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The brain

The portion of the central nervous system contained within the cranium.

Neurons and neuroglia #'s in the brain

100 billion neurons and 10 - 50 trillion neuroglia

4 major parts of the adult brain

1. brain stem
2. cerebellum
3. diencephalon
4. cerebrum

Brain stem

Continuous with the spinal cord and consists of the medulla oblongata, pons and midbrain

Location of Cerebellum

Posterior to brain stem

Location of diencephalon

Superior to brain stem.
- consists of thalamus, hypothalamus and epithalamus

Cerebrum

Supported on the diencephalon and brain stem
- largest part of the brain

Protective coverings of the brain

Cranium and the cranial meninges
- surround and protect the brain

Cranial meninges

Continuous with the spinal meninges
- have the same basic structures
- bear the same names:
1. outer dura mater
2. middle arachnoid mater
3. inner pia mater

2 layers of cranial dura mater

(spinal dura mater has only one)
2 dural layers around the brain are fused together except where they separate to enclose the dural venous sinuses that drain venous blood from the brain and deliver it into the internal jugular veins.

Epidural space around brain?

No, no space around brain

Blood-brain barrier - function and anatomy

Protects brain cells from harmful substances and pathogens by preventing passage of many substances from blood into brain tissue
- consists mainly of tight junctions that seal together the endothelial cells of brain capillaries, along with a thick basement membrane around the capillaries.
- then, the processes of many astrocytes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of the tight junctions.

Substances that do cross the BBB

- A few water soluble substances, such as glucose, cross by active transport
- others, such as creatine, urea and most ions cross very slow
- lipid soluble substances: oxygen, carbon dioxide , alcohol and most anesthetic agents easily cross the barrier.

Breakdown of the BBB

Possible by trauma, toxins and inflammation

Oxygen and glucose use by the brain

Brain only makes up 2% of total body weight but consumes about 20% of the oxygen and glucose used, even at rest.
Neurons synthesize ATP almost exclusively from glucose via reactions that use oxygen.
Almost no glucose is stored in the brain, so the supply must be continuous.
If blood entering the brain has a low level of glucos, mental confusion, dizziness, convulsion and loss of consciousness may occur.

Importance of brain blood flow

Even a brief slowing of brain blood flow may cause unconsciousness.

Cerebrospinal fluid

- a clear, colorless liquid that protects the brain and spinal cord from chemical and physical injuries. It also carries oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia.
- CSF continuously circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space (between the arachnoid mater and pia mater).

ventricles

four CSF-filled cavities within the brain

lateral ventricle

one in each hemisphere of the cerebrum

septum pellucidum

Anteriorly, the lateral ventricles are separated by a thin membrane

third ventricle

a narrow cavity along the midline superior to the hypothalamus and between the right and left halves of the thalamus

fourth ventricle

lies between the brain stem and the cerebellum.

The CSF contributes to homeostasis in three main ways

1. Mechanical protection
CSF serves as a shock-absorbing medium that protects the delicate tissues of the brain and spinal cord from jolts that would otherwise cause them to hit the bony walls of the cranial and vertebral cavities. The fluid also buoys the brain so that it "floats" in the cranial cavity.

2. Chemical protection
CSF provides an optimal chemical environment for accurate neuronal signaling. Even slight changes in the ionic composition of CSF within the brain can seriously disrupt production of action potentials and postsynaptic potentials.

3. Circulation
CSF allows exchange of nutrients and waste products between the blood and nervous tissue.

choroid plexuses

sites of CSF production
- networks of capillaries (microscopic blood vessels) in the walls of the ventricles. The capillaries are covered by ependymal cells that form cerebrospinal fluid from blood plasma by filtration and secretion.

blood-cerebrospinal fluid barrier

- Because the ependymal cells are joined by tight junctions, materials entering CSF from choroid capillaries cannot leak between these cells; instead, they must pass through the ependymal cells.
- This barrier permits certain substances to enter the CSF but excludes others, protecting the brain and spinal cord from potentially harmful blood-borne substances.

arachnoid villi

CSF is gradually reabsorbed into the blood through these fingerlike extensions of the arachnoid that project into the dural venous sinuses

brain stem

the part of the brain between the spinal cord and the diencephalon; it consists of the (1) medulla oblongata, (2) pons, and (3) midbrain.
- Extending through the brain stem is the reticular formation, a netlike region of interspersed gray and white matter.

medulla oblongata

- is continuous with the superior part of the spinal cord; it forms the inferior part of the brain stem
- begins at the foramen magnum and extends to the inferior border of the pons, a distance of about 3 cm (1.2 in.).
- The medulla's white matter contains all sensory (ascending) and motor (descending) tracts that extend between the spinal cord and other parts of the brain.
- Relays sensory input and motor output between other parts of the brain and the spinal cord.
- Vital centers regulate heartbeat, blood vessel diameter, and breathing (together with pons)
- Other centers coordinate swallowing, vomiting, coughing, sneezing, and hiccupping.
- Contains nuclei of origin for cranial nerves VIII, IX, X, XI, and XII.

pyramids

Some of the white matter forms bulges on the anterior aspect of the medulla.
- These protrusions are formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord

decussation of pyramids

Just superior to the junction of the medulla with the spinal cord, 90% of the axons in the left pyramid cross to the right side, and 90% of the axons in the right pyramid cross to the left side.
- explains why each side of the brain controls movements on the opposite side of the body.

cardiovascular center

The medulla also contains several nuclei, masses of gray matter where neurons form synapses with one another. Several of these nuclei control vital body functions.
- The cardiovascular center regulates the rate and force of the heartbeat and the diameter of blood vessels.

medullary rhythmicity area of the respiratory center

adjusts the basic rhythm of breathing.

pons

lies directly superior to the medulla and anterior to the cerebellum and is about 2.5 cm (1 in.) long
- consists of both nuclei and tracts
- bridge that connects parts of the brain with one another; relays impulses from one side of the cerebellum to the other and between the medulla and midbrain.
- These connections are provided by bundles of axons. Some axons of the pons connect the right and left sides of the cerebellum. Others are part of ascending sensory tracts and descending motor tracts.
- some nuclei in the pons are the pneumotaxic area and the apneustic area
- also contains nuclei associated with the following four pairs of cranial nerves: trigeminal (V) nerves, abducens (VI) nerves, facial (VII) nerves, and vestibulocochlear (VIII) nerves.

Pneumotaxic area and apneustic area

Together with the medullary rhythmicity area, they help control breathing.

midbrain or mesencephalon

- extends from the pons to the diencephalon
- is about 2.5cm long
- The cerebral aqueduct passes through the midbrain, connecting the third ventricle above with the fourth ventricle below. Like the medulla and the pons, the midbrain contains both tracts and nuclei.
- Relays motor output from the cerebral cortex to the pons and sensory input from the spinal cord to the thalamus.
- Superior colliculi coordinate movements of the eyeballs in response to visual and other stimuli, and the inferior colliculi coordinate movements of the head and trunk in response to auditory stimuli. Most of substantia nigra and red nucleus contribute to control of movement.
- Contains nuclei of origin for cranial nerves III and IV.

reticular formation

In addition to the well-defined nuclei already described, much of the brain stem consists of small clusters of neuronal cell bodies (gray matter) interspersed among small bundles of myelinated axons (white matter).
- The broad region where white matter and gray matter exhibit a netlike arrangement
- extends from the upper part of the spinal cord, throughout the brain stem, and into the lower part of the diencephalon.

reticular activating system

Neurons within the reticular formation have both ascending (sensory) and descending (motor) functions.
- This part of the reticular formation consists of sensory neurons that project to the cerebral cortex
- helps maintain consciousness and is active during awakening from sleep
- The reticular formation's main descending function is to help regulate muscle tone, the slight degree of contraction in normal resting muscles.

cerebellum

- Compares intended movements with what is actually happening to smooth and coordinate complex, skilled movements.
- Regulates posture and balance.
- May have a role in cognition and language processing.
- second only to the cerebrum in size
- occupies the inferior and posterior aspects of the cranial cavity.
- posterior to the medulla and pons and inferior to the posterior portion of the cerebrum
- In superior or inferior views, the shape of the cerebellum resembles a butterfly

transverse fissure

a deep groove, which along with the tentorium cerebelli, separates the cerebellum from the cerebrum

vermis

The central constricted area of the cerebellum

cerebellar hemispheres

the lateral wings/lobes of the cerebellum
- Each hemisphere consists of lobes separated by deep and distinct fissures.
- govern sub-conscious aspects of skeletal muscle movements.
- contribute to equilibrium and balance.

cerebellar cortex

The superficial layer of the cerebellum
- consists of gray matter in a series of slender, parallel ridges called folia

folia

gray matter of the cerebellar cortex made up of a series of slender, parallel ridges

arbor vitae

tracts of white matter deep to the grey matter of the cerebellar cortex

diencephalon

extends from the brain stem to the cerebrum and surrounds the third ventricle; it includes the thalamus, hypothalamus, and epithalamus.

thalamus

measures about 3 cm (1.2 in.) in length and makes up 80% of the diencephalon, consists of paired oval masses of gray matter organized into nuclei with interspersed tracts of white matter
- Relays almost all sensory input to the cerebral cortex. - Provides crude perception of touch, pressure, pain, and temperature.
- Includes nuclei involved in movement planning and control.

hypothalamus

a small part of the diencephalon located inferior to the thalamus. It is composed of a dozen or so nuclei in four major regions
- Controls and integrates activities of the autonomic nervous system and pituitary gland.
- Regulates emotional and behavioral patterns and circadian rhythms.
- Controls body temperature and regulates eating and drinking behavior.
- Helps maintain the waking state and establishes patterns of sleep.
- Produces the hormones oxytocin and antidiuretic hormone (ADH).

epithalamus

consists of the pineal gland and habenular nuclei.

pineal gland

about the size of a small pea and protrudes from the posterior midline of the third ventricle
- onsidered part of the endocrine system because it secretes the hormone melatonin

melatonin

As more melatonin is liberated during darkness than in light, this hormone is thought to promote sleepiness. Melatonin also appears to contribute to the setting of the body's biological clock.

cerebrum

the "seat of intelligence."
- provides us with the ability to read, write, and speak; to make calculations and compose music; and to remember the past, plan for the future, and imagine things that have never existed before.
- Sensory areas are involved in the perception of sensory information; motor areas control muscular movement; and association areas deal with more complex integrative functions such as memory, personality traits, and intelligence.
-Basal ganglia coordinate gross, automatic muscle movements and regulate muscle tone.
Limbic system functions in emotional aspects of behavior related to survival.

cerebral cortex

The outer rim of gray matter of the cerebrum
- 2-4 mm thick
- contains billions of neurons.
- Deep to the cerebral cortex lies the cerebral white matter.

gyri

During embryonic development, when brain size increases rapidly. Thus, the gray matter of the cortex enlarges much faster than the deeper white matter
As a result, the cortical region rolls and folds upon itself.
These are the folds.
aka convolutions

fissures

The deepest grooves between folds of gyri

Sulci

shallower grooves between folds of gyri

longitudinal fissure

the most prominent fissure in the brain
- divides the brain into L and R hemispheres.

corpus callosum

a broad band of white matter that containing axons that connects the cerebral hemispheres. Extends between them.
(sits deep inside the brain)

4 lobes of the cerebral hemisphere

frontal, parietal, temporal, and occipital lobes
- named after the bones they sit under.

central sulcus

separates the frontal lobe from the parietal lobe.

precentral gyrus

a major gyrus
- located immediately anterior to the central sulcus
- contains the primary motor area of the cerebral cortex

postcentral gyrus

a major gyrus
- located immediately posterior to the central sulcus
- contains the primary somatosensory area of the cerebral cortex.

lateral cerebral sulcus (fissure)

separates the frontal lobe from the temporal lobe.

parieto-occipital sulcus

separates the parietal lobe from the occipital lobe

insula

cannot be seen at the surface of the brain because it lies within the lateral cerebral sulcus, deep to the parietal, frontal, and temporal lobes

cerebral white matter

consists of myelinated and unmyelinated axons in three types of tracts: association tracts, commissural tracts and projection tracts

association tracts

contain axons that conduct nerve impulses between gyri in the same hemisphere.

Commissural tracts

contain axons that conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in the other cerebral hemisphere.
- Three important groups of commissural tracts are the corpus callosum (the largest fiber bundle in the brain, containing about 300 million fibers), anterior commissure, and posterior commissure.

Projection tracts

contain axons that conduct nerve impulses from the cerebrum to lower parts of the CNS (thalamus, brainstem, or spinal cord) or from lower parts of the CNS to the cerebrum.

Basal ganglia

- control automatic movements of skeletal muscles and muscle tone.
- Deep within each cerebral hemisphere
- three nuclei (masses of gray matter) that are collectively termed this
- receive input from the cerebral cortex and provide output back to motor parts of the cortex.
- the nuclei of the basal ganglia have extensive connections with one another.
- A major function is to help regulate initiation and termination of movements.
- help initiate and terminate some cognitive processes, such as attention, memory, and planning, and may act with the limbic system to regulate emotional behaviors.

limbic system

Encircling the upper part of the brain stem and the corpus callosum is this ring of structures on the inner border of the cerebrum and floor of the diencephalon
- sometimes called the "emotional brain" because it plays a primary role in a range of emotions, including pain, pleasure, docility, affection, and anger

Functional Organization of the Cerebral Cortex

Specific types of sensory, motor, and integrative signals are processed in certain regions of the cerebral cortex

sensory areas

receive sensory information and are involved in perception, the conscious awareness of a sensation
- Sensory information arrives mainly in the posterior half of both cerebral hemispheres, in regions behind the central sulci.
- In the cortex, primary sensory areas have the most direct connections with peripheral sensory receptors.

motor areas

initiate movements
-Motor output from the cerebral cortex flows mainly from the anterior part of each hemisphere

association areas

deal with more complex integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence.
- consist of some motor and sensory areas, plus large areas on the lateral surfaces of the occipital, parietal, and temporal lobes and on the frontal lobes anterior to the motor areas.
- Association areas are connected with one another by association tracts

primary somatosensory area

located directly posterior to the central sulcus of each cerebral hemisphere in the postcentral gyrus of each parietal lobe.
- extends from the lateral cerebral sulcus, along the lateral surface of the parietal lobe to the longitudinal fissure, and then along the medial surface of the parietal lobe within the longitudinal fissure.
- receives nerve impulses for touch, proprioception (joint and muscle position), pain, itching, tickle, and temperature and is involved in the perception of these sensations.
- A "map" of the entire body is present in the primary somatosensory area: Each point within the area receives impulses from a specific part of the body
- the size of the cortical area receiving impulses from a particular part of the body depends on the number of receptors present there rather than on the size of the body part.
- The primary somatosensory area allows you to pinpoint where sensations originate, so that you know exactly where on your body to swat that mosquito.

primary visual area

located at the posterior tip of the occipital lobe mainly on the medial surface
- receives visual information and is involved in visual perception.

primary auditory area

located in the superior part of the temporal lobe near the lateral cerebral sulcus
- receives information for sound and is involved in auditory perception.

primary gustatory area

located at the base of the postcentral gyrus superior to the lateral cerebral sulcus in the parietal cortex
- receives impulses for taste and is involved in gustatory perception.

primary olfactory area

located in the temporal lobe on the medial aspect
- receives impulses for smell and is involved in olfactory perception.

primary motor area

located in the precentral gyrus of the frontal lobe
- Each region in the primary motor area controls voluntary contractions of specific muscles or groups of muscles
- Electrical stimulation of any point in the primary motor area causes contraction of specific skeletal muscle fibers on the opposite side of the body
- As is true for the primary somatosensory area, body parts do not "map" to the primary motor area in proportion to their size. More cortical area is devoted to those muscles involved in skilled, complex, or delicate movement. For instance, the cortical region devoted to muscles that move the fingers is much larger than the region for muscles that move the toes.

Broca's speech area

- located in the frontal lobe close to the lateral cerebral sulcus, is involved in the articulation of speech.
- In most people, Broca's speech area is localized in the left cerebral hemisphere.
- Neural circuits established between Broca's speech area, the premotor area, and primary motor area activate muscles of the larynx, pharynx, and mouth and breathing muscles.
- The coordinated contractions of your speech and breathing muscles enable you to speak your thoughts.

somatosensory association area

just posterior to and receives input from the primary somatosensory area, as well as from the thalamus and other parts of the brain
- This area permits you to determine the exact shape and texture of an object without looking at it, to determine the orientation of one object with respect to another as they are felt, and to sense the relationship of one body part to another.
- Another role of the somatosensory association area is the storage of memories of past sensory experiences, enabling you to compare current sensations with previous experiences. For example, the somatosensory association area allows you to recognize objects such as a pencil and a paperclip simply by touching them.

prefrontal cortex (frontal association area)

an extensive area in the anterior portion of the frontal lobe that is well-developed in primates, especially humans
- This area has numerous connections with other areas of the cerebral cortex, thalamus, hypothalamus, limbic system, and cerebellum.
- concerned with the makeup of a person's personality, intellect, complex learning abilities, recall of information, initiative, judgment, foresight, reasoning, conscience, intuition, mood, planning for the future, and development of abstract ideas

visual association area

located in the occipital lobe
- receives sensory impulses from the primary visual area and the thalamus.
- It relates present and past visual experiences and is essential for recognizing and evaluating what is seen. For example, the visual association area allows you to recognize an object such as a spoon simply by looking at it.

auditory association area

located inferior and posterior to the primary auditory area in the temporal cortex
- allows you to recognize a particular sound as speech, music, or noise.

Wernicke's area

aka posterior language area
a broad region in the left temporal and parietal lobes, interprets the meaning of speech by recognizing spoken words.
- It is active as you translate words into thoughts. The regions in the right hemisphere that correspond to Broca's and Wernicke's areas in the left hemisphere also contribute to verbal communication by adding emotional content, such as anger or joy, to spoken words.

common integrative area

bordered by somatosensory, visual, and auditory association areas.
- receives nerve impulses from these areas and from the primary gustatory area, primary olfactory area, the thalamus, and parts of the brain stem.
- integrates sensory interpretations from the association areas and impulses from other areas, allowing the formation of thoughts based on a variety of sensory inputs. It then transmits signals to other parts of the brain for the appropriate response to the sensory signals it has interpreted.

premotor area

a motor association area that is immediately anterior to the primary motor area.
- Neurons in this area communicate with the primary motor cortex, the sensory association areas in the parietal lobe, the basal ganglia, and the thalamus. The premotor area deals with learned motor activities of a complex and sequential nature. It generates nerve impulses that cause specific groups of muscles to contract in a specific sequence, as when you write your name. The premotor area also serves as a memory bank for such movements.

frontal eye field area

in the frontal cortex; is sometimes included in the premotor area
-controls voluntary scanning movements of the eyes—like those you just used in reading this sentence.

language areas

Broca's speech area, Wernicke's area, and other language areas are located in the left cerebral hemisphere of most people, regardless of whether they are left-handed or right-handed. Injury to language areas of the cerebral cortex results in aphasia (a-FĀ-zē-a; a- = without; -phasia = speech), an inability to use or comprehend words

hemispheric lateralization - anatomy

Functional asymmetry
- Although the brain is almost symmetrical on its right and left sides, subtle anatomical differences between the two hemispheres exist. For example, in about two-thirds of the population, the planum temporale, a region of the temporal lobe that includes Wernicke's area, is 50% larger on the left side than on the right side. This asymmetry appears in the human fetus at about 30 weeks of gestation. Physiological differences also exist; although the two hemispheres share performance of many functions, each hemisphere also specializes in performing certain unique functions.

hemispheric lateralization - physiology

left hemisphere receives somatic sensory signals from and controls muscles on the right side of the body, whereas the right hemisphere receives sensory signals from and controls the left side of the body. In most people the left hemisphere is more important for reasoning, numerical and scientific skills, spoken and written language, and the ability to use and understand sign language.
Conversely, the right hemisphere is more specialized for musical and artistic awareness; spatial and pattern perception; recognition of faces and emotional content of language; discrimination of different smells; and generating mental images of sight, sound, touch, taste, and smell to compare relationships among them.

brain waves

electrical signals involving brain neurons generating millions of nerve impulses (action potentials)

electroencephalogram (EEG)

A record of brain waves
- Brain waves generated by neurons close to the brain surface, mainly neurons in the cerebral cortex, can be detected by sensors called electrodes placed on the forehead and scalp.

four types of brain waves

Alpha, beta, theta and delta

alpha waves

These rhythmic waves occur at a frequency of about 8-13 cycles per second. (The unit commonly used to express frequency is the hertz [Hz]. One hertz is one cycle per second.) Alpha waves are present in the EEGs of nearly all normal individuals when they are awake and resting with their eyes closed. These waves disappear entirely during sleep.

beta waves

The frequency of these waves is between 14 and 30 Hz. Beta waves generally appear when the nervous system is active—that is, during periods of sensory input and mental activity.

theta waves

These waves have frequencies of 4-7 Hz. Theta waves normally occur in children and adults experiencing emotional stress. They also occur in many disorders of the brain.

delta waves

The frequency of these waves is 1-5 Hz. Delta waves occur during deep sleep in adults, but they are normal in awake infants. When produced by an awake adult, they indicate brain damage.

cranial nerves

The 12 pairs of cranial nerves are so-named because they pass through various foramina in the bones of the cranium.
- Like the 31 pairs of spinal nerves, they are part of the peripheral nervous system (PNS). Each cranial nerve has both a number, designated by a roman numeral, and a name (see Figure 14.5). The numbers indicate the order, from anterior to posterior, in which the nerves arise from the brain. The names designate a nerve's distribution or function.

Pneumonic for Cranial Nerve numbers

Oh, Oh, Oh, To Touch and Feel Very Green Vegetables, AH!

Cranial Nerve I

Olfactory nerve
Major function: Smell

Cranial Nerve II

Optic nerve
Major function: Vision

Cranial Nerve III

Oculomotor nerve
Major function: Control some of the muscles moving the eyeballs, changes in size of pupil and shape of lens

Cranial Nerve IV

Trochlear nerve
Major function: Control some of the muscles moving the eyeballs

Cranial Nerve V

Trigeminal Nerve
Major function: Carry nerve impulses associated with head sensations and chewing muscles

Cranial Nerve VI

Abducens Nerve
Major function: Control some of the muscles moving the eyeballs

Cranial Nerve VII

Facial Nerve
Major function: Carry nerve impulses associated with taste, salivation and muscles of facial expression

Cranial Nerve VIII

Vestibulocochlear Nerve
Major function: Carry nerve impulses associated with hearing and equilibrium

Cranial Nerve IX

Glossopharyngeal Nerve
Major function: Carry nerve impulses association with swallowing, salivation and taste

Cranial Nerve X

Vagus Nerve
Major function: Carry nerve impulses to and from many organs in the thoracic and abdominal cavities

Cranial Nerve XI

Accessory Nerve
Major function: Control head and shoulder muscles

Cranial Nerve XII

Hypoglossal nerve
Major function: Control tongue muscles

Cranial Nerve 'zero'

Located anterior to the first nerves
- Innervate the vomeronasal organs, which may have a function in detecting pheromones, chemical signals passed subconsciously from one individual to another.
- Pheromones have effects on reproductive and social behaviours.

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