Transcript Peripheral Nervous System

Peripheral Nervous System
Ch. 13

Sensory receptors:
Classified according to location and type
of stimulation
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Location:
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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)
- Nociceptors (pain)
Nerves:
Nerve consists of parallel bundles of
peripheral axons enclosed by connective
tissue coverings:
- Epineurium
- Perineurium (surrounds fascicle)
- Endoneurium (surrounds axon)
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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
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PNS nerves classified as cranial or spinal
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123-
45-
Regeneration of a severed nerve:
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
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Cranial nerves:
12 pairs
Classified as sensory, motor or mixed
First two pairs attach to the forebrain
Remaining ten pairs attach to the
brainstem
Olfactory nerve (I)
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Sensory
Sense of smell
Olfactory bulbs that terminate into
filaments piercing the cribriform plate of
the ethmoid bone.
Clinical: person is asked to identify an
odor
Anosmia: lack of smell
Optic nerve (II)
-
Sensory
Vision
Not a true nerve but an extension of the
brain
Begins at the retina, converges at the
optic chiasma, partial crossing over of the
fibers to enter the thalamus. Optic
radiations take impulse to the visual
cortex in the occipital lobe.
Oculomotor Nerve (III)
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Motor
Motor fibers to the 4 of the six eye
muscles
Eyeball movement
Pupil constriction
Trochlea Nerve (IV)
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Motor
Movement of one eye muscle: superior
oblique muscle
Downward and lateral movement of the
eyeball.
Trigeminal nerve (V)
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Mixed
Largest cranial nerve
Sensory to the face, controls muscles of
mastication (temporalis and masseter)
Three divisions: V1- Ophthalmic division
V2- Maxillary division
V3- Mandibular division
Nucleus located in the pons
Abducens (VI)
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Motor
Innervates the lateral rectus muscle of the
eye
Moves eyeball laterally
Facial Nerve (VII)
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Mixed
Exits at the stylomastoid foramen
Controls muscles of facial expression
Controls lacrimal and salivary glands
Taste of anterior 2/3 of tongue
Bell’s palsy; unilateral facial paralysis
Vestibulocochlear Nerve (VIII)
-
Sensory
Vestibulo branch: equilibrium
Cochlear branch: hearing
Travels through the internal acoustic
meatus
Glossopharyngeal Nerve (IX)
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Mixed
Fibers emerge from medulla and exit the
jugular foramen.
Innervates part of the tongue and pharynx
Taste for bitter on the posterior 1/3 of the
tongue (Bitter Back 9)
Swallowing and gag reflex
Vagus (X)
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Mixed
Only cranial nerve to extend below the
head and neck into thorax and abdomen
Heart rate, breathing and digestive
function.
Sensory from the viscera
Recurrent laryngeal nerve branches
innervate larynx (voice box)
Spinal Accessory Nerve (XI)
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Motor
Innervates trapezius and
sternocleidomastoid muscle
Clinical: ask patient to shrug shoulders
against resistance
Hypoglossal Nerve (XII)
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Motor
Tongue movements: swallowing and
speech.
Oh, oh, oh, to touch and feel very
green vegetables- AH
Or
On occasion our trusty truck acts
funny- very good vehicle anyhow
Spinal nerves
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31 pairs of spinal nerves
Mixed nerves
(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
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Branches (one passing through
intervertebral foramen):
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
Formation of Spinal Nerves
Formation of Spinal Nerves
Brachial plexus
Arises from spinal nerves C4-T1
Serves the arm and shoulder
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Median nerve: Flexor muscles of the anterior
forearm and small muscle in hand (thenar
eminence).
Radial nerve: extensor muscle of posterior
forearm and triceps brachii
Musculocutaneous nerve: biceps brachii
Axillary nerve: deltoid
CT Surgery
Lumbosacral plexus
Lumbar plexus: Arises from spinal nerves
L1- L4
Sacral plexus: L4-S4
- Innervates lower limb, buttocks and pelvic
muscles
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Femoral nerve: Quadriceps and sartorius
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Obturator nerve: Adductor muscles
Sciatic nerve: 2 nerves
- tibial nerve
- common fibular nerve
Tibial: hamstrings
Common fibular: anterior tibialis
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Sacral Plexus
Simple Reflex
Flexor Reflex
Crossed-Extensor reflex