Brain stem 1

Medulla Oblongata

Development of the brain

Brain Stem• Located :between the cerebrum and the SC

• Consists of :the midbrain, pons, and medulla oblongata.

• Each region is about an inch in length.

Microscopically, it consists of deep grey matter surrounded by white matter fiber tracts

CONNECTIONS WITH CEREBELLUM:

• Each part of brain stem is connected to cerebellum by cerebellar peduncles (superior, middle & inferior).

FUNCTIONS OF BRAIN STEM1. Pathway of tracts between

cerebral cortex & spinal cord.

2. Site of origin of nuclei of cranial nerves (from 3rd to 12th).

3. Site of emergence of cranial nerves (from 3rd to 12th).

4. Contains groups of nuclei & related fibers known as reticular formation responsible for: control of level of consciousness, perception of pain, regulation of cardiovascular & respiratory systems.

Medulla is broad above: joins with pons & narrow below: continuous with spinal cord

Length is about 3cm, width is about 2cm at its upper end

Surfaces shows series of fissuresAnterior median fissurePosterior median fissure Spinal cord

Medulla oblongata

Most inferior region of the brain stem.

Becomes the spinal cord at the level of the foramen magnum.

External structure of the medulla

Medulla Oblongata

External features

• It is divided into right & left halves by anterior & posterior median fissures

• Each half again into ant, post , lat region by anterolateral & posterolateral sulci

• The ant. region in the form of a longitudinal elevation called pyramid

• Anterior external arcuate fibres run transversely across upper part of the pyramid

• Lateral region shows an oval elevation, the olive.• It is produced by a mass of greymater- inferior

olivary nucleus

Anterior median fissure

Pyramid

Anterolateral fissure

Olive

MEDULLA – VENTRAL SURFACE Ventral median fissure: • Continuation of ventral median

fissure of spinal cord• Divides the medulla into 2 halves • Its lower part is masked by

decussation of most of pyramidal (corticospinal) fibers (75%-90%).

Pyramid: • An elevation, lies on either side of

ventral median fissure • Produced by corticospinal tract.

Olive: • An elevation, lies lateral to the

pyramid.• Produced by inferior olivary

nucleus (important in control of movement).

Nerves emerging from Medulla (4 nerves):

• Hypoglossal (12th): from sulcus between pyramid & olive

• Glossopharyngeal (9th), vagus (10th) & cranial part of accessory (11th): from sulcus dorsolateral to olive (from above downwards)

• The features differ in the caudal part (closed medulla) and the cranial part (open medulla)

MEDULLA – DORSAL SURFACE

open medulla closed medulla

CLOSED MEDULLA

Cavity: central canal. Composed of:1-Dorsal median sulcus: divides the closed medulla into 2 halves.2-Fasciculus gracilis: on either side of dorsal median sulcus.3-Gracile tubercle: an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus.4-Fasciculus cuneatus: on either side of fasciculus gracilis.5-Cuneate tubercle: an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus.

OPEN MEDULLA Cavity: 4th ventricle On either side, an

inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral):

1. Hypoglossal triangle: overlies hypoglossal nucleus.

2. Vagal triangle: overlies dorsal vagal nucleus.

3. Vestibular area: overlies vestibular nuclei.

Internal features

Traversed by the Central Canal.

Includes the Motor Decussation.

Includes the Spinal Nucleus of Trigeminal (Trigeminal sensory nucleus) :

It is a large sensory nucleus. It is the brain stem continuation of the Substantia Gelatinosa of spinal cord.

Closed MedullaSubstantia Gelatinosa

• The Nucleus Extends : • Through the whole length of

the brain stem and into upper segments of spinal cord.

• It lies in all levels of M.O, medial to the spinal tract of the trigeminal.

• It receives pain and temperature from face, forehead.

• Its tract is present in all levels of M.O. is formed of descending fibers that terminate in the trigeminal nucleus.

TRIGEMINAL SENSORY NUCLEUS & TRACT

• It is the Motor Decussation.

• Formed by pyramidal fibers, (75-90%) cross to the opposite side

• They descend in the lateral white column of the spinal cord as the lateral corticospinal tract.

• The uncrossed fibers form the ventral corticospinal tract.

PYRAMIDAL DECUSSATION

Traversed by the Central Canal. Larger size Gracile & Cuneate nuclei, concerned

with proprioceptive deep sensations of the body. Axons of Gracile & Cuneate nuclei form the

internal arcuate fibers; Sensory Decussation. Pyramids are prominent ventrally.

MID MEDULLA

SENSORY DECUSSATION

lemniscus = ribbon

• Formed by the crossed internal arcuate fibers

• Medial Leminiscus:– Composed of the

ascending internal arcuate fibers after their crossing.

– Lies adjacent to the middle line ventral to the central canal

– Terminates in thalamus.

On the ventral aspect : The pyramid is clear, with

medial lemniscus on either sides of middle line dorsal to the pyramid

Inferior Olivary Nucleus:– A convoluted mass of

gray matter. Has a hilum directed medially, lies posterolateral to the pyramids & lateral to the medial leminiscus.

– It is concerned with the control of movement.

Open Medulla

Its dorsal surface forms: The lower part of the floor of the 4th ventricle.

• The Inferior Cerebellar Peduncle is dorsolateral in position, connecting M.O. with cerebellum.

• Dorsal and lateral to the Inferior cerebellar peduncle lie the Cochlear nuclei (dorsal and ventral).

Open Medulla

Beneath the floor of 4th ventricle lie :

1. Hypoglossal Nucleus lies just lateral to the midline.

2. Dorsal Nucleus of Vagus lateral to the hypoglossal nucleus, contains preganglionic parasympathetic fibers.

Medial longitudinal fasciculus lies close to the midline, ventromedial to the hypoglossal nucleus, dorsal to the medial lemniscus. It links the vestibular nuclei with nuclei of extraocular ms. (3,4&6) to help coordination of head & eye movements.

3. Vestibular nuclei complex : is composed of medial, lateral, inferior & superior nuclei, concerned with equilibrium.4. Nucleus Ambiguus: lie deep to the floor and dorsal to olivary nucleus gives motor fibers to constrictors of the pharynx & intrinsic muscles of the larynx.5. Solitary nucleus: lie ventrolateral to dorsal nucleus of vagus, receive taste sensation from the tongue along the facial (VII), glossopharyngeal (IX) and vagus (X) cranial nerves.

Vestibular nucleiN. solitariousSensory nucleus for CN VII, IX, X

Spinal trigeminal tractCN V, VII, IX, X

N. ambiguus Motor nucleus for CN IX, X & XI

Dorsal motor nucleus of X

Sensation behind ear

Posterior 1/3 of the tongue

Stylopharyngeus (lifts pharynx)

Cranial Nerves of the Medulla

Dorsal motor nucleus of XParasympathetic, preganglionic

N. solitariousSensory nucleus for CN VII, IX, XTaste, epiglottis CardiorespiratoryN. ambiguus Motor nucleus for CN IX, X & XIPharynx Larynx

Spinal trigeminal tractCN V, VII, IX, XEar

CN X: Vagus Nerve

• Nuclei in the medulla are associated with autonomic control, cranial nerves, and motor/sensory relay.

• Autonomic nuclei:1-Cardiovascular centersAlter the rate and force of cardiac contractionsAlter the tone of vascular smooth muscle2-Respiratory rhythmicity centersReceive input from the pons3-Additional CentersEmesis, deglutition, coughing, hiccupping, and sneezing

The End