Chapter 15: The Brain and Cranial Nerves

What is the major function of the brain?

Registers sensations, makes decisions, and stores memory

What is the centerpiece of the CNS?

The brain

What structure surrounds and protects the brain?

The skull

What are the cranial meninges?

Connective tissue coverings around the brain continuous with spinal meninges

What are the three cranial meninges?

Dura mater, arachnoid layer, and pia mater

What is the dura mater?

Outer meningeal layer that forms a protective bag around the brain

What type of tissue composes the dura mater?

Dense irregular connective tissue

What is the epidural space?

Space between the skull and dura mater containing adipose tissue

What is the function of the epidural space?

Cushions the brain

What is the arachnoid layer?

Middle meningeal layer

Why is it called the arachnoid layer?

Its fibers resemble a spider web

Is the arachnoid layer vascular or avascular?

Avascular

What is the subdural space?

Space between the dura mater and arachnoid layer filled with interstitial fluid

What is the pia mater?

Innermost meningeal layer

What is unique about the pia mater?

It is transparent and highly vascular

What is the function of blood vessels in the pia mater?

Supply oxygen and nutrients to brain neurons

What is the subarachnoid space?

Space between the pia mater and arachnoid layer containing CSF

What is meningitis?

Inflammation of the meninges

What causes meningitis?

Bacteria or viruses

What are symptoms of meningitis?

Headache, stiff neck, high fever, and vomiting

Can meningitis be fatal?

Yes

What is cerebrospinal fluid (CSF)?

Fluid that nourishes and protects the brain and spinal cord

Where does CSF circulate?

Subarachnoid space and ventricles of the brain

What is CSF composed of?

Water, glucose, ions, proteins, and leukocytes

What are the three functions of CSF?

Buoyancy, protection, and chemical stability

How does CSF provide buoyancy?

Supports the brain

How does CSF provide protection?

Prevents the brain from striking the cranium and contains leukocytes

How does CSF provide chemical stability?

Delivers nutrients and removes metabolic wastes

What is the choroid plexus?

Network of capillaries in the walls of the ventricles

Which cells cover the choroid plexus?

Ependymal cells

What do ependymal cells of the choroid plexus do?

Secrete CSF

Why can't blood waste enter CSF easily?

Ependymal cells are tightly joined together

What is hydrocephalus?

Excess accumulation of CSF in the ventricles

What effect does hydrocephalus have?

Causes head enlargement and increased brain pressure

How is hydrocephalus treated?

Surgery

Through what structure does CSF flow between ventricles?

Cerebral aqueduct

Where does CSF flow after the cerebral aqueduct?

Central canal of the spinal cord

Why does the brain require a large blood supply?

To provide oxygen and nutrients to neurons

How quickly can neurons die without oxygen?

Within 4 minutes

What is the blood-brain barrier (BBB)?

Barrier preventing many substances from entering the brain

What forms the blood-brain barrier?

Tight ependymal cells and astrocytes around capillaries

What types of substances cross the BBB most easily?

Lipid-soluble substances

What substances can pass through the BBB?

Amino acids, electrolytes, and sugars

What substances are blocked by the BBB?

Urea, toxins, and many waste products

Why is BBB damage dangerous?

It is often deadly

What are the four principal parts of the brain?

Brain stem, cerebellum, diencephalon, and cerebrum

What is the brain stem?

Structure connecting the spinal cord to the diencephalon

What structures make up the brain stem?

Medulla oblongata, pons, midbrain, and reticular formation

What is the medulla oblongata?

Inferior portion of the brain stem

Where does the medulla extend?

From the foramen magnum to the pons

What are the pyramids?

Bulges containing motor tracts in the medulla

What is the decussation of pyramids?

Region where motor tracts cross over

What side of the body does the left medulla control?

Right side

What do the nucleus gracilis and nucleus cuneatus do?

Relay sensory information to the thalamus and cerebrum

What do the nucleus gracilis and nucleus cuneatus form together?

Medial lemniscus

What is the cardiovascular center?

Region regulating heart rate, force, and blood vessel diameter

What is the medullary rhythmicity area?

Region regulating breathing rhythm

What is the vasomotor center?

Region regulating blood pressure through vessel diameter changes

What is the olive?

Oval structure that relays posture and equilibrium information to the cerebellum

What is the pons?

Brain stem structure superior to the medulla that acts as a bridge

What are cerebellar peduncles?

Fiber bundles connecting the pons and cerebellum

What areas of the pons regulate breathing?

Pneumotaxic and apneustic areas

What is the midbrain?

Portion of the brain stem between the pons and diencephalon

What passes through the midbrain?

Cerebral aqueduct

What do cerebral peduncles do?

Carry impulses from the pons and medulla to the thalamus

What are the corpora quadrigemina?

Four rounded elevations in the midbrain tectum

What are the superior colliculi?

Reflex centers for eye and head movements

What are the inferior colliculi?

Reflex centers for auditory stimuli

What is the substantia nigra?

Dark pigmented region controlling subconscious muscle activity

What pigment is found in the substantia nigra?

Melanin

What neurotransmitter-producing neurons degenerate in Parkinson's disease?

Dopamine neurons in the substantia nigra

What is the red nucleus?

Midbrain structure coordinating muscular movements

Why is the red nucleus red?

Large blood supply

What is the medial lemniscus?

White matter tract carrying touch and pressure information to the thalamus

What is the reticular formation?

Brain stem area of mixed gray and white matter

What are the functions of the reticular formation?

Pain modulation, sleep regulation, consciousness, and filtering stimuli

What is the cerebellum?

Second largest part of the brain

Where is the cerebellum located?

Posterior to the medulla and pons

What separates the cerebellum from the cerebrum?

Transverse fissure

What is the vermis?

Central portion of the cerebellum

What is the cerebellar cortex?

Superficial layer of the cerebellum

What attaches the cerebellum to the brain stem?

Cerebellar peduncles

What are Purkinje cells?

Myelinated neurons of the cerebellum

What is the arbor vitae?

White branching layer formed by Purkinje cells

What are the functions of the cerebellum?

Posture, balance, skilled movements, hand-eye coordination, and equilibrium

What is the diencephalon?

Region forming the walls of the third ventricle

What structures make up the diencephalon?

Thalamus and hypothalamus

What is the pineal gland?

Small gland in the diencephalon that secretes melatonin

What hormone does the pineal gland produce?

Melatonin

What is the function of melatonin?

Regulates biological clock and promotes sleepiness

What percentage of the diencephalon is the thalamus?

About 80%

What is the intermediate mass?

Gray matter bridge connecting both sides of the thalamus

What is the primary function of the thalamus?

Relay station for impulses to the cerebrum

What is cognition?

Awareness and acquisition of knowledge

Where is the hypothalamus located?

Inferior to the thalamus

What are the mammillary bodies?

Relay centers for smell reflexes

What gland is attached to the hypothalamus?

Pituitary gland

What connects the pituitary gland to the hypothalamus?

Infundibulum

What is the main role of the hypothalamus?

Regulation of homeostasis

How does the hypothalamus affect the ANS?

Controls cardiac and smooth muscle activity