A&P Chapter 7 The Nervous System 1. Outline the structural organization of the nervous system. ---structural classification, which includes all nervous system organs has two subdivisions --central nervous system (CNS) consists of brain and spinal cord --peripheral nervous system (PNS) is part outside the CNS and consists mainly of nerves that extend from brain and spinal cord -spinal nerves carry impulses to and from spinal cord -cranial nerves carry impulses to and from the brain 2. Outline the functional organization of the nervous system. ---functional scheme is concerned ONLY with PNS structures ---sensory (afferent) division conducts impulses TO THE CENTRAL NERVOUS SYSTEM --sensory fibers from skin, skeletal muscles, and joints called somatic sensory (afferent) fibers --sensory fibers from visceral organs called visceral sensory fibers (visceral afferents) --sensory division keeps CNS constantly informed of events going on both inside and outside the body ---motor (efferent) division carries impulses FROM THE CENTRAL NERVOUS SYSTEM to effector organs, the muscles, and glands --impulses activate muscles/glands --they effect (bring about) a motor response --**motor division has two subdivisions -somatic nervous system and autonomic nervous system 3. Discuss the autonomic nervous system: Level of control, effectors, and two distinct divisions. ---autonomic nervous system (ANS) is motor subdivision of PNS that controls body activities automatically (involuntary) ---composed of special group of neurons that regulate cardiac muscle, smooth muscles, and glands ---ANS also called involuntary nervous system ---ANS composed of two distinct systems: sympathetic and parasympathetic ---both serve same organs but cause essentially opposite effects --counterbalance each other’s activities to keep body systems running smoothly ---preganglionic axons of sympathetic division release acetylcholine; postganglionic axons release norepinephrine and/or epinephrine (called adrenergic fibers) ---preganglionic axons and postganglionic axons of the parasympathetic division release acetylcholine (called cholinergic fibers) ---sympathetic part mobilizes body during extreme situations (fear, exercise, or rage) --E for exercise, excitement, emergency, and embarrassment ---parasympathetic division allows body to “unwind” and conserve energy --D for digesting, defecation, and diuresis (urination) 4. Discuss the somatic motor nervous system: effectors activated and neurotransmitter released. ---somatic motor nervous system allows us to consciously, or voluntary control skeletal muscles ---this subdivision often referred to voluntary nervous system ---in somatic division, cell bodies of motor neurons are inside central nervous system and their axons (in spinal nerves) extend all the way to skeletal muscles they serve ---skeletal muscle are the effectors of the somatic motor nervous system ---neurotransmitter is acetylcholine 5. Outline the cells of nerve tissue. ---nervous tissue composed of two principal types of cells --neurons and supporting cells ---supporting cells in CNS are lumped together as neuroglia (nerve glue) ---neuroglia (also called glia) support, insulate, and protect delicate neurons ---astrocytes account for nearly half of neural tissue --brace and anchor neurons to blood capillaries --form a living barrier between capillaries and neurons and play role in making exchanges between the two --help protect neurons from harmful substances in blood --help control chemical environment by picking up excess ions and recapturing released neurotransmitters ---microglia are phagocytes that dispose of debris-dead brain cells, bacteria, etc. ---ependymal cells line cavities of brain and spinal cord --beating of their cilia help circulate the cerebrospinal fluid that fills those cavities and forms protective cushion around CNS ---oligodendrocytes wrap their flat extensions around nerve fibers, producing fatty insulating coverings called myelin sheaths ---**neuroglia are NOT able to transmit nerve impulses and they never lose their ability to divide --most brain tumors are gliomas or tumors formed by glial cells ---supporting cells in PNS come in two major varieties --Schwann cells form myelin sheaths around nerve fibers that are found in PNS --satellite cells act as protective, cushioning cells ---neurons (nerve cells) are highly specialized to carry impulses (transmit messages) ---all neurons have cell body (soma) and one or more slender processes extending from cell body --neuron processes that conduct electrical impulses toward cell body are dendrites --neuron processes that conduct electrical impulses away from cell body are axons ---neuron may have 100s of dendrites but only ONE axon --axons branch profusely at terminal end forming 100s to 1000s of axonal termials 6. State the functions of the various parts of a neuron. ---cell body contains the nucleus and is the metabolic center of the neuron ---dendrites responsible for transmitting electrical impulses to the cell body ---the axon is responsible for transmitting the electrical impulse away from the cell body to either another neuron or to the effector ---most long neurons are covered with whitish, fatty material called myelin --myelin protects and insulates the fibers and increase the transmission rate of nerve impulses ---axons outside CNS are myelinated by Schwann cells-specialized supporting cells that wrap tightly around axon jelly-roll fashion --when wrapping done, tight coil of wrapped membranes called the myelin sheath encloses axon --most of Schwann cell cytoplasm ends up just beneath the outermost part of its plasma membrane --this part of Schwann cell, external to myelin sheath called the neurilemma ---since myelin sheath is formed by many individual Schwann cells, it has gaps or indentations called nodes of Ranvier at regular intervals ---myelin sheaths in neurons of CNS are formed by the oligodendrocytes --CNS myelin sheaths lack a neurilemma 7. Distinguish between nuclei and ganglia; nerves and tracts; white matter and gray matter. ---cell bodies are found in the CNS in clusters called nuclei --this well-protected location essential to well-being of nervous system ---small collections of cell bodies called ganglia are found in a few sites outside CNS in the PNS ---bundles of nerve fibers (neuron processes) running through CNS are called tracts ---bundles of nerve fibers (neuron processes) running through PNS are called nerves ---terms white matter and gray matter refer respectively to myelinated versus unmyelinated regions of the CNS ---as general rule, white matter consists of dense collections of myelinated fibers (tracts) ---gray matter contains mostly unmyelinated fibers and cell bodies 8. Outline the classification of neurons. ---neurons may be classified according to how they function or according to their structure ---FUNCTIONAL classification based on direction impulse is traveling relative to CNS ---there are sensory, motor, and association neurons ---sensory (afferent) neurons carry impulses from sensory receptors (in internal organs or skin) to the CNS --cell bodies of sensory neurons always found in a ganglion outside the CNS --inform about what is happening inside and outside the body ---motor (efferent) neurons carry impulses from CNS to viscera, and/or muscles and glands --cell bodies of motor neurons always located in CNS ---association (interneurons) neurons connect sensory and motor neurons in neural pathways --association neuron’s cell bodies always located in CNS ---STRUCTURAL classification based on number of processes extending from cell body ---multipolar neuron has several processes --since all motor and association neurons are multipolar this is most common structural type ---bipolar neuron has two processes-a dendrite and an axon --rare in adults, found only in some special sense organs (eye, ear) where they act as sensory receptor cells ---unipolar neuron has single process emerging from cell body --very short and divides almost immediately into proximal (central) and distal (peripheral) fibers --unique in that only small branches at end of peripheral process are dendrites --remainder of peripheral process and central process function as axons --this in unipolar neuron, axon conducts impulse both toward and away from cell body --sensory neurons found in PNS ganglia are unipolar 9. Explain the resting state of a neuron. ---plasma membrane of a resting (inactive) neuron is polarized ---means there are fewer positive ions sitting on inner surface of neuron’s plasma membrane than there are on its outer face in the tissue fluid that surrounds it ---major positive ions inside the cell are potassium (K+) and major positive ions outside the cell are sodium (Na+) ions ---**as long as the inside remains more negative as compared to the outside, the neuron will stay inactive (resting) ---resting potential of neuron is about –70 millivolts 10. Explain the action potential. ---could be called “nerve impulse” ---stimulus changes permeability of “patch” of membrane and sodium ions diffuse rapidly into cell ---this changes polarity of membrane at that location --inside becomes more positive; outside becomes more negative ---event called depolarization ---is stimulus is strong enough, (at or above threshold level) action potential is initiated ---depolarization of first membrane patch causes permeability changes in adjacent membrane, and event is repeated ---membrane potential goes from –70 mv to + 30 mv ---action potential propagates rapidly along entire length of membrane 11. Explain the repolarization that follows an action potential. ---after area (patch) of membrane depolarizes, it repolarizes ---membrane permeability changes and potassium ions diffuse OUT OF CELL ---restores negative charge inside cell and positive outside ---repolarization occurs in same direction as depolarization ---**sodium-potassium pump used to restore ionic conditions of the resting neuron ---resting potential of –70 mv restored 12. Define reflexes and distinguish somatic and autonomic reflexes. ---reflex is a rapid, predictable and involuntary response to a stimulus ---reflexes occur over neural pathways called reflex arcs ---somatic reflexes include all reflexes that stimulate the skeletal muscles --dendrite of sensory neuron carries impulse to CNS --processing of impulse may or may not occur in CNS --axon of motor neuron carries impulse to effector --pull hand away from hot object = somatic reflex ---autonomic reflexes regulate activity of smooth muscles, the heart, and the glands --secretion of saliva and size of eye pupils are two examples ---ALL reflex arcs have minimum of five elements --(1) sensory receptor which reacts to stimulus --(2) effector organ (muscle or gland eventually stimulated) --(3) afferent neuron/(4) efferent neuron to connect the two --(5) integration center located in CNS ---two-neuron reflex (patellar knee-jerk) is most simple ---three-neuron reflex (flexor or withdrawal reflex) more complex 13. Who is responsible for losing IO #13? 14. Describe examples of somatic reflexes: Patellar and withdrawal. ---patellar reflex: receptors in patellar tendon --effectors are upper leg muscles that cause leg extension ---withdrawal reflex: touching a hot object or finger stick ---can be used as diagnostic tool 15. List the functions of the cerebrum. ---speech, memory, logic, emotional response, consciousness, interpretation of sensation, voluntary movements 16. List the functions of the basal nuclei (basal ganglion). ---modify instructions from the cerebrum to the skeletal muscles ---problems with basal nuclei lead to inability to carry movements in normal way --Huntington’s chorea (disease) results in inability to control muscles, individual exhibits abrupt, jerky, and almost continuous movements --sufferers helped by drugs that block dopamine’s effect --Parkinson’s disease results in individual having trouble initiating movement or in getting muscles going -have persistent hand tremor in which thumb and index finger make continuous circles with one another -due to deficit of neurotransmitter dopamine 17. List the functions of the thalamus. ---part of the diencephalon (innerbrain) that sits atop the brain stem and enclosed by cerebral hemispheres ---thalamus encloses the third ventricle of the brain ---relay station for sensory impulses headed toward cerebrum ---provides “crude” recognition of whether sensation about to have is pleasant or unpleasant --actual interpretation occurs in neurons of cerebral cortex 18. Summarize the functions of the hypothalamus. ---also part of the diencephalon ---an important autonomic nervous system center ---plays role regulation of body temperature, water balance, and metabolism ---also center for many drives and emotions --important part of the limbic system (emotional-visceral brain) ---thirst, appetite, sex, pain, and pleasure centers located in hypothalamus ---regulates the pituitary gland and produces two hormones: ADH and oxytocin 19. Summarize the functions for the midbrain. ---midbrain small part of the brain stem ---anteriorly composed of two bulging fiber tracts (cerebral peduncles) that convey ascending and descending impulses ---dorsally composed of four rounded protrusions called corpora quadrigemina which are reflex centers involved with vision and hearing 20. Summarize the functions of the pons. ---pons is rounded structure that protrudes just below midbrain ---as “bridge,” ascending and descending impulses pass through this area ---contains important nuclei involved in breathing 21. Summarize the functions of the medulla oblongata. ---medulla oblongata most inferior part of brain stem ---merges into spinal cord below with no obvious change in structure ---like pons, is an important fiber tract area ---contains many nuclei that regulate vital visceral activities ---heart rate, blood pressure, breathing, swallowing, and vomiting 22. Summarize the functions of the cerebellum. ---like cerebrum, cerebellum has 2 hemispheres and convoluted surface ---has outer cortex made up of gray matter and inner region of white matter ---provides precise timing for skeletal muscle activity, controls balance and equilibrium ---because of its activity, body movements are smooth and coordinated ---continually monitors the brain’s intentions with actual body performance by monitoring body position and amount of tension in various body parts 23. Explain how the CNS is protected. ---CNS protected by enclosure within bone (skull and vertebral column), by a watery cushion (cerebrospinal fluid), and by enclosing within membranes (meninges) ---is also protected from harmful substances in blood by the blood-brain barrier 24. Discuss the meninges and define meningitis. ---three connective tissues membranes covering and protecting CNS structures are called meninges ---dura mater is the leathery, outermost layer --is double-layered membrane where surrounds brain --periosteal layer is attached to inner surface of skull --meningeal layer forms outermost covering of brain and continues as dura mater of spinal cord ---arachnoid mater is weblike middle meningeal layer --its threadlike extensions span subarachnoid space to attach it to innermost membrane, the pia mater ---pia mater (gentle mother) clings tightly to surface of brain and spinal cord by following every fold ---meningitis is an inflammation of the meninges and is serious threat to the brain because bacterial or viral meningitis may spread to nervous tissue of CNS ---condition of brain inflammation is called encephalitis ---meningitis usually diagnosed by taking sample of CSF from subarachnoid space 25. Discuss cerebrospinal fluid: Origin, where it circulates, composition, tapping, and hydrocephalus. ---cerebrospinal fluid (CSF) continually formed from blood by the choroid plexuses (clusters of capillaries that hang from roof in each of brain’s ventricles ---forms watery cushion in and around brain and cord that protects fragile nervous tissue from blows & other trauma ---CSF continually moving from lateral hemispheres into third ventricle, then through cerebral aqueduct of midbrain into fourth ventricle dorsal to pons/medulla oblongata ---some fluid reaching 4th ventricle continues down central canal of spinal cord but MOST circulates into subarachnoid space through three openings in wall of 4th ventricle ---fluid returned to blood through arachnoid villi ---CSF contains water, glucose, proteins, and sodium chloride ions ---lumbar spinal tap used to collect sample of CSF for testing ---is something affects CSF drainage, it begins to accumulate and exert pressure on brain ---results in hydrocephalus (water on the brain) --risks and treatments 26. Define selected traumatic brain injuries. ---head injuries are leading cause of accidental death in U.S. ---brain damage caused NOT only by injury at site of blow, but also by effect of ricocheting brain hitting opposite end of skull ---concussion occurs when brain injury is slight --dizzy, brief unconsciousness but no permanent brain damage ---contusion is result of marked tissue destruction --brain stem contusion results in coma (hours to lifetime) ---cerebral edema is swelling of brain due to inflammatory response to injury ---intracranial hemmorhage is bleeding from ruptured vessels 27. Discuss cerebrovascular accidents: Cause, opposite side, and aphasias. ---commonly called strokes and are third leading cause of death in U.S. ---CVAs occur when blood circulation to brain area is blocked by blood clot or ruptured blood vessel --vital brain tissue dies ---after CVA, often possible to determine area of brain damage by observing patient’s symptoms --left-sided paralysis, right motor cortex likely damaged ---aphasias common result of damage to left cerebral hemisphere where language areas located ---motor aphasia involves damage to Broca’s area and a loss of ability to speak ---sensory aphasia in which person loses ability to understand written or spoken language ---**temporary brain ischemic (transient ischemic attack or TIA) is uncompleted “stroke” --last from 5 to 50 minutes --numbness, temporary paralysis, and impaired speech --symptoms not permanent, but are RED FLAG that warn of more serious impending CVAs 28. Generally describe Alzheimer’s Disease. ---progressive degenerative disease of brain that ultimately results in dementia (mental deterioration) ---may begin in middle age ---have memory loss (particularly of recent events), become moody, irritable, confused, and sometimes violent --ultimately, hallucinations occur ---structural changes occur in brain in area concerned with cognitive functions and memory --abnormal protein deposits (plaques) and twisted fibers appear within neurons and there is local brain atrophy ---influx of calcium into brain cells implicated 29. Discuss the spinal cord: Conduction system, reflex center, where it ends, and number of nerves given off. ---cylindrical spinal cord (approx. 42 cm/17 in long) is continuation of brain stem ---provides two-way conduction pathway to and from brain ---is major reflex center (spinal reflexes completed at this level) ---enclosed within vertebral column, extends from foramen magnum of skull to first or second lumbar vertebra --ends just below ribs ---meningeal coverings do NOT end at L2 but extend well beyond end of spinal cord in vertebral column ---**not possible to damage cord below L3, good place to draw CSF ---collection of spinal nerves at inferior end of vertebral canal called cauda equina (horse’s tail) ---31 pairs of spinal nerves arise from the spinal cord 30. Describe the gray matter of the spinal cord: Shape, content, and results of damage. ---gray matter of spinal cord looks like butterfly or letter “H” in xs ---gray matter surrounds the central canal of cord which contains CSF ---two dorsal (posterior) horns and two ventral (anterior) horns ---dorsal horns contain association neurons (interneurons) so is sensory in nature ---ventral horns contain cell bodies of motor neurons of the somatic (voluntary) nervous system ---damage of ventral root results in flaccid paralysis of muscles served --nerve impulses DO NOT reach muscles affected, so no voluntary movement possible-muscles begin to atrophy because no longer stimulated ---damage to dorsal root (or its ganglion) results in loss of sensation from body area served 31. Describe the white matter of the spinal cord: Organization, composition, and tracts. ---white matter composed of myelinated fiber tracts ---organized into columns (regions) by irregular shape of gray matter --posterior, lateral, and anterior columns --each column contains number of fiber tracts make up of axons with same destination and function ---descending tracts are motor (efferent) ---ascending tracts are sensory (afferent) ---posterior column has ONLY ascending tracts (sensory) ---anterior and lateral columns contain both ascending and descending tracts 32. Discuss spinal transection: Results, quidriplegia, and paraplegia. ---spinal cord transected (cut crosswise) or crushed, spastic paralysis results ---muscles stay healthy because still stimulated by spinal reflex arcs and movement of muscles does occur ---ALL movements are involuntary ---because spinal cord carries both sensory and motor impulses, loss of feeling or sensory input occurs in body areas below the point of cord destruction ---if spinal injury occurs high in the cord and affects all four limbs, the individual is a quadriplegic ---if injury low enough that only legs are affected, the individual is a paraplegic 33. Describe the anatomy of a typical nerve. ---nerve is a bundle of neuron fibers found outside the CNS ---within nerve, neuron fibers (processes) are wrapped in protective connective tissue coverings ---each fiber surrounded by endoneurium-->groups of fibers then surrounded by perineurium to form fiber bundles, or fascicles -->all fascicles bound together by tough fibrous sheath called epineurium to form cordlike nerve ---nerves carrying both sensory and motor fibers are called mixed nerves (all spinal nerves are mixed nerves) ---are afferent (sensory) nerves that carry impulses toward CNS and efferent (motor) nerves that carry impulses away from CNS 34. Summarize the cranial nerves: number of pairs and discuss the vagus. ---there are 12 pairs of cranial nerves that serve the head and neck ---only one pair of cranial nerves, the vagus nerves, extends to thoracic and abdominal cavities ---most cranial nerves are mixed nerves except for the optic, olfactory, and vestibulocochlear nerves which are purely sensory ---“Oh, oh, oh, to touch and feel very good velvet, ah.” ---olfactory, optic, oculomotor, trochlear, trigemnal, abducens, facial, vestibulocochlear, glosspharyngeal, vagus, accessory, hypoglossal 35. Describe the spinal nerves: Number of pairs, formation, naming, and rami. ---31 pairs of spinal nerves formed by combination of ventral and dorsal roots of spinal cord ---spinal nerves are named for the region of the cord from which they arise ---cervical (8); throacic (12); lumbar (5); sacral (5); and coccygeal (1) ---almost immediately after being formed, each spinal nerve divides into dorsal and ventral rami making each spinal nerve only about ½ inch long ---rami contain both sensory and motor fibers ---smaller dorsal rami serve skin and muscles of posterior trunk whereas ventral rami form complex networks of nerves called plexuses which serve the motor and sensory needs of the limbs ---ventral rami of T1 through T12 form intercostal nerves which supply muscles between ribs/skin and truck of anterior and lateral trunk 36. Outline the plexuses: Formation and four major ones. ---ventral rami form complex networks of nerves called plexuses which serve the motor and sensory needs of the limbs ---formed by ventral rami of spinal nerves other than T1-T12 ---Cervical (C1-C5); Brachial (C5-C8, T1); Lumbar (L1-L4); and Sacral (L4-L5, S1-S4) ---major nerves of body emanate from a plexus 37. Name and give function for four major nerves of the body: Phrenic, radial, ulnar, and sciatic. ---phrenic nerve = breathing ---radial nerve = damage causes wrist drop ---ulnar nerve = clawhand, can’t spread fingers ---sciatic nerve = largest nerve in body; sciatica (pain along peripheral distribution of nerve) 38. Summarize the function of the autonomic nervous system. ---ANS is motor subdivision of PNS that controls body activities automatically ---composed of special group of neurons that regulate cardiac muscle, smooth muscles (walls of visceral organs and blood vessels), and glands ---relative stability of homeostasis depends on workings of ANS ---ANS called the involuntary nervous system 39. Compare the ANS with somatic motor division. ---somatic motor division cell bodies are inside the CNS and their axons extend to skeletal muscle they serve ---autonomic system has chain of two motor neurons --first of each pair is in the brain or spinal cord --its axon (preganglionic axon) leaves CNS to synapse with second motor neuron in a ganglion outside CNS --axon of second neuron (postganglionic axon) extends to organ it serves ---autonomic nervous system has two arms: sympathetic and parasympathetic 40. Describe the autonomic 2-neuron pathway. ---see #39 above 41. State the divisions of the ANS. ---see #39 above 42. Describe the parasympathetic division. ---most active when body is at rest and not threatened in any way ---sometimes called “resting and digesting system” ---mainly concerned with promoting normal digestion and elimination of urine and feces, and with conserving body energy particularly by decreasing demands on cardiovascular system ---acetylcholine is neurotransmitter pre- and postganglionic 43. Describe the sympathetic division. ---acetylcholine as preganglionic; norepinephrine and epinephrine as postganglionic ---called the “fight or flight” system ---increases heart rate, blood pressure, blood glucose levels, dilates bronchioles of lungs, dilation of skeletal blood vessels, and withdrawal of blood from digestive organs ---**important to note that only sympathetic division controls blood vessels