BIOL 2457 1st EditionExam # 3 Study Guide Lectures: 24 - 34Chapter 12 Nervous TissueKnow receptors, know parasympathetic and sympathetic divisions, Know CSF, Know of the histology of the nervous system: neurons, know chemical synapses, Know of IPSP, Know nervous system structures, know of summation, Know repair of PNS, Know speed of impulse propagationReceptors-Sensory Receptors: Parts of neurons or specialized cells that monitor changes in the internal or external environmentParasympathetic Division-Parasympathetic division (slow down heart rate)SNS: Neurons from cutaneous and special sensory receptors to the CNS, Motor neurons to skeletal muscle tissue (Voluntary)ANS: Sensory neurons from visceral organs to CNS, Motor neurons to smooth & cardiac muscle and glands, Sympathetic division (speeds up heart rate)Central nervous system (CNS) Consists of the brain and spinal cordPeripheral nervous system (PNS) Consists of cranial and spinal nerves that contain both sensory and motor fibers, Connects CNS to muscles, glands & all sensory receptorsCSF-Ependymal cells: Line ventricles of the brain and central canal of the spinal cord, Produce, monitor, assist in CSF circulationHistology of Nervous System: Neurons-Functional units of the nervous system: Have capacity to produce action potentials, Electrical excitability, Cell body, Single nucleus with prominent nucleolus, Nissl bodies (chromatophilic substance), Rough ER & free ribosomes for protein synthesis, Neurofilaments give cell shape and support, Microtubules move material inside cell, Lipofuscin pigment clumps (harmless aging), Cell processes = dendrites & axonsChemical Synapses-Action potential reaches end bulb and voltage-gated Ca+2 channels open, Ca+2 flows inward triggering release of neurotransmitter, Neurotransmitter crosses synaptic cleft & binds to ligand-gated receptors, The more neurotransmitter released, the greater the change in potential of thepostsynaptic cell, Synaptic delay is 0.5 msec, One-way information transferIPSP-An inhibitory postsynaptic potential is called an IPSP, It results from the opening of ligand-gated Cl- or K+ channels, It causes the postsynaptic cell to become more negative or hyperpolarized, The postsynaptic cell is less likely to reach thresholdNervous System Structures-Brain and 12 pairs of cranial nerves and their branches Spinal cord and thirty-one pairs of spinal nerves which emerge from the spinal cord. Ganglia located outside the brain and spinal cord, Small masses of nervous tissue, containing primarily cell bodies of neurons. Enteric plexuses which help regulate the digestive system. Sensory receptors, Parts of neurons or specialized cells that monitor changes in the internal or external environment.Summation-If several presynaptic end bulbs release their neurotransmitters at about the same time, the combined effect may generate a nerve impulse due to summationSummation may be spatial or temporal.Summation of effect of neurotransmitters released from 2 or more firings of the same end bulb in rapid succession onto a second neuronSummation of effects of neurotransmitters released from several end bulbs onto one neuronRepair of PNS-When there is damage to an axon, usually there are changes, called chromatolysis, which occur in the cell body of the affected cell; this causes swelling of the cell body and peaks between 10 and 20 days after injury.By the third to fifth day, degeneration of the distal portion of the neuronal process and myelin sheath (Wallerian degeneration) occurs; afterward, macrophages phagocytize the remains. Retrograde degeneration of the proximal portion of the fiber extends only to the first neurofibral node.Regeneration follows chromatolysis; synthesis of RNA and protein accelerates, favoring rebuilding of the axon and often taking several months.Axons & dendrites may be repaired if Neuron cell body remains intact, Schwann cells remain active and form a tube, Scar tissue does not form too rapidlyChromatolysis, 24-48 hours after injury, Nissl bodies break up into fine granular massesBy 3-5 days, Wallerian degeneration occurs (breakdown of axon & myelin sheath distal to injury)Retrograde degeneration occurs back one node, Within several months, regeneration occurs Neurolemma on each side of injury repairs tube (schwann cell mitosis) Axonal buds grow down the tube to reconnect (1.5 mm per day)Speed of Impulse Propagation-The propagation speed of a nerve impulse is not related to stimulus strength. Larger, myelinated fibers conduct impulses faster due to size & saltatory conduction Fiber types, A fibers largest (5-20 microns & 130 m/sec), Myelinated somatic sensory & motor to skeletal muscle, B fibers medium (2-3 microns & 15 m/sec), Myelinated visceral sensory & autonomic preganglionic, C fibers smallest (.5-1.5 microns & 2 m/sec), Unmyelinated sensory & autonomic motorChapter 13 The Spinal Cord and Nerves Know spinal nerves, internal anatomy of the spinal cord, know reflexesSpinal nerves-Number and type: 31 pairs, Mixed nerves Location: Cervical (C1-C8), Thoracic (T1-T12), Lumbar (L1-L5), Sacral (S1-S5), CoccygealConnective tissue coverings: Epineurium, Perineurium, EndoneuriumWhite ramus (myelinated axons)Gray ramus (unmyelinated axons that innervate glands and smooth muscle)Dorsal ramus (sensory and motor innervation to the skin and muscles of the back)Ventral ramus (supplying ventrolateral body surface, body wall and limbs)Each pair of nerves monitors one dermatomeDermatome is the area of the skin that provides sensory input to the CNS via one pair of spinal nerves. [the trigeminal nerve]Internal Anatomy of the Spinal Cord-Gray matter horns: Posterior (dorsal) horns, Anterior (ventral) horns, Lateral hornsWhite matter columns: Types, Anterior, Posterior, LateralForm tracts: Ascending – sensory, Descending – motorReflexes-Reflex - automatic, sudden, involuntary response to a stimulusSpinal reflex – occurs when the integration takes place in the spinal cordReflex arc - pathway followed by nerve impulses that produce a reflex Reflex arc components (5 steps): Sensory receptor, Sensory neuron, Integrating center, Motor neuron, EffectorStretch reflex – causes contraction of a skeletal muscle in response to stretching of the muscleTendon reflex – operates as a feedback mechanism to control muscle length by causing muscle contractionFlexor (withdrawal) reflex - causes withdrawal of a part of the body in response to a painful stimulus, Works with crossed extensor