ANS

• SNS


  Somatic Nervous System
• ANS


  Autonomic Nervous System
• Somatic Nervous System (SNS)


  • Cell bodies of somatic neurons are located in the CNS
  • Their axons extend to skeletal muscles where they have an excitatory effect
  • Usually controlled consciously
• Autonomic Nervous System (ANS)


  • Cell bodies of the preganglionic neurons are located in the CNS
  • Their axons extend to ganglia where they synapse with postganglionic neurons
  • The postganglionic axons can have an excitatory or inhibitory effect on Smooth muscle, Cardiac muscle, Glands
  • Usually controlled unconsciously
• Fig. 14.1
• Tab. 14.1
• Anatomy of the Autonomic Nervous System


  • Subdivided into the Sympathetic division, Parasympathetic division, Enteric nervous system
  • Sympathetic and Parasympathetic divisions differ structurally in Location of their preganglionic neuron cell bodies within the CNS, Location of their autonomic ganglia
• The Sympathetic Division


  1. Preganglionic cell bodies are in the lateral horns of the spinal cord gray matter from T1 to L2

  2. Preganglionic axons pass through the ventral roots to the white rami communicates to the sympathetic chain ganglia

  3. From there, four courses are possible
• The Sympathetic Division


  1. Preganglionic axons synapse (at the same or a different level) with postganglionic neurons, which exit the ganglia through the gray rami communicates and enter spinal nerves

  2. Preganglionic axons synapse (at the same or a different level) with postganglionic neurons, which exit the ganglia through sympathetic nerves
• The Sympathetic Division


  1. Preganglionic axons pass through the chain ganglia without synapsing to form splanchnic nerves. Preganglionic axons then synapse with postganglionic neurons in collateral ganglia

  2. Preganglionic axons synapse with the cells of the adrenal medulla
• The Parasympathetic Division


  1. Preganglionic cell bodies are in nuclei in the brainstem or the lateral parts of the spinal cord gray matter from S2 to S4

  2. Preganglionic axons from the brain pass to ganglia through cranial nerves

  3. Preganglionic axons from the sacral region pass through the pelvic splanchnic nerves to the ganglia

  4. Preganglionic axons pass to terminal ganglia within the wall of, or near, the organ that is innervated
• Tab. 14.2
• The Enteric Nervous System

  • Consist of nerve plexuses within the wall of the digestive tract
  • Has contributions from three sources: Sensory neurons that connect the digestive tract to the CNS, ANS motor neurons that connect the CNS to the digestive tract, Enteric neurons, which are confined to the enteric plexuses
• Distribution of Autonomic Nerve Fibers


  • Sympathetic, parasympathetic and sensory neurons intermingle in autonomic nerve plexuses
  • Sympathetic axons reach organs through spinal, sympathetic, and splanchnic nerves
  • Parasympathetic axons reach organs through cranial and pelvic splanchnic nerves
  • Sensory neurons run alongside sympathetic and parasympathetic neurons within nerves and nerve plexuses
• Fig. 14.5
• Acetylcholine


  Released by cholinergic neurons: All preganglionic neurons, All parasympathetic postganglionic neurons, Some sympathetic postganglionic neurons
• Norepinephrine (or epinephrine)


  Released by adrenergic neurons: Most sympathetic postganglionic neurons
• Receptors of the ANS

  • Acetylcholine binds to Nicotinic receptors (found in all postganglionic neurons, excitatory) and Muscarinic receptors (found in all parasympathetic effector organs and some sympathetic effector organs, excitatory or inhibitory)
  • Norepinephrine and epinephrine bind to Alpha and beta receptors (found in most sympathetic effector organs, excitatory or inhibitory)
• Fig. 14.6
• Regulation of the ANS

  • Autonomic reflexes control most of the activity of visceral organs, glands, and blood vessels
  • Autonomic reflex activity can be influenced by the hypothalamus and higher brain centers
  • The sympathetic and parasympathetic divisions can influence the activities of the enteric nervous system through autonomic reflexes
  • The enteric nervous system can function independently of the CNS through local reflexes
• Functional Generalizations About the ANS

  • Both divisions of the ANS produce stimulatory and inhibitory effects
  • Most organs are innervated by both divisions – Usually, each division produces an opposite effect on a given organ
  • Either division alone or both working together can coordinate the activities of different structures
  • The sympathetic division produces more generalized effects than the parasympathetic division
  • Sympathetic activity generally prepares the body for physical activity
  • Parasympathetic activity is more important for resting conditions