New—Lab 3: The brainstem

Neuroanatomy lab navigation

Parts of the brainstem

lab03-00a-brainstem-vector

Midbrain

Mesencephalon

lab03-00b-brainstem-vector

Pons

Metencephalon

lab03-00c-brainstem-vector

Medulla

Myelencephalon

See Figure 3.1, Review 3.1, and Review 3.2.

  • The basal subdivision of the brainstem is the most anterior and contains mostly the descending fiber tracts.
  • The tegmentum is the location of the cranial nerve nuclei, ascending fiber tracts, and the reticular formation. In the medulla, it also contains important neurons that are involved in cardiovascular and breathing reflexes.
  • The tectum, which is posterior to the tegmentum, is really only prominent in the midbrain and is grossly represented by the superior and inferior colliculi. It contains the nuclei that are involved in vision, hearing, and reflexive control of pupillary constriction. Tectospinal tracts originating in the tectum supply the postural muscles that directly initiate reflexive movement to auditory and visual stimuli.
  • Brain stem vascular lesions lead to multiple signs that may seem unrelated but can often be localized to a specific brain stem region. Knowledge of the brain stem anatomy will help with the localization. Examples of this will be presented in the functional neuroanatomy and circulation lecture.

Figure 3.1. Subdivisions of the brainstem; mid-sagittal plane. Three subdivisions of the brainstem:

    1. Tectum

    2. Tegmentum

    3. Basal region 


Figure from Neuroanatomy: 
A Laboratory Guide (2e); Jansen and Lampa (2018).

Review 3.2.

Subdivisions of the brainstem; mid-sagittal plane. 
 (Tap the right arrow for labels)

Specimen from Neuroanatomy Collection, Washington State University College of Veterinary Medicine.

Check yourself

On a sagittal image of a brainstem, locate the tegmentum and tectum (Figure 3.1 and Review 3.2).

The general regions of the brain stem will be a review from FMS 501. The portions of the brain stem and their specific important nuclear groups and tracts contained within will be discussed in the Functional Neuroanatomy and Circulation LGA sessions.

Utilize the external topography of the brain stem to locate internal structures as you a beginning to learn the cross sectional and and the related significance to lesion localization.

Examine the external topography of the brainstem and cerebellum and identify the following structures (Figure 3.2 and Figure 3.3):

    • Midbrain
      • Superior and inferior colliculi
      • Cerebral peduncles (aka crus cerebri)
      • Axons of cranial nerves III and IV
    • Pons
      • Basal pons (aka basis pontis or base of pons)
      • Middle cerebellar peduncle
      • Axons of cranial nerve V
    • Pons/Medulla junction
      • Axons of cranial nerves VI, VII, and VIIII
    • Medulla
      • Pyramids
      • Olives (inferior olivary nucleus)
      • Axons of cranial nerves IX, X, XI, XII
    • Cerebellum (pictured in Figure 3.3)
      • Vermis: Separates two cerebellar hemispheres
    • Cerebellar tonsil
Go to cranial nerves in the brain
Figure 3.2. Ventral and dorsal surfaces of the brainstem. 
From Brainstem II: Pons and Cerebellum; Essential Neuroscience, 3e, 2015; 
Copyright © Wolters Kluwer.
Figure 3.3. Cerebellar anatomy. The Brain Stem and Cerebellum, Waxman SG. Clinical Neuroanatomy, 28e; 2017. Copyright © 2018 McGraw-Hill Education. All rights reserved.

Note the exit points of the cranial nerve axons from medial to lateral on the brainstem (Figure 3.2 and Figure 3.4).

The cerebellopontine angle is located laterally at the junction of the caudal pons and cerebellum. A patient with a tumor in this area would have what signs or symptoms related to cranial nerve dysfunction?

 

Thought question
Describe a common benign neoplasm that could affect structures in this region.

The cerebellar tonsil may herniate into the brainstem, leading to significant mortality with increases in intracranial pressure.

Figure 3.4. Inferior surface of the cerebrum and brainstem with cranial nerves. (Note the attachment points of Cranial Nerves I–XII to the cerebrum, diencephalon, and brainstem.) Wikimedia.org.

Table 3.1. Review of cranial nerves: Numbers, names, and basic functions

Number

Name

Basic function (afferent or efferent)

I

Olfactory

Transmits smell to CNS

II

Optic

Transmits visual information to CNS

III

Oculomotor

Innervates inferior rectus, superior rectus, levator palpebrae superioris, medial rectus and inferior oblique; visceral motor (parasympathetic [PS] to sphincter pupillae and ciliary muscle)

IV

Trochlear

Innervates the superior oblique muscle

V

Trigeminal

  • Ophthalmic
  • Maxillary
  • Mandibular

Transmits somatic afferent sensory information from the face, cornea, and anterior portion of the tongue; innervates muscles of mastication, palate, and middle ear (Mandibular n.)

VI

Abducens

Innervates lateral rectus muscle

VII

Facial

Transmits taste from anterior portion of the tongue; provides motor innervation to muscles of the face; supplies visceral motor (PS) information to mucous glands in nasal and oral cavities, salivary glands, and lacrimal gland

VIII

Vestibulocochlear

Transmits hearing and balance information from the inner ear

IX

Glossopharyngeal

Transmits taste and general sensations from posterior portion of the tongue and pharynx, innervates pharyngeal muscles, supplies visceral motor information to the parotid salivary gland

x

Vagus

Transmits sensations from larynx and pharynx, supplies visceral motor information to thoracic and abdominal viscera to descending colon; supplies innervation to laryngeal and pharyngeal muscles

XI

Accessory

Innervates trapezius and sternocleidomastoid; innervation to laryngeal muscles via vagus

XII

Hypoglossal

Innervates muscles of the tongue

Image credits

Unless otherwise noted, images are from Adobe Stock.

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Headshot of Steve Lampa, PhD · Clinical Associate Professor
Steve Lampa
PhD · Clinical Associate Professor
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