Brain and cranial nerves

Question 1

Information processing takes place at several levels within the central nervous system. Describe where and what types of processing occur at the lowest, intermediate, and highest levels.

Answer 1

At the lowest level (spinal cord) are reflex responses to sensory input. There is not consciousness involved.

Lower regions of the brain, such as the brainstem, basal ganglia, and cerebellum, control most unconscious activities, such as blood pressure, respiration, muscle tone, coordination, and posture.

At the highest level, the cerebrum integrates conscious activities, processes and stores information, and provides the neuronal circuitry for abstract thought processes.

Question 2

Brainstem

Answer 2

The brain stem consists of the medulla oblongata,

pons, and midbrain. Its lower end is a continuation of the spinal cord.

Question 3

Diencephalon

Answer 3

The diencephalon, sitting atop the midbrain of the

brainstem, consists primarily of the hypothalamus and the thalamus.

Question 4

Cerebrum

Answer 4

The cerebrum spreads over the diencephalon like the

cap of a mushroom and occupies most of the space of the cranial vault.

Question 5

Cerebellum

Answer 5

The cerebellum is inferior to the cerebrum and

posterior to the brainstem.

Question 6

Give a brief description of the cranial vault and the meninges.

Answer 6

The brain is protected by the cranial bones that form the cranial vault, and the cranial meninges. The cranial meninges are continuous with the spinal meninges and surround the brain much as they do the spinal cord. There are, however, two major differences: separations of the dura to form the dural (venous) sinuses) and folds of the dura

Question 7

Dural sinus

Answer 7

The dura mater consists of an inner and an outer
portion. In certain places these layers are separated to form large venous structures called the dural sinuses (superior sagittal, inferior sagittal, straight, and transverse (lateral) sinuses). are the routes of venous blood flow from the brain.

Question 8

Falx cerebri

Answer 8

– A second difference is the formation of three large
sheet-like extensions of the dura that separate the larger parts of the brain. The falx cerebri is a large extension of the dura that extends between the two cerebral hemispheres.

Question 9

Falx cerebelli

Answer 9

The falx cerebelli is a large extension of the dura

mater that extends between the two cerebellar hemispheres

Question 10

Tentorium cerebelli

Answer 10

The tentorium cerebelli separates the

cerebral hemispheres from the cerebellar hemispheres

Question 11

Describe the flow of cerebrospinal fluid (CSF).

Answer 11

The brain and spinal cord are nourished and protected against injury by cerebrospinal fluid (CSF).

CSF continuously circulates through the subarachnoid space around the brain and through the cavities within the brain called the ventricles and the central canal of the spinal cord.

There are four CSF-filled cavities within the brain called the ventricles.

Ventricles 1 and 2 are the two lateral ventricles (right and left), one located within each hemisphere of the cerebrum.

Each lateral ventricle empties via an interventricular foramen (of Monro) into the third ventricle, a vertical slit located in the midline between the right and left halves of the thalamus.

The third ventricle drains via the cerebral aqueduct (of Sylvius) into the fourth ventricle, located between the brain stem and the cerebellum.

From the fourth ventricle CSF moves through the median aperture to enter the central canal of the spinal cord, and through the two lateral apertures to enter the subarachnoid space.

Question 12

describe the Mechanical protection of the CSF

Answer 12

The fluid serves as a shock-absorbing
medium to prevent the brain and spinal cord from crashing against their bony surroundings. In essence, CSF “floats” the CNS within the bony chambers of the cranial vault and the vertebral canal.

Question 13

describe the Chemical protection offered by the CSF

Answer 13

– CSF provides an optimal chemical environ-

ment for accurate neuronal activity; slight changes in ionic composition seriously disrupt neuronal homeostasis

Question 14

describe the circulation of CSF and its role in homeostasis

Answer 14

CSF is a medium for exchange of nutrients and

wastes between the blood and the nervous tissue.

Question 15

Describe the functions of the choroid plexuses, ependymal cells, and the arachnoid villi (granulations) as concerns cerebrospinal fluid.

Answer 15

CSF is produced by the choroid plexuses, networks of blood capillaries covered by ependymal cells in the walls of the ventricles that bulge into the ventricular cavity.

The capillaries become covered by the ependymal cells lining the ventricles, so that the CSF formed is an ultrafiltrate of the blood.

This relationship of the blood capillaries with ependyma creates the blood-cerebrospinal fluid barrier, permitting certain substances to pass into the CSF, but excluding others that may be harmful to the CNS.

From the subarachnoid space around the brain, the CSF is reabsorbed into the blood by finger-like projections of the arachnoid membrane called arachnoid villi or granulations that project into the superior sagittal sinus.

Normally, CSF is reabsorbed into the blood at the same rate it is made by the choroid plexuses (about 20 mL/hour). What would occur if production exceeded reabsorption?

Question 16

location of the medulla

Answer 16

The medulla oblongata is continuous with the

inferior spinal cord and the superior pons. It lies just inside the cranial vault, superior to the foramen magnum.

Question 17

grey matter in medulla

Answer 17

The gray matter of the medulla consists of
nuclei that function in the regulation of processes necessary for immediate survival: blood pressure, heart rate, respiration, swallowing, coughing, vomiting, etc.

Question 18

white matter in medulla

Answer 18

The medulla contains all ascending and
descending tracts that communicate between the brain and spinal cord. These tracts form the white matter of the medulla.

Question 19

cranial nerves in medulla

Answer 19

Also found in the medulla gray matter are
the motor nuclei for cranial nerves XII, XI, X, IX, and part of VIII. The sensory neuron cell bodies for these cranial nerves are located outside the medulla in various ganglia.

Question 20

location of the pons

Answer 20

The pons lies directly superior to the medulla,

anterior to the cerebellum, and inferior to the midbrain.

Question 21

grey matter of the pons

Answer 21

The gray matter of the pons consists of two

nuclei that are involved in the alteration of basic respiratory pattern.

Question 22

white matter of the pons

Answer 22

The pons consists mostly of white matter,
tracts passing between the lower and higher CNS structures, as well as communicating the cerebellum with the rest of the CNS.

Question 23

cranial nerves of the pons

Answer 23

In addition to the centers, the motor nuclei
of cranial nerves part of VIII, VII, VI, and V are also located in the pontine gray matter. The sensory neuronal cell bodies are located in ganglia outside the pons.

Question 24

midbrain location

Answer 24

The midbrain extends from the superior portion of

the pons to the inferior border of the diencephalon.

Question 25

dorsal portion of the midbrain

Answer 25

The dorsal portion of the midbrain, called 
the tectum (roof), is divided into four rounded eminences (a natural elevation) of gray matter called the corpus quadrigemina.  There are two superior colliculi and two inferior colliculi

The two upper elevations are the superior colliculi, gray matter nuclei associated with reflex movements of the eyes, head, and neck in response to visual and other stimuli.

The two lower elevations, the inferior colliculi, consists of gray matter nuclei involved in reflex movements of the head and trunk in response to auditory stimuli

Question 26

Ventral portion fo the midbrian

Answer 26

The ventral portion of the midbrain is all
white matter, consisting of two groups of fiber tracts: the cerebral peduncles and the medial lemniscus.

The cerebral peduncles pass motor fibers from the cerebrum through the brain stem. They also carry some sensory information passing to the cerebrum from the spinal cord.

The medial lemniscus is a band of sensory fiber tracts passing from the lower CNS to the thalamus. In particular, the medial lemniscus carries impulses for discriminative touch, proprioception, pressure, and vibrations.

Question 27

cranial nerves of the midbrain

Answer 27

Also located in the tectum are the motor
neurons for cranial nerves IV and III; the sensory neuron cell bodies associated with these cranial nerves are located in the ganglia outside the midbrain.

Question 28

Describe the thalamus of the diencephalon.

Answer 28

The thalamus (“inner chamber”) is an oval structure above the midbrain, forming 4/5 of the diencephalon.

The thalamus consists of paired masses of gray matter organized into nuclei that form the lateral walls of the third ventricle.

The two halves of the thalamus, right and left, are joined by the massa intermedia, a bridge of gray matter that crosses the midline through the third ventricle.

The thalamus is the principal relay station for sensory impulses, except smell, that reach the cerebral cortex from the spinal cord, brain stem, and other parts of the cerebrum.

The neurons of the thalamus provide some crude appreciation of some sensations (pain, temperature, pressure) and have some role in emotions and memory.

Each pair of nuclei within the thalamus has a specific role in this relay function in that each is specific for a specific modality (sensation).

Question 29

Describe the hypothalamus of the diencephalon.

Answer 29

The hypothalamus is small portion of the diencephalon (about 1/5) lying below the thalamus.

Like the thalamus, the hypothalamus is also primarily gray matter dividing into pairs of nuclei.

Each nucleus pair is responsible for the control of a particular homeostatic function. The hypothalamus is, therefore, one of the major controllers of homeostasis

Question 30

what are the functions of the hypothalamus

Answer 30

1) integration between the nervous and endocrine 
systems
2) control of the autonomic nervous system
3) regulation of rage and aggression
4) regulation of body temperature
5) regulation of food intake
6) regulation of thirst
7) regulation of sleep-wake patterns
8) regulation of sex drive.

Question 31

cerebrum location

Answer 31

Supported on the diencephalon and brain stem and

forming the bulk of the brain, thus filling most of the cranial vault, is the cerebrum.

Question 32

cerebral cortex

Answer 32

The surface of the cerebrum is composed of gray matter
2-4 mm thick called the cerebral cortex. It consists of approximately 6 billion neuronal cell bodies and their associated dendritic zones.

Question 33

cerebral white matter

Answer 33

Beneath the cerebral cortex is the cerebral white

matter consisting of axons traveling to and from the cortex. It is often referred to as the internal capsule.

Question 34

cerebral function

Answer 34

– The neurons of the cerebral cortex are the seat of

intelligence, consciousness, and where we “see,” “hear,” “smell,” “taste,” and “feel.”

Question 35

Gyrus/sulcus

Answer 35

During development, as the gray matter outgrows
the white matter, the gray matter is thrown into rolls and it folds upon itself. Each shallow fold is a gyrus and each groove between the gyri is a sulcus.

Question 36

fissures

Answer 36

The deep grooves of the cerebrum are called fissures.
The three most prominent fissures are the longitudinal fissure, separating the two cerebral hemispheres, the lateral fissure, lying between the temporal and parietal lobes, and the transverse fissure

Question 37

Corpus callosum

Answer 37

The two cerebral hemispheres are connected

internally by a large bundle of whiter matter called the corpus callosum.

Question 38

Name the lobes of the cerebrum named for the bones which cover them.

Answer 38

Each cerebral hemisphere is further subdivided into lobes by sulci or fissures. The lobes are named for the cranial bones that cover them: frontal, parietal, temporal, and occipital

Question 39

Insula

Answer 39

A fifth portion of the cerebrum, the insula, cannot be seen from the exterior of the cerebrum. It lies deep within the lateral fissure, under the parietal, temporal, and frontal lobes

Question 40

Describe the following types of fibers found in the cerebral white matter: association

Answer 40

– Association fibers transmit impulses between

the gyri of one hemisphere, associating information between different inputs and outputs.

Question 41

Describe the following types of fibers found in the cerebral white matter: commissural

Answer 41

– Commissural fibers transmit impulses from
the gyri one of the hemispheres to the gyri of the other hemisphere, passing through either the corpus callosum, the anterior commissure, or the posterior commissure.

Question 42

Describe the following types of fibers found in the cerebral white matter: projection

Answer 42

Projection fibers form descending or ascending

tracts that communicate the cerebral cortex with the spinal cord and other lower brain structures.

Question 43

grey matter: What are the basal ganglia?

Answer 43

The basal ganglia (cerebral nuclei) consist of several groups of paired nuclei found within the white matter of the cerebrum. The nuclei are interconnected by many nerve fibers with each other, and receive numerous inputs from the cerebral cortex, thalamus, and hypothalamus.

Question 44

what is the function of the basal ganglia

Answer 44

The basal ganglia function in the control of large, learned, semi-voluntary skeletal muscle movements, such as swinging the arms when walking, laughing, etc., and in the regulation of muscle tone.

Question 45

What is the limbic system?

Answer 45

The limbic system is a ring of structures surrounding the inner border of the cerebrum and the floor of the diencephalon, encircling the midbrain. It is formed by gyri of the insular lobe, nuclei associated with the basal ganglia, hypothalamus, and the thalamus, the olfactory bulbs, and bundles of interconnecting white matter

Question 46

what is the function of the limbic system

Answer 46

The limbic system, often called the emotional brain, functions in emotional aspects of behavior related to survival, memory, smell, pleasure and pain, rage and aggression, docility and tameness, affections, sexual desire, etc.

Question 47

What are the functional areas of the cerebral cortex?

Answer 47

Specific types of sensory, motor, and integrative signals are processed in specific regions of the cerebral cortex called functional areas. In general, the areas are divided into three types: primary sensory, primary motor, and association

Question 48

Sensory areas

Answer 48

Sensory areas receive sensory input, and
integrate and interpret the sensations. There are at least 20 different specific areas for each of the individual modalities.

Question 49

motor areas

Answer 49

Motor areas contain the neuronal cell bodies
of origin for practically all motor activities. They are divided into at least 5 different areas associated with muscular activity.

Question 50

Association areas

Answer 50

Association areas make up several
main areas that serve to connect the sensory and motor areas. They provide integrative and interpretive functions, such as memory, emotion, relationships between sensations, etc.

Question 51

Describe the cerebellum.

Answer 51

The cerebellum is located in the inferior and posterior aspect of the cranial cavity, inferior to the occipital lobes of the cerebrum and posterior to the brain stem.

The cerebellum is separated from the cerebrum by a fold of dura known as the tentorium cerebelli.

The cerebellum is designed like the cerebrum, with 2 cerebellar hemispheres divided into 3 lobes each, a cerebellar cortex, an inner white matter, and several cerebellar nuclei.

The white matter of the cerebellum serves to connect the cerebellar cortex and the cerebellar nuclei with each other and with all of the other pertinent CNS structures.

The cerebellar gray matter functions to compare intended bodily movement with what is actually happening, to help in regulating smooth, sequential skeletal muscle contractions, and to control muscle tone, balance, and posture.

Question 52

Describe the cranial nerves. How many are there? From where do they originate? How do they exit the skull?

Answer 52

There are 12 pairs of cranial nerves, 10 of which originate in the brainstem. All pass through specific foramina of the skull to leave the cranial cavity.

Question 53

Where are the cell bodies of origin of the motor and sensory components of the cranial nerves?

Answer 53

Motor neuron cells bodies are in the gray matter of the brainstem. The sensory neuron cell bodies are all found in ganglia located outside the brain.

Question 54

How are the cranial nerves designated?

Answer 54

Roman numerals indicate the order in which they arise from the brain, anterior to posterior. The names indicate their distribution or function.

Question 55

CN I Olfactory

Answer 55

origins – arises from the olfactory epithelium within the nasal
cavity
sensory functions – sense of smell
motor function - none

Question 56

CNII Optic

Answer 56

origins – arises from retinal epithelium of the eye
sensory functions – sense of sight
motor functions – none

Question 57

CNIII Oculomotor

Answer 57

origins – arises from the midbrain
sensory functions – proprioceptive to muscles served
motor functions – levator palpebrae superioris, superior
rectus, medial rectus, inferior rectus, and inferior oblique muscles of eyeball; parasympathetic to ciliary muscle of eye for focusing lens and to sphincter and dilator pupillae muscle of iris for regulating pupillary diameter

Question 58

CNIV Trochlear

Answer 58

origins – arises from the midbrain
sensory functions – proprioceptive to muscle served
motor functions – superior oblique muscle of eyeball

Question 59

CNV Trigeminal

Answer 59

origins – arises from the midbrain
sensory functions – touch, pain, and temperature from skin
of front half of the head, eyeball, nasal cavity, oral cavity (not taste), part of pharyngeal mucosa
motor functions – muscles of mastication (chewing)
(masseter, temporalis, lateral and medial pterygoids)

Question 60

CNVI Abducens

Answer 60

origins – arises from the pons
sensory functions – proprioception to muscle served
motor functions – lateral rectus muscle of eyeball

Question 61

CNVII Facial

Answer 61

origins – arises from the pons
sensory functions – anterior 2/3 of tongue for taste,
proprioceptive for muscles of facial expression
motor functions – muscles of facial expression, lacrimal and
salivary glands secretion.

Question 62

CNVIII Auditory (vestibulocochlear)

Answer 62

origins – arises from the cochlear and vestibular portions of
the inner ear
sensory functions – senses of equilibrium and hearing
motor functions – none

Question 63

CNIX Glossopharyngeal

Answer 63

origins – arises from the medulla
sensory functions – posterior 1/3 of tongue for taste, carotid
sinus and body related to blood pressure control, proprioceptive for muscles of swallowing
motor function – muscles of swallowing and salivary glands

Question 64

CNX Vagus

Answer 64

sensory functions – aortic sinus and body related to blood
pressure control, mucosa of respiratory and digestive systems
motor functions – muscles of the bronchial tree, digestive
tract, pancreas, liver, and glands of the GI system

Question 65

CNXI Accessory

Answer 65

origins – arises from the medulla
sensory functions– proprioceptive for the muscles served
motor functions – muscles of the pharynx for swallowing,
larynx, soft palate, sternocleidomastoid, and trapezius.

Question 66

CNXII Hypoglossal

Answer 66

origins – arises from the medulla
sensory functions – proprioceptive for the muscles served motor functions – intrinsic and extrinsic muscles of the
tongue