MEDULLA OBLONGATA.

PONS. MIDBRAIN: TECTUM, CEREBRAL PEDUNCLES, AQUEDUCT OF BRAIN.

Cerebrum

Diencephalon

Truncus

encephali

Cerebellum

5

Development

Development

Development

Development

Development

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BRAIN STEM

Slide 7.38b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 7.15a

BRAIN STEM

Attaches to the spinal cord

Parts of the brain stem

Midbrain

Pons

Medulla oblongata

Brain Stem

• Located btwn the cerebrum and the SC – Provides a pathway for tracts running btwn higher

and lower neural centers.

• Consists of the midbrain, pons, and medulla oblongata. – Each region is about an inch in length.

• Microscopically, it consists of deep gray matter surrounded by white matter fiber tracts.

• Produce automatic behaviors necessary for survival.

The human brain stem This composite structure extends from the top of the spinal cord into the center of

the forebrain. The pons, pineal gland, and colliculi are ordinarily surrounded by the cerebral cortex.

Brainstem: 3 major divisions

•Midbrain

•Pons

•Medulla

Brainstem

– Cranial nerve deficits in association with motor and sensory deficit

– Diplopi,

– vertigo,

– dysartria,

– dysphagia,

– disequilibrium

VENTRICLES IN BRAINSTEM

• Mesencephalon cerebral aqueduct

• Metencephalon 4th ventricle

• Mylencephalon 4th ventricle

TRUNCUS ENCEPHALI

MYELENCEPHALON PONS MESENCEPHALON

vermis

Occipital

Lobe Thalamus

Corpus callosum

Hypothalamus

Fornix

Anterior

commissure

Optic nerve

4th ventricle

Posterior commissure

pyramid

Mammillary body

Quadrigeminal

cistern

internal capsule basal ganglia

optic nerve optic tract

hypothalamus mammillary body

cerebral peduncle

interpeduncular fossa

flocculus

inferior olivary

nuclear complex

cerebellum

cerebellar tonsil

pyramid

pyramidal decussation

pons

optic chiasm

Anterior view of brainstem

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

Middle cerebellar

peduncle

Superior colliculus

Inferior colliculus Cerebral

peduncle

Superior cerebellar

peduncle

Inferior cerebellar

peduncle

Medulla

4th ventricle

Posterior view of brainstem

The Brainstem: Midbrain

Small section superior to the pons.

Part of the auditory pathways and visual reflexes

Also involved in regulating muscle tone/activity and coordination

Midbrain

Mostly composed of tracts of nerve fibers

Reflex centers for vision and hearing

Cerebral aquaduct – 3rd-4th ventricles

Midbrain

• Contains ascending and descending tracts to the cerebrum and thalamus.

• Reflex center for eye muscles.

• Also involved with processing visual and auditory information (connects head movements with visual and auditory stimuli).

Midbrain

• Located btwn diencephalon and pons.

– 2 bulging cerebral peduncles on the ventral side. These contain:

• Descending fibers that go to the cerebellum via the pons

• Descending pyramidal tracts

– Running thru the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain.

– The roof of the aqueduct (the tectum) contains the corpora quadrigemina

• 2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli

• 2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli

•Cranial nerves 3&4 (oculomotor and trochlear) exit from the midbrain

•Midbrain also contains the headquarters of the reticular activating system

Midbrain

• On each side, the midbrain contains a red nucleus and a substantia nigra – Red nucleus contains numerous blood vessels and receives

info from the cerebrum and cerebellum and issues subconscious motor commands concerned w/ muscle tone & posture

– Lateral to the red nucleus is the melanin-containing substantia nigra which secretes dopamine to inhibit the excitatory neurons of the basal nuclei.

• Damage to the substantia nigra would cause what?

Midbrain

THE BRAINSTEM: PONS

Superior to Medulla oblongata.

Contains more ascending and descending pathways.

Relays information from cerebrum to cerebellum.

Also includes sleep and respiratory centers.

Pons

The bulging center part of the brain stem

Mostly composed of fiber tracts

Includes nuclei involved in the control of breathing

PONS

• Connects the two halves of the cerebellum.

• Regulates breathing.

Pons • Literally means “bridge”

• Wedged btwn the midbrain & medulla.

• Contains: – Sensory and motor nuclei for 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 rhythm

– Nuclei & tracts that process and relay info to/from the cerebellum

– Ascending, descending, and transverse tracts that interconnect other portions of the CNS

The Brainstem: Medulla oblongata

Most inferior portion, functions as a conduction pathway (descending motor neuron pathways decussate here) Reflex centers for:

regulating heart rate

blood vessel diameter

coughing, sneezing

breathing

swallowing

MEDULLA OBLONGATA

The lowest part of the brain stem

Merges into the spinal cord

Includes important fiber tracts

Contains important control centers

Heart rate control

Blood pressure regulation

Breathing

Swallowing

Vomiting

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MEDULLA OBLONGATA • Composed of nerve tracts

to and from the brain (these tracts cross over left to right and right to left)

• May be regarded as an extension of the spinal cord

• Almost all of the cranial nerves arise from this region

Medulla Oblongata

Contains control centers for many subconscious activities • Respiratory rate • Heart rate • Arteriole constriction • Swallowing • Hiccupping • Coughing • Sneezing

Medulla Oblongata

Medulla Oblongata • Most inferior region of the brain stem.

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

• Ventrally, 2 ridges (the medullary pyramids) are visible. – 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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Medulla Oblongata • Nuclei in the medulla are associated w/

autonomic control, cranial nerves, and motor/sensory relay.

• Autonomic nuclei: – Cardiovascular centers

• Alter the rate and force of cardiac contractions

• Alter the tone of vascular smooth muscle

– Respiratory rhythmicity centers • Receive input from the pons

– Additional Centers

• Emesis, deglutition, coughing,

hiccupping, and sneezing

Medulla Oblongata

• Sensory & motor nuclei of 5 cranial nerves:

– Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12)

• Relay nuclei – Nucleus gracilis and nucleus

cuneatus pass somatic sensory information to the thalamus

– Olivary nuclei relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex.

Components of the brainstem • Sensory ascending pathways (dorsal):

– Relay nuclei, tracts

• Motor descending pathways (ventral) – Tracts, motor nuclei brainstem

• Cerebellar pathways – Tracts, cerebellar afferent and efferent nuclei

• Cranial nerve sensory and motor tracts – Cranial nerve nuclei, nerve entry and exit points

• CPGs: rhythmic chewing, respiration, cardiovascular regulation & gain adjustments for reflexes

• Modulatory systems: locus coeruleus, raphe & substantia nigra – Chemically coded nuclei

Ascending sensory pathways Fine discriminative touch, conscious proprioception

• Fasciculus gracilis: Terminates in the nucleus gracilis (medulla)

• Fasciculus cuneatus: Terminates (medulla) in the cuneate and accessory cuneate nuclei

Sensations of pain and temperature

• Lateral Spinothalamic Tract

– origin dorsal horn cells of the gray matter

– Fibers cross contralaterally through the anterior commissure and ascend to the VPL nucleus

Transmits sensations of touch

• Ventral Spinothalamic Tract

– origin cells of the posterior horn

– Fibers cross to the opposite side in the anterior commissure

Descending motor pathways Voluntary movement

• Lateral Corticospinal Tract

– Originates in large pyramidal cells (precentral gyrus)

– cross to the opposite side of the cord at the pyramidal decussation & terminate in the dorsal horn cells

• Ventral Corticospinal Tract

– Originates in the pyramidal cells (motor area of the cortex)

Impulses related to equilibrium and antigravity reflexes

• Vestibulospinal Tract

– Fibers originate in the vestibular nuclei of the medulla and terminate at level of the sacral spinal nerves

Connects vestibular complex and head and eye movement coordination center in medulla

• Medial Longitudinal Fasciculus

– Contains both ascending and descending fibers

Motor Hierarchy •Lateral group (extremities; fine motor control)

•Corticospinal tract

•Rubrospinal tract

•Medial group (axial musculature; rhythmic and postural movements)

•Vestibulospinal tract

•Tectospinal tract

•Reticulospinal tract

•“Final common path”: motor pool

Reticular Formation

• Extensive network of neurons that runs thru the medulla and projects to thalamic nuclei that influence large areas of the cerebral cortex.

– Midbrain portion of RAS most likely is its center

• Functions as a net or filter for sensory input.

– Filter out repetitive stimuli. Such as?

– Allows passage of infrequent or important stimuli to reach the cerebral cortex.

– Unless inhibited by other brain regions, it activates the cerebral cortex – keeping it alert and awake.

How might the “sleep centers” of your brain

work? Why does alcohol make you tired?

Reticular Formation

• “Core” of brainstem (midbrain, pons and medulla) composed of loosely organized neurons, outside of the major nuclear groups of the brainstem.

• Medial-to-lateral: raphe nuclei, gigantocellular region, small cell region

• Participate in widespread connections

• Rostral continuation of interneuronal network found in spinal cord

Dorsal Column/Medial Lemniscal system

•Secondary neuron is in brainstem: nucleus gracilis and cuneatus=dorsal column nuclei

•Output of dorsal column nuclei crosses midline and forms recognizable bundle: medial lemniscus

•Medial lemniscus fibers synapse in the thalamus in the ventroposterior nuclei

•Thalamic axons synapse in primary somatosensory cortex in several somatotopic maps with some segregation of submodalities

Tracing through the brainstem: Dorsal Column/Medial Lemniscal System

Corticospinal Tract

Ядра

черепних

нервів

Ядра

черепних

нервів

моторное ядро VI

слюноотделительные

ядра VII и IX

мостовое чувствит. ядро V

ядра нижней оливы

среднемозговое

чувствит. ядро V

моторное ядро IV

моторное ядро III

вегетативное ядро III

дорзальное ядро X

(вегетативное)

моторное ядро XII

двойное ядро (IX и X)

спинальное чувствит. ядро V

пучок ядра одиночного пути

X

IV

VIII

r. spinalis XI

r. cranialis XI

III

Ganglion

n. trigeminalis

V

VI

VII

ganglii

IX

ганглии

Нижня

поверхня

мозку

Восходящие и

нисходящие пути

ствола головного

мозга и мозжечка

Роль нейронов дыхательного центра

ствола головного мозга в управлении

дыханием.

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