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Chapter 11Central Nervous System
Central Nervous System
Meninges• membranes surrounding CNS• protect CNS• three layers
• dura mater – outer, tough• arachnoid mater - weblike• pia mater – inner, delicate
Meninges of the Spinal Cord
Ventricles• interconnected cavities• within cerebral hemispheres and brain stem• continuous with central canal of spinal cord• filled with cerebrospinal fluid (csf)
• lateral ventricles- most CSF made here• third ventricle• fourth ventricle
Cerebrospinal Fluid
• circulates in ventricles, central canal of spinal cord, and subarachnoid space• completely surrounds brain and spinal cord; “float”• clear liquid• nutritive and protective
Spinal Cord Structure• extends foramen magnum to 2nd lumbar vertebra
Cross Section of Spinal Cord
Spinal Cord Functions
• center for spinal reflexes
• conduit for nerve impulses to and from the brain
Reflex ArcsReflexes – automatic, subconscious responses to stimuli
Knee-jerk Reflex
Withdrawal Reflex
Crossed-Extensor Reflex
• flexor muscles contract• flexor muscles on opposite side inhibited• extensor muscles on opposite side contract for balance
Brain
Functions• interprets sensations• determines perception• stores memory• reasoning• makes decisions• coordinates muscular movements• regulates visceral activities• determines personality
Major Parts• cerebrum
• two cerebellar hemispheres• diencephalon• brain stem•midbrain•pons•medulla oblongata
• cerebellum
Structure of Cerebrum• corpus callosum• connects hemispheres
• convolutions • bumps or gyri
• sulci• shallow grooves
• longitudinal fissure•deep groove •separates hemispheres
• transverse fissure•deep groove •separates cerebrum from cerebellum
Lobes of Cerebrum
• Frontal• Parietal• Temporal• Occipital
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
Functions of Cerebrum
• interpretation• initiating voluntary movements• storing memory• retrieving memory• reasoning• center for intelligence and personality
Motor Areas• Primary Motor Areas
• frontal lobes• control voluntary muscles
• Broca’s Area• anterior to primary motor cortex• usually in one hemisphere• controls muscles needed for speech
Motor Areas
Sensory Areas
• Sensory Area• parietal lobe• interprets sensations on skin
• Visual Area• occipital lobe• interprets vision
• Auditory Area• temporal lobe• interprets hearing
Sensory Areas
Association Areas
Frontal Lobe Association Areas• concentrating• planning• problem solving• judging
Parietal Lobe Association Areas• understanding speech• using words to express thought•sensory touch, temperature and pain
Temporal Lobe Association Areas• memory•emotions• hearing
Occipital Lobe Association Areas• combine visual images with other sensory experiences
Hemisphere Dominance
Left Hemisphere- analytical, reasoning, math/science
Right Hemisphere- artsy, musical, creative
• 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
Diencephalon• between cerebral hemispheres and above the brainstem• surrounds third ventricle
• thalamus*• hypothalamus*• optic tracts• optic chiasm• infundibulum• posterior pituitary• mammillary
Diencephalon
Thalamus• gateway for sensory impulses heading to cerebral cortex• receives all sensory impulses (except smell)• channels impulses to appropriate part of cerebral cortex for interpretation
Hypothalamus• maintains homeostasis by regulating visceral activities •HR, BP, temp., water balance, hunger…
• links nervous and endocrine systems
Limbic System
Consists of• portions of frontal lobe• portions of temporal lobe• hypothalamus• thalamus
Functions• controls emotions• produces feelings• interpret sensory impulses
Brain Stem
Three Parts1. Midbrain2. Pons3. Medulla Oblongata
Midbrain
• between diencephalon and pons• contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain
Pons
• rounded bulge on underside of brainstem• looks like a booty• between midbrain and medulla oblongata•relays nerve impulses to and from medulla oblongata and cerebellum•helps regulate rate and depth of breathing
Medulla Oblongata
• enlarged continuation of spinal cord
• contains cardiac, vasomotor (blood pressure), and respiratory control centers
• contains various nonvital reflex control centers (coughing, sneezing, vomiting)
Reticular Formation
• complex network of nerve fibers scattered throughout the brain stem• extends into the diencephalon• filters incoming sensory information • arouses cerebral cortex into state of wakefulness•Injury can lead to a coma
Types of Sleep
Slow Wave• person is tired• decreasing activity of reticular system• restful• dreamless• reduced blood pressure and respiratory rate• ranges from light to heavy• alternates with REM sleep
Rapid Eye Movement (REM)• some areas of brain active• heart and respiratory rates irregular• dreaming occurs
Cerebellum
• inferior to occipital lobes• posterior to pons and medulla oblongata• two hemispheres• cerebellar cortex – gray matter•integrates sensory information concerning position of body parts• coordinates skeletal muscle activity• maintains posture