Brainstem and Cerebellum Anatomy

Brainstem and Cerebellum

• The brainstem and cerebellum are crucial parts of the central nervous system.
• The brain consists of the telencephalon (cerebrum), diencephalon, brainstem, and cerebellum.

Divisions of the CNS

• Telencephalon/Cerebrum: the largest part of the brain, divided into two hemispheres.
• Diencephalon: connects the midbrain to the cerebrum and comprises the epithalamus, thalamus, subthalamus, and hypothalamus. It is located deep inside the brain.
• Midbrain/Mesencephalon
• Pons
• Cerebellum: a fist-sized portion of the brain, located at the back of the head above the brainstem, and it has two hemispheres.
• Bulbus/Medulla oblongata

Brainstem Overview

• The oculomotor nerve (III) is located at the interpeduncular fossa and leaves between the midbrain and pons.
• The trochlear nerve (IV) exits the brainstem on its posterior surface between the midbrain and pons.
• The trigeminal nerve (V) leaves the pons from its anterolateral surface.
• The abducens (VI), facial (VII), and vestibulocochlear (VIII) nerves leave the brainstem at the medullopontine sulcus.
• The glossopharyngeal (IX), vagus (X), and accessory (XI) nerves leave the brainstem from the retroolivary groove.
• The hypoglossal nerve (XII) leaves the brainstem from the preolivary groove, located between the pyramid of the medulla and the oliva (inferior olivary complex).

Medulla Oblongata (Bulbus)

• The IX, X, and XII cranial nerves are associated with the medulla oblongata.
• The pre-olivary and retro-olivary grooves are anatomical landmarks of the medulla oblongata.
• Nucleus of hypoglossal nerve.
• Gracile nucleus (Goll's nucleus), cuneate nucleus (Burdach's nucleus), and accessory cuneate nucleus.
• Nuclei of the solitary tract.
• Inferior olivary complex (oliva); related to voluntary movement and determining the direction of sound.
• Raphe nuclei; seratonine.
• Spinal nucleus of the trigeminal nerve.
• Nucleus ambiguus.
• Vestibular nuclei; related to balance.
• Cochlear nuclei; related to hearing.
• Inferior salivatory nucleus.
• Dorsal (posterior) nucleus of the vagus nerve.
• Common special sense nucleus of VII, IX, & X.
• The brainstem nucleus relates to taste sense and reflex control of the cardiovascular and respiratory systems.
• The spinal nucleus of the trigeminal nerve is between the C3 spinal cord segment and the pons.
• Second-order neurons of pain and temperature senses from the head and face.
• First-order neurons are located at the sensory ganglia of the V, VII, IX, & X cranial nerves.
• The motor nerve for nerves IX, X, and XI
• Axons travel inside these nerves and reach the muscles of the larynx, pharynx, soft palate, and some muscles of the esophagus.
• The parasympathetic nucleus of the glossopharyngeal nerve (IX).
• Parasympathetic axons provide secretion of the parotid gland.
• The parasympathetic nucleus of the vagus nerve (X) is the dorsal (posterior) nucleus
• Axons provide parasympathetic innervation to thoracic and intra-abdominal organs of the digestive tract between the esophagus and left colic (splenic) flexure.

Pons

• The basilar part of the pons (anterior) includes longitudinal pontine fibers, transverse pontine fibers, and pontine nuclei.
• The tegmentum of the pons (posterior) contains the CN nuclei of V, VI, VII, and VIII.
• Principal sensory nucleus of the trigeminal nerve.
• Motor nucleus of the trigeminal nerve.
• Superior salivatory nucleus.
• Superior vestibular nucleus.
• Cochlear nuclei.
• Second-order neurons of pressure and touch senses from the head and face.
• First-order neurons are located at the sensory ganglia of cranial nerves V, VII, IX, & X.
• This nucleus is related to the cornea reflex.
• Masticatory muscles + anterior belly of the digastric, mylohyoid, tensor tympani, and tensor veli palatini.
• The parasympathetic nucleus of the facial nerve (VII).
• The superior salivatory nucleus's upper portion is known as the lacrimal nucleus
• Parasympathetic axons provide the lacrimal, sublingual, submandibular, and minor gland secretion.

Midbrain

• The cerebral peduncle and tegmentum of the midbrain are anatomical structures.
• The quadrigeminal (tectal) plate is an important part of the midbrain.
• The interpeduncular fossa is a region located between the cerebral peduncles.
• The cerebral crus is part of the midbrain structure.
• The midbrain structures include the cerebral crus, substantia nigra, red nucleus, tegmentum, and cerebral aqueduct.
• Dopamine deficiency in the substantia nigra causes Parkinson's disease.
• The quadrigeminal (tectal) plate is a key feature.
• The midbrain includes the pineal gland, superior colliculus, inferior colliculus, and trochlear nerve.
• Mesencephalic nucleus of the trigeminal nerve: carries proprioceptive information from the face region, including muscles of eye movement and mastication.
• Trochlear nerve nucleus: the trochlear nerve leaves the brainstem from its posterior surface at the border of the midbrain and pons, just below the inferior colliculus.
• Innervates the superior oblique muscle of the eyeball.
• Occulomotor nucleus.
• Innervates the rectus superior, rectus inferior, rectus medialis, obliquus inferior muscles of the eyeball, and levator palpebrae superioris.
• Controls the pupilla via the Edinger-Westphal nucleus
• This nucleus is related to pupillary light reflex and connects to Edinger-Westphal's nucleus (parasympathetic nucleus of III).
• The pretectal nucleus of one side connects to Edinger-Westphal's nucleus, causing constriction of the pupil with light exposure.
• Miosis on the same side is called the direct pupillary light reflex, while miosis on the opposite side is called the indirect (consensual) pupillary light reflex.
• The red nucleus is at the level of the superior colliculus and is related to flexor muscle tone.
• It operates when swinging the arms while walking.

Cerebellum

• The primary function is the coordination of movements, continuation of posture, and balance by arranging muscle tone.
• The cerebellum has two hemispheres connected by a vermis.
• Cerebellar nuclei include the dentate, emboliform, globose, and fastigial nuclei.
• The dentate nucleus (D) is the most laterally positioned and largest cerebellar nucleus and is related to the coordination of movement.
• The emboliform (E) and globose (G) nuclei relate to muscle tone, known as the nucleus interpositus and have connections with the spinal cord.
• The fastigial nucleus (F) is the most medially positioned and is related to the vestibular system.
• The cerebellum is active in voluntary and involuntary muscular activities and provides balance.
• It ensures movements are made to fit their purpose and with coordination.
• Cerebellar lesions result in ipsilateral symptoms.
• There is no loss of motor function or sensation, but cerebellar ataxia (ataxic gait) is the most characteristic symptom.
• Patients cannot walk straight and appear drunk.
• Disequilibrium (balance disorder) and vertigo may occur, leading to falls toward the lesion side and dizziness.
• Hypotonia, decreased muscle tone, and slowed reflexes are common.
• Dissynergia is the impaired coordination of regular movements.
• Patients cannot perform the finger-to-nose test.
• There is a negative rebound phenomenon due to impaired antagonist muscle action.
• Dysmetria, disorder in the range of movement.
• Tremor is seen in the limbs, more distinct when reaching for a target, and absent at rest.
• When the cerebellum is damaged, the patient cannot perform the finger-tip coordination test properly.
• Patients cannot stand still with their feet together and eyes closed.

Diencephalon

• The diencephalon is located between the cerebral hemispheres and the midbrain.
• The four parts of the diencephalon are the thalamus (dorsal thalamus), subthalamus (ventral thalamus), epithalamus, and hypothalamus.
• The epithalamus is the posterosuperior part of the diencephalon, containing the pineal gland and habenular nuclei.
• Habenular nuclei are part of the limbic system and are related to emotions and behavior.
• They also participate in the regulation of visceral and endocrine activities.
• Plays an important role in sleep mechanisms
• The pineal gland (pineal body, epiphysis) is an endocrine gland shaped like a small pine cone at the roof of the diencephalon.
• The pineal gland converts light signals into endocrine signals from the external environment falling on the retina and responds.
• Activity of the gland increases in the dark
• Melatonin is secreted from pinealocytes as a result of activity of the gland in darkness.
• Affects metabolic functions.
• The subthalamus (ventral thalamus) is below the thalamus.
• It is related to motor function.
• The subthalamic nucleus regulates muscle activity.
• The thalamus (dorsal thalamus) is the largest part of the diencephalon.
• The thalamus organizes sensory information, except smell, before it reaches the cerebral cortex.
• The thoughts, regulation of creativity, emotions & behavior, interpretation, awareness of the environment, attention, and alertness
• The ventral posterolateral nucleus (VPL) regulates the somatic sensory pathways.
• 3rd order neurons.
• The brain area takes sensory information from the trunk and limbs.
• The 3rd order neurons from VPL and VPM reach the primary somatic sensory area BAs: 3,1,2.
• Neurons related to taste senses reach the primary taste cortex BA 43
• Anterior nuclei of the thalamus are related to memory, behavior, and emotion, these features are part of the limbic system.
• These areas are related to sleep and memory.
• Ventral anterior and lateral nuclei (motor thalamus): regulate motor pathways from basal nuclei to the cerebral cortex.
• Control voluntary movements.
• Metathalamus contains small bumps, the lateral and medial geniculate bodies.
• The third-order neurons for the visual system originate from the lateral geniculate body (nucleus)
• Lateral geniculate body provides the orientation of the visual system to visual input.
• The third-order neurons of the auditory system originate from the medial geniculate body (nucleus).
• Medial geniculate body provides the information about intensity and duration of sound.
• The hypothalamus is in the ventral part of the diencephalon and controls visceromotor & endocrine activities, regulating body temperature.
• Front and medial parts of the hypothalamus control the parasympathetic system, while the back and lateral parts control the sympathetic system.
• The preoptic area regulates body temperature (thermoregulation) and creates the feeling of thirst
• The suprachiasmatic nucleus receives impulses from the retina and regulates circadian rhythms, playing a part in the sleep-wake cycle.
• The supraoptic nucleus relates to water balance.
• Majority of the ADH (vasopressin) is produced in this nucleus, helping vasoconstriction
• Decreased ADH production results in diabetes insipidus, leading to increased polyurea and compensatory thirst.
• The anterior hypothalamic nucleus regulates body temperature and has parasympathetic effects as well
• The nucleus decreases the body temperature using vasodilation to create sweating.
• The paraventricular nucleus produces oxytocin (Oxt), related to lactation
• Oxytocin causes milk production during childbirth by contracting the uterus
• In the hypothalamus. lateral areas, the ventromedial nucleus provides sensations of satiety.
• Hunger and a feeling of fullness is related to this area of the brain.
• The posterior nucleus of the hypothalamus regulates body temperature using sympathetic effects and controlling optimal body temperature levels
• Mammillary nucleus, located inside the mammillary bodies, is connected to processes of emotions and short-term memory