LECTURE 9 INTRO CNS

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jskunz
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LECTURE 9 INTRO CNS
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2013-03-06 21:03:45
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Intro nervous system CNS
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nervous/cns
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  1. Anatomic types of neurons
    • (morphologic) - the categories of neurons based on the number of dendrites and physical relationship of the cell body to the axon and dendrite.
    • Three types are described: pseudounipolar, bipolar, and multipolar
  2. ANS
    • Autonomic nervous system - those parts of the nervous system that are motor to involuntary effectors.
    • includes some parts of both the CNS and the PNS
  3. axon
    • the single process of a neuron that carries an impulse away from the cell body. 
    • At the terminal end(s), impulses are synaptically transmitted to other neurons or to effectors
  4. CNS
    • central nervous system - the brain and spinal cord
    • receives sensory impulses
    • processes and stores information
    • sends motor impulses out to effectors
  5. cerebellum
    • the second largest part of the brain
    • has two hemispheres united by a cerebellar vermis
    • functions in the coordination of skeletal muscle activity
  6. CSF
    Cerebrospinal fluid - the water based medium which occupies the ventricles and interconnecting channels of the brain, the central canal of the spinal cord, the subarachnoid space, and the osseous labyrinth of the temporal bone
  7. cerebrum
    • the largest part of the brain
    • includes the left and right cerebral hemispheres and some intervening structures
  8. dendrite
    • a neuronal process that carries an impulse toward the cell body of a neuron
    • multipolar neurons have multiple dendrites
    • bipolar and pseudounipolar neurons have one dendrite each
  9. depolarization
    • a physiological term indicating an elevation in the intracytoplasmic voltage.
    • If it reaches threshold potential, an action potential is triggered, consisting of rapid further depolarization followed by repolarization to re-establish the resting voltage
  10. functional types of neurons
    • the categories of neurons based on the origin and destination of their impulses
    • Four types exist: somatic efferent, somatic afferent, visceral efferent, and visceral afferent neurons
  11. gray matter
    • those parts of the brain and spinal cord that are darker in color than white matter
    • owes it's pigmentation to the presence of large #'s of neuronal cell bodies, which, with their complement of organelles, impart the darker color
  12. meninx
    • (pl = meninges) - one of the three connective tissue proper encasements of the brain and spinal cord.
    • trabecular space btwn the innermost meninx (pia mater) and the middle one (arachnoid mater) contains cerebrospinal fluid and is called the subarachnoid space
  13. efferent impulse/neuron
    • motor impulse
    • a nervous impulse emanating from the brain or spinal cord/a neuron that carries such an impulse.
    • Motor impulses are destined for glandular epithelium or muscle tissue
  14. myelin
    • a lipid material manufactured by neurolemmocytes and oligodendrocytes.
    • the insulating medium in myelinated neurons
  15. neurotransmitter
    • a chemical involved in synaptic impulse transmission
    • manufactured by neurons and sensory recepters
    • released under appropriate stimulation
  16. PNS
    • peripheral nervous system - nerves, ganglia, and sensory receptors
    • generates sensory impulses
    • carries sensory and motor impulses to and from the CNS
  17. repolarization
    • that part of an action potential consisting of a rapid drop in voltage after the potential has been raised by depolarization.
    • effected by a rapid out-rush of potassium ions from the cytoplasm
  18. afferent impulse/neuron
    • sensory impulse
    • an impulse destined for the CNS/a neuron that carries such an impulse
    • generated by sensory receptors and then are conducted in the brain or spinal cord
  19. sodium-potassium pump
    • the active transport mechanism found in most types of body cells that moves THREE SODIUM IONS OUT and TWO POTASSIUM IONS INTO the cell for each ATP epended
    • are especially important in muscle cells and neurons
  20. synapse
    • a junction of a neuron or sensory receptor with another cell
    • sensory receptors synapse with neurons
    • neurons synapse variously with other neurons, with muscle cells, or with glandular epithelial cells
  21. white matter
    • those parts of the brain and spinal cord that are notably whiter in color than the remainder (gray matter)
    • consists mainly of myelinated axons, and myelin is a white-colored lipid material
  22. Two major divisions of the nervous system
    CNS and PNS
  23. Structures that comprise CNS
    brain and spinal cord
  24. structures that comprise PNS
    cranial nerves, spinal nerves, a number of ganglia, and some specialized sensory receptors
  25. ANS and it's function
    Autonomic nervous system - a consists of those parts of the CNS and PNS that control involuntary muscle tissue and glandular epithelium
  26. Functions of PNS
    • Converting (transducing) various forms of energy to sensory impulses - specialized receptor cells are required for some of these conversions
    • Conducting sensory impulses into the CNS via the cranial and spinal nerves (these nerves serve as extensions of brain and spinal cord, consist of bundles of processes)
    • Distributing the motor impulses which originate the brain and spinal cord to the muscle tissue and glands of the body (these outgoing impulses travel same cranial and spinal nerves as incoming, but carried by different n. cells)
  27. Functions of CNS
    • receiving the sensory impulses carried by the cranial and spinal nerves
    • processing and storing information
    • sending motor impulses to muscle tissue and glandular epithelium
  28. general sensation
    heat, cold, touch, pressure, pain
  29. special senses
    sight, hearing, smell, taste, body position, balance
  30. neurons
    • the functional cells of the nervous system
    • anatomically and physiologically specialized for the conduction of electrochemical energy commonly called nervous impulses
    • only cell in the nervous system that are capable of transmitting nervous impulses
  31. multipolar neurons
    • have several dendrites and a single axon (which may have numerous branches
    • all interneurons are multipolar
  32. interneurons
    • neurons located totally within the CNS.
    • All are multipolar
  33. Bipolar neurons
    • have single dendrite and single axon.
    • least numerous neuronal type
    • found only in the retina of the eye, in the internal ear and the nasal mucosa
    • carry sensory impulses interpreted by CNS as vision, body balance/position, audition and olfaction
  34. pseudounipolar neurons
    • resemble neurons except that the cell body is offset which occurs because the axonal process fuses directly to the single dendritic process with a single combined connection making direct contact with the cell body
    • carry all sensory information except for that regegated to bipolar neurons
  35. Functional classification of neurons
    • 4 groups:
    • somatic efferent
    • visceral efferent
    • somatic afferent
    • visceral afferent
  36. Somatic efferent neurons
    the multipolar neurons which supply motor impulses to skeletal muscle. Cell bodies located in brain and spinal cord, axons distributed to all of skeletal muscles
  37. visceral efferent neurons
    • These neurons and the CNS centers which control them comprise the ANS system
    • sends motor impulses
    • multipolar neurons which form a two neuron chain to smooth muscle cells, cardiac muscle cells, and glandular epithelium
    • 1st neurons called preganglionic neruons
    • 2nd neurons called postganglionic neurons
  38. preganglionic neurons
    • first neurons in the two neuron chain in visceral efferent neurons
    • located in the brain and spinal cord
  39. postganglionic neurons
    • second neurons in the tow neuron chain of visceral efferent neurons
    • located in autonomic ganglia in the peripheral nervous system
  40. somatic afferent neurons
    • those which carry sensory info from the skin, skeletal muscles, bones, joints, vision, audition, and the sense of balance and body position
    • cell bodies are located in the sensory ganglia of the cranial and spinal nerves as well as in the retina
    • most are pseudounipolar but a few are bipolar (those in the retina and internal ear)
  41. visceral afferent neurons
    • carry sensory impulses from deep body systems as well as those involved in the special senses of smell and taste
    • (olfaction, gustation)
    • cell bodies are located in the sensory ganglia of the cranial and spinal nerves and in the nasal mucosa
    • most are pseudounipolar but those ass. with the sense of smell are bipolar
  42. (fiber) tracts
    groups of processes within the brain and spinal cord
  43. nerves
    • groups of processes which are located OUTSIDE THE CNS
    • enclosed in connective tissue ensheathments
    • ex: cranial and spinal nerves
  44. Nuclei
    • Groups of neuronal cell bodies WITHIN THE CNS
    • (singular: nucleus - not to be confused the the nucleus of a cell)
  45. ganglia
    • groups of neuronal cell bodies in the perpheral nervous system
    • 2 distinct types: sensory and autonomic
    • (singular: ganglion)
  46. Sensory ganglia
    • associated with the cranial and spinal nerves
    • located near the attachment of these nerves to the brain and spinal cord
    • contain the cell bodies of pseudounipolar neurons  (both SA and VA) which convey general sensory impulses into the CNS
  47. Autonomic ganglia
    • contain the cell bodies of visceral efferent neurons
    • found in many locations
    • 3 types: terminal, sympathetic trunk, named peripheral ganglia
    • serve as synaptic sites btwn the 1st and 2nd neurons in the two neuron chain of the autonomic nervous system
  48. neuroglia
    • also called glial cells
    • support and aid the function of neurons
    • Several types: neurolemmocytes, oligodendrocytes, astrocytes, microglia, satellite cells and ependymal cells
  49. Neurolemmocytes
    • formally known as "Schwann" cells
    • flattened cells that form electrically insulating layers around axons in the PNS called myelin sheaths
    • insulating property called myelin
    • covers about a linear millimeter of axon by forming several snug wraps around it
  50. myelin sheaths
    • electrically insulating layers around axons in the PNS
    • their insulating property is derived from a lipid material in their cytoplasm called myelin
  51. myelin
    a lipid material which insulates myelin sheaths
  52. myelinated
    • axons in the PNS that are surrounded by neurolemmocytes
    • myelination affects the speed of nerve impulse conduction because the depolarization occurs only at the junctions of the ensheathing neurolemmocytes
    • In other words, it "skips" over the neurolemmocytes themselves by saltatory conduction
  53. unmyelinated
    axons in the PNS that lack neurolemmocytes
  54. Neuroglia which support PNS only
    neurolemmocytes and satellite cells
  55. Neuroglia which support CNS only
    oligodendrocytes, microglia, astrocytes, ependymal
  56. Oligodendrocytes
    cells which form myelin sheaths around axons within the CNS
  57. Astrocytes
    • the largest and most numerous of glial cells
    • form blood-brain barrier by being physically interspersed btwn blood vessels and neurons w/i the brain
    • for a final filter for all materials that reach the neurons from bloodstream
  58. microglia
    • phagocytic cells w/i CNS
    • are mobile and ingest foreign and degenerated materal
  59. ependymal cells
    • cuboidally shaped cells that line the ventricles (fluid filled spaces) of the brain and the central canal of the spinal cord
    • in certain locations they are modified and secrete the cerebral spinal fluid
  60. satellite cells
    • PNS supporting cells
    • found in ganglia
    • don't know what they do exactly
  61. Differentiate myelin and myelin sheath
    • MYELIN SHEATHS are made up of neurolemmocytes which form electrically insulating layers around axons in the PNS
    • MYELIN is a lipid material in the neurolemmoctyes cytoplasm which is the insulating property
  62. why are neurons able to conduct electrical (nervous) impulses
    • because their cytoplasm is charged (negatively) compared to their extracellular environment
    • potential difference due to neg. charged protien ions in cytoplasm & because excess of +charged sodium ions which are actively transported out of the cells by sodium-potassium pump
  63. resting potential
    • about -65 millivolts
    • the charge caused by the negatively charged protein ions in the neruon's cytoplasm and the excess of + charged sodium ions when at rest
  64. depolarization
    • charge reversal
    • happens when a neuron is stimulated such (by neurotransmitters from other neurons) that some of the Na+ ions readily DIFFUSE back through the cell membrane, a measurable momentary change in electrical potential occurs (meaning a positively charged cytoplasm)
  65. threshold
    • the critical level reached in depolarization, around -40 mv.
    • the membrane becomes temporarily permeable to sodium
    • Sodium rushes in by SIMPLE DIFFUSION
    • Sodium rushing in causes charge with positively charged cytoplasm & keeps going up. when it reaches 40 mv., Na+ gates close and K gates begin to open
  66. repolarization
    • When the charge of cytoplasm reaches about +40 mv. makes the membrane temporarily permeable to potassium, and enough K+ rush out of the cell to re-establish the original resting voltage
    • Cell membrane then becomes impermeable (once again) to both Na+ and K+ until the next impulse occurs
  67. nervous impulse
    the movement of depolarization and repolarization down the cell's membrane
  68. saltatory conduction
    process by which myelinated neuron impulses "skip" over the neurolemmocyteds
  69. Three basic types of cells with which a neuron can synapse
    • other neurons
    • muscle cells
    • glandular epithelial cells
  70. Role of the sodium-potassium pump
    • establishes the resting differences in sodium and potassium concentrations inside and outside the cell membrane
    • as depolarization and repolarization move down a cell's membrane they constitute a nervous impulse
  71. Role of neurotransmitters
    • a chemical substance that is released when the electrical impulse of the first neuron reaches the synapse, which initiates the release
    • diffuses across synaptic gap, interacts w/ the cell membrane of the next neuron and (if enuf is relased) either initiates an impulse - excitatory neurotransmitter - or inhibits an impulse in the next cell - inhibitory n.
    • # of different neuro's have been identified
    • released from synaptic vesicles stored in the ends of axons
  72. synapses
    special junctions between two neurons which consist of a narrow gap btwn the axon of the first neuron and usually the dendrite or the cell body of the second one
  73. what prevents neurotransmitters from initiating additional impulses
    rapid enzymatic decomposition of the neurotransmitters
  74. most common neurotransmitters in the PNS
    • acetylcholine
    • norepinephrine
  75. What does nervous tissue develop from?
    the outer one of the three primary germ layers (ectoderm)
  76. neural plate
    the area of the ectoderm overlying the notochord which thickens early in development
  77. neural groove
    when the neural plate invaginates the ectoderm longitudinally a few days after thickening
  78. neural tube
    • after a few days, the neural groove deepens and finally pinches off the the surface of the ectoderm and becomes the neural tube (dorsal hollow neural tube)
    • develops into the brain (anteriorly) and the spinal cord (posteriorly)
  79. neural crests
    • formed from groups of cells which separate from each side of the neural tube
    • develop into sensory neurons, autonomic neurons, neurolemmocytes, melanocytes, and chromaffin cells
  80. 6 major parts of the brain
    • Also called the definitive brain
    • (1) cerebrum
    • (2) epithalamus, thalamus, and hypothalamus (together)
    • (3) mesencephalon
    • (4) pons
    • (5) cerebellum
    • (6) medulla oblongata
  81. vesicles
    • three bulges that develops at the enterior end of the neural tube
    • destined to form the brain: prosencephalon, mesencephalon, and rhombencephalon
  82. prosencephalon
    • forebrain
    • divides into the telencephalon and diencephalon
  83. telencephalon
    • develops FROM the prosencephalon (forebrain)
    • forms INTO the cerebrum
  84. diencephalon
    • develops FROM the prosencephalon (forebrain)
    • divides into the epithalamus, thalamus, and hypothalamus (which surround the third ventricle)
  85. Three vesicle stage
    • Prosencephalon (forebrain)
    • Mesencephalon (midbrain)
    • Rhombencephalon (hindbrain)
  86. Five vesicle stage
    • Telencephalon
    • Diencephalon
    • Mesencephalon
    • Metencephalon
    • Myelencephalon
  87. Mesencephalon
    midbrain, does not divide further
  88. Rhombencephalon
    • hind brain
    • divides into the metencephalon and myelencephalon
  89. Metencephalon
    • develops FROM the Rhombencephalon (hindbrain)
    • subdivides into the Pons and Cerebellum
  90. myelencephalon
    • develops FROM the Rhombencephalon (hindbrain)
    • subdivides into the medulla oblongata
  91. anencephaly
    when the brain simply fails to develop
  92. microencephaly
    when the brain develops incorrectly
  93. spina bifida
    then the spinal cord is exposed near the surface of the body by failure of the surrounding vertebral column to properly enclose it
  94. encephalon
    brain
  95. cerebrum
    • largest part of the brain
    • has over 1000 named parts
    • major center of sensory perception, thought, memory and motor output
  96. cerebral gyri
    • singular = gyrus
    • the numerous rounded ridges on the outer portion of the cerebrum
  97. cerebral sulci and fissures
    • singular = sulcus
    • grooves on the cerebrum which separate the numerous rounded ridges
  98. cerebral hemispheres
    • major part of the cerebrum which is divided into left and right
    • each hemisphere is further divided into five lobes: frontal, parietal, temporal, occipital, and insular lobes
  99. frontal lobe
    • subdivision of the cerebrum
    • anteriorly situated (deep to the frontal bone and part of the parietal bone)
    • major function is voluntary control of skeletal muscle activity
    • also has roles in verbal communication and thought
  100. parietal lobe
    • subdivision of the cerebrum
    • behind the frontal lob and separated from it by the central sulcus
    • major function is general sensory perception
  101. temporal lobe
    • subdivision of the cerebrum
    • inferior to the frontal and parietal lobes, separated from the by the later sulcus
    • involved with the interpretation of sound and the sense of body position and balance
  102. occipital lobe
    • subdivision of the cerebrum
    • forms the posterior portion of the cerebral hemisphere
    • anterior aspect is separated from the parietal lob by the parieto-occipital sulcus
    • has several roles in visual interpretation and coordination of eye movements
  103. insular lobe
    • (insula) underlies the frontal, parietal, and temporal lobes.
    • believed to be at least one center of "memory"
    • integrates other cerebral activities
  104. portions of the cerebrum that are not part of the cerebral hemispheres
    the rhinencephalon and the corpus callosum
  105. rhinencephalon
    • paired, consists primarily of the olfactory bulb and the medial and lateral olfactory gyri
    • the olfactory bulb extends forward and the fibers of the first pair of cranial nerves attach to it
  106. corpus callosum
    a large interconnection between the left and right cerebral hemispheres
  107. lateral ventricle
    • space surrounded by each hemisphere of the cerebrum
    • filled with CSF (cerebrospinal fluid)
  108. functions of the hypothalamus
    • Regulate heart rate and blood pressure
    • Thermoregulation (sweating, shivering, vasomotion)
    • Water and electrolyte balance (ADH secretion and thirst center)
    • Hunger and satiety feelings
    • Sleep and wakefulness regulation
    • Sexual responsiveness
    • Production of major emotional states
    • Production of several hormones acting on the pituitary gland & two hormones released from pituitary (ADH and oxytocin)
  109. epithalamus
    • subdivision of the diencephalon
    • thin; formes the roof of the third ventricule
    • posterior-most part is the PINEAL BODY (GLAND)
  110. pineal body (gland)
    • the posterior-most part of the epithalamus
    • produces the hormone melatonin
  111. thalamus
    • subdivision of the diencephalon
    • forms the lateral walls of the third ventricle and serves as a relay center for most general sensory impulses originating below the head
  112. hypothalamus
    • subdivision of the diencephalon
    • forms the floor of the third ventricle
    • although relatively small, plays a number of important functional roles
    • roles include centers for thirst, hunger, satiety, sleep, wakefulness, sexual responsiveness, and cardiovascular control
    • also produces several hormones
  113. optic chiasm
    • continues anteriorly as the optic nerves
    • projects forward from the hypothalamus
  114. mesencephalon
    • the smallest of the major parts of the brain
    • serves as a reflex center for audition and vision
    • contains the motor nuclei of the oculomotor and trochlear (3rd and 4rth) cranial nerves
    • surrounds the mesencephalic aqueduct
  115. mesencephalic aqueduct
    • also called the cerebral aqueduct
    • filled with CSF (cerebral spinal fluid)
    • connects the third ventricle to the fourth ventricle
  116. pons
    • lie anterior to the nesencephalon
    • forms a rounded bulge in the underside of the brain
    • contains motor nuclei for cranial nerves 5,6,7
    • contains sensory nucleus for cranial nerve 8
    • serves as a bridging connection between the medulla oblongata and mesencephalon
    • also has connections to the cerebellum
    • contains two respiratory centers
  117. cerebellum
    • second largest subdivision of the brain
    • occupies the posterior cranial fossa
    • diveded into ten cerebellar lobules
    • forms distinctive rounded mass inferior to the occipital lobes
    • contains white matter
    • coordinates the motor impulses to skeletal muscles
    • connected to rest of nervous system by three pairs of giber bundles called cerebellar peduncles
  118. arbor vitae
    white matter within the cerebellum which appears to be shaped like a tree in a median section
  119. cerebellar hemispheres are joined where?
    at the centrally located body by a "worm-shaped" sturcture called the cerebellar vermis
  120. cerebellar peduncles
    • 3 pairs = Superior, Middle, and Inferior
    • fiber bundles which connect the cerebral hemispheres to the rest of the nervous system
  121. spinal cord
    • direct, inferior continuation of the medulla oblongata
    • passes through the foramen magnum of occipital bone
    • extends inferiorly through the vertebral canal
    • contains ascending (sensory) and descending (motor) fiber tracts, cell bodies of motor neurons, and cell bodies of interneurons (neurons btwn neurons)
    • endlosed within connective tissue encasements (meningses) that are continuous with those around brain
    • tapers as it courses inferiorly
  122. anterior median fissure
    anterior indents of the spinal cord
  123. posterior median sulus
    posterior indents of the spinal cord
  124. cervical and lumbosacral intumescences
    • both subtle swellings of the spinal cord
    • these enlargements occur because of the increased # of neurons and fiber tracts in those areas which are associated with the limbs
  125. conus medullaris
    • a conical projection where the spinal cord ends inferiorly
    • at level of L1/L2
  126. spinal nerves
    • emerge from spinal cord as anterior and posterior rootlets which coalesce to form the roots of 31 to 33 pairs of nerves
    • pass through the intervertebral foramina and are distributed segmentally to the body
  127. cauda equina
    • spinal nerves that originate from the lower part of the spinal cord and continue beyond its L1/L2 termination
    • so named cause of it's resemblance to a horses tail
  128. gray matter
    • centrally located in spinal cord, shaped like "X" or "H"
    • surrounded by white matter
    • contains a large # of neurons which impart a darker color than the surrounding white matter
    • consists mainly of myelinated axons in ascending or descending fiber tracts
    • surrounds tiny central canal
    • divided into ANTERIOR GRAY COLUMN and POSTERIOR GRAY COLUMN - in thoracic region small LATERAL GRAY COLUMN
  129. anterior gray column
    • "ventral"
    • contains mostly somatic efferent neurons whose axons are carried to the skeletal muscles by the spinal nerves
  130. posterior gray column
    • "dorsal"
    • contains mostly interneuron cell bodies involved in somatic reflex arcs or in relaying sensory impulses up to the brain
  131. lateral gray column
    • located in thoracic region, small identifiable column
    • contains some of the presynaptic sympathetic neurons
  132. white matter (of the spinal cord)
    • divided into three areas
    • funiculi
    • anterior,posterior
    • lateral
  133. funiculi
    • white matter in spinal cord
    • consist of named bundles of axons (fiber tracts) that transmit sensory impulses up to the brain (acsending tracts) or carry motor impulses down from the brain (descending tracts)
  134. why does the spinal cord widen in two places
    • called the cervical and lumbosacral intumescences
    • occur because of the increased # of neurons and fiber tracts in those areas which are associated with the limbs
  135. concussion
    • "bruising" of the brain tissue which may result in temporary unconsciousness or an extended coma
    • can also have amnesia and delirium
  136. Diseases of the CNS resulting from degenerative conditions of myelin ensheathments
    tay-sachs, multiple sclerosis
  137. paraplegia
    if only the inferior limbs are involved with paralysis
  138. hemiplegia
    if the superior and inferior limb on the same side of the body are paralyzed
  139. epilepsy
    involves periodic, temporary loss of consciousness and varying degrees of convulsive seizures
  140. neuroses
    group of mental illnesses in which contact with reality is maintained
  141. psychoses
    group of mental illnesses in which contact with reality is lost
  142. Poliomyelitis
    • "polio"
    • a viral disease that destroys motor neurons in the anterior column of gray matter in the spinal cord
    • because these are S.E. neurons, paralytic deficits occur in the skeletal muscles supplied to them
    • has been controlled in parts of the world by immunization
  143. Meningitis
    • caused by a bacterial or viral infection involving the meninges
    • may be limited to the meninges of the spinal cord or may also affect those covering the brain and cause encphalitis
    • some cases are fatal
  144. Syphilis
    • a S.T.D. caused by a spirochete bacterium
    • has large # of physical manifestations including several that affect the brain and spinal cord
  145. Tay-Sachs
    • disease that is a heritable condition caused by excess accumulation of one of the lipid components in myelin
    • causes progressive symptoms that culminate in death in early childhood
  146. multiple sclerosis
    • a chronic progressive disease that destroys myelination
    • affected areas are invaded by fibrous connective tissue which form scars called scleroses
    • affected individuals have wide variety of symptoms depending on areas in body affected
    • often have periods of clinical remission but eventually suffer permanent paralysis and then death
  147. degenerative diseases of CNS primarily affecting the elderly
    parkinson's disease and alzheimers
  148. Parkinsons's disease
    • involves destruction of neurons within the basal nuclei of the brain resulting in muscular tremors, speech deficits and other symptoms
    • some pt.s can improve by drugs which affect neurotransmitter metabolism
  149. Alaheimer's disease
    a progressive mental deterioration of unknown cause that begins in middle age.
  150. hydrocephalus
    • also known as water on the brain
    • condition in which there is an abnormal amount of CSF in the ventricles of the brain
    • may be caused by intracranial pressure within the brain and progressive enlargement of the head
    • can cause death
  151. Nervous tissue develops from the outermost of the three germ layers (ectoderm) Explain why so few nervous system structures are located at the body surface
    During development, the ectoderm that forms nervous tissue forms a plate, a groove and then a tube that separates from the rest of the ectoderm and assumes a position buried in the underlying mesoderm
  152. Why is gray matter (light) gray and white matter whiter?
    The gray ("dirty" white) results from a higher concentrations of neuron cell bodies (where the organelles are concentrated) and the white results from the color of the myelin within the oligodendrocytes
  153. Explain how axons of myelinated neurons conduct impulses faster than those which are not myelinated
    • The phenomenon of impulse conduction is similar in myelinated and unmyelinated axons.
    • In unmyelinated neurons, the depolar/repolarization must occur along the whole extent of the axonal cell membrane.
    • In myelinated neurons, depolar/repolarization "skips" across the insulating cells (neurolemmocytes of oligodendrocytes) and only occurs at minute gaps (nodes) btwn them.
    • can be likened to two individuals racing up a stair with one taking every step and the other skipping steps
  154. How does synaptic transmission of nervous impulses occur
    by chemicals called neurotransmitters, which are released when an impulse reaches the end of an axon. They diffuse across a minute gap (called a synaptic cleft) and interact with the cell membrane of the next cell which could be glandular epithelial cell, muscle cell, or another neuron. Depending on chemical composition, may excite or inhibit the next cell
  155. Nerve impulse transmission involves a rapid depolarization followed immediately by a repolarization. What causes the depolarization? The repolarization?
    • Depolarization (rising voltage) occurs due to a rapid diffusion of sodium ions into the cytoplasm through the suddenly (sodium) permeable cell membrane
    • Repolarization (falling voltage) occurs due to a rapid outflux of potassium ions
  156. Signif. trauma to the cerebral hemispheres may have relatively little effect on brain function. Why?
    Large parts of the brain (especially the cerebral cortex) do not appear to have significant functions.
  157. Where is the local anesthetic deposited in "epidural" anesthesia?
    The anesthetic is deposited on the surface of the dura mater. It reaches nervous tissue by diffusion
  158. Why are concussion type injuries closely monitored for several hours after their occurrence?
    The trauma may have ruptured blood vessels.  Extravasation of blood can put pressure of the brain since the skull is not expandable
  159. Explain why a severed spinal cord cannot heal back together and function
    • Axonal regeneration occurs very slowly and the severed ends cannot be held in correct apposition for the months required.
    • In addition, scar tissue (conn. t.p.) tends to invade the injury and prevent regeneration
  160. Why can a vertebral canal be penetrated with a needle at L2/L3 with no concern about damage to the spinal cord?
    The spinal cord ceases growing before the vertebral column (it is shorter than v. column).  The cord itself ends at the level of junction of the 1st and 2nd lumbar vertebrae in a conical projection termed the conus medullaris. The last several pairs of spinal nerves arise segmentally from the homonymous cord segments above this termination. They continue inferiority below the end of the spinal cord and leave the v. canal at the appropriate intervertebral foramina. This bondle of nerves below the cord is called the cauda equina
  161. Why do many sensory and motor tracts decussate at the medulla oblongata?
    No one know why. This is the anatomic phenomenon that explains why the left part of the brain deals with sensory and motor impulses involving the right side of the body (and vice versa)
  162. How do inhibitory neurotransmitters work?
    Inhibitory neurotransmitters hyperpolarize the next cell by lowering it's resting voltage. This inhibits impulse initiation because the cell's voltage must be elevated to the threshold level to start an impulse
  163. If the prosencephalon were damaged during early embryogenesis, what definitive part of the brain might be defective?
    The cerebrum and all derivatives of the diencephalon (epithalamus, thalamus, and hypothalamus)
  164. Once complex locomotor skills like serving a tennis ball or skating backwards have been mastered, an individual can do them without "thinking" about what is involved. How is this handled by the CNS?
    The cerebellum is heavily involved in the coordination of skeletal muscle activity. It must first be "taught" what to do, but once these motor patterns are learned, the cerebellum allows an "auto-pilot" sort of control wherein an individual can perform complex motor tasks w/o much conscious involvement
  165. Why is nerve impulse transmission described as an electrochemical phenomenon?
    The impulse itself is produced by the diffusion of ions (charged sodium and potassium atoms) At synapses, chemicals (neurotransmitters) are involved
  166. Where is CSF found?
    Cerebrospinal fluid is found in the ventricles of the brain, mesencephalic aqueduct, central canal of spinal cord, subarachnoid space, and btwn the osseus and membranous labyrinth
  167. What disease syndrome can result from blockage of flow of CSF?
    Hydrocephalus. It can sometimes be treated by surgical installation of bypasses (shunts) that allow CSF to flow around blockages
  168. What is the difference between a motor impulse and a sensory impulse?
    There is no difference in the impulses, themselves. Motor impulses are destined for muscles and glands.  Sensory impulses are directed toward the spinal cord and/or brain
  169. Do neurons function as "2-way streets" for impulse transmission?
    No. A given neuron transmits in one direction only. Thus, a particular neuron is only involved with outgoing or incoming impulses
  170. Sensory neurons always synapse with...
    other neurons. Some motor neurons, on the other hand, synapse with muscle cells, some synapse with glandular epithelial cells, and some synapse with other neurons.

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