AVS 271 Anatomy and Physiology

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AVS 271 Anatomy and Physiology

• Lecture 11
• October 3, 2008
• Nervous System
• Chapter 10

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Peripheral Nervous System

• Afferent division
• Sensory neurons
• Efferent division
• Somatic system
• Autonomic system
• Sympathetic division
• Parasympathetic division

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Sensory System

• Awareness of the internal and external
  environment is brought about by the neural
  mechanisms that process afferent information
• The initial step is the transformation of
  stimulus energy into graded potentials
  (receptor potentials) and then into action
  potentials in sensory (afferent) neurons
• The pattern of action potentials in
  particular sensory neurons is a code that
  provides information about the initial
  stimulus

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Sensory System

• Part of the nervous system that consists
  of sensory receptors that receive stimuli
  from the external or internal environment,
  the neural pathways that conduct information
  from the receptors to the brain (afferent
  neurons), and those parts of the brain
  (interneurons) that process the information
• If necessary, actions (i.e., effects) can be
  initiated by efferent neurons
• E.g., blood pressure, body temperature, etc.

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Sensory Information

• Information processed by the sensory system
  may or may not lead to conscious awareness
  of the stimulus
• Regardless of whether the information
  reaches consciousness, it is called sensory
  information
• Sensation
• Awareness of a stimulus
• Perception
• Interpretation of a sensation

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Sensory Receptors

• Neural activity is initiated at the border
  between the nervous system and the internal
  and external environment by sensory
  receptors
• Mechanoreceptors (touch)
• Nociceptors (pain)
• Thermoreceptors (temperature)
• Chemoreceptors (oxygen / carbon dioxide)
• Special senses (Chapter 11)
• Sight, smell, taste, hearing / balance

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Sensory Receptors
e.g., touch / pressure
e.g., taste bud
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Stimulus Transduction

• The process by which a stimulus (e.g.,
  touch) is transformed into an electrical
  response (i.e., action potential)
• Stimulus transduction involves the opening
  or closing of ion channels in the
  specialized receptor membrane, which
  initiates a graded potential called the
  receptor potential
• Mechano gated (e.g., blood pressure
  baroreceptors) and ligand gated (e.g., taste
  bud receptors) channels

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Receptor Potential
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Local Anesthetics

• Local anesthetics such as lidocaine produce
  their effect (i.e., loss of sensory
  information) by preventing voltage gated
  sodium channels from opening in the plasma
  membrane of neurons
• What does that do ?

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Efferent Division

• Somatic nervous system
• Innervates skeletal muscle (motor neurons)
• Single neuron between CNS and muscles
• Can lead only to muscle contraction
• Autonomic nervous system
• Innervate smooth muscle, cardiac muscle,
  glands, gastro intestinal tract
• Two neuron chain (connected by synapse in
  ganglion) between CNS and effector organ
• Can be excitatory or inhibitory

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Efferent Division
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Autonomic Division
Sympathetic system
Parasympathetic system
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Neurotransmitters
Skeletal muscle ( )
e.g., heart ( - )
e.g., heart ( )
e.g., heart ( )
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