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Chapter 11 Nervous System II

• Brain

• Spinal cord

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Meninges of the brain

Meninges •  membranes surrounding CNS •  protect CNS •  three layers

•  dura mater – outer, tough •  arachnoid mater – thin, weblike •  pia mater – inner, very thin

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Meninges of the Spinal Cord

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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)

•  lateral ventricles •  third ventricle •  fourth ventricle •  cerebral aqueduct

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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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Spinal Cord

•  slender column of nervous tissue continuous with brain •  extends downward through vertebral canal •  begins at level of foramen magnum and terminates near first and 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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Reflex Arcs

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General Components of a Spinal Reflex

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Tracts of the Spinal Cord

•  Ascending tracts conduct sensory impulses to the brain •  Descending tracts conduct motor impulses from the brain to motor neurons reaching muscles and glands

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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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Structure of Cerebrum •  corpus callosum

•  connects cerebral hemispheres

•  convolutions •  bumps or gyri

•  sulci •  shallow grooves

• fissures • Deep grooves

•  longitudinal fissure •  separates hemispheres

•  transverse fissure •  separates cerebrum from cerebellum

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Lobes of Cerebral Hemispheres

•  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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Sensory Areas •  Cutaneous Sensory Area

•  parietal lobe •  interprets sensations on skin

•  Visual Area •  occipital lobe •  interprets vision

•  Auditory Area •  temporal lobe •  interprets hearing

•  Sensory Area for Taste •  near bases of the central sulci

•  Sensory Area for Smell

•  arise from centers deep within the cerebrum

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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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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 24

Basal Nuclei

•  masses of gray matter deep within the cerebral hemispheres • interact with other areas of the brain to facilitate voluntary movement

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Memory

Short Term • Thought to be electric in nature • 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

Memory is a consequence of leaning

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Brain Waves

• Alpha waves - awake by resting

• Beta waves (higher frequency) - person is actively engaged in mental activity or under tension

• Theta waves (lower frequency) - normal in children, some adults produce them in early stages of sleep or times of emotional stress

• Delta waves - occur during sleep

Recordings of the activity of the cerebral cortex

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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 •  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 •  links nervous and endocrine systems

Other parts • Optic tract and optic chiasma, infundibulum, pituitary gland, mammillary bodies, and pineal gland

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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 Parts 1.  Midbrain 2.  Pons 3.  Medulla Oblongata

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Midbrain

•  between diencephalon and pons •  contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain •  cerebral aqueduct •  cerebral peduncles – bundles of nerve fibers •  corpora quadrigemina – centers for visual and auditory reflexes

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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 • Transmits impulses between the cerebrum and centers within the 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, swallowing, vomiting)

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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

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Types of Sleep

Slow Wave •  non-REM sleep •  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) •  paradoxical sleep •  some areas of brain active •  heart and respiratory rates irregular •  dreaming occurs

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Cerebellum

•  inferior to occipital lobes •  posterior to pons and medulla oblongata •  two hemispheres •  vermis connects hemispheres •  cerebellar cortex – gray matter •  arbor vitae – white matter •  cerebellar peduncles – nerve fiber tracts •  dentate nucleus – largest nucleus in cerebellum •  integrates sensory information concerning position of body parts •  coordinates skeletal muscle activity •  maintains posture

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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

•  Consists of the nerves that branch from the CNS

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Structure of a Peripheral Nerve

Connective tissue coverings • epineurium – outer, dense covering • perineurium – middle layer of loose connective tissue • endoneurium – inner layer made up of a small amount of loose connective tissue

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Nerve Fiber Classification

•  Sensory Nerves – conduct impulses into brain or spinal cord

•  Motor Nerves – conduct impulses to muscles or glands

•  Mixed Nerves – contain both sensory nerve fibers and motor nerve fibers; most nerves

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Nerve Fiber Classification

General somatic efferent fibers •  carry motor impulses from CNS to skeletal muscles

General visceral efferent fibers •  carry motor impulses away from CNS to smooth muscles and glands

General somatic afferent fibers •  carry sensory impulses to CNS from skin and skeletal muscles

General visceral afferent fibers •  carry sensory impulses to CNS from blood vessels and internal organs

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Nerve Fiber Classification

Special somatic efferent fibers •  carry motor impulses from brain to muscles used in chewing, swallowing, speaking, and forming facial expressions

Special visceral afferent fibers •  carry sensory impulses to brain from olfactory and taste receptors

Special somatic afferent fibers •  carry sensory impulses to brain from receptors of sight, hearing, and equilibrium

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Cranial Nerves

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Functions of 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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Spinal Nerves Dorsal root (posterior or sensory root)

•  axons of sensory neurons in the dorsal root ganglion

Dorsal root ganglion •  cell bodies of sensory neurons whose axons conduct impulses inward from peripheral body parts

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Spinal Nerves Ventral root (anterior or motor root)

•  axons of motor neurons whose cell bodies are in spinal cord

Spinal nerve •  union of ventral root and dorsal root

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Autonomic Nervous System

•  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 • Most organs have dual innervation

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Autonomic Nerve Fibers

•  all are neurons are motor (efferent)

•  preganglionic fibers •  axons of preganglionic neurons •  neuron cell bodies in CNS

•  postganglionic fibers •  axons of postganglionic neurons •  neuron cell bodies in ganglia

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Control of Autonomic Activity

•  Controlled largely by CNS

•  Medulla oblongata regulates cardiac, vasomotor and respiratory activities

•  Hypothalamus regulates visceral functions, such as body temperature, hunger, thirst, and water and electrolyte balance

•  Limbic system and cerebral cortex control emotional responses 50

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

Concussion •  brain jarred against cranium •  loss of consciousness •  temporary loss of memory •  mental cloudiness •  headache •  recovery usually complete

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