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HUMAN ANATOMY LECTURE TEN NERVOUS SYSTEM FUNCTIONS • Maintains homeostasis • Sensory input - monitors and responds to environmental changes • Relates past and present experiences • Control of skeletal muscles • Higher mental functions - consciousness, memory, thinking ORGANIZATION Components • Brain, spinal cord, nerves, sensory receptors Subdivisions • Central Nervous System (CNS) - brain - spinal cord • Peripheral Nervous System (PNS) - sensory receptors - nerves PERIPHERAL NERVOUS SYSTEM • Includes all neural tissue outside of the CNS • Delivers sensory information to CNS and carries motor commands to peripheral tissues and organs Divisions of the PNS (1) Sensory/Afferent - transmits info from sensory receptors to CNS (2) Motor/Efferent - transmits impulses from CNS to effector organs (muscles and glands) - further divided MOTOR DIVISIONS OF THE PNS Somatic Nervous System - from CNS to skeletal muscles • • • • Voluntary Single neuron system Contain SYNAPSES - junction of a nerve cell with another cell Reflexes Autonomic Nervous System - from CNS to smooth muscle, cardiac muscle, and some glands • Involuntary or subconscious control • Two neuron system - (1) CNS to ganglion (2) ganglion to effector • Divisions of the ANS: Sympathetic - prepares body for stress Parasympathetic - resting state (digestion, urination, etc) AUTONOMIC NERVOUS SYSTEM STRUCTURES WITHIN THE PNS • Sensory Receptors - endings of neuron dendrites - specialized to detect environmental stimulus (pain, touch, temperature, pressure, sound, light, odor) • Nerve - bundle of neurons and their sheaths - connects CNS to sensory receptors, muscles, glands Cranial Nerves - originate from brain (12 pairs) Spinal Nerves - originate from spinal cord (31 pairs) • Ganglion - collection of neuron cell bodies outside the CNS • Plexus - extensive network of axons, sometimes cell bodies, located outside the CNS CELLS OF THE NERVOUS SYSTEM Neurons (nerve cells) • Receive stimuli and transmit action potentials • Consist of: cell body (soma) dendrites - input axons - output Neuroglia (glial cells) • Support and protect neurons • Several different types PARTS OF THE NEURON Cell Body • • • Contain nucleus, organelles for ATP and protein synthesis, nissl bodies, cytoskeleton, cytoplasm NISSL BODIES - concentrated areas of rough ER AXON HILLOCK - site of axon attachment Dendrite • • Receive sensory input and carries toward cell body DENDRITIC SPINES - site of axon synapses Axon • • • • • • Carries impulse away from cell body COLLATERALS - side branches AXOPLASM - axon cytoplasm AXOLEMMA - specialized cell membrane May be surrounded by a myelin sheath AXON TERMINALS - presynaptic endings TYPES OF NEURONS Functional Classification • Sensory/Afferent Neurons - impulse travels from sensory receptor to CNS - cell bodies located in peripheral sensory ganglia near spinal cord - unipolar Somatic Sensory Neurons - info from external environment Visceral Sensory Neurons - info from internal environment • Motor/Efferent Neurons - impulse travels from CNS to effector (muscle or gland) - multipolar Somatic Motor Neurons - innervate skeletal muscles - have conscious control over Visceral Motor Neurons - innervate smooth and cardiac muscle, glands - impulse travels along 2 VMN with synapse inbetween (1st is preganglionic fiber, 2nd is postganglionic fiber) • Interneurons - located within CNS - distribute sensory info and coordinate motor activity - connect afferent and efferent neurons Structural Classification A. Unipolar - dendrite and axon are a single process - cell body off to the side - sensory neurons of PNS B. Bipolar - have separate dendrite and axon - located in sensory organs (retina of eye, nasal cavity) C. Multipolar - many dendrites and single axon - neurons within CNS and efferent neurons NEUROGLIA • Nonneuronal cells of CNS and PNS • Differ between CNS and PNS • Several different kinds Astrocytes (CNS) • • • Most numerous in CNS Processes form feet that cover surfaces of neurons and blood vessels Many functions: - blood-brain barrier: regulates substances entering brain - creates structure like a cytoskeleton - guide neuronal development - regulates composition of extracellular brain fluid Ependymal Cells (CNS) • Line brain ventricles and spinal cord (similar to epithelial cells) • Some form CHOROID PLEXUS - secrete cerebrospinal fluid • Cilia help move CSF through brain • Have long processes on basal surface that extend into brain tissue Microglia (CNS) • Smallest and fewest in number • Wander through nervous tissue - specialized to phagocytize microorganisms, necrotic tissue, foreign substances Oligodendrocytes (CNS) • Have long processes that form myelin sheaths around neurons (white matter) • Each may wrap around several neurons Schwann Cells or Neurolemmocytes (PNS) • Wrap around a portion of an axon forming myelin sheath • Shields axon from interstitial fluid Satellite Cells (PNS) • Surround cell bodies in ganglia • Provide support and nutrients