Brain and Cranial Nerves Structures

Pia Mater

Thin innermost layer adhering to brain

Arachnoid Mater

Subarachnoid Space

Space between pia mater and arachnoid mater with cerebrospinal fluid flowing

Dura Mater

Tough outer layer with two sublayers

• Meningeal Layer: Deeper layer

• Periosteal layer: Superficial to meningeal layer

Both fuse except where they separate to form dural venous sinuses

Cerebrum

Made of left and right hemispheres and divided into 4 lobes

• Surface is the cerebral cortex

Frontal Lobe

Deep to frontal bone and forms anterior part of cerebral hemisphere

• Ends at central sulcus

• Lateral sulcus is the inferior border

Function: voluntary movement, concentration, verbal communication, decision making, planning, personality, and primary motor control.

Parietal Lobe

Superior-posterior part of each hemisphere, just under parietal bones

• Terminates anteriorly at central sulcus, laterally at lateral sulcus, and posteriorly at the parieto-occipital sulcus

Function: general sensory reception and controls somatosensory information

Temporal Lobe

Inferior to lateral sulcus under temporal bone

Function: involved with auditory and olfactory information

Occipital Lobe

Posterior region of each hemisphere, underneath occipital bone

Function: Process incoming visual information and stores visual memories

Insula

Internal lobe

• Deep to lateral sulcus and temporal lobe

Function: Involved in emotional processing and gustatory information

Diencephalon

Internal region of the brain

Epithalamus

Region above thalamus

• Pineal gland: secretes melatonin to regulate circadian rhythm

• Habenular nucleus: aids in relaying information from limbic system (emotional center) to midbrain

Thalamus

Oval in the center

• Large relay station for sensory information that will be projected to sematosensory cortex

Hypothalamus

Region below thalamus

• Regulates body temperature (homeostasis)

• Master control of both autonomic nervous system and endocrine system

• Stalk-like infundibulum that extends inferiorly from hypothalamus to attach to pituitary gland of endocrine system

Brainstem

Passageway for all tracts between cerebrum and spinal cord

• Controls autonomic functions we are not aware of (key in survival)

Midbrain

Superior portion of brain stem and has white and gray matters that help produce dopamine to relay happy sensation throughout

• Substantia nigra: houses neurons that produce dopamine

Pons

Bulging region of anterior brainstem (shaped like a P)

• Key in controlling autonomic function of breathing rate

• Relay information from facial nerve to take in sensory information around face and tongue

• Aid in localizing sound

Medulla Oblangata

The most inferior part of brainstem and is key in SURVIVAL

• Several Autonomic Nuclei:

  • Cardiac Center: regulates heart rate, blood pressure, and other cardiac muscle related

  • Vasomotor Center: controls blood pressure by contributing to size and dilation of blood vessels

  • Medullary respiratory center: regulates respiratory rate

Cerebellum

Second largest part of the brain; also has left and right CEREBELLAR hemispheres

• Have anterior and posterior lobes and narrow vermis sits on midline between

• Folds of cerebellar cortex are called folia

Function: balance coordination center and helps us understand proprioception, where our body is in relation to space overall (general proprioception coordination center)

Arbor Vitae

The tree-like branching pattern of white matter inside the cerebellum

Corpus Callosum

Large commisural tract that connects left and right cerebral hemispheres

Precentral Gyrus

Elevated ridge in frontal lobe just anterior to central sulcus

Postcentral Gyrus

Elevated ridge in parietal lobe immediately posterior to central sulcus

Longitudinal Fissure

Divides the cerebral hemispheres into left and right halves that extends along the midsagittal brain

Central Sulcus

Shallow groove that separate precentral and postcentral gyrus

Gyrus

Folds/elevated ridges of brain tissue

Sulcus

Depressions of the folds/shallow grooves and separates gyrus

Fissure

Deeper grooves/depressions that separate large regions of the brain

General organization of gray matter and white matter

Gray matter is the darker surface of the brain and forms cerebral cortex

• Contains motor neurons and interneuron cell bodies

• Have unmyelinated axons that will run down into brain so all white matter axons are going to run deep into brain to distribute information to central processing area

White matter are made up of myelinated axons and deep to gray matter

• Distributes information in a circular direction to allow for communication between different region of the brain

What are the structures that protect the CNS and what is their major role?

• All 3 meninges are protective connective tissue that separates brain from bones of cranium, protect blood vessels of brain, and form large veins for draining of blood from brain, contains circulating cerebrospinal fluid

• Cerebrospinal fluid is an important structure around the brain produced by ependymal cells to help provide buoyancy, act as an insulator by providing liquid cushion, and stabilizes the environment by transporting nutrients and removes wastes from the brain

• Blood Brain Barrier maintained by astrocytes are created by capillaries which filters blood and cerebrospinal fluid—produced and secreted through ventricles by ependymal cells

• BBB is a selective barrier that lines blood vessels to prevent harmful substances in the blood from entering brain tissue

Falx Cerebri

Part of the dural septa—meningeal layer of dura mater that’s extending into cranial cavity to form double layer dura

• Projects into longitudinal fissure

• Separates left and right cerebral hemispheres to provide support by partitioning brain from cranial bones

Tentorium Cerebelli

Horizontal folds that separates cerebrum from cerebellum

Falx Cerbelli

Separates left and right cerebellar hemispheres

Formation and Function of Dural Venous Sinuses

Gaps between two layers of dura mater

• When periosteal and meningeal layers unfuse to create this space

• Drains and collects venous (deoxygenated) blood from brain tissue

• Drains cerebrospinal fluid from the subarachnoid space

Choroid Plexus

Network of capillaries lined by ependymal cells

• Blood from capillaries is filtered by ependymal cells to form cerebrospinal fluid

• There are choroid plexuses that secrete cerebrospinal fluid in each ventricle

Lateral Ventricle

• Largest; there are 2, one in each cerebral hemisphere

• Produces the most CSF

Third Ventricle

Located in diencephalon

• Communicates with lateral ventricles through interventricular foramen

• Communicates with fourth ventricle through cerebral aqueduct

Fourth Ventricle

Between pons and cerebellum

• Merges with central canal of spinal cord

Primary Sematosensory Cortex

Located within postcentral gyrus; provide conscious awareness of somatic sensation

• Receives general somatosensory information from mechanoreceptors, baroreceptors, nociceptors, and thermoreceptors

Primary Auditory Cortex

Located in the temporal lobe

• Processes auditory information

Primary Visual Cortex

Located in the occipital lobe

• Processes visual information

Primary Olfactory Cortex

Located in the temporal lobe

• Provides awareness of smell

Primary Gustatory Cortex

Located in the Insula

• Processes taste information

Difference between primary sensory cortex and its association area

Primary sensory cortex received general sensory information from receptors. Its association area integrates and interprets than information to give it meaning

• Example: The primary somatosensory cortex detect touch via mechanoreceptors and the somatosensory association area interpret and integrate this information with the shape, texture, and identity of an object 

Premotor Cortex

Located in frontal lobe just anterior to precentral gyrus

• An associate area that coordinates skilled motor cortex

Somatosensory Association Area

Located in the parietal lobe just posterior to postcentral gyrus

• Association area that integrates and interprets general sensory information

Auditory Association Area

Located in the temporal lobe; posteroinferior to primary auditory cortex

• Interprets characteristics of sound and stores memories of sound

Visual Association Area

Located in occipital lobe; surrounds primary visual cortex

• Processes visual information

Wernicke Area

Located in left cerebral hemisphere, overlapping the parietal and temporal lobes

Primary Motor Cortex

Located within precentral gyrus

• Controls voluntary skeletal muscle activity

Motor Speech Area aka Broca Area

Located within the inferolateral portion of the left frontal lobe

• Controls muscular movements necessary for vocalization

Frontal Eye Field

Anterior to premotor cortex

• Helps control and regulate eye movements

How does sensory and motor homunculus relate area of the brain to function

The motor homunculus is a visual representation on the precentral gyrus (primary motor cortex) that shows how different body parts are controlled by specific regions of the cortex

• Example: Body parts requiring fine motor control, such as the hands, face, and tongue, occupy larger areas of the homunculus.

Sensory homunculus: the visual representation on the postcentral gyrus (primary somatosensory cortex) that shows how different body parts are mapped according to their sensitivity to touch and sensation

• Example: Body regions with more sensory receptors, like the hands, lips, and face, take up larger areas on the homunculus.

Larger the area

• More innervation and more motor control (finer as well)

• More innervation, more sensory receptors, and more sensitive

I. Oculomotor Nerve

Sensory

• Smell

II. Optic Nerve

Sensory

• Vision

III. Oculomotor Nerve

Motor

• Eye/eyelid control, pupil, lens shape

IV. Trochlear Nerve

Motor

• Eye movement (superior oblique)

V. Trigeminal Nerve

Both

• Chewing, sensation for head and face

VI. Abducens Nerve

Motor

• Lateral eye movement (lateral rectus)

VII. Facial Nerve

Both

• Facial expression, salivation, taste, and tears

VIII. Vestibulocochlear Nerve

Sensory

• Hearing and equilibrium (balance/orientation)

IX. Glossopharyngeal Nerve

Both

• Salivation, taste, and swallowing

X. Vagus Nerve

Both

• Visceral muscle movement

XI. Accessory Nerve

Motor

• Head and shoulder control

XII. Hypoglossal Nerve

Motor

• Tongue movements, speech, and swallowing

Hydrocephaly

Increase of pressure in the brain as a result of increase in CSF

Meningitis

The inflammation of meninges

• Increase in inflammation causes an increase of swelling of meninges leading to increase in pressure on both brain and spinal cord

General pathway or circulation of cerebrospinal fluid

1. Cerebrospinal fluid is produced by choroid plexus inside ventricles

2. Cerebrospinal fluid is going to travel from lateral ventricle → third ventricle via interventricular foramen → fourth ventricle via cerebral aqueduct

3. Cerebrospinal fluid will continue down to specific gap of meninges called subarachnoid space and will flow into the spinal cord

4. Cerebrospinal fluid is eventually going to drain back out to dural venous sinus