Brain & Cranial Nerves

CNS composition

• brain and spinal cord

• meninges- entire CNS surrounded by 3 membranes

  • layers of meninges that surround brain are the same as spinal cord

• Dura mater- outer most layer; thickest and toughest

  • outer layer- (osteal, endosteal, or perosteal)

    • fused to perosteum

  • meningeal/ inner layer-

• Venous sinus-

  • between outer and inner layer of dura, space with blood vessels and these

  • contains blood that has been to a tissue and is on its way back to the heart

• Arachnoid layer- inside the dura mater

• subarachnoid space-

  • inside arachnoid; cerebrospinal fluid filled space

  • forms a CUSHION between CNS and surrounding bone

  • SUPPORTS CNS

  • provides a CIRCULATORY function that would be accomplished by blood vessels elsewhere

• Choroid plexuses-

  • small blood vessels or capillaries in ventricles that produce CSF

  • one in each of the four brain ventricles

• CSF-

  • brain and spinal cord have interior cavities that are also filled with CSF

  • CSF produced in Ventricles (cavities) of the brain

  • flows through ventricles, central canal of spinal cord, and subarachnoid space

• Pia mater- inner layer; lies on the surface of the CNS

Terms to describe regions of the brain at diff stages of development

Mature Brain

• Cerebrum

• diencephalon

• Cerebellum (dorsal part)

• mesencephalon (midbrain)

• pons/pons varolii (ventral part)

• medulla oblongata

Brain Ventricles and CSF

• lateral ventricles

  • 2 most superior cavities

• septum pellucidum/pellucidum septum

  • two cavities separated ny this thin wall/partition

    • septum- thin wall dividing two chambers

• interventricular foramina/ foramina of Monro

  • CSF flows from lateral ventricles through this into 3rd ventricle

• third ventricle/diencephaletic chamber

  • NO 1st or 2nd ventricle (lateral ventricles)

  • surrounded by diencephalon

• aqueducts of Sylvius/ mesencephalic aqueduct/ cerebral aqueduct

  • from 3rd ventricle, CSF flows through this into the 4th ventricle

  • NOT IN CEREBRUM

• fourth ventricle

  • 4 Exits from this:

  • central canal of the spinal cord

    • CSF can go into

  • median foramen/ foramen of Magendie

    • single, midline opening

    • allows CSF to flow into subarachnoid space

  • lateral foramina/foramina of Luschka

    • 2 lateral openings

    • allow CSF to flow into subarachnoid space

Blood flow

• ventricles- cavities of brain that CSF is produced in

• Choroid plexuses-CSF produced in ventricles of brain from the blood vessels

  • fluid must be reabsorbed into blood at same rate of production

  • b/c no room for swelling because CNS surrounded by bone

• Superior sagittal sinus-

  • venous sinus in dura mater along the midline above the brain

  • indicated blood is going back to heart to be pumped somewhere else

• Arachnoid villi/arachnoid granulations-

  • extensions of the arachnoid layer that extrude through the dura into the blood of the superior sagittal sinus

  • This is where CSF passes back into blood

Blood-brain Barrier (BBB)

• not a lot of exchange between blood and tissues comparatively

• Blood-brain barrier (BBB)

  • anatomic & physiologic factor that prevents passage of substances from blood into tissue of brain

  • endothelial cells that line blood vessels have tight junctions

    • prevent substances from getting between cells

  • Blood vessels, capillaries, in the brain surrounded by ASTROCUTES

    • they form physical barrier in addion to the wall of blood vessel

    • also secrete chemicals that affect permeability of vessels

• Why some conditions cannot be treated in brain

  • chemicals in blood cant get into tissue

  • Parkinsons disease cant be given intravenous dopamine

  • dopamine cant get out of the blood vessels in the brain

Circumventricular organs

• LACK the BBB

• are in the wall surrounding the third ventricle

• monitor concentrations and conditions in the blood

  • must respond to changes to maintain homeostasis

  • so there has to be more communication between the blood and these organs

• Choroid plexuses have NO ASTROCYTES and are fairly permeable

  • although there is a “blood-CSF barrier” created by the tight junctions between the endothelial cells

Brain and blood supply

• good blood supply CRITICAL to brain

• has extremely high metabolic rate so it uses O2 rapidly and creates waste products rapidly

• also must use carbs to get energy

  • cannot utilize fats or proteins as a source of energy

• can increase blood flow by increasing heart rate

• can increase respiratory rate to increase concentration of O2 in blood and decrease concentration of CO2

glucose + oxygen → carbon dioxide + water + energy

• reaction shows how cells use O2 in the process of producing energy and produce CO2 as a waste product

carbon dioxide + water → carbonic acid ; carbonic acid → H⁺ + bicarbonate ion (HCO₃^-1)

• when CO2 is produced, causes increase in number of H ions, or a drop in pH

• in normal healthy adult, brain more sensitive to buildup of CO2 and H ions than it is to drop in O2 concentration

• sensitive to all three concentrations

Brain Stem

• brain stem

  • most inferior part, inside cranial cavity

  • similar appearance to spinal cord

  • composed of medulla oblongata, pons, and midbrain

• medulla oblongata

  • most inferior part of brain stem

  • extends from foramen magnum to pons

  • composed primarily of ascending descending tracts

  • decussate- many of these nerve tracts cross midline

  • pyramids- large motor tracts that decussate

    • fibers cross midline; why right side= left and left= right

  • olives- lateral swellings of medulla where it has connections to the cerebellum through inferior cerebellar peduncles

  • some nuclei in medulla that maintain some basic life functions

    • include involuntary centers for heart rate, respiratory rate, and blood flow (vessel diameter)

• pons (“bridge”)/ pons variolii-

  • part of the brain step superior to medulla

  • primarily ascending & descending tract

  • connected to cerebellum through middle cerebellar peduncles

  • nuclei in pons that affect respiratory center of the medulla to help control breathing cycles

  • pneumotaxic area and the apneustic area- centers of pons

• midbrain/ mesencephalon

  • part of brain stem superior to pons

  • contains the aqueduct of Sylvius

  • Superior cerebellar peduncles connect midbrain to cerebellum

  • cerebral peduncles- ventral part of midbrain consists of a pair of fiber bundles

    • contain ascending and descending tracts that connect upper parts of the brain with lower parts of the brain and spinal cord

  • tectum- dorsal part of the midbrain

    • corpora quadrigemina- four small mounds

      • superior colliculi- two upper mounds involved in reflexive movement of the eyes due to a visual stimulus

      • inferior colliculi- lower mounds involved in reflexive movement of the head and trunk due to an auditory stimulus. “STARTLE” REFLEX

• substantia nigra-

  • nucleus of cells near cerebral peduncles

  • involved with regulating SUBCONSCIOUS muscle movement

  • area degenerates in people with Parkinson’s disease

• reticular formation

  • dispersed gray matter located in the spinal cord, medulla, pons, and midbrain

  • functions in the level of consciousness and arousal from sleep

Cerebellum

• dorsal to the brain stem

• transverse fissure- deep groove between cerebrum and the cerebellum

  • contains the tetorium cerebelli

• tentorium cerebelli- extension of the dura matter

• has two hemispheres and a vermis

• Falx cerebelli- extension of dura mater between two hemispheres

• Arbor vitae- gray matter of cerebellum surrounds white matter and the internal white matter looks like a tree

• Folia cerebelli- horizontal ridges of gray matter

  • involved in reflex control and coordination of skeletal muscle movement

  • affects muscle tone and muscles that maintain equilibrium or posture

• Ataxia- disturbance of balance

  • caused by trauma & drugs

diencephalon

• between midbrain and cerebrum

• 3rd ventricle in diencephalon

  • READ DESCRIPTIONS OF DIENCEPHALON CAREFULLY

• integrates conscious & unconscious sensory information and motor commands

• consists of epithalamus, thalamus, and hypothalamus

  • INTERMEDIATE MASS OF THE THALAMUS that extends through third ventricle

Epithalamus

• above third ventricle and consists of pineal body and posterior commissure

• pineal body/gland

  • endocrine gland that produces the hormone melatonin

  • posterior commissure connects cerebrum with midbrain

  • Habe nuclei of the epithalamus are involved in emotional responses to some odors

Thalamus

• relay station for sensory and motor impulses to and from the cerebral cortex

• involved in pain perception, temp perception memory, touch, ext.

• part of the limbic system (emotional brain that affects memory) READ THE BOOK

Hypothalamus

• structure responsible for maintaining homeostasis

• affect body structures through autonomic nervous system &/or endocrine system

• controls food intake, concentration of the blood, concentration of urine, etc. READ BOOK

Diencephalon in OPENSTAX pg 526-527

🧠 Brain Development Overview

• Three primary brain vesicles become five secondary vesicles during development.

• Prosencephalon splits into:

  • Telencephalon → becomes the cerebrum

  • Diencephalon → forms the thalamus, hypothalamus, and other structures.

• The eye cup develops from the diencephalon → later becomes the retina, a rare case of CNS tissue becoming peripheral.

🔁 Why Diencephalon Matters

• It remains the only brain region that keeps its embryonic name.

• Located between the cerebrum and rest of the nervous system; acts as a passage for almost all brain signals.

• Name translates to “through brain,” reflecting its role as a central connector.

👁 Key Developmental Connections

• Retina originates from the diencephalon → connects to thalamus and hypothalamus via optic tract.

• Optic tract also links to the midbrain (mesencephalon), which neighbors the diencephalon.

• Cerebellum develops from the metencephalon → connects strongly to the pons; also links to the medulla and midbrain.

🧩 Adult Structures & CNS

• Brain stem: Made of midbrain (mesencephalon), pons (metencephalon), and medulla (myelencephalon).

• Cerebellum: Large, separate structure; no direct link to cerebrum.

• Olfactory system: The only pathway that bypasses the diencephalon and connects straight to the cerebrum.

📚 Diencephalon Subregions

• Lies deep beneath the cerebrum, forms walls of the third ventricle.

• Includes any brain part with “thalamus” in its name:

  • Thalamus: Relay center between cerebrum and body.

  • Hypothalamus: Controls homeostasis via autonomic and endocrine functions.

  • Epithalamus: Includes pineal gland.

  • Subthalamus: Contains subthalamic nucleus (part of basal nuclei).

cerebrum

• largest part of brain

• part of brain involved with conscious thought and intellectual processes

• 2 cerebral hemispheres separated by a deep groove, the longitudinal fissure

• falx cerebri- extension of the dura mater extends down into longitudinal fissure

• cortex- outer part of the cerebrum that is

  • composed of gray matter (contains cell bodies of neurons)

  • interior of cortex is white matter (contains myelinated fibers)

• basal/cerebral nuclei/basal ganglia - deep areas of gray matter that are surrounded by white matter

corpus callosum

• structure that contains fibers crossing the midline

• main connection between right side of brain and left side

• covered with gyri, sulci, and fissures

• gyri- ridges

• sulci- shallow grooves

• fissures- deep grooves

Cerebral hemisphere lobes

• frontal lobe- separated from parietal lobe by central sulcus

  • precentral gyrus- most posterior gyrus of the frontal lobe (anterior to central sulcus)

  • post central gyrus- most anterior gyrus of the parietal lobe

• Temporal lobe- lateral fissure separates frontal and temporal

  • Insula/island of Reil- within this fissure is a mass of gray matter

• Parietal lobe- separated from the occipital lobe by the parietooccipital fissure

Functions of cerebral hemispheres

Each hemisphere receives sensory information from and sends motor commands to OPPOSITE SIDE OF THE BODY.

• when giving function to a specific area, NOT PRECISE

• some areas of brain are destroyed in some individuals, other parts can perform function of the missing tissue

Left

• spoken and written language, numerical and scientific skills

Right

• musical and artistic talent, insight, and imagination

White matter

• white due to the presence of myelin

• part of brain would contain fibers

• Tracts- bundles of fibers in the CNS

• Association fibers- connect gyri in the same hemisphere

• commissural fibers- connect gyri in opposite hemispheres

• CORPUS CALLOSUM- largest mass of commissural fibers

• projection fibers- ascending and descending fibers

• internal capsule- all of the fibers of the white matter together

Gray matter

• in cerebrum consists of basal nuclei and the cerebral cortex

• basal nuclei (basal ganglia)- paired masses of gray matter that are important in ordinary voluntary muscle movements

  • do not initiate the movement, but are involved in the coordination of the movement

  • claustrum, caudate nucleus, putamen, etc.

limbic system- basal nuclei, parts of cerebral hemisphere, and the diencephalon

• functional grouping of structures, not anatomic

• involved in EMoTIONS

Functional areas associated with the cerebral cortex

• READ CHAPTER 14 IN TEXTBOOK

• motor area- area that controls muscular movement

• sensory area- sensory information is conducted to here for interpretation

  • relatively small

• association areas- surrounds sensory areas

  • larger areas that evaluate and interpret sensory information

• primary visual area- receives information that produces a visual image

  • determines significance of an image

  • occipital lobe

• general sensory area/ primary somatosensory- located on postcentral gyrus

  • sensory information from skin, muscles, and visceral receptors from various parts of the body come here

• primary auditory area- superior part of the temporal lobe

• primary olfaction area- medial surface of the temporal lobe

• primary gustatory area- base of the postcentral gyrus

• primary motor area- on the precentral gyrus

  • initiates impulses to muscles on the opposite side of the body

• Premotor area/ somatic motor association area- anterior to the motor area

  • learned, complex movements loke writing

• Speech motor area/ Broca’s area- on frontal lobe above the lateral fissure

  • speaking

• also integrative centers that receive input from several association areas of the brain

Summary of ch 14

🧠 14.1 Sensory Perception

• Special senses: Olfaction, gustation, audition, equilibrium, and vision (linked to specific organs).

• General senses: Somatosensation (touch, pressure, vibration, temperature, pain) and visceral senses.

• Sensory receptor types:

  • Structural: Free nerve endings, encapsulated endings, specialized cells.

  • Location-based: Interoceptors, exteroceptors, proprioceptors.

  • Function-based:

    • Chemoreceptors: For smell, taste, fluid balance, pain.

    • Mechanoreceptors: For touch, hearing, balance.

    • Thermoreceptors: Temperature detection.

    • Photoreceptors: Light sensitivity.

• Sensory nerve pathways:

  • Spinal nerves: Mixed sensory/motor; sensory info enters via dorsal root.

  • Cranial nerves: Some purely sensory (olfactory, optic, vestibulocochlear), others mixed.

🧠 14.2 Central Processing

• Sensory input routes:

  • Through spinal cord (body) or brainstem (head/organs) → thalamus in diencephalon.

  • Exception: Olfactory signals directly reach frontal/temporal lobes.

• Major spinal tracts:

  • Dorsal column system: Carries touch & proprioception; decussates in medulla.

  • Spinothalamic tract: Carries pain & temperature; decussates in spinal cord.

• Other sensory pathways:

  • Auditory: Processes frequency & localization via brainstem.

  • Vestibular: Influences cerebellum, spinal cord, and cortex.

  • Visual: Segregates field info; has dorsal (movement/action) and ventral (memory/form) streams.

🧠 14.3 Motor Responses

• Motor system origin: Frontal lobe → premotor/supplemental areas → primary motor cortex.

• Upper motor neuron tracts:

  • Corticobulbar & corticospinal tracts control voluntary movement.

• Extrapyramidal system:

  • Maintains balance, posture, and tone via brainstem centers (superior colliculus, red nucleus, vestibular nuclei, reticular formation).

• Lower motor neurons:

  • Synapse in spinal cord → skeletal muscle via neuromuscular junctions.

  • Motor unit size varies by precision (e.g., quadriceps vs. eye muscles).

• Reflexes:

  • Simple circuits with sensory → motor neuron pathways.

  • Examples: Withdrawal reflex, corneal blink reflex, stretch reflex via muscle spindle.

Cranial Nerves

• twelve pair of cranial nerves

  • motor, sensory, mixed

  • no completely motor nerves

• Proprioception- sense of motion or body position

  • ability to know if your arm is straight or bent with eyes closed

• primary motor nerves/motor nerves- some cranial nerves have almost all motor fibers but just a very small number of proprioceptive fibers that convey the sense of position

Oh Oh Oh To Touch And Feel Very Good Virgins Are Horny

Some Say Marry Money But My Brother Says Big Brains Matter More

Cranial nerve I

• olfactory nerve

• sensory

• convey the sense of smell or olfaction

• nerve passes through the cribriform plate of the ethmoid bone

Cranial nerve II

• optic

• sensory

• sense of vision

• nerve passes from the back of the eye to the optic chiasm where some of the fibers cross the midline

• optic tracts pass back from the optic chiasm

Cranial nerve III

• oculomotor

• primary motor

• six muscles attached tothe outside of the wall of the eye

• extrinsic ocular muscle point the eye in different directions

• four of these six muscles are innervated by this nerve

Cranial nerve IV

• trochlear nerve

• primary motor

• nerve innervates one of the two extrinsic ocular muscles that is not innervated by cranial nerve III

• muscle called the superior oblique

• smallest of the cranial nerves

cranial nerve V

• trigeminal

• mixed

• largest of the cranial nerves

• motor- this nerve innervates the muscles of mastication

  • relatively strong muscles of the face that are used in chewing

• sensory- nerve conveys sensory information from the anterior part of the tongue but not taste

  • conveys sensory information about the cheeks, skin, and teeth

• Tic Douloureax/ trigeminal neuralgia- extremely painful condition with this nerve. MOST SEVERE PAIN in humans

Cranial nerve VI

• abducens

• primary motor

• lateral rectus muscle- nerve innervates the sixth extrinsic ocular muscle

Cranial nerve VII

• facial

• mixed

• motor- nerve innervates the relatively weak muscles of facial expression

  • Bell’s Palsy- paralysis of this nerve causes one side of the face to sag

• Sensory- nerve conveys sense of taste from the anterior part of the tongue

Cranial nerve VIII

• vestibulocochlear. auditory, acoustic, statoacoustic

• sensory

• sensory- nerve conveys sense of hearing and equilibrium

Cranial nerve IX

• glossopharyngeal

• mixed

• motor- nerve innervates the muscles involved in swallowing and gagging

• sensory- nerve conveys sensory information from the throat and posterior part of the tongue including taste

Cranial nerve X

• vagus

• mixed

• “wanderer”- READ TEXT FOR DETAILS

  • fibers in the neck, head, thorax, and abdomen

  • sensory and motor fibers run to and from the pharynx, larynx, lungs, heart, and digestive tract

Cranial Nerve XI

• Accessory Spinal

• spinal accessory

• primarily motor

• innervates muscles of the upper back and neck

Cranial nerve XII

• hypoglossal

• primarily motor

• innervates muscles of the tongue

Sayings

Some Say Marry Money But My Brother Says Big Brains Matter More

Oh Oh Oh To Touch And Feel Very Good Virgins are Horny