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