• The central nervous system includes:

• The brain and the spinal cord.

• The peripheral nervous system includes:

• The cranial nerves come from the brain and the spinal nerves, that come from the spinal cord and ganglia which are clusters of neuron cell bodies located outside of the central nervous system (on the inferior surface of the brain). There are 12 pairs of cranial nerves. Numbered by positions, beginning with the most anteriorly placed nerve. Some cranial nerves have a mixture of motor and sensory axons, but will be classified as primarily motor or primarily sensory.

• Olfactory Nerves (latin for "to smell")
  • Located in the Anterior Cranial Fossa
    
  • Passes through the Cribiform Formina and synapses in the Olfactory bulbs.
    
  • Sensory function relay impulses of Smell from mucous membranes of the nasal cavity.
  • Dendrites and cell bodies of olfactory neurons are positioned within the mucosa which covers the superior nasal conchae and adjacent nasal septum.
  • axons of these specialized "chemoreceptors" pass through the cribiform plate of the ethmoid bone, bypass the thalamus, and eventually make connections leading to the olfactory areas in the cerebral crotex of the temporal lobes.
  • Only nerve to have regeneration abilities
  
  

• Optic Nerve (to see)
  
  • Sensory nerve conducts impulses from the photoreceptors in the retina of the eye to the visual cortex (for sight) within the occipital lobes of the cerebrum.
  • Enters via Optic Foramen of the sphenoid bone and left and right nerves unit at and forms the optic chiasma to the opposite side of the brain.
  • Forwards information to occipital lobe.
    

• Oculomotor ("eye" and "moving")
  • Leaves cranium via Superior Orbital Fissure and travels to eye and eyelid for movement.
  • Motor nerve
  • Located in the Oculomotor and Edinger Westphal nuclei within mesencephalon (midbrain)
  • Innervates many of the outer muscles that move the eye.
  • Innervates the internal muscles that dilate the pupil or innervate muscles to change the shape of the lens of focusing.
    

• Trochlear (Trochlea meaning "Pulley")
• a very small motor nerve
  
  • Located in the Trochlear nucleus within mesencephalon and passes through the superior orbital fissure of the sphenoid bone to innervate one of the extrinsic muscles that controls downward and lateral movement of the eyeball.
  • Leaves cranium via Superior orbital fissure and travels to oblique
  **(Oculomotor leaves the Superior Orbital Fissure)**

• Trigeminal (Trigeminous threefold)
  
  • Located in the Pons and exits the cranium through several foramen.
  • The large trigeminal nerve is a mixed nerve with both motor and sensory functions.
  • Innervates muscles of mastication.
  • The sensory function of this nerve are most extensive and are involved in sensations of touch, temperature, and pain from specific regions of the face.
  • Sensory fibers v1: (Ophthalmic nerve branch) Superior orbital fissure and travel to trigeminal ganglion before entering pons.
  • Sensory fibers v2: (Maxillary nerve branch) Enters via Foramen Rotundum and travel to trigeminal ganglion, before entering pons.
  • Motor fibers v3: (mandibular nerve branch) Exit cranium via Foramen Ovale to supply muscles.
  • Motor functions of this nerve are less extensive. Innervates muscles involved with chewing (masseter, temporalis, and medial and lateral pterygoid).

• Abducens (drawing away")
  • This motor nerve leaves the brainstem at the junction of the pons and medulla and passes through the superior orbital fissure of the sphenoid bone.
  • Controls the lateral rectus muscle of the eye. (This muscle is one of six that controls eye movement.)
  • Its nucleus is located on the floor of the fourth ventricle.
  • This nerve is the most commonly affected nerve in people with tuberculosis.
    

• Facial
  • Nuclei within the pons and emerges through several cranial foramen.
  • Innervates muscles of facial expression, most salivary glands, taste sensations from anterior 2/3 of tongue.
  • Sensory fibers travel from the tongue through a tiny foramen to enter the skull. Sensory function is to receive impulses of taste from the anterior portion of the tongue (chemoreceptors for sweet) and eventually convey them to the gustatory (taste) areas of the insula and cerebral cortex.
  • Somatic motor fibers leave pons enters temporal bone through internal auditory canal and emerge through stylomastoid foramen to supply the musculature.
  
  

• Vestibulocochlear (vestibulum and cochlea of ear)
  • This nerve is purely a sensory nerve composed of two parts.
  • it sends information to several regions of the brain, including the cerebellum.
  • Auditory and Equilibrium sensations to the brain.
  • Vestibular branch (responsible for monitoring equilibrium and balance) found in the hair cells in vestibule of inner ear. Cochlear branch (responsible for hearing) found in the cochlea in the inner ear.
  • Merge together into the cranial cavity through the internal auditory canal and travel to the junction of the pons and medulla oblongata.
  
  

• Glossopharyngeal (tongue/pharynx)
  • Sensory fiber locations include the taste buds, mucosa of posterior 1/3 of tongue and carotid bodies. Motor fiber located in nuclei in the medulla oblongata.
  • Tastes and touch sensations of tongue, innervates pharynx and parotid salivary glands.
  • Sensory fibers travels from posterior 1/3 of tongue and carotid bodies along nerve through the inferior superior ganglion into the jugular foramen to the pons.
  • Motor fibers leave cranium through the jugular foramen to the stylopharyngeus.
  • Parasympathetic motor fibers travel to optic ganglion to the parotid gland.

• Vagus (wandering)
  • It originates in the medulla oblongata.
  • Innervates structures in head, neck, thoracic and abdominal cavities.
  • Motor component innervates most throat (pharynx) and Larynx (voice box) muscles.
  • Exits cranium via jugular foramen.
  • Sensor neuron cell bodies located in superior and inferior ganglia. Sensory component receives input from the: External auditory canal and eardrum, pharynx, larynx, heart, lungs, esophagus, abdominal organs (except lower part of large intestines).
    
  
  

• Accesory
  • O: cranial root; motor nuclei in medulla oblongata.
  • O: Spinal root; motor nuclei in spinal cord.
  • Spinal root enters via foramen magnum; which merge with cranial roots and exits via jugular foramen.
  • Innervates trapezius, sternocleidomastoid and some pharynx muscles.
    

• Hypoglossal
• Cranial nerve used to move the tongue straight out and to taste bitter. Exits via the hypoglossal canal.

oh

oh

oh
to
touch
and
feel
very
grateful
very
achy
housewife

2. Sensory, Motor, or Both types of neurons:
Some
Say
Marry
Money
But
My
Brother
Says
Big
Brains
Matter
Most


You can learn the functions of the cranial nerves involved with moving the eye (number III, IV, and VI) by using this eye simulator. University of Toronto has provided videos showing how to do a cranial nerve exam.

Spinal Nerves
The term spinal nerve refers to the mixed spinal nerve, it is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen. All spinal nerves are part of the peripheral nervous system (PNS).

Formation of the spinal nerves
Inside the spinal cord, there is grey matter, surrounded by white matter. From out of the grey matter, two dorsal roots (one on the left side, and one on the right side) and two ventral roots emerge. (Dorsal means back, ventral means front.) As the body is symmetrical, the same thing happens on both the left and right side of the body. This happens in each vertebra of the spine.

• The dorsal roots contain afferent sensory axons. The dorsal roots of each side continue outwards, along the way forming a dorsal root ganglion (also called a spinal ganglion).

• The ventral roots contain efferent motor axons. Similar to the dorsal roots, the ventral roots continue out from the spinal column, and meet and mix with their corresponding dorsal nerve root at a point after the ganglion.

a mixed spinal nerve is the combinitaion of the dorsal roots and ventral roots.

Importance of the spinal nerves
The muscles that is on one particular spinal root supplies are that nerve's myotome, and the dermatomes these are the areas of sensory innervation on the skin for each spinal nerve.
This is of great importance in the diagnosis of neurological disorders, as lesions of one or more nerve roots result in typical patterns of neurologic defects (muscle weakness, loss of sensation) that allow localisation of the causating lesion.
Nerve: Spinal nerve

Spinal Nerve Disorders

• Compressive Neuropathy - happens when spinal nerves that leave the spinal canal are compressed and swell. Effects may temporarily or permanently damage or destroy nerves. A herniated, ruptured or slipped disc may cause nerves to become compressed. Pain may radiate into buttocks, down the legs and into the ankles and feet.
• Sciatica- pain in lower back, buttocks and legs in addition to muscle weakness and difficulty controlling legs caused by compression or irritation of sciatic nerve. Symptoms are usually felt on one side of the body. Sciatica is a set of symptoms caused by various disorders, it is not a disorder in itself.
• Spinal Meningitis- inflammation of membranes in the spinal cord and brain due to an infection. May require hospitalization. Sensitivity to light and neck pain are common symptoms as well as fever, weakness, fatigue and muscle spasms.
• Spina Bifida- birth defect in which the spinal cord does not completely form, vertebrae on the open portion of the spinal cord don't form completely and are unfused and open. This allows part of the spinal cord to stick out through this opening in the bones. Spina bifida can be closed after birth, though it results in permanent nerve damage.

TABLE OF MOTOR INNERVATIONS

Plexus	Branches	Anterior Rami	Motor Innervations
Cervical Plexuses	Ansa cervicalis, superior root, inferior root	C1 to C4	Hyoid muscles
	Phrenic	C3 to C5	Diaphragm
	Segmental Branch	C1 to C4	Anterior & Middle Scalenes
Brachial Plexuses	Axillary nerve	C5 to C6	Deltoid, Teres Minor
	Median Nerve	C5 to T1	Most Ant. Forearm & Thumb muscles
	Musculocutaneous Nerve	C5 to C7	Ant. Arm muscles,
	Radial Nerve	C5 to T1	Post. Arm, Post. Forearm muscles, Brachial radial
	Ulnar Nerve	C8 to T1	Ant. Forearm muscles, Hypothenar, Palmar interossei, Dorsal interossei, Adductor Pollicis
Small Branches of BP	Dorsal Scapular	C5	Rhomboids, levator scapulae
	Long thoracic	C5 to C7	serratus anterior
	lateral pectoral	C5 to C7	Pectoralis major
	medial pectoral	C8 to T1	Pectoralis major and minor
	Nerve to subclavius	C5 to C6	Subclavius
	suprascapular	C5 to C6	Supraspinatus, Infraspinatus
	Subscapular nerves	C5 to C6	Subscapularis, Teres major
	Thoracodorsal	C6 to C8	Latissimus Dorsi
Lumbar Plexuses	Femoral Nerve	L2 to L4	Ant. Thigh Muscles, Pecineus
	Obturator Nerve	L2 to L4	Med. Thigh Muscles, Obturator Externus
small branches of LP	Iliohypogastric	L1	Partial innervation of abd. Muscles
	Ilioinguinal	L1	Partial innervation of abd. Muscles
Sacral Plexuses	Sciatic Nerve	L4 to S3	Post. Thigh muscles, Post. Leg muscles, Plantar foot muscles, short head of biceps femoris
	Tibial Nerve	L4 to S3	Post. Thigh muscles, Post. Leg muscles, Plantar foot muscles
	Common Fibular Nerve	L4 to S2	Short head of Biceps Femoris
	Deep Fibular Nerve	L4 to S1	Ant. Leg muscles, dorsum foot muscles
	Superficial Fibular Nerve	L5 to S2	Lat. Leg muscles
small branches of SP	Inferior gluteal nerve	L5 to S2	Gluteus maximus
	Superior gluteal nerve	L4 to S1	Gluteus Medius, gluteus minimus and tensor fasciae latae
	Pudendal	S2 to S4	Muscles of perineum, external anal sphincter, external urethral sphincter

Case Study

In the News

• Here is a blog entry from a woman who regretted her decision to have an epidural
• This study about nanotech treatments for regrowing the spinal cord in mice that is showing promising results.

Glossary

Cranial nerves are originated from brainstem and they mainly control the functions of the anatomic structures of the head.

There are 12 pairs of cranial nerves:

• olfactory - Smell
• optic - Vision
• oculomotor - Moves eyes
• trochlear - Moves eyes
• trigeminal - Facial feeling
• abducent - Moves eyes
• facial - Facial expression
• vestibulo - cochlear Hearing/balance
• glossopharyngeal - Taste/swallowing
• vagus - Heart/digestive/lungs
• accessory - Trapezius/sternocleidomastoid
• hypoglossal - Moves tongue
  

Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the body. There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.

Connections to other body systems

Axial Skeleton

• Especially the Foramen of the Sphenoid bone. Cranial nerves main route to exit and enter the cranium is through various openings. example: (Supraorbital fissure & Foramen Magnum)

The Lungs, Heart and Abdomen

• The vagus nerve also named the "Pneumogastric nerve", starts from the brain and goes past the head into the abdominal region. "Pneumo" can think of Pneumonia; which affects the respiratory system. "Gastric" is another term for the Digestive System.
  
• The vagus nerve also mediated parasympathetic innervation of the heart.
  

Review Questions

1. Which one of the following doesn't have a sensory function?
*a. Abducens
b. Facial
c. Vagus
d. Trigeminal

2. Which one of the following nerves does not leave the cranium via the superior orbital fissure?
*a. Trigeminal
b. Trochlear
c. Oculomotor
d. Abducnes

3. The ________ is sometimes referred to as the "emotional brain"
a. Hypothalamus
*b. Limbic system
c. Thalamus
d. Wernicke's area

4. Which nerve is a mixed nerve arises from the medulla and is distributed to numerous organs?
a. *X Vagus nerve
b. XI spinal accessory
c. XII hypoglossal nerve
d. IV trochlear nerve

5. What nerve is found in the cribiform plate of the ethmoid bone?
a. Trigeminal
b. *Olfactory
c. Vagus
d. All the above

6. Parasympathetci innervation of the heart is mediated by what nerve?
a. Facial
b. Trigeminal
*c. Vagus
d. Glossopharyngeal

7. Mr. Smith is complaining that he is having difficulty swallowing, which nerve is most likely the cause of the problem?
a. Facial
b. Glossopharyngeal
*c. Vagus
d. Trigeminal

8. When you want to turn your child's frown upside down which nerve would be most likely involved?
a. Trigeminal
b. Glossopharyngeal
c. Vagus
*d. Facial

9. This nerve is the shortest length of all 12 of the peripheral nerves.
a. Oculomotor
*b. Olfactory
c. Facial
d. Optic

10. This nerve is the only nerve out of the 12 that is not ensheathed by the perineurium, epineurium, and endoneurim.
a. Oculomotor
*b. Optic
c. Trigeminal
d. Facial