1 Chapter 11 Brain Anatomy & Functions. 2 Meninges Membranes surrounding CNS Protect CNS Three...
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Transcript of 1 Chapter 11 Brain Anatomy & Functions. 2 Meninges Membranes surrounding CNS Protect CNS Three...
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Chapter 11Brain Anatomy & Functions
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Meninges
• Membranes surrounding CNS• Protect CNS• Three layers• Dura mater • Outer layer• Adheres to cranial bones• Tough
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• Arachnoid mater • Thin, weblike
• Pia mater • Inner layer•Adhere directly to
brain•Very thin• Fibrous and
vascular
Meninges
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• Spinal Cord• Same three layers
• Provides protection
Meninges
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Ventricles
• Interconnected cavities •Within cerebral hemispheres and brain stem •Continuous with central canal of spinal cord
• Filled with cerebrospinal fluid (CSF)
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• Lateral ventricles
• Third ventricle
• Fourth ventricle
• Cerebral aqueduct
Ventricles
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Ventricles
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Cerebrospinal Fluid
• Secreted by choroid plexus• Circulates in ventricles, central canal of spinal cord, and subarachnoid space• Completely surrounds brain and spinal cord between the meninges
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• Clear liquid• 80-150 ml in CNS• Contains proteins,
glucose, and salts• Nutritive and protective
• Shock absorber• Helps maintain stable
ion concentrations in CNS
Cerebrospinal Fluid
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Spinal Cord
• Slender column of nervous tissue continuous with brain
• Extends downward through vertebral canal
• Begins at level of foramen magnum & terminates near first & second lumbar
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Cross Section of Spinal Cord
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Functions of Spinal Cord
• Center for spinal reflexes
• Conduit for nerve impulses to and from the brain
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Reflex Arcs
Reflexes – automatic, subconscious responses to stimuli within or outside the body
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Brain
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Brain
Functions• Interprets sensations• Determines perception• Stores memory• Reasoning• Makes decisions• Coordinates muscular movements• Regulates visceral activities• Determines personality
Major Parts• Cerebrum
• Two hemispheres• Basal nuclei • Diencephalon• Brainstem• Cerebellum
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Brain
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Brain Development
Three Major Vesicles1. Forebrain2. Midbrain3. Hindbrain
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Brain Development
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• Looks like cap of a mushroom
• Spread over diencephalon
• 7/8 total mass • Fills most of
cranium
Cerebrum
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• Result from displacement & distortion of neurons at the moment of impact
• Concussion•Abrupt but temporary loss of consciousness
following a blow to the head or the sudden stopping of a moving head
•No visible bruising but post traumatic amnesia may occur
Clinical Application: Cerebrum
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• Contusion•Visible bruising of the brain due to trauma
and blood leaking from microscopic vessels
• Pia mater is torn
•Results in unconsciousness for several minutes to many hours
Clinical Application: Cerebrum
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• Laceration• Tearing of the brain, usually from skull
fractures or gunshot wound
• Large blood vessels bleed into the brain and can cause cerebral hematoma, and increase cranial pressure
Clinical Application: Cerebrum
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Lobes of Cerebral Hemispheres
• Name of lobe corresponds with name of cranial bone
• Frontal• Parietal• Temporal• Occipital• Insula
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Functions of the Cerebrum• Interpreting impulses
• Initiating voluntary movements
• Storing information as memory
• Retrieving stored information
• Reasoning
• Seat of intelligence and personality
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Functional Regions of Cerebral Cortex
Cerebral Cortex – thin layer of gray matter that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system
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• Cerebral Cortex • Surface of cerebrum
• Convolutions • Folds in cerebrum• Bumps or gyri
• Sulci• Shallow grooves
• Fissures• Deep grooves
Structure of Cerebrum
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Structure of Cerebrum
• Corpus callosum• Connects cerebral hemispheres
• Longitudinal fissure• Separates hemispheres
• Transverse fissure• Separates cerebrum from cerebellum
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Sensory Areas
• Cutaneous Sensory Area
• Parietal lobe
• Interprets sensations on skin
• Visual Area• Medial Occipital lobe
• Interprets vision
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• Primary Gustatory• Taste
• Near bases of the central sulci
• Primary Olfactory • Smell
• Arise from centers deep within the cerebrum
Sensory Areas
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• Auditory Area• Superior part
of temporal lobe near lateral cerebral sulcus
• Interprets hearing
Sensory Areas
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Sensory Areas
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Association Areas
• Regions that are not primary motor or primary sensory areas• Widespread throughout the cerebral cortex• Analyze and interpret sensory experiences• Provide memory, reasoning, verbalization, judgment, emotions
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Association Areas
Frontal Lobe Association Areas• Concentrating• Planning• Complex problem solving
Parietal Lobe Association Areas• Understanding speech• Choosing words to express thought
Temporal Lobe Association Areas• Interpret complex sensory experiences • Store memories of visual scenes, music, and complex patterns
Occipital Lobe Association Areas• Analyze and combine visual images with other sensory experiences
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Hemisphere Dominance
• The left hemisphere is dominant is most individuals
• Dominant hemisphere controls
• Speech• Writing• Reading• Verbal skills• Analytical skills• Computational skills
• Nondominant hemisphere controls
• Nonverbal tasks• Motor tasks• Understanding and interpreting musical and visual patterns• Provides emotional and intuitive thought processes
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• Anatomical• Frontal lobe of left hemisphere is smaller
• Left handed people•Right parietal and occipital lobes are narrower
Hemisphere Differences
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• Right Hemisphere• Left handed
• Music and artistic awareness
• Space and patter perception
• imagination
• Left Hemisphere• Right handed
• Numerical and scientific skills
• Sign language and reasoning
Hemisphere Differences
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Memory
Short Term• Working memory• Closed neuronal circuit• Circuit is stimulated over and over• When impulse flow ceases, memory does also• Unless it enters long-term memory via memory consolidation
Long Term• Changes structure or function of neurons• Enhances synaptic transmission
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Motor Areas
• Primary Motor Areas• frontal lobes• control voluntary muscles
• Broca’s Area• anterior to primary motor cortex• usually in left hemisphere• controls muscles needed for speech
• Frontal Eye Field• above Broca’s area• controls voluntary movements of eyes and eyelids
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Motor Areas
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Functions of the Cerebral Lobes
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Diencephalon
• Between cerebral hemispheres and above the brainstem• Surrounds third ventricle
• Thalamus• Hypothalamus• Optic tracts• Optic chiasma• Infundibulum• Posterior pituitary• Mammillary bodies• Pineal gland
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Diencephalon
Thalamus•Oval structure above midbrain
•Gateway for sensory impulses heading to cerebral cortex
• Receives all sensory impulses (except smell)
• Channels impulses to appropriate part of cerebral cortex for interpretation
•Interpretation of pain, temperature, and pressure
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Hypothalamus• Small portion inferior to thalamus• Protected by sella turcica • Maintains homeostasis by regulating visceral
activities • Water concentrations• Hormone concentrations• Blood temperature
• Links nervous and endocrine systems
Diencephalon
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• Homeostatic functions• Regulates autonomic nervous system• Reception & integration of sensory impulses from
viscera• Mind over body (stress--heart rate increases)• Rage & aggression• Regulates body temperature• Regulates food intake (hunger & full feelings)• Thirst• Sleep patterns
Diencephalon
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Diencephalon
Consists of• portions of frontal lobe• portions of temporal lobe• hypothalamus• thalamus• basal nuclei• other deep nuclei
Functions• controls emotions• produces feelings• interprets sensory impulses
Limbic System
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Brain Stem
Three Parts1. Midbrain2. Pons3. Medulla Oblongata
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Midbrain
•“Mesencephalon”
•Between diencephalon and pons
• Contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain
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• Cerebral aqueduct– Connects 3rd & 4th
ventricles of brain• Cerebral peduncles – bundles
of nerve fibers– Motor pathway between
cerebrum & lower parts of nervous system
• Corpora quadrigemina – centers for visual and auditory reflexes
Midbrain
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Pons
• Rounded bulge on underside of brainstem
• Between medulla oblongata and midbrain
• Helps regulate rate and depth of breathing
• Relays nerve impulses to and from medulla oblongata and cerebellum
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Medulla Oblongata
• Enlarged continuation of spinal cord• Conducts ascending and descending impulses between brain and spinal cord• Contains 3 reflex centers
• Cardiac•Heart rate & force of contraction
• Vasomotor•Controls diameter of blood vessels
• Respiratory •Controls breathing patterns
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• Contains various nonvital reflex control centers – Coughing
– Sneezing
– Swallowing
– Vomiting
Medulla Oblongata
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• Reticular Formation• Complex network of nerve fibers scattered throughout the brain stem
• Extends into the diencephalon
• Connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum
• Filters incoming sensory information
• Arouses cerebral cortex into state of wakefulness
Medulla Oblongata
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Cerebellum
• Inferior to occipital lobes• Posterior to pons and medulla oblongata• Two hemispheres
• Vermis connects hemispheres• Cerebellar cortex
• Gray matter on surface• Arbor vitae
• White matter inside•Tree-like pattern
• Cerebellar peduncles • nerve fiber tracts
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• Dentate nucleus • Largest nucleus in
cerebellum• Integrates sensory
information concerning position of body parts
• Coordinates skeletal muscle activity
• Maintains posture
Cerebellum
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• Damage results in• Lack of muscle control
• Change of speech pattern
• Severe dizziness
• Disturbances of gait (walking)
Cerebellum
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Life-Span Changes
• Brain cells begin to die before birth• Over average lifetime, brain shrinks 10%• Most cell death occurs in temporal lobes• By age 90, frontal cortex has lost half its neurons• Number of dendritic branches decreases• Decreased levels of neurotransmitters• Fading memory• Slowed responses and reflexes• Increased risk of falling• Changes in sleep patterns that result in fewer sleeping hours
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Clinical Application
Cerebral Injuries and Abnormalities
Cerebral Palsy• Motor impairment at birth• Caused by blocked cerebral blood vessels during development• Seizures• Learning disabilities
Cerebrovascular Accident• Stroke• Sudden interruption in blood flow• Brain tissues die