BRAIN STRUCTURE. THE BRAIN STEM - PowerPoint Presentation

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BRAIN STRUCTURE.

THE BRAIN STEM

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Nervous System



CNS

(central nervous system) Brain Spinal Cord PNS (peripheral nervous system) Peripheral Nerves Ganglia

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Gross Divisions of the Brain



Cerebrum

(cerebral hemisphere) Diencephalon Cerebellum Brainstem

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Development

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Brainstem

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Brain Stem

Located

btwn cerebrum and spinal cordProvides a pathway for tracts running

btwn higher and lower neural centers.Consists of the midbrain,, pons, and medulla oblongata.Each region about 2.5 cm in length.Deep gray matter surrounded by white matter fiber tracts.Produces automatic behaviors necessary for survival.

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vermis

Occipital Lobe

Thalamus

Corpus callosum

Hypothalamus

Fornix

Anterior commissure

Optic nerve

4

th

ventricle

Posterior commissure

pyramid

Mammillary body

Quadrigeminal cistern

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internal capsule

basal ganglia

optic nerve

optic tracthypothalamusmammillary bodycerebral peduncleinterpeduncular fossaflocculusinferior olivary nuclear complexcerebellum

cerebellar tonsil

pyramid

pyramidal decussation

pons

optic chiasm

Anterior view of brainstem

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optic tract

optic nerve

hypothalamus

optic chiasm

middle cerebellar peduncle

trigeminal nerve

vestibulocochlear nerve

flocculus

cuneate tubercle

inferior olivary nuclear complex

anterior median fissure

pyramid

pons

cerebral

peduncle

Lateral view of brainstem

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Middle cerebellar peduncle

Superior colliculus

Inferior colliculus

Cerebral peduncleSuperior cerebellar peduncle

Inferior cerebellar peduncle

Medulla

4

th

ventricle

Posterior view of brainstem

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Basic

Strucrure

of

Brain Stem1. Roof plate (tectum)2. Tegmentum3. Basal portion

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Basilar (Basal) Portion

Descending Fibers from Cerebral Cortex

1. Corticospinal Tract

2. Corticobulbar Tract3. Corticopontocerebellar Fiber Corticopontine Fiber Pons Proper (Ventral Pons) Pontocerebellar Fiber

Pyramidal Tract

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Roof Plate

Midbrain

Superior Colliculus: vision Inferior Colliculus: hearingClosed Medulla Nucleus Gracilis et Cuneatus: discriminative touch sensationcf. Cerebellum: equilibrium

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Tegmentum

Cranial nerve nuclei

Precerebellar nuclei Reticular formationTracts Ascending cortical pathways Cerebellar circuits Descending tracts Composite bundles

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Cranial Nerves

Columns

ofBrain StemMotor Column 1. GSE 2. SVE 3. GVESensory Column 4. VA (GVA & SVA) 5. GSA 6. SSA

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Components of

Cranial Nerves

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Ventricles in brainstem

Mesencephalon 

cerebral aqueductMetencephalon 

4th ventricleMylencephalon  4th ventricle

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Components of the brainstem

Sensory ascending pathways (dorsal):

Relay nuclei, tractsMotor descending pathways (ventral)

Tracts, motor nuclei brainstemCerebellar pathwaysTracts, cerebellar afferent and efferent nucleiCranial nerve sensory and motor tractsCranial nerve nuclei, nerve entry and exit pointsAutonomic centers: rhythmic chewing, respiration, cardiovascular regulation & gain adjustments for reflexesModulatory systems: locus coeruleus, raphe & substantia nigraChemically coded nuclei

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Brainstem: 3 major divisions

Midbrain

Pons

Medulla

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Medulla Oblongata

Most inferior region of the brain stem.

Becomes the spinal cord at the level of the foramen magnum.Two ridges (

medullary pyramids) are visible ventrally. These are formed by the large motor corticospinal tracts.Right above the medulla-SC junction, most of these fibers cross over (decussate).

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A.

Anterolateral

Surface:The anterior median fissure.

The pyramid: formed by the pyramidal (corticospinal) tract.Pyramidal decussation.The olive: formed by the inferior olivary nucleus.The anterolateral sulci: gives exit to the hypoglossal nerves.The posterolateral sulci: gives exit to the glossopharyngeal, vagus and cranial accessory nerves.The inferior cerebellar peduncle.External Features of the Medulla Oblongata

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B. The posterior surface of the medulla oblongata:

1. The posterior surface of the upper half (open medulla):

from medial to lateral:

a. Posterior median fissure. b. Inferior fovea. c. Hypoglossal trigone (triangle). d. Vagal trigone. e. Vestibular trigone. 2. The posterior surface of the lower half (closed medulla): from medial to lateral: a. Posterior median fissure. b. Gracile tract. c. Cuneate tract.

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Medulla Oblongata

Nuclei in the medulla are autonomic nuclei, cranial nerves nuclei, and relay (motor/sensory) nuclei.

Autonomic nuclei:

Cardiovascular centersAlter the rate and force of cardiac contractionsAlter the tone of vascular smooth muscleRespiratory rhythmicity centersReceive input from the ponsAdditional CentersEmesis, deglutition, coughing, hiccupping, and sneezing

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Medulla Oblongata

Sensory & motor nuclei of 5 cranial nerves:

Auditory/Vestibular (8), Glossopharyngeal

(9), Vagus (10), Accessory (11), and Hypoglossal (12)Relay nucleiNucleus gracilis and nucleus cuneatus convey somatic sensory information to the thalamusOlivary nuclei relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex.

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Medulla summary

Crossing point of motor pathways

Autonomic centers

Cardiac centerRespiratory centerVasomotor centerCenters of cough, vomiting, swallow, hiccup Cranial nerves (nuclei):CN IX - Glossopharyneal CN X - VagusCN XI - Accessory

CN

XII – Hypogloss

als

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Pons

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Pons

Btwn

the midbrain & medulla and in front of cerebellum and IV ventricle. Contains:

Sensory and motor nuclei of 4 cranial nerves Trigeminal (5), Abducens (6), Facial (7), and Auditory/Vestibular (8)Respiratory nuclei:Apneustic & pneumotaxic centers work w/ the medulla to maintain respiratory rhythmNuclei & tracts that process and relay info to/from the cerebellumAscending, descending, and transverse tracts that interconnect other portions of the CNS

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Corpus

trapezoideum

1. Vestibular nerve

2. Cochlear nerve4. Tuberculum 7. Superior olivary nucleus.8. Trapezoid body.9. Trapezoid nucleus.10. Central acoustic tract (lateral lemniscus).

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A. The anterior surface of the

pons

presents with: 1. The basilar groove: for basilar artery. 3. The middle

cerebellar peduncle. 4. The trigeminal nerve. 5. The abducent nerve. 6. The facial nerve. 7. The vestibule-cochlear nerve.External Features of the Pons

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B. The posterior surface of the

pons

: presents with:

1. The median longitudinal sulcus: the middle line. 2. The medial eminence: for facial nucleus. 3. The facial colliculus: it produced by the facial nucleus. 4. The medullary stria: transverse nerve fibers which separate posterior surface of pons from that of medulla oblongata. 5. Superior fovea. 6. Vestibular trigon.

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Pontine nuclei:

part of the

cortico-ponto-cerebellar pathway.

2. Transverse fibers: pontocerebellar fibers.3. Longitudinal fibers: include pyramidal and cortico-pontine fibers.4. Nuclei of the trigeminal nerve:a. Motor nucleus.b. Sensory nuclei.5. Nucleus of the abducent nerve.6. Nuclei of the facial nerve:Motor nucleus. b. Superior salivary nucleus: parasympathetic function.Internal structures of the pons

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Locus

coeruleus

Physiological reactions to stress and panic.

Described in ХVIII c. by  F. Vicq-d’Azyr, (J. C. Reil).Dark blue, due to melanin in the neurons.nucleus pigmentosus pontisMain site of norepinephrin

synthesis in the brain.

Locus

coeruleus

-noradrenergic system

 or 

LC-NA system

.

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Connections

Projections –

far and wide reaching

Spinal cord, brain stem, cerebellum, hypothalamus, thalamus, amygdala, cerebral cortex. Afferents from Cerebellum, hypothalamus, amygdala, cingulate cortex, nuclei raphae pontis

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Functions

Neuroplasticity

Arousal-dream

Attention and memoryEmotionsBehavior flexibility, behavior inhibition and stress Balance

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7. Nuclei of the

vestibulocochlear

nerve.

8. Lateral lemniscus: for auditory sensation.9. Spinal lemniscus: a band of ascending fibers carrying pain, temperature and crude touch from the opposite side of the body below the head.10. Trigeminal lemniscus: a band of ascending fibers carrying pain, temperature and touch and proprioception from the opposite side of the face and scalp.11. Medial lemniscus:

deep sensation and fine touch from

the opposite side of the body below the head.

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Pons summary

Respiratory center

Norepinephrine

centerModulation of pain and panicControl of homeostasisCranial nerves:Trigeminal (V), Abducent (VI), Facial (VII), Vestibulocochlear (VII)

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Midbrain

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Midbrain

Btwn

diencephalon and pons

.2 bulging cerebral peduncles on the ventral side. These contain:Descending fibers to cerebellum via ponsDescending pyramidal tractsCerebral aqueduct runs thru the midbrain; connects the 3rd and 4th ventricles of the brain.The roof (tectum) of the aqueduct contains the corpora quadrigemina2 superior colliculi control reflex movements of the eyes, head and neck in response to visual stimuli

2

inferior

colliculi

control reflex movements of the head, neck, and trunk in response to auditory stimuli

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A. The anterior surface of the midbrain

presents:

1. Two cerebral peduncles. 2.

Interpeduncular fossa/posterior perforated substance 2. Oculomotor nerve: emerging from the medial side of the cerebral peduncle.External features of the midbrain

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B. The

posterior surface of the midbrain: presents the following features:

1. Four colliculi which include: a. Two superior colliculi (Visual function).

b. Two inferior colliculi (Auditory function). 2. Two superior cerebellar peduncles. 3. Superior medullary velum (membrane): lies between the two superior cerebellar peduncles. 4. The trochlear nerve.C. The lateral surface of the midbrain: presents the following features: 1. Brachium of superior colliculus. 2. Brachium of inferior colliculus.

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On transverse section of the midbrain, the cerebral (

Sylvius) aqueduct divides it into two main parts:

1. Tectum

: the smaller dorsal part behind the Sylvius aqueduct, and consists of: a. Two Superior Colliculi: reflex centers of vision. b. Two Inferior Colliculi: reflex centers of hearing.Internal Structures of the Midbrain

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2. Two cerebral peduncles:

the larger ventral part

in front of aqueduct, it consists of three parts: a.

Crus cerebri: the most anterior part which consists of pyramidal and corticonuclear fibers. b. Substantia Nigra: a thick lamina of gray mater. An extrapyramidal center. c. Tegmentum: the posterior part of the cerebral peduncle. Contains ascending tracts, nuclei of III & IV cranial nerves, reticular formation of the midbrain.

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Cranial nerves 3&4 (

oculomotor

and

trochlear) exit from the midbrainMidbrain also contains the headquarters of the reticular activating system

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Midbrain

On

each side contains red nucleus

and substantia nigraRed nucleus - rich in blood vessels; - info from cerebrum and cerebellum; - subconscious control of muscle tone & postureSubstantia nigra - ventral to the red nucleus; - melanin-containing; - secretes dopamine; - inhibits the excitatory neurons of the basal nuclei.Damage to the substantia nigra would cause what?

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The main nuclei of the midbrain:

1. Nucleus of

oculomotor nerve.

2. Nucleus of the trochlear nerve. 3. Red nucleus: important extrapyramidal centre. 4. Mesencephalon nucleus of the trigeminal nerve: for deep sensation. 5. Inferior colliculus: a centre for auditory reflexes. 6. Superior colliculus: a centre for visual reflexes. 7. Substantia nigra: an extrapyramidal centre. 8. Reticular formation.Internal Structures of the Midbrain

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Brain death tests

1.

Body temperature below

35°C.2. Fixed pupils, no reaction to light.3. Corneal reflex absent.4. Vestibulo-ocular reflex absent. 5. Cranial nerve reflexes absent. 6. Vomiting reflex absent.7. Respiratory movements absent if ventilation is stopped for 10 min.