NEUROANATOMY

ANS

NERVOUS SYSTEM

• 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.

grey

Somatic innervation – single neuron!!

ANS – 2 multipolar neurons!!

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 titanium-

encased 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 out-

patient 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 dopamine-

producing 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.