peripheral nervous system chapter 13. sensory receptor types nociceptors – respond to excess heat,...
TRANSCRIPT
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Peripheral Nervous System
Chapter 13
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Sensory Receptor Types
• Nociceptors– Respond to excess heat, pressure, or
chemicals– Tissue damage– All parts of the body but brain
• Thermoreceptors– Temperature of skin and blood– Maintains homeostatic control via the
hypothalmus• Photoreceptors
– Light absorbing pigments– Light detection
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Sensory Receptor TypesMechanoreceptors• Touch, pressure, & vibrations• Bend or stretch PM of
receptor cell = changing permeability– Stretch receptors – position of
body parts– Hair cells - sound waves and
H2O movements
Chemoreceptors• Chemicals in the internal &
external environment– O2 in arterioles– Osmoreceptors - changes in
[blood solute]– Pheromone detection
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Sensory Receptor Locations
• Exteroceptors– Stimuli outside the body– Skin and special sense organs
• Interoceptors– Stimuli within the body– Chemical messengers, tissue stretch, and temperature
• Proprioceptors– Internal stimuli– Monitor position and stretch of joints, tendons, and
muscles
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Sensory Receptor StructuresUnencapsulated
• Free nerve endings– Most body tissues– Temperature and painful
stimuli– Capsaicin and itch
• Merkel discs– Deeper epidermal layers– Light touch
• Hair follicle receptors– Shaft of hair follicle– Light touch and hair bending
Encapsulated
• Meissner’s corpuscles– Dermal papillae of sensitive and
hairless skin– Discriminative touch
• Pacinian corpuscles– Deep in the dermis– Deep pressure initially, vibration
• Ruffini endings– Deep dermis and hypodermis– Deep continuous pressure
• Muscle spindles– Perimysium of skeletal muscle– Detect muscle stretch & initiate a reflex
• Golgi tendon– Insertion tendons– Activation inhibits contracting muscle
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Sensory Input• All senses trigger the same TYPE of signal
– Distinction occurs in activated brain area– Typically graded response, but AP’s possible
• Sensory receptors detect sensations and carry to the brain– Awareness of environmental change
• Brain constructs perceptions by integrating sensations with other information– Neuronal communication involving multiple brain
areas
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The Working Brain
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Sensory Adaptation
• Sensory receptors become less responsive– Fewer action potentials
• Limits reactions to normal background stimuli– Shower or hot tub
temperature– Odors over time
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Decoding Nerves
• Epineurium – covers nerve• Perineurium – covers fascicle• Endoneurium – cover axon• Direction of transmission
– Sensory afferents go to CNS• Dorsal root ganglia
– Motor efferents come from CNS• Sympathetic & parasympathetic
ganglia– Mixed carry both; most nerves
• Classified as cranial or spinal
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Nerve Fiber Regeneration• Mature neurons don’t divide*• Cell body damage = death• Cut/compressed axons regenerate
– Separated ends seal off and swell– Distal end of injury disintegrates
• Lack of nutrients• Neurilemma maintained in endoneurium
– Schwann cells proliferate & encourage axon growth
• Guide ‘sprouting’ axons to original contacts
• Greater distance decreases chances• Regrowth never exact = retraining• Extremely rare in CNS
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Cranial Nerves
• Ventral portion of the brain
• Sensory, motor, or mix
• 1st 2 pairs attach to forebrain
• Remainders originate on brainstem
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Numbers Cranial Nerve FunctionI OLFACTORY Smell (sensory)
II OPTIC Vision (sensory)
III OCULOMOTOR Eye movement (motor)(medial, inferior, superior rectus muscle & inferior oblique muscle)
IV TROCHLEAR Eye movements (motor)(superior oblique muscle)
V TRIGEMINAL Temperature, pain, crude touch of face (sensory) & mastication (motor)
VI ABDUCENS Eye movement (motor)(lateral rectus muscle)
VII FACIAL Taste (2/3 of anterior tongue) (sensory)Facial expressions (motor)
VIII VESTIBULOCOCHLEAR* Hearing & Equilibrium (sensory)
IX GLOSSOPHRAYNGEAL Taste (1/3 of posterior tongue) (sensory)Pharynx (swallowing & gag reflex) (motor)
X VAGUS Senses blood pressure (sensory)Stimulate heart rate and digestive organs (motor)
XI (SPINAL) ACCESSORY Head and neck movement (motor)e.g. trapezius, levator scapula
XII HYPOGLOSSAL Tongue movement (motor)
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Testing Cranial Nerves for Disorders• Olfactory
– Smell substances– Anosima
• Optic– Eye chart– Anopsias
• Oculomotor– Follow object; pupil reflex– Strabismus, double vision, ptosis
• Trochlear– See oculomotor
• Trigeminal – Corneal reflex; close/move jaws; touch
face with objects• Abducens
– See oculomotor
• Facial– Make various faces; tasting substances– Bell’s palsy, loss of taste, can’t close eye
• Vestibulocochlear– Tuning fork; distance of sound– Deafness, vertigo, tinnitus
• Glossopharyngeal– Swallowing & gag reflex; say ‘ah’
• Vagus– See glossopharyngeal– Horseness, swallowing problems, death
• (Spinal) accessory– Move head/shoulders against resistance
• Hypoglossal– Stick out, retract, & move tongue to sides
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Spinal Nerve Anatomy• Roots
– Dorsal root: peripheral receptors (sensory) to spinal cord
– Ventral root: ventral horn to skeletal muscles (motor)
• Branches: laterally pass through intervertebral foramen– Dorsal ramus: dorsal trunk– Ventral ramus: limbs & rest of trunk– Meningeal branch: meninges and blood
vessels• Plexus
– Criss cross joining of ventral rami– Excludes T2 – T12
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• 8 cervical– Cervical plexus– Brachial plexus
• 12 thoracic– Intercostal nerves & enlargements
• 5 lumbar– Lumbar plexus
• 5 sacral– Sacral plexus
• 1 coccygeal– Tailbone & perineum
31 Pairs of Spinal Nerves
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Cervical Nerves • Cervical plexus
– Phrenic nerve: diaphragm• Irritation causes hiccups
• Brachial plexus C5 – C8– Median nerve: flexor muscles of the anterior forearm
and small hand muscles• Carpal tunnel syndrome and suicide attempts
– Radial nerve: extensor muscle of posterior forearm and triceps brachii
• ‘Saturday night paralysis’– Ulnar nerve: similar to median nerve
• ‘Funny bone’ and paralysis/distortion of medial fingers
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Lumbosacral Plexus• Innervates lower limbs, buttocks, and pelvic
muscles• Lumbar plexus L1 – L4
– Femoral nerve: quadriceps and sartorius• Branches to saphenous
– Obturator nerve: adductor muscles• Sacral plexus L4 – S4
– Sciatic nerve: entire lower leg (except femoral innervation)
• Tibial: hamstrings• Common fibular nerve: anterior tibialis
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• Receptor– Senses stimulus
• Sensory neuron (afferents)– Message to the CNS
• Integration center– Synapses in CNS
• Monosynaptic (single motor or sensory neuron)• Polysynaptic (multiple interneurons)
• Motor neuron (efferents)– Message to effectors
• Effector– Muscle fibers or glands
• Reflexes are rapid, predictable responses to a stimulus– Somatic and autonomic
Reflex Arc
http://a248.e.akamai.net/7/248/430/20080327144023/www.mercksource.com/ppdocs/us/common/dorlands/dorland/images/arc_reflex%20a.(1).jpg
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Classifying Reflexes• Somatic: activate skeletal muscle
– Spinal: integration center is spinal cord (brain not required)• Stretch: ensures muscle length maintained (knee-jerk reflex)
– All monosynaptic and ipsilateral• Flexor reflex: withdrawl from painful stimuli (glass or hot stove)
– Polysynaptic and ipsilateral– Common pairing with crossed extensor in weighted limbs (contralateral)
• Superficial: cutaneous stimulation (plantar reflex)– Cranial nerve: integration center is brain stem
• Corneal: stimulation causes blinking
• Autonomic (visceral): activate smooth or cardiac muscle– Pupillary light: controls diameter of pupil (inside/outside)– Ciliospinal: ipsilateral pupil dilation from pain/stimuli