BIOL 2401The Peripheral Nervous System Notes

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

 _________________________: hairs follicles richly innervated; trigger reflex blinking

o _________________________

 Transparent mucous membrane that lines eyelids

 _________________________: 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