Introduction

The brain is far more complex than the spinal cord.

The brain contains roughly 20 billion neurons.

Excitatory and inhibitory interactions among the extensively interconnected neuronal pools ensure that the response can vary to meet changing circumstances.

An Introduction to the Organization of the Brain

Protection and Support of the Brain

 Protection, support, and nourishment of the brain involves:

Bones of the skull

Cranial meninges

Dura mater
Arachnoid mater
Pia mater

Cerebrospinal fluid

Blood–brain barrier

Vessels of the cardiovascular system

Blood Supply to the Brain

The Cerebrum

 The cerebrum is the largest, most superior portion of the human brain.

 Each cerebral hemisphere receives sensory information from and generates motor commands to the opposite side of the body.

 The two hemispheres have some functional differences, although anatomically they appear to be identical.

The Diencephalon

 The diencephalon connects the cerebrum to the brain stem both structurally and functionally.

 The functions that occur in the diencephalon are almost exclusively subconscious.

Epithalamus — controls the circadian rhythm

Thalamus — relays information

Hypothalamus — coordinates the nervous and endocrine systems

The Mesencephalon

The mesencephalon, or midbrain, is the most superior portion of the brain stem.

Nuclei coordinate visual and auditory reflexes.

Corpora quadregemina
Superior colliculi — visual
Inferior colliculi — auditory

Limbic system nuclei

Coordinate involuntary movements of skeletal muscles

Cerebral peduncles

Nerve bundles to and from the brain/spinal cord

The Pons

 The pons mainly functions:

As a house for cranial nerve nuclei V, VI, VII, and VIII

To help regulate respiration

To help coordinate involuntary skeletal muscle movements and muscle tone

In relaying information to and from the brain/spinal cord

The Pons

The Cerebellum

 The cerebellum has two primary functions:

Adjusts the postural muscles of the body to maintain balance

Programs and fine-tunes voluntary and involuntary movements

The Medulla Oblongata

The medulla oblongata physically connects the brain with the spinal cord.

It is so important that, if it is severely compromised, the victim will likely die.

The medulla oblongata is a relay station, house for cranial nerve nuclei, and most importantly, controls visceral functions like blood pressure, breathing, and heart rate.

The Medulla Oblongata

The Cranial Nerves

Cranial nerves are components of the peripheral nervous system that connect to the brain rather than to the spinal cord.

Twelve pairs of cranial nerves

Cranial nerves are numbered using Roman numerals

Each cranial nerve attaches to the brain near the associated sensory or motor nuclei

Olfactory Nerve (N I)

 Primary function: special sensory (smell)

 Origin: receptors of olfactory epithelium

 Passes through: cribriform plate of ethmoid

 Destination: olfactory bulbs

The Optic Nerve (N II)

Primary function: special sensory (vision)

Origin: retina of eye

Passes through: optic canal of sphenoid

Destination: diencephalon by way of the optic chiasm

The Oculomotor Nerve (N III)

Primary function: motor, eye movements

Origin: mesencephalon

Passes through: superior orbital fissure of sphenoid

Destination:

Somatic motor: superior, inferior, and medial rectus muscles; the inferior oblique muscle; the levator palpebrae superioris muscle
Visceral motor: intrinsic eye muscles

The Trochlear Nerve (N IV)

Primary function: motor, eye movements

Origin: mesencephalon

Passes through: superior orbital fissure of sphenoid

Destination: superior oblique muscle

The Trigeminal Nerve (N V)

Primary function: Mixed (sensory and motor)

Ophthalmic and maxillary branches sensory
Mandibular branch mixed

Origin:

Ophthalmic branch (sensory): orbital structures, nasal cavity, skin of forehead, superior eyelid, eyebrow, and part of the nose
Maxillary branch (sensory): inferior eyelid, upper lip, gums, and teeth; cheek; nose, palate, and part of the pharynx
Mandibular branch (mixed): sensory from lower gums, teeth, and lips; palate and tongue (part); motor from motor nuclei of pons

Passes through:

Ophthalmic branch through superior orbital fissure
Maxillary branch through foramen rotundum

Mandibular branch through foramen ovale

Destination:

Ophthalmic, maxillary, and mandibular branches to sensory nuclei in the pons

Mandibular branch also innervates muscles of mastication

The Abducens Nerve (N VI)

Primary function: motor, eye movements

Origin: pons

Passes through: superior orbital fissure of sphenoid

Destination: lateral rectus muscle

The Facial Nerve (N VII)

Primary function: mixed (sensory and motor)

Origin:

Sensory from taste receptors on anterior two thirds of tongue

Motor from motor nuclei of pons

Passes through: internal acoustic meatus of temporal bone, along facial canal to reach stylomastoid foramen

Destination:

Sensory to sensory nuclei of pons

Somatic motor: muscles of facial expression

Visceral motor: lacrimal (tear) gland and nasal mucous glands via pterygopalatine ganglion; submandibular and sublingual salivary glands via submandibular ganglion

The Vestibulocochlear Nerve (N VIII)

Primary function: special sensory: balance and equilibrium (vestibular branch) and hearing (cochlear branch)

Origin: receptors of the inner ear (vestibule and cochlea)

Passes through: internal acoustic meatus of the temporal bone

Destination: vestibular and cochlear nuclei of pons and medulla oblongata

The Glossopharyngeal Nerve (N IX)

Primary function: mixed (sensory and motor)

Origin:

Sensory from posterior one third of the tongue, part of the pharynx and palate, the carotid arteries of the neck

Motor from motor nuclei of medulla oblongata

Passes through: jugular foramen between occipital and temporal bones

Destination:

Sensory fibers to sensory nuclei of medulla oblongata

Somatic motor: pharyngeal muscles involved in swallowing

Visceral motor: parotid salivary gland, after synapsing in the otic ganglionThe Vagus Nerve (N X)

Primary function: mixed (sensory and motor)

Origin:

Visceral sensory from pharynx (part), auricle, external acoustic meatus, diaphragm, and visceral organs in thoracic and abdominopelvic cavities

Visceral motor from motor nuclei in the medulla oblongata

Passes through: jugular foramen between occipital and temporal bones

Destination:

Sensory fibers to sensory nuclei and autonomic centers of medulla oblongata

Somatic motor to muscles of the palate and pharynx

Visceral motor to respiratory, cardiovascular, and digestive organs in the thoracic and abdominal cavities.

The Accessory Nerve (N XI)

Primary function: motor

Origin: motor nuclei of spinal cord and medulla oblongata

Passes through: jugular foramen between occipital and temporal bones

Destination:

Internal branch innervates voluntary muscles of palate, pharynx, and larynx

External branch controls sternocleidomastoid and trapezius muscles

The Hypoglossal Nerve (XII)

Primary function: motor, tongue movements

Origin: motor nuclei of the medulla oblongata

Passes through: hypoglossal canal of occipital bone

Destination: muscles of the tongue