Download Neuroanatomy I

NEUROANATOMY
ANS
NERVOUS SYSTEM
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Central
Peripheral
Somatic
Autonomic
SOMATIC NERVOUS SYSTEM
- Somatic sensory system – transmits sensations of touch,
pain, temperature and position from sensory receptors
- Somatic motor system – innervates skeletal muscles –
contraction
Somatic = voluntary, concious actions
AUTONOMIC NERVOUS SYSTEM
- Sympathetic – „fight or flight”
- Parasympathetic – „ rest and digest”
Autonomic - regulates the body's
unconscious actions.
SYMPATHETIC? PARASYMPATHETIC?
The name of this system can be traced to the concept of sympathy,
in the sense of "connection between parts", first used medically
by Galen.
Sympathetic and parasympathetic divisions typically function in
opposition to each other. This natural opposition is better
understood as complementary in nature rather than antagonistic.
For an analogy, one may think of the sympathetic division as the
police responders and the parasympathetic division as the court
system.
The sympathetic division typically functions in actions requiring
quick responses.
AUTONOMIC (VISCERAL) NERVOUS (MOTOR)
SYSTEM
- Target/effector organ (efferent fibers): smooth (involuntary) muscle, modified
cardiac muscle (the intrinsic stimuating and conducing tissue of the heart) and
glandular cells.
- Afferent fibers – autonomic reflexes and visceral pain impulses conduction.
- Regulation of visceral function – efferent and afferent fibers.
Somatic innervation – single neuron!!
ANS – 2 multipolar neurons!!
grey
A) presynaptic (preganglionic) –
matter of CNS
B)postsynaptic (postganglionic) –
autonomic ganglia.
Ganglion - group of nerve cell bodies located in
the ANS. Ganglia house the cell bodies
of afferent nerves.
GANGLIA
Three major groups of ganglia:
-Dorsal root ganglia (also known as the spinal
ganglia) contain the cell bodies of sensory (afferent)
neurons.
- Cranial nerve ganglia, contain the cell bodies of
cranial nerve neurons.
-Autonomic ganglia contain the cell bodies
of autonomic nerves.
The efferent nerve fibers and ganglia of ANS are
organized in two divisions:
A) Sympathetic – Thoracolumbar
B) Parasympathetic - Craniosacral
SYMPATHETIC (THORACOLUMBAR)
Cell bodies of presynaptic neurons are located in
interomediolateral cell columns (IMLs) (R&L)
IML’s are a part of grey matter of the thoracic (T1-T12)
and the upper lumbar (L1- L2/3) segments of the spinal
cord.
They are organized somatotopically.
Cell bodies of postsynaptic neurons of the sympathetic
NS occur in 2 locations:
A) Paravertebral ganglia (R&L)
B) Prevertebral ganglia
A) Paravertebral ganglia (R&L)
The sympathetic trunks are two ganglioned nerve trunks that
extend the whole lenght of vertebral column.
They are arranged thus:
• Cervical ganglia- 3 ganglia (superior, middle and inferior)
• Thoracic ganglia - 11 or 12 ganglia
• Lumbar ganglia - 4 or 5 ganglia
• Sacral ganglia - 4 or 5 ganglia
Superior paravertebral (cervical) ganglion (base of the cranium)
Ganglion impar (level of the coccyx)
B) Prevertebral ganglia
Are in the plexuses that round the origins of the main
branches of the abdominal aorta
The nerves that synapse in the prevertebral ganglia
innervate the pelvic viscera.
These include:
1. The celiac ganglia (which can include the aorticorenal
ganglion),
2. Superior mesenteric ganglia, and
3. Inferior mesenteric ganglia.
EFFERENT NERVE FIBERS OF
THORACOLUMBAR DIVISON
The IML’s of the spinal cord (Th1-L3) possess the cell bodies of
of the preganglionic neurons. The myelinated axons of these cells
leave the cord in the anterior nerve roots and pass via the white
rami communicantes (white- covered with myelin) to the
paravertebral ganglia of the sympathetic trunk. Once these fibers
(preganglionic) reach the ganglia they are distributed as follows:
PREGANGLIONIC FIBERS
1)
Ascend and then synapse when appropriate nerves are superior to
the part of IML involved (inervation of neck and upper limb)
2)
Descend and then synapse when spinal nerves involved are inferior
to to the part of IML’s involved (innervation of lower limb)
3)
Ented and synapse immediately at the same level – when
appropriate nerves are at approximately same level as the part of the
IML’s involved ( innervation of middle trunk)
4)
Pass through the ST without synapsing. These myelinated fibers
leave the sympathetic trunk to reach prevertebral ganglia.
(innervation of abdominopelvic viscera only)
Term splanchnic is used to describe visceral organs.
POSTGANGLIONIC FIBERS
1)Innervation of neck, body wall and limbs: from
paravertebral ganglia of sympathetic trunks through grey
rami communicantes to spinal nerves.
Vasomotion – contraction of the blood vessels
Pilomotion – „goose bumps” contraction of arrector
muscle
Sudomotion – sweating
2)Innervation of head (plus dilator muscle of iris). These
nerves have cell bodies in superior cervical ganglion and
they travel through cephalic arterial branch (peri-arterial
plexus of nerves) and follow branches of carotid artery to
reach their destination in head.
SPLANCHNIC NERVES
Include both efferent and afferent nerves to and from viscera. (through
white rami comminicantes)
A)Cardiopulmonary splanchnic nerve – postsynaptic nerves for viscera
of the thoracic cavity (heart, lungs, esophageus etc). Begin in
paravertebral ganglions of ST.
B)Abdominopelvic splanchnic nerves (greater, lesser and least thoracic
and lumbar) – presynaptic nerves for the viscera of abdominopelvic
cavity (stomach, intestines etc.) Begin in IML’s and synapse in
prevertebral ganglia. Then thy for peri-arterial plexuses, which follow
branches of the abdominal aorta to their destination.
C)Innervation of adrenal medulla - pass through prevertebral ganglia
without synapsing and terminates directly on cells of adrenal gland.
(EXCEPTION!)
PARASYMPATHETIC
(CRANIOSACRAL)
Presynaptic parasympathetic nerve cell bodies are located in two sites within
CNS and their fibers exit by two routes. Hence the craniosacral term.
A)Cranial part - in the grey matter of brainstem, the fibers exit the CNS within
cranial nerves III, VII, IX and X.
Innervation of head (III,VII and IX) and thoracic and abdominal viscera (to the lext colic flexure) (X)
B)Sacral part – in grey matter of S2-S4 segments (Intermediomedial cell
column) of spinal cord, the fibers exit the CNS within sacral spinal nerves S2-S4
and the pelvic splanchnic nerves that arise from the anterior rami.
Innervation of pelvic viscera and GI (descending and sigmoid colon and rectum)
PARASYMPATHETIC - GANGLIA
From the CNS to target organ – 2 neurons.
Preganglionic nerve is long and synapses either in terminal ganglia which is
located just by or on the target organ (n.X and S2-S4) or in parasympathetic
ganglia of spinal nerves:
1.ciliary ganglion (sphincter pupillae, ciliary muscle) (n. III – occulomotor)
2.pterygopalatine ganglion (lacrimal gland, glands of nasal cavity) (n. VII –
facial)
3. submandibular ganglion (submandibular and sublingual glands) (n. VII –
facial
)
4.otic ganglion (parotid gland) (n. IX - glossopharyngeal)
Postganglionic nerve is short.
SYMPATHETIC VS
PARASYMPATHETIC
Parasympathetic distributes only to head, visceral cavities of
the trunk and erectile tissues of the external genitalia.
DOES NOT reach the body wall or limbs.
Except from S2-S4 its fibers are not part of spinal nerves.
Sympathetic: presynaptic fibers are short, postsynaptic long.
Parasympathetic: presynaptic very long, postsynaptic short.
Because postsynaptic cell bodies are located in or on the
wall of the target organ.
HOW DOES THE ANS WORK ON
BLOOD VESSELS?
Vasoconstriction – sympathetic excitation of
smooth muscles of vessels.
Vasodilation – decresaed sympathetic excitation
of smooth muscles of vessels (exceptions:
coronary, skeletal muscle and external genitalia –
excitation results in vasodilation).
IMPORTANT AUTONOMIC
INNERVATIONS
EYE
Upper lid
Superior cervical sympathetic ganglion sympathetic postganglionic fibers  smooth
muscle fibers of the levator palpabrae superioris.
IRIS
Dilator pupillae:
Superior cervical sympathetic ganglion sympathetic postganglionic fibers in short and
long ciliary nerves
Sphincter pupillae:
Edinger-Westphal nucleus  n. III ciliary ganglion ->postganglionic fibers in short
ciliary nerves
LACRIMAL GLAND
Superior salivary nucleus  n. VII -> pterygopalatine ganglion ------- lacrimal nerve
Superior cervical sympathetic ganglion sympathetic postganglionic fibers in plexus of
the internal carotid artery ------- lacrimal nerve
HORNER’S SYNDROME
1. constriction of the pupil
2. slight droping of the eyelid (ptosis)
3. enophthalmos
4. vasodilation of skin arterioles
5. loss of sweating (anhydrosis)
HIRSCHPRUNG’S DISEASE
Also called congenital megacolon or congenital aganglionic megacolon, is a
form of megacolon that occurs when part or all of the large intestine or
antecedent parts of the gastrointestinal tract have no ganglion cells and therefore
cannot function. During normal prenatal development, cells from the neural
crest migrate into the large intestine (colon) to form the networks of nerves
called the Auerbach plexus (between the smooth muscle layers of the
gastrointestinal tract wall) and the submucosal plexus (Meissner plexus) (within
the submucosa of the gastrointestinal tract wall). In Hirschsprung's disease, the
migration is not complete and part of the colon lacks these nerve bodies that
regulate the activity of the colon. The affected segment of the colon cannot relax
and pass stool through the colon, creating an obstruction. In most affected
people, the disorder affects the part of the colon that is nearest the anus. In rare
cases, the lack of nerve bodies involves more of the colon.
VISCERAL AFFERENT FIBERS
Provides information about the condition of the body’s internal
environment. This information is integrated in the CNS often
triggering visceral or somatic reflexes or both.
Visceral reflexes regulate bood pressure and chemistry by altering
such functions as heart and respiratory rates and vascular
resistance.
Visceral sensation that reaches a concious level is generally
perceived as pain that is either poorly localized or felt as crumps
or that may conver a feeling of hunger, fullness or nausea.
VISCERAL PAIN
Visceral pain is pain that results from the activation
of nociceptors of the thoracic, pelvic, or bdominal viscera (organs).
Visceral structures are highly sensitive to distension ,
stretch), ischemia and inflammation, but relatively insensitive to
other stimuli that normally evoke pain such as cutting or burning.
Visceral pain is diffuse, difficult to localize and often referred to a
distant, usually superficial, structure. The pain may be described
as sickening, deep, squeezing, and dull.
VAGUS NERVE STIMULATION
Vagus nerve stimulation or vagal nerve stimulation (VNS)
is a medical treatment that involves delivering electrical
impulses to the vagus nerve. It is used as an adjunctive
treatment for certain types of
intractable epilepsy and treatment-resistant depression.
VAGUS NERVE ACTION.
Vagus, the tenth cranial nerve, arises from the medulla and carries both afferent
and efferent fibers. The afferent vagal fibers connect to the nucleus of
the solitary tract which in turn projects connections to other locations in the
central nervous system. Little is understood about exactly how vagal nerve
stimulation modulates mood and seizure control but proposed mechanisms
include alteration of norepinephrine release by projections of solitary tract to
the locus coeruleus, elevated levels of inhibitory GABA related to vagal
stimulation and inhibition of aberrant cortical activity by reticular activation
system.
Because the vagus nerve is associated with many different functions and brain
regions, research is being done to determine its usefulness in treating other
illnesses, including various anxiety disorders, Alzheimer's
disease, migraines, fibromyalgia, obesity, and tinnitus.
DIRECT VAGUS NERVE STIMULATION
This is currently the only widely used method of therapeutic VNS. It requires the
surgical implantation of a stimulator device. The VNS devices consist of a titaniumencased generator about the size of a pocket watch with a lithium battery to fuel the
generator, a lead wire system with electrodes, and an anchor tether to secure leads to
the vagus nerve. The battery life for the pulse generator is "between 1 [and] 16 years,
depending on the settings. Implantation of the VNS device is usually done as an outpatient procedure. The procedure goes as follows: an incision is made in the upper
left chest and the generator is implanted into a little "pouch" on the left chest under
the clavicle. A second incision is made in the neck, so that the surgeon can access
the vagus nerve. The surgeon then wraps the leads around the left branch of the
vagus nerve, and connects the electrodes to the generator. Once successfully
implanted, the generator sends electric impulses to the vagus nerve at regular
intervals The left vagus nerve is stimulated rather than the right because the right
plays a role in cardiac function such that stimulating it could have negative cardiac
effects.
NEUROANATOMY: BRAIN, VENTRICLES, MENINGES
CENTRAL NERVOUS SYSTEM
The CNS consists of the brain and spinal
cord. The pricipal roles of the CNS are to
integrate and coordinate incoming and outgoing
neural signals and to carry out higher mental
functions, such as thinking and learning.
BRAIN - STRUCTURE
1. Telencephalon(Cerebrum)
2. Diencephalon
3. Brainstem
A)Midbrain
B)Pons
C) Medulla oblongata
4. Cerebellum
ANATOMICAL PLANES
An anatomical plane is a hypothetical plane used to transect the
human body, in order to describe the location of structures or the
direction of movements. In human, three basic planes are used:
1. Saggital (lateral)
2. Coronal (frontal)
3. Horizontal (transverse, axial)
WHITE AND GRAY MATTER
A nucleus is a collection of nerve cell bodies in the
CNS. A boundle of nerve fibers (axons) within the CNS
connecting neighboring or distant nuclei of the cerebral
cortex is a tract.
The brain and spinal cord are composed of gray
matter and white matter. The nerve cell bodies lie within
and constitute the gray metter; the interconnecting fiber
tract systems form the white matter.
CEREBRUM
The cerebrum is a large part of the brain containing
the cerebral cortex (of the two cerebral hemispheres), as
well as several subcortical structures, including
the hippocampus, basal ganglia, and olfactory bulb.
The cerebrum is also divided into approximately
symmetric left and right hemispheres.
CEREBRAL CORTEX
The cerebral cortex is the cerebrum's outer layer of neural tissue.
It is divided into two cortices, along the sagittal plane: the left and
right cerebral hemispheres divided by the medial longitudinal
fissure.
The cerebral cortex is composed of gray matter, consisting mainly
of cell bodies and capillaries. It contrasts with the underlying white
matter, consisting mainly of the white myelinated sheaths of
neuronal axons.
Each cortical ridge is called a gyrus, and each groove or fissure
separating one gyrus from another is called a sulcus.
BRODMANN AREA
A Brodmann area is a region of the cerebral
cortex defined by its cytoarchitecture, or
histological structure and organization of cells
It is correlated closely to diverse cortical
functions.
FRONTAL LOBE
- Pimary motor cortex
- Secondary motor cortex
- Broca’s motor speech area
PARIETAL LOBE
- Primary somesthetic area
- Secondary somesthetic area
TEMPORAL LOBE
- Primary auditory area
- Secondary auditory area
- Wernicke’s sensory speach area
OCCIPITAL LOBE
- Primary visual area
- Secondary visual area
IMPORTANT WHITE MATTER
STRUCTURES
-
Semioval centre
Corona radiata
Corpus callosum
Internal capsule
Cerebral peduncles (midbrain)
SEMIOVAL CENTER
The semioval center is the white matter found
underneath the grey matter on the surface of the
cerebrum.
The white matter, located in each hemisphere
between the cerebral cortex and nuclei, as a whole
has a semioval shape. It consists of cortical
projection fibers, association fibers and cortical
fibers. It continues ventrally as the corona radiata.
CORONA RADIATA
The corona radiata is a white matter sheet that
continues ventrally as the internal capsule and
dorsally as the semioval center. This sheet of both
ascending and descending axons carries most of
the neural traffic from and to the cerebral cortex.
The corona radiata is associated with the
corticospinal tract, the corticopontine tract, and
the corticobulbar tract.
CORPUS CALLOSUM
The corpus callosum also known as the
callosal commissure, is a wide, flat bundle of
neural fibers about 10 cm long beneath
the cortex in the brain at the longitudinal fissure.
It connects the left and right cerebral
hemispheres and facilitates interhemispheric
communication. It is the largest fibre pathway in
the brain.
Rostrum, genu, trunk and splenium – parts.
CEREBRUM
The cerebrum is a large part of the brain containing
the cerebral cortex (of the two cerebral hemispheres), as
well as several subcortical structures, including
the hippocampus, basal ganglia, and olfactory bulb.
The cerebrum is also divided into approximately
symmetric left and right hemispheres.
OLFACTORY BULB
The olfactory bulb (bulbus olfactorius) is a neural structure
of the cerebrum involved in olfaction, or the sense of smell.
Olfactory bulb is on the inferior (bottom) side of the brain.
The olfactory bulb is supported and protected by
the cribriform plate of the ethmoid bone, which separates it
from the olfactory epithelium, and which is perforated
by olfactory nerve axons. The bulb is divided into two
distinct structures: the main olfactory bulb and the
accessory olfactory bulb.
BASAL NUCLEI
The basal ganglia (or basal nuclei) comprise multiple
subcortical nuclei.
Basal ganglia nuclei are strongly interconnected with
the cerebral cortex, thalamus, and brainstem, as well as
several other brain areas. The basal ganglia are associated
with a variety of functions including: control of voluntary
motor movements, procedural learning, routine behaviors
or "habits" such as bruxism, eye movements, cognition and
emotion.
COMPONENTS OF BASAL
GANGLIA
TELENCEPHALON
- Caudate nucleus
- Putamen
- Globus pallidus
DIENCEPHALON AND MIDBRAIN
- substantia nigra,
- subthalamic nucleus.
- red nucleus
TERMINOLOGY
• Striatum (nucleus caudatus and putamen)
• Nucleus lentiformis (globus pallidus and
putamen)
BASAL GANGLIA - FUNCTION
Currently, popular theories implicate the basal
ganglia primarily in action selection; that is, it
helps determine the decision of which of several
possible behaviors to execute at any given time. In
more specific terms, the basal ganglia's primary
function is likely to control and regulate activities
of the motor and premotor cortical areas so that
voluntary movements can be performed
smoothly.
BASAL GANGLIA
IMPAIRMENT
The importance of these subcortical nuclei for normal brain function and
behavior is emphasized by the numerous and diverse neurological conditions
associated with basal ganglia dysfunction, which include:
- disorders of behavior control such as Tourette syndrome, hemiballismus,
and obsessive–compulsive disorder
- dystonia;
- addiction;
- movement disorders
a)
Parkinson's disease, which involves degeneration of the dopamineproducing cells in the SUBSTANTIA NIGRA
b)
Huntington's disease, which primarily involves damage to the
STRIATUM.
LIMBIC SYSTEM
The limbic system is a complex set of brain structures located on both sides of
the thalamus, right under the cerebrum. It is not a separate system but a collection of
structures from the cerebrum, diencephalon, and midbrain. It includes:
- olfactory bulbs,
- hippocampus,
- hypothalamus,
- amygdala,
- fornix,
- mammillary body,
- limbic cortex,
The limbic system supports a variety of functions
including emotion, behavior, motivation, long-term memory, and olfaction. Emotional
life is largely housed in the limbic system, and it has a great deal to do with the formation
of memories.
HIPPOCAMPUS
The hippocampus (named after its resemblance to the seahorse), is a
major component of the brain. Human brain has 2 hippocampi: one in
each side of the brain. It belongs to the limbic system and plays
important roles in the consolidation of information from short-term
memory to long-term memory and spatial navigation. The hippocampus
is located under the cerebral cortex; it is located in the medial temporal
lobe, underneath the cortical surface. It contains two main interlocking
parts: the hippocampus proper (also called Ammon's horn) and
the dentate gyrus.
In Alzheimer's disease, the hippocampus is one of the first
regions of the brain to suffer damage; memory loss
and disorientation are included among the early symptoms.
DIENCEPHALON
The diencephalon consists of structures that are
lateral to the third ventricle, and include
the thalamus, the hypothalamus,
the epithalamus and the subthalamus.
Diencephalon connects the midbrain to the
cerebral hemispheres.
THALAMUS
The thalamus is a vital structure lying deep within the
brain that has several important functions, such as
sensory and motor function, attention, memory,
speech, and emotion. Various thalamic nuclei with
extensive nerve networks send signals all around the
structures of the brain including the cerebral cortex.
Thalamic lesions cause a wide variety of clinical
symptoms; therefore, anatomical knowledge of the
thalamus is important in clinical situations.
HYPOTHALAMUS
The hypothalamus is a portion of the brain that contains a number
of small nuclei with a variety of functions. One of the most
important functions of the hypothalamus is to link the nervous
system to the endocrine system via the pituitary
gland (hypophysis).
The hypothalamus is located below the thalamus and is part of
the limbic system. It forms the ventral part of the diencephalon.
The hypothalamus is responsible for
certain metabolic processes and other activities of the autonomic
nervous system. It synthesizes and secretes
certain neurohormones, called releasing hormones and these in
turn stimulate or inhibit the secretion of pituitary hormones.
HYPOTHALAMUS ANATOMY
The hypothalamus occupies the ventral diencephalon and is
composed of numerous fiber tracts and nuclei situated
symmetrically about the third ventricle. In sagittal section, the
hypothalamus is roughly diamond shaped; although its boundaries
are not sharply demarcated, its perimeters can be correlated using
neuroanatomic landmarks.
Rostrally, the hypothalamus extends from the anterior
commissure, lamina terminalis, and optic chiasm. Caudally, the
hypothalamus extends to the periaqueductal gray matter of the
midbrain, approximated by (from ventral to dorsal) the
mammillary bodies, interpeduncular fossa, and cerebral
peduncles.
In the coronal plane, the boundaries of the hypothalamus are
more distinct. Superiorly, the hypothalamus is divided from the
thalamus by a groove in the lateral wall of the third ventricle, the
hypothalamic sulcus. The lateral surface is contiguous with the
thalamus and subthalamus and is bordered by the internal capsule
and optic tracts. Medially, the hypothalamus is bound by the
ependyma of the third ventricle. Finally, the inferior surface is
continuous with the floor of the third ventricle.
The external surface of the hypothalamic floor projects into the
interpeduncular cistern. A median protuberance, the tuber
cinereum lies between the optic chiasm (rostrally) and mammillary
bodies (caudally) and is continuous anteriorly with the lamina
terminalis. This projection continues as the infundibulum,
terminating inferiorly on the pituitary gland.
EPITHALAMUS
The epithalamus comprises the habenular trigone, the pineal
gland, and the habenular commissure. It is wired with the limbic
system and basal ganglia.
The function of the epithalamus is to connect the limbic system to
other parts of the brain. Some functions of its components include
the secretion of melatonin by the pineal gland (involved
in circadian rhythms), and regulation of motor pathways
and emotions.
SUBTHALAMUS
The subthalamus is a part of the diencephalon. Its most prominent
structure is the subthalamic nucleus. The subthalamus connects to
the globus pallidus, a basal nucleus.
The subthalamus is located ventral to the thalamus, medial to
the internal capsule and lateral to the hypothalamus. It is a region
formed by several grey matter nuclei and their associated white
matter structures, namely:
- The subthalamic nucleus
- Zona incerta
- Subthalamic fasciculus,
- Fields of Forel
- Ansa lenticularis
BRAINSTEM
1. Midbrain (continuous with the cerebral
hemisphere above)
2. Pons
3. Medulla oblongata (continuous with the spinal
cord below)
The brainstem is located in posterior cranial
fossa.
CRANIAL NERVES
The III and IV nerves emerge from the
surface of the midbrain.
The V from the pons.
The VI , VII and VIII nerves emerge at
the junction of the pons and medulla.
The IX, X, XI and XII nerves emerge
from the surface of the medulla.
MIDBRAIN
Parts of the midbrain
The midbrain comprises two lateral halves, called the cerebral
peduncles; which is again divided into an anterior part, the crus
cerebri, and a posterior part, tegmentum, by a pigmented band of
gray matter, substantia nigra.
The narrow cavity is the cerebral aqueduct, which connects the
3rd and 4th ventricles.
The tectum is the part of the midbrain posterior to the cerebral
aqueduct; it has four small surface swellings two superior and two
inferior colliculi.
PONS
Pons has a convex anterior surface marked by transversely running
fibers which laterally forms a bundle called middle cerebellar
peduncle.
Main Features
The trigeminal nerve emerges from the anterior surface at its
junction with middle cerebellar peduncle.
Presents a basilar sulcus in the midline which lodges basilar artery.
In the groove between Pons and the medulla oblongata, there
emerge, from medial to lateral, abducent, facial and
vestibulocochlear nerves.
Posterior surface of the pons is limited laterally by superior cerebellar peduncle
and forms the upper part of the floor of the 4th ventricle.
Main Features:
The floor is divided into symmetrical halves by a median sulcus.
Lateral to this sulcus is an elongated elevation, the medial eminence, which is
bounded laterally by a sulcus limitans.
Inferior end of medial eminence is slightly expanded to form facial colliculus,
which is produced by facial nerve.
The upper end of sulcus limitans presents a bluish-gray coloration and the area
is called substantia ferruginosa.
Area vestibule lies lateral to sulcus limitans.
Parts of the Pons
a posterior part, the tegmentum, and
an anterior basilar part
MEDULLA OBLONGATA
The medulla oblongata is conical in shape. Its broad part joins the pons
above and narrow part becomes continuous with the spinal cord. The
junction between medulla and spinal cord coincides with the level of the
upper border of Atlas (first cervical vertebra).
Its length is about 3 cm and its width is about 2cm at its upper end.
It is divided into
1. A lower closed part with central canal and
2. An upper open part posteriorly which is related to the lower part of
the 4th ventricle
Features on the anterior surface of Medulla Oblongata
Anterior median fissure, is an upward continuation of similar fissure present on
the spinal cord
Anterolateral sulcus, on each side, is in line with the ventral roots of spinal cord
-Gives attachment to the rootlets of the hypoglossal nerve
Pyramid is an elevation on each side of the midline between anterior median
fissure and anterolateral sulcus.
Composed of bundles of nerve fibers of corticospinal tract that descends
from the cerebral cortex to the spinal cord
-Tapers inferiorly where the majority of fibers cross over to the opposite side,
obliterating the medulla. These crossing fibers constitute the decussation of the
pyramid.
Olive is a prominent, elongated oval swelling that lies in the upper part of
medulla posterolateral to the pyramid separated by anterolateral sulcus.
The elevation is produced by the underlying inferior olivary nucleus.
Features on posterior surface of the medulla oblongata
Posterior median sulcus is upward continuation of the similar fissure on the
spinal cord.
Posterolateral sulcus lies in line with the dorsal roots of spinal nerves.
Gives attachment to the rootlets of IX, X and XI cranial nerves.
Between the posterior median sulcus and posterolateral sulcus, the medulla
contains tracts (asccending) that enter it from the posterior funiculus of the
spinal cord.
Fasciculus gracilis lies medially and fasciculus cuneatus lies laterally
Both fasciculi end in rounded elevations called gracile tubercle (nucleus
gracilis) and cuneate tubercle (nucleus cuneatus) respectively.
Just above these tubercles, medulla is occupied by a triangular fossa which
forms the lower part of the 4th ventricle.
This fossa is bounded on each side by inferior cerebellar peduncle which
connect the medulla to cerebellum.
Features on the posterior part of the medulla that forms the floor
of the 4th ventricle:
Presents median sulcus, on each side of which there is a
longitudinal elevation called the median eminence (continuous
above in the pontine part of the floor of 4th ventricle). The
eminence is bounded laterally by sulcus limitans.
The sulcus limitans is marked by a depression called inferior
fovea. The part of the medulla below fovea presents hypoglossal
triangle medially and vagal triangle laterally.
Between the vagal triangle, above and gracile tubercle, below lies a
small area called area postrema.
The lowest part of the floor is called the calamus scriptorius (for its
resemblance to a nib).
The inferior angle where the lateral margins of the floor meet is
called obex.
The ventricular system is a set of
communicating cavities within the brain. These
structures are responsible for the production,
transport and removal of cerebrospinal
fluid, which bathes the central nervous system.
FUNCTIONS OF CEREBROSPINAL FLUID
Cerebrospinal fluid is an ultrafiltrate of plasma that surrounds the brain and
spinal cord.
It serves three main functions:
Protection – It acts as a cushion for the brain, limiting neural damage in cranial
injuries.
Buoyancy – By being immersed in CSF, the net weight of the brain is reduced
to approximately 25 grams. This prevents excessive pressure on the base of the
brain.
Chemical stability – The CSF creates an environment to allow for proper
functioning of the brain. E.g. Maintaining low extracellular K+ for synaptic
transmission.