brain stem 1
DESCRIPTION
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 . - PowerPoint PPT PresentationTRANSCRIPT
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