Brain + Cranial Nerves

Six Major Regions of the Brain

- Cerebrum

- Diencephalon

- Cerebellum

- Mesencephalon

- Pons

- Medulla

Cerebrum

- Biggest area of the brain

- Conscious thought process, intellectual functions

> Being aware of what is going on (senses + voluntary movement)

- Memory storage + thought processing

- Conscious + subconscious regulation of skeletal muscle contractions

- Has gyri

- Has sulcus

- Has longitudinal fissure

- Has transverse cerebral fissure

Gyri

- Elevations

- Single elevation = gyrus

- Increases surface area

Sulcus

- In-between gyri

- Shallow depression

- Creates the different lobes of the brain

Longitudinal Fissure

- Deep depression

- In-between the right + left lobe

- Divides right + left hemispheres of the brain

Transverse Cerebral Fissure

- In-between cerebrum and cerebellum

- Deep depression

Brain Lobes

- Frontal lobe

- Parietal lobe

- Occipital lobe

- Temporal lobe

Frontal + Parietal Lobes

Has central sulcus in-between them

Parietal + Occipital Lobes

Has parieto-occipital sulcus in-between them

Lateral Sulcus

Divides the temporal lobe from all three other lobes

Cerebral Cortex

- Having a group of neuronal cell bodies at the surface of CNS

- Each hemisphere controls the opposite side of the body

- Gray matter on the surface

Corpus Callosum

Bundle of axons that decussate between the two hemispheres and allows them to communicate with each other

Commissural Fibers

- Fibers that connect the two hemispheres

- Includes:

> Corpus callosum

> Anterior commissure

Association Fibers

Connects areas of the cerebral cortex within the same hemisphere

Association Fibers Examples

- Arcuate fibers

- Longitudinal fasciculi

Projection Fibers

- Groups of axons that link other regions of the brain spinal cord

- Is able to make connections between the cerebrum and other parts of the brain

Frontal Lobe

- Conscious control of the skeletal muscles

- Problem solving, reasoning, planning, etc.

Frontal Lobes Components

- Precentral gyrus

- Premotor cortex

- Prefrontal cortex

Precentral Gyrus

- Aka primary motor cortex

- Anterior to the central sulcus

- Sends nerve impulses towards the muscles (initiation of movement)

- Has pyramidal cells

Pyramidal Cells

Large neurons that allow conscious control of the skeletal muscle movement

Premotor Cortex

- Anterior to precentral gyrus

- Plans motor movement

- Sends information to precentral gyrus

Premotor Cortex Example

Thinking about picking up a pen

Prefrontal Cortex

- Anterior to premotor cortex

- Area for:

> Thinking

> Problem solving

> Concentration

> Personality, morality, judgement, etc.

Parietal Lobe

- Overall related to sensation

- Includes:

> Post-central gyrus

> Somatosensory association area

Post-Central Gyrus

- Aka primary somatosensory cortex

- Posterior to central sulcus

- Where sensations are consciously felt

Somatosensory Association Area

- Posterior to post-central gyrus

- Allows us to understand texture, size, and shape

Occipital Lobe

- Related to vision

- Related to perception of visual stimuli

- Includes:

> Visual cortex

> Visual association area

Visual Cortex

Anything you see

Visual Association Area

Being able to recognize a face

Temporal Lobe

- Lateral sides of the brain

- Related to hearing + smelling

- Includes:

> Auditory cortex

> Olfactory cortex

Insula

- Inside the cerebrum

- Includes:

> Gustatory cortex (taste)

Cerebellum

- Means "little brain"

- Second largest part of the brain

- Coordination of complex skeletal muscle movement

- Allows us to coordinate repetitive body movements

- Has vermis

- Has primary fissure

- Has folia

- Has cerebellum cortex

- Has arbor vitae

- Has purkinje cells

Cerebellum Example

Being able to dance, ride a bike, etc.

Vermis

Separates right + left hemisphere of the cerebellum

Primary Fissure

Separates the anterior + posterior lobe of the cerebellum

Folia of Cerebellum

- Folds

- Equivalent to cerebrum gyri

Cerebellum Cortex

Gray matter in the surface

Arbor Vitae

- White matter

- Looks like the tree of life

Purkinje Cells

Neuronal cell bodies responsible for coordinated movement

Molecular Layer of Purkinje Cells

- Aka synaptic layer

- Where the dendrites are found

- Outer layer

Purkinje Layer of Purkinje Cells

- Aka intermediate layer

- Where purkinje cell bodies are found

- Middle layer

Granular Layer of Purkinje Cells

- Aka receptive layer

- Where axons are found

- Inner layer

- Has tightly packed small neurons

Diencephalon

- Completely inside of the cerebrum

- Divided into three regions:

> Epithalamus

> Thalamus

> Hypothalamus

Epithalamus

Has the pineal gland

Pineal Gland

- Endocrine gland that produces melatonin

- Affects modulation of wake sleep patterns

- Blood brain barrier is absent

Thalamus

- Under the epithalamus

- Has right + left sides connected via inter-thalamic adhesion

- Relay station for all sensory information coming from spinal cord + eyes + ears (95%)

- Largest mass (nuclei) of neuronal cell bodies found within the CNS

Hypothalamus

- Below the thalamus

- Center of homeostasis

- Has temperature control center + centers that regulate internal balance

- Highest control center over the autonomic motor neurons

- Greatly affected by a person's emotional stress

> Hypothalamus is wired to limbic system (center of emotions)

- Controls release of hormones by the pituitary gland

- Links the nervous system + endocrine system via the pituitary gland

- Produces hormones

Hypothalamus Examples

- Controls thirst that gives us desire to drink

- Increases or decreases heart rate

Pituitary Gland

- Connected by infundibulum to the hypothalamus

- Major endocrine gland

- Blood brain barrier is absent

Brainstem

- Three main areas:

> Mesencephalon

> Pons

> Medulla oblongata

Mesencephalon

- Aka midbrain

- Located in the middle of the two brain regions (diencephalon/cerebrum + pons/ medulla oblongata)

- Has a role in moving our eyes

> Extrinsic eye muscles are innervated by nerves coming out of the mesencephalon

- Processes sight, sound, and associative reflex

Associative Reflex Example

Reacting unexpectedly to a loud sound

Pons

- Relay station between cerebellum and cerebrum

- Coordinates skeletal muscular activity

- Has a role in breathing pattern

> Has centers that regulate the activity of the respiratory reflex center in the medulla oblongata

Medulla Oblongata

- Right under the pons

- Connects the brain + spinal cord

- Relay station for spinal cord + rest of brainstem

- Cardiac + respiratory reflex centers

- Vagus nerve (#10) comes out of here

- Related to autonomic centers that regulate cardiovascular, respiratory, + digestive systems

- Regulates basic vital functions

Components That Protect the Brain

- Bones of the skull

- Cranial meninges

- CSF

- Blood brain barrier

- Rich blood supply

Layers of Brain (Superficial to Deep)

- Scalp

- Epicranial aponeurosis

- Periosteum of cranium

- Bones of the skull (cranium)

- Cranial meninges

Epicranial Aponeurosis

Tough layer of dense fibrous tissue

Periosteum Cranium

Vascular connective tissue that involves the bone

Cranial Meninges

- Connective tissue layers that connect the soft tissue of the brain from the skull

- Dura mater

- Arachnoid mater

- Pia mater

Cranial Dura Mater

- Toughest

- Right under the cranium

- Two layers:

> Periosteal layer

> Meningeal layer

Periosteal Layer

- Closer to the skull

- Attaches to inner surface of the skull

- Layer felt within the anterior fontanelle of a baby

- Only found in the brain

Meningeal Layer

- True layer that covers the brain

- Extends the vertebral canal as the spinal dura mater

Dural Venous Sinus

- Blood filled space caused by the separation of the two dura mater layers

- Filled with venous blood

- Majority of the blood from the brain drains into it

- The jugular vein gets blood supply from this sinus

- Veins of the brain empty themselves into this sinus which delivers blood to the internal jugular vein in the neck

Jugular Vein

Drains blood out of the brain

Cranial Arachnoid Mater

- Resembles a spider web due to arachnoid trabeculae

- Encloses and protects blood vessels that supplies the brain

Arachnoid Trabeculae

- Collagen fibers

- Anchors the cerebral blood vessels to their place

Cranial Pia Mater

- Softest

- Delicate connective tissue that attaches to the brain itself

- Right on top of cerebral cortex

- Contours every gyrus of cerebral cortex

- Has blood vessels

- Nourishes brain cells

Cranial Subdural Space

- Between the cranial dura + arachnoid mater

- Has the potential to be filled with fluid when necessary

- Does not normally exist

Cranial Subdural Space Example

- Subdural hematoma

- This is the space that gets filled with blood

Superior Sagittal Sinus

- Between the right + left cerebral hemispheres in the superior side

- Receives blood from cerebral veins

- Receives CSF from subarachnoid space via arachnoid granulation

Subarachnoid Space

- Between the arachnoid + pia mater

- A true space

- CSF flows through

Arachnoid Granulation

- Projections that go into the superior sagittal sinus

- Extensions of the arachnoid mater

- CSF is able to reach superior sagittal sinus

> Due to fluid pressure, CSF is forced into the bloodstream from the subarachnoid space (gets recycled)

Dura Septa

- Folds

- Extensions of the dura mater that goes deep into the brain

- Subdivides cranial cavity

- Supports the brain

- Limits brain movement

Falx Cerebri

Dura mater folds located between right + left hemispheres of the cerebrum (along with the longitudinal fissure)

Falx Cerebelli

Dura mater folds located between right + left hemispheres of the cerebellum

Tentorium Cereblli

Dura mater folds located along the transverse cerebral fissure

Crista Gali

- Feature of the ethmoid bone

- Point of attachment in the inferior, anterior aspect of the falx cerebri

- Anchors the brain

Sella Turcica

- Feature of the sphenoid bone

- Has the pituitary gland sitting on it

- Pituitary gland is encased by the diaphragm sellae

Diaphragma Sellae

- Fold of the dura mater

- Lines the sella turcica

- Anchors dura mater to sphenoid bone

Infundibulum

Structure that connects pituitary gland and the hypothalamus

Brain Ventricles

- Fluid filled cavities

- Has CSF

CSF Sequence Through the Brain Ventricles

- Lateral ventricle

- Interventricular foramen

- Third ventricle

- Aqueduct of midbrain

- Fourth ventricle

LIT AF

Lateral Ventricle

- Paired

- Found in the cerebrum hemispheres

- Extends from anterior horn (frontal lobe) to posterior horn (occipital lobe) + inferior horn (temporal lobes)

- Has no direct connection between the two lateral ventricles

- Most of it is located within the parietal lobe

Interventricular Foramen

Allows communication between the lateral and third ventricle

Third Ventricle

- Is in-between the right + left sides of the thalamus

- Fluid filled space

- Interthalamic adhesion is needed to have the two thalami surrounding the third ventricle

Aqueduct of Midbrain

Allows communication between third and fourth ventricle

Fourth Ventricle

- Located between the pons + cerebellum

- Communicates with the central canal of the spinal cord

Septum Pellucidum

Separates the two lateral ventricles

Choroid Plexus

- Vascularized membrane

- "Choroid" = blood vessels

- "Plexus" = network

- Blood vessels are surrounded by ependymal cells

Directionality of CSF

- One way flow

- Directionality of CSF is due to the ciliated ependymal cells

- A normal adult replaces about 150 mL of CSF every 8 hours

- Ependymal cells takes nutrients from blood to make CSF

Median + Lateral Apertures

- Two openings that communicate with subarachnoid space in the brain + spinal cord

- This is the way through which CSF leaves the brain from the fourth ventricle

- About 90% of CSF travels through here

Central Canal

- 10% of which CSF travels through

- Runs through entire spinal cord

Arachnoid Villi

- Works as a one way valve

- When CSF pressure is less than venous pressure, arachnoid villi will not let blood pass into ventricular system and vice versa

Hydrocephalus

- Results from overproduction of CSF

- Can also result from obstruction at some point within the ventricular system

- Can be related to problems with CSF reabsorption

Hydrocephalus in New Borns

- Found in new borns because skull bones are fused together

- Causes increased pressure and results in a very large head

Hydrocephalus in Adults

- Found in adults because rigidity of the skull keeps pressure within

- Can lead to brain damage due to compression of brain blood vessels + crushes soft nervous tissue

Treatment of Hydrocephalus

Treated by draining CSF by making a little hole in the ventricle + using a little tube to drain it into the abdominal cavity

CSF Functions

- Prevents contact of neural tissue with the surrounding bones

- Reduces the weight of the brain from 1500 g to 50 g

- Allows brain to float so that it doesn't get crushed on its own weight

- Protects brain from blows + other trauma

- Transports nutrients to CNS tissue

- Transports waste away from the CNS

Blood Brain Barrier

- Irregulates substances between blood + brain tissue

- Made up of capillary endothelial cells

- Surrounded + formed by astrocytes

- Tight junctions block the passage of material between the endothelial cells

- Only lipid soluble compounds are able to go through the lipid bilayer

- Allows nutrients to go in and nourish brain tissue

- Allows waste to get out of brain tissue

Nutrients Going into BBB Examples

- Glucose

- O2