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C HAPT E R T H I R T E E N
THE NERVOUS
SYSTEM: NEURAL
TISSUE
Two organ systems coordinate and
direct activities of body
• Nervous system
– Swift, brief responses to stimuli
• Endocrine system
– Adjusts metabolic operations
– Directs long-term changes
Nervous system includes all neural
tissue in body
• Central Nervous System
– Brain and spinal cord
• Peripheral Nervous System
– All neural tissue outside CNS
Functional divisions of nervous
system
• Afferent
– Sensory information from receptors to CNS
• Efferent
– Motor commands to muscles and glands
– Somatic division
• Voluntary control over skeletal muscle
– Autonomic division
• Involuntary regulation of smooth and cardiac muscle, glands
Cells in Nervous Tissue
• Neurons
• Neuroglia
Neuroglia (Glia)
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•
•
•
•
•
about half the volume of cells in the CNS
smaller than neurons
5 to 50 times more numerous
do NOT generate electrical impulses
divide by mitosis
Four types in the CNS
–
–
–
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Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Astrocytes
• Largest of glial cells
• Most numerous
• Star shaped with many processes
projecting from the cell body
• Help form and maintain blood-brain barrier
• Provide structural support for neurons
• Maintain the appropriate chemical
environment for generation of nerve impulses/action potentials
• Regulate nutrient concentrations for neuron survival
• Regulate ion concentrations - generation of action potentials by neurons
• Take up excess neurotransmitters
• Assist in neuronal migration during brain development
• Perform repairs to stabilize tissue
Oligodendrocytes
• Most common glial cell
type
• Each forms myelin sheath
around the axons of
neurons in CNS
• Analogous to Schwann
cells of PNS
• Form a supportive
• fewer processes than astrocytes
network around CNS
• round or oval cell body
neurons
Microglia
• few processes
• derived from mesodermal cells
that also give rise to monocytes
and macrophages
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Small cells found near blood vessels
Phagocytic role - clear away dead cells
protect CNS from disease through phagocytosis of microbes
migrate to areas of injury where they clear away debris of
injured cells - may also kill healthy cells
Ependymal Cell
• Make CSF = cerebrospinal fluid
– Water, glucose, ions, urea, lactic acid
– Transports nutrients to cells of brain and spinal
cord and carries away wastes
• Epithelial cells
• Lining choroid plexus
– Capillary network found in the ventricles of the
brain
– Ependymal cells surround these capillaries
– Filter blood plasma to create CSF
Representative Neuron
http://www.horton.ednet.n
s.ca/staff/selig/Activities/n
ervous/na1.htm
1. cell body or soma
-single nucleus with prominent nucleolus
-Nissl bodies
-rough ER & free ribosomes for protein
synthesis
-proteins then replace neuronal cellular
components for growth
and repair of damaged axons in the PNS
-neurofilaments or neurofibrils
give cell shape and support bundles of
intermediate filaments
-microtubules move material
inside cell
-lipofuscin pigment clumps
(harmless aging) - yellowish
brown
Neurons
2. Cell processes =
dendrites (little trees)
- the receiving or input
portion of the neuron
-short, tapering and
highly branched
-surfaces specialized
for contact with other
neurons
-cytoplasm contains
Nissl bodies &
mitochondria
3. Cell processes = axons
•
•
•
•
•
•
•
•
•
•
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Conduct impulses away from cell bodypropagates nerve impulses to another neuron
Long, thin cylindrical process of cell
contains mitochondria, microtubules &
neurofibrils - NO ER/NO protein synth.
joins the soma at a cone-shaped elevation =
axon hillock
first part of the axon = initial segment
most impulses arise at the junction of the
axon hillock and initial segment = trigger
zone
cytoplasm = axoplasm
plasma membrane = axolemma
Side branches = collaterals arise from the
axon
axon and collaterals end in fine processes
called axon terminals
Swollen tips called synaptic end bulbs
contain vesicles filled with neurotransmitters
Divisions of the nervous system
• Sensory pathway
– Ascending
– Information from sensory
receptors to CNS
• Motor pathway
– Descending
– Information from CNS to
skeletal muscle or glands
– Direct pathways – cause
precise, voluntary movements
– Indirect pathways – result in
involuntary movement (from
brain stem)
Functional Classification of Neurons
• Sensory (afferent) neurons
– transport sensory information from skin, muscles,
joints, sense organs & viscera to CNS
• Motor (efferent) neurons
– send motor nerve impulses to muscles & glands
• Interneurons (association) neurons
– connect sensory to motor neurons
– 90% of neurons in the body
An Introduction to the Organization
of the Brain
Major Regions of the Brain
Figure 15.1 Major Divisions of
the Brain
http://www.wisconline.com/objects
/framz.asp?objID
=OTA502
The Cranial Nerves
I - Olfactory
II - Optic
III - Oculomotor
IV-Trochlear
V - Trigeminal
VI - Abducens
VII - Facial
VIII – Vestibulocochler
or Acoustic
IX - Glossopharyngeal
X - Vagus
XI – Accessory
or Spinal Accessory
XII - Hypoglossal
-cranial nerves – 12 pairs
-considered part of the peripheral nervous system (PNS)
-olfactory & optic contain only sensory axons = sensory nerves
-some are motor nerves – e.g. oculomotor, trochlear etc….
-remaining are mixed nerves – both motor and sensory axons
-“some say my mother bought my brother some bitter beer, my, my”
http://www.wisc-online.com/objects/index.asp?objID=AP11504
The Olfactory Nerve (I)
• Carries sensory information
– Sense of smell from nasal mucosa to brain
• Branches enter skull through cribiform plate
– Synapses within olfactory bulbs
• The optic nerve (II) (sensory)
– Carries visual information
– enters skull through optic canal
of the sphenoid
-right and left join at the
optic chiasma (site of cross-over)
-continue to brain as optic tracts
•The oculomotor nerve (III)
[Motor]
–Primary source of innervation for extra-ocular
muscles
–also carries postganglionic fibers that
innervate the ciliary muscles (lens shape)
–exits through superior orbital fissure
•The trochlear nerve (IV) [Motor]
–Smallest cranial nerve
–Innervates superior oblique eye muscle
–also provides proprioception info
–exits through S.O.F
•The abducens nerve (VI) [Motor]
–Innervates lateral rectus muscle of eye
–exits through S.O.F
The Trigeminal Nerve (V) [Mixed]
• Largest cranial nerve
• Mixed nerve
– sensory – touch, pain & thermal
– Ophthalmic branch
– sensory – upper eyelid, eyeball
lacrimal glands, side of nose, forehead
and scalp
• Maxillary branch
– sensory – nose, palate, part
of pharynx, upper teeth, upper
lip and lower eyelid
• Mandibular branch
– sensory – tongue, cheek,
lower teeth, skin over mandible
and side of head anterior to ear
-motor – muscles of chewing
-inferior alveolar nerve (branch of mandibular)
-often anesthetized in dental procedures – lower jaw
-numbs to mental nerve (branch of the IAN)
-superior alveolar nerve (branch of the maxillary)
-numbs the upper jaw
The Facial Nerve (VII) [Mixed]
– Mixed nerve
– Controls
muscles of
scalp and face
– Pressure
sensations
from face
– Taste
sensations
from tongue
Facial Nerve VII
• efferent branches supply
muscles of facial
expression
– also carries preganglionic
parasympathetic fibers to the
lacrimal, sub-mandibular
and sub-maxillary glands
• afferent branches serves a
tiny patch of skin behind
the ear
– also provides taste
information and sensation to
the body of the tongue
Facial Nerve VII
•
Greater Petrosal
– branches off before exiting skull
– motor fibers + Pre/para fibers to pterygopalatine
ganglion
– postganglionic fibers leave the ganglion to join
with branches of the maxillary division or V ->
lacrimal gl, nasal cavity and minor salivary
glands of the palate (motor)
– also taste sensation
•
Chorda Tympani
– parasympathetic, motor for SMn and SL
salivary glands
– sensory for taste at the body of the tongue
– crosses the tympanic membrane before exiting the
skull
– travels with the lingual n. to the floor of the mouth
•
Posterior Auricular, Digastric and Stylohyoid
– branches after VII exits the stylomastoid f.
– all are motor – epicranial m., digastric and
stylohyoid muscles
•
facial expression
– temporal (anterior to ear), zygomatic (inferior
orbicularis oculi + ZMj, ZMn), buccal (upper lip,
nose, buccinator, risorius and orbicularis oris),
mandibular ( lower lip and mentalis) and
cervical (plastysma)
The Vestibulocochlear Nerve (VIII) [Sensory]
• Vestibular nerve
– Monitors sense of balance, position and movement
• Cochlear nerve
– Monitors hearing
The Glossopharyngeal Nerve (IX) [Mixed]
• Innervates the tongue,
pharyngeal muscles,
stylopharyngeus m.
– Controls swallowing
– the efferent portion
also sends pre/para
fibers to the parotid
gland (salivation)
• also receives sensory
info from taste
receptors and general
sensation from the
tongue
The Vagus Nerve (X) [Mixed]
• Vital to autonomic control
of visceral function
• large efferent portion to the
soft palate, pharynx and
larynx
• many other
parasympathetic fibers to
the organs of the gut,
respiratory and CV
systems
• small afferent portion
receives sensory
information from around
the ear and for taste info
from the epiglottis
• passes through the jugular
foramen
• The accessory nerve (XI)
– Internal branch
• Innervates swallowing muscles
– External branch
• Controls muscles associated with pectoral girdle
•The hypoglossal
nerve (XII)
–Voluntary motor
control over tongue
movements
Trigeminal Nerve and Branches
• bulge in the dorsal root of V = trigeminal ganglion
– also called the semilunar ganglion
• ganglion = collection of neuronal cell bodies
• comprised of a motor root and a sensory root
• motor root
– supplies the muscles of mastication
– exits via the foramen ovale in the sphenoid
– travels with mandibular division of V (V3)
• sensory root divides into three portions
– 1. Opthalmic
– 2. Maxillary
– 3. Mandibular
Opthalmic Division
• smallest division = V1
• sensory information from: conjuctiva, cornea, eyeball,
orbit, forehead, ethmoid and frontal sinuses
• also part of dura mater
• carries its sensory info by way of the superior orbital
fissure along with III, IV & VI
• formed from the union of:
the frontal, lacrimal and
nasociliary branches
• Frontal branch: supraorbital + supratrochlear
– SO: forehead, anterior scalp
– ST: bridge of nose, upper eyelid, medial forehead
– runs along roof of orbit
• Lacrimal branch
– lateral eyelid, conjuctiva & lacrimal gland
– also provides post/para fibers to the lacrimal gland – tear production
• Nasociliary branch: infratrochlear + ciliary nerves + anterior
ethmoid n.
–
–
–
–
runs superior to II within the orbit
IT: medial eyelid skin, side of nose
Ciliary: eyeball
AE: nasal cavity &
paranasal sinuses
Maxillary Division
•
•
•
•
•
V2
sensory information from: maxilla & skin, maxillary sinuses, nasal cavity,
palate & nasopharynx + part of dura mater (meningeal branches)
forms in the pterygopalatine fossa
enters skull through the foramen rotundum
prior to branching = pterygopalatine ganglion
– parasympathetic relay station for branches that
arise from the facial nerve
•
branches:
–
–
–
–
–
–
–
zygomatic
infraorbital
anterior superior alveolar
middle superior alveolar
posterior superior alveolar
greater & lesser palatine
nasopalatine
• Zygomatic
– zygomaticotemporal + zygomaticofacial
– enters pterygopalatine fossa through the infraorbital fissure and joins to contribute to the
maxillary nerve
– zygo.facial – skin of cheek
• through the frontal process of the zygomatic bone and enters the orbit thru the lateral wall
– zygo.temporal – skin of the temporal bone
• through the temporal process of the zygomatic bone and travels along the lateral wall of the
orbit
• Infraorbital: IO
– formed from cutaneous branches
from the upper lip, medial portion of cheek
lower eyelid and side of nose
- runs into the infraorbital foramen of
the maxilla
- travels along the infraorbital canal
with the infraorbital blood vessels
- joins with the anterior superior
alveolar nerve
• Anterior Superior Alveolar (ASA)
– sensation + pain from the maxillary central incisors, lateral incisors,
canines and their tissues + facial gingiva
– originates as dental branches supplying the pulp + interdental branches
of the associated periodonteum = dental plexus of the maxilla
– joins with the IO within the IO canal
• Middle Superior Alveolar (MSA)
– sensation + pain from the maxillary premolars and first molar +
periodonteum and their buccal gingiva
- originates from dental, interdental and interradicular branches (dental
plexus) – pulp and periodonteum
- forms this plexus with the ASA and PSA
- joins the IO
- MSA is not present in all patients
- can be replaced by the ASA or PSA
• Posterior Superior Alveolar (PSA)
– sensation from 2nd and 3rd molar, root of 1st , their
periodonteum + buccal gingiva, maxillary sinuses
– joins the IO in the pterygopalatine fossa
– branches:
a. dental branches + interdental + interradicular
(dental plexus)
b. internal branches – exit from the posterior superior alveolar
foramina (with the posterior superior alveolar arteries)
c. external – receive information from buccal gingiva and
associated molars
•
Nasapalatine
–
–
–
–
•
Greater palatine (GP)
–
–
–
–
•
originates in the mucosa of the anterior hard palate posterior to the maxillary teeth
enters the skull through the incisive foramen
travels along the nasal septum
receives sensory info from the anterior hard palate, lingual gingiva of anterior
maxillary teeth
and nasal septum
lies between the periosteum and bone of the anterior hard palate
sensory for the posterior hard palate + posterior lingual gingiva
enters through the greater palatine foramen near the 2nd or 3rd molar
travels through the pterygopalatine canal with the GP blood vessels
Lesser Palatine (LP)
– sensory for the palatine tonsils and soft palate
– enters through the LP foramen (near the junction of the palatine and the pterygoid
processes of the sphenoid)
– joins with the GP in the canal
– joined by the nasal branches which
receive info from the nasal cavity
Mandibular Division
• V3
• forms from the union of smaller anterior and
larger posterior trunks in the infratemporal
fossa
• passes through the foramen ovale
• joins with the Opthal. and Maxillary at the
trigeminal ganglion
• before dividing into the trunks – sends off small
meningeal branches to the dura mater + small
muscular branches to the medial pterygoid m.
• anterior trunk = buccal + muscular branches
• posterior trunk = auriculotemporal, lingual
and inferior alveolar branches
• Buccal nerve – sensory
– sensory
– skin of cheek, buccal mucosa and buccal gingiva of posteior
mandibular teeth
– found on the surface of the buccinator and travels deep to the
masseter
• Muscular branches
–
–
–
–
–
motor
from the motor/ventral root of V
deep temporal branch – motor to temporalis
masseteric branch – motor to masseter
lateral pterygoid branch
• Auriculotemporal
– travels with the
superficial temporal
artery and vein
– sensory for external ear
and scalp
– also carries
parasympathetic fibers
from IX and
communicates with II
• Lingual
– sensory from the body of tongue, floor
of mouth, and lingual gingiva
– passes from the medial to the lateral side
of the duct of submandibular gland
– base of tongue – runs between the
medial pterygoid and mandible (slightly
medial to the inferior alveolar nerve)
– near the root of the last mandibular
molar is can be visualized clinically (can
be damaged upon extraction of 3rd
molar)
– communicates with the submandibular
ganglion located superior to the SMn
gland (part of Parasympathetic NS)
• Inferior Alveolar (IAN)
– sensory from mandibular teeth
– merger of the mental and the incisive
– travels through the mandibular canal and
is joined by the mandibular dental
plexus
– exits through the mandibular foramen
– joined by a mylohyoid branch
– can be found paired on one or both sides
• with two mandibular canals and foramen
Mental branch of the IAN = mental nerve
- union of several external branches
- sensory from the chin, lower lip and labial mucosa
- enters the skull at the mental foramen
- then merges with the lingual branch of the IAN
Lingual branch of the IAN
- made up of dental branches from anterior mandibular teeth, interdental
branches form the surrounding periodonteum = dental plexus
-sensory information for the anterior mandibular teeth
Mylohyoid branch of the IAN = mylohyoid nerve
- joins with the mental and lingual after it emerges from the mandibular
foramen
- pierces the sphenomandibular ligament
- runs in the mylohyoid groove then onto the mylohyoid muscle
- motor commands to this muscle + anterior belly of the digastric
(posterior belly is innervated by the facial nerve)