INTRODUCTION TO BRAIN&

BRAINSTEM

Kaan Yücel M.D., Ph.D. 28. April.2014 Monday

The brain (encephalon) is divided into three major divisions. 1) Hindbrain (Rhombencephalon)I. Medulla oblongataII. PonsIII. CerebellumPons and cerebellum are called as metencephalon.2) Midbrain (Mesencephalon)3) Forebrain (Prosencephalon)I. Telencephalon (Cerebrum)II. Diencephalon (between brain)

BRAINSTEMoldest part of the CNS.

medulla oblongata, pons, and midbrain

occupies the posterior cranial fossa of the skull.

stalklike in shape and connects the narrow spinal cord with the expanded forebrain.

BRAINSTEMcontains 10 cranial nerves, and most of the motor and sensory systems pass through this important region.

a relatively small region (approximately 7 cm long)

links the forebrain (i.e., cerebral cortex) and spinal cord and all messages going between the two areas must go through the brain stem.

2 cm in length connects the pons and cerebellum with the forebrain. cerebral hemispheres connected to brainstem by 2 large fiber tracts cerebral peduncles

The dorsal aspect of the midbrain the tectum (L., roof] paired superior and inferior colluculi (singular, colliculus). corpora quadrigeminasuperior colliculi centers for visual reflexesinferior colliculi lower auditory centers

Tegmentum: Anterior part of midbrainBetween Cerebral aqueduct

Midbrain

MidbrainThe midbrain comprises two lateral halves

cerebral pedunclesanterior part: crus cerebri

substantia nigra posterior part: tegmentum

Substantia nigrao Large motor nucleus between tegmentum & crus cerebri

o Concerned with muscle tone

o Connected to the cerebral cortex, spinal cord, hypothalamus, and basal nuclei.

Midbrain

Midbrain

Pons

Pons

Medulla [oblongata] In the posterior cranial fossa, lying beneath the tentorium cerebelli and above the foramen magnum.

Related anteriorly to the basal portion of the occipital bone and the upper part of the odontoid process of the axis and posteriorly to the cerebellum.

Medulla oblongata Not only contains many cranial nerve nuclei that are concerned with vital functions (e.g., regulation of heart rate and respiration), but it also serves as a conduit for the passage of ascending and descending tracts connecting the spinal cord to the higher centers of the nervous system

Medulla oblongata

Medulla oblongata

Medulla oblongata

BRAINSTEM

midbrainpons

medulla

Nuclei of 12 cranial nerves10 of them in the brainstem

Of the last 4XII,XI,X, IX

Of the other 4VIII,VII,VI,V

Of the IV & III

I Olfactory Purely sensory Telencephalon

Smelling

II Optic Sensory Retinal ganglion cellsSeeing

III Oculomotor Mainly motor MidbrainEye movements & pupillary reflex

IV Trochlear Motor MidbrainIntorts the eyeball.

V Trigeminal Both sensory and motor PonsReceives sensation from the face and innervates the muscles of mastication.

VI Abducens Mainly motor PonsAbducts the eye.

VII Facial Both sensory and motor Pons Provides motor innervation to the muscles of facial expression. Receives the special sense of taste from the anterior 2/3 of the tongue and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland.

VIII Vestibulocochlear Mostly sensory PonsHearing and balance

IX Glossopharyngeal Both sensory and motor MedullaReceives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils.

X Vagus Both sensory and motor Medulla

Innervation to most laryngeal and pharyngeal muscles (except the stylopharyngeus, which is innervated by the glossopharyngeal).

Parasympathetic fibers to nearly all thoracic and abdominal viscera till the proximal two-thirds of the transverse colon.

Receives the special sense of taste from the epiglottis.

A major function: controls muscles for voice and resonance and the soft palate.

XI Accessory (often separated into the cranial accessory and spinal accessory nerves) MedullaMainly motor Cranial and Spinal RootsControls the sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus nerve (CN X). Symptoms of damage: inability to shrug, weak head movement.

XII Hypoglossal mainly motor MedullaProvides motor innervation to the muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation.

Reticular formationo The reticular formation (L. reticulum, “little net”) consists of various

distinct populations of cells embed in a network of cell processes occupying the central core of the brainstem.

o The reticular formation and the olfactory and limbic systems are interrelated as a result of their participation in visceral functions and behavioral responses.

Reticular formationMore than 100 nuclei scattered throughout the tegmentum of the midbrain, pons and medulla have been identified as being part of the brainstem reticular formation.

Reticular formation

1- The regulation of the level of consciousness, and ultimately cortical alertness

2- The control of somatic motor movements

3- The regulation of visceral motor or autonomic functions

4- The control of sensory information

Autonomic Nervous SystemSympathetic Parasympathetic

Anatomical differences, differences in the neurotransmitters, differences in the physiologic effects

The autonomic nervous system and the endocrine system control the internal environment of the body.

The various activities of the autonomic and endocrine systems are integrated within the hypothalamus.

Autonomic Nervous SystemSympathetic part prepares and mobilizes the body in an emergency, when there is sudden severe exercise, fear, or rage.

Parasympathetic part aims at conserving and storing energy, in the promotion of digestion and the absorption of food by increasing the secretions of the glands of the gastrointestinal tract and stimulating peristalsis.

Autonomic Nervous SystemParasympathetic systemBrainstem and sacral segments of the spinal cord

Edinger-Westfall nucleus midbrain mediates the diameter of the pupil in response to light

Superior and inferior salivatory nuclei pons & medulla mediatie salivary secretion and the production of tears)

Dorsal motor nucleus of the vagus nerve Medulla controls the motor responses of the heart, lungs, and gut (e.g., slowing of the heart rate and constriction of the bronchioles).

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Cerebral aqueduct (aqueduct of Slyvius)o A narrow channel connecting third and fourth ventricles

o Lined with ependyma

o Surrounded by a layer of gray matter: central gray

o Direction of flow of CSF 3rd ventricle 4 th ventricle

o No choroid plexus

Fourth ventricle