Chapter 14: The Brain and Cranial Nerves

Chapter Objectives

BRAIN ORGANIZATION

1. Introduce the principle parts of the brain in terms of their relative positions.

2. Describe the ventricles and where in the brain they are located

THE CEREBRUM

3. Define gyrus, sulcus, and fissure. Give the location of the Central sulcus and its

surrounding gyri.

4. Discuss the locations of the cerebral lobes.

5. Describe the cerebral cortex.

6. Define the location and purpose of the motor regions of the cerebral cortex including the

following regions: primary motor region, premotor area, Broca’s area, and primary eye

field area.

7. Define the location and purpose of the sensory regions of the cerebral cortex including

the following regions: somatosensory region, somatosensory association area, and the

primary sensory areas for the visual, auditory, gustatory, and olfactory systems.

8. Define the location and purpose of the association regions of the cerebral cortex

including the following regions: Prefrontal area and Wernicke’s area.

9. Describe the pathway destinations for the three types of white matter tracts within the

cerebrum (Association, Commissural, and Projection).

10. Identify the nuclei of the Basal nuclei (ganglia), describe the functions of the Basal nuclei

and describe one disorder associated with the Basal nuclei.

DIENCEPHALON

11. Discuss the structures of the Diencephalon and functions for each structure.

THE BRAIN STEM

12. List the structures that make up the brain stem.

13. Discuss the structures of the Midbrain and functions for each structure.

14. Describe the Pons.

15. Discuss the structures of the Medulla and functions for each structure.

16. Identify the vital reflex centers of the medulla oblongata and their functions.

CEREBELLUM

17. Describe the location of the Cerebellum and its functions.

FUNCTIONAL BRAIN SYSTEMS

18. List the component structures of the limbic system, and discuss their contribution to

behavioral responses and mental functions.

19. Indicate the distribution of nuclei that constitute the reticular formation and describe the

function of the reticular formation.

MENINGES

20. Identify the three layers of the meninges and their extensions that surround the brain and

spinal cord.

21. List the functions of CSF and where it is formed in the brain.

CRANIAL NERVES

22. Define a cranial nerve and identify the 12 pairs of cranial nerves by name, number, type,

which hole in the skull they pass through and function.

Chapter Lecture Notes

Regions of the Brain

Cerebrum (Fig 14.1 & Table 14.2)

Diencephalon

Brain Stem

Cerebellum

Ventricles

Ventricles – hollow chambers within the brain that are filled with cerebrospinal fluid and lined

with ependymal cells (Fig 14.3 & 14.4)

Four ventricles

Paired Lateral ventricles - cerebrum

Third ventricle - diencephalon

Fourth ventricle - brain stem

Cerebrum

Cerebrum - supported on brain stem and form bulk of brain (Fig 14.11)

Lateral ventricles

Cranial nerves 1 & 2

Surface features

Lobes - frontal, parietal, temporal, occipital

Gyrus - upfolds - increases surface area (surface area = 25 square feet)

Sulcus - shallow grooves

Central sulcus - divides parietal from frontal lobe

Precentral gyrus - motor in function

Postcentral gyrus - sensory in function

Lateral cerebral sulcus - divides frontal from temporal lobe

Fissures - deep grooves

Longitudinal fissure - divides the right from left hemispheres

Cortex (bark of tree) = outer gray - 2-4mm thick - 6 layers of cell bodies; divided into 3

functional areas (Fig 14.11 & 14.15)

EEG - electrical activity of cortex (Fig 14.16)

Motor - control voluntary muscle movements -in frontal lobe anterior to central sulcus

Primary motor area - precentral gyrus - controls muscle movement on opposite side of

body (pathway is pyramidal system) (Fig 16.8)

Premotor area - anterior to primary motor

Controls learned skilled movements - generates action potentials that enable specific

groups of muscles to contract in specific sequence like writing, typing,

playing musical instruments (deals with learned motor activities of a complex

and sequential nature)

Broca's area - generally on left side - in frontal lobe just superior to lateral cerebral sulcus

Broca's area programs motor cortex to move tongue, lips and speech muscles to

articulate words

Frontal eye field area - just anterior to premotor area

Controls voluntary scanning movements of eye - searching for a word in a dictionary

or looking for a book on a shelf or a person in a crowd

Sensory - interpretation of sensory impulses; posterior to central sulcus

Postcentral gyrus - primary somatosensory (sensory) - localize points on body where

sensations such as touch, pressure, pain, taste, & temperature originate (Fig 16.8)

Somatosensory association area - Integrate and interpret sensations - permit you to

determine shape and texture of object without looking at it - store memories of

past experiences - can compare sensations with previous experience

Primary visual area = occipital lobe

Visual association area = relates present to past visual experience with recognition

and evaluation of what is seen

Primary auditory area - temporal lobe - interprets basic characteristics of sound such as

pitch and rhythm

Auditory association area - determines if sound is speech, music, or noise

Primary olfactory area - temporal lobe on medial side - interprets sensations related to

smell

Primary gustatory area - in parietal lobe at base of postcentral gyrus - interprets

sensations related to taste

Association areas - intellectual processes - occupies greater portions of lateral surfaces of

occipital, parietal, temporal, and frontal lobes anterior to motor areas

Association areas are concerned with memory, emotions, reasoning, will, judgment,

personality and intelligence

Prefrontal area – “executive decision area”

Allows moral judgments

Motivation and foresight to plan; also allows us to predict consequences of our

actions

Regulation of emotional behavior and mood

Functional center for aggression - one method used to eliminate uncontrollable

aggression in mental hospital was to surgically remove or destroy the

prefrontal regions (prefrontal lobotomy) - it eliminates aggression but also

eliminates motivation

Wernicke's area - stores information for speech content, arranges words of vocabulary

into meaningful speech according to rules of grammar; it plans what to say

Middle White Matter = tracts of myelinated nerve fibers (axons) (Fig 14.12)

Association fibers - connect and transmit nerve impulses between gyri in same hemisphere

Commissural fibers - transmit nerve impulses from gyri in one hemisphere to corresponding

gyri in opposite hemisphere

Example: corpus callosum

Projection fibers - form ascending and descending tracts that transmit impulses to and from

cerebrum to other parts of brain and spinal cord

Basal Nuclei - paired gray inner matter of cerebrum (Fig 14.13)

Technically it is nuclei but common usage is basal ganglia

Parts include:

Lentiform nucleus - receives input from substantia nigra in brain stem

Putamen

Globus pallidus

Caudate nucleus - receives input from substantia nigra

Substantia nigra (in midbrain) - inhibits unwanted motor activity from basal nuclei by

releasing dopamine

Basal nuclei help control muscle tone by inhibiting contraction of unwanted muscular

activity

Associated with control of large subconscious movements like swinging arms when

walking/facial expression

Basal nuclei coordinate slower contractions, whereas cerebellum is more involved with

coordination of quick movements

Disorder - Parkinson's - decrease in neurotransmitter dopamine from Substantia nigra to

Basal nuclei; result is tremors

Diencephalon

Thalamus - "inner room" - 2 oval masses joined by a bridge called intermediate mass

(interthalamic adhesion) (Fig 14.1 & 14.9)

2 masses form lateral walls of 3rd ventricle

Thalamus is bounded laterally by internal capsule

Gateway to cerebral cortex

Incoming sensory neurons are sorted, regrouped and then sent onto proper area of cerebral

cortex where interpretation is made

All sensory except olfactory synapse here before being relayed to sensory part of

cerebrum

Thalamus could also be referred to as the "sensory relay station"

Hypothalamus (Fig 14.1 & 14.10)

Connected to pituitary gland via infundibulum

Mammillary body - olfactory reflexes as related to emotions

Controls many functions related to homeostasis: (main visceral control center)

Controls autonomic nervous system

Mind over body phenomenon - extensive connections between hypothalamus and cortex -

thoughts influence our visceral functions - "the thought of __ makes me sick to

my stomach"

Serves as a link between nervous system and endocrine system

Control endocrine system: Stimulates anterior pituitary to release its hormones

Control endocrine system: Produces hormones found in posterior pituitary

Control body temperature - initiates sweating (cooling) or shivering (warming)

Governs eating habits

Governs thirst

Pacemaker to drive biological rhythms

Maintain waking state and sleeping patterns

Center for emotional response and behavior - it lies at the "heart" of the limbic system

Pleasure center

Rage and aggression

Pineal gland - reproductive function in most animals; in humans it produces melatonin that helps

regulate sleep/wake cycle and some aspects of mood

Brain Stem

Brain stem - control of involuntary function

Midbrain - cranial nerves 3, 4 (Fig 14.7)

Corpora quadrigemina - Posterior side (tectum = roof)

Superior colliculi - reflex center for movement of eye, head, neck and trunk in

response to visual stimuli (contains fibers from optic tract)

Inferior colliculi - reflex center for movement of eye, head, neck and trunk in

response to auditory stimuli (contains fibers from auditory tract)

Cerebral aqueduct - connects 3rd and 4th ventricles

Cerebral peduncles - Anterior side

Contain motor and sensory tracts and are the main connections for tracts between

upper parts of brain and lower parts of brain and spinal cord

Peduncles were thought to form vertical pillars that seem to hold up cerebrum; hence

"little feet" that hold up the cerebrum

Red nucleus - has numerous blood vessels that give it red color

Center for integrating information about muscle tone and posture

Substantia nigra - pigmented nuclei included as part of basal nuclei

Pons - connects medulla with midbrain and connects cerebellum with cerebrum (Fig 14.1)

Cranial nerves 5-8

4th ventricle

Medulla (Fig 14.6)

Cranial nerves 8-12

Pyramids – Anterior side

Pyramids are composed of largest motor (descending) tracts that pass from cerebral

cortex to spinal cord

Decussation of pyramids – crossing of tracts from one side to another (80% of motor

tracts cross in medulla)

Contains all sensory (ascending) tracts that connect the spinal cord & brain

Vital reflex centers of medulla:

Cardiac center - regulate heart rate and force of contraction

Respiratory center - controls rate and depth of respiration

Vasomotor center - adjusts blood vessel diameter to regulate blood pressure

Nonvital centers:

Swallowing, vomiting, coughing, sneezing, hiccupping

Cerebellum

Coordinates movement of skeletal muscle, especially quick movements (Fig 14.8)

Maintenance of balance and equilibrium

Helps in maintenance of posture

Processes input from sensory receptors - through connections with cerebral cortex, cerebellum

refines and coordinates muscle movements

Does not initiate movement

Not involved in sensory perception

Injury or removal of cerebellum results in impairment of muscle coordination and not

paralysis

Hand-eye coordination is one example of cerebellum function

Functional Brain Systems

Functional Brain Systems - networks of neurons that work together but span large distances

within brain, so cannot be localized to a specific region

Limbic system - mostly interconnected gray matter that includes components of cerebrum and

diencephalons (Fig 14.14)

Wishbone shaped and encircles brainstem (limbus = ring)

Limbic system has extensive connections to the prefrontal cortex

Sometimes called emotional brain

Functions in emotional aspects of behavior related to survival

Limbic system associated with pleasure, pain, rage, fear, aggressiveness

Communication between the cerebral cortex and limbic system explains why emotions

sometimes overrides logic and conversely why reason can stop us from

expressing emotions in inappropriate situations

Plays role in memory processing

Because of relationship of memory to emotions, events that cause strong emotional

response are remembered more efficiently that those that do not

Parts include:

Hippocampus - (sea horse) gyrus of the temporal lobe - in floor of the lateral ventricle

Hippocampus along with cortex function in memory

Amygdala - end of caudate nucleus - role in memory

Fornix - tracts that link the limbic system together, specifically connects hypothalamus to

hippocampus (fornix = arch)

Cingulate gyrus - above the corpus callosum (cingulate = belt)

Olfactory bulb

Mammillary bodies - part of hypothalamus (odors can trigger memory)

Parts of thalamus and hypothalamus

Pathway from limbic system project into hypothalamus and exert widespread effect

on body via autonomic nervous system and endocrine system (most limbic

output is relayed through hypothalamus)

Since the hypothalamus is clearinghouse for emotional response and autonomic

nervous system, it is not surprising that some people under unrelenting

emotional stress fall prey to emotional-induced illness such as increased blood

pressure, irritable bowel syndrome, heartburn

Reticular formation - gray matter interspersed among white fibers that are found in spinal cord,

medulla, pons, midbrain and diencephalon; has both sensory and motor functions (over

90 separate nuclei) (Fig 14.7)

Fibers (axons) make extensive connections to diencephalon, cerebellum, cerebrum

RAS - reticular activating system - control general wakefulness or alertness of brain

Injury to formation results in unconsciousness or deep coma (coma can result from

poison, hypoxia, hypoglycemia, ischemia, infection, acid-base disorder, trauma)

Alerts cerebral cortex to incoming sensory signals from ears, eyes and skin to activate

person

Filters sensory impulses entering the brain and accepts and enhances relay of certain

sensory impulses to cerebrum while rejecting others

Protects brain from constant barrage of sensory "noise" that would be overwhelming

(being aware of all stimuli in environment; colors, shapes, odors, sounds)

Filters out 99% of sensory and enhance only important

Hyperactivity in children is due in part to inability to filter out unnecessary sensory

input

Meninges

Dura mater – outermost layer that is double membraned where it surrounds skull (Fig 14.2)

Periosteal layer - outer layer - adheres to inner surface of skull (does not exist around spinal

cord)

Meningeal layer - inner layer - forms true external covering of brain and continues around

cord

Dura layers are fused together except where they form the dural sinuses that collect venous

blood from brain and cerebrospinal fluid from arachnoid villi and then direct the

blood and cerebrospinal fluid into the internal jugular of neck

Meningeal dural mater extends inward to form flat septa (wall) that anchor brain to skull

Falx cerebri (falx = sickle) - dips into longitudinal fissure between cerebrum (attached to

crista galli of the ethmoid)

Falx cerebelli – between cerebrum and cerebellum

Arachnoid mater – middle layer

Weblike extensions of collagen and elastic fibers

never dips into sulcus

Arachnoid villi protrudes through the dura mater and into dural sinuses

Pia mater – innermost layer composed of delicate connective tissue and is richly invested with

tiny blood vessels

clings tightly to brain and into sulcus

Subarachnoid space – space between arachnoid mater and pia mater

contains cerebrospinal fluid (CSF) and blood vessels serving brain

Cerebrospinal fluid - cushions, protects and nourishes brain and spinal cord

contains O2, glucose, proteins, Na+, K+, Ca2+, Cl-

Choroid plexus in the brain ventricles form cerebrospinal fluid (Fig 14.4)

Circulates from ventricles, through and around the spinal cord and back to the brain where it

is reabsorbed at the superior sagittal sinus

Volume - 150 ml (1/2 cup)

Replaced every 3 - 4 hours

Clear fluid

Cranial Nerves

12 pairs - know names, numbers, functions and where they pass through the skull

Oh, Oh, Oh, To Touch And Feel Very Green Vegetables – AH (Fig 14.5 & Table 14.4)

On Old Olympic Towering Tops A Finn And German Viewed Some Hops

I. Olfactory (Fig 14.17)

Passes through cribriform plate

Sensory - Smell

II. Optic (Fig 14.18)

Passes through optic foramen

Sensory - Sight

III. Oculomotor (Fig 14.19)

Passes through superior orbital fissure

Motor - Eye movement

IV. Trochlear (Fig 14.19)

Passes through superior orbital fissure

Motor - Eye movement

V. Trigeminal (Fig 14.20)

Ophthalmic - passes through superior orbital fissure

Maxillary - passes through foramen rotundum

Mandibular - passes through foramen ovale

Mixed

Sensory - facial sensations

Motor- chewing - (masseter/temporalis)

VI. Abducens (Fig 14.19)

Passes through superior orbital fissure

Motor - Eye movement

VII. Facial (Fig 14.21)

Passes through stylomastoid foramen

Mixed

Sensory - anterior 2/3 taste

Motor – salivation and facial expression

VIII. Vestibulocochlear (Auditory) (Fig 14.22)

Passes through internal auditory (acoustic) meatus

Sensory

Vestibular - for equilibrium

Cochlear- for hearing

IX. Glossopharyngeal (Fig 14.23)

Passes through jugular foramen

Mixed

Sensory - posterior 1/3 taste

Motor – salivation and swallowing

X. Vagus (vagrant) (Fig 14.24)

Passes through jugular foramen

Mixed

Sensory – monitors functioning of the organs of thorax and abdomen

Motor – parasympathetic regulation of the organs of the thorax and abdomen

XI. Accessory (Spinal) (Fig 14.25)

Passes through jugular foramen

Motor - Controls the Trapezius and Sternocleidomastoid muscles

XII. Hypoglossal (Fig 14.26)

Passes through hypoglossal canal

Motor - Tongue movements during speech and swallowing

III, IV, VI, XI, XII are primarily motor but have a sensory part that is for proprioception