Brainstem Anatomy and Function

Brain Stem and Cerebellum Overview

• The brain stem connects the brain to the spinal cord.
• The cerebellum is part of the metencephalon in the hindbrain.

Brain Divisions

• The hindbrain (rhombencephalon) includes the medulla oblongata and metencephalon (pons and cerebellum).
• The midbrain is also called mesencephalon.
• The forebrain (prosencephalon) contains the diencephalon and telencephalon.

Brain Stem Anatomy and Functions

• The brain stem contains the medulla oblongata, pons, and midbrain.
• The brainstem includes the ascending and descending tracts that extend along its length and originate or terminate in nerve nuclei within the brainstem.
• The brainstem contains 10 nuclei of the cranial nerves (III-XII) and their roots.
• Nerve fibers in the nuclei of the brainstem either begin or terminate in the structure.
• The reticular formation (formatia reticularis) is in this area, influencing human senses, the sensation of pain, and regulation of cardiovascular and respiratory systems.
• The fourth ventricle and cerebral aqueduct are also located here.

Brainstem Organization

• The anterior (ventral) part of the brain stem is the basis.
• The middle section is the tegmentum.
• The posterior (dorsal) part is the tectum (only in the midbrain)
• Functions include the conduit, cranial nerve, and integrative functions.
• The brainstem volume occupies 2% (30 cm3) of the total brain volume.

Myelencephalon

• Anteriorly, it features the anterior median fissure and sulci (anterolateral and posterolateral).
• The pyramid and roots of cranial nerves (VI, VII, VIII, IX, X, XI, XII) originate in the myelencephalon.
• Sulci (anterolateral and posterolateral), the pyramid, and the olive are present, as are inferior cerebellar peduncles.
• Cuneate and gracile tubercles and the roots of cranial nerves (VI, VII, VIII, IX, X, XI, XII) are also key features.

Pons Anatomy

• It has the basilar sulcus, middle cerebellar peduncles, and the roots of the trigeminal nerve (V).
• Middle cerebellar peduncles and the roots of the trigeminal nerve (V) are present.

Mesencephalon

• Cerebral peduncles, posterior perforated substance, and roots of cranial nerves (III, IV) are found here.
• Cerebral peduncles, corpora quadrigemina: superior and inferior colliculi and their brachii, and roots of cranial nerves (III, IV) originate their.
• Features the cerebral peduncles, corpora quadrigemina seu lamina tecti (superior and inferior colliculi and their brachii), and roots of cranial nerves (IV).

Rhomboid Fossa

• Includes the superior and inferior medullary velum, median sulcus, medial eminence, hypoglossa and vagal trigones, facial colliculus, and vestibular area.

Brain Stem Tegmentum: Ascending Tracts and Nuclei

• Gracilis et cuneatus – fasciculi and nuclei.
• Medial lemniscus and its decussation.
• Lateral lemniscus.
• Spinothalamic tract.
• Anterior spinocerebellar tract.
• Also features gracile and cuneate fasciculi and their nuclei, medial lemniscus and its decussation, as well as the anterior and spinocerebellar tracts
• Additionally has anterolateral fasciculus (ALF) or spinothalamic tract.

Cranial Nerve Nuclei in Brain Stem Tegmentum (III-XII)

• Motor nuclei are present.
• Sensory nuclei are present.

More Structures in the Brain Stem Tegmentum

• Includes the trapezoidal body and lateral lemniscus and the cochlear and superior olivary nuclei.
• Vental posteromedial nucleus of thalamus
• Trigeminal lemniscus
• Medial lemniscus
• Spinal thalamic tract

Additional Features

• Trigeminal nerve nuclei.
• Trigeminal lemniscus.
• Spinal tract of the trigeminal nerve are structures in the tegmentum
• Vestibular nuclei.
• Medial longitudinal fasciculus are located here

Fiber and Nerve Integration

• Fibers from nerves can converge into a single nucleus.
• Fibers from nuclei can converge into a single nerve.
• A mixed nerve will connect to several nuclei.

Functional Organization of Cranial Nerves

• There are 4 somatic motor nuclei (nn. III, IV, VI, XII).
• There are 3 branchiomeric nuclei (nn. V, VII, IX, X, XI) involved in mimicry, chewing, palate, pharynx, and laryngeal muscles.
• There are 4 parasympathetic (visceral motor) nuclei (nn. III, VII, IX, X).
• Sensory functions include: special somatic afferent (n. VIII), general somatic afferent (nn. V, IX, X), and special visceral afferent (nn. VII, IX, X).
• There are specialized regions that manage general and specific inputs such as visceral afferent, somato afferent, special somato afferent, and general somatic efferent nuclei.

Brain Stem Encephalic Structure

• The brain stem includes a complex of heterogeneous neurons known as the reticular formation (formatia reticularis).
• Neurons of these nuclei influence human sensations, pain sensation, and regulate the cardiovascular and respiratory systems.
• Neurons of the reticular formation associate with nuclei of the cranial nerves, cerebellum, and motor mechanisms of the brain stem and spinal cord.
• These neurons influence human movements, posture, and skeletal muscle tone.
• The fourth ventricle and cerebral aqueduct are located in the brain stem.

Role and Location

• The liquor exists in the cerebral aqueduct, median and lateral apertures of fourth ventricle, and the choroid plexus.

Cerebellum Functions and Anatomy

• The cerebellum (Latin for "little brain") is a key part of the hindbrain (metencephalon) with motor control functioning
• Can also be involved in cognitive functioning regulation and motor control
• Its movement-related functions are well-established
• Does not initiate movement, but contributes to coordination, precision, and accurate timing.
• The cerebellum contains cerebellar hemispheres, the vermis, and fissures (primary, horizontal, and posterior), and lobes (anterior, posterior, and flocculonodular).
• It also includes cerebellar cortex, central nuclei (fastigial, dentate, interpose – emboliform, and globose).
• The cerebellum contains tracts (posterior and anterior spinocerebellar, olivocerebellar, vestibulocerebellar, ponto cerebellar, and cerebellorubral fibers).
• The body consists of Hemispheres and Vermis. Middle and Inferior peduncles exist
• On the Cerebellars surface Fisures exist

Cerebellum Lobes

• Anterior lobe I-IV.
• Posterior lobe V-IX.
• Flocculonodular lobe X.
• Cortex 85% and primary Fissue

Internal Structure

• Cerebral crus
• Medial longitudinal fasciculus
• Nuclear layer of the Medulla oblongata
• Superior cerebellar peduncie
• Linguistic1
• Vermis

Explore the primary functions, anatomical divisions, and key structures of the brainstem. This includes the medulla oblongata, pons, and midbrain. Test your knowledge of cranial nerve nuclei, the reticular formation, and other components.