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Nerve Tissue & The Nervous System David L. McWhorter, Ph.D. NERVOUS SYSTEM ORGANIZATION CONSISTS OF TWO OVERLAPPING PAIRS OF SUBSYSTEMS… CENTRAL AND PERIPHERAL NERVOUS SYSTEMS WHICH ARE DEFINED BY LOCATION: 1. CNS INCLUDES THE BRAIN AND SPINAL CORD PNS INCLUDES ALL OTHER NERVE TISSUE (CRANIAL NERVES, PERIPHERAL NERVES, GANGLIA, NERVE PLEXUSES) AUTONOMIC AND SOMATIC NERVOUS SYSTEMS WHICH ARE DEFINED BY FUNCTION & HAVE CNS AND PNS COMPONENTS: 2. ANS CONTROLS INVOLUNTARY VISCERAL FUNCTIONS (EG, SMOOTH MUSCLE CONTRACTION) SOMATIC NERVOUS SYSTEM CONTROLS SOMATOSENSORY PERCEPTION (EG, TOUCH, HEAT, COLD) AND VOLUNTARY SOMATOMOTOR FUNCTIONS (EG, SKELETAL MUSCLE CONTRACTION) There are two cell types that make up nervous tissue… 1. 2. Neurons Glial cells NERVOUS SYSTEM CELLS: NEURONS FUNDAMENTAL STRUCTURAL & FUNCTIONAL UNIT OF NERVOUS SYSTEM > 100 MILLION SPECIALIZED TO RECEIVE, INTEGRATE, & TRANSMIT ELECTROCHEMICAL MESSAGES NERVE IMPULSES OR ACTION POTENTIALS THREE MAIN PARTS: 1. 2. 3. CELL BODY DENDRITES AXON MAIN TYPES OF NEURONS (NUMBER OF NEURITES [PROCESSES]) BIPOLAR MULTIPOLAR 1 DENDRITE AND 1 AXON UNCOMMON AND FOUND ONLY IN SPECIAL SITES: COCHLEAR & VESTIBULAR GANGLIA OF CN XIII, OLFACTORY NERVE, RETINA MOST NEURONS IN BODY MORE THAN TWO PROCESSES EXAMPLES INCLUDE: MOTOR NEURONS AND AUTONOMIC NEURONS PSEUDOUNIPOLAR SINGLE PROCESS CLOSE TO CELL BODY DIVIDED INTO 2 BRANCHES PERIPHERAL PROCESS (top) CENTRAL PROCESS CELL BODY NOT INVOLVED IN IMPULSE CONDUCTION FOUND IN SPINAL DORSAL ROOT GANGLIA AND SENSORY GANGLIA OF CRANIAL NERVES V, VII, IX, AND X NEURON: CELL BODY (SOMA, PERIKARYON [G. AROUND + NUCLUEUS) CONTAINS NUCLEUS AND SURROUNDING CYTOPLASM, EXCLUSIVE OF CELL PROCESSES NUCLEUS IS LARGE, CENTRAL, AND EUCHROMATIC (PROMINENT NUCLEOLUS) ABUNDANT FREE AND RER-ASSOCIATED POLYRIBOSOMES APPEAR AS CLUMPS OF BASOPHILIC MATERIAL COLLECTIVELY CALLED NISSL BODIES CNS CELL BODIES (POLYGONAL SHAPE) PNS CELL BODIES (ROUND SHAPE) NEURON: DENDRITES (G., TREE) USUALLY SHORT AND DIVIDE LIKE BRANCHES OF A TREE PRINCIPAL SIGNAL RECEPTION AND PROCESSING SITES ON NEURONS MOST SYNAPSES BETWEEN NEURONS OCCUR AT DENDRITIC SPINES SMALL "DOOR KNOB" SHAPED EXTENSIONS FROM THE SURFACES OF THE DENDRITIC PROCESSES INVOLVED IN PLASTIC CHANGES THAT UNDERLIE ADAPTATION, LEARNING, AND MEMORY NEURON: AXON (G., AXIS) USUALLY VERY LONG, SINGLE PROCESS WITH A CONSTANT DIAMETER SPECIALIZED TO CONDUCT NERVE IMPULSES TO OTHER CELLS ORIGIN HAS A SHORT PYRAMIDSHAPED REGION CALLED THE AXON HILLOCK DISTAL PORTION USUALLY BRANCHED (COLLATERAL BRANCHES) AND ITS TERMINAL PORTIONS ARE CALLED END BULBS OR BOUTONS MAY ALSO RECEIVE INFORMATION FROM OTHER NEURONS…MAINLY MODIFIES TRANSMISSION OF ACTION POTENTIALS TO OTHER NEURONS FORM INTERACTIONS WITH OTHER NEURONS OR NON-NERVE CELLS CALLED SYNAPSES PLASMA MEMBRANE AND CYTOPLASM OF AN AXON ARE CALLED AXOLEMMA AND AXOPLASM, RESPECTIVELY DENDRITE VERSUS AXON HISTOLOGY ENTIRE AXON USUALLY NOT VISIBLE IN SECTIONED MATERIAL ABSENCE OF NISSL-RELATED BASOPHILIA AT ORIGIN DISTINGUISHES AXON FROM DENDRITES NERVOUS SYSTEM CELLS: NEUROGLIA (GLIAL CELLS OR SUPPORTING CELLS) CNS NEUROGLIA: ASTROCYTES OLIGODENDROCYTES PHAGOCYTIC CELLS EPENDYMAL CELLS FORM MYELIN IN CNS MICROGLIA MOST POPULOUS GLIAL CELL PART OF BLOOD- BRAIN BARRIER HELP MAKE UP CHOROID PLEXUS PNS NEUROGLIA: SCHWANN CELLS FORM MYELIN IN PNS CNS TERMS NUCLEUS IS A GROUP OF CELL BODIES INVOLVED IN A COMMON FUNCTION TRACT: (PATHWAY) LOCATED IN THE GRAY MATTER COLLECTIONS OF MYELINATED AXONS CONNECTING NEIGHBORING OR DISTANT NUCLEI LOCATED IN THE WHITE MATTER MENINGES: C.T. LAYERS BETWEEN CNS AND SKULL & VERTEBRAL CANAL CNS TERMS: BLOOD-BRAIN BARRIER CNS TISSUE RECEIVES OXYGEN AND NUTRIENTS FROM CAPILLARIES IN PIA MATER STRUCTURAL AND FUNCTIONAL BARRIER THAT PROTECTS CNS NEURONS FROM MANY EXTRANEOUS INFLUENCES: (i>o) 1. 2. 3. NONFENESTRATED ENDOTHELIAL CELLS JOINED BY TIGHT JUNCTIONS Basement membrane (basolamina) CYTOPLASMIC PNS COMPONENTS PERIPHERAL (SPINAL) NERVES (31 PAIRS): 8-CERVICAL 12-THORACIC 5-LUMBAR 5-SACRAL 1-COCCYGEAL CRANIAL NERVES (12 PAIRS) EMERGE FROM FORAMINA IN SKULL & COVERED BY MENINGES NUMBERED I THROUGH XII FROM ANTERIOR TO POSTERIOR 11 OF 12 PAIRS ARISE FROM BRAIN GANGLIA: CLUSTERS OF NEURON CELL BODIES TWO MAJOR TYPES 1. 2. 11TH PAIR ARISES MOSTLY FROM SUPERIOR PART OF SPINAL CORD CRANIOSPINAL AUTONOMIC NERVE PLEXUSES: NETWORK OF PERIPHERAL NERVES THREE MAJOR NERVE PLEXUSES… PERIPHERAL (SPINAL) NERVE (31 PAIRS) ARISES FROM SPINAL CORD VIA NERVE ROOTLETS CONVERGE TO FORM TWO NERVE ROOTS: 1. 2. VENTRAL ROOT DORSAL ROOT VENTRAL AND DORAL ROOTS UNITE TO FORM PERIPHERAL NERVE PERIPHERAL NERVE DIVIDES INTO TWO RAMI: 1. 2. ANTERIOR RAMUS POSTERIOR RAMUS PERIPHERAL NERVES CONSISTS OF: BUNDLES OF NERVE FIBERS (AXONS) HELD TOGETHER BY C.T. SHEATHS NEURONS BETWEEN SENSORY AND MOTOR NEURONS THAT GOVERN COORDINATED ACTIVITY PERIPHERAL (SPINAL) NERVE: FOUR TYPES OF NERVE FIBERS SOMATIC SENSORY AND MOTOR FIBERS: 1. GENERAL SOMATIC AFFERENT (GSA) FIBERS 2. TRANSMIT SENSATIONS FROM BODY TO SPINAL CORD (EG., PAIN, TEMPERATURE, TOUCH, & PRESSURE) GENERAL SOMATIC EFFERENT (GSE) FIBERS TRANSMIT IMPULSES TO SKELETAL MUSCLES VISCERAL SENSORY AND MOTOR FIBERS: 3. GENERAL VISCERAL AFFERENT (GVA) FIBERS 4. TRANSMIT REFLEX OR PAIN FROM MUCOUS MEMBRANES, GLANDS, AND BLOOD VESSELS BACK TO CNS GENERAL VISCERAL EFFERENT (GVE) FIBERS TRANSMIT IMPULSES TO SMOOTH AND CARDIAC MUSCLE AND GLANDULAR TISSUES PERIPHERAL (SPINAL) NERVE: HISTOLOGY LONGITUDINAL OR OBLIQUE SECTION: “WAVINESS” OF BUNDLES LIGHTER STAINING THAN CONNECTIVE TISSUE DUE TO MYELIN CROSS-SECTION: BUNDLES OF DARKSTAINING AXONS SURROUNDED BY LIGHT/ABSENT MYELIN SHEATH PRESENCE OF DARKSTAINING CT SHEATHS ENDONEURIUM PERINEURIUM EPINEURIUM PNS: CRANIOSPINAL GANGLIA DORSAL ROOT GANGLIA (SPINAL GANGLIA) CRANIAL NERVE GANGLIA GANGLIA HISTOLOGY CELL BODIES ARE USUALLY ROUND WHAT ARE THE “YELLOWBROWN PATCHES?” PNS: AUTONOMIC GANGLIA (3) SYMPATHETIC GANGLIA: PARAVERTEBRAL (CHAIN) GANGLIA PREVERTEBRAL GANGLIA PARASYMPATHETIC GANGLIA: WITHIN WALL OF ORGAN THEY SUPPLY AUTONOMIC NERVOUS SYSTEM DESCRIBED AS “VISCERAL MOTOR (EFFERENT) SYSTEM” THAT SUPPLIES: CONSISTS OF TWO NEURONS THAT SYNAPSE IN AN AUTONOMIC GANGLION CELL BODY OF FIRST NEURON IS IN CNS PREGANGLIONIC FIBER CELL BODY OF SECOND NEURON IS IN PNS (AUTONOMIC GANGLION) SMOOTH MUSCLE CONDUCTION SYSTEM OF HEART GLANDS POSTGANGLIONIC FIBER ANS SUBDIVIDED INTO: SYMPATHETIC NERVOUS SYSTEM PARASYMPATHETIC NERVOUS SYSTEM ANS: SYMPATHETIC NERVOUS SYSTEM PREGANGLIONIC CELL BODIES: SPINAL CORD GRAY MATTER (T1-L3 SPINAL SEGMENTS) POSTGANGLIONIC CELL BODIES: PARAVERTEBRAL & PREVERTEBRAL GANGLIA ANS: PARASYMPATHETIC NERVOUS SYSTEM PREGANGLIONIC CELL BODIES: BRAINSTEM GRAY MATTER GRAY MATTER OF SPINAL SEGMENTS S2-S4 CRANIAL DIVISION SACRAL DIVISION POSTGANGLIONIC CELL BODIES: CRANIAL GANGLIA TARGET ORGANS ANS SUMMARY SOMATIC NERVOUS SYSTEM CONTROLS SOMATOSENSORY PERCEPTION CONTROLS SOMATOMOTOR (VOLUNTARY) FUNCTIONS TOUCH, HEAT, COLD TAKES 3 neurons SKELETAL MUSCLE CONTRACTION Takes 2 neurons ACETYLCHOLINE IS MOST COMMON SOMATIC NEUROTRANSMITTER CONCLUSION: IMPORTANT POINTS OF LECTURE (SLIDE 1 OF 2) WHAT DO BRAIN AND SPINAL CORD COMPRISE? WHAT DO CRANIAL NERVES, PERIPHERAL NERVES, GANGLIA, NERVE PLEXUSES COMPRISE? WHAT ARE COLLECTIONS OF CELL BODIES CALLED IN THE CNS? PNS? WHAT ARE COLLECTIONS OF AXONS IN THE CNS? PNS? WHAT ARE THE TWO CHIEF COMPONENTS OF THE BLOOD BRAIN BARRIER? WHAT ARE A NETWORK OF PERIPHERAL NERVES? LIST THE FIRST TWO YOU WILL ENCOUNTER? WHAT IS THE CHIEF COMPONENT OF A PERIPHERAL NERVE? WHICH CELL(S) MAKE MYELIN IN THE CNS AND PNS? WHICH STRUCTURE CONTAINS ONLY SENSORY FIBERS? MOTOR FIBERS? BOTH SENSORY AND MOTOR? WHERE ARE SENSORY CELL BODIES LOCATED? CONCLUSION: IMPORTANT POINTS OF LECTURE (SLIDE 2 OF 2) WHAT IS LOCATED IN THE SPINAL CORD GRAY MATTER (T1-L3 SPINAL SEGMENTS)? WHAT IS THE SECOND NEURON OF THE MOTOR COMPONENT OF THE ANS CALLED AND WHERE IS IT LOCATED? WHERE ARE THE POSTGANGLIONIC SYMPATHETIC CELL BODIES LOCATED? WHAT IS LOCATED IN THE MEDULLA AND MIDBRAIN NUCLEI (CNS GRAY MATTER) AND GRAY MATTER OF SPINAL SEGMENTS S2-S4? WHERE ARE POSTGANGLIONIC PARASYMPATHETIC CELL BODIES LOCATED? WHICH AUTONOMIC FIBER TYPE HAS A SHORT PREGANGLIONIC AXON AND A LONG POSTGANGLIONIC AXON THAT SECRETES NOREPINEPHRINE?