11/12/2012
Chapter 19
The Brain and the Cranial Nerves
Copyright 2009 John Wiley & Sons, Inc.
Introduction
Brain- portion of the central nervous system
contained within the cranium.
About 100 billion neurons and 10–50 trillion
neuroglia with a mass of about 1300 g (almost 3
lb) in adults.
On average, each neuron forms 1000 synapses
with other neurons.
Thus, the total number of synapses, about a
thousand trillion (1015), is larger than the
number of stars in the galaxy.
Copyright 2009 John Wiley & Sons, Inc.
The Brain
Copyright 2009 John Wiley & Sons, Inc.
1
11/12/2012
Brain Organization , Protection, and
Blood Supply
The brain and spinal cord develop from ectoderm
arranged in a tubular structure called the neural tube.
The anterior part of the neural tube creates three regions
called primary brain vesicles:
prosencephalon, mesencephalon, and
rhombencephalon.
Copyright 2009 John Wiley & Sons, Inc.
Development of the brain
Copyright 2009 John Wiley & Sons, Inc.
Development of the Brain
Mesencephalon becomes midbrain and aqueduct of the
midbrain (cerebral aqueduct).
Prosencephalon becomes the telencephalon and diencephalon.
Telencephalon becomes the cerebrum and lateral ventricles.
Diencephalon forms the thalamus, hypothalamus,
epithalamus, third ventricle.
Rhombencephalon becomes the metencephalon and
myelencephalon.
Metencephalon becomes the pons, cerebellum, upper part of
the fourth ventricle.
Myelencephalon forms the medulla oblongata, lower part of
the fourth ventricle.
Copyright 2009 John Wiley & Sons, Inc.
2
11/12/2012
The Brain
Four major parts:
Brain stem- continuous with the spinal cord
Consists of the medulla oblongata, pons, and
midbrain.
Cerebellum- posterior to the brain stem
Diencephalon- superior to the brain stem
Consists of the thalamus, hypothalamus, and
epithalamus.
Cerebrum- supported on the diencephalon and brain
stem
Copyright 2009 John Wiley & Sons, Inc.
Protective Coverings of the Brain
Cranial meninges: dura mater, arachnoid mater, and
pia mater.
continuous with the spinal meninges
Cranial dura mater has two layers
(spinal dura mater has only one)
fused together except where they enclose the dural
venous sinuses (endothelial lined venous channels)
that drain venous blood from the brain.
no epidural space
Copyright 2009 John Wiley & Sons, Inc.
Protective Coverings of the Brain
Three extensions of the dura mater separate parts of the
brain.
1. Falx cerebraI separates the two hemispheres of the
cerebrum.
2. Falx cerebelli separates the two hemispheres of the
cerebellum.
3. Tentorium cerebelli separates the cerebrum from
the cerebellum.
Copyright 2009 John Wiley & Sons, Inc.
3
11/12/2012
Protective Coverings of the Brain
Copyright 2009 John Wiley & Sons, Inc.
Brain Blood Flow and the Blood–
Brain Barrier
The blood–brain barrier (BBB) protects brain cells from harmful
substances and pathogens.
Tight junctions seal together the endothelial cells of brain capillaries.
Astrocytes secrete chemicals that maintain the permeability of the
tight junctions.
A few water-soluble substances cross very slowly
glucose, creatine, urea, and most ions
Proteins and most antibiotic drugs—do not pass from the blood into
brain tissue.
Lipid- soluble substances access brain tissue freely
oxygen, carbon dioxide, alcohol, and most anesthetic agents
Trauma, certain toxins, and inflammation can cause a breakdown of the
blood–brain barrier.
Cerebrospinal fluid (CSF)
Cerebrospinal fluid (CSF) a clear, colorless liquid
protects the brain and spinal cord against chemical and
physical injuries.
carries oxygen, glucose, and other needed chemicals
from the blood to neurons and neuroglia.
continuously circulates through cavities in the brain and
spinal cord and around the brain and spinal cord in the
subarachnoid space.
Copyright 2009 John Wiley & Sons, Inc.
4
11/12/2012
Formation of CSF in the Ventricles
Lateral ventricle- in each hemisphere of the cerebrum.
Separated by a thin membrane, septum pellucidum.
Third ventricle- narrow cavity along the midline superior to the
hypothalamus and between the right and left halves of the thalamus.
Fourth ventricle- between the brain stem and the cerebellum.
The total volume of CSF is 80 to 150 mL (3 to 5 oz) in an adult.
CSF contains glucose, proteins, lactic acid, urea, cations (Na+, K+, Ca+,
Mg+), anions (Cl- and HCO3 -), and some white blood cells.
Copyright 2009 John Wiley & Sons, Inc.
Location of ventricles within a
“transparent” brain.
Copyright 2009 John Wiley & Sons, Inc.
CSF Contributes to Homeostasis
Mechanical protection- shock- absorbing medium that
protects the brain and spinal cord.
Chemical protection- provides an optimal chemical
environment for accurate neuronal signaling in neurons
that border the fluid.
Circulation- a medium for minor exchange of nutrients
and waste products between the blood and nervous
tissue.
Copyright 2009 John Wiley & Sons, Inc.
5
11/12/2012
CSF Production
Choroid plexuses- networks of blood capillaries in the
walls of the ventricles covered by ependymal cells joined
tightly by tight junctions.
Ependymal cells form CSF from blood plasma by
filtration and secretion.
Blood cerebrospinal fluid barrier permits certain
substances to enter the CSF but excludes others
Copyright 2009 John Wiley & Sons, Inc.
Circulation of CSF
The CSF- formed in the choroid plexuses of each lateral ventricle:
flows into the third ventricle via two oval openingsinterventricular foramina.
through the aqueduct of the midbrain (cerebral
aqueduct), through the midbrain, into the fourth
ventricle.
enters the subarachnoid space through three
openings in the roof of the fourth ventricle
median aperture and the paired lateral apertures,
one on each side.
through the subarachnoid space around the surface of
the brain and spinal cord.
Copyright 2009 John Wiley & Sons, Inc.
Circulation of CSF
CSF is reabsorbed into the blood via arachnoid
villi
fingerlike extensions that project into the dural venous
sinuses, especially the superior sagittal sinus.
Normally, CSF is reabsorbed as rapidly as it is
formed by the choroid plexuses
rate of about 20 mL/hr (480 mL/day)
helps maintains a constant pressure
Copyright 2009 John Wiley & Sons, Inc.
6
11/12/2012
Pathway of circulating cerebral spinal fluid
Copyright 2009 John Wiley & Sons, Inc.
Pathway of circulating cerebral spinal fluid,
sagittal section of brain and spinal cord
Copyright 2009 John Wiley & Sons, Inc.
Brainstem
Between the spinal cord and diencephalon
Medulla, Pons, Midbrain, and Reticular
Formation
Copyright 2009 John Wiley & Sons, Inc.
7
11/12/2012
Medulla Oblongata in relation to the rest
of the Brain Stem
The medulla oblongata- continuation of the superior part of the spinal cord;
forms the inferior part of the brain stem
begins at the foramen magnum and extends to the inferior border of the
pons.
Copyright 2009 John Wiley & Sons, Inc.
Internal Anatomy of Medulla Oblongata
Copyright 2009 John Wiley & Sons, Inc.
Internal Anatomy of Medulla Oblongata
Pyramids- large bulge
Nuclei
Consists of descending motor tracts
cardiovascular and reparatory control areas
Olive- lateral to Pyramids
Inferior Olivary Nucleus- contains proprioceptors
for joints and muscles
Copyright 2009 John Wiley & Sons, Inc.
8
11/12/2012
Pons
Consists of both nuclei and tracts- about 2.5 cm (1 in.)
Bridge that connects different parts of the brain.
Connect the right and left sides of the cerebellum.
Two major structural components:
Ventral region forms the pontine nuclei .
Dorsal region is more like the brainstem, the medulla and
midbrain.
Peumotaxic and apneustic areas- Other nuclei in the pons
Contains ascending and descending tracts and nuclei of cranial
nerves.
With the medullary rhythmicity area they help control breathing.
Copyright 2009 John Wiley & Sons, Inc.
Midbrain
Midbrain (mesencephalon) extends from the pons to the
diencephalon and is about 2.5 cm (1 in.) long.
Aqueduct of the midbrain (cerebral aqueduct) passes through the
midbrain
connecting the third ventricle with the fourth ventricle.
midbrain contains both tracts and nuclei.
Cerebral peduncles- pair of tracts in anterior part of the midbrain
Contain axons of corticospinal, corticopontine, and corticobulbar motor
neurons
conduct nerve impulses from the cerebrum to the spinal cord,
medulla, and pons.
Contain axons of sensory neurons that extend from the medulla to the
thalamus.
Copyright 2009 John Wiley & Sons, Inc.
Midbrain
Tectum- posterior part of the midbrain.
Superior colliculi- two superior elevations.
Inferior colliculi- two inferior elevations
Serve as reflex centers for visual activities- tracking, image scanning,
accommodation, movement of eyes, head, and neck due to vision
Part of the auditory pathway
Relaying impulses from the receptors for hearing in the ear to the
thalamus.
Contains several nuclei:
Left and right substantia nigra- large, darkly pigmented nuclei
Red nuclei- synapses bet axons from the cerebellum and cerebral
cortex
Function with the cerebellum to coordinate muscular movements.
Copyright 2009 John Wiley & Sons, Inc.
9
11/12/2012
Midbrain
Copyright 2009 John Wiley & Sons, Inc.
Reticular Formation
Broad region where white matter and gray matter exhibit a netlike
arrangement.
Ascending (sensory) and descending (motor) functions.
Reticular activating system(RAS)- Part of the reticular
formation
consists of sensory axons that project to the cerebral cortex.
Helps maintain consciousness and is active during awakening
from sleep.
Main descending function- help regulate muscle tone, the slight
degree of contraction in normal resting muscles.
Copyright 2009 John Wiley & Sons, Inc.
The Cerebellum
Flocculonodular lobe- inferior surface
Cerebellar cortex- superficial
consists of gray matter in a series of slender, parallel ridges called folia.
Arbor vitae- tracts of white matter, deep to the gray matter
Cerebellar nuclei- gray matter
contributes to equilibrium and balance.
form axons carrying impulses from the cerebellum to other brain centers
and the spinal cord.
Cerebellar peduncles- three paired- inferior, middle, superior
attach the cerebellum to the brain stem.
bundles of white matter consist of axons that conduct impulses between
the cerebellum and other parts of the brain.
Copyright 2009 John Wiley & Sons, Inc.
10
11/12/2012
The Cerebellum
Transverse fissure (a deep groove), and the Tentorium cerebelli,
(supports the posterior part of the cerebrum)- separate the
cerebellum from the cerebrum.
Vermis (central constricted area) and the lateral “ wings” or lobes
are the cerebellar hemispheres.
Each hemisphere consists of lobes separated by deep and
distinct fissures.
Anterior lobe and posterior lobe
govern subconscious aspects of skeletal muscle contraction
makes possible all skilled muscular activities
Ex. catching a baseball, dancing, speaking.
Copyright 2009 John Wiley & Sons, Inc.
Cerebellum
Copyright 2009 John Wiley & Sons, Inc.
The Diencephalon
Forms a central core of brain tissue just superior to the midbrain.
Surrounded by the cerebral hemispheres
Contains numerous nuclei
Involved in sensory and motor processing between higher and
lower brain centers.
Extends from the brain stem to the cerebrum and surrounds the third
ventricle
Includes the thalamus, hypothalamus, and epithalamus.
Hypophysis or Pituitary gland- Projects from the hypothalamus
Optic tracts carrying neurons from the retina enter this region of the
brain.
Copyright 2009 John Wiley & Sons, Inc.
11
11/12/2012
Thalamus
Measures about 3 cm (1.2 in.) in length.
Intermediate mass (interthalamic adhesion) (gray matter) joins
the right and left halves of the thalamus in 70% of human brains.
Internal medullary lamina- (white matter) divides the gray matter
into right and left halves
Major relay station Sensory impulses from the spinal cord, brain stem, and midbrain
to the primary sensory areas of the cerebral cortex
Transmitting information from the cerebellum and basal ganglia
to the primary motor area of the cerebral cortex.
Role in the regulation of autonomic activities and maintenance of
consciousness.
Axons connecting the thalamus and cerebral cortex pass through
the internal capsule.
Copyright 2009 John Wiley & Sons, Inc.
Thalamus
Seven major groups of nuclei are on each side of the thalamus:
1. Anterior nucleus connects to the hypothalamus and limbic system.
Emotions, regulation of alertness and memory
2. Medial nuclei connect to the cerebral cortex, limbic system, and
basal ganglia.
Emotion, memory, learning, awareness, cognition
3. Nuclei in the lateral group connect to the superior colliculi, limbic
system, and cortex in all lobes of the cerebrum.
Expression of emotions
4. Five different nuclei are part of the ventral group.
Motor function, somatic sensation
- touch, pressure, proprioception, vibration, hot, cold, pain
-auditory and visual
Copyright 2009 John Wiley & Sons, Inc.
Thalamus
.
5 Intralaminar nuclei within the internal medullary lamina and make
connections with the reticular formation, cerebellum, basal ganglia,
and wide areas of the cerebral cortex.
Pain perception, integration of sensory and motor information,
arousal (RAS)
6. Midline nucleus forms a thin band adjacent to the third ventricle
presumed function in memory and olfaction.
7. Reticular nucleus surrounds the lateral aspect of the thalamus,
next to the internal capsule.
Monitors, filters, and integrates activities
Copyright 2009 John Wiley & Sons, Inc.
12
11/12/2012
Thalamus
Copyright 2009 John Wiley & Sons, Inc.
Hypothalamus: 4 Major Regions
It is composed of a dozen or so nuclei in four major regions:
1. The mammillary region, and mammilary bodies adjacent to the
midbrain, is the most posterior part of the hypothalamus.
- relay for reflexes and smell
2. The tuberal region, the widest part of the hypothalamus, includes
the dorsomedial, ventromedial, and arcuate nuclei, plus the stalklike
infundibulum , median emminence
3. The supraoptic region, lies superior to the optic chiasm, contains
the paraventricular nucleus, supraoptic nucleus, anterior
hypothalamic nucleus, and suprachiasmatic nucleus.
4. The preoptic region contains the medial and lateral preoptic nuclei
- autonomic activities
Copyright 2009 John Wiley & Sons, Inc.
Hypothalamus
Controls many body activities.
One of the major regulators of
homeostasis.
Receives sensory impulses
related to both somatic and
visceral senses.
Receives impulses from
receptors for vision, taste, and
smell.
Copyright 2009 John Wiley & Sons, Inc.
13
11/12/2012
Epithalamus
Posterior to the thalamus
Consists of the pineal gland and habenular nuclei.
Size of a small pea
Protrudes from the posterior midline of the third ventricle.
Part of the endocrine system because it secretes the
hormone melatonin.
Copyright 2009 John Wiley & Sons, Inc.
Circumventricular Organs (CVOs)
Parts of the diencephalon because they lie in the wall of the third
ventricle
monitor chemical changes in the blood because lack a blood–
brain barrier.
Includes part of the hypothalamus, pineal gland, pituitary gland, and
a few other nearby structures.
Function- coordination of homeostatic activities of the endocrine and
nervous systems
Regulate blood pressure, hunger, thirst, fluids
Copyright 2009 John Wiley & Sons, Inc.
The Cerebrum
The largest portion of the human brain
Consists of the cerebral hemispheres and the basal ganglia.
Cerebral cortex an outer rim of gray matter
an internal region of cerebral white matter, and gray matter nuclei
deep within the white matter.
The folds are called gyri or convolutions.
The deepest grooves between folds are known as fissures; the
shallower grooves between folds are termed sulci
Longitudinal fissure- separates the right and left cerebral
hemispheres
Falx cerebri- dural covering, lines the longitudinal fissure
Copyright 2009 John Wiley & Sons, Inc.
14
11/12/2012
The Cerebrum
Copyright 2009 John Wiley & Sons, Inc.
Lobes of the Cerebrum
The lobes: frontal, parietal, temporal, and occipital lobes.
Central sulcus separates the frontal lobe from the parietal lobe.
Precentral gyrus- a major gyrus
Postcentral gyrus
located immediately posterior to the central sulcus
contains the primary somatosensory area of the cerebral cortex.
Lateral cerebral sulcus (fissure) separates the frontal lobe from the
temporal lobe.
located immediately anterior to the central sulcus
contains the primary motor area of the cerebral cortex.
Insula- below the surface within the lateral cerebral sulcus
Parieto-occipital sulcus separates the parietal lobe from the
occipital lobe.
Cerebral White Matter
The cerebral white matter consists primarily of myelinated axons in
three types:
1. Association tracts- axons that conduct nerve impulses between
gyri in the same hemisphere.
2. Commissural tracts- axons that conduct nerve impulses from gyri in
one cerebral hemisphere to corresponding gyri in the other cerebral
hemisphere.
Three important groups of commissural tracts- corpus callosum,
anterior commissure, and posterior commissure.
3. Projection tracts- axons that conduct nerve impulses from the
cerebrum to lower parts of the CNS (thalamus, brainstem, or spinal
cord) or from lower parts of the CNS to the cerebrum.
Copyright 2009 John Wiley & Sons, Inc.
15
11/12/2012
Basal Ganglia
Basal ganglia- three nuclei (masses of gray matter)
Corpus striatum- lentiform + caudate nuclei.
Deep within each cerebral hemisphere.
Two are side-by-side, just lateral to the thalamus.
Globus pallidus and putamen.
Together they are the lentiform nucleus.
Caudate nucleus- third
(refers to striations of the internal capsule as it passes among the
basal ganglia).
Receives input from sensory cortex-output to motor
cortex, and works with the limbic system
Regulates starting and stopping movements
Control subcutaneous contractions
Start and stop cognition
Copyright 2009 John Wiley & Sons, Inc.
Basal Ganglia
Copyright 2009 John Wiley & Sons, Inc.
The Limbic System
1. Cingulate gyrus, (above the corpus callosum), and
parahippocampal gyrus, (in the temporal lobe below).
1. Hippocampus- part of parahippocampal gyrus extends into floor
of lateral ventricle.
2. Dentate gyrus- between hippocampus and parahippocampal gyrus.
3. Amygdala- several groups of neurons near the tail of the caudate
nucleus.
4. Septal nuclei- in the septal area formed by regions under the corpus
callosum and paraterminal gyrus (a cerebral gyrus).
5. Mammillary bodies of the hypothalamus- two round masses close
to midline, near the cerebral peduncles.
6. Two nuclei of the thalamus- anterior nucleus and medial nucleus,
participate in limbic circuits.
7. Olfactory bulbs- flattened bodies of the olfactory pathway, rest on
the cribriform plate.
8. Fornix, stria terminalis, stria medullaris, medial forebrain
bundle, and mammillothalamic tract.
16
11/12/2012
The Limbic System
The limbic system is
sometimes called the
“emotional brain”
plays a primary role in a range
of emotions, including pain,
pleasure, docility, affection,
and anger.
Involved in olfaction (smell)
and memory.
Experiments have shown that
when different areas of an
animals’ limbic system are
stimulated, the animals’
reactions indicate that they are
experiencing intense pain or
extreme pleasure.
Copyright 2009 John Wiley & Sons, Inc.
Functional Areas of the Cerebrum
Copyright 2009 John Wiley & Sons, Inc.
Sensory and Motor Areas
Sensory Areas
Sensory impulses arrive in the posterior half of both cerebral
hemispheres
Primary sensory areas have the most direct connections with
peripheral sensory receptors
Secondary and Association Sensory areas integrate sensations
Primary Motor Area
Located in the precentral gyrus of the frontal lobe
Control voluntary contractions
Primary somatosensory area, body parts do not “map” to the primary
motor area in proportion to their size.
Broca’s speech area is located in the frontal lobe close to the
lateral cerebral sulcus.
Copyright 2009 John Wiley & Sons, Inc.
17
11/12/2012
Lateralization
Brain is almost symmetrical
Subtle anatomical differences between the two hemispheres
exist.
For example, about two- thirds of the population, the planum
temporale, a region of the temporal lobe that includes Wernicke’s
area, is 50% larger on the left side than on the right side.
This asymmetry appears in the human fetus at about 30 weeks of
gestation.
Physiological differences also exist; although the two hemispheres
share performance of many functions
Each hemisphere also specializes in performing certain unique
functions- hemispheric lateralization.
Copyright 2009 John Wiley & Sons, Inc.
Brain Waves
At any instant, brain neurons generate millions of nerve impulses
(action potentials)- brain waves.
Brain waves generated by neurons close to the brain surface,
mainly in the cerebral cortex
Can be detected by sensors, electrodes placed on the forehead
and scalp- electroencephalogram or EEG.
Study normal brain functions, such as changes that occur
during sleep
Diagnose variety of brain disorders, such as epilepsy, tumors,
metabolic abnormalities, sites of trauma, and degenerative
diseases.
Copyright 2009 John Wiley & Sons, Inc.
Cranial Nerves-PNS
The 12 pairs of cranial nerves pass through foramina cranial and
arise from the brain inside the cranial cavity
Five are mixed nerves because they contain axons of both sensory
and motor neurons.
The cell bodies of motor neurons lie in nuclei within the brain.
Cranial nerves III, VII, IX, and X include both somatic and autonomic
motor axons.
The cell bodies of sensory neurons are located in ganglia outside
the brain (except all proprioceptive sensory neurons in the head
region have their cell bodies in the mesencephalic ganglion nucleus.
Copyright 2009 John Wiley & Sons, Inc.
18
11/12/2012
Olfactory (I) Nerve
Olfactory (I) nerve (sensory); contains axons that conduct nerve
impulses for olfaction.
Olfactory epithelium occupy the superior part of the nasal cavity,
cover inferior surface of the cribriform plate and extend down the
superior nasal concha.
Olfactory nerves end in the brain, in paired masses of gray matterolfactory bulbs, two extensions of the brain that rest on the
cribriform plate.
Within the olfactory bulbs, axon terminals of olfactory receptors form
synapses with the dendrites. The axons neurons make up the
olfactory tracts, which extend posteriorly from the olfactory bulbs
Primary Olfactory area in the Temporal Lobe.
Copyright 2009 John Wiley & Sons, Inc.
Olfactory (I) Nerve
Copyright 2009 John Wiley & Sons, Inc.
Optic (II) Nerve
Optic (II) nerve (sensory)- contains axons that conduct nerve
impulses for vision.
In the retina, rods and cones initiate visual signals and relay them to
bipolar cells, which pass the signals on to ganglion cells.
Axons of all the ganglion cells in the retina of each eye join to form
an optic nerve, which passes through the optic foramen.
The two optic nerves merge to form the optic chiasm Within the
chiasm, axons from the medial half of each eye cross to the
opposite side; axons from the lateral half remain on the same side.
Posterior to the chiasm, the regrouped axons, some from each eye,
form the optic tracts.
Most axons in the optic tracts end in the lateral geniculate nucleus
of the thalamus.
Primary Visual area is in the Occipital lobe
Copyright 2009 John Wiley & Sons, Inc.
19
11/12/2012
Optic (II) Nerve
Copyright 2009 John Wiley & Sons, Inc.
Oculomotor (III) Nerve
Oculomotor- motor nerve.
Extends anteriorly and divides into superior and inferior branches,
both pass through the superior orbital fissure into the orbit.
Axons in the superior branch innervate superior rectus (an extrinsic
eyeball muscle) and levator palpebrae superioris (the muscle of
the upper eyelid).
Axons in the inferior branch supply
Medial rectus, inferior rectus, and inferior oblique muscles—all
extrinsic eyeball muscles
Ciliary muscle attached to lens of eye and Circular muscle of the iris
Copyright 2009 John Wiley & Sons, Inc.
Trochlear (IV) Nerve
The trochlear (motor)- smallest and the only one from the posterior
of the brain stem.
Originates in the trochlear nucleus in the midbrain, and axons from
the nucleus exit the brain on its posterior aspect and pass through
the superior orbital fissure.
These somatic motor axons innervate the superior oblique muscle
of the eyeball,(extrinsic eyeball muscle)- controls movement of the
eyeball.
Proprioceptive sensory axons from the superior oblique muscle
begin their course toward the brain in the trochlear nerve but
eventually leave the nerve to join the ophthalmic branch of the
trigeminal nerve.
Copyright 2009 John Wiley & Sons, Inc.
20
11/12/2012
Abducens (VI) Nerve
The abducens (VI) nerve (motor)- originates from the abducens
nucleus in the pons.
Somatic motor axons extend from the nucleus to the lateral rectus
muscle of the eyeball (extrinsic eyeball muscle) through the
superior orbital fissure of the orbit.
The abducens nerve is named because nerve impulses cause
abduction (lateral rotation) of the eyeball.
Copyright 2009 John Wiley & Sons, Inc.
Oculomotor (III) Nerve, Troclear (IV)
and Abducens (VI) nerves
Copyright 2009 John Wiley & Sons, Inc.
Trigeminal (V) Nerve
The trigeminal (V) nerve (mixed nerve)- largest of the cranial
nerves.
The trigeminal nerve has three branches: ophthalmic, maxillary,
and mandibular .
Ophthalmic nerve, smallest branch, passes into the orbit via the
superior orbital fissure.
Maxillary nerve intermediate in size, between the ophthalmic and
mandibular nerves and passes through the foramen rotundum.
Mandibular nerve, largest branch, passes through the foramen
ovale.
Copyright 2009 John Wiley & Sons, Inc.
21
11/12/2012
Trigeminal (V) Nerve
Copyright 2009 John Wiley & Sons, Inc.
Facial (VII)Nerve
Facial (VII) nerve (mixed cranial nerve).
Its sensory axons extend from the taste buds of the anterior two
thirds of the tongue through the geniculate ganglion, a cluster of
cell bodies of sensory neurons that lie beside the facial nerve, and
end in the pons .
Axons of branchial motor neurons arise from a nucleus in the
pons, pass through the petrous portion of the temporal bone, and
innervate facial, scalp, and neck muscles.
Nerve impulses along these axons cause contraction of the muscles
of facial expression, plus the stylohyoid muscle, the posterior belly of
the digastric muscle, and the stapedius muscle.
Parasympatheric neurons pass through pterygopalatine and
submandibular ganglia to the lacrimal, nasal, palatine, sublingual,
and submandibular salivary glands.
Copyright 2009 John Wiley & Sons, Inc.
Facial (VII)Nerve
Copyright 2009 John Wiley & Sons, Inc.
22
11/12/2012
Vestibulocochlear (VIII) Nerve
Vestibulocochlear (VIII) nerve formerly known as the
acoustic or auditory nerve. (sensory)
Has two branches, the vestibular branch and the
cochlear branch.
Vestibular branch carries impulses for equilibrium
Cochlear branch carries impulses for hearing.
Copyright 2009 John Wiley & Sons, Inc.
Vestibulocochlear (VIII) Nerve
Copyright 2009 John Wiley & Sons, Inc.
Glossopharyngeal (IX) Nerve
The glossopharyneal nerve is a mixed nerve.
Sensory axons from taste buds and somatic sensory
receptors on the posterior one third of the tongue, from
proprioceptors in swallowing muscles suppied by the
motor portion, from baroreceptors in the carotid sinus,
and chemoreceptors from the carotid body.
Sensory neuron cell bodies are in the superior and
inferior ganglia, and pass through the jugular foramen to
the medulla.
Motor neurons begin in the medulla and pass through
the jugular foramen, and innervate the Stylopharyngeus
muscle.
Copyright 2009 John Wiley & Sons, Inc.
23
11/12/2012
Vagus (X) Nerve
A mixed cranial nerve from the head and neck into the thorax and
abdomen.
Sensory axons in the vagus nerve arise from:
the skin of the external ear,
a few taste buds in the epiglottis and pharynx
proprioceptors in muscles of the neck and throat.
Somatic motor neurons, arise from nuclei in the medulla oblongata
and supply muscles of the pharynx, larynx, and soft palate used in
swallowing and vocalization.
Axons of autonomic motor neurons (parasympathetic) in the
vagus nerve originate in nuclei of the medulla and end in the lungs
and heart. Also supply glands of the gastrointestinal tract and
smooth muscle of the respiratory passageways, esophagus,
stomach, gallbladder, small intestine, and most of the large intestine.
Copyright 2009 John Wiley & Sons, Inc.
Vagus (X) Nerve
Copyright 2009 John Wiley & Sons, Inc.
Accessory (XI) Nerve
The accessory (XI) nerve is a
mixed cranial nerve.
The cranial portion is part of the
vagus nerve.
The accessory nerve is the “old”
spinal part of the nerve.
Motor axons arise in the anterior
gray horn of the first five segments
of the cervical portion of the spinal
cord.
The accessory nerve conveys
motor impulses to the
sternocleidomastoid and trapezius
muscles to coordinate head
movements.
Copyright 2009 John Wiley & Sons, Inc.
24
11/12/2012
Hypoglossal (XII) Nerve
The hypoglossal (XII) nerve is
motor cranial nerve.
The somatic motor axons originate
in the hypoglossal nucleus in the
medulla blongata, pass through
the hypoglossal canal, and supply
the muscles of the tongue.
Conduct nerve impulses for
speech and swallowing.
Sensory axons that originate from
proprioceptors in the tongue
muscles begin their course toward
the brain in the hypoglossal nerve
and end in the medulla oblongata.
Copyright 2009 John Wiley & Sons, Inc.
Origin of the Nervous System
Process Diagram Step-by-Step
Copyright 2009 John Wiley & Sons, Inc.
Future neural crest
Neural plate
Ectoderm
1.
Notochord
HEAD END
Neural plate
Neural folds
Neural groove
1.
Endoderm
Mesoderm
Neural crest
Ectoderm
Neural folds
Somite
2.
2.
Neural tube
3.
Notochord
Endoderm
Neural groove
Cut edge of amnion
Neural crest
Neural tube
TAIL END
Somite
3.
(a) Dorsal view
Notochord
Ectoderm
Endoderm
Copyright 2009 John Wiley & Sons, Inc.
(b) Transverse sections
25
11/12/2012
Development of the Brain and Spinal
Cord (Fig. 19.27)
Copyright 2009 John Wiley & Sons, Inc.
26