Download PNS - Introduction and Cranial Nerves

Introduction and
Cranial Nerves
1. Cranial Nerves
2. Spinal Nerves
PNS has both a sensory
and motor division
Motor Division has two
subgroups:
1. Somatic division
2. Autonomic
Classification
1. Mechanoreceptors
2. Thermoreceptors
1. Exteroceptors
3. Photoreceptors
2. Interoceptors
4. Chemoreceptors
3. Proprioceptors
5. Nociceptors
(1) Most are ‘simple’ receptors
(2) Eyes and Ears are ‘complex’ receptors
(3) Unencapsulated
– Free; C-type fibers; temperature and pain
(4) Encapsulated
– Mechanoreceptors
1. Receptor Level
• Sensory Receptor
• Transduction ------ Generator
Potential
2. Circuit Level
• Ascending pathways
• Sensory Cortex
3. Perceptual Level
• Projection
• Perceptual detection; Magnitude
estimation; Spatial
discrimination; Feature
abstraction; Quality
discrimination; Pattern
recognition
Mechanoreceptor
Respond to
mechanical force
Free nerve endings; Merkel discs;
Meissner’s corpuscle ; Pacinian
corpuscles
Thermoreceptor
Sensitive to
Temperature
changes
Free nerve endings
Chemoreceptor
Responds to
chemical changes
in the body
Free nerve endings
Nociceptor
Responds to pain
Free nerve endings
Photoreceptor
Responds to light
energy
Retina
Unencapsulated
Free nerve; Merkel discs and
Hair Follicle Receptors
Most abundant in epithelia and
CT of the body
Encapsulated
Meissner’s ; Pacinian
Enclosed in CT capsule; most all
are mechanoreceptors
1. Many individual neurons
are included in a bundle or
fasicle!
2. Neurons-Axons may be
motor or sensory – ‘mixed’;
or purely sensory or motor.
3. What you see at the left
would be considered to be
either a cranial or spinal
nerve!
1. Most CNS fibers do not regenerate
(hippocampus)
2. PNS may regenerate if:
– Axon is damaged
– Cell body is damaged (NO!)
3. Process of regeneration
(1) Nerves containing both afferent and efferent neurons.
(2) Most peripheral nerves are ‘mixed’
(3) Exceptions
– CN I – olfactory
– CN II – optic
(4) CN I and II – Forebrain
– III-XII (brain stem)
(5) Parasympathetic: motor only!
• 12 pairs of cranial nerves
– Base of the brain
– 10 of 12 : Brain Stem
• May be purely sensory or motor; mixed;
parasymathetic
I. Olfactory Nerve
• Receptors in nasal cavity attach
to olfactory bulb
• Olfactory tract
• Terminates in primary olfactory
cortex
• Sensory function
II. Optic Nerve
• Originate in retina; nerves form
tracts and synapse in thalamus
• Primary visual cortex
• Sensory function
III. Occulomotor Nerve
• Origin midbrain to the eye
• Somatic motor serve the 6
extrinsic eye muscles
• Parasymphthetic function
• Sensory function
IV. Trochlear Nerve
• Origin: midbrain
• Somatic motor - superior
oblique muscle
V. Trigeminal Nerves
• Origin: face
• From face to Pons
• Sensory function
• conveys information from
scalp, eyelids, nose, nasal
cavity, etc.
VI. Abducens
• Origin: Pons
• Somatic Motor function to
lateral rectus muscle
VII. Facial
• Origin: Pons
• Mixed nerve serves lateral parts of
face; 5 branches; motor nerves
skeletal muscles of face
VIII. Vestibulocohlear
Origin: Cochlea and Vestibule
Mainly sensory
IX. Glossopharyngeal
• Origin: Medulla
• Terminates at throat
• Mixed nerve that innervates parts
of the tongue and pharynx
X. Vagus Nerve
• Origin: Medulla
• Only CN passes to neck and thorax
• Mixed Nerve: Most motor fibers
are PS; some are somatic serving
skeletal muscles of pharynx and
larynx
XI. Accessory Nerve
• Origin: Ventral rootlets of spinal
cord (C1-C5)
• Mixed nerve; mostly motor; serves
trapezius and sternocleidomastoid
XII. Hypoglossal Nerve
• Origin: Medulla to tongue
• Mixed, mostly motor