Nervous System

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Chapter 12

• Nervous System

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Outline

• Nervous Tissue
• The Nerve Impulse
• Action Potential
• Central Nervous System
• The Spinal Cord
• The Brain
• Peripheral Nervous System
• Nerves and Ganglia
• Drug Abuse
• Degenerative Nervous System Diseases

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Nervous Tissue

• Nervous Tissue contains two types of cells.
• Neurons transmit nerve impulses between parts of
  the nervous system.
• Neuroglia support, nourish, insulate, and protect
  neurons.

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Neuron Structure

• Neurons are classified according to function.
• Sensory neurons take impulses from a sensory
  receptor to the CNS.
• Interneurons receive input from sensory neurons,
  and other neurons, and then communicate with
  motor neurons.
• Motor neurons take nerve impulse away from the
  CNS to an effector that carries out responses to
  environmental change.

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Neuron Structure

• Neurons contain three basic parts.
• Cell body contains nucleus and other organelles.
• Dendrites receive signals from sensory receptors
  or other neurons.
• Axon conducts nerve impulses.

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Types of Neurons
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Myelin Sheath

• Some axons are covered by a protective myelin
  sheath.
• Formed by Schwann cells containing myelin in
  plasma membranes.
• Nodes of Ranvier are gaps on the axon with no
  myelin sheath.

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The Nerve Impulse

• The nervous system uses the nerve impulse to
  convey information.
• Resting potential is the voltage level when an
  axon is not conducting an impulse.

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The Nerve Impulse

• Sodium-potassium pump causes greater
  concentration of Na outside the axon, and
  greater concentration of K inside the axon.
• Unequal ion distribution causes inside of axon to
  be negative relative to the outside.

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Action Potential

• An action potential is a rapid change in polarity
  across an axomembrane as the nerve impulse
  occurs.
• All-or-none once threshold is reached.
• Sodium gates open, allowing Na to move inside
  the axon.
• Potassium gates open, allowing K to move outside
  the axon.

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Action Potential

• Propagation of an action potential
• Each preceding portion causes an action potential
  in the next portion of an axon.
• As soon as an action potential has moved on, the
  previous portion of an axon undergoes a
  refractory period in which the sodium gates are
  unable to open.

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Transmission across a Synapse

• Transmission across a synaptic cleft is carried
  out by neurotransmitters stored in synaptic
  vesicles.
• Depending on the neurotransmitter and the
  receptor, the response of the postsynaptic neuron
  can be towards excitation or inhibition.
• Integration is the summing of signals received by
  a postsynaptic neuron.

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Transmission and Integration
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• Human Nervous System
• Central Nervous System
• Peripheral Nervous System

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The Central Nervous System

• The central nervous system (CNS) is made up of
  the spinal cord and the brain.
• Both are wrapped in protective membranes,
  meninges, with spaces between meninges filled
  with cerebrospinal fluid.
• CNS is composed of two types of nervous tissue.
• Gray matter Short, nonmyelinated fibers.
• White matter - Myelinated axons.

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The Spinal Cord

• The spinal cord extends from the base of the
  brain through the foramen magnum into the
  vertebral canal.

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• Spinal Cord
• Central Canal
• White
• Ascending (dorsal) and descending (ventral)
  myelinated axons
• Gray matter
• Sensory
• Dorsal root ganglia
• Dorsal root
• Dorsal horn
• Interneuron
• Lateral horn
• Intermediate zone
• Motor
• Ventral horn
• Ventral root

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Functions of the Spinal Cord

• The spinal cord provides a means of communication
  between the brain and the peripheral nerves that
  leave the cord, and is a center for reflex
  actions.

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The Brain

• Brain
• cerebrum or cerebral hemispheres,diencephalon,
  brainstem (midbrain, pons, medulla oblongata) and
  cerebellum
• The Cerebrum.
• The cerebrum, telencephalon, is the largest
  portion of the human brain.
• Communicates with, and coordinates activities of,
  other parts of the brain.
• Divided into left and right cerebral hemispheres.
• Divided by longitudinal fissure.

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The Human Brain
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The Brain

• Gray matter of cerebrum consists of cerebral
  cortex and basal nuclei.
• Cerebral cortex is a highly convoluted outer
  layer that covers the cerebral hemispheres.
• Basal nuclei are masses located deep within white
  matter.
• White matter consists of long myelinated axons
  organized into tracts.

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• Major anatomical components of the brain
• Labeled 2-7
• Note reference to forebrain (cerebral hemisphere,
  diencephalon, basal ganglia), midbrain (midbrain)
  and hindbrain (cerebellum and brainstem)

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Introduction to the Anatomical Divisions of the
Brain

• Brain stem
• Midbrain
• Controls many sensory and motor functions, ex.
  pupillary light reflex
• Pons
• Conveys information about movement from cerebral
  hemisphere to cerebellum
• Medulla Oblongata
• Several centers responsible for autonomic
  functions, ex. heart beat, respiration
• Cerebellum
• Separated from the brain stem by the fourth
  ventricle
• Lies behind the pons and is connected to the
  brainstem by fiber tracts called peduncles
• Modulates the force and range of movement
  involved in learning motor skills

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Anatomical Divisions of the Brain

• Diencephalon
• Circles the third ventricle.
• Contains three major structures thalamus,
  epithalamus, hypothalamus (also subthalamus)
• Integration of sensory inputs, relay center and
  hormonal regulation
• Cerebral Hemispheres
• Consists of cerebral cortex with four lobes
  (frontal, parietal, occipital, temporal), basal
  ganglia, hippocampus, and amygdala
• Characteristic gyri (hills or bumps) and sulci
  (grooves or valleys)
• Sensory and motor processing, cognitive thought,
  perception, emotion, personality, learning and
  memory

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Lobes of Cerebral Hemisphere
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Reticular Activating System

• Reticular formation is a complex network of
  nuclei and fibers extending the length of the
  brain stem.
• Relay center
• RAS- attention, alertness

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The Limbic System

• Limbic system is a complex network of tracts and
  nuclei.
• Blends primitive emotions and higher mental
  functions into a united whole.
• Composed of hippocampus and amygdala.

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Limbic System
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Higher Mental Functions

• Memory is the ability to hold a thought in mind
  or to recall events from the past.
• Short-term versus long-term.
• Skill memory.
• Learning takes place when we retain and utilize
  past memories.
• Language and speech depends on motor centers in
  the occipital and temporal lobes.

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Language and Speech

• Left and right brain have different functions.
• Left Hemisphere
• Verbal, Logical, Analytical, Rational.
• Right Hemisphere
• Nonverbal, Intuitive, Creative.