Anatomy of the Brain Stem

External features

Anterior view

The anterior surface of medulla oblongata is grooved by an anteromedian fissure,on either side of which are the swellings due to the pyramidal tracts. These

pyramids, in turn, are separated from the olivary eminences by the anterolateral sulcus along which the rootlets of the 12th cranial nerve emerge.

Between the olive and the inferior cerebellar peduncle there is yet another groove corresponding to the posterolateral sulcus of the spinal cord; emerging from this groove are the rootlets of cranial nerves IX, X and XI

The pons lies between the medulla and the midbrain and is connected to the cerebellum by the middle cerebellar peduncles.

Its ventral surface presents a shallow median groove and numerous transverse ridges, which are continuous laterally with the middle cerebellar peduncle.

Its junction with the medulla is marked close to the ventral midline by the emergence of the 6th

7th and 8th cranial nerves nerves.

5th cranial nerves leave the lateral part of the pons near its upper border.

The anterior surface of the midbrain is formed by the cerebral peduncles (descending cerebral pathways).

The fibres of the 3rd nerves emerge between the two cerebral peduncles in the interpeduncular fossa.

Posterior view

The posteromedian sulcus of the spinal cord is continued half-way up the medulla, where it widens out to form the posterior part of the 4th ventricle.

On either side of the fissure the posterior columns of the spinal cord expand to form two distinct tubercles, the gracile and cuneate nuclei

The dorsal surface of the pons forms the upper part of the floor of the 4th ventricle

The dorsal surface of the midbrain presents corpora quadrigeminia,including two inferior,and two superior colliculi .

The corpora quadrigemina are reflex centers involving vision and hearing

Internal structure

Cranial nerve nuclei

Non-cranial nerve nuclei

Ascending and descending pathways

Reticular formation

Cranial nerve nuclei are referred to those nuclei located in the brain stem, where the cranial nerves originate or terminate except the olfactory and optic nerve

Non-cranial nerve nuclei are referred to those nuclei which are not linked directly to any cranial nerves functionally or structurally

Ascending pathways include 1) pathways originate in the spinal cord and pass

the brain stem to higher region of the brain; 2) pathways originate in the brain

stem to higher region of the brain

Descending pathways originate in the same motor area of the cortex, but terminate in 1) spinal cord and 2) brain stem

Reticular formation is recognized as an extensive field of intermingled grey and white matter outside the fiber bundles and nuclei of the brain stem

Long ascending pathways

Passing fibrous bundles which originate in the spinal cord:

1) Medial lemniscus: fibrous bundle formed by relayed fibers from fasciculi gracilis,

cuneatus. The fibers relay in gracile and cuneate nuclei, and decussate with fibers of opposite side, finally end in the ventral posteriomedial nucleus of thalamus

2) Spinothalamic lemniscus： composed of anterior and posterior spinothalamic tracts, and terminate in the ventral posterolateral nucleus of thalamus

Long ascending pathways

Fibrous bundles originated in the brain stem:

1) Trigeminal lemniscus: formed by fibers from contralateral spinal and pontine nuclei of trigeminal n. It conducts the tactile, pressure, pain and thermal impulses to the ventral posterolateral nucleus of thalamus

2) Lateral lemniscus: formed by the fibers from the ipsilateral and controlateral cochlear nuclei; some of fibers end in the inferior colliculus, others traverse the brachium of inferior colliculus to the nucleus of medial geniculate body

Long descending pathways

Pyramidal tract : descending fiber bundles originated in motor cortex to lower motor neurons in brain stem and spinal cord, It includes 1) corticospinal tract and 2) corticonuclear tract

The cerebellum

The cerebellum is the integrative organ for the coordination and fine-tuning of movement and for the regulation of muscle tone.

it is situated in the post cr fossa behind the pons & medulla.

EXTERNAL FEATURES

The cerebellum consists of two cerebellar hemispheres that are united to each other by the median vermis.

it has 2 surfaces sup & inf.

The sup surface is convex. The two hemispheres are continued each other on this surface.

The inf surface shows a deep median notch called the vallecula which separates the rt & lft hemispheres.

Internal structure

It consists of a cortex of grey matter (in which all the afferent fibres terminate) covering a mass of white matter, in which deep nuclei of grey matter are buried.

The cerebellar cortex contains several maps of the skeletal muscles in the body

The topographic arrangement of these maps indicates that the vermis controls the axial and proximal musculature of the limbs, the intermediate part of the hemisphere controls distal musculature, and the lateral part of the hemisphere is involved in motor planning.

THE DIENCEPHALON

The diencephalon is a midline structure

which is largely embedded in the cerebrum, and therefore hidden from the surface view.

Its cavity is the 3rd ventricle the hypothalamic sulcus extending from the interventricular foramen to the cerebral aqueduct, divides each half of the diencephalon in to dorsal & ventral parts.

Further sub divisions are follows

A . Dorsal part of the diencephalon

Thalamus ( dorsal thalamus )

Metathalamus, including the med & lat geniculate bodies and

Epithalamus, including the pinial body & habenula

B . Ventral part of the diencephalon

Hypothalamus,

Subthalamus ( ventral thalamus )

THALAMUS

The thalamus serves as the major sensory

relay for the ascending tactile, visual,auditory,

and gustatory information that ultimately reaches

the cerebrum cortex.

HYPOTHALAMUS

The hypothalamus is composed of numerous

nuclei that have afferent and efferent connections

with widespread regions of the nervous system,

including the pituitary gland, the autonomic

system, and the limbic system .It takes part in the

control of many visceral & metabolic activities

META THALAMUS

It consists of medial & lateral geniculate bodies

Which are situated on either side of the midbrain, below the thalamus

Medial geniculate body

It is an oval elevation situated just below the pulvinar of the thalamus & lat to the sup colliculus

It represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC).

Lateral geniculate body

This is a small elevation situated anterolateral to the med geniculate body, below the thalamus.

It is the primary processing center for visual information received from the retina of the eye

Anatomy of Spinal Cord

EXTERNAL FEATURES

It is the lower elongated cylindrical part of the CNS and connect with the brain above

It occupies upper 2/3rd of the vertebral canal

It extends from the foraman magnum to the lower border of the L1 or upper border of the L 2

In neonates, the spinal cord extends approximately to vertebra LIII, but can reach as low as vertebra LIV.

It is about 45 cm in length

The lower end is called the conus medullaris

From here a prolongation of pia mater, the filum terminale descends to be attached to the back of the coccyx.

It has six external longitudinal fissures and sulci. They are a deep anterior median fissure, a shallow posterior median sulcus, a pair of anterolateral sulcus and a pair of posterolateral sulcus lying lateral to them.

The anterolateral sulcus and posterolateral sulcus marks the sites of attachment for the anterior and posterior roots of each pair of spinal nerves.

It also has two enlargement called cervical and lumbosacral enlargement which represent the aggregations of cell bodies that supply the muscles and skin of upper limbs and lower limbs.

The spinal cord gives off 31 pairs of spinal nerves. 8 cervical,12 thoracic, 5 lumbar, 5 sacral, & 1 coccygeal, each nerve is attached to the spinal cord by 2 roots, ventral ( motor) , & dorsal ( sensory ), each dorsal root bears a ganglion, the ventral & dorsal nerve unites to form the nerve trunk, which soon divides into ventral & dorsal rami

The part of spinal cord that gives off one pair of spinal nerve we call it a segment of spinal cord

Below the lower end of the spinal cord the roots of spinal nerves form a bundle known as the cauda equina (because of resemblance to the tail of a horse)

In transverse section of the cord is seen the central canal around which is the H-shaped grey matter, surrounded in turn by the white matter which contains the long ascending and descending tracts.

Gray matter

When seen in transverse section the grey matter of the spinal cord forms an “ H “ shaped mass and is surrounded by white matter.

It is divisible into 1) Ventral Horn(column ) 2) Dorsal Horn (column ) 3) intermediate zone .In some parts of spinal cord it presents as a lateral horn (column ) 4)The right & left halves of spinal cord are connected across the midline by the grey commisure, which is traversed by the central canal

The Ventral horn contains several nuclei with large motor neurons to control the movement of skeleton muscles of trunk and limbs

The dorsal horn is dominated by neurons that respond to sensory stimulation.

All incoming sensory fibers in spinal nerves enter the dorsolateral part of the cord adjacent to the dorsal horn in a dorsal root. Neurons in the dorsal horn project to higher levels of the CNS to carry sensations to them

Sympathetic and parasympathetic neurons locate in the intermediate zone espacially in the thoracic and sacral part of spinal cord.

White matter

The white matter of the sp cord is divisible into right & left halves in front by the anterior median fissure & behind by the posterior median sulcus

Each half of the white matter is divided into 1) post funiculus 2)lateral funiculus 3)anterior funiculus

The white matter of the rt & lft sides is continuous across the midline through the anterior white commisure which lies ant to the grey commisure

The nerve fibers in the white matter are of two general types:

1. long , ascending fibers projecting to the upper parts of the brain

2. long, descending fibers projecting from the upper parts of the brain to the spinal gray matter

ASCENDING TRACTS

1.Fasiculus gracilis and Fasiculus cuneatus

They convey sensory fibres subserving fine

touch and proprioception (position sense), mostly

uncrossed, to the gracile and cuneate nuclei in the

medulla oblongata.

2 . The lateral and anterior spinothalamic tracts

They transmit information to the thalamus about pain, temperature and crude touch

DESCENDING TRACTS

Corticospinal tracts – descends from the cerebral cortex to the sp cord. It consists of 2 parts 1) the lat corticospinal tract, which lies in the lateral funiculus. 2) the ant corticospinal tract which lies in the ant funiculus

The corticospinal tracts are responsible for voluntary movements control.

2 . Rubrospinal tracts

3 . Olivospinal tracts

Techniques used to read the X ray finding

Migraine and its types

it has been estimated that 18 million women and 6 million men in the United states suffer from sever Migraine headaches.

Migraine can usually be distinguished clinically from the two other common types of headaches :

Migraine: present as a pulsatile,throbbing pain

a. Cluster headaches : as excruciating,sharp and steady pain.

b. Tension-type headaches: as dull pain,with a persistent,tightening feeling in the head.

Patients with severe migraine headaches report one to five attacks per month of moderate to severe pain, usually unilateral. The headaches affect patient for a major part of their lives and result in considerable health losts.

Types of Migraine

There are two main types of migraine headaches.

The first, migraine without aura(previously called common migraine), is a severe,unilateral,pulsating headaches that typically lasts from 2 to 72 hours. These headaches are often aggravated by physical activity and are accompained by nausea, Vomiting , Photophobia (hypersensitivity to light), and Phonophobia (hypersensitivity to sound).

Approximately 85 percent of patients with migraine do not have aura.

In the Second type, Migraine with aura (previously called classic migraine),

the headache is preceded by neurologic symptoms called auras,which can be visual,sensory,and/or cause speech or motor disturbances.Most commonly,these prodromal symptoms are visual, occuring approximately 20 to 40 minutes before headache pain begins. In the 15 percent of Migraine patients whose headaches is preceded by an aura, the aura itself allows similar.

For both types of Migraine, women are three-fold more likely than men to experience either type of Migraine.

BIOLOGIC BASIS OF MIGRAINE HEADACHES:

The first manifestation of migraine with aura is a spreading depression of neuronal activity accompanied by reduced blood flow in the most posterior part of the cerebral hemisphere. This hypoperfusion gradually spreads forward over the surface of the cortex to other contiguous areas of the brain. The vascular alteration is accompanied by functional changes; for example, the hypoperfused regions show an abnormal response to changes in arterial partial pressure of CO2. The hypoperfusion persists throughout the aura and well into the headache phase, after which hyperperfusion occurs. Patients who have Migraine without aura do not show hypoperfusion. However the pain of both types of Migraine may be due to Extracranial and Intracranial arterial dilation. This stretching leads to release of neuroactive molecules, such as Substance P.

Thoracic landmarks