THE PERIPHERAL NERVOUS SYSTEM
PNS provides links from and to world outside our body
Consists of all neural structures outside brain and spinal cord
Survival depends on _________________________ (awareness of changes in internal and external
environments) and on _________________________ (conscious interpretation of those stimuli)
_________________________: For sensation to occur, a stimulus must excite a receptor, and action
potentials must reach the CNS
_________________________ must occur—energy of stimulus is converted into graded potential called
_________________________ (APs in a sensory neuron) or _________________________ (in a
separate receptor cell)
_________________________: Change in sensitivity in presence of constant stimulus
_________________________: specialized to respond to stimuli (changes in environment)
o Receptors are classified by type of stimulus and body location
o Classification by stimulus type:
_________________________—respond to mechanical force: touch, pressure, vibration,
and stretch
_________________________—respond to changes in temperature
_________________________—respond to light
_________________________—respond to chemicals in solution
_________________________—respond to stimuli that cause pain
o Classification by location:
_________________________– respond to stimuli arising outside of the body
Include receptors in skin for touch, pressure, pain, and temperature and most
receptors of the special senses
_________________________- Respond to stimuli within the body
Include chemical changes, tissue stretch, and temperature
_________________________- Respond to stretch in skeletal muscles, tendons, joints,
ligaments, and connective tissue coverings of bones and muscles
Inform the brain of the body’s movements
VISION
70% of body’s sensory receptors are in eye
, Nearly half of cerebral cortex is involved in visual processing
The eye consists of the eyeball and accessory structures
Accessory structures include:
o _________________________
Shade eyes from sunlight and prevent perspiration from reaching eye
o _________________________
Thin, skin-covered folds that protect eye anteriorly
Eyelids blink reflexively to protect eyes from foreign objects and keep eyes moist
_________________________: space between conjunctiva-covered eyeball and
eyelid (where contact lens rests and medication may be applied)
Clinical – Homeostatic Imbalance
_________________________: inflammation of the conjunctiva resulting in reddened,
irritated eyes
_________________________: highly contagious conjunctival infection caused by
bacteria or viruses
o _________________________
Consists of lacrimal gland and ducts that drain into nasal cavity
_________________________ is located in orbit above lateral end of eye and releases
_________________________ (tears)
Blinking spreads tears downward where they enter the _________________________
and eventually empties them into nasal cavity
o _________________________
Six straplike extrinsic eye muscles
Originate from bony orbit and insert on eyeball
Enable eye to follow moving objects, maintain shape of eyeball, and hold it in
orbit
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