Chapter 8Nervous System I

Cell Types of Neural Tissue• neurons• neuroglial cells

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Divisions of the Nervous System

• Central Nervous System• brain• spinal cord

• Peripheral Nervous System• peripheral nerves

• cranial nerves• spinal nerves

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Divisions of Peripheral Nervous System

Sensory Division• picks up sensory information and delivers it to the CNS

Motor Division• carries information to muscles and glands

Divisions of the Motor Division• Somatic – carries information to skeletal muscle• Autonomic – carries information to smooth muscle, cardiac muscle, and glands

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Functions of Nervous System

Sensory Function• sensory receptors gather information• information is carried to the CNS• sensory neurons- afferent

Integrative Function• interneurons• sensory information used to create

• sensations• memory• thoughts• decisions

Motor Function• decisions are acted upon • impulses are carried to effectors• motor neurons

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Neuron Structure

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Myelination of Axons

White Matter• contains myelinated axons

Gray Matter• contains unmyelinated structures• cell bodies, dendrites

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Classification of Neurons

Sensory Neurons• afferent• carry impulse to CNS

Interneurons• link neurons• in CNS

Motor Neurons• carry impulses away from CNS• carry impulses to effectors

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The Synapse

Nerve impulses pass from neuron to neuron at synapses

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Synaptic Transmission

Neurotransmitters are released when impulse reaches synaptic knob

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Reflex Arcs

Reflexes – automatic, subconscious responses to stimuli

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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 cerebellar hemispheres• diencephalon• brain stem• cerebellum

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Brain Stem

Three Parts1. Pons2. Medulla Oblongata3. Midbrain

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Pons

• 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 cardiac, vasomotor, and respiratory control centers• contains various nonvital reflex control centers (coughing, sneezing, vomiting)

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Reticular Formation

• filters incoming sensory information • arouses cerebral cortex into state of wakefulness

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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

• temperature• sleep-wake cycles• water balance• appetite

• links nervous and endocrine systems8-16

Cerebellum

• inferior to occipital lobes• posterior to pons and medulla oblongata• integrates sensory information concerning position of body parts• coordinates skeletal muscle activity• maintains posture

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Lobes of Cerebrum

• Frontal• Parietal• Temporal• Occipital

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Structure of Cerebrum

• cerebral cortex• corpus callosum

• connects hemispheres• convolutions

• bumps or gyri• sulci

• grooves• longitudinal fissure

• separates hemispheres• transverse fissure

• separates cerebrum from cerebellum 8-19

Functions of Cerebrum

• interpretation• initiating voluntary movements• storing memory• retrieving memory• reasoning• center for intelligence and personality

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Motor and Sensory Areas

• Cutaneous Sensory Area

• parietal lobe• interprets sensations on skin

• Visual Area• occipital lobe• interprets vision

• Auditory Area• temporal lobe• interprets hearing 8-21

• Primary Motor Areas• frontal lobes• control voluntary muscles

Hemisphere Dominance

• In over 90% of population, left hemisphere is dominant

• 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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Memory

Short Term• working memory• circuit is stimulated over and over• when impulse flow stops, memory disappears

Long Term• changes structure and function of neurons• enhanced synaptic transmission• strong emotion, repetition, and building on previous memories stimulate

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Spinal Cord Functions

• center for spinal reflexes

• conduit for nerve impulses to and from the brain

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Spinal Cord Structure

• extends foramen magnum to 2nd lumbar vertebra

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Meninges

Meninges• membranes surrounding CNS• protect CNS• three layers

• dura mater – outer, tough• arachnoid mater - weblike• pia mater – inner, delicate

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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• clear liquid• nutritive and protective• helps maintain stable ion concentrations in CNS

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Peripheral Nervous System

• Cranial nerves arising from the brain• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

• Spinal nerves arising from the spinal cord• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera

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Cranial Nerves

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Spinal Nerves

• mixed nerves• 31 pairs

• 8 cervical (C1 to C8)• 12 thoracic (T1 to T12)• 5 lumbar (L1 to L5)• 5 sacral (S1 to S5)• 1 coccygeal (Co)

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Autonomic Nervous System

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• functions without conscious effort• controls visceral activities• regulates smooth muscle, cardiac muscle, and glands• efferent fibers typically lead to ganglia outside CNS

Two Divisions• sympathetic – prepares body for fight or flight situations• parasympathetic – prepares body for resting and digesting activities