I. Peripheral nervous system:

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I. Peripheral nervous system Cranial nerves,
spinal nerves and the autonomic nervous
system Somatic processes Autonomic
processes II. The senses
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• Cranial nerves (p. 235)
• 12 pairs of nerves
• Arise from brain stem (except for olfactory)
• Olfactory 2. Optic (vision)
• 3. Oculomotor (eye movement)
• 4. Trochlear (eye movement)
• 5. Trigeminal (various facial movements)
• 6. Abducens (eyes) 7. Facial (sense and motion)
• 8. Vestibulcochlear(hearing, balance)
• 9. Glossopharyngeal (swallowing)
• 10. Vagus (speech, swallowing, heart rate)
• 11. Accessory (swallowing, supporting head)
• 12. Hypoglossal (speaking, chewing, swallowing)

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Spinal nerves are grouped 31 pairs of mixed
nerves 8 pairs of cervical 12 pairs of
thoracic 5 pairs of lumbar 5 pairs of sacral 1
pair of coccygeal serve different regions of
the body Dorsal root- sensory input Ventral root-
motor output
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Spinal nerves are organized and sorted
in plexuses Cervical (neck) and phrenic nerves
(diaphragm) C1-4 Brachial (C4-8, T1) upper
limbs Lumbosacral (T12-S5) lower abdomen, lower
limbs
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Autonomic system controls visceral
functions Sympathetic Parasympathetic May act
antagonistically on same organ Sympathetic-
fight or flight Parasympathetic- rest and
recover preganglionic, postganglionic fibers
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sympathetic
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parasympathetic
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See p. 245 for function
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What is sensed? Somatic senses-touch,
temperature, pressure, pain (mechanical
forces) Sound- another mechanical
perception Vision- light Chemicals- smell,
taste Sensory input is projected by cortex (we
know what is being sensed)
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With prolonged stimulation, some senses undergo
adaptation Not pain receptors!
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What causes pain (nocireception)? Tissue
damage Oxygen deprivation (due to loss of blood
flow) Referred pain is felt in viscera (nerves
serve a variety of organs) Acute pain fibers
are thin and myelinated Chronic pain fibers are
unmyelinated Both can be triggered by the same
stimulus
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Pain is perceived in the thalamus, but
interpreted by the cerebral cortex Pain is
modulated by enkephalins and serotonin (produced
by CNS) and endorphins (hypothalamus, pituitary
gland)
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Special senses Smell Taste- chemoreceptors Heari
ng- mechanoreceptors Vision- photoreceptors
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Smell- olfactory receptor cells Olfactory bulbs-
interpretation in temporal lobes and frontal
lobes Olfactory tracts direct impulses to
limbic system
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Taste- four major sensations sweet, sour, salt,
bitter Other sensations- metallic,
umami Depends on what type of receptor is
engaged Pathway facial, glossopharyngeal,
vagus nerves Interpretive center in parietal lobe
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Hearing and equilibrium Structures
Interpretive pathways
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Organ of Corti is the hearing structure Hair
cells are located there They can be depolarized
upon stimulation Release neurotransmitters and
stimulate nearby neurons (ultimately
to vestibulocochlear nerve) Interpreted at
temporal lobe (both of them)
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Equilibrium Static- position of
head Vestibule utricle-horizontal
movement saccule- vertical Maculae contain
otoliths (calcium carbonate) hair cells move
against them
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Dynamic equilibrium Semicircular canals in
labyrinth Each contains a sesnory region called
crista ampullaris help perceive
movement Input from eyes and positional
receptors Nystagmus- eyes continue to move even
after spinning stops Vertigo- perception of
movement after it has stopped
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Vision eyes (why are they positioned in the
head as they are?) lacrimal gland extrinsic
muscles (lots of them, p. 269) eye
socket lots of vasculature
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accommodation
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Retina Photoreceptors are located there Rods
and cones associated with pigmented epithelium
(absorbs excess light) Overlaid by neurons (see
next slide) Rods- degree of light Cones- visual
acuity, color Fovea centralis- cones only, no
neurons
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Disorders of senses Destruction of receptors
and/or sensory neurons Temporary (infections,
swelling) Hearing conduction or nerve
deafness Vision shape of eye, plasticity of
lens, muscle imbalances, distortion of lens,
lack of cones (color blindness)! Is correction
possible?