The Brain and Cranial Nerves. The Brain

The Brain and Cranial Nerves The Brain • • • (1) Made up of a trillion cells (neurons) Weighs about 3 pounds Has four principle parts Brain stem – m...
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The Brain and Cranial Nerves

The Brain • • • (1)

Made up of a trillion cells (neurons) Weighs about 3 pounds Has four principle parts Brain stem – medulla oblongata, pons, and midbrain (2) Diencephalon – thalamus and hypothalamus (3) Cerebrum – largest part of the brain (4) Cerebellum

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Meninges •

Protective coverings of the central nervous system. There are three layers: (1) Dura mater – tough and fibrous (2) Arachnoid – looks like a spider’s web (3) Pia mater – gentle inner layer that adheres directly to the brain and spinal cord

Cerebrospinal Fluid (CSF) • Production and distribution (see next slide) (1) Secreted by the choroid plexus of the Lateral Ventricles (2) Passes through the interventricular foramen into the third ventricle (3) The choroid plexus of the third ventricle adds more CSF (4) The CSF then passes through the cerebral aqueduct into the fourth ventricle (5) The choroid plexus of the fourth ventricle adds more CSF (6) The CSF passes through lateral and medial apertures into the subarachnoid space and central canal of the spinal cord (7) The CSF is reabsorbed into veins through the arachnoid villi

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Composition of CSF • Totals about 3 to 5 fluid ounces • Clear and colorless – contains, proteins, glucose, urea, salts, and lymph fluid • Consistency of water • Serves as a shock absorber • Delivers nutritive substances • Removes wastes and toxic substances

Blood Supply to the Brain • Brain needs a lot of oxygen and nutrients • Brain is only 2% of the body weight but uses 20% of the oxygen • Blood flow to the brain is effected by concentrations of carbon dioxide and oxygen in the blood • An increase in CO2 = increase in H+ • An increase in H+ causes the arteries to the brain to vasodilate and increase the blood flow to ensure an adequate supply of oxygen and nutrients

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Brain Stem • Is composed of three parts (1) Medulla oblongata (2) Pons (3) Midbrain

Medulla Oblongata • Continuation of the upper portion of the spinal cord • Contains ascending and descending tracts running between brain and spinal cord and the decussation of pyramids • Contains two vital reflex centers: (1) Cardiovascular center – regulates heart rate and force of contraction (2) Respiratory center – regulates the basic rhythm of breathing

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The Pons • Means bridge – connects the medulla and spinal cord with the cerebrum • Connects with the cerebellum • Contains two vital centers: (1) Pneumotaxic center (2) Apneustic area Together these area define the limit of respiration

The Midbrain • The cerebral aqueduct runs through the middle • Contains the Corpora Quadrigemina which in turn is composed of: Superior colliculi vision reflex center Inferior colliculi auditory reflex center

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The Reticular Formation • Runs through medulla, pons and midbrain • Functions include: (1) Aids in regulating muscle tone (2) Tells the cerebral cortex that sensory information is coming in from the spinal cord (3) The reticular activating system maintains consciousness, arousal from sleep

The Diencephalon • Has two principle parts: (1) Thalamus (2) Hypothalamus

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The Thalamus • Forms the lateral walls of the third ventricle • Is the interpretive center for sensory impulses like - pain - temperature - light touch - pressure

The Hypothalamus • Is a collection of nuclei, each with a specific function • Forms the floor of the third ventricle • Receives information from peripheral nerve related to sound, taste, smell, somatic receptors • Receives information from visceral receptors related to blood pressure, and other physiological factors important to body function • Monitors the body’s water concentration, hormone concentration, body temperature, and release of hormones from the pituitary gland.

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Functions of the Hypothalamus • Controls and regulates the Autonomic Nervous System • Reception and integration of sensory input from the viscera (internal organs) • Intermediate between endocrine and nervous system • Center for mind over body phenomenon • Rage and aggression • Controls normal body temperature • Hunger and satiety center • Thirst center • Waking and sleeping states • Controls biological rhythms

The Cerebrum • The surface of the cerebrum is composed of gray matter and is known as the cerebral cortex • The center of the cerebrum contains white matter • The cortex is highly folded with: - gyri the folds or bumps - Sulci the shallow grooves between the gyri

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Fissures • Are deep sulci and include: Longitudinal fissure separates the cerebral hemispheres Lateral fissure separates frontal lobe from temporal lobe Transverse fissure separates the cerebrum from the cerebellum Central sulcus separates the frontal lobe from the parietal lobe

White Matter of the Brain •

White matter is composed of myelinated fibers running in three directions (1) Association fibers run between gyri of the same hemisphere (2) Commissural fibers run between gyri of one hemisphere to the same gyri on the opposite hemisphere (3) Projection fibers run between the cerebrum and the spinal cord

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The Limbic System • Is a collection of areas of gray matter inside the white matter of the inner brain • Functions: - emotional aspects of behavior related to survival - memory - pleasure and pain - rage

Limbic System Illustration

Functional Areas of the Brain • The cerebral cortex is divided into: - sensory areas - motor areas - association areas

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Sensory Areas Primary Somesthetic Area (general sensory) Receives input from cutaneous, muscular and visceral receptors from the entire body via the thalamus

Sensory Areas Somesthetic Association Area Receives input from the thalamus and Primary Somesthetic Areas Integrates and interprets sensations

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Sensory Areas Visual Association Area Receives input from the input from the retina of the eye Interprets shape, color, and movement

Sensory Areas Visual Association Area Receives input from the Primary Visual Area Relates past to present visual experiences

Sensory Areas Primary Auditory Area Receives input from cochlea of ear Interprets basic character of sound

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Sensory Areas Auditory Association Area Receives input from Primary Auditory Area Determines if sound is music, speech, or noise Relates sounds to previous experience

Sensory Areas Gnostic Area Receive information from Auditory Association Area Interprets speech

Sensory Areas Primary Gustatory Area Receives input from taste buds Interprets sensations related to taste

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Sensory Areas Primary Olfactory Area Receives input from taste buds Interprets sensations related to smell

Motor Areas Primary Motor Area Controls specific muscles or groups of muscles

Motor Areas Frontal Eyefield Area Voluntary scanning movement of the eyes

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Motor Areas Language Area Translate thought into speech Also called Broca’s Area or Motor speech area

The Postcentral Gyrus • The gyrus directly behind the Central Sulcus is the Primary Somesthetic Area • Sensory information from the entire body comes into this gyrus • The fraction of this gyrus that functions for any particular area of the body is an indication of how important that region is to sensory input

The Somatosensory Cortex

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The Precentral Gyrus • The gyrus directly in front of the Central Sulcus is the Primary Motor Area • Motor information for the entire body comes from this area • The fraction of the gyrus that functions for any particular area of the body is an indication of how important that region is for movement

The Motor Cortex

Electroencephalogram (EEG) • Millions of action potentials are occurring in the brain at any moment • The electrical activity they generate produce wave forms that we can interpret

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Types of Brain Waves (1) Alpha waves are present in normal individuals when their eyes are closed, but are not present when asleep (2) Beta waves are present in individuals experiencing sensory input and an active mind (3) Theta waves are present in children and adults in emotional stress (4) Delta waves are present during deep sleep

Brain Wave Illustration

Brain Lateralization (Split-brain concept) • Cerebral Hemispheres are not exactly alike structurally or functionally • Some people are more right-brained and some people are more left-brained

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Left Hemisphere • People who primarily use the left hemisphere of their brains tend to: - right-hand control - spoken and written language - numerical and scientific skills - ability to use and understand sign language - reasoning

Right Hemisphere • People who primarily use the right hemisphere of their brains tend to: - Left hand control - musical and artistic awareness - space and pattern perception - insight and imagination - generating mental images of sight, sound, touch, taste, and smell in order to compare relationships

Cerebellum • Motor area of the brain • Controls coordinating subconscious movements of skeletal muscle • Receives input from: - muscles, tendons and joints - Equilibrium receptors in the ear - visual receptors in the eye Predicts the future position of a body part Plays a role in emotional development

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Illustration of the Cerebellum

Cranial Nerves • There are twelve pairs of cranial nerves • They originate on the brain and exit through holes (foramina) in the skull • Some carry only sensory information • Some carry both sensory and motor information

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