CHAPTER 9: THE NERVOUS SYSTEM

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CHAPTER 9 THE NERVOUS SYSTEM
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FUNCTIONS OF THE NERVOUS SYSTEM?

• it helps you perceive and react to the world
  around you
• it controls vital involuntary processes like
  respiration and digestion

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FUNCTIONS OF THE NERVOUS SYSTEM?

• it coordinates all bodily functions to maintain
  homeostasis
• it detects changes, makes decisions based on the
  information received, then stimulates muscles or
  glands to respond

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ORGANIZATION OF THE NERVOUS SYSTEM?

• composed of the brain, spinal cord, neurons, and
  neuroglia
• central nervous system (CNS) brain spinal
  cord
• peripheral nervous system (PNS) sensory motor
  neurons

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ORGANIZATION OF THE NERVOUS SYSTEM?

• somatic nervous system (voluntary)
• autonomic nervous system (involuntary)
• sympathetic nervous system fight or flight
• parasympathetic nervous system controls the
  bodys internal environment at rest

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THE CENTRAL NERVOUS SYSTEMTHE BRAIN?

• oversees the daily operations of the body
• interprets the vast amounts of information it
  receives
• also responsible for thoughts, feelings,
  emotions, talents, memories
• weighs 3 pounds, 2 of total body weight
• contains 100 billion neurons (nerve cells) 1000
  billion neuroglia

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THE CENTRAL NERVOUS SYSTEMTHE BRAIN?

• 4 major parts of the brain
• cerebrum
• diencephalon
• lower brain stem
• cerebellum

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THE BRAIN?

• cerebrum
• the largest portion of the brain, highly folded
• made of 2 cerebral hemispheres (right left)
• in gt90 of the population, the left hemisphere is
  dominant for right-handed control,
  language-related activities such as speech,
  writing, reading and for verbal, analytical,
  and scientific skills

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THE BRAIN?

• the right hemisphere controls the left hand and
  it specializes in nonverbal functions including
  the orientation of the body in space, musical
  artistic awareness, imagination, emotional
  intuitive thinking, and generating mental images
  of sight, sound, touch, taste, smell

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THE BRAIN?

• the cerebral hemispheres are connected by the
  corpus callosum and they are divided into 4
  lobes
• frontal, parietal, temporal, occipital

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THE BRAIN?

• white matter lies beneath the cerebral cortex
• composed of the myelinated axons of cortical
  neurons
• many axons of the brain spinal cord cross over,
  so that the left side of the brain controls the
  right side of the body vice versa (R-L, L-R)

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THE BRAIN?

• cerebral cortex surface layer composed of gray
  matter
• 2-4 mm thick
• highly folded, has a large surface area
• important in sensory processing motor responses
• contains control centers for speech, taste,
  hearing, vision, body sensation, motor
  intellectual function

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THE BRAIN?

• functional regions of the cerebral cortex
• motor areas
• govern muscular movements (R-L, L-R)
• motor speech area Brocas area

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THE BRAIN?

• sensory areas
• interpret impulses from sensory receptors,
  producing feelings or sensations
• cutaneous senses, vision, hearing, taste, smell
  (also R-L, L-R)

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THE BRAIN?

• association areas
• concerned with integrative functions such as
  concentration, planning, complex problem solving,
  judging consequences of behavior, personality
  traits, intelligence, understanding speech,
  choosing words to express thoughts feelings,
  reading, memory of visual scenes music, visual
  recognition

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THE BRAIN?

• diencephalon upper brain stem or forebrain
• contains important relay centers for information
  entering and exiting the brain

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THE BRAIN?

• 2 major regions
• thalamus serves as a relay station for all
  sensory impulses (except smell) to the cerebral
  cortex
• registers conscious recognition of pain temp,
  and light touch discriminates between pleasant /
  not pleasant knowledge / cognition

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• hypothalamus maintains homeostasis
• links the CNS to the endocrine system
• regulates heart rate, blood pressure, body temp,
  water electrolyte balance, hunger, thirst,
  sleep, wakefulness, stimulation of the pituitary
  gland

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• both are part of the limbic system which controls
  emotional experience and expression
• it produces feelings such as fear, anger,
  pleasure, and sorrow which guide a person towards
  behaviors that increase their chance of survival

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lower brain stem 4 parts?

• midbrain a relay center for visual auditory
  information
• Pons a relay center between the neurons of the
  cerebral hemispheres and the cerebellum controls
  the rate and depth of breathing

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lower brain stem 4 parts?

• medulla oblongata a relay center control
  centers including a cardiac center, vasomotor
  center, respiratory center also includes
  nuclei that are reflex centers for coughing,
  sneezing, swallowing, vomiting, hiccups

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lower brain stem 4 parts?

• reticular formation a network of neurons
  responsible for maintaining consciousness and
  awakening from sleep decreased activity sleep,
  no activity coma

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THE BRAIN?

• cerebellum a reflex center which functions in
  the coordination of skeletal muscle contractions,
  in the maintenance of normal muscle tone,
  posture, balance

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THE BRAIN?

• like the cerebrum, it consists of 2 hemispheres
  composed mainly of white matter covered by a thin
  layer of gray matter
• damage to the cerebellum will likely result in
  tremors, loss of muscle tone, loss of
  equilibrium, inaccurate movements of voluntary
  muscles, a reeling walk

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THE BRAIN?

• protection of the brain?
• 3 protective layers (meninges) surround the brain
  spinal cord
• dura mater - outer
• arachnoid layer - middle
• pia mater - inner

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• cerebrospinal fluid a clear liquid that
  cushions the brain and acts as an exchange medium
  for nutrients waste
• the cranium protects the brain and bony vertebrae
  protect the spinal cord

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The spinal cord?

• starts at the medulla oblongata runs down
  through the vertebral column ending with the
  cauda equina (horses tail)
• composed of a rigid inner core of gray matter
  shaped like a butterfly surrounded by white
  matter
• 31 pairs of spinal nerves form pathways of
  communication between the spinal cord and the
  rest of the body

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The spinal cord?

• spinal nerves have a dorsal root a ventral root
• the dorsal root receives sensory information
  (pressure, heat) and passes it to the brain
• the ventral root sends motor information from the
  brain to muscles and glands to respond to stimuli
• interneurons are located within the spinal cord
  they connect neurons together

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THE PERIPHERAL NERVOUS SYSTEM

• It consists of 12 pairs of cranial nerves that
  connect the brain with the head neck 31 pairs
  of spinal nerves that connect the CNS with the
  rest of the body

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THE PERIPHERAL NERVOUS SYSTEM

• SOMATIC NERVOUS SYSTEM?
• consists of cranial spinal nerves that connect
  the CNS to the skin skeletal muscles
• it oversees conscious activities

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SOMATIC NERVOUS SYSTEM?

• cranial nerves table 9.6
• most are mixed, but some are purely sensory
  others are primarily motor
• the names of the nerves indicate their primary
  functions, or the general distribution of their
  fibers
• some are somatic, some are autonomic

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SOMATIC NERVOUS SYSTEM?

• I olfactory nerves (smell)
• II optic nerves (sight)
• III oculomotor (moves eyelids)
• IV trochlear (moves the eye)
• V trigeminal (ophthalmic, maxillary,
  mandibular)
• VI abducens (move the eye)
• VII facial (move the face, taste)
• VIII vestibulocochlear (balance, hearing)
• IX glossopharyngeal (swallowing)
• X vagus (speech, swallowing, heartbeat)
• XI accessory (move neck back)
• XII hypoglossal (moves the tongue)

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SOMATIC NERVOUS SYSTEM?

• 31 pairs of spinal nerves are not named
  individually, but for the level from which they
  arise and then they are numbered
• 8 cervical nerves
• 12 thoracic nerves
• 5 lumbar nerves
• 5 sacral nerves
• 1 coccygeal
• forms the cauda equina at the end

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SOMATIC NERVOUS SYSTEM?

• each spinal nerve emerges from the spinal cord in
  2 roots
• dorsal root is posterior and it has an
  enlargement called the dorsal root ganglion. It
  contains sensory neurons.
• ventral root is anterior it contains motor
  neurons

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SOMATIC NERVOUS SYSTEM?

• the main portion of spinal nerves combine to form
  complex networks called plexuses this allows
  fibers associated with the same part to reach it
  together
• cervical plexus
• brachial plexus
• lumbosacral plexus

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SOMATIC NERVOUS SYSTEM?

• a spinal reflex involves nerves and the spinal
  cord not the brain
• example the patellar reflex
• reflexes are involuntary and typically
  self-protective

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AUTONOMIC NERVOUS SYSTEM?

• connects the CNS to viscera (heart, stomach,
  intestines)
• controls unconscious activities such as
  respiration heartbeat

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AUTONOMIC NERVOUS SYSTEM?

• 2 divisions
• sympathetic fight or flight
• activated by physical or emotional stress
• 1 major function is shunting blood from one part
  of the body to another
• redirects blood flow from the digestive organs
  towards the heart skeletal muscles

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AUTONOMIC NERVOUS SYSTEM?

• parasympathetic maintains homeostasis
• brings the body back to normal after fight or
  flight
• induces the body to conserve energy

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• under normal conditions, both the sympathetic and
  the parasympathetic are activated to some degree

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TRANSMISSION OF NERVE IMPULSES

• nerves bundles of nerve fibers
• neurons nerve cells

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TRANSMISSION OF NERVE IMPULSES

• 3 types of neurons?
• 1. sensory neurons
• receive information from the environment via
  receptors
• send impulses to the brain or spinal cord

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TRANSMISSION OF NERVE IMPULSES

• 2. interneurons
• transmit impulses between sensory
• and motor neurons
• 3. motor neurons
• transmit impulses from the brain spinal
  cord to an effector (muscle or gland) to bring
  about a response

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• NEURON STRUCTURE
• cell body
• contains nucleus organelles
• Found in the brain or spinal cord

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• dendrites
• extend from the cell body
• receive stimuli
• conduct impulses toward the cell body

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• axon
• up to 3 feet long
• carries impulses away from the cell body
• most axons are covered by a myelin sheath
• insulated the axon
• speeds up transmission of impulses
• myelin is produced by Schwann cells
• gaps in the sheath are called nodes of Ranvier

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• branches at the end (axon terminal) contain
  neurotransmitters
• chemicals within bridge the gap (synaptic cleft)
  between the axon terminal of 1 neuron to the
  dendrites of the next
• essentially forms a circuit

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NEURON FUNCTION

• the nervous system operates on electrical
  activity within the neurons and chemical flow
  between the neurons
• nerve impulses a series of chemical and
  electrical changes that travel like a wave over
  the length of a neuron in response to a stimulus
• requires oxygen and energy
• produces carbon dioxide and heat

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NEURON FUNCTION

• neurons have an electrical charge that is
  different than the fluid surrounding them, this
  difference in charge is called a potential

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NEURON FUNCTION

• potentials are created by the interplay of ions
  (charged particles)
• affected by their ability to pass through the
  cell membrane
• affected by their concentration inside outside
  the cell
• affected by their or charge

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NEURON FUNCTION

• resting potential?
• at rest not sending or receiving a signal
• outside has a net positive charge, many Na ions
• inside has a net negative charge, many proteins
  and K
• the sodium-potassium pump actively moves Na out
  and K in
• this charge difference the resting potential
  -70 millivolts

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NEURON FUNCTION

• action potential?
• the minimum level of stimulus required to produce
  an impulse threshold stimulus
• when stimulated, the sodium gates open Na
  flows into the cell
• this flow causes more sodium gates to open

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NEURON FUNCTION

• due to the influx of Na ions, the inside of the
  cell becomes positively charged and the outside
  becomes negatively charged (due to the absence of
  Na ions) depolarization
• the action potential starts where the cell body
  joins the axon and the impulse travels along the
  neuron

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NEURON FUNCTION

• as the impulse passes, the sodium gates close
  stopping the flow of Na into the cell
• Potassium channels open, letting K ions out of
  the cell
• as K ions flow out, the cell is repolarized (now
  negative inside / positive outside)

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NEURON FUNCTION

• the resting membrane potential (-70 millivolts)
  must be restored before another action potential
  can occur refractory period
• the sodium-potassium pump restores the original
  concentrations of Na ions K ions on both
  sides of the membrane
• this costs the cell energy / ATP to keep the pump
  going

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NEURON FUNCTION

• the action potential continues to move along the
  axon until it reaches the end / axon terminals
• all-or-none like
• muscle fiber
• contraction

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NEURON FUNCTION

• synapse the location at which a neuron can
  transfer an impulse to another cell (neuron,
  muscle, gland)

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NEURON FUNCTION

• vesicles at the tips of the axon terminal are
  filled with neurotransmitters chemicals that
  cross the synaptic cleft to allow communication
  between neurons

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NEURON FUNCTION

• excitatory neurotransmitters trigger the next
  action potential
• acetylcholine, norepinephrine

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NEURON FUNCTION

• inhibitory neurotransmitters decrease
  permeability to sodium ions, inhibiting the next
  action potential
• dopamine, GABA, glycine

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