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An Introduction to the Brain and Cranial Nerves

• The Adult Human Brain

• Ranges from 750 cc to 2100 cc

• Contains almost 97% of the body’s neural tissue

• Average weight about 1.4 kg (3 lb)

• Male versus Female

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14-1 The Brain

• Six Regions of the Brain

1. Cerebrum

2. Cerebellum

3. Diencephalon

4. Mesencephalon

5. Pons

6. Medulla oblongata

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14-1 The Brain

• Cerebrum

• Largest part of brain

• Controls higher mental functions

• Divided into left and right cerebral hemispheres

• Surface layer of gray matter (neural/cerebral cortex)

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14-1 The Brain

• Cerebellum

• Second largest part of brain

• Coordinates repetitive body movements

• Two hemispheres

• Covered with cerebellar cortex

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Figure 14-1 An Introduction to Brain Structures and Functions

CEREBRUM

• Conscious thought processes,

• Memory storage and processing• Conscious and subconscious regulation

of skeletal muscle contractions

intellectual functions

CEREBELLUM

• Coordinates complexsomatic motorpatterns

other somatic motorcenters in brain andspinal cord

Fissures

Sulci

Gyri

Left cerebralhemisphere

• Adjusts output of

Spinalcord

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14-1 The Brain

• Diencephalon

• Located under cerebrum and cerebellum

• Links cerebrum with brain stem

• Three divisions of the diencephalon

1. Left thalamus

2. Right thalamus

3. Hypothalamus

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14-1 The Brain

• Diencephalon

• Thalamus

• Relays and processes sensory information

• Hypothalamus

• Hormone production

• Emotion

• Autonomic function

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14-1 The Brain

• Diencephalon

• Pituitary gland

• Major endocrine gland

• Connected to hypothalamus

• Via infundibulum (stalk)

• Interfaces nervous and endocrine systems;

example, Fight or Flight

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14-1 The Brain

• The Brain Stem

• Processes information between:

• Spinal cord and cerebrum or cerebellum

• The brain stem is made up of the following 3 parts:

• Midbrain

• Pons

• Medulla oblongata

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14-1 The Brain

• Midbrain

• Also called mesencephalon

• Processes sight, sound, and associated reflexes

• Maintains consciousness; sleep

• Pons

• Connects cerebellum to brain stem

• Is involved in somatic and visceral motor control

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14-1 The Brain

• Medulla Oblongata

• Connects brain to spinal cord

• Relays information

• Regulates autonomic functions

• Heart rate, blood pressure, and digestion

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Figure 14-1 An Introduction to Brain Structures and Functions

DIENCEPHALON

THALAMUS

• Relay and processingcenters for sensoryinformation

• Centers controlling

HYPOTHALAMUS

emotions, autonomicfunctions, andhormone production

MIDBRAIN

• Generation of reflexiveand auditory data

somatic motorresponses

consciousness

PONS

MEDULLA OBLONGATA

function (cardiovascular, respiratory, anddigestive system activities)

• Relays sensory information to thalamus andto other portions of the brain stem

• Autonomic centers for regulation of visceral

Brainstem• Processing of visual

• Maintenance of

• Relays sensory information to cerebellum and thalamus• Subconscious somatic and visceral motor centers

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14-1 The Brain

• The Brain

• The brain is a large, delicate mass of neural tissue

• Containing internal passageways and chambers filled with cerebrospinal fluid

• Each of the six major brain regions has specific functions

• Ascending from the medulla oblongata to the cerebrum, brain functions become more complex and variable

• Conscious thought and intelligence

• Are produced in the neural cortex of the cerebral hemispheres

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14-3 The Medulla Oblongata

• The Medulla Oblongata

• Allows brain and spinal cord to communicate

• Coordinates complex autonomic reflexes

• Controls visceral functions: Cardiovascular centers

and Respiratory rhythmicity centers

• Nuclei in the Medulla

• Autonomic nuclei control visceral activities

• Sensory and motor nuclei of cranial nerves

• Relay stations along sensory and motor pathways

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14-4 The Pons

• The Pons

1. Sensory and motor nuclei of cranial nerves (V, VI, VII, VIII)

2. Nuclei involved with respiration

• Apneustic center and pneumotaxic center

• Modify respiratory rhythmicity center activity

3. Nucei that process and relay information to and from

cerebellum

4. Ascending, descending, and transverse tracts

• Transverse fibers (axons)

• Link nuclei of pons with opposite cerebellar hemisphere

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14-5 The Cerebellum

• Functions of the Cerebellum

1. Adjusts postural muscles

2. Fine-tunes conscious and subconscious movements

• Disorders of the Cerebellum: Ataxia

• Damage from trauma or stroke

• Intoxication (temporary impairment)

• Disturbs muscle coordination

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Table 14-4 Components and Functions of the Midbrain

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14-7 The Diencephalon

• The Diencephalon

• Integrates sensory information and motor commands

• Thalamus, epithalamus, and hypothalamus

• The pineal gland

• Found in posterior epithalamus

• Secretes hormone melatonin

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14-7 The Diencephalon

• The Thalamus

• Filters ascending sensory information for primary

sensory cortex

• Relays information between basal nuclei and cerebral

cortex

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14-7 The Diencephalon

• Five Groups of Thalamic Nuclei

1. Anterior group

• Anterior nuclei

• Part of limbic system (emotions)

2. Medial group

• Provides awareness of emotional states

3. Ventral group

• Relays sensory information

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14-7 The Diencephalon

• Five Groups of Thalamic Nuclei

4. Posterior group

• Pulvinar nucleus (sensory)

• Lateral geniculate nucleus (visual)

• Medial geniculate nucleus (auditory)

5. Lateral group

• Affects emotional states

• Integrates sensory information

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14-7 The Diencephalon

• Eight Functions of the Hypothalamus

1. Provides subconscious control of skeletal muscle

2. Controls autonomic function

3. Coordinates activities of nervous and endocrine

systems

4. Secretes hormones

• Antidiuretic hormone (ADH) by supraoptic nucleus

• Oxytocin (OT; OXT) by paraventricular nucleus

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14-7 The Diencephalon

• Eight Functions of the Hypothalamus

5. Produces emotions and behavioral drives

• The feeding center (hunger)

• The thirst center (thirst)

6. Coordinates voluntary and autonomic functions

7. Regulates body temperature

• Preoptic area of hypothalamus

8. Controls circadian rhythms (day–night cycles)

• Suprachiasmatic nucleus

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14-8 The Limbic System

• Is a functional grouping that:

• Establishes emotional states

• Links conscious functions of cerebral cortex with autonomic

functions of brain stem

• Facilitates memory storage and retrieval

• Stimulation or inhibition affects emotions (rage, fear, pain,

sexual arousal, pleasure)

• Amygdaloid body: Acts as interface between the limbic

system, the cerebrum, and various sensory systems

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14-9 The Cerebrum

• The Cerebrum

• Is the largest part of the brain

• Controls all conscious thoughts and intellectual

functions

• Processes somatic sensory and motor information

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14-9 The Cerebrum

• Three Functional Principles of the Cerebrum

1. Each cerebral hemisphere receives sensory

information from, and sends motor commands to,

the opposite side of the body

2. The two hemispheres have different functions,

although their structures are alike

3. Correspondence between a specific function and a

specific region of cerebral cortex is not precise

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14-9 The Cerebrum

• Functions of Basal Nuclei

• Involved with:

• The subconscious control of skeletal muscle tone

• The coordination of learned movement patterns

(walking, lifting)

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14-9 The Cerebrum

• Motor and Sensory Areas of the Cortex

• Central sulcus separates motor and sensory areas

• Motor areas

• Precentral gyrus of frontal lobe

• Directs voluntary movements

• Primary motor cortex

• Is the surface of precentral gyrus

• Pyramidal cells

• Are neurons of primary motor cortex

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14-9 The Cerebrum

• Motor and Sensory Areas of the Cortex

• Sensory areas

• Postcentral gyrus of parietal lobe

• Receives somatic sensory information (touch,

pressure, pain, vibration, taste, and temperature)

• Primary sensory cortex

• Surface of postcentral gyrus

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14-9 The Cerebrum

• Special Sensory Cortexes

• Visual cortex

• Information from sight receptors

• Auditory cortex

• Information from sound receptors

• Olfactory cortex

• Information from odor receptors

• Gustatory cortex

• Information from taste receptors

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14-9 The Cerebrum

• Association Areas

• Sensory association areas

• Monitor and interpret arriving information at sensory

areas of cortex

• Somatic sensory association area

• Interprets input to primary sensory cortex (e.g.,

recognizes and responds to touch)

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14-9 The Cerebrum

• Sensory Association Areas

• Visual association area

• Interprets activity in visual cortex

• Auditory association area

• Monitors auditory cortex

• Somatic motor association area (premotor cortex)

• Coordinates motor responses (learned movements)

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14-9 The Cerebrum

• Integrative Centers

• Are located in lobes and cortical areas of both

cerebral hemispheres

• Receive information from association areas

• Direct complex motor or analytical activities like

consequences, pro’s and con’s, action versus

reaction, predictions, etc…

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14-9 The Cerebrum

• General Interpretive Area

• Also called Wernicke’s area

• Present in only one hemisphere

• Receives information from all sensory association

areas

• Coordinates access to complex visual and auditory

memories

• Where spoken language is understood

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14-9 The Cerebrum

• Other Integrative Areas

• Speech center

• Is associated with general interpretive area

• Coordinates all vocalization functions

• Prefrontal cortex of frontal lobe

• Integrates information from sensory association areas

• Performs abstract intellectual activities (e.g., predicting

consequences of actions)

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Table 14-8 The Cerebral Cortex

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14-9 The Cerebrum

• Hemispheric Lateralization

• Functional differences between left and right

hemispheres

• Each cerebral hemisphere performs certain functions

that are not ordinarily performed by the opposite

hemisphere

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14-9 The Cerebrum

• The Left Hemisphere

• In most people, left brain (dominant hemisphere) controls:

• Reading, writing, and math

• Decision making

• Speech and language

• The Right Hemisphere

• Right cerebral hemisphere relates to:

• Senses (touch, smell, sight, taste, feel)

• Recognition (faces, voice inflections)

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Figure 14-16 Hemispheric Lateralization

Left Cerebral Hemisphere

LEFT HAND

Prefrontalcortex

Speech center

Writing

Auditory cortex

General interpretive center(language and mathematical

calculation)

Visual cortex(right visual field)

CORPUS

CALLOSUM

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Figure 14-16 Hemispheric Lateralization

Right Cerebral Hemisphere

RIGHT HAND

Prefrontalcortex

Anterior commissure

Analysis by touch

Auditory cortex

Spatial visualizationand analysis

Visual cortex(left visual field)

CORPUS

CALLOSUM

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• Monitoring Brain Activity

• Brain activity is assessed by an electroencephalogram

(EEG)

• Electrodes are placed on the skull and then patterns of

electrical activity (brain waves) are printed out

• Four Categories of Brain Waves

1.Alpha waves

2.Beta waves

3.Theta waves

4.Delta waves

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14-9 The Cerebrum

• Alpha Waves

• Found in healthy, awake adults at rest with eyes

closed

• Beta Waves

• Higher frequency

• Found in adults concentrating or mentally stressed

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14-9 The Cerebrum

• Theta Waves

• Found in children

• Found in intensely frustrated adults

• May indicate brain disorder in adults

• Delta Waves

• During sleep

• Found in awake adults with brain damage

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14-9 The Cerebrum

• Synchronization

• A pacemaker mechanism

• Synchronizes electrical activity between hemispheres

• Brain damage can cause desynchronization

• Seizure

• Is a temporary cerebral disorder

• Changes the electroencephalogram

• Symptoms depend on regions affected