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Brain Development and Tissue Organization
Brain Development and Tissue Organization
a. Embryonic Development of the Brain
By the late fourth week of development, this growth has formed three primary brain vesicles, which eventually give rise to all the different regions of the adult brain.
The forebrain is called the prosencephalon; the midbrain is called the mesencephalon; and the hindbrain is called the rhombencephalon.
By the fifth week of development, the three primary vesicles further develop into a total of five secondary brain vesicles:
The telencephalon: arises from the prosencephalon and eventually forms the cerebrum.
The diencephalon arises from the prosencephalon and eventually forms the thalamus, hypothalamus and epithalamus.
The mesencephalon is the only primary vesicle that does not form a new secondary vesicle.
The metencephalon arises from the rhombencephalon and eventually forms the pons and the cerebrum.
The myelencephalon also derives from the rhombencephalon and it eventually forms the medulla oblongata.
b. Organization of Neural Tissue Areas in the Brain
Two distinct tissue areas are recognized within the brain and spinal cord.
The gray matter houses motor neuron and interneuron cell bodies, dendrites, telodendria and unmyelinated axons.
The white matter derives it color from the myelin in the lyelinated axons.
During brain development, an outer, superficial region of gray matter forms from migrating peripheral neurons.
As a result, the external layer of gray matter, called the cerebral cortex, covers the surface of most of the adult brain.
The white matter lies deep to the gray matter of the cortex.
Finally, within the masses of white matter, the brain also contains discrete internal clusters of gray matter called cerebral nuclei, which are oval, spherical, sometimes irregularly shaped clusters of neuron cell bodies.
Support and Protection of the Brain
Support and Protection of the Brain
The brain is protected and isolated by multiple structures.
The bony cranium provides rigid support, while protective connective tissue membranes called meninges surround, support, stabilize and partition portion of the brain.
CSF acts as a cushioning fluid.
Finally, the brain has a blood-brain barrier to prevent harmful materials from leaving the bloodstream.
Cranial Meninges
The cranial meninges are three connective tissue layers that separate the soft tissue from the bones of the cranium, enclose and protect blood vessels that supply the brain, contain and circulate CSF.
From deepest to superficial, the cranial meninges are the pia mater, the arachnoid mater and the dura mater.
Pia Mater
The pia mater is the innermost of the cranial meninges.
It is a thin layer of delicate areolar connective tissue that is highly vascularized and tightly adheres to the brain, following every contour of the surface.
Arachnoid Mater
The arachnoid mater, also called the arachnoid membrane, lies external to the pia mater.
The term arachnoid means "resembling a spider web", and this meninx is so named because it is partially composed of a delicate web of collagen and elastic fibers, termed the arachnoid trabeculae.
Immediately deep to the arachnoid mater is the subarachnoid space.
The arachnoid trabeculae extend throught this space from the arachnoid mater to the underlying pia mater.
Between the arachnoid mater and the overlying dura matter is a potential space, the subdural space.
Dura Mater
The dura mater is an external tough, dense irregular connective tissue layer composed of two fibrous layers.
Within the cranium, the dura mater is composed of two layers.
The meningeal layer lies deep to the periosteal layer.
The periosteal layer, the more superficial layer, forms the periosteum on the internal surface of the cranial bones.
The meningeal layer is usually fused to the periosteal layer, except in specific areas where the two layers separate to form large, blood-filled spaces called dural venous sinuses.
The dural venous sinuses are, in essence, large veins that drain blood from the brain and transport the blood to the internal jugular veins that help drain blood circulation of the head.
The dura mater and the bones of the skull may be separated by the potential epidural space, which contains the arteries and veins that nourish the meninges and bones of the cranium.
Cranial Dural Septa
The meningeal layer of the dura mater extends as flat partitions intoo the cranial activity at four locations.
Collectively, these double layers of dura mater are called cranial dura septa.
These membranous partitions spaces separate specific parts of the brain and provide additional stabilization and support to the entire brain.
There are four cranial dura septa:
The Falx Cerebri
It is the largest of the four dural septa.
This large, sickle-shaped vertical fold of dura mater, located in the mid-sagittal plane projects into the longitudinal fissure between the left and right cerebral hemisphere.
Anteriorly, its inferioir portion attaches to the crista galli of the ethmoid bone, posterioly its inferior portion attaches to the internal occipital crest.
Running within the margin of this dural septa are two dural venous sinses: the super sagittal sinus and the inferior sagittal sinus.
The Tentorium Cerebelli
It is a horizontally oriented fold of dura mater that separates the occipital and temporal lobes of the cerebrum from the cerebellium
It is named for the fact that it forms a dural tent over the cerebellum.
The transverse sinuses run within its posterior border.
The anterior surface of the tentorium cerebelli has a gap or opening, called the tentorial notch, to allow for the passage of the brainstem.
The Falx Cerebelli
Extending into the mid-sagittal line inferior to the tentorium cerebelli is the falx cerebelli, a sickle-shaped vertical partition that divides the left and right cerebellar hemispheres.
A tiny occipital sinus runs in its posterior vertical border.
The Diaphragma Sellae
The smallest of the dural septa is the diaphragma sellae, which forms a roof over the sella turcica of the sphenoid bone;
A small opening within it allows for the passage of a thin stalk, called the infundibulum, that attaches the pituitary gland to the base of the hypothalamus.
Brain Ventricules
Ventricules are cavities or expansions within the brain that are derived from the lumen of the embryonic neural tube.
There are four ventricules in the brain.
Two lateral ventricules are in the cerebrum, separated by a thin medial partition called the septum pellucidum.
Within the diencephalon is a smaller ventricule called the third ventricule.
Each lateral ventricule communicates with the third ventricule though an opening called the interventricular foramen.
A narrow canal called the cerebral aqueduct, passes through the mesencephalon and connects the third ventricule with the tetrahedron-shaped fourth ventricule.
The fourth ventricule is located between the pons/medulla and the cerebrum.
Cerebrospinal Fluid
Cerebrospinal Fluid (CSF) is a cleat, colorless liquid that ciruclates in the ventricules and the asubarachnoid space.
CSF performs the several important functions:
Buoyancy
Protection
Environmental Stability
CSF Formation
It is formed by the choroid plexus in each ventricule.
The choroid plexus is composed of a layer of ependymal cells and the capillaries that lie within the pia mater.
CSF is produced by secretion of a fluid from the ependymal cells that originates from the blood plasma.
CSF Circulation
CSF is produced by the choroid plexus in the ventricules
CSF flows from the third ventricule through the cerebral aqueduct into the fourth ventricule.
CSF in the fourth ventricule flows into the subarachnoid space by passing through the paired lateral apertures or the single median aperture, and into the central canal of the spinal cord.
As the CSF flows through the subarachnoid space, it removes waste products and provides buoyancy to support the brain.
Excess CSF flows into the arachnoid villi, then drains into the dural venous sinuses. Pressure allows the CSF to be released into the blood without permitting any venous blood to enter the subarachnoid space. The greater pressure on the CSF in the subarachnoid space ensures that CSF moves into the venous sinuses.
Blood-Brain Barrier
Nervous tissue is protected from the general circulation by the blood-brain barrier (BBB), which strictly regulates what substances can enter the interstitial fluid of the brain.
The BBB keeps the neurons in the brain from being exposed to drugs, waste products in the blood, and variations in levels of normal substances that could adversely affect the brain function.
Cerebrum
Cerebrum
The cerebrum is the location of conscious thought processes and the origin of all complex intellectual functions.
The cerebrum is formed from the telencephalon.
The surface of the cerebrum folds into elevated ridges, called gyri, which allow a greater amount of cortex to fit into the cranial activity.
Adjacent gyri are separated by shallow sulci or deeper grooves called fissures.
Cerebral Hemispheres
The cerebrum is composed to two halves, called the left and right cerebral hemispheres.
The paired cerebral hemisphere are separated by a deep longitudinal fissure that extends along the mid-sagittal plane.
The cerebral hemispheres are separate from one another, except at a few locations where bundles of axons are called tracts from white matter regions that allow for communication between them.
The largest of these white matter tracts, the corpus callosum, connects the hemispheres.
Lobes of the Cerebrum
Each cerebral hemisphere is divided into five anatomically and functionally distinct lobes.
The Frontal Lobe
It lies deep to the frontal bone and forms the anterior part of the cerebral hemisphere.
The frontal lobe ends posteriorly at a deep groove called the central sulcus that marks the boundary with the parietal lobe.
The inferior border of the frontal lobe is marked by the lateral sulcus, a deep groove that separates the frontal and parietal lobes from the temporal lobe.
An important anatomic feature of the frontal lobe is the pre-central gyrus, which is a mass of nervous tissue immediately anterior to the central sulcus.
The frontal lobe is primarily concerned with voluntary motor functions, decision making, planning and personality.
The Parietal Lobe
It lies internal to the parietal bone and forms the superoposterior part of each cerebral hemisphere.
It terminates anteriorly at the central sulcus, posteriorly at a relatively indistinct parieto-occiptal sulcus, and latrally at the lateral sulcus.
An important anatomic feature of this lobe is the postcentral gyrus, which is a mass of nervous tissue immediately posterior to the central sulcus.
The parietal lobe is involved with general sensory functions such as evaluating the shape and texture of objects being touched.
The Temporal Lobe
It lies inferior to the lateral sulcus and underlies the temporal bone.
The lobe is involved with hearing and smell.
The Occipital Lobe
It forms the posterior region of each hemisphere and immediately underlies the occipital bone.
This lobe is responsibile for processing incoming visual information and storing visual memories.
The Insula
It is a small lobe deep to the lateral sulcus.
Its primary functions are interpretation of taste and memory.
Functional Areas of the Cerebrum
Motor Areas
The cortical areas that control motor functions are housed within the frontal lobes.
The primary motor cortex, also called the somatic motor area, is located within the precentral gyrus of the frontal lobe.
Neurons there control voluntary skeletal muscles activity. The axons of these neurons project contralaterally to the brainstem and spinal cord. Thus, the left primary moto cortex controls the right side voluntary muscles and vise versa.
The innervation of the primary motor cortex to various body parts can be diagrammed as a motor homunculus.
The motor speech area, previously called the BROCA Area, is located in most individuals within the inferolateral portion of the left frontal lobe. This region is reponsible for controlling the muscular movements necessary for vocalization.
The front eye field is on the superior surface of the middle frontal gyrus, which is immediately anterior to the premotor cortex in the frontal lobe. These cortical areas control and regulate the eye movements needed for reading coordinating binocular vision.
Sensory Areas
The cortical areas within the parietal, temporal and occipital lobes typically are involved with conscious awareness of sensation.
The primary somatosensory cortex is housed within the postcentral gyrus of the parietal lobes. Neurons in this cortex receive general somatic sensory information from touch, pressure, pain and temperature receptors.
The primary visual cortex, located at the occipital lobe, receivves and processes incoming visual information.
The primary auditory cortex, located in the temporal lobe, receives and processes auditory information.
The primary gustatory cortex is in the insula and is involved in processing taste information
The primary olfactory cortex, located in the temporal lobe, provides conscious awareness of health.
Association Areas
The primary motor and sensory cortical regions are connected to adjacent association areas that either process and interpret incoming data or coordinate a motor response.
Association areas integrate new sensory inputs with memories of past experiences.
The premotor cortex, also called the somatic motor association area, is located in the frontal lobe, immediately anterior to the precentral gyrus. It permits us to process motor information and is primarily responsible for coordinating learned skill motored activities.
The somatosensory association area is located in the parietal lobe and lies immediately posterior to the primary somatosensory cortex. It interprets sensory information and is responsible for integreating and intepreting sensations to determine the texture, temperature, pressure and shape of objects. It also allows us to identify objects while our eyes are closed.
The auditory association area is located within the temporal lobe, posteroinferior to the primary auditory cortex. Within this area, the cortical neurons interpret the characteristics of sound and store memories of sounds heard in the past.
The visual association area is located in the occipital lobe and surrounds the primary visual area. It enables us to process visual information by analyzing color, movement and form and to use this information to identify the things we see.
A functional brain region acts like a multi-association area between lobes for integrating information from individual association areas. One functional brain region is the WERNICKE Area, which is typically located only within the left hemisphere, where it overlaps the parietal and temporal lobes. The Wernicke area is involved in recognizing, understanding, and comprehending spoken or written language.
Another functional brain region, called the gnostic area, is composed of regions of the parietal, occipital and temporal lobes. This region integrates all sensory, visual and auditory information being processed by the association areas witthin these lobes. Thus, it provides comprehensive understanding of a current activities.
Higher-Order Processing Centers
These centers process incoming information from several different association areas and ultimately direct either extremely complex motor activity or complicated analytical functions in response.
Central White Matter
The central white matter lies deep to the gray matter of the cerebral cortex and is composed primarily of myelinated axons.
Most of these axons are grouped into bundles called tracts:
Association Tracts
It connects different regions of the cerebral cortex within the same hemisphere.
Short association tracts are composed of arcuate fibers; they connect neighboring gyri within the same lobe.
The longer association tracts, which are composed of longitudinal fasciulli, connect gyri in different lobes of the same hemisphere.
Commissural Tracts
It extends between the cerebral hemispheres through axonal bridges called commissures.
The prominent commissural tracts that link the left and right cerebral hemisphere include the large, C-shaped corpus callosum and the smaller anterior and posterior commissures.
Projections Tracts
It link the cerebal cortex to the inferior brain regions and the spinal cord.
Cerebral Nuceli
The cerebral Nuclei are paired, irregular masses of gray matter buried deep within the central white matter in the basal region of the cerebral hemispheres inferior to the floor of the lateral ventricle.
Cerebral Nuclei have the following components:
The C-shaped Caudate nucleus
It has an enlarged head and a slender, arching tail that parallels the swinging curve of the lateral ventricule.
When a person begins to walk, the neurons in the nucleus stimulate the appropriate muscles to produce the pattern and rhythm of arm and leg movements associated with walking.
The Amygdaloid Body
It is an expanded region at the tail of the caudate nucleus.
It participates in the expressions of emotions, control of behavioral activities and development of moods.
The Putamen and The Globus Pallidus
They are two masses of gray matter positioned between the bulging external surface of the insula and lateral wall of the diencephalon.
The putamen and globus pallidus combine to form a larger body, the lentiform nucleus, which is usually a compact, almost rounded mass.
The putamen functions in controlling muscular movement at the subconscious level, while the globus pallidus both excites and inhibits the activities of the thalamus to control and adjust muscle tone.
The Claustrum
It is a thin silver of gray matter formed by a layer of neurons located immediately to the cortex of the insula and derived from that cortex.
It processes visual information at a. subconscious level.
The term corpus striatum describes the striated or striped appearance of the internal capsule as it passes among the caudate nucleus and the lentiform nucleus.
Diencephalon
Diencephalon
The Diencephalon is a part of the of the prosencephalon sandwiched between the inferior regions of the cerebral hemispheres.
The components of the diencephalon include:
Epithalamus
The epithalamus partially forms the posterior roof of the diencephalon and covers the third ventricule.
The posterior portion of the epithalamus houses the pineal gland and the habenular nuclei.
The Pineal gland is an endocrine gland. It secretes the hormone melatonin, which appears to help regulate day-night cycle known as the body circadian rhythm.
The Habenular Nuclei help relay signals from the limbic system to the mesencephalon and are involved in visceral and emotional response to colors.
Thalamus
The thalamus refers to paired oval masses of gray matter that lie on each side of the third ventricule.
The thalamus forms the superolateral walls of the third ventricule.
The interthalamic adhesion is a small, midline of gray matter that connects the right and left thalamic bodies.
Each part of the thalamus is a gray matter composed of about a dozen major thalamic nuclei that are organized into groups, axons from these nuclei project to particular regions of the cerebral cortex.
The thalamus is the principal and final relay point for sensory information that will be processed and projected to the primary somatosensory cortex. Only a relatively small portion of the sensory information that arrives at the thalamus is forwarded to the cerebrum because the thalamus acts as an information filter.
Hypothalamus
The hypothalamus is the anteroinferior region of the diencephalon.
A thin, stalklike infundibulum extends inferiorly from the hypothalamus to attach to the pituitary gland.
Functions of the Hypothalamus
Master control of the Autonomic Nervous System.
Master Control of the Endocrine System.
Regulation of Body Temperature.
Control of Emotional Behavior.
Control of Food Intake.
Control of Water Intake.
Regulation of Sleep-Wake Rhythms.
Brainstem
Brainstem
The brainstem connects to the prosencephalon and cerebellum to the spinal cord.
Three regions form the brainstem:
Mesencephalon
The mesencephaon (midbrain) is the superior portion of the brainstem.
Extending through the mesencephalon is the cerebral aqueduct connecting the third and fourth ventricules, it is surrounded by a region called the periaqueductal gray matter.
Cerebral Peduncles are motor tracts located on the anterolateral surfaces of the mesencephalon.
The tegmentum is sandwiched between the substantia nigra and the periaqueductal gray matter.
The tegmentum contains the pigmented red nuclei and the reticular formation.
The tegmentum integrates information from the cerebrum and cerebellum and issues involuntary motor commands to the erector spinae muscles of the back to help maintain posture while standing, bending at the waist, or walking.
The substantia nigra consists of bilaterally symmetrical nuclei within the mesencephalon.
Its name derives from its almost black appearance, which is due to melanin pigmentation.
The substantia nigra is squeezed between the cerebral peduncles and the tegmentum.
It houses clusters of neurons that produce the neurotransmitter dopamine, which affects brain processes that control movement, emotional response, and ability to experience pleasure and pain.
The Tectum is the posterior region of the mesencephalon dorsal to the cerebral aqueduct.
It contains two pairs of sensory nuclei, the superior and inferior colliculi, which are collectively called the tectal plate. These nuclei are relay stations in the processing pathway of visual and auditory sensations.
The superior colliculi are the superior nuclei. They are called visual reflex center because they help visually track moving objects and control reflexes.
The paired inferior colliculi are the auditory reflex centers, meaning that they control reflexive turning of the head and eyes in the direction of a sound.
Pons
The pons is a bulging region on the anterior part of the brainstem that forms from part of the metencephalon.
Housed within the pons are sensory and motor tracts that connect to the brain and spinal cord.
In addition, the middle cerebellar peduncles are transverse groups of fibers that connect the pons to the cerebellum.
The pons aolso houses two autonomic respiratory centers, the pneumotaxic center and the apneustic center.
These centers regulate the rate and depth of breathing and both of them influence and modify the activity of the respiratory center in the medulla oblongata.
Medulla Oblongata
The medulla oblongata, or simply the medulla, is formed from the myelencephalon.
It is the most inferior part of the brainstem and is continuous with the spinal cord inferiorly.
The posterior portion of the medulla resembles the spinal cord with its flattened, round shape and narrow central canal.
As the central canal extends anteriorly toward the pons, it enlarges and becomes the fourth ventricle. All communication between the brain and spinal cord involves tracts that ascend or descend through the medulla oblongata.
Several external landmarks are visible on the medulla oblongata.
The anterior surface exhibits two longitudinal ridges called the pyramids, which house the motor projection tracts called the corticospinal (pyramidal) tracts.
In the posterior region of the medulla, most of these axons cross to the opposite side of the brain at a point called the decussation of the pyramid.
As a result of the crossover, each cerebral hemisphere controls the voluntary movements of the opposite side of the body.
Immediately lateral to each pyramid is a distinct bulge, called the olive, which contains a large fold of gray matter called the inferior olivary nucleus.
The inferior olivary nuclei relay ascending sensory impulses, especially proprioceptive information, to the cerebellum. Additionally, paired inferior cerebellar peduncles are tracts that connect the medulla oblongata to the cerebellum.
Within the medulla oblongata are additional nuclei that have various functions.
The cranial nerve nuclei are associated with the vestibulocochlear (CN VIII), glossopharyngeal (CN IX), vagus (CN X), accessory (CN XI), and hypoglossal (CN XII) cranial nerves. In addition, the medulla oblongata contains the paired nucleus cuneatus and the nucleus gracilis, which relay somatic sensory information to the thalamus.
The nucleus cuneatus receives posterior root fibers corresponding to sensory innervation from the arm and hand of the same side.
The nucleus gracilis receives posterior root fibers carrying sensory information from the leg and lower limbs of the same side.
Bands of myelinated fibers composing a medial lemniscus exit these nuclei and decussate in the inferior region of the medulla oblongata. The medial lemniscus projects through the brainstem to the ventral posterior nucleus of the thalamus.
The medulla oblongata contains several autonomic nuclei, which regulate functions vital for life. Autonomic nuclei group together to form centers in the medulla oblongata. Following are the most important autonomic centers in the medulla oblongata and their functions:
The Cardiac Center
The Vasomotor Center
The Respiratory Center
Other nuclei in the medulla oblongata are involved in coughing, sneezing, salivating, swallowing, gagging, and vomiting
Cerebellum
Cerebellum
The cerebellum is the second largest part of the brain, and it develops from the metencephalon.
The cerebellum has a complex, highly convuluted surface covered by a layer of cerebellar cortex.
The folds of the cerebellar cortex are called folia.
The cerebellum is composed of left and right cerebellar hemispheres.
Each hemisphere consists of two lobes, the anterior lobe and the posterior lobe, which are separated by the primary fissure.
Along the midline, a narrow band of cortex known as the vermis separates the left and right cerebellar hemispheres.
The vermis receives sensory input reporting torso position and balance. Its output to the vestibular nucleus helps maintain balance. Slender flocculonodular lobes lie anterior and inferior to each cerebeullar hemisphere.
The cerebellum is partitioned internally into three regions:
An outer gray matter layer of cortex, an internal region of white matter, and the deepest gray matter layer, which is composed of cerebellar nuclei.
The white matter of the cerebellum is called the arbor vitae because its distribution pattern resembles the branches of a tree.
The cerebellum coordinates and fine-tunes skeletal muscle movements and ensures that skeletal muscle contraction follows the correct pattern leading to smooth, coordinated movements.
The cerebellum stores memories of previously learned movement pattern. This function is performed indirectly, by regulating activity along both the voluntary and involuntary motor pathway at the cerebral cortex, cerebral nuclei, and motor centers in the brainstem.
Cerebellar Peduncles
Three thick tracks, called peduncles, link the cerebellum with the brainstem.
The superior cerebellar peduncles connect the cerebellum to the mesencephalon.
The middle cerebellar peduncles connect the pons to the cerebellum.
The inferior cerebellar peduncles connect the cerebellum to the medulla oblongata.
It is these extensive communications that enable the cerebellum to fine tune skeletal muscle movements and interpret all body proprioceptive movement.
Limbic System
Limbic System
The Limbic System is composed of multiple cerebral and diencephalic structures that collaboratively process and experience emotions.
It is a collective name for the human brain structures that are involved in motivation, emotion and memory with an emotional association.
The limbic system affects memory formation by integrating past memories of physical sensations with emotional states.
The structures of the limbic system form a ring or border around the diencephalon. The brain structures commonly recognized are:
The Cingulate Gyrus
It is an internal mass of cerebral cortex located within the longitudinal fissure and superior to the corpus callosum.
This mass of tissue may be seen only in sagittal section, and it surrounds the diencephalon.
It receives input from the other components of the limbic system.
It focuses attention on emotionally significant events and appears to bring them into consciousness.
The Parahippocampal Gyrus
It is a mass of cortical tissue in the temporal lobe.
Its function is associated with the hippocampus.
The Hippocampus
It is a nucleus located superior to the parahippocampal gyrus that connects to the diencephalon via a structure called the fornix.
As its names implies, this nucleus is shaped like a seahorse.
Both the hippocampus and parahippocampal gyrus are essential in storing memories and forming long term memory.
The Amygdaloid Body
It connects to the hippocampus.
It is involved in several aspects of emotion, especially fear.
It can also help store and code memories based on how a person emotionally perceives them.
The Olfactory Bulbs, Olfactory Tracts and Olfactory Cortex are part of the limbic system as well, since particular odors can provoke certain emotions or be associated with certain memories.
The Fornix
It is a thin tract of white matter that connects the hippocampus with other diencephalon limbic system structures.
Various nuclei in the diencephalon, such as the anterior thalamic nuclei, the habenular nuclei, the septal nuclei, and the mammillary bodies, interconnect other parts of the limbic system and contribute to its overall function.
Cranial Nerves
Cranial Nerves
Cranial nerves are part of the peripheral nervous system and originate on the inferior surface of the brain.
There are 12 pairs of cranial nerves. They are numbered according to their positions, beginning with the most anteriorly placed nerve and using Roman numerals, sometimes preceded by the prefix CN .
The name of each nerve generally has some relation to its function. Thus, the 12 pairs of cranial nerves are the olfactory (CN I), optic (CN II), oculomotor (CN III), trochlear (CN IV), trigeminal (CN V), abducens (CN VI), facial (CN VII), vestibulocochlear (CN VIII), glossopharyngeal (CN IX), vagus (CN X), accessory (CN XI), and hypoglossal (CN XII).
Mmemonic
Oh (Olfactory)
Once (Optic)
One (Oculomotor)
Takes (Trochlear)
The (Trigeminal)
Anatomy (Abducens)
Final (Facial)
Very (Vestibulocochlear)
Good (Glossopharyngeal)
Vacations (Vagus)
Are (Accessory)
Heavenly (Hypoglossal)
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