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

• Neurons transmit nerve impulses between parts of
  the nervous system
• Neuroglia support and nourish neurons

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Neuron Classification -- Functional

• Sensory transmit impulses from a sensory
  receptor (that detects environmental change) to
  the CNS
• Interneurons neurons in CNS between sensory and
  motor neurons
• Motor transmit nerve impulses from the CNS to an
  effector (muscle or gland that carries out
  responses to environmental change)

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Functional Classes of Neurons
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Neuron Structure

• Cell body contains nucleus and other organelles
• Dendrites sends signals from sensory receptors
  or other neurons to cell body
• Axon conducts nerve impulses from cell body

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Myelin Sheath

• Schwann cells wrap plasma membranes (myelin)
  around axons
• Nodes of Ranvier gaps in the myelin sheath

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Function of Myelin Sheath

• insulates axon
• speeds nerve impulse transmission

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The Resting Potential

• Cell Membranes are polarized at rest
• net negative charge on inside
• net positive charge on outside

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Action Potential Nerve Impulse

• 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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Propagation of an Action Potential

• depolarization of preceding portion of axon
  causes an depolarization in the next portion of
  the axon (i.e., self-propagating)
• refractory period time during which the sodium
  gates are unable to open immediately behind the
  action potential, insures one-way transmission

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The Synapse

• point of communication between two neurons or a
  neuron and effector (muscle or gland)

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Synaptic Cleft
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Neurotransmitter Receptor
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Synaptic Integration

• summing of excitatory and inhibitory signals
  received by a postsynaptic neuron (depending on
  the neurotransmitter and the receptor, the
  response of the postsynaptic neuron can be
  towards excitation or inhibition)

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Synaptic Integration Graph
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More Synapses
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The Central Nervous System

• Consists of the spinal cord and brain
• Two types of nervous tissue
• Gray matter nonmyelinated fibers cell bodies
• White matter myelinated axons

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The Meninges

• protective connective tissue membranes
• Cerebrospinal fluid in subarachnoid space of
  meninges protects brain

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The Spinal Cord

• Extends from the base of the brain through the
  foramen magnum into the vertebral canal

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Functions of the Spinal Cord

• communication between the brain and peripheral
  nerves leaving the cord
• spinal reflex actions

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Gray and white matter in spinal cord
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Parts of the Brain

• Cerebrum (cerebral hemispheres)
• diencephalon
• cerebellum
• brainstem

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Parts of the Brain
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The Cerebrum

• 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
  by longitudinal fissure
• Seat of Intellect
• Conscious perception voluntary body movements

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Cerebral Lobes
Frontal
Parietal
Occipital
Temporal
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Cerebral White and Gray Matter

• Gray Matter
• Cerebral cortex highly convoluted outer layer
  that covers the cerebral hemispheres
• Basal nuclei are masses located deep within white
  matter
• White matter myelinated axons organized into
  tracts

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Functional Areas of the Cerebrum
primary motor
primary sensory
primary visual
auditory association
visual association
primary auditory
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Diencephalon
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Diencephalon

• consists of hypothalamus and thalamus
• encircles the third ventricle.
• The brain stem contains the midbrain, pons, and
  medulla oblongata.
• Reticular formation is a complex network of
  nuclei and fibers extending the length of the
  brain stem.

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Cerebellum
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Functions of the Cerebellum

• Integrates sensory input from joints, muscles,
  eyes, ears
• to fine tune body movements
• reconciles actual to intended and makes
  needed adjustments

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The Brain Stem
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Functions of Brain Stem

• Many Vital Reflexes controlled here
• cardiovascular centers
• breathing centers
• vomiting, coughing, hiccuping, sneezing, and
  swallowing centers

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Reticular Activating System
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The Limbic System
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The Limbic System

• a complex network of tracts and nuclei
• Blends primitive emotions and higher mental
  functions into a united whole
• Composed of hippocampus and amygdala
• the emotional brain

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Higher Mental Functions

• Memory the ability to recall thoughts and past
  events
• Short-term versus long-term.
• Skill memory.
• Learning retention and utilization of memory
• Language and speech depends on motor centers in
  the occipital and temporal lobes.

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Learning

• The Hippocampus and Amygdala play a crucial role
• the brain undergoes structural and chemical
  changes (See Scientific American

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Language and Speech
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Brain Lateralization

• Left and right brain differ in function
• Left Hemisphere more Verbal, Logical, Analytical,
  Rational
• Right Hemisphere more Nonverbal, Intuitive,
  Creative

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Drug Addiction
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The addicted Brain, Scientific American, March
2004, Eric G. Nestler and Robert C. Malenka
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Peripheral Nervous System

• nerves are bundles of axons wrapped in connective
  tissue
• ganglia are swellings in nerves containing cell
  neuron cell bodies

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Cranial nerves

• transmit impulses to and from the brain

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Spinal nerves

• transmit impulses to and from the spinal cord

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Somatic Nervous System

• nerves that transmit sensory information from
  external sensory receptors to the CNS and motor
  commands away from the CNS to skeletal muscles
• Reflexes are automatic responses to a stimulus.

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Somatic Reflex Arcs
receptor
afferent path
control center
efferent path
effector
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Autonomic Nervous System

• regulates cardiac and smooth muscles and glands
• Sympathetic division fight or flight responses
  E situations (exercise, excitement, emergency,
  embarrassment)
• Parasympathetic division relaxation, SLUD
  (salivation, lacrimation, urination, defecation)

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Comparison of Sympathetic to Parasympathetic
(short)
(long)
(short)
(long)
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Sympathetic versus Parasympathetic

• short preganglionic fiber
• short post-ganglionic fiber
• postganglionic neurotransmitter usually
  epinephrine/ norepinephrine
• E situations

• long preganglionic fiber
• short post-ganglionic fiber
• postgabglionic neurotransmitter is acetylcholine
• SLUD

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Drug Abuse

• Drugs that affect the nervous system have two
  general effects
• Impact limbic system
• Promote or decrease action of a particular
  neurotransmitter
• Drug abuse is apparent when a person takes a drug
  at a dose level and under circumstances that
  increase the potential for a harmful effect

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Drug Actions at a Synapse
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Drug Abuse

• Alcohol.
• Nicotine.
• Causes neurons to release dopamine
• Excess dopamine has reinforcing effect that leads
  to dependence
• Cocaine.
• Prevents synaptic uptake of dopamine
• Continued use causes body to produce less dopamine

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Drug Abuse

• Heroin.
• Binds to receptors meant for endorphins
• Continued use causes body to produce fewer
  endorphins
• Marijuana.
• Binds to receptor for anandamide
• Brain impairment?

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Homeostasis

• Governance of internal organs and the regulation
  of blood and tissue fluid usually takes place
  below the level of consciousness
• Heart Rate
• Breathing Rate

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Degenerative Nervous System Diseases

• Alzheimer disease
• Presence of abnormal neurons
• Plaques
• Neurofibrillary tangles
• Parkinson disease.
• Overactive basal nuclei due to the degeneration
  of dopamine-releasing neurons in the brain

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Review

• 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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