PHYSIOLOGY & PATHOPHYSIOLOGY BSC 100 (AY 2020-2021) Mr. Lecturer’s Name, RPh TOPIC 7: NERVOUS SYSTEM FUNCTIONS OF NERVOUS SYSTEM STRUCTURAL CLASSIFICATION Central Nervous System (CNS) ▪ ▪ ▪ brain & spinal cord (occupy dorsal body cavity) integrating & command centers of NS interpret incoming sensory information & issue instructions Peripheral Nervous System (PNS) ▪ ▪ ▪ ▪ Sensory Input ▪ ▪ gathered information sensory receptors = monitor changes Integration ▪ ▪ processes & interprets sensory input decides on response Motor Output ▪ all parts of NS outside the CNS Spinal nerves - carry impulses to & from the spinal cord Cranial nerves - carry impulses to & from the brain Communication lines; link all parts of body FUNCTIONAL CLASSIFICATION Sensory Division / Afferent Division ▪ convey impulses to CNS from sensory receptors Somatic Sensory (Afferent) Fibers ▪ Sensory fibers delivering impulses from skin, skeletal muscles, and joints Visceral Sensory (Afferent) Fibers ▪ Sensory fibers transmitting impulses from the visceral organs effector = causes a response or effect Motor Division / Efferent Division ORGANIZATION OF THE NERVOUS SYSTEM ▪ ▪ carries impulses from CNS to effector organs, the muscles and glands effect a motor response Somatic Nervous System (SNS) ▪ voluntarily control skeletal muscles Autonomic Nervous System (ANS) ▪ involuntary control activity of smooth muscle, cardiac muscle, and glands Sympathetic Nervous System ▪ fight / flight Parasympathetic Nervous System ▪ rest / digest NEUROGLIA / GLIAL CELLS / GLIA ▪ ▪ supporting cells support, insulate & protect neurons MUKSAN, S.M. 1 Topic 7: Nervous System CNS NEUROGLIA Astrocytes (star-shaped cells) PNS NEUROGLIA Schwann cell ▪ ▪ ▪ ▪ living barrier bet capillaries & neurons determine capillary permeability control chemical environment in brain by “mopping up” leaked potassium ions Microglia (spiderlike phagocytes) ▪ health of nearby neurons & dispose of debris, s.a dead brain cells & bacterium form myelin sheaths, has nuerilemma Satellite cells ▪ protective, cushioning cells for peripheral neuron cell bodies ▪ transmit messages (nerve impulses) NEURONS Ependymal cells ▪ ▪ line central cavities of brain & spinal cord circulate cerebrospinal fluid filling cavities & forms protective watery cushion around CNS CELL BODY ▪ metabolic center of neuron Nucleus ▪ transparent w/ large nucleolus Cytoplasm Oligodendrocytes ▪ ▪ wrap flat extensions tightly around nerve fibers myelin sheath - fatty insulating coverings, no nuerilemma (“neuron husk”) ▪ ▪ usual organelles lacks centrioles (amitotic neurons) Nissl bodies ▪ specialized rough ER Neurofibrils ▪ intermediate filaments for cell shape MUKSAN, S.M. 2 Topic 7: Nervous System PROCESSES / FIBERS Dendrites ▪ convey incoming electrical signals to cell body CLASSIFICATION OF NEURONS FUNCTIONAL CLASSIFICATION ▪ acc to direction nerve impulse travels relative to CNS Axons ▪ ▪ ▪ generate nerve impulses typically conduct them away each neuron has only one axon Axon Hillock ▪ conelike region of cell where axon arise Axon Terminals ▪ collateral branches of axons ▪ contain neurotransmitters Synaptic Cleft ▪ ▪ gap bet neurons synapse - functional junction, where impulse is transmitted from one neuron to another Sensory Neurons / Afferent Neurons ▪ ▪ ▪ carry impulses from sensory receptors (in internal organs or the skin) to the CNS cell bodies are always found in a ganglion outside the CNS dendrite endings ass w/ receptors Types of sensory receptors MYELIN SHEATHS ▪ protects & insulates fibers ▪ increases transmission rate of nerve impulses Schwann cells (PNS) ▪ ▪ ▪ Nodes Of Ranvier – gaps / indentations bet myelin sheath many Schwann cells → single myelin sheath neurilemma – imp in fiber regeneration Oligodendrocytes (CNS) ▪ ▪ many flat extensions coil around as many as 60 different fibers at the same time 1 oligodendrocyte → many myelin sheaths TERMINOLOGY Nuclei ▪ clusters of cell bodies found in CNS Ganglia Motor Neurons / Efferent Neurons ▪ ▪ Small collections of cell bodies in PNS Tracts ▪ ▪ carry impulses from CNS to viscera and/or muscles and glands cell bodies are usually located in the CNS Bundles of nerve fibers (neuron processes) in CNS Nerves Interneurons / Association Neurons ▪ ▪ ▪ Bundles of nerve fibers (neuron processes) in PNS connect motor & sensory neurons in neural pathways cell bodies are typically located in CNS White Matter ▪ myelinated fibers Gray Matter ▪ unmyelinated fibers MUKSAN, S.M. 3 Topic 7: Nervous System permeability properties of the cell’s plasma membrane change for a very brief period STRUCTURAL CLASSIFICATION ▪ based on the number of processes ▪ Multipolar Neuron Depolarization ▪ ▪ ▪ several processes all motor & interneurons inward rush of Na+ changes polarity of neuron’s membrane Graded Potential ▪ ▪ Bipolar neurons ▪ ▪ ▪ ▪ two processes: one axon & one dendrite rare in adults only in some special sense organs (eye, nose) act in sensory processing as receptor cells. Action Potential (Nerve Impulse in Neurons) ▪ all-or-none response ▪ either conducted or not Repolarization ▪ ▪ Unipolar Neurons ▪ ▪ ▪ ▪ single process emerging from cell body as if cell body were on a “cul-de-sac” off the “main road” that is the axon process is very short divides into proximal (central - dendrites) & distal (peripheral - axons) processes Sensory neurons found in PNS ganglia local electrical situation where inside is more + than inside if stimulus is strong enough & Na influx is great enough, local depolarization (graded potential) activates neuron to initiate & transmit action potential (long-distance signal) ▪ after Na ions rush to neuron, membrane permeability changes again, becoming impermeable to Na but permeable to K ions K ions are allowed to diffuse out of neuron into interstitial fluid very rapidly out flow of positive ions from cell restores the electrical conditions at the membrane to polarized or resting state Sodium-Potassium Pump ▪ ▪ Restores initial concentrations of Na & K 3 Na out; 2 K in Saltatory Conduction ▪ ▪ Myelinated neurons conduct impulses faster Jumping from node to node Transmission of the Signal at Synapses Neurotransmitter NERVE IMPULSES TWO MAJOR FUNCTIONAL PROPERTIES Irritability ▪ ▪ cross synapse to transmit signal from one neuron to the next, or to target cell ability to respond to a stimulus & convert it to nerve impulse Conductivity ▪ ability to transmit impulse to other neurons, muscles, or glands Electrical Conditions of a Resting Neuron’s Membrane ▪ polarized ▪ fewer positive ions sitting on inner face of neuron’s plasma membrane than there are on its outer face ▪ PISO (K in Na out) ▪ As long as inside remains more negative (fewer positive ions) than the outside, the neuron will stay inactive Action Potential Initiation and Generation ▪ most neurons in body are excited by neurotransmitter chemicals released by other neurons MUKSAN, S.M. 4 Topic 7: Nervous System REFLEXES ▪ ▪ ▪ rapid, predictable, & involuntary responses to stimuli one-way streets: once it begins, it always goes in the same direction preprogrammed response to a given stimulus TYPES OF REFLEXES Somatic Reflexes ▪ ▪ all reflexes that stimulate skeletal muscles involuntary reflexes Autonomic reflexes ▪ ▪ regulate activity of smooth muscles, heart, & glands digestion, elimination, blood pressure, & sweating REFLEX ARCS ▪ neural pathways where reflexes occur ▪ involve both CNS & PNS structures FIVE ELEMENTS OF REFLEX ARCS 1. Receptor ▪ reacts to a stimulus 2. Sensory Neuron 3. Integration Center ▪ synapse or interneurons between sensory & motor neurons 4. Motor Neuron 5. Effector ▪ muscle or gland eventually stimulated SIMPLE REFLEX ARCS Two-Neuron Reflex Arc ▪ patellar or knee-jerk reflex (simplest type in humans) MUKSAN, S.M. 5 Topic 7: Nervous System Three-Neuron Reflex Arc ▪ ▪ flexor or withdrawal reflex limb is withdrawn from a painful stimulus HOMEOSTATIC IMBALANCE Multiple Sclerosis (MS) ▪ autoimmune disease ▪ destroys myelin sheaths around CNS fibers by converting them to hardened sheaths called scleroses ▪ nerve signals do not always reach the intended target ▪ tx: injections of interferon Sedatives & Anesthetics ▪ block nerve impulses by altering membrane permeability to ions, mainly sodium ions ▪ no sodium entry = no action potential Spinal Reflexes ▪ ▪ Cold & Continuous Pressure ▪ hinder impulse conduction because they interrupt blood circulation (delivery of oxygen and nutrients) to the neurons involve only spinal cord neurons occur without brain involvement MUKSAN, S.M. 6
