The Nervous System.


Overview of the Nervous System.

  • Nervous system characteristics:
    -Rapid response.

    -Brief duration.
  • Endocrine system characteristics:
    -Slower response
    -Long duration.
  • Central nervous system (CNS):
    -Spinal cord.
  • Peripheral nervous system (PNS):
    -All the neural tissue outside CNS
    -Afferent division (sensory input).
    -Efferent division (motor output).
    Somatic nervous system
    Autonomic nervous system.
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CNS and PNS neurons and Pathways in the CNS

CNS Neurons:

  • White matter- Bundles of axons (tracts) that share origins, destinations, and functions.
  • Grey Matter- Collections of nerve cell bodies.

PNS Neurons:

  • Ganglia- Groupings of neuron cell bodies.
  • Nerves- Bundle of axons supported by connective tissue.
    -Spinal nerves (
    To/from spinal cord).
    -Cranial nerves
    (To/from brain).


  • Ascending pathways.
    -Carry information from
    sensory receptors to processing centers in the brain.
  • Descending pathways.
    -Carry commands from specialized CNS centers to skeletal muscles.
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Pathways in the CNS and Sensory Receptors.

  • General Senses:
    -Nociceptors (pain receptors).
    -Thermoreceptors (temperature).
    -Mechanoreceptors (physical distortion).
    -Chemoreceptors (concentration of chemical substances).
    -Baroreceptors (pressure).
    Proprioceptors (position of joints).
  • Special Senses:
    -Olfaction (smell).

    -Gustation (taste)
    -Vision (sight)
    -Equilibrium (balance)
    -Hearing (sound).
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Pain Pathways.

  • Nociceptors detect tissue damage and show no adaptation,
  • Nociceptors are commonly found in superficial parts of skin, joint capsules, periosteum of bones, walls of blood vessels.
  • Deep tissues and visceral organs have fewer nociceptors.
  • Detect thermal, mechanical and chemical damage; severe damage may stimulate all 3 types of receptors hence “burning”, “throbbing”, “aching” or “sharp” descriptors of pain.
  • Pain messages are conducted to the CNS.
  • Neurotransmitters at synapses in CNS can modify pain messages:
    -Neurotransmitters Glutamate and Substance P “facilitate” pain.

    -Naturally occurring Endorphins and Encephalins “inhibit” pain.
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The Brain.

  • Meninges.
    Layers that surround and protect the brain and spinal cord (CNS).

       -Dura mater (tough mother).

    Pia mater (delicate mother).

Brain Regions:

  • Cerebrum.
    Conscious thought, intellectual activity, memory, origin of complex patterns of movement.
  • Diencephalon.
  • Midbrain.
    Process visual, auditory information, generate involuntary movements.
  • Pons.
    Links to cerebellum, involved in control of movement.
  • Medulla Oblongata.
    Relay sensory information, regulate autonomic function (cardivascular and respiritory).
  • Cerebellum.
    -Overseas postural muscles, stores patterns of movement, fine tunes most movements.
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Functions of brain structures.

  • Brain Ventricles.
    The four hollow chambers in the center of the brain filled with cerebrospinal fluid (CSF).
  • Cerebral Cortex.
    Primary motor cortex (precentralgyrus).
       -Directs voluntary movement.

    -Primary sensory cortex (postcentralgyrus).

       -Receives somatic sensation (touch, pain, pressure, temperature).

    -Association areas
       -Interpret sensation
       -Coordinate movement.
  • Thalamus.
    Relay and filter all ascending (sensory) information.
    -Coordinate voluntary and involuntary motor behavior.
  • Hypothalamus.
    -Produce emotions and behavioral drives.
    Coordinate nervous and endocrine systems.Coordinate voluntary and autonomic functions.
    -Secrete hormones
    -Regulate body temperature.
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Key Note and Reflex.

Key Note:

The 12 pairs of cranial nerves are responsible for the special senses of smell, sight, and hearing/balance, and control movement of the eye, jaw, face, tongue, and muscles of the neck, back, and shoulders.They also provide sensation from the face, neck, and upper chest and autonomic innervation to thoracic and abdominopelvic organs.


  • An automatic involuntary motor response to a specific stimulus.
    -Step 1- Arrival of stimulus and activation of receptor.
    -Step 2- Activation of a sensory neuron.
    -Step 3- Information processing in CNS.
    -Step 4- Activation of a motor neuron.
    -Step 5- Response by effector.
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Autonomic Nervous System and Homeostasis.

  • Branch of the nervous system that coordinates cardiovascular, digestive, excretory and reproductive functions and it does this automatically.
  • Homeostasis:
    -The basis of all homeostais is:
       -Receptors detect change.
       -Control centre receives/ sends messages.
       -Effectors reverse change.
       -Homeostasis achieved.
  • Two divisions of the ANS:
    Sympathetic division.
        -“Fight or flight” system
    -Parasympathetic division
        -“Rest and digest” system.

The two divisions of the ANS operate largely without our awareness. The sympathetic division increases alertness, metabolic rate, and muscular abilities. The parasympathetic division reduces metabolic rate and promotes visceral activities such as digestion.

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Effects of Sympathetic and Parasympathetic activat

Sympathetic Activation:

  • Generalized response in crises.
  • Increased alertness.
  • Feeling of euphoria and energy.
  • Increased cardiovascular activity.
  • Increased respiratory activity.
  • Increased muscle tone.

Parasympathetic Activation:

  • Relaxation.
  • Food processing.
  • Energy absorption.
  • Brief effects at specific sites.
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