1. Brain stem 1
Medulla Oblongata

2. Development of the brain

3. 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.

4. 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).

5. FUNCTIONS OF BRAIN STEM
Pathway of tracts between cerebral cortex & spinal cord.
Site of origin of nuclei of cranial nerves (from 3rd to 12th).
Site of emergence of cranial nerves (from 3rd to 12th).
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.

6. Medulla Oblongata External structure of the medulla
Most inferior region of the brain stem.
Becomes the spinal cord at the level of the foramen magnum.
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 fissures
Anterior median fissure
Posterior median fissure
Medulla oblongata
Spinal cord

7. 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

8. Pyramid
Olive
Anterolateral fissure
Anterior median fissure

9. 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.

10. 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)

11. MEDULLA – DORSAL SURFACE
The features differ in the caudal part (closed medulla) and the cranial part (open medulla)
open medulla
closed medulla

12. 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.
CLOSED MEDULLA

13. OPEN MEDULLA Cavity: 4th ventricle
On either side, an inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral):
Hypoglossal triangle: overlies hypoglossal nucleus.
Vagal triangle: overlies dorsal vagal nucleus.
Vestibular area: overlies vestibular nuclei.

14. Internal features

15. Closed Medulla 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.
Substantia Gelatinosa

16. TRIGEMINAL SENSORY NUCLEUS & TRACT
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.

17. PYRAMIDAL DECUSSATION
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.

18. MID MEDULLA 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.

19. SENSORY DECUSSATION 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.
lemniscus = ribbon

21. Open Medulla 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.

22. 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).

23. 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.

24. 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.

25. Cranial Nerves of the Medulla
N. solitarious
Sensory nucleus for CN VII, IX, X
Vestibular nuclei
Posterior 1/3 of the tongue
Dorsal motor nucleus of X
N. ambiguus
Motor nucleus for CN IX, X & XI
Spinal trigeminal tract
CN V, VII, IX, X
Stylopharyngeus (lifts pharynx)
Sensation behind ear

26. CN X: Vagus Nerve Dorsal motor nucleus of X N. solitarious
Parasympathetic, preganglionic
N. solitarious
Sensory nucleus for CN VII, IX, X
Taste, epiglottis Cardiorespiratory
N. ambiguus
Motor nucleus for CN IX, X & XI
Pharynx Larynx
Spinal trigeminal tract
CN V, VII, IX, X
Ear

27. Nuclei in the medulla are associated with autonomic control, cranial nerves, and motor/sensory relay.
Autonomic nuclei:
1-Cardiovascular centers
Alter the rate and force of cardiac contractions
Alter the tone of vascular smooth muscle
2-Respiratory rhythmicity centers
Receive input from the pons
3-Additional Centers
Emesis, deglutition, coughing, hiccupping, and sneezing

28. The End