SUMMER PBP PROGRAM: STRUCTURE AND
FUNCTIONS – PHYSIOLOGY DIVISION OF
NERVOUS SYSTEM AND CRANIAL NERVES
Detron M. Brown, MPH
THE NERVOUS SYSTEM
The Nervous System
Central Nervous System (CNS)
Brain
Peripheral Nervous System (PNS)
Spinal Cord
•
Somatic Nervous System
voluntary movements via
skeletal muscles
Motor Neurons
•
Sympathetic
- “Fight-or-Flight” responses
Sensory Neurons
Autonomic Nervous System
organs, smooth muscles
Parasympathetic
- maintenance
DIVISIONS OF THE AUTONOMIC NERVOUS
SYSTEM
•
The sympathetic division is the nervous system that prepares the body for action .
•
The Parasympathetic part of the systems allows it to return to a resting state.
Action/Rest
Sensory (Afferent) vs. Motor (Efferent)
sensory (afferent) nerve
e.g., skin
Neurons that send signals from the senses, skin, muscles,
and internal organs to the CNS
motor (efferent) nerve
Neurons that transmit from the CNS to the muscles,
glands, and organs
Gray’s Anatomy 38 1999
e.g., muscle
THE WITHDRAWAL
REFLEX
The Peripheral Nervous System (PNS) > Cranial Nerves
OLFACTORY (I) NERVE
• The olfactory nerves consist of a collection of many sensory
nerve fibers that extend from the olfactory epithelium to the
olfactory bulb.
• Olfactory receptors in the olfactory mucosa in the nasal cavity
receive information about smells which travel to the brain
through the cranial nerve which extend from the olfactory
epithelium to the olfactory bulb.
• Olfactory receptor neurons continue to be born throughout life
and extend new axons to the olfactory bulb.
The Peripheral Nervous System (PNS) > Cranial Nerves
OPTIC (II) NERVE
• The optic nerve is considered part of the central nervous system.The myelin on the optic nerve
is produced by oligodendrocytes rather than Schwann cells and it is encased in the meningeal
layers instead of the standard endoneurium, perineurium, and epineurium of the peripheral
nervous system.
• The optic nerve travels through the optic canal, partially decussates in the optic chiasm, and
terminates in the lateral geniculate nucleus where information is transmitted to the visual cortex.
• Axons responsible for reflexive eye movements terminate in the pretectal nucleus.
OCULOMOTOR NERVE
• The oculomotor nerve is the third paired cranial nerve.
• The oculomotor nerve contains two nuclei, including the Edinger-Westphal nucleus, which supplies
parasympathetic nerve fibers to the eye to control pupil constriction and accommodation.
• The oculomotor nerve originates at the superior colliculus and enters through the superior orbital
fissure to control the levator palpabrae superioris muscles, which hold the eyelids open.
TROCHLEAR (IV) NERVE
• The trochlear nerve innervates the superior oblique muscle of
the eye.
• The trochlear nerve contains the smallest number of axons of
all the cranial nerves and has the greatest intracranial length.
• The two major clinical syndromes that can arise from damage
to the trochlear nerve are vertical and torsional diplopia.
The Peripheral Nervous System (PNS) > Cranial Nerves
TRIGEMINAL (V) NERVE
• The sensory function of the trigeminal nerve is to provide the
tactile, motion, position, and pain sensations of the face and
mouth.The motor function activates the muscles of the jaw,
mouth, and inner ear.
• The trigeminal nerve has three major branches on each side,
the opthalmic nerve, maxillary nerve, and mandibular nerve,
which converge on the trigeminal ganglion.
• The trigeminal ganglion is analogous to the dorsal root ganglia
of the spinal cord, which contain the cell bodies of incoming
sensory fibers from the rest of the body.
The Peripheral Nervous System (PNS) > Cranial Nerves
ABDUCENS (VI) NERVE
• The abducens nerve exits the brainstem at the junction of the
pons and the medulla and runs upward to reach the eye,
traveling between the dura and the skull.
• The long course of the abducens nerve between the brainstem
and the eye makes it vulnerable to injury at many levels.
• In most mammals besides humans, it also innervates the
musculus retractor bulbi, which can retract the eye for
protection.
The Peripheral Nervous System (PNS) > Cranial Nerves
FACIAL (VII) NERVE
• The facial nerve (cranial nerve VII) is responsible for the
muscles that determine facial expression as well as the
sensation of taste in the front of the tongue and oral cavity.
• The facial nerve's motor component begins in the facial
nerve nucleus in the pons and the sensory component
begins in the nervus intermedius.The nerve then runs
through the facial canal, passes through the parotid gland,
and divides into five branches.
• Voluntary facial movements, such as wrinkling the brow,
showing teeth, frowning, closing the eyes tightly (inability
to do so is called lagophthalmos), pursing the lips, and
puffing out the cheeks, all test the facial nerve.
The Peripheral Nervous System (PNS) > Cranial Nerves
VESTIBULOCOCHLEAR (VIII) NERVE
• The vestibulocochlear nerve comprises the cochlear nerve
which transmits hearing information and the vestibular nerve
which transmits balance information.
• The cochlear nerve travels away from the cochlea of the inner
ear where it starts as the spiral ganglia.
• The vestibular nerve travels from the vestibular system of the
inner ear.
The Peripheral Nervous System (PNS) > Cranial Nerves
GLOSSOPHARYNGEAL (IX) NERVE
• The glossopharyngeal nerve (cranial nerve IX) is responsible for
swallowng and gagging, along with other functions.
• The glossopharyngeal nerve receives input from general and special
sensory fibers in the back of the throat.
• The glossopharyngeal nerve has five components: branchial motor,
visceral motor, visceral sensory, general sensory, and special sensory
components.
The Peripheral Nervous System (PNS) > Cranial Nerves
VAGUS (X) NERVE
• The vagus nerve (cranial nerve X) sends information about the body's
organs to the brain and carries some motor information back to the
organs.
• The vagus nerve has axons which originate from or enter the dorsal
nucleus of the vagus nerve, the nucleus ambiguus, and the solitary
nucleus in the medulla.
• The vagus nerve is responsible for heart rate, gastrointestinal
peristalsis, sweating, to name a few.
The Peripheral Nervous System (PNS) > Cranial Nerves
ACCESSORY (XI) NERVE
• Cranial nerve XI is responsible for tilting and rotating the head,
elevating the shoulders, and adducting the scapula.
• Most of the fibers of the accessory nerve originate in neurons
situated in the upper spinal cord.The fibers that make up the
accessory nerve enter the skull through the foramen magnum
and proceed to exit the jugular foramen with cranial nerves IX
and X.
• Due to its unusual course, the accessory nerve is the only
nerve that enters and exits the skull.
The Peripheral Nervous System (PNS) > Cranial Nerves
HYPOGLOSSAL (XII) NERVE
• It controls tongue movements of speech, food manipulation,
and swallowing.
• While the hypoglossal nerve controls the tongue's involuntary
activities of swallowing to clear the mouth of saliva, most of the
functions it controls are voluntary, meaning that the execution
of these activities requires conscious thought.
• Proper function of the hypoglossal nerve is important for
executing tongue movements associated with speech.Many
languages require specific uses of the nerve to create unique
speech sounds, which may contribute to the difficulties some
adults encounter when learning a new language.