CH:13 Nervous System: Brain and Cranial Nerves

representational hemisphere

because it is concerned with visuospatial relationships and analyses. It is the seat of imagination and insight, musical and artistic skill, perception of patterns and spatial relationships, and comparison of sights, sounds, smells, and tastes

frontal eye field

within the frontal lobe immediately superior to the motor speech area. This cortical area controls and regulates the eye movements needed for reading and coordinating binocular vision. Some investigators include the frontal eye fields within the premotor area

gyri

folds of brain tissue

midbrain

or mesencephalon, is the superior portion of the brainstem

cerebellar cortex

outer gray matter

epithalamus

partially forms the posterior roof of the diencephalon and covers the third ventricle. The posterior portion of the epithalamus houses the pineal gland and the habenular nuclei.

pineal gland

pineal body, is an endocrine gland (see section 17.11a). It secretes the hormone melatonin, which appears to help regulate day-night cycles known as the body's circadian rhythm. (Some companies are marketing the sale of melatonin in pill form as a cure for jet lag and insomnia, although this cure has yet to be proven.)

cranial nerve nuclei

pons also houses sensory and motor cranial nerve nuclei for the trigeminal (CN V), abducens (CN VI), and facial (CN VII) cranial nerves. Some of the nuclei for the vestibulocochlear cranial nerve (CN VIII) also are located there.

caudal

posterior is synonymous with caudal (meaning "toward the tail")

medullary respiratory center

regulates the respiratory rate. It is composed of a ventral respiratory group and a dorsal respiratory group. These groups are influenced by the pontine respiratory center (see section 23.5c). The primary function of the medullary respiratory center is to rhythmically initiate nerve signals that cause contraction of breathing muscles

habenular (hă-ben′ū-lăr; habena = strap) nuclei

relay signals from the limbic system (see section 13.7a) to the midbrain and are involved in visceral and emotional responses to odors.

habenular nuclei

relay signals from the limbic system (see section 13.7a) to the midbrain and are involved in visceral and emotional responses to odors.

subarachnoid space

which contains cerebrospinal fluid (discussed in section 13.2c). The arachnoid trabeculae extend through this space from the arachnoid to the underlying pia mater. Both the arachnoid trabeculae and cerebrospinal fluid support cerebral arteries and veins within the subarachnoid space. Page 496 INTEGRATE

Wernicke area

which is typically located only within the left hemisphere. The Wernicke area is involved in recognizing, understanding, and comprehending Page 507spoken or written language. As you may expect, the Wernicke area and the motor speech area must work together for fluent communication to occur.

contusion

TBI where there is bruising of the brain due to trauma that causes blood to leak from small vessels into the subarachnoid space (a fluid-filled space surrounding the brain)

peduncles

Three thick nerve tracts, called peduncles, connect the cerebellum with the brainstem (see figure 13.20b). The superior cerebellar peduncles connect the cerebellum to the midbrain (see section 13.5a). The middle cerebellar peduncles connect the cerebellum to the pons (see section 13.5b). The inferior cerebellar peduncles connect the cerebellum to the medulla oblongata

third ventricle

Within the diencephalon is a smaller, thinner ventricle Each lateral ventricle is connected with the third ventricle through an opening called the interventricular foramen (formerly called the foramen of Munro

cerebrospinal fluid

a clear, colorless liquid that circulates within the ventricles and subarachnoid space. CSF bathes the exposed surfaces of the central nervous system and completely surrounds it. CSF performs several important functions: Buoyancy. The brain floats within the CSF, thereby reducing its apparent weight by more than 95%; this prevents the brain from being crushed under its own weight. Without CSF to support it, portions of the brain would sink through the foramen magnum. Protection. CSF provides a liquid cushion to protect delicate neural structures from sudden movements. When you try to walk quickly in a swimming pool, your movements are slowed as the water acts as a "movement buffer." CSF likewise helps slow movements of the brain if the skull or body moves suddenly and forcefully. Environmental stability. CSF transports nutrients and chemical messengers to the brain and removes waste products from the brain. Additionally, CSF protects nervous tissue from chemical fluctuations that would disrupt neuron function. The waste products and excess CSF are eventually transported into the venous circulation.

superior olivary nuclei

are located in the inferior portion of the pons. Each nucleus receives auditory input and is involved in the pathway for sound localization.

Cerebral peduncles

are motor tracts located on the anterolateral surfaces of the midbrain. Descending axon bundles of the pyramidal system (corticospinal tracts; see section 14.4c) project through the cerebral peduncles and relay voluntary motor commands from the primary motor cortex of each cerebral hemisphere

superior colliculi

are the superior nuclei. They are called visual reflex centers because they help visually track moving objects and control reflexes such as turning the eyes and head in response to a visual stimulus. For example, the superior colliculi are at work when you think you see a large animal running at you and turn suddenly toward the image

cranial meninges

are three connective tissue layers that separate and support the soft tissue of the brain from the bones of the cranium, enclose and protect some of the blood vessels that supply the brain, and contain and help circulate cerebrospinal fluid. From deep (closest to the brain) to superficial Page 495(farthest from the brain), the cranial meninges are the pia mater, the arachnoid mater, and the dura mater

inferior cerebellar peduncles

are tracts that connect the medulla oblongata to the cerebellum

middle cerebellar peduncles

are transverse axons that connect the pons to the cerebellum

motor speech

area used to be called Broca area and is located, in most individuals, in the left frontal lobe

inferior colliculi

auditory reflex centers, meaning that they control reflexive turning of the head and eyes in the direction of a sound, such as a sudden, loud bang

medial lemniscus

Bands of myelinated sensory axons extend from the medulla oblongata, through the pons and midbrain, to the thalamus

cerebral lateralization or hemispheric lateralization

Each hemisphere tends to be specialized for certain tasks Higher-order centers in both hemispheres tend to have different but complementary functions.

olive

Immediately lateral to each pyramid is a distinct bulge, called the olive, which contains a large fold of gray matter called the inferior olivary nucleus. The inferior olivary nuclei relay ascending sensory nerve signals, especially proprioceptive information, to the cerebellum

categorical hemisphere

In most people, the left hemisphere is the categorical hemisphere. It usually contains the Wernicke area and the motor speech area. It is specialized for language abilities and is important in performing sequential and analytical reasoning tasks, such as those required in science and mathematics. This hemisphere appears to direct or partition information into smaller fragments for analysis. The term categorical hemisphere reflects this hemisphere's function in categorization and identification.

decussation of the pyramids

In the anterior region of the medulla, most of the axons of the pyramidal tracts cross to the opposite side of the brain at a point called the decussation (dē-kŭ-sā′shŭn; decussate = to cross in the form of an X) of the pyramids. As a result of the crossover, each cerebral hemisphere controls the voluntary movements of the opposite side of the body

reticular formation

Projecting vertically through the core of the midbrain, pons, and medulla is a loosely organized mass of gray matter called the reticular formation (figure 13.27). The reticular formation extends slightly into the diencephalon and the spinal cord as well. This functional brain system has both motor and sensory components. The motor component of the reticular formation communicates with the spinal cord and is responsible for regulating muscle tone (especially when the muscles are at rest). This motor component also assists in autonomic motor functions, such as respiration, blood pressure, and heart rate, by working with the autonomic centers in the medulla and pons

Functional Brain Systems

The brain has two important functional systems that work together for a common purpose. These are considered functional brain systems because their structures are not confined to one major region of the brain but are located throughout two or more regions of the brain. These systems are the limbic system and the reticular formation.

cerebral hemispheres

The paired cerebral hemispheres are separated by a narrow, deep cleft called the longitudinal fissure, which extends along the midsagittal plane. The cerebral hemispheres are separate from one another, except at a few locations where bundles of axons called tracts form white matter regions that allow for communication between them (see figure 13.14). The largest of these white matter tracts, the corpus callosum (kōr′pŭs kal-lō′sŭm; corpus = body, callosum = hard) connects the hemispheres (see a midsagittal section of the corpus callosum in figure 13.1c). The corpus callosum provides the main method of communication between these hemispheres. cerebral hemispheres receive their sensory information from, and project motor commands to, the opposite side of the body. The right cerebral hemisphere controls the left side of the body, and vice versa. regions of the brain that are responsible for controlling speech and understanding verbalization are frequently located in the left cerebral hemisphere divided into five anatomically distinct lobes. Four of these lobes are visible on the external surface and are named for the overlying cranial bones: the frontal, parietal, temporal, and occipital lobes (figure 13.12a). The fifth lobe, called the insula, is not visible at the surface of the hemispheres.

pontine respiratory center

The pons houses autonomic nuclei in the pontine respiratory center (previously called the pneumotaxic [nū-mō-tăk′sik] center). This vital center, along with the medullary respiratory center within the medulla oblongata, regulates the skeletal muscles of breathing. The primary function of the pontine respiratory center is to regulate a smooth transition between breathing in and breathing out

choroid plexus

The production of CSF by the brain occurs at a rate of about 500 milliliters (mL) (or 1/2 liter) per day, with the volume of CSF in the subarachnoid space at any given time ranging between 100 mL and 160 mL. Cerebrospinal fluid is initially formed by the choroid plexus (ko′royd plek′sŭs; chorioeides = membrane, plexus = a braid), a region of specialized tissue in each ventricle. The choroid plexus is composed of a layer of glial cells called ependymal (ep-en′di-măl; ependyma = an upper garment) cells (see section 12.4b) and the blood capillaries that lie within the pia mater (figure 13.8). Thus, in order to enter a ventricle, fluid within the blood must cross these structures: blood capillary wall, the pia mater, and an ependymal cell.

reticular activating system (RAS),

The sensory component of the reticular formation is responsible for alerting the cerebrum to incoming sensory information. This sensory component is called the reticular activating system (RAS), and it contains sensory axons that project to the cerebral cortex. The RAS processes visual, auditory, and touch stimuli and uses this information to keep us in a state of mental alertness. Additionally, the RAS arouses us from sleep. The sound of an alarm clock can awaken us because the RAS receives this sensory stimulus and sends it to the cerebrum. Conversely, under conditions of little or no stimuli, such as when you are in bed with the lights out and no sounds are disturbing you, the RAS is not stimulated and you find it easier to sleep.

tentorium cerebelli

a horizontally oriented fold of dura mater that separates both the occipital and temporal lobes of the cerebrum from the cerebellum transverse sinuses are within its posterior border, whereas the straight sinus is within its midsagittal region. The anterior surface of the tentorium cerebelli has a gap, or opening, called the tentorial notch (or tentorial incisure), to allow for the passage of the brainstem.

Arachnoid Mater

also called the arachnoid membrane, lies external to the pia mater. The term arachnoid means "resembling a spider web," and this meninx is so named because it is partially composed of a delicate web of collagen and elastic fibers, termed the arachnoid trabeculae

primary motor cortex

also called the somatic motor area, is specifically located within the precentral gyrus of the frontal lobe (figure 13.12). Neurons in this area control voluntary skeletal muscle activity. The axons of these neurons project contralaterally (to the opposite side) within either the brainstem or the spinal cord. Thus, the left primary motor cortex controls the skeletal muscles on the right side of the body and the right primary motor cortex controls the skeletal muscles on the left side of the body.

occipital sinus

another dural venous sinus) is within its posterior vertical border.

pyramids

anterior surface exhibits two longitudinal ridges called the pyramids (pir′ă-mid), which house the motor projection tracts called the corticospinal (pyramidal) tracts that extend through the medulla oblongata

Ventricles

are cavities or expansions within the brain that are derived from the neural canal (the lumen of the embryonic neural tube). All of the ventricles are lined with ependymal cells (see section 12.4b) and contain cerebrospinal fluid. The ventricles are connected with one another as well as with the central canal of the spinal cord our ventricles within the brain

fourth ventricle

cerebral aqueduct (ak′we-dŭkt) (also called the mesencephalic aqueduct and formerly called the aqueduct of Sylvius) passes through the midbrain and connects the third ventricle with the tetrahedron-shaped is located between the pons, medulla oblongata, and cerebellum. It opens to the subarachnoid space via paired lateral apertures and a single median aperture. The fourth ventricle narrows at its inferior end before it merges with the slender central canal of the spinal cord.

brain is composed of four major regions

cerebrum, diencephalon, brainstem, and cerebellum

gray matter

color from the cell bodies and dendrites of the neurons that compose it. One indication that a general brain structure is composed of gray matter is that these areas are often (though not always) designated as Cortex, which is a superficial layer of gray matter (like the bark of a tree), or Nucleus, or center, which are clusters of neuron cell bodies within gray matter that are either close to the surface or deep within the brain function of each of the different regions of gray matter, in either the brain or the spinal cord, is to serve as an integrating and processing area. Specifically, the synapses within the gray matter allow for integration and processing to occur.

cardiovascular center

composed of both the cardiac center, which regulates both the heart's rate and its force of contraction to alter cardiac output (see section 19.5b), and the vasomotor center, which controls the contraction and relaxation of smooth muscle within the walls of the smallest arteries (the arterioles) to alter these vessels' diameter. Both cardiac output and blood vessel diameter influence blood pressure

Limbic System

composed of multiple cerebral and diencephalic structures that collectively process and experience emotions. Thus, the limbic system is sometimes referred to as the emotional brain. The structures of the limbic system form a ring or border around the diencephalon. Although neuroanatomists continue to debate the components of the limbic system, the brain structures commonly recognized cingulate parahippocampal gyrus hippocampus amygdaloid body olfactory bulbs, olfactory tracts, and olfactory cortex fornix anterior thalamic nuclei, the habenular nuclei of the epithalamus, the septal nuclei, and the mammillary (mam′i-lār-ē; mammilla = nipple) bodies of the hypothalamus

superior cerebellar peduncles

connect the midbrain to the cerebellum

cerebral aqueduct

connecting the third and fourth ventricles (see section 13.2b); it is surrounded by a region called the periaqueductal gray matter

brainstem

connects the cerebrum, diencephalon, and cerebellum to the spinal cord. Three regions form the brainstem. From superior to inferior, these include the midbrain, the pons, and the medulla oblongata

substantia nigra

consists of bilaterally symmetric nuclei within the midbrain (figure 13.21). Its name derives from its almost black appearance due to melanin pigmentation. The substantia nigra houses clusters of neurons that produce the neurotransmitter dopamine, which affects brain processes to control movement, emotional response, and ability to experience pleasure and pain. Degeneration of these cells in the substantia nigra is a pathology that underlies Parkinson disease

corpus callosum

corpus callosum provides the main method of communication between these hemispheres.

fissures

deep grooves in the brain

insula (in′sū-lă; island) is a small lobe

deep to the lateral sulcus. It can be observed by laterally reflecting (pulling aside) the temporal lobe. The insula's lack of accessibility has prevented aggressive studies of its function, but the cerebral cortex of the insula is apparently involved in memory and the interpretation of taste.

nervous system

derived from ectoderm

white matter

derives its color from the bundles of myelinated axons that compose it. These bundles of myelinated axons within the CNS are called tracts and are located on or close to the surface (outer white matter) or deep (inner white matter) (figure 13.4). Tracts within the brain typically have specific names (e.g., corpus callosum, internal capsule, peduncles). Note that the white matter in the spinal cord is subdivided into Page 493funiculi and white commissures (figure 13.4d), which are described in section 14.3a. (Recall from section 12.1c that, within the peripheral nervous system [PNS], bundles of axons are called nerves and aggregates or clusters of cell bodies are called ganglia.)

thalamus

forms the superolateral walls of the third ventricle (figure 13.17), and its paired oval masses of gray matter that lie on either side of the third ventricle (figure 13.18). When viewed in midsagittal section, the thalamus is located between the anterior commissure and the pineal gland. The interthalamic adhesion (or intermediate mass) is a small, midline mass of gray matter that connects the right and left thalamic bodies. Each part of the thalamus has about a dozen major thalamic nuclei that are organized into groups; axons from these nuclei project to particular regions of the cerebral cortex. Sensory nerve signals from all the conscious senses except olfaction converge on the thalamus and synapse in at least one of its nuclei. For example, the ventral posterior nuclei relay sensory information to the primary somatosensory cortex of the parietal lobe, whereas auditory information is relayed through the medial geniculate nuclei. The thalamus is the principal and final relay point for incoming sensory information that is processed and then projected to the appropriate lobe of the cerebral cortex. Only a relatively small portion of the sensory information that arrives at the thalamus is forwarded to the cerebrum because the thalamus acts as an information filter

lobes of brain

frontal, parietal, occipital, temporal, insula(under part of frontal lobe)

primary somatosensory cortex

housed within the postcentral gyrus of the parietal lobes. Neurons within this cortex receive general somatic sensory information from receptors of the skin regarding touch, pressure, pain, and temperature, as well as sensory input from proprioceptors from the joints and muscles regarding the conscious interpretation of body position. We typically are conscious of the sensations received by this cortex

sensory homunculus

imilar to a motor homunculus (figure 13.13b). The surface area of somatosensory cortex devoted to a body region indicates the amount of sensory information collected within that region. Thus, the lips, fingers, and genital region occupy larger portions of the homunculus, whereas the trunk of the body has proportionately fewer receptors, so its associated homunculus region is Page 506smaller

Two lateral ventricles

in the cerebrum, separated by a thin medial partition called the septum pellucidum

Higher-order brain functions

include learning, memory, and reasoning. These functions occur within the cerebral cortex and involve multiple brain regions connected by complicated networks and arrays of axons. Both conscious and unconscious processing of information are involved in higher-order brain functions, and this processing may be continually adjusted or modified.

Consciousness

includes an awareness of sensation, voluntary control of motor activities, and the activities necessary for higher mental processing. It involves the simultaneous activity of large areas of the cerebral cortex. Levels of consciousness exist on a continuum. The highest state of consciousness and cortical activity is alertness, in which the individual is responsive, aware of self, and well oriented to person, place, and time.

cerebrum is divided

into two halves, called the left and right cerebral hemispheres. Each hemisphere may be further subdivided into five functional areas called lobes.

pons

is a bulging region on the anterior part of the brainstem (figures 13.20 and 13.22). Sensory and motor tracts are located within the pons and extend through it to connect to the brain and spinal cord

electroencephalogram (EEG)

is a diagnostic test where electrodes are attached to the head to record the electrical activity of the brain (figure 13.28). This procedure is performed to investigate sleep disorders and lesions, and to determine if an individual is in a coma or a persistent vegetative state (see Clinical View 13.12: "Pathologic States of Consciousness"). EEGs also may evaluate a seizure, which is an event of abnormal electrical activity in the brain. There are different types of seizures, some of which may result in a brief blackout and others that may result in shaking and muscle spasms. Epilepsy is the condition where a person experiences repeated seizures over time

primary olfactory cortex

is also located within the temporal lobe and provides conscious awareness of smells

premotor cortex

is called the somatic motor association area, and it is located within the frontal lobe immediately anterior to the precentral gyrus. It is primarily responsible for coordinating learned, skilled motor activities, such as moving the eyes in a coordinated fashion when reading a book or playing the guitar. An individual who has sustained trauma to this area would still be able to understand written letters and words but would have difficulty reading because his or her eyes couldn't follow the lines on a printed page.

motor speech area (also known as the Broca area

is located in most individuals within the inferolateral portion of the left frontal lobe (figure 13.12). This region is responsible for regulating the breathing and controlling the muscular movements necessary for vocalization.

primary auditory cortex

is located within the temporal lobe, where it receives and processes auditory information. The auditory association area is located within the temporal lobe, posteroinferior to the primary auditory cortex. Within this association area, the cortical neurons interpret the characteristics of sound and store memories of sounds heard in the past. The next time a song is playing over and over in your head, you will know that this auditory association area is responsible

Blood-Brain Barrier.

is markedly reduced or missing in three distinct locations in the CNS: the choroid plexus, hypothalamus, and pineal gland. The capillaries of the choroid plexus must be permeable to produce CSF, and the hypothalamus and pineal gland produce certain hormones that must have ready access to the blood.

medulla oblongata

is often simply called the medulla. It is the most inferior part of the brainstem and is continuous with the spinal cord inferiorly. The most inferior portion of the medulla has a flattened, rounded shape and narrow central canal. As this tubelike opening extends (superiorly and anteriorly) toward the pons, the central canal enlarges and becomes the inferior portion of the fourth ventricle. All communication between the brain and spinal cord involves tracts that ascend or descend through the medulla oblongata

pia mater

is the innermost of the cranial meninges. It is a thin layer of delicate areolar connective tissue that tightly adheres to the brain and follows every contour of the brain surface.

tectum

is the most posterior region of the midbrain. It contains two pairs of sensory nuclei, the superior and inferior colliculi, which are collectively called the tectal plate (quadrigeminal plate, or corpora quadrigemina). These nuclei are relay stations in the processing pathway of visual and auditory sensory input

Dura Mater

is the strongest of the meninges, as its Latin name indicates. This outer, dense irregular connective tissue covering is composed of two layers. The meningeal (mĕ-nin′jē-ăl, men′in-jē′ăl) layer is immediately superficial to the arachnoid. The periosteal (per-ē-os′tē-ăl) layer, the more superficial layer, forms the periosteum on the internal surface of the cranial bones

cerebral cortex

is the surface layer of gray matter of the cerebrum and that the cerebral nuclei are the internal, deep gray matter within the cerebrum. The cerebral gray matter, like all gray matter, functions as centers of integration and processing.

primary gustatory cortex

is within the insula and is involved in processing taste information

frontal lobe

lies deep to the frontal bone and forms the anterior part of the cerebral hemisphere figures 13.11 and 13.12a. The frontal lobe ends posteriorly at a deep groove called the central sulcus that marks its boundary with the parietal lobe. The inferior border of the frontal lobe is marked by thelies deep to the frontal bone and forms the anterior part of the cerebral hemisphere figures 13.11 and 13.12a. The frontal lobe ends posteriorly at a deep groove called the central sulcus that marks its boundary with the parietal lobe. The inferior border of the frontal lobe is marked by the lateral sulcus, a deep groove that separates the frontal and parietal lobes from the temporal lobe. An important anatomic feature of the frontal lobe is the precentral gyrus, which is the mass of nervous tissue immediately anterior to the central sulcus. The frontal lobe is primarily concerned with voluntary motor functions (including motor functions involved with speech), concentration, verbal communication, decision making, planning, and personality.,

central white matter

lies deep to the gray matter of the cerebral cortex. It is composed primarily of myelinated axons, as described in section 13.1c. Most of these axons are grouped into bundles called tracts, which are classified as association tracts, commissural tracts, or projection tracts (figure 13.14).

parietal lobe

lies deep to the parietal bone and forms the superoposterior part of each cerebral hemisphere. It terminates anteriorly at the central sulcus, posteriorly at a relatively indistinct parieto-occipital sulcus, and laterally at the lateral sulcus. An important anatomic feature of this lobe is the postcentral gyrus, which is the mass of nervous tissue immediately posterior to the central sulcus. The cerebral cortex of the parietal lobe is involved with general sensory functions, such as evaluating the shape and texture of objects being touched and sensory input regarding body position from proprioceptors within our joints and muscles.

occipital lobe

lies internal to the occipital bone and forms the posterior region of each hemisphere. The cerebral cortex of the occipital lobe is responsible for processing incoming visual information and storing visual memories.

temporal lobe

lies internal to the temporal bone and inferior to the lateral sulcus. The cerebral cortex of this lobe is involved with hearing and smell.

prefrontal cortex

located in the most anterior (rostral) portions of the frontal lobes (figure 13.12). The prefrontal cortex is associated with many higher intellectual functions such as complex thought, judgment, expression of personality, planning future behaviors, and decision making. By retrieving and coordinating information from multiple areas of the brain, the prefrontal cortex also will evaluate potential consequences of one's actions, and in so doing will modulate one's behavior based on societal norms. Interestingly, the prefrontal cortex continues to develop into our teens and 20s, as the axons continue to myelinate in this region and unnecessary synapses are removed. As a result, neuroscientists hypothesize, the reason many teenagers may have difficulty in planning and are impulsive, emotional, and risk takers is because the prefrontal cortex has not fully matured.

primary visual cortex

located within the occipital lobe, where it receives and processes incoming visual information. The visual association area is located within the occipital lobe and it surrounds the primary visual area. It enables us to process visual information by analyzing color, movement, and form and to use this information to identify the things we see. For example, when we look at a face, the primary visual cortex receives bits of visual information, but the visual association area is responsible for integrating all of this information into a recognizable picture of a face

somatosensory association area

located within the parietal lobe and lies immediately posterior to the primary somatosensory cortex. It integrates sensory information and interprets sensations to determine the texture, temperature, pressure, and shape of objects. The somatosensory association area allows us to identify known objects without seeing them. For example, even when our eyes are closed, we can tell the difference between the coarse feel of a handful of dirt; the smooth and round shape of a marble; and the thin, flat, rounded surface of a coin because those interpretations of the textures and shapes have already been stored in the somatosensory association area.

Cerebrum

location of conscious thought processes and the origin of all complex intellectual functions. It is readily identified as the two large hemispheres on the superior aspect of the brain

rostral

meaning "toward the nose", anterior

cranial dural septa

meningeal layer of the dura mater extends as flat partitions into the cranial cavity at four locations. Collectively, these double layers of dura mater are called falx cerebri, tentorium cerebelli, falx cerebelli, and diaphragma sellae (figure 13.6). The falx cerebri (falks sē-rē′bri; falx = sickle) is the largest of the four dural septa. This large, sickle-shaped, vertical fold of dura mater is located in the midsagittal plane and projects into the longitudinal fissure between the left and right cerebral hemispheres. Anteriorly, its inferior portion attaches to the crista galli of the ethmoid bone; posteriorly, its inferior portion attaches to the internal occipital crest (see section 8.2b). Located within the superior and inferior margins of this dural septum are two dural venous sinuses: the superior sagittal sinus and the inferior sagittal sinus, respectively.

brainstem has three regions

midbrain, pons, and medulla oblongata

cerebellum

s the second largest part of the brain. It coordinates fine control over skeletal muscle actions and stores memories of movement patterns, such as the playing of scales on a piano. three regions: an outer gray matter called the cerebellar cortex, an internal region of white matter, and the deepest gray matter layer that is composed of cerebellar nuclei. The internal region of white matter is called the arbor vitae (ar′bōr vī′tē; arbor = tree, vita = life) because its distribution pattern resembles the branches of a tree The cerebellum does not initiate skeletal muscle movement. Rather, it coordinates and fine-tunes skeletal muscle movements that were initiated by the cerebrum, and it ensures that skeletal muscle contraction follows the correct pattern, leading to smooth, coordinated movements. The cerebellum stores memories of previously learned movement patterns. This function is performed indirectly, by regulating activity along both the voluntary and involuntary motor pathways at the cerebral cortex, cerebral nuclei, and motor centers in the brainstem. The cerebrum initiates a movement and sends a "rough draft" of the movement to the cerebellum, which then coordinates and adjusts it. For example, the controlled, precise movements a classical guitarist makes when playing a concerto result from fine-tuning by the cerebellum. Without the cerebellum, the guitarist's movements would be choppy and sloppy, without precise coordination between the two hands also helps with balance and coordination

diencephalon 2

sandwiched between the inferior regions of the cerebral hemispheres and for this reason is often referred to as the "in-between brain." The diencephalon components include the epithalamus, the thalamus, and the hypothalamus (figure 13.17). The 3rd ventricle also is associated with the diencephalon (see figure 13.7).

tegmentum

sandwiched between the nuclei of the substantia nigra and the periaqueductal gray matter. The tegmentum contains the pigmented red nuclei and the reticular formation. The reddish color of these nuclei is due to both blood vessel density and iron pigmentation in the neuronal cell bodies. The tegmentum integrates information from the cerebrum and cerebellum and issues involuntary motor commands to the erector spinae muscles of the back (see section 11.4) to help maintain posture while standing, bending at the waist, or walking.

sulci

shallow grooves of brain tissue

falx cerebelli,

sickle-shaped, vertical partition that divides the left and right cerebellar hemispheres

petalias

tend to have shape asymmetries of the frontal and occipital lobes of the brain Right-handed individuals typically have right frontal petalias, meaning that the right frontal lobe projects farther than the left frontal lobe, and left occipital petalias, meaning that the left occipital lobe projects farther than the right occipital lobe. Conversely, left-handed individuals are inclined to have the reverse pattern (left frontal and right occipital petalias).

diencephalon

thalamus, hypothalamus, epithalamus

hypothalamus

the anteroinferior region of the diencephalon. A thin, stalklike infundibulum (in-fŭn-dib′ū-lŭm; funnel) extends inferiorly from the hypothalamus to attach to the pituitary gland (figure 13.19). Master control of the autonomic nervous system Master control of the endocrine system Regulation of body temperature. Control of food intake Control of water intake Regulation of sleep-wake (circadian) rhythms Control of emotional behavior

diaphragma sellae

the smallest of the dural septa. It forms a roof over the sella turcica of the sphenoid bone. A small opening within it allows for the passage of a thin stalk, called the infundibulum, that attaches the pituitary gland to the base of the hypothalamus

cerebellar hemispheres

three regionsleft and right cerebellar hemispheres (figure 13.24). Each hemisphere consists of two lobes, the anterior lobe and the posterior lobe, which are separated by the primary fissure. A narrow band of nervous tissue known as the vermis (ver′mis; worm) lies along the midline between the left and right cerebellar lobes. The cerebellar hemispheres and vermis have surface folds called folia (fō′lē-ă; folium = leaf). (These folds are similar to the gyri of the cerebrum.)