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Structural Components of PNS
- Sensory receptors- detect stimuli
- Motor endings- innervate effectors
- Nerves and Ganglia- bundles of axons and clusters of cell bodies
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Peripheral Sensory Receptors- Free Nerve Endings
Monitor most types of general sensory info, touch, pain, pressure, proprioception, temp.)
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Peripheral Sensory Receptors- Complete Receptor Cells
Monitor special senses, (taste, vision, hearing, balance)
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Peripheral Sensory Recprtors-Location
- Exteroceptors- stimuli outside the body
- Interoceptors- stimuli inside the body
- Proprioceptors- musculoskeletal
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Peripheral Sensory Receptors- Stimulus Detected
- Mechanoreceptors- mechanical forces
- Thermoreceptors- temperature
- Chemoreceptors- chemicals
- Photoreceptors- light
- Nocireceptors- pain
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Peripheral Sensory Receptors- Structure
- Free nerve endings- abundant in epithelia and its corresponding CT
- -Merkel discs-light touch
- -Hair follice- wrap around follicles, light touch, rapid adapting
- -Itch receptor- located in dermis
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Encapsulated Nerve Endings
- -One or more end fibers of sensory neurons enclosed in CT capsule
- -All are mechanoreceptors
- -Amplify stimulus or filter stimuli
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-Encapsulated NE- Meissner's corpuscles
Beneath epidermis, fine touch - mostly areas w/o hair
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Encapsulated NE- Pacinian Corpuscles
Located in deep CT (hypodermis) sense vibration
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Encapsulated NE- Ruffini's Corpuscles
- -Located in dermis, joint capsules, hypodermis
- -Monitor continuous pressure
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Encapsulated NE- Proprioceptors
- -Muscle spindles - measure change in muscle length
- -Golgi Tendon Organs- near muscle tendon junction, measure tension in tendon
- -Joint kinesthetic receptors-measure stretch in synovial joints
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Peripheral Motor Endings- Skeletal Muscle
- -One neuromuscular junction associated with each muscle fiber
- -Axon terminals release neurotransmitter, which crosses to sarcolemma
- -Motor unit: a motor neuron and all muscle fibers it innervates(all fibers contract)
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Periperal Motor Endings- Visceral Muscle and Glands
-Visceral motor axon swells into row of knobs(varicosities), releases neurotransmitter
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Cranial Nerves
- -12 pairs, numbered I-XII (rostal to caudal)
- -First 2 pairs attach to forebrain, and rest attach to brain stem
- -Generally serve head and neck
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I- Olfactory
- -smell
- -sensory only
- -most superior, most anterior arises from forebrain
- -input goes to riencephalon
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II- Optic
- -vision
- -sensory only
- -input- rods and cones in retina, goes through thalamus, then to occipital lobe
- -arises from forebrain
- -Severed=blindness
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III- Oculomotor
- -Primarily motor- report back the position of the eyeball
- -Controls 4-6 muscles(skeletal) that move eye in orbit and iris(autonomic)
- -Somatic branch of NS
- -Arises from midbrain
- -Severed= eyeball droop/no movement
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IV- Trochlear (pulley)
- -small mixed nerve, comes from midbrain
- -innervates superior oblique muscle of eye that is responsible for downward and outward (latertal) movement
- -Damage impairs movement
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V-Trigeminal
- -Mixed nerve- largest cranial nerve
- -Arises from pons
- -3 different nerves- opthalamic, maxillary, mandibular
- -Motor Func.deal with chewing
- -Sensory Func.- info from skin & musclesof face, teeth
- -Novicain Nerve
- -Trauma=impaired chewing, lack of sensation in face
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VI- Abducens
- -Originates from inferior pons
- -Mostly motor
- -Innevates lateral rectus muscle of eye(abducts)
- -Damage causes crossed eyes(esotropia)
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VII-Facial
- -Arises from pons
- -Mixed Nerve
- -Inervates muscle of facial expression(skeletal)
- -Innervates salivary glands(exocrine)- autonomic
- -Taste sensation, anterior 2/3 of tongue(sweet)
- -Damage= inability to contract facial musc., distorted taste
- -Bell's palsy- affected side of face to sag
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VIII- Vestibulochlear(auditory)
- -Only cranial nerve that doesnt exit cranium through foramen
- -Purely sensory
- -Arises from both pons and medulla
- -2 main branches
- --Vestibular nerve- balance (damage= dizziness/imbalnace)
- --Cochlear nerve- hearing(damage=sensory deafness)
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IX-Glossopharyngeal(glossa=tongue, pharynx=throat)
- -Mixed nerve
- -Originates in medulla
- -Innervates muscles of throat and tongue
- -Innervates salivary glands
- -Controls taste in post 1/3 of tongue(bitter/sour)
- -Damage=loss of bitter/sour taste, impairs swallowing)
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X-Vagus
- -Arises from Medulla
- -Goes through thoracic and abdominal cavity
- -Key autonomic nerve, mixed
- -Both vagus nerves damaged= death
- -Damage to one= vocal impairment, difficulty swallowing, visceral issues
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XI-Accessory
- -Arises from medulla and part of spinal cord
- -Motor only
- -Moves head/neck/shoulders(shrug)
- -Damge= difficulty w/ movement
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XII-Hypoglossal
- -Motor only
- -Originates in medulla
- -Innervates tongue muscles
- -Damage= difficulty speaking, swallowing, protruding tongue
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Cranial Nerves
- -Sensory neuron cell bodies are located in receptor organs or cranial sensory ganglia
- -Motor neuron cell bodies located in ventral gray matter of brain stem
- -Purely sensory, purely motor, mixed
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Spinal Nerves
- -31 pair(62 nereves)
- -Exit spinal column via intervertebral foramina
- -Nerves C1-C7 leave above corresponding vertebrae
- -Thoracic nerves leave below corresponding vertebrae
- -Lumbar, sacral, and coccygeal also leave below corr. bones
- -All are mixed
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Spinal Nerve Anatomy-Roots
- -Structures that enter and exit spinal cord, are sensory only or motor only
- -Converge together in order to exit invertebral foramen
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Spinal Nerve Anatomy- Rami
- -Branches that occur after sensory and motor re-join
- -Dorsal(posterior) ramus
- -Ventral(anterior) ramus
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Spinal Nerve Anatomy- Sympathetic Rami
- -2 branches from each spinal nerve that connect to sympathetic trunk ganglion, part of ANS
- -Composed of gray ramus and white ramus
- -Serve as a place where sympathetic nerves separate from somatic motor neurons
- -Consider them as sideroads that carry impulses up and down b/w segements
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Nerve Plexuses
- -In most spinal nerves, the anterior rami combine and spolit again as plexuses
- -Nerve Plexus= network of nerves(fromed by anterior/ventral rami)
- -Within plexus, fibers from different rami crisscross
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Cervical Plexus
- -Includes anterior rami of C1-C4 and part of C5
- -Branches innervate skin and muscles of neck, portions of head and shoulders
- -Some fibers combine w/ cranial nerves
- -Phrenic nerve- innervates diaphragm(sensory and motor)
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Brachial Plexus
- -Primarily serves arm muscles, some neck and shoulder
- -Formed by C5-T1- very complex
- -Median Nerve- innervates most muscles of anterior forearm and laterall palm
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Lumbar Plexus
- -Formed by mostly L1-L4
- -Serves muscles of abdomen, anterior/medial parts of leg
- -Obturator Nerve- runs through obturator foramen
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Sacral Plexus
- -Formed by L4-S5
- -Serves muscle of pelvic area, posterior/lateral parts of leg, lower back, dorsal and plantar foot
- -Sciatic Nerve- largest nerve in body, passes through pelvis and down back of leg(2 nerves- tibial and common fibular)
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Joint Innervation
- -Every joint capsule receives sensory branches from several nerves
- -Hilton's Law- any nerve that innervates a muscle producing movement at a joint also innervatesthe joint itself(and skin over it)
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Dermatomes-Skin Innervation
- -Area of skin innervated by cutaneous branches from a single spinal nerve
- -All spinal nerves except C1 involved
- -Trunk Region- Horizontal
- -Limb Regions- Vertical (sort of)
- -Trunk dermatomes can overlap A LOT, limbs LESS overlap
- -Clinical Use- pinpoint level of sopinal injuries, anesthesia
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PNS Disorders
- -Shingles- viral infection of sensory neurons involving the skin, rash of scaly, painful blisters- along a dermatome, stems from chickenpox, virus lies dormant in sensory ganglion
- -Myasthenia- Disorder of neuromuscular junction, weakening of muscles, autoimmune disorder(destroys ACh receptors)
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