Chapter 15 - Brain: Cranial Nerves

the brain

serves as the major center for registering sensations, making decisions, and storing memory

centerpiece of the CNS

the Brain

The Skull

composed of bone, surrounds and protects the brain

cranial meninges

continuous with spinal meninges: dura mater, arachnoid layer, pia mater

dura mater

outer layer that forms a protective bag around the brain

what is the dura mater composed of?

dense irregular connective tissue

epidural space

space between the skull and the dura mater and serves as a pad around the brain

what tissue does the epidural space contain?

adipose tissue

the arachnoid layer

the middle layer of the meninges and is avascular

What tissues does the arachnoid layer contain?

a large supply of collagen and elastic fibers

why is arachnoid layer called that?

it looks like a spider web under the microscope

subdural space

a space between the dura mater and the arachnoid layer

what is subdural space filled with?

interstitial fluid

pia mater

innermost of the meninges, a transparent layer of connective tissue that adheres to and covers the brain and spinal cord.

vascularity of the pia mater

highly vascular as blood vessels supply nutrients and oxygen to the neurons of the brain

subarachnoid space

space between the pia mater and the arachnoid layer

what does the subarachnoid layer contain?

cerebrospinal fluid

meningitis

inflammation of the meninges which can be caused be either bacteria or viruses

signs and symptoms of meningitis

headache, stiff neck, high fever, and vomiting

Cerebrospinal fluid

nourishes and protects the brain and spinal cord.

where does cerebrospinal fluid circulate?

through the subarachnoid space and within the brain through the ventricles

ventricles

open spaces within the brain

What is CSF composed of?

water, glucose, ions, proteins, and leukocytes

what are the functions of CSF?

buoyancy, protection, chemical stability

Bouyancy function of CSF

provide support to the brain

protection function of CSF

prevents the brain from striking the cranium and the leukocytes in the CSF fight infectious agents

Choroid Plexus

a network of capillaries in the walls of the ventricles of the brain

choroid plexus is covered by

ependymal cells

what do ependymal cells secrete do?

secrete CSF

why are ependymal cells hooked tightly together?

so blood waste materials cannot enter into CSF

Hydrocephalus

disorder in which excess CSF accumulates in the ventricles of the brain causing the head to bulge

what does hydrocephalus cause?

increase in pressure on the brain which can be treated via surgery

How does CSF flow through the brain?

through passageways known as ventricles

Cerebral aqueduct for CSF

where CSF flows to nourish the cerebellum and brainstem

where does CSF flow to from the cerebral aqueduct?

into the central canal of the spinal cord

blood supply to the brain

a huge blood supply to the brain to carry oxygen and nutrients to the neurons that make up the brain

how long until loss of oxygen leads to neuron death?

4 minutes

Blood-Brain Barrier

(BBB) prevents the passageway of certain compounds (including urea, creatine, some ions) into the brain

what is the blood brain barrier formed by?

the tight attachment of ependymal cells in brain capillaries and the presence of astrocytes tightly attached against the external wall of brain capillaries

What are substances that can cross the BBB?

ones that are soluble in lipids

how do some compounds cross the BBB?

by water

What substances that can easily pass through the BBB?

amino acids, electrolytes, and sugars

Compounds which cannot penetrate the BBB

wastes such as urea and toxins

damage to the BBB is often

deadly

What are the principal parts of the brain?

brain stem, cerebellum, diencephalon, and the cerebrum

brain stem

connects the spinal cord to the diencephalon

what does the brain stem consist of?

the medulla oblongata, the pons, the midbrain, and the reticular formation

medulla oblongata

forms the interior portion of the brain stem

where is the medulla located/

begins at the foramen magnum and extends upward to the pons

what tracts do the medulla contain?

ascending and descending tracts that connect the spinal cord and the brain

What are the major parts of the medulla?

the pyramids, decussation of pyramids, nucleus gracilis, nucleus cuneatus, cardiovascular center, medial lemniscus, medullary rhythmicity area, vasomotor center, olive, pons

pyramids

part of medulla, bulges on the anterior portion of the medulla containing motor tracts that pass from the cerebrum to the spinal cord

decussation of pyramids

region on the medulla where nerves from pyramids cross over each other.

neurons on left side of medulla control effectors

on the right side of the body

nucleus gracilis and nucleus cuneatus

relay sensory information to the thalamus and the cerebrum for conscious awareness

Medial Lemniscus

where the nucleus gracilis and nucleus cuneatus fuse

The Cardiovascular Center

regulates the rate and force of the heartbeat and the diameter of blood vessels

The Medullary Rhythmicity Area

adjusts the rhythm of breathing

The Vasomotor Center

regulates blood pressure by dilating or constricting blood vessels

The Olive

an oval structure that extends from the right and left lateral surfaces of the medulla and carries impulses to the cerebellum that regulate posture and equilibrium

the pons

superior to the medulle, serves as a bridge that connects the spinal cord and medulla to the remainder of the brain

The Cerebellar Peduncles

part of pons, bundles of nerve fibers that connect the pons and the cerebellum

The Pnneumotaxic and Apneustic Area

part of the pons that regulates breathing

Midrain

extends from the pons to the diencephalon

Cerebral aqueduct (midbrain)

part of midbrain that connects the third and fourth ventricles

The Cerebral Peduncles

part of the midbrain that carries impulses from the pons and medulla to the thalamus

Corpora quadrigemina

part of midbrain, 4 rounded elevations located at the posterior portion of the midbrain, found in the Tectum

What are the 4 elevations in the corpora quadrigemina or the midbrain?

- The Superior Colliculi - 2 of these, serve as reflex centers for eye and head movements

- The Inferior Colliculi - 2 of these serve as reflex centers or auditory stimuli

Substantia Nigra

parts of the midbrain, two of these darkly pigmented areas that control subconscious muscle activity.

What is the primary pigment in the Substantia Nigra?

melanin

What does the Substantia Nigra suppress?

suppresses unwanted motor movements during muscle contraction

Parkinsons Disease cause

dopamine containing neurons in the substantia nigra degenerate causing tremors

The Red Nucleus

neurons in the midbrain that coordinate muscular movements in the body

why are the red nucleus red?

due to a large blood supply

The Medial Lemniscus

a band of white matter that extends through the medulla , pons, and midbrain.

What does the medial lemniscus carry impulses for?

touch and pressure from the medulla to the thalamus

The reticular formation

an area of the brain stem that consists of gray matter interspersed with white matter

What are the three functions of the reticular formation?

1. Pain modulation by preventing some pain impulses from reaching the brain.

2. Regulating sleep and consciousness

3. Screening out inconsequential stimuli from reaching the brain.

The Cerebellum

occupies the inferior and posterior aspects of the cranial cavity and is posterior to the medulla and pons

What is the second largest part of the brain?

cerebellum

what is the largest portion of the brain?

cerebrum

How is the cerebellum separated from the cerebrum?

the transverse fissure

The Vermis

the central portion of the cerebellum

Hemispheres

lobes of the cerebellum

Cerebellar Cortex

the superficial layer of the cerebellum

How is the cerebellum connected to the brain stem?

cerebellar peduncles

Purkinje Cells

myelinated neurons that form a visible white layer in the cerebellum.

What is the white layer of purkinje cells in the cerebellum?

arbor vitae

What are the four functions of the cerebellum?

1. Regulates posture and balance

2. allows for skilled motor movements

3. regulates hand-eye coordination

4. regulates equilibrium

Diencephalon

begins at the midbrain and extends upward forming the walls of the third ventricle

what does the diencephalon consist of?

thalamus and hypothalamus

The Pineal Gland

pea sized structure located in the diencephalon

function of pineal gland

not entirely clear, but does secrete melatonin to regulate the body's bio clock and promote sleepiness

Thalamus

comprises 80% of the diencephalon

Intermediate Mass

a bridge of gray matter that connects the right and left sides of the thalamus

what are the two functions of the thalamus?

1. serves as a relay station for impulses from the spinal cord to the cerebrum

2. Cognition

cognition

the awareness and acquisition of knowledge

Hypothalamus

located inferior to the thalamus

Mammillary bodies

part of the hypothalamus, serve as relay stations for reflexing relating to sense of smell

pituitary gland (hypophysis)

attaches to the hypothalamus via a stalk known as the infundibulum