The Autonomic Nervous System

1
The Autonomic Nervous System
2
Characteristics of the ANS

• A part of the PNS
• Actions are involuntary (not under conscious
  control)
• Regulated by centers in the hypothalamus and
  brain stem regions of the CNS
• The motor part is subdivided into the sympathetic
  division and the parasympathetic division

3
Components of the ANS

• Autonomic sensory receptorslocated mainly in
  visceral organs
• Autonomic sensory neuronssend information to the
  CNS from the receptors
• Autonomic integrating centersin the CNS
  (hypothalamus and brain stem)
• Autonomic motor neuronssend information from the
  CNS to effectors regulate visceral activities
• Autonomic effectorscardiac muscle, smooth
  muscle, and glands

4
Components of the ANS (continued)

• The motor neuron part of the ANS consists of 2
  motor neurons
• The first motor neuron (preganglionic neuron) has
  its cell body in the CNS its axon (myelinated)
  extends from the CNS to an autonomic ganglion
• The second motor neuron (postganglionic neuron)
  has its cell body in an autonomic ganglion its
  axon (unmyelinated) extends from the ganglion to
  an effector

5
Components of the ANS (continued)

• Autonomic motor neurons release either
  acetylcholine or norepinephrine (somatic motor
  neurons release only acetylcholine)
• Most body organs receive nerve impulses from both
  sympathetic and parasympathetic neurons
• The two divisions of the ANS typically work
  opposite one another

6
Sympathetic Division

• The cell bodies of sympathetic preganglionic
  neurons are located in the thorax and lumbar
  regions of the spinal cord, so this division is
  also called the thoracolumbar division
• Operates during times of physical or emotional
  stress (E situationsexercise, emergency,
  excitement, embarrassment)

7
Sympathetic Division (continued)

• Triggers fight-or-flight responses
• Effects
• Dilation of the pupils of the eyes
• Increase in heart rate and blood pressure
• Dilation of airways and increase in respiration
  rate
• Decrease in digestive activities
• Increase in blood sugar (glucose) levels
• Increase in perspiration

8
Parasympathetic Division

• The cell bodies of parasympathetic preganglionic
  neurons are located in the brain stem and sacral
  region of the spinal cord, so this division is
  also called the craniosacral division
• Operates during times of rest and recovery (rest
  and digest) reduce body functions that support
  physical activity

9
Parasympathetic Division (continued)

• Effects
• Constriction of the pupils of the eyes
• Decrease in heart rate and blood pressure
• Constriction of airways and decrease in
  respiration rate
• Increase in digestive activities
• Decrease in blood sugar
• Decrease in perspiration