1 / 63

THE NERVOUS SYSTEM: NEURAL TISSUE

C H A P T E R T H I R T E E N. THE NERVOUS SYSTEM: NEURAL TISSUE. Two organ systems coordinate and direct activities of body. Nervous system Swift, brief responses to stimuli Endocrine system Adjusts metabolic operations Directs long-term changes.

mercer
Download Presentation

THE NERVOUS SYSTEM: NEURAL TISSUE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. C H A P T E R T H I R T E E N THE NERVOUS SYSTEM: NEURAL TISSUE

  2. Two organ systems coordinate and direct activities of body • Nervous system • Swift, brief responses to stimuli • Endocrine system • Adjusts metabolic operations • Directs long-term changes

  3. Nervous system includes all neural tissue in body • Central Nervous System • Brain and spinal cord • Peripheral Nervous System • All neural tissue outside CNS

  4. Functional divisions of nervous system • Afferent • Sensory information from receptors to CNS • Efferent • Motor commands to muscles and glands • Somatic division • Voluntary control over skeletal muscle • Autonomic division • Involuntary regulation of smooth and cardiac muscle, glands

  5. Cells in Nervous Tissue • Neurons • Neuroglia

  6. Neuroglia (Glia) • about half the volume of cells in the CNS • smaller than neurons • 5 to 50 times more numerous • do NOT generate electrical impulses • divide by mitosis • Four types in the CNS • Astrocytes • Oligodendrocytes • Microglia • Ependymal cells

  7. Astrocytes • Largest of glial cells • Most numerous • Star shaped with many processes projecting from the cell body • Help form and maintain blood-brain barrier • Provide structural support for neurons • Maintain the appropriate chemical environment for generation of nerve impulses/action potentials • Regulate nutrient concentrations for neuron survival • Regulate ion concentrations - generation of action potentials by neurons • Take up excess neurotransmitters • Assist in neuronal migration during brain development • Perform repairs to stabilize tissue

  8. Oligodendrocytes • Most common glial cell type • Each forms myelin sheath around the axons of neurons in CNS • Analogous to Schwann cells of PNS • Form a supportive network around CNS neurons • fewer processes than astrocytes • round or oval cell body

  9. Microglia • few processes • derived from mesodermal cells • that also give rise to monocytes • and macrophages • Small cells found near blood vessels • Phagocytic role - clear away dead cells • protect CNS from disease through phagocytosis of microbes • migrate to areas of injury where they clear away debris of injured cells - may also kill healthy cells

  10. Representative Neuron http://www.horton.ednet.ns.ca/staff/selig/Activities/nervous/na1.htm • -neurofilaments or neurofibrils give cell shape and support - bundles of • intermediate filaments • -microtubules move material inside cell • -lipofuscin pigment clumps (harmless aging) - yellowish brown • 1. cell body or soma • -single nucleus with prominent nucleolus • -Nissl bodies • -rough ER & free ribosomes for protein synthesis • -proteins then replace neuronal cellular components for growth • and repair of damaged axons in the PNS

  11. Neurons 2. Cell processes = dendrites (little trees) - the receiving or input portion of the neuron -short, tapering and highly branched -surfaces specialized for contact with other neurons -cytoplasm contains Nissl bodies & mitochondria

  12. 3. Cell processes = axons • Conduct impulses away from cell body-propagates nerve impulses to another neuron • Long, thin cylindrical process of cell • contains mitochondria, microtubules & neurofibrils - NO ER/NO protein synth. • joins the soma at a cone-shaped elevation = axon hillock • first part of the axon = initial segment • most impulses arise at the junction of the axon hillock and initial segment = trigger zone • cytoplasm = axoplasm • plasma membrane = axolemma • Side branches = collaterals arise from the axon • axon and collaterals end in fine processes called axon terminals • Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters

  13. http://bcs.whfreeman.com/thelifewire/content/chp44/4401s.swf Excitability • Ability of cell membrane to conduct electricity • Skeletal muscle fibers • Most neurons • Changes in membrane potential induces an action potential (AP) • the PM of neurons exhibits a membrane potential = electrical voltage difference across the membrane • in excitable cells like neurons this potential = resting potential • due to differences in sodium and potassium ion concentration in and out of the cell • potassium is higher inside cell, sodium is higher outside • inside of the cell has a higher concentration of negative phosphate ions and proteins = potential of -40 to -90 mV • the cell is said to be polarized • membrane has sodium/potassium pumps • to maintain specific concentrations of these ions in • & out of the neurons and therefore maintain the • resting membrane potential • -move three Na+ out and 2 K+ in • -inside of the neuron is slightly • negative

  14. Action Potential • Resting membrane potential is -70mV • threshold usually -55 MV • Depolarization is the change from -70mV to +30 mV • Repolarization is the reversal from +30 mV back to -70 mV) http://www.blackwellpublishing.com/matthews/channel.html • action potential = nerve impulse • takes place in two stages: depolarizing phase (more positive) and repolarizing phase (more negative - back toward resting potential) • followed by a hyperpolarizing phase or refractory period in which no new AP can be generated

  15. depolarization (increase in MP) results from opening of Na+ channels. Once threshold is reached, more Na+ channels open and a rapid increase in MP results outflow of K+ restores the MP. Na+ channels begin to open and K+ channels close. K+ outflow results in hyperpolarization (below resting) results in a refractory period. more slowly, depolarization also opens K+ channels which permit the outflow of K+ . The Na+ close the MP becomes more negative returning to resting

  16. Local Anesthetics • Prevent opening of voltage-gated Na+ channels • Nerve impulses cannot pass the anesthetized region • Novocaine and lidocaine – blocks nerve impulses along nerves that detect pain

  17. Synapse • Synapse • Site of intercellular communication between 2 neurons or between a neuron and an effector (e.g. muscle) • Originates in the soma • Travels along axons • Permit communication between neurons and other cells • Initiating neuron = presynaptic neuron • Receiving neuron = postsynaptic neuron • two types: chemical & electrical • NT will cause either and excitatory or inhibitory response • If the NT depolarizes the postsynaptic neuron= excitatory

  18. Neurotransmitters • More than 100 identified • Some bind receptors and cause channels to open • Others bind receptors and result in a second messenger system • Results in either excitation or inhibition of the target • botulism causes paralysis through blockage of AcH release from motor • neurons • 1. small molecules: e.g. Acetylcholine (ACh) • -All neuromuscular junctions use ACh • -ACh also released at chemical synapses in the PNS and by some CNS neurons • -Can be excitatory at some synapses and inhibitory at others 2. Amino acids: glutamate & aspartate & GABA • Stimulate most excitatory neurons in the CNS (about ½ the neurons in the brain) • Binding of glutamate to receptors opens calcium channels = excitatory response • GABA (gamma amino-butyric acid) is an inhibitory neurotransmitter for 1/3 of all brain synapses Valium is a GABA agonist - enhancing its inhibitory effect

  19. Neurotransmitters 3. Biogenic amines: modified amino acids • catecholamines:norepinephrine (NE), epinephrine, dopamine (tyrosine) • serotonin - concentrated in neurons found in the brain region = raphe nucleus • derived from trytophan • sensory perception, temperature regulation, mood control, appetite, sleep induction • feeling of well being • NE - role in arousal, awakening, deep sleep, regulating mood • epinephrine (adrenaline) - flight or fight response • dopamine - emotional responses and pleasure, decreases skeletal muscle tone • Parkinsons - muscle stiffness due to degeneration of dopanergic nerves • patients given L-Dopa (dopamine precursor) • amphetamines promote dopamine and NE release • isoproterenol binds to epinephrine receptors • - used in asthma to mimic the effects of epinephrine • schizophrenia - excess of dopamine • Zyprexa blocks dopamine and serotonin receptors • -antagonizes the effects of serotonin and dopamine • cocaine: blocks transporters for dopamine reuptake • Prozac, Paxil: blocks transporters for serotonin reuptake Other types: Nitric oxide - formed on demand in the neuron then release (brief lifespan) -role in memory and learning -produces vasodilation - Viagara enhances the effect of NO

  20. Neuropeptides • widespread in both CNS and PNS • excitatory and inhibitory • act as hormones elsewhere in the body • -Substance P -- enhances our perception of pain • -opoid peptides: endorphins - release during stress, exercise • enkephalins - analgesics • (200x stronger than morphine) • -pain-relieving effect by blocking the release of • substance P • dynorphins - regulates pain and emotions • **acupuncture may produce loss of pain sensation because of release of opioid-like substances such as endorphins or dynorphins

  21. Divisions of the nervous system • Sensory pathway • Ascending • Information from sensory receptors to CNS • Motor pathway • Descending • Information from CNS to skeletal muscle or glands • Direct pathways – cause precise, voluntary movements • Indirect pathways – result in involuntary movement (from brain stem)

  22. Functional Classification of Neurons • Sensory (afferent) neurons • transport sensory information from skin, muscles, joints, sense organs & viscera to CNS • Motor (efferent) neurons • send motor nerve impulses to muscles & glands • Interneurons (association) neurons • connect sensory to motor neurons • 90% of neurons in the body

  23. Sensory Neurons • Afferent division of PNS • Deliver sensory information from sensory receptors to CNS • free nerve endings: bare dendrites associated with pain, itching, tickling, heat and some touch sensations • Exteroceptors: located near or at body surface, provide information about external environment • Proprioceptors: located in inner ear, joints, tendons and muscles, provide information about body position, muscle length and tension, position of joints • Interoceptors: located in blood vessels, visceral organs and NS -provide information about internal environment -most impulses are not perceived – those that are, are interpreted as pain or pressure

  24. Sensory Neurons • Sensory receptors cont… • mechanoreceptors: detect pressure, provide sensations of touch, pressure, vibration, proprioception, blood vessel stretch, hearing and equilibrium • thermoreceptors: detect changes in temperature • nociceptors: respond to stimuli resulting from damage (pain) • photoreceptors: light • osmoreceptors: detect changes in OP in body fluids • chemoreceptors: detect chemicals in mouth (taste), nose (smell) and body fluids -analgesia: relief from pain -drugs: aspirin, ibuprofen – block formation of prostaglandins that stimulate the nociceptors -novocaine – block nerve impulses along pain nerves -morphine, opium & derivatives (codeine) – pain is felt but not perceived in brain (blocks morphine and opiate receptors in pain centers)

  25. Motor Neurons • Efferent pathways • Stimulate peripheral structures • Somatic motor neurons • Innervate skeletal muscle • Visceral motor neurons • Innervate all other peripheral effectors • Preganglionic and postganglionic neurons

  26. Somatic nervous system (SNS): 1. sensory - neurons that convey sensory information from somatic receptors in the head, body wall, senses - to the CNS 2. control of motor output - neurons that conduct voluntary impulses to skeletal muscles -contributions from the basal ganglia, cerebellum, brain stem and SC 3. one neuron pathway – somatic motor neurons synapse directly with the effector 4. neurotransmitter – usually acetylcholine 5. effectors – skeletal muscles 6. responses - contraction

  27. Autonomic nervous system (ANS): • sensory - neurons that convey info from autonomic sensory receptors in the visceral organs - to the CNS • 2. control of motor output - neurons that conduct impulses from the CNS to • smooth and cardiac muscle & glands • 3. two neuron pathway – preganglionic neurons extend from CNS and synapse with postganglionic neurons in an autonomic ganglion, postganglionic neurons then synapse with the effector • 4. neurotransmitter – preganglionic – ACh • -postganglionic – ACh or norepinephrine • 5. effectors – smooth & cardiac muscle, glands, • 6. responses – contraction or relaxation of SM • -increased or decrease heart contraction • -increased or decreased gland secretions

  28. - motor output branch has two divisions: 1. sympathetic 2. parasympathetic -most organs are innervated by both divisions which have opposing functions e.g. sympathetic – increases heart rate parasympathetic – decreases rate -

  29. An Introduction to the Organization of the Brain

  30. Major Regions of the Brain Figure 15.1 Major Divisions of the Brain http://www.wisc-online.com/objects/framz.asp?objID=OTA502

  31. The Cranial Nerves

  32. I - Olfactory II - Optic III - Oculomotor IV-Trochlear V - Trigeminal VI - Abducens VII - Facial VIII - Acoustic IX - Glossopharyngeal X - Vagus XI - Accessory XII - Hypoglossal • -cranial nerves – 12 pairs • -considered part of the peripheral nervous system (PNS) • -olfactory & optic contain only sensory axons = sensory nerves • -some are motor nerves – e.g. oculomotor, trochlear etc…. • remaining are mixed nerves – both motor and sensory axons • “some say my mother bought my brother some bitter beer, my, my” http://www.wisc-online.com/objects/index.asp?objID=AP11504

  33. The Olfactory Nerve (I) • Carries sensory information • Sense of smell from nasal mucosa to brain • Branches enter skull through cribiform plate • Synapses within olfactory bulbs

  34. The optic nerve (II) (sensory) • Carries visual information • enters skull through optic canal of the sphenoid -right and left join at the optic chiasma (site of cross-over) -continue to brain as optic tracts

  35. The oculomotor nerve (III) [Motor] • Primary source of innervation for extra-ocular muscles • also carries postganglionic fibers that innervate the ciliary muscles (lens shape) • exits through superior orbital fissure • The trochlear nerve (IV) [Motor] • Smallest cranial nerve • Innervates superior oblique eye muscle • also provides proprioception info • exits through S.O.F • The abducens nerve (VI) [Motor] • Innervates lateral rectus muscle of eye • exits through S.O.F

  36. The Trigeminal Nerve (V) [Mixed] • Largest cranial nerve • Mixed nerve • sensory – touch, pain & thermal • Ophthalmic branch • sensory – upper eyelid, eyeball lacrimal glands, side of nose, forehead and scalp • Maxillary branch • sensory – nose, palate, part of pharynx, upper teeth, upper lip and lower eyelid • Mandibular branch • sensory – tongue, cheek, lower teeth, skin over mandible and side of head anterior to ear -motor – muscles of chewing -inferior alveolar nerve (branch of mandibular) -often anesthetized in dental procedures – lower jaw -numbs to mental nerve (branch of the IAN) -superior alveolar nerve (branch of the maxillary) -numbs the upper jaw

  37. The Facial Nerve (VII) [Mixed] • Mixed nerve • Controls muscles of scalp and face • Pressure sensations from face • Taste sensations from tongue

  38. Facial Nerve VII • efferent branches supply muscles of facial expression • also carries preganglionic parasympathetic fibers to the lacrimal, sub-mandibular and sub-maxillary glands • afferent branches serves a tiny patch of skin behind the ear • also provides taste information and sensation to the body of the tongue

  39. Facial Nerve VII • Greater Petrosal • branches off before exiting skull • motor fibers + Pre/para fibers to pterygopalatine ganglion • postganglionic fibers leave the ganglion to join with branches of the maxillary division or V -> lacrimal gl, nasal cavity and minor salivary glands of the palate • also taste sensation • Chorda Tympani • parasympathetic, motor for SMn and SL salivary glands • sensory for taste at the body of the tongue • crosses the tympanic membrane before exiting the skull • travels with the lingual n. to the floor of the mouth • Posterior Auricular, Diagastic and Stylohyoid • branches after VII exits the stylomastoid f. • all are motor – epicranial m., diagastic and stylohyoid muscles • facial expression • temporal (anterior to ear), zygomatic (inferior orbicularis oculi + ZMj, ZMn), buccal (upper lip, nose, buccinator, risorius and orbicularis oris), mandibular ( lower lip and mentalis) and cervical (plastysma)

  40. The Vestibulocochlear Nerve (VIII) [Sensory] • Vestibular nerve • Monitors sense of balance, position and movement • Cochlear nerve • Monitors hearing

  41. The Glossopharyngeal Nerve (IX) [Mixed] • Innervates the tongue, pharyngeal muscles, stylopharyngeus m. • Controls swallowing • the efferent portion also sends pre/para fibers to the parotid gland (salivation) • also receives sensory info from taste receptors and general sensation from the tongue

  42. The Vagus Nerve (X) [Mixed] • Vital to autonomic control of visceral function • large efferent portion to the soft palate, pharynx and larynx • many other parasympathetic fibers to the organs of the gut, respiratory and CV systems • small afferent portion receives sensory information from around the ear and for taste info from the epiglottis • passes through the jugular foramen

  43. The accessory nerve (XI) • Internal branch • Innervates swallowing muscles • External branch • Controls muscles associated with pectoral girdle • The hypoglossal nerve (XII) • Voluntary motor control over tongue movements

  44. Trigeminal Nerve and Branches • bulge in the dorsal root of V = trigeminal ganglion • also called the semilunar ganglion • ganglion = collection of neuronal cell bodies • comprised of a motor root and a sensory root • supplies the muscles of mastication • exits via the forament ovale in the sphenoid • travels with mandibular division of V (V3) • sensory root divides into three portions • 1. Opthalmic • 2. Maxillary • 3. Mandibular

  45. Opthalmic Division • smallest division = V1 • sensory information from: conjuctiva, cornea, eyeball, orbit, forehead, ethmoid and frontal sinuses • also part of dura mater • carries its sensory info by way of the superior orbital fissure along with III, IV & VI • formed from the union of: the frontal, lacrimal and nasociliary branches

  46. Frontal branch: supraorbital + supratrochlear • SO: forehead, anterior scalp • ST: bridge of nose, upper eyelid, medial forehead • runs along roof of orbit • Lacrimal branch • lateral eyelid, conjuctive & lacrimal gland • also provides post/para fibers to the lacrimal gland – tear production • Nasociliary branch: infratrochlear + ciliary nerves + anterior ethmoid n. • runs superior to II within the orbit • IT: medial eyelid skin, side of nose • Ciliary: eyeball • AE: nasal cavity & paranasal sinuses

  47. Maxillary Division • V2 • sensory information from: maxilla & skin, maxillary sinuses, nasal cavity, palate & nasopharynx + part of dura mater (meningeal branches) • forms in the pterygopalatine fossa • enters skull through the foramen rotundum • prior to branching = pterygopalatine ganglion • parasympathetic relay station for branches that arise from the facial nerve • branches: • zygomatic • infraorbital • anterior superior alveolar • middle superior alveolar • posterior superior alveolar • greater & lesser palatine • nasopalatine

  48. Zygomatic • zygomaticotemporal + zygomaticofacial • enters pterygopalatine fossa through the infraorbital fissure and joins to contribute to the maxillary nerve • zygo.facial – skin of cheek • through the frontal process of the zygomatic bone and enters the orbit thru the lateral wall • zygo.temporal – skin of the temporal bone • through the temporal process of the zygomatic bone and travels along the lateral wall of the orbit • Infraorbital: IO • formed from cutaneous branches from the upper lip, medial portion of cheek lower eyelid and side of nose • runs into the infraorbital foramen of the maxilla • travels along the infraorbital canal with the infraorbital blood vessels • joins with the anterior superior alveolar nerve

  49. Anterior Superior Alveolar (ASA) • sensation + pain from the maxillary central incisors, lateral incisors, canines and their tissues + facial gingiva • originates as dental branches supplying the pulp + interdental branches of the associated periodonteum = dental plexus of the maxilla • joins with the IO within the IO canal • Middle Superior Alveolar (MSA) • sensation + pain from the maxillary premolars and first molar + periodonteum and their buccal gingiva • originates from dental, interdental and interradicular branches (dental plexus) – pulp and periodonteum • forms this plexus with the ASA and PSA • joins the IO • MSA is not present in all patients • can be replaced by the ASA or PSA

More Related