Nervous System 3

• Afferent


  Carrying information into the central nervous system, usually considered synonymous with sensory information
• Efferent


  Carrying information away from the central nervous system, usually considered synonymous with motor information
• Somatic


  Relating to the body wall and limbs (muscles, skin, bones, joints)
• Visceral


  Relating to the internal organs (heart, lungs, digestive system, kidneys, reproductive system, etc.)
• Autonomic nervous system (ANS)


  The division of the nervous system controlling the viscera
• ANS


  • Together with the endocrine system controls the body's internal organs
  • Has control over: circulation of blood, activity of the gastrointestinal tract, body temperature
• Preganglionic neurons


  Originate in the central nervous system (CNS); preganglionic efferent axons are lightly myelinated
• Postganglionic neurons


  Originate in the ganglion located outside the CNS; postganglionic neurons are not myelinated
• Parasympathetic nervous system


  • Active at rest
  • Conserves body energy and maintains body activities at basal levels – homeostasis
• Parasympathetic preganglionic neurons


  Arise from brain stem & from S2-S4 (Craniosacral)
• Sympathetic nervous system


  • Is activated
  • Vasoconstriction shunts blood from skin and digestive viscera to heart, brain & skeletal muscles
• Preganglionic sympathetic neurons


  Arise from lateral horns of T1-L2 (thoracolumbar spinal cord)
• Spinal Cord and Spinal Nerves

  • 8 cervical nerves
  • 12 thoracic nerves
  • 5 lumbar
  • 5 sacral
  • 1 coccygeal
• During development, the bone of the vertebral column elongates more than the spinal cord. Nerves still exit from the appropriate intervertebral spaces (in bone)
• Many nerves innervating the limbs form plexi (like a 'network')
• Each spinal nerve consists of

  • Axons of motor neurons that innervate a group of muscles
  • Axons of sensory neurons that innervate a defined area of skin
  • Axons of sympathetic neurons to structures in the body wall that control body temperature (blood vessels, sweat glands etc.)
• Dermatomes and Myotomes


  Areas supplied by single spinal nerves, providing sensory and motor supply of an adjacent muscle mass (myotome) and the cutaneous supply of an area of skin (dermatome)
• Reflex


  Rapid, involuntary motor response to a stimulus
• Reflex arc


  Receptor, sensory neuron, integration centre, motor neuron, and effector
• Spinal reflex


  Somatic spinal reflexes provide information on integrity of the reflex pathway and degree of excitability of the Spinal cord
• Simple monosynaptic neural circuit

  1. Extensor muscle stimulated

  2. Muscle spindle stimulated

  3. Primary afferent excited

  4. Primary afferent stimulates alpha motor to extensor

  5. Alpha motor neuron stimulates extensor to contract

  6. Primary afferent neuron stimulates inhibitory interneuron

  7. Interneuron inhibits alpha motor neuron to flexor muscle
• Motor Unit


  A motor neuron and all the skeletal muscle fibres it innervates (these contract together)