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THE PERIPHERAL NERVOUS SYSTEM

2. PART I THE PERIPHERAL NERVOUS SYSTEM & REFLEX ACTIVITY
THE PNS, SENSORY RECEPTORS & NERVES
THE PERIPHERAL NERVOUS SYSTEM & REFLEX ACTIVITY

3. I. Peripheral Nervous System (PNS)
The PNS provides links from and to the world outside our bodies.
It includes all neural structures outside the brain and spinal cord, that is the sensory receptors, peripheral nerves, and efferent motor endings.

4. II. Sensory Receptors & SEnsation
Specialized to respond to changes in environment, called stimuli.
Activation of sensory receptors trigger nerve impulses along afferent PNS fibers to the CNS.
Sensation (awareness of stimuli) and perception (interpretation of the meaning of stimuli) occur in the brain

5. B. Receptor Classification by Stimulus Type
Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch
Thermoreceptors – sensitive to changes in temperature
Photoreceptors – respond to light energy (e.g., retina)
Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry)
Nociceptors – sensitive to pain-causing stimuli

6. II. SENSORY RECEPTORS AND SENSATION
Survival depends upon sensation and perception
Sensation is the awareness of changes in the internal and external environment
Perception is the conscious interpretation of those stimuli
A pebble caught in a shoe causes the sensation of localized pressure, but the perception of it is an awareness of discomfort. Perception determines how we will respond to stimuli.

7. ___________ are stimulated when sound waves vibrate hair cells in the inner ear.
Mechanoreceptors
Thermoreceptors
Photoreceptors
Nociceptors
Answer: a. Mechanoreceptors

8. iii. Nerves Structure of a Nerve
A nerve is a cordlike organ that is part of the peripheral nervous system.
Nerves consist of bundles of peripheral axons enclosed by connective tissue wrappings.

9. Connective Tissue Coverings
a. Structure of a Nerve
Connective Tissue Coverings
Axon with myelin sheath
Endoneurium – surrounds individual nerve fibers
Perineurium – bundles and surrounds groups of fibers into fascicles
Epineurium – surrounds all fascicles to form a nerve

10. Structure of a Nerve

11. B. Classification of Nerves
Sensory (afferent) – carry impulses to the CNS
Motor (efferent) – carry impulses from CNS
Mixed – sensory and motor fibers carry impulses to and from CNS

12. PART II
CRANIAL NERVES
THE PERIPHERAL NERVOUS SYSTEM & REFLEX ACTIVITY

13. i. Cranial Nerves
Cranial Nerves – 12 pairs of nerves that arise from the brain
They have sensory, motor, or both sensory and motor functions
Each nerve is identified by a number (I through XII) and a name

14. Cranial Nerve I: Olfactory
Function: S – smell
Clinical Testing: sniff aromatic substances
Homeostatic Imbalance: Fracture of ethmoid bone leads to anosmia

15. Cranial Nerve II: Optic
Function: S – vision
Clinical Testing: eye chart
Homeostatic Imbalance: Damage to optic nerve results in blindness in eye served by nerve

16. Cranial Nerve III: Oculomotor
Function: M – moves eyeball; raises upper eyelid; constricts pupil for focusing
Clinical Testing: pupillary reflex w/ penlight; ability to follow objects with eyes
Homeostatic Imbalance: In oculomotor nerve paralysis, eye cannot be moved up, down, or inward, and at rest, eye rotates laterally; upper eyelid droops, double vision, and difficulty focusing on close objects

17. Cranial Nerve IV: Trochlear
Function: M – moves eyeball
Clinical Testing: same as cranial nerve III
Homeostatic Imbalance: Trauma to, or paralysis of, a trochlear nerve results in double vision and reduced ability to rotate eye inferolaterally

18. Cranial Nerve V: Trigeminal
Function: B – sensations of face, chewing
Clinical Testing: corneal reflex test; safety pin and hot/cold objects; movement of jaw
Tic douloureux or trigeminal neuralgia, caused by inflammation of trigeminal nerve, widely considered the most excruciating pain known

19. Cranial Nerve VI: Abdcuens
Function: M – moves eyeball
Clinical Testing: same as cranial nerve III
Homeostatic Imbalance: In abducens nerve paralysis, eye cannot be moved laterally, at rest, affected eyeball rotates medially

20. Cranial Nerve VII: Facial
Function: B – facial muscles; tearing; taste
Clinical Testing: taste test, symmetrical movement of face; ammonia fumes
Homeostatic Imbalance: Bell’s palsy, characterized by paralysis of facial muscles on affected side and partial lost of taste sensation

21. Cranial Nerve VIII: Vestibulocochlear
Function: S – hearing, balance
Clinical Testing: hearing test
Homeostatic Imbalance: Lesions of cochlear nerve results in deafness, whereas damage to vestibular division produces dizziness, rapid involuntary eye movements, loss of balance, nausea, and vomiting

22. Cranial Nerve IX: Glossopharyngeal
Function: B – salivation, swallowing, taste
Clinical Testing: gag and swallowing reflexes
Homeostatic Imbalance: Injury to or inflammation of glossopharyngeal nerve impairs swallowing and taste

23. Cranial Nerve X: Vagus
Function: B – swallowing, regulation of HR, breathing, digestion, taste
Clinical Testing: same as cranial nerve IX
Homeostatic Imbalance: Vagal nerve paralysis can lead to loss of voice. Total destruction of both vagus nerves is incompatible with life.

24. Cranial Nerve XI: Accessory
Function: M – moves head and neck
Clinical Testing: rotate head and shrug shoulders against resistance
Homeostatic Imbalance: Injury to spinal root of one accessory nerve causes head to turn toward injury side

25. Cranial Nerve XII: Hypoglossal
Function: M – moves tongue
Clinical Testing: protrude and retract tongue
Homeostatic Imbalance: Damage to hypoglossal nerve results in difficulties in speech and swallowing

26. Cranial nerve mnemonics
Cranial Nerve Name
Name Mnemonic
Function Mnemonic I
Olfactory On
Some II
Optic
Occasion
Say
III
Oculomotor
Our
Marry IV
Trochlear
Trusty
Money V
Trigeminal
Truck
But VI
Abducens
Acts My
VII
Facial
Funny
Brother
VIII
Vestibulocochlear
Very
Says IX
Glossopharyngeal
Good
Big X
Vagus
Vehicle
Brains XI
Accessory
Any
Matter
XII
Hypoglossal
How
More

27. Cranial Nerves