The Brain and Cranial

Nerves

Cerebrum

Largest part of brain

Controls higher mental functions

Divided into left and right cerebral hemispheres

Surface layer of gray matter (neural cortex)

Also called cerebral cortex

Folded surface increases surface area

Elevated ridges (gyri)

Shallow depressions (sulci)

Deep grooves (fissures)

Three Functional Principles of the Cerebrum

Each cerebral hemisphere receives sensory

information from, and sends motor commands to, the

opposite side of the body

The two hemispheres have different functions,

although their structures are alike

Correspondence between a specific function and a

specific region of cerebral cortex is not precise

White Matter of the Cerebrum Association fibers connect within on

hemisphere Arcuate fibers

– Short– Connect one gyrus to another

Longitudinal fasiculi– Longer bundles– Connect frontal lobe to other lobes in same hemisphere

Commissural fibers connect two hemispheres Projection fibers link cerebral cortex with

diencephalon, brain stem, cerebellum, and spinal cord

Motor and Sensory Areas of the Cortex Central sulcus separates motor and sensory areas

The percentages of total cerebral cortex volume for the different lobes are:

frontal lobe = 41% temporal lobe = 22% parietal lobe = 19% occipital lobe = 18%

Hemispheric Lateralization

Functional differences

between left and right

hemispheres

Each cerebral

hemisphere performs

certain functions that are not ordinarily performed by the opposite hemisphere

The Basal Nuclei of the Cerebrum

Also called cerebral nuclei

Are masses of gray matter embedded in white

matter of cerebrum

Direct subconscious activities

control of skeletal muscle tone

coordination of learned movement patterns (walking,

lifting)

Cerebellum

Second largest part of brain

Two hemispheres

Covered with cerebellar cortex

Coordinates repetitive body movements

Adjusts postural muscles

Fine-tunes conscious and subconscious movements

Diencephalon

Located under cerebrum and cerebellum

Links cerebrum with brain stem

Made up of:

Thalamus

– Relays and processes sensory information

Hypothalamus

– Hormone production

– Emotion

– Autonomic function

Pituitary Gland

– Major endocrine gland

– Interfaces nervous and endocrine systems

The Brain Stem Processes information between

Spinal cord and cerebrum or cerebellum

Includes

Mesencephalon

Pons

Medulla oblongata

Mesencephalon Also called midbrain

Processes sight, sound, and

associated reflexes

Maintains consciousness

Pons Connects cerebellum to brain stem

Is involved in somatic and visceral motor control

Medulla oblongata Connects brain to spinal cord

Relays information

Regulates autonomic functions: heart rate, blood pressure, and

digestion

Embryological DevelopmentEmbryological Development

Determines organization of brain structures

Neural tube- origin of brain

Ventricles of Brain

Origin Neural tube encloses neurocoel

Neurocoel expands to form chambers (ventricles) lined with

ependymal cells

Each cerebral hemisphere contains one large lateral

ventricle

Third ventricle

Ventricle of the diencephalon

Lateral ventricles communicate with third ventricle:

– via interventricular foramen (foramen of Monro)

Fourth ventricle

Extends into medulla oblongata

Becomes continuous with central canal of the spinal cord

Connects with third ventricle: via narrow canal in

mesencephalon (aqueduct of midbrain)

Brain Protection and Support

Physical protection

Bones of the cranium

Cranial meninges

Cerebrospinal fluid

Biochemical isolation

Blood–brain barrier

The Cranial Meninges Dura mater

Inner fibrous layer (meningeal layer)

Outer fibrous layer (endosteal layer) fused to periosteum

Venous sinuses between two layers

Arachnoid mater Covers brain

Contacts epithelial layer of dura mater

Subarachnoid space: between arachnoid mater and pia mater

Pia mater Attached to brain surface by astrocytes

Cerebrospinal Fluid (CSF)

Surrounds all exposed surfaces of CNS

Interchanges with interstitial fluid of brain

Functions of CSF

Cushions delicate neural structures

Supports brain

Transports nutrients, chemical messengers, and

waste products

CSF formation & circulation

CSF circulates

From choroid plexus

through ventricles to

central canal of spinal cord

Into subarachnoid space

around the brain, spinal

cord, and cauda equina

Reabsorbed by arachnoid

granulations in

subarachnoid space

Brain Protection and Support

Blood–Brain Barrier

Isolates CNS neural tissue from general circulation

Allows chemical composition of blood and CSF to differ

Astrocytes control blood–brain barrier by releasing

chemicals that control permeability of endothelium

Four Breaks in the BBB Portions of hypothalamus secrete hypothalamic hormones

Posterior lobe of pituitary gland secretes hormones ADH and oxytocin

Pineal glands for pineal secretions

Choroid plexus where special ependymal cells maintain blood–CSF barrier

The Limbic System

Establishes emotional states

Links conscious functions of cerebral cortex with

autonomic functions of brain stem

Facilitates memory storage and retrieval

Four Categories of Brain Waves Alpha waves

Found in healthy, awake adults at rest with eyes closed Beta waves

Higher frequency Found in adults concentrating or mentally stressed

Theta waves Found in children Found in intensely frustrated adults May indicate brain disorder in adults

Delta waves During sleep Found in awake adults with brain damage

Brain Waves are analyzed with the use of an EEG or electroencephalogram

Cranial Nerves

12 pairs connected to brain

Four Classifications of Cranial Nerves

Sensory nerves: carry somatic sensory information,

including touch, pressure, vibration, temperature, and

pain

Special sensory nerves: carry sensations such as

smell, sight, hearing, balance

Motor nerves: axons of somatic motor neurons

Mixed nerves: mixture of motor and sensory fibers