The surface of the brain is the cortex, where the neurons for higher order processing are located. Sensory information from the environment is interpreted, motor commands are given to the muscles, cognitive functions are located in the cortex, and there are areas responsible for behaviour. The two cerebral hemispheres are not symmetrical in function and some functions show more representation in one hemisphere than the other (e.g. language).


The brain can be thought of as having a large number of approximately discrete areas dedicated to various roles.

  • Amygdala: Lying deep in the center of the limbic emotional brain, the size and shape of an almond, monitors the needs of basic survival including sex, emotional reactions/anger/fear. It inspires aversive cues, such as sweaty palms and is associated with a range of mental conditions including depression and autism. It is larger in male brains, often enlarged in the brains of sociopaths, shrinks in the elderly.
  • Brain stem: The part of the brain that connects to the spinal cord, controls heart rate, breathing, digesting foods and sleeping. Lowest, most primitive area of the human brain.
  • Cerebellum: Two peach-size mounds of folded tissue located at the top of the brain stem, controls coordinated movement and is involved in some learning pathways.
  • Cerebrum: This is the largest brain structure in humans and accounts for about two-thirds of the brain’s mass. It is divided into two sides — the left and right hemispheres—that are separated by a deep groove down the center from the back of the brain to the forehead. These two halves are connected by long neuron branches called the corpus callosum which is relatively larger in women’s brains than in men’s. The cerebrum is positioned over and around most other brain structures, and its four lobes are specialized by function but are richly connected. The outer 3 millimeters of “gray matter” is the cerebral cortex which consists of closely packed neurons that control most of our body functions, including the mysterious state of consciousness, the senses, the body’s motor skills, reasoning and language.
  • The frontal lobe is the most recently-evolved part of the brain and the last to develop in young adulthood. Its dorso-lateral prefrontal circuit organizes responses to complex problems, plans steps to an objective, searches memory for relevant experience, adapts strategies to accommodate new data, guides behavior with verbal skills and houses working memory. Its orbitofrontal circuit manages emotional impulses in socially appropriate ways for productive behaviors including empathy, altruism, interpretation of facial expressions. Stroke in this area typically releases foul language and fatuous behavior patterns.
  • The temporal lobe controls memory storage area, emotion, hearing, and, on the left side, language.
  • The parietal lobe receives and processes sensory information from the body including calculating location and speed of objects.
  • The occipital lobe processes visual data and routes it to other parts of the brain for identification and storage.
  • The hippocampus: located deep within the brain, it processes new memories for long-term storage. It is among the first functions to falter in Alzheimer's.
  • The hypothalamus: located at the base of the brain where signals from the brain and the body’s hormonal system interact: maintains homeostasis, monitors blood pressure and body temperature, as well as controlling body weight and appetite.
  • The thalamus: located at the top of the brain stem, the thalamus acts as a two-way relay station, sorting, processing, and directing signals from the spinal cord and mid-brain structures up to the cerebrum, and, conversely, from the cerebrum down the spinal cord to the nervous system.

The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.
This brain region has been implicated in planning complex cognitive behavior, personality expression, decision making and moderating social behavior. The basic activity of this brain region is considered to be orchestration of thoughts and actions in accordance with internal goals.

The motor cortex can be divided into several main parts:

  • the primary motor cortex is the main contributor to generating neural impulses that pass down to the spinal cord and control the execution of movement. However, some of the other motor cortical fields also play a role in this function.
  • the premotor cortex is responsible for some aspects of motor control, possibly including the preparation for movement, the sensory guidance of movement, the spatial guidance of reaching, or the direct control of some movements with an emphasis on control of proximal and trunk muscles of the body.
  • the supplementary motor area (or SMA), has many proposed functions including the internally generated planning of movement, the planning of sequences of movement, and the coordination of the two sides of the body such as in bi-manual coordination.
  • the posterior parietal cortex is sometimes also considered to be part of the group of motor cortical areas. It is thought to be responsible for transforming multisensory information into motor commands, and to be responsible for some aspects of motor planning, in addition to many other functions that may not be motor related.
  • the primary somatosensory cortex, especially the part called area 3a, which lies directly against the motor cortex, is sometimes considered to be functionally part of the motor control circuitry.

Other brain regions outside the cerebral cortex are also of great importance to motor function, most notably the cerebellum, the basal ganglia, and the red nucleus, as well as other subcortical motor nuclei. Here is a pretty awesome animation of the location of the medulla oblongata, the lower half of the brain stem, which controls respiration (chemoreceptors), is a cardiac center (sympathetic, parasympathetic system), a vasomotor center (baroreceptors) and contains the reflex centers of vomiting, coughing, sneezing, and swallowing:


The sensory cortex can refer informally to the primary somatosensory cortex, or it can be used as an umbrella term for the primary and secondary cortices of the different senses (two cortices each, on left and right hemisphere): the visual cortex on the occipital lobes, the auditory cortex on the temporal lobes, the primary olfactory cortex on the uncus of the piriform region of the temporal lobes, the gustatory cortex on the insular lobe (also referred to as the insular cortex), and the primary somatosensory cortex on the anterior parietal lobes. Just posterior to the primary somatosensory cortex lies the somatosensory association cortex, which integrates sensory information from the primary somatosensory cortex (temperature, pressure, etc.) to construct an understanding of the object being felt. Inferior to the frontal lobes are found the olfactory bulbs, which receive sensory input from the olfactory nerves and route those signals throughout the brain. Not all olfactory information is routed to the olfactory cortex. Some neural fibers are routed directly to limbic structures, while others are routed to the supraorbital region of the frontal lobe. Such a direct limbic connection makes the olfactory sense unique.


The basal ganglia (or basal nuclei) are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas. The basal ganglia are associated with a variety of functions, including voluntary motor control, procedural learning relating to routine behaviors or "habits" such as bruxism, eye movements, and cognitive/emotional functions. Currently popular theories implicate the basal ganglia primarily in action selection, that is, the decision of which of several possible behaviors to execute at a given time. Experimental studies show that the basal ganglia exert an inhibitory influence on a number of motor systems, and that a release of this inhibition permits a motor system to become active. The "behavior switching" that takes place within the basal ganglia is influenced by signals from many parts of the brain, including the prefrontal cortex, which plays a key role in executive functions.

The main components of the basal ganglia are the striatum, the globus pallidus, the substantia nigra, and the subthalamic nucleus. The largest component, the striatum, receives input from many brain areas but sends output only to other components of the basal ganglia. The pallidum receives input from the striatum, and sends inhibitory output to a number of motor-related areas. The substantia nigra is the source of the striatal input of the neurotransmitter dopamine, which plays an important role in basal ganglia function. The subthalamic nucleus receives input mainly from the striatum and cerebral cortex, and projects to the globus pallidus. Each of these areas has a complex internal anatomical and neurochemical organization.

The basal ganglia play a central role in a number of neurological conditions, including several movement disorders. The most notable are Parkinson's disease, which involves degeneration of the dopamine-producing cells in the substantia nigra pars, and Huntington's disease, which primarily involves damage to the striatum. Basal ganglia dysfunction is also implicated in some other disorders of behavior control such as Tourette syndrome, hemiballismus, obsessive–compulsive disorder, and Wilson's disease.
The basal ganglia have a limbic sector whose components are assigned distinct names: the nucleus accumbens, ventral pallidum, and ventral tegmental area. There is considerable evidence that this limbic part plays a central role in reward learning, particularly a pathway from the ventral tegmental area to the nucleus accumbens that uses the neurotransmitter dopamine. A number of highly addictive drugs, including cocaine, amphetamine, and nicotine, are thought to work by increasing the efficacy of this dopamine signal. There is also evidence implicating overactivity of the VTA dopaminergic projection in schizophrenia.


Blood supply

The blood supply of the brain is provided by right common carotid (a branch of the brachiocephalic) and the left common carotid, arising directly from the aorta; and the vertebral arteries, arising from the subclavians. The CCAs pass laterally to the trachea, partially covered by the sternocleidomastoid muscle. The CCA, internal jugular vein and vagus nerve are enclosed by the carotid sheath, which lies anterior to the cervical sympathetic chain. The CCA gives no branches in the neck and terminates at the upper border of the thyroid cartilage of the larynx (C3) by dividing into the external and internal carotids.

The external carotid is anterior to both the internal jugular vein and the internal carotid. Level with the neck of the mandible, it enters the parotid gland and terminates as the maxillary/superficial temporal arteries. Its branches are:

  • superior thyroid, anastomosing with the inferior thyroid from the subclavian to supply the thyroid and parathyroid glands, pharynx and larynx
  • superior laryngeal
  • lingual loops around the hyoid bone and passes deep to the hyoglossus to supply the tongue
  • facial gives a branch to the palatine tonsils, makes and S bend around the submandibular gland before turning under the inferior border of the mandible onto the face; passes superiorly to the medial corner of the eye
  • occipital and posterior auriculars supply the scalp
  • superficial temporal passes in front of the ear with the auriculotemporal nerve to supply the scalp
  • maxillary supplies the muscles of mastication, upper and lower jaws and teeth and the nasal cavity; it also gives a branch to the cranial cavity: the middle meningeal artery

At the CCA bifurcation are the carotid sinuses, which monitor blood pressure (baroceptors) and the carotid bodies, which monitor blood composition (chemoceptors); both are supplied by CN IX. The internal carotid has no branches in the neck and enters the skull through the carotid canal, carrying a plexus of postganglionic sympathetic fibres; it gives an ophthalmic branch before terminating as the anterior and middle cerebral arteries. The ophthalmic artery supplies the orbital contents and gives supraorbital and supratrochlear branches that supply the forehead and scalp and anastomose with the superficial temporal artery. The most important orbital artery is the central artery of the retina.

The vertebral arteries arise from the first part of the subclavian artery and pass through the foramina transversaria of cervical vertebrae C1-C6 to reach the foramen magnum, , piercing the meninges and joining on the anterior aspect of the pons to form the basilar artery. They supply the upper part of the spinal cord, the brainstem, cerebellum, posterior cerebral cortex and vestibular apparatus.


The internal carotids and vertebrals supply the brain and are connected by vessels lying beneath the forebrain in the subarachnoid space. The vertebral arteries merge to form the basilar artery, which is connected via the posterior cerebral and posterior communicating arteries with the internal carotid. The circle of Willis is completed by the anterior cerebral and anterior communicating branches. The arrangement is variable and anastomosis is present and important if vessels are blocked by disease or emboli.

CSF flow

Cerebrospinal fluid (CSF) is a clear colorless bodily fluid produced in the choroid plexus of the brain. It acts as a cushion or buffer for the cortex, providing a basic mechanical and immunological protection to the brain inside the skull and serves a vital function in cerebral autoregulation of cerebral blood flow. The CSF occupies the subarachnoid space (the space between the arachnoid mater and the pia mater) and the ventricular system around and inside the brain and spinal cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain, as well as the central canal of the spinal cord.

CSF serves four primary purposes:

  • buoyancy: The actual mass of the human brain is about 1400 grams; however, the net weight of the brain suspended in the CSF is equivalent to a mass of 25 grams. The brain therefore exists in neutral buoyancy, which allows the brain to maintain its density without being impaired by its own weight, which would cut off blood supply and kill neurons in the lower sections without CSF.
  • protection: CSF protects the brain tissue from injury when jolted or hit. In certain situations such as auto accidents or sports injuries, the CSF cannot protect the brain from forced contact with the skull case, causing hemorrhaging, brain damage, and sometimes death.
  • chemical stability: CSF flows throughout the inner ventricular system in the brain and is absorbed back into the bloodstream, rinsing the metabolic waste from the CNS through the blood–brain barrier. This allows for homeostatic regulation of the distribution of neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness and syncope. To use Davson's term, the CSF has a "sink action" by which the various substances formed in the nervous tissue during its metabolic activity diffuse rapidly into the CSF and are thus removed into the bloodstream as CSF is absorbed.
  • prevention of brain ischemia: The prevention of brain ischemia is made by decreasing the amount of CSF in the limited space inside the skull. This decreases total intracranial pressure and facilitates blood perfusion.

The blood–brain barrier (BBB) is a separation of circulating blood from the brain extracellular fluid (BECF) in the central nervous system (CNS). It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion of microscopic objects (e.g., bacteria) and large or hydrophilic molecules into the cerebrospinal fluid (CSF), while allowing the diffusion of small hydrophobic molecules (O2, CO2, hormones). Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins. This barrier also includes a thick basement membrane and astrocytic endfeet.

CSF is secreted by the choroid plexuses found primarily in the ventricles. The rate of production varies between about 300-500 mL/day and the ventricular volume is about 75 mL. CSF is similar to blood plasma but has less albumin and glucose. After production, CSF flows from the lateral ventricles into the 3rd ventricle via the intraventricular foramina of Munro and then passes into the 4th ventricle via the central aqueduct of Sylvius and then into the subarachnoid space via the foramina of Lushka and Magendie. From the subarachnoid space at the base of the brain, CSF flows rostrally over the cerebral hemispheres and or down into the spinal cord.

CSF reabsorption occurs in the superior sagittal and related venous sinuses. Arachnoid granulations are minute pouches of the arachnoid membrane projecting through the dura into the venous sinuses. The mechanisms of CSF absorption are not clear but involve the movement of all CSF constituents into venous blood.

Hydrocephalus is a dilatation of the ventricular system and is seen in cerebral atrophy (e.g. dementia - compensatory hydrocephalus). It also occurs as a result of increased pressure in the ventricular system secondary to a CSF obstruction (obstructive hydrocephalus). This typically occurs at the outlets from the 4th ventricle into the subarachnoid space, where the obstruction may be linked to the presence of a tumour, congenital malformations or the sequelae of a previous infection. The flow of CSF from the 3rd to the 4th ventricle may be impaired by central aqueduct stenosis. Hydrocephalus is also seen in conditions of CSF oversecretion (e.g. tumours of the choroid plexus) as well as in spina bifida, where CSF reabsorption is reduced. The presenting features of hydrocephalus are classically those of increased intracranial pressure: early morning headaches, nausea, vomiting and in acute cases, altered consciousness with periods of visual loss. The most common cause of increased intracranial pressure is a glial tumour producing an effect by virtue of its mass. Such tumours, when found in the posterior fossa, can also cause hydrocephalus directly, and in so doing contribute to raised intracranial pressure. The treatment of obstructive hydrocephalus focusses on draining CSF using a variety of shunts linking the ventricles to the atria of the heart or to the peritoneal cavity.


Venous drainage of the head is to the dural sinuses, lying between the layers of the dura. They are lined with endothelium and have no valves. All drain eventually to the internal jugular vein. The superior sagittal sinus is in the superior margin of the falx cerebri and drains posteriorly into the right transverse sinus and right sigmoid sinus. The inferior sagitta sinus is in the inferior margin of the falx cerebri and drains posteriorly into the straight sinus (which also receives blood from the great cerebral vein, the **left transverse sinus and the left sigmoid sinus, which leaves the skull via the jugular foramen, forming the left internal jugular vein.


The cavernous sinuses are complex venous channels lying either side of the pituitary fossa, enclosing the internal carotid artery and CN VI. They receive blood from the ophthalmic veins and the adjacent sinuses and then drain via the petrosal sinuses into the sigmoid sinuses on either side. Cranial nerves III, IV, Va and Vb lie embedded in the dura of the lateral wall of the cavernous sinus. Because the cavernous sinuses are connected to the face via the ophthalmic veins, it is possible for infection to spread quickly and centrally, resulting in embolism and sepsis. Such an infection affects the cranial nerves associated with the cavernous sinuses (III, IV, Va/Vb and VI) and blocks the venous drainage of the orbit.


The internal jugular starts at the continuation of the sigmoid sinus at the margins of the jugular foramen and lies deep to the sternocleidomastoid, ending by joining with the subclavian to form the brachiocephalic vein. On the left, the junction is at the point where the thoracic duct returns lymph to the venous system. On the right is the smaller right lymphatic duct. The internal jugular receives veins that accompany the arterial branches of the external carotid artery.

The maxillary and superficial temporal veins join together in the parotid gland, forming the retromandibular vein, which divides into anterior and posterior divisions. The posterior joins with the posterior auricular to form the external jugular vein, which empties into the subclavian vein. The anterior jugular begins begins below the chin and runs close to the midline before also draining into the external jugular. The facial vein accompanies the artery as it crosses the face and drains with the anterior division of the retromandibular vein into the external jugular. The facial veins are connected with the intracranial dural venous sinuses via the ophthalmic veins.


Cavernous sinus thrombosis (CST) is the formation of a blood clot within the cavernous sinus. The cause is usually from a spreading infection in the nose, sinuses, ears, or teeth. Staphylococcus aureus and Streptococcus are often the associated bacteria. Cavernous sinus thrombosis symptoms include: decrease or loss of vision, chemosis, exophthalmos (bulging eyes), headaches, and paralysis of the cranial nerves which course through the cavernous sinus. This infection is life-threatening and requires immediate treatment, which usually includes antibiotics and sometimes surgical drainage.

Signs and symptoms of obstructive lesions to the major arteries of the head depend on what region each supplies, but typically include: sudden numbness or weakness of the face, arm or leg, especially on one side of the body, sudden confusion, trouble speaking or understanding, sudden trouble seeing in one or both eyes, sudden trouble walking, dizziness, loss of balance or coordination and sudden, severe headache with no known cause.

Motor and sensory pathways

The internal structure of the cord is two symmetrical halves, divided partially by the dorsal median sulcus and the ventral midline fissure. The centre of the spinal cord, the spinal canal, is a continuation of the ventricular system of the brain. The dorsal horns of the cord contain the synapses of the sensory fibres from the periphery; the ventral horns contain the cell bodies of the motor neurons; the lateral horn is found in the thoracic segments and contains cell bodies of preganglionic sympathetic neurons of the ANS. The white matter, surrounding the grey matter, contains the ascending and descending fibre tracts.


Afferent fibres entering the dorsal horn divide into ascending/descending tracts and terminate quickly by synapsing in the grey matter. Rexed's laminae are layers receiving different nervous inputs, grouped by function:

  • the posteromarginal zone (lamina I) is the dorsal-most tip of the grey matter, receiving A-delta sensory fibres and interneurons from the substantia gelatinosa (laminae II and III). The efferents from the porsteromarginal zone form the **anterolateral tracts.
  • the substantia gelatinosa (laminae II and III) receives small A-delta and unmyelinated C-fibres which are associated with pain signals. Efferents project to the spinothalamic and spinoreticulartracts
  • the nucleus propria (laminae IV and V) makes up the better part of the dorsal horn and receives most somatosensation and proprioception fibers, projecting to many of the ascending tracts in the white matter
  • the thoracic nucleus is found between C8 and L3 and receives inputs from the fibres of many of the proprioceptive organs. The efferent neurons ascend in the posterior cerebellar tract.

The ventral horn is divided into three regions that innervate specific regions of the body:

  • the medial group is found in most segments of the cord; its efferent fibers innervate the muscles of the axial skeleton, including the intercostal muscles and the abdominal musculature
  • the central group is in the cervical and lumbosacral regions and provides innervation of the diaphragm at C3-C5; above this region, it is the origin of the spinal part of the accessory nerve.
  • the lateral group is found in the lumbosacral and cervical regions and supplies fibres innervating the limbs.

The lateral horn is found in T1-L2 and in the sacral region, where is gives off preganglionic sympathetic, respectively parasympathetic fibres.

The white matter is organised as a series of tracts carrying sensory and motor signals. The same organisation is seen at each level of the cord.


1. The corticospinal tract, carrying voluntary motor signals regulating skilled movements, gives off branches to inhibit other areas of cortex and the subcortical motor regions. Fibres from the primary and secondary motor cortices and the parietal cortices converge at the posterior limb of the internal capsule. As the corticospinal tract passes through the midbrain, the fibres regulating lower body movement become located on the lateral part of the tract; the fibres form bundles passing through the pons and develop into the pyramids of in the anterior surface of the medulla, where most of the fibres decussate

  • the lateral corticospinal tract is formed from those fibres that decussate and provides innervation to all spinal cord segments
  • the anterior corticospinal tract forms from the few fibres that do not decussate and is present only in the cervical and upper thoracic regions

2. The vestibulospinal tract integrates signals help maintain balance and posture, through excitatory action on the extensor muscles and inhibitory activity on the flexors. It arises from the lateral vestibular nucleus and projects down the length of the spinal column without decussating

3. The reticulospinal tract is a descending tract that originates in the reticular formation and modulates the function of the kotor neurons in the spinal column to regulate course voluntary movements and reflex activity

4. The rubrospinal tract originates from the red nucleus (a structure in the rostral midbrain involved in motor coordination, located in the tegmentum of the midbrain next to the substantia nigra) and decussates to travel with the lateral corticospinal tract. It provides a manor pathway for voluntary movement outside the corticospinal tract, often of large muscles, and is important in regulating walking.

5. The dorsal columns contain the signals from large myelinated sensory fibres, which are concerned with proprioception and
discriminative touch. The fibres are primary afferents originating in the periphery and ascend in the dorsal columns to synapse in the medulla at the nucleus gracillis and nucleus cuneatus. The fibres of progressively higher spinal roots are added laterally to the dorsal columns as they ascend towards the medulla. Two divisions can be identified:

  • the fasiculus gracilis is located medially and contains fibres from the lumbar and sacral parts of the body
  • the fasciculs cuneatus is located laterally and contains fibres from the thoracic and cervical roots.

6. The anterolateral columns are lateral and ventral to the ventral horn and consist of three structures, named based on the part of the brain to which they project:

  • the spinothalamic tract carries pain and temperature (as well as non-discriminating touch and pressure); it contains neurons originating in laminae I and V of the dorsal horn and decussate at the level of entry, ventral to the central canal and ascend in the tract before running parallel to the medial lemniscus. The lateral tract projects to the centre of the thalamus and reticular formation and is involved in pain and temperature, but not touch sensation. The anterior tract projects to the ventral posterolateral part of the thalamus and to nearby regions that are not directly associated with somatosensation.
  • the spinoreticular tract contains sensory neurons synapsing on laminae VII and VIII of the dorsal horn and ascending to the reticular formation and thalamus with information involved in the regulation of consciousness; most fibres do not decussate
  • the spinomesencephalic tract is involved in conveying the affective part of pain and follows a similar path to the spinoreticular tract (but its fibres originate in laminae V and I) and terminates in the periaqueductal gray matter and mesencephalic reticular formation, as well as the amygdala.

7. The spinocerebellar tracts conveys joint and proprioceptive information to the cerebellum, allowing movement feedback. There are two major divisions:

  • the posterolateral spinocerebellar tract consists of neurons originating in Clarke's column on the ipsilateral dorsal horn; these fibres receive afferents from muscle spindles, Golgi tendon fibres and joint receptors of the trunk/lower limbs, providing data about body posture and movement; they ascend to inferior cerebellar peduncle and enter the cerebellum, where they terminate.
  • the anterior spinocerebellar tract consists of fibres also originating in Clarke's column but that decussate before ascending to the cerebellum via the superior cerebellar peduncle to provide information about the skin and fascia (complementing the joint/posture/tendon/movement information provided by the posterolateral spinocerebellar tract).

Lissauer's tract contains neurons that enter the tip of the dorsal horn, carrying information related to pain and temperature to the substantia gelatinosa.


Cranial nerves

Odor Of Orangutan Terrified Tarzan After Forty Voracious Gorillas Viciously Attacked Him: I – Olfactory, II – Optic, III – Oculomotor, IV – Trochlear, V – Trigeminal, VI – Abducens, VII – Facial, VIII – Vestibulocochlear, IX – Glossopharyngeal, X – Vagus, XI – Spinal accessory, XII – Hypoglossal.

A useful mnemonic for remembering which nerves are motor (M), sensory (S), or both (B) is, "Some Say Money Matters But My Brother Says Big Brains Matter Most".

Number Name Sensory/Motor/Both Origin Nuclei Function
I Olfactory Purely Sensory Telencephalon Anterior olfactory nucleus Transmits the sense of smell from the nasal cavity. Located in olfactory foramina in the cribriform plate of ethmoid.
II Optic Purely Sensory Diencephalon Ganglion cells of retina Transmits visual signals from the retina of the eye to the brain. Located in the optic canal.
III Oculomotor Mainly Motor Anterior aspect of midbrain Oculomotor nucleus, Edinger-Westphal nucleus Innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements. Also innervates the sphincter pupillae and the muscles of the ciliary body. Located in the superior orbital fissure.
IV Trochlear Mainly Motor Dorsal aspect of midbrain Trochlear nucleus Innervates the superior oblique muscle, which depresses, rotates laterally, and intorts the eyeball. Located in the superior orbital fissure.
V Trigeminal (Va ophthalmic, Vb maxillary, Vc mandibular) Both Pons Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus Receives sensation from the face and innervates the muscles of mastication. Located in the superior orbital fissure (ophthalmic nerve - V1), foramen rotundum (maxillary nerve - V2), and foramen ovale (mandibular nerve - V3).
VI Abducens Mainly Motor Anterior margin of pons Abducens nucleus Innervates the lateral rectus, which abducts the eye. Located in the superior orbital fissure.
VII Facial Both Pons (cerebellopontine angle) above olive Facial nucleus, Solitary nucleus, Superior salivary nucleus Provides motor innervation to the muscles of facial expression, posterior belly of the digastric muscle, and stapedius muscle. Also receives the special sense of taste from the anterior 2/3 of the tongue and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland. Located in and runs through the internal acoustic canal to the facial canal and exits at the stylomastoid foramen.
VIII Acoustic or Vestibulocochlear (or auditory-vestibular nerve or acoustic nerve) Mostly sensory Lateral to CN VII (cerebellopontine angle) Vestibular nuclei, Cochlear nuclei Senses sound, rotation, and gravity (essential for balance and movement). More specifically, the vestibular branch carries impulses for equilibrium and the cochlear branch carries impulses for hearing. Located in the internal acoustic canal.
IX Glossopharyngeal Both Medulla Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils. Located in the jugular foramen.
X Vagus Both Posterolateral sulcus of medulla Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles (except the stylopharyngeus, which is innervated by the glossopharyngeal). Also provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure. Receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance and the soft palate. Symptoms of damage: dysphagia (swallowing problems), velopharyngeal insufficiency. Located in the jugular foramen.
XI Accessory (or cranial accessory nerve or spinal accessory nerve) Mainly Motor Cranial and Spinal Roots Nucleus ambiguus, Spinal accessory nucleus Controls the sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus nerve (CN X). Symptoms of damage: inability to shrug, weak head movement. Located in the jugular foramen.
XII Hypoglossal Mainly Motor Medulla Hypoglossal nucleus Provides motor innervation to the muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in the hypoglossal canal.
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