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Nervous System Cells • Neurons = functional cellular unit of nervous system; action potentials • Neuroglial cells = support, nourish, or protect neurons Oligodendroglial & Schwann cells = insulate neurons with myelin (Gnathostomes) Astrocytes = transport nutrients (& signal neurons at synapse); CNS only Microglia = engulf bacteria; CNS only Ependymal cells = cilliated cells that line central canal & ventricles; CNS only Neural Tissue Motor Neuron cell body axon myelin under a Schwann cell dendrite axon hillock synaptic terminal node of Ranvier Neuron Function • Signal propagates down an axon as ion channels open along the axon (changing voltage) – electrical signal • At the end of the axon vessicles containing neurotransmitter release– chemical signal Schwann Cells & Oligodendroglia Subphylum Vertebrata myelin (Schwann cells & oligodendrocytes) brain Nervous System Development • Three ectodermal sources. • Neural tube – becomes C.N.S., optic “nerve,” retina, and pre-ganglionic motor nerves. CNS derived only from neural tube. • Neural crest – becomes post-ganglionic nerves and peripheral glia. • Neurogenic placodes – become postganglionic cranial nerve (V, VII, IX, X) AND olfactory, vestibular, and lateralis sensory receptor cells. Vertebrate Neurula (section) somite notochord coelom gut intermediate mesoderm lateral plate mesoderm Vertebrate Embryo (section) neural crest cells sclerotome dermatome myotome splanchnic mesoderm somatic mesoderm gut coelom Vertebrate Embryo (section) neural crest cells sclerotome dermatome myotome gut coelom Vertebrate Embryo (section) neural crest cells vertebra dermatome myotome gut coelom Vertebrate Embryo (section) will form dorsal root ganglion vertebra dermatome myotome developing skin gut will form other ganglia coelom Neurogenic Placodes (post-ganglionic cranial nerves V, VII, IX, & X) Brain Development • Neurons migrate from the ependymal layer more superficially; 1st migrate least. • The anterior neural tube forms: -Prosencephalon (Forebrain) -Mesencephalon (Midbrain) -Rhombencephalon (Hindbrain) rhombomeres = segmental divisions Brain Developmental Regions • Prosencephalon = FOREBRAIN Telencephalon cerebrum & olfactory lobes Diencephalon thalamus, hypothalamus • Mesencephalon = MIDBRAIN optic lobes / superior colliculi & tegmentum • Rhombencephalon = HINDBRAIN Metencephalon cerebellum & pons Myelencephalon medulla oblongata Spinal Nerves Development sensory inter- motor notochord Amniote Embryo (section) Nervous System Overview • Central Nervous System (CNS) = brain and spinal cord; myelin from oligodendroglia (astrocytes in synapse) Tract= region of axons; Nucleus or Cortex = region of cell bodies • Peripheral Nervous System (PNS) = nerves and ganglia; myelin from Schwann cells (also can cover synapse) Nerve = bundle of axons Ganglion = bundle of cell bodies PNS Overview • Cranial Nerves = attached to brain; many have ganglia; numbered with Roman numerals from anterior to posterior • Spinal Nerves = attached to spinal cord; most have ganglia; distinctly segmental dorsal root ventral root Peripheral Nervous System • Sensory (Afferent) = brings info. to CNS • Motor (Efferent) = takes info. from CNS • Visceral = innervates smooth muscle or organs in the coelom • Somatic = innervates skel. muscle and skin • Pre-ganglionic = cell bodies in the CNS; between CNS & a ganglion • Post-ganglionic Nerves = cell bodies in a ganglion; between a ganglion & another ganglion or a non-neural tissue Nervous System Overview Spinal nerves • Spinal Nerves = segmental from spinal cord • Dorsal Root = afferent (sensory) nerve • Dorsal Root Ganglion = afferent (sensory) neuron cell bodies • Ventral Root = efferent (motor) nerve • Sypathetic chain = chain of ganglia ventral to spinal cord Human Spinal Nerves • Cervical Plexus (C1-C5) also innervates diaphragm (Phrenic nerves) • Brachial Plexus (C5-T1) innervates arm • Intercostal / Thoracic Nerves (T2-T12) • Lumbar Plexus (T12-L5) • Sacral Plexus (L5-Co2) also innervates legs (Sciatic nerves) Human Thoracic Spinal Nerve Human Thoracic Spinal Nerves dorsal root ventral root dorsal root ganglion spinal nerve sypathetic ganglion Human Thoracic Spinal Nerves Sensory Neurons Human Thoracic Spinal Nerves Motor Neurons Shingles Herpes/chicken pox virus dormant in spinal or cranial nerve Cranial Nerves • 10-13 nerves arising from the brain; numbered anterior to posterior. • 0 - nervus terminalis sensory for blood vessels of olfactory epithelium • I - olfactory “nerve” (ethmoid foramina) sensory fibers that innervate the olfactory epithelium • II - optic nerve (optic canal) sensory “nerve;” innervates retina not a true nerve; an extension of brain Cranial Nerves • III - oculomotor nerve (superior orbital fiss.) motor nerve for 4 of the 6 extrinsic eye muscles • IV - trochlear nerve (superior orbital fissure) motor nerve for 1 of the 6 extrinsic eye muscles • V - trigeminal nerve (3 branches) (foramina ovale and spinosum & superior orbital fissure) sensory for skin of head; motor for 1st arch muscles (mandibular branch) Trigeminal/Gasserion Ganglion • VI - abducens nerve (superior orbital fissure) motor nerve for 1 of the 6 extrinsic eye muscles Cranial Nerves • VII - facial nerve (3 branches) (stylomastoid foramen) - Facial/Geniculate Ganglion sensory for taste buds and head lateralis system; motor for 2nd arch muscles (hyomandibular branch) • VIII - auditory nerve (Vestibulocochlear) sensory for inner ear/vestibule (internal aud. meatus) • IX - glossopharyngeal nerve (jugular for.) sensory for taste and pharynx; motor for 3rd arch muscles (1st branchial arch branch) – Superior & Inferior Glossopharyngeal Ganglia • IX - vagus nerve (jugular foramen) sensory and motor for mouth, pharynx, outer ear, and most viscera – Superior & Inferior Vagus Ganglia Posterior-Most Cranial Nerves • XI - spinal accessory nerve (amniotes only) (foramen magnum) sensory & motor for branchiomeric muscles (e.g., trapezius, sternomastoid) = branch of vagus in non-amniotes • XII - hypoglossal nerve (amniotes only) (hypoglossal canal) motor & sensory for tongue muscles = occipital nerves in non-amniotes Shark-like Vertebrate somitomeres 1-7 mandibular arch hyoid arch somites 1-4 1st branchial arch Special Sensory Cranial Nerves optic II olfactory I terminal 0 mandibular arch auditory VIII hyoid arch 1st branchial arch Segmental Cranial Nerves III IV V VI VII IX X XII XI mandibular arch hyoid arch 1st branchial arch Segmental Cranial Nerves IV III V VI VII IX II VIII X XII XI 0 I mandibular arch hyoid arch 1st branchial arch Suprabranchial Placodes • Form ganglia for the trigeminal, facial, glossopharyngeal, & vagus cranial nerves. III IV V VI VII IX 0 X XII XI II I VIII CNS • Spinal Cord = CNS dorsal to notochord and posterior to head • Central canal = canal within spinal cord • Brain = enlarged anterior CNS • Ventricles = cavities in brain • Cerebrospinal fluid (CSF) = fills ventricles & central canal • Choroid plexus = tuft of capillaries that secrete CSF Meninges • Meninges = layers of connective tissue surrounding CNS Non-tetrapods = 1 (primitive meninx) Non-mammal tetrapods = 2 (dura matter + secondary meninx) Mammals = 3 • Dura matter = outermost • Arachnoid = middle • Pia matter = innermost CNS • Gray matter = many cell bodies; >integration • White matter = few cell bodies; many axons with myelin (in Gnathostomes); >transport • Gray matter ancestrally deep; white matter superficial, EXCEPT superficial in forebrain in amniotes, teleosts, hagfishes, and a few chondrichthyans Spinal Cord cauda equina Brain Regions • Prosencephalon = FOREBRAIN Telencephalon cerebrum & olfactory lobes Diencephalon thalamus, hypothalamus, epiphysis, hypophysis, optic nerves • Mesencephalon = MIDBRAIN; tectum superior colliculi & inferior colliculus tegmentum • Rhombencephalon = HINDBRAIN Metencephalon cerebellum & pons Myelencephalon medulla oblongata Brain Regions Teleost Brain Regions Pros- Mes- Rhomb- Bird Brain Regions Pros- Mes- Rhomb- Telencephalon • Olfactory lobes • Cerebrum, large in mammals & birds, lateral ventricles. • In mammals, dorsal pallium forms the 6 layered neocortex. • gyri = folds of neocortex • sulci = grooves of neocortex • Actinopterygiians = gray matter everts; single medial ventricle • All other vertebrates = gray matter inverts; 2 lateral ventricles Diencephalon • Thalamus, Hypothalamus, & Median Ventricle (3rd). • Optic nerves cross and enter brain at optic chiasma (neurons pass through the diencephalon, synapse in the mesencephalon). • Dorsal epiphysis (pineal & parietal organ) & Ventral hypophysis (pituitary). Mesencephalon • Tectum (anterior = optic lobes / superior colliculi; posterior = auditory tectum / inferior colliculus) & Tegmentum. • Optic ventricle in non-mammals, cerebral aqueduct in mammals. • Mammals have small paired superior colliculi (optic tectum) and median inferior colliculus (auditory). Metencephalon • Cerebellum & pons (only in birds & mammals). • Fourth ventricle. • Actinopterygii = Cerebellum expanded for processing lateral line information • Birds & Mammals = Cerebellum expanded and folded (folds = folia); pons present. Myelencephalon • Medulla oblongata. • Fourth ventricle. • Structurally very similar to spinal cord. • No complex intergration. Human Brain Ventricles Brain Evolution Subphylum Vertebrata 2 meninges 1 meninx cerebellum cerebrum everts; large optic tectum enlarged cerebrum neocortex with gyri & sulci; small optic lobes, 3 meninges Sensory Receptors • Sensory Receptor Cells = respond to a physical property and can generate an action potential (some are specialized neurons) Chemoreception / Smell • Chemoreception = reception of a chemical stimulus; smell & taste • Olfactory epithelium = chemo-receptive epithelium associated with the nares (smell); paired in Gnathostomes. Develop from… Olfactory Placodes that invaginate to form the olfactory epithelium. Olfactory Epithelium • Olfactory neuron = sensory cell of olfactory epithelium; cilia receptors • Sustentacular cell = supporting cell of an olfactory epithelium • Basal cell = can form other cells of the olfactory epith Chemoreception / Smell • Turbinates = bone that extends into the nasal cavity of amniotes; more olfactory surface area (well developed in mammals on maxilla and ethmoid). • Vomeronasal organ (VNO)= chemoreceptive epithelium; different innervation than olfact. Associated with phermone response. Chemoreception / Taste • Taste Buds = groups of chemo-receptive cells (gustatory cells) in the oral cavity (taste) • Gustatory cells have microvilli (not cillia) for picking up chemical signals. Mechanoreception • Mechnoreception = response to changes in mechanical force; hearing, balance, lateralis • Hair Cells = mechanoreceptive cells with cillia (called stereocillia) and a long cillium (called a kinocillium) • Neuromast organ = cluster of hair cells and supporting cells Lateralis System • Lateralis system = neuromasts on skin surface or in canals; sense water motion • On head and along body (lateral line) except in hagfishes and amniotes. (Amphibians lose it at metamorph.) • Lateralis Placodes = form neuromasts. Otic Placodes – Hearing/Balance • Otic (Labyrinth) placodes sink in and form the Vestibules (Labyrinths) • Vestibule = semicircular canals and portions filled with endolymph; balance/hearing • Vestibular System = compartments and semicircular canals in otic region; filled with endolymph; balance/hearing • Neuromasts at bases of semicircular canals and in sacculus & utriculus chambers. • Cupula w/ otoconia or otoliths. Vestibular System • Hagfishes = 1 semicircular canal • lampreys = 2 semicircular canals • gnathostomes = 3 semicircular canals • Actinopterygiians = large otoliths • One region of the vestibule functions in sound reception. (lagena) • Cochlea = coiled lagena in most mammals Mammalian Vestibular System semicircular canal utriculus sacculus lagena (cochlea) Ear Ossicles • Middle ear = region adjacent to vestibule containing ossicles • Stapes (Columella) = Hyomandibula modified for sound transmission in tetrapods • Incus = Quadrate modified for sound transmission in mammals • malleus = Articular modified for sound transmission in mammals Human Ear Inner Ear Hair Cells Electroreception • Modified lateralis system in aquatic veretbrates. • Ampullae of Lorenzini = electroreceptive organs in chondrichthyans Photoreception / Sight • Photoreception = sensory response to light stimulus; sight. Vertebrate eye. • Eye develops from neural (optic vessicle) and generalized ectoderm (optic placode). Optic vessicle retina, iris, & intrinsic muscles. Optic placode lens & cornea. • Optic “nerve” = extension of brain Eye Development Vertebrate Eye Retina Cutaneous Sensory Systems • Free sensory receptors = “naked” dendrites in a tissue; pain • Encapsulated sensory receptors = dendrites covered in connective tissue; touch, temperature, & pressure • Associated sensory receptors = dendrites wrapped around another structure (e.g., hair, feather); movement of the structure Cutaneous Sensory Systems Free Encapsulated Associated Proproiception • Proprioception = sensation of muscle position and activity. • Tendon organ = sensory dendrite associated with the collagen of a tendon. tendon tension • Intrafusal muscle cells = modified sensory muscle cells, monitored by an intrinsic sensory dendrite. muscle tension Sensory Receptors Subphylum Vertebrata turbinates vomeronasal organ brain paired olfactory epithelia; myelin (Schwann cells & oligodendrocytes) Amniota vomeronasal organ lost turbinates * Groups in which many subgroups have lost the vomeronasal organ ** superficial gray matter in teleosts Subphylum Vertebrata ** turbinates; c.n. XI & XII; VNO; lateralis lost; stapes superficial gray matter myelin; pair. olf. epi.; 3 semicirc. canals 2 semicircular canal; lateralis syst. & nerves brain; 1 semicircular canal; 0-X cranial nerves Amniota cochlea coiled malleus, incus, curved cochlea (lagena) turbinates VNO lost elongate lagena (cochlear duct)