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Lecture 18PDF - Unit#9 The Nervous System The Peripheral...

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Unit #9 The Nervous System The Peripheral Nervous System
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Peripheral Nervous System PNS is the nervous system outside the brain and spinal cord – Provides vital links to the body and outside world – Nerves allow the CNS to receive information and initiate action Contains sensory inputs and motor outputs – Categorized as Somatic or visceral General or special
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Fig. 14.1 Central nervous system (CNS) Peripheral nervous system (PNS) Motor (efferent) division Sensory (afferent) division Sympathetic division Parasympathetic division Somatic sensory General: Touch, pain, pressure, vibration, temperature, and proprioception in skin, body wall, and limbs Special: Hearing, equilibrium, vision Visceral sensory General: Stretch, pain, temperature, chemical changes, and irritation in viscera; nausea and hunger Special: Taste, smell Somatic nervous system Motor innervation of all skeletal muscles Autonomic nervous system (ANS) Motor innervation of smooth muscle, cardiac muscle, and glands
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Basic Structural Components of PNS Sensory receptors àฏ pick up stimuli from inside or outside the body – Can be free nerve endings of sensory neurons or complete receptor cells Nerves and ganglia – Nerves àฏ bundles of peripheral axons – Ganglia àฏ clusters of peripheral neuronal cell bodies Motor endings àฏ axon terminals of motor neurons – Innervate effectors (muscle fibers and glands)
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Peripheral Sensory Receptors Receptors can be classified based on: – Location • Exteroreceptors àฏ sensitive to stimuli arising from outside the body • Interoreceptors àฏ receive stimuli from internal viscera • Proprioceptors àฏ l ocated in skeletal muscles, tendons, joints, and ligaments – Stimulus detected Mechanoreceptors, thermoreceptors, chemoreceptors, photoreceptors, nociceptors – Structure Special senses and general sensory receptors (free nerve endings & encapsulated nerve endings)
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Fig. 14.3 Lamellar corpuscle (deep pressure) Hair follicle receptor (hair movement) Free nerve endings (pain and temperature) Bulbous corpuscle (pressure) Tactile corpuscle (touch, light pressure) Epithelial tactile complexes (light touch) Epidermis Dermis and hypodermis Secondary sensory endings (type II fiber) γ Efferent (motor) fiber to muscle spindle Primary sensory endings (type Ia fiber) Connective tissue capsule Muscle spindle Tendon Sensory fiber Tendon organ α Efferent (motor) fiber to extrafusal muscle fibers Extrafusal muscle fiber Intrafusal muscle fibers Fig. 14.2
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