C0) – one pair Spinal Nerves The adult spinal cord ends at the level between the first and second lumbar vertebrae, so the lumbar, sacral, and coccygeal nerves descend beyond the end of the cord, forming a structure called the cauda equina (horse’s tail). Spinal Nerves Injuries and Disorders of the Nervous System Injuries to the Brain and Spinal Cord traumatic brain injury cerebral palsy spinal cord injury Traumatic Brain Injury violent impact to head mild moderate severe Traumatic Brain Injury Cerebral Palsy damage to brain before birth during birth during infancy motor function impairment Spinal Cord Injuries C1–C3: usually fatal C1–C4: quadriplegia C5–C7: paralysis of lower extremities T1–L5: paraplegia Corepics/Shutterstock.com Common Diseases and Disorders of the CNS Meningitis: infection that affects the delicate membranes -called meninges (men-in'-jeez) -- that cover the brain and spinal cord. Bacterial meningitis can be deadly and contagious among people in close contact. Viral meningitis tends to be less severe and most people recover completely without specific therapy. Fungal meningitis is a rare form of meningitis and generally occurs only in people with weakened immune systems. Multiple sclerosis: unpredictable, often disabling disease of the central nervous system that disrupts the flow of information within the brain, and between the brain and body. Common Diseases and Disorders of the CNS Epilepsy: CNS disorder (neurological disorder) in which nerve cell activity in the brain becomes disrupted, causing seizures or periods of unusual behavior, sensations and sometimes loss of consciousness. Parkinson’s disease: progressive disorder of the nervous system that affects movement. Dementia and Alzheimer’s disease: Alzheimer's is the most common form of dementia, a general term for memory loss and other intellectual abilities serious enough to interfere with daily life. Review and Assessment Match these words with 1–4 below: quadriplegia, multiple sclerosis, dementia, cerebral palsy. 1. inflammation destroys myelin sheath 2. loss of memory and thinking 3. loss of function below the neck 4. may begin before birth