Peripheral Nervous System

Peripheral Nervous System

A.Sensory Receptors

Classified according to location and type of stimulation Diagram
- Location:
  - Exteroceptors - stimulation arising outside of the body (touch, pain, and temperature)
  - Interoceptors - stimulation arising inside the body (chemical messengers, stretching of tissue, and internal temperature)
  - Proprioceptors - respond to internal stimuli, but located only in skeletal muscle, tendons, joints, and ligaments and C.T. covering bones and muscles.
- Stimulus detected:
  - Mechanoreceptors (touch, pressure, vibrations)
  - Thermoreceptors (temperature)
  - Photoreceptors (light)
  - Chemoreceptors (smell, taste, blood chemistry)
  - Nocireceptors (pain)
General sensory receptors Diagram
- Unencapsulated
  - Free dendritic endings
    - Found in most body tissues and most dense in connective tissue
  - Modified free dendritic endings (Merkel cells)
    - In basal layer of epidermis of skin
  - Root hair plexuses
    - Surrounding hair follicles
- Encapsulated
  - Meissner's corpuscles
    - Located in dermal papillae of hairless skin
    - Nipples, external genitalia, fingertips, soles of feet, eyelids
  - Krause's end bulbs
    - Found in connectissue mucosae (mouth and conjunctiva of eye) and hairless skin near body openings (lips)
  - Pacinian corpuscles
    - Subcutaneous layer of skin
    - Mesentary, tendons, ligaments, joint capsules, fingertips, soles of feet, external genitalia, nipples
  - Ruffini's corpuscles
    - Located deep in the dermis, hypodermis and found in joint capsules
  - Muscle spindles
    - Skeletal muscles

B.NervesDiagram

Nerve consists of parallel bundles of peripheral axons enclosed by connective tissue coverings:
- Epineurium
- Perineurium (surrounds fascicle)
- Endoneurium (surrounds axon)
Direction of transmission:
- Mixed nerves - contain both sensory and motor fibers and transmit to and away from CNS
- Sensory nerves - contain sensory fibers carrying impulses toward the CNS
- Motor nerves - contain sensory fibers carrying impulses away from the CNS
PNS nerves classified as cranial or spinal

C.Regeneration of Nerve Fibers (cut or compressed axons)

Separated ends seal off and swell
Axon and myelin sheath (of injured site) disintegrates
Schwann cells and macrophages migrate to site to phagocytize debris
Neurilemma remains intact and schwann cells proliferate
Axon "sprouts", guided by schwann cells, gap to original contact

D.Cranial Nerves (twelve pair) Diagram

Cranial Nerve I	Olfactory	Smell
Cranial Nerve II	Optic	Vision
Cranial Nerve III	Oculomotor	Motor function (movement of eyelid and eyball) Sensory function (muscle sense)
Cranial Nerve IV	Trochlear	Motor function (movement of eyeball) Sensory function (muscle sense)
Cranial Nerve V	Trigeminal	Motor function (chewing) Sensory function (touch, pain, and temperature)
Cranial Nerve VI	Abducens	Motor function (movement of eyeball) Sensory function (muscle sense)
Cranial Nerve VII	Facial	Motor function (facial expression and secretion of saliva and tears) Sensory function (muscle sense )
Cranial Nerve VIII	Vestibulocochlear	Hearing and equilibrium
Cranial Nerve IX	Glassopharyngeal	Motor function (secretion of saliva) Sensory function (taste)
Cranial Nerve X	Vagus	Motor function (smooth muscle contraction and relaxation and secretion of digestive fluids) Sensory function (muscle sense)
Cranial Nerve XI	Accessory	Motor function (swallowing and head movements) Sensory function (muscle sense)
Cranial Nerve XII	Hypoglossal	Motor function (movement of tongue during speech and swallowing) Sensory function (muscle sense)

E.Spinal Nerves (31 pairs)Diagram

(8) Cervical - cervical and brachial plexus
(12) Thoracic - intercostal nerves and cervical and lumbosacral enlargement
(5) Lumbar - lumbar plexus
(5) Sacral - sacral plexus
(1) Coccygeal
Branches (one passing through intervertebral foramen): Diagram

Dorsal ramus (deep muscles and skin of the dorsal surface of the trunk)
Ventral ramus (muscles and structures of the upper and lower limbs and the lateral and ventral trunk)
Mengeal branch (vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges)

Plexi: cervical, brachial, lumbar, and sacral

F.Reflex and Reflex ArcDiagram

Reflex = rapid, predictable motor response to a stimulus
Five components to reflex arcs:
1. Receptor (site of stimulus)
2. Sensory neuron (transmits afferent impulses to CNS)
3. Integration Center:
  - Monosynaptic reflex (single motor or sensory neuron)
  - Polysynaptic reflex (multiple interneurons)
4. Motor neuron (conducts efferent impulses)
5. Effector (muscle or gland)