Chapter 9: ANS

Question 1

What does the ANS do?

Answer 1

It manages our physiology by regulating organs/organ systems and their smooth muscle and glands

• innervates organs NOT under voluntary control
• cardiac muscle, smooth muscle, organs, blood vessels, glands

Question 2

Name the 2 divisions of the ANS and what they are associated with.

Answer 2

1. Sympathetic: fight or flight
2. Parasympathetic: rest and digest

They usually have antagonistic effects on each other

Question 3

Discuss the autonomic neurons.

Answer 3

1. Somatic motor neurons: cell bodies in spinal cord and 1 neuron traveling from spinal cord to effector
   ie. voluntary, skeletal muscle
2. Autnomic motor neurons: 2 sets of neurons in PNS; preganglionic neuron and postganglionic neuron

Question 4

Discuss the sympathetic division of the ANS.

Answer 4

• “Thoracolumbar division”
• preganglionic axons exit T1 - L2
• Short preganglionic axons and long post ganglionic axons (pre. synpase right outside spinal cord - paravertebral ganglia)
• travel with spinal nerves
• most act as a unit = mass activation (makes sense b/c fight or flight)
  …
• white rami communicantes: myelinated axons exit spinal cord ventral root and diverge onto white rami communicantes (on ramp to super highway)
• gray rami communicantes: unmyelinated axons; postganglionic neurons; return to spinal nerves and travel to effectors (off ramp)

Question 5

Discuss the parasympathetic division of the ANS.

Answer 5

• “Craniosacral division”
• Preganglionic axons exit midbrain, medulla, pons, and S2 - S4
• Preganglionic axons long; Postganglionic axons are short and innervate organs
• Do NOT travel with spinal nerves

ie. vagus nerve

Question 6

Be able to discuss an example of the antagonistic effects of the sympathetic and parasympathetic divisions of the ANS.

Answer 6

ie. Heart Rate:
If symp division is activated, HR increase
If parasymp division activated, HR decreases

Question 7

Discuss ANS neurotransmitters.

Answer 7

ALL PREganglionic = ACh
Parasymp POSTganglionic = ACh
Symp POSTganglionic = Norepinephrine

Question 8

Discuss the 3 ways Symp and Parasymp divisions can work together.

Answer 8

1. Usually antagonistic (i.e. HR, pupil dilation)
2. Complementary (cause similar effects to same target)
   ie. salivation:
   - Parasymp stimulates watery saliva
   - Symp constricts blood vessels so secretion is thicker
   Therefore, overload of parasymp = a lot of drooling but overload of symp = cotton mouth
3. Cooperative (produce diff effects that work together to produce desired effect)
   ie. micturition:
   Parasymp aids in detrusor muscle contraction
   Symp activity on internal urethral sphincter decreases to allow it to relax and the bladder to empty.

Question 9

Discuss the control of the ANS by the higher brain centers.

Answer 9

Hypothalamus - MAJOR regulatory center of the ANS
- body temp, hunger, thirst

Medulla - directly controls activity of ANS
- cardiovascular, pulmonary, urinary, reproductive, and digestive systems

Limbic system - autonomic responses during emotional states (blushing, pallor, fainting, sweating, racing HR)

Also influence from cerebral cortex and cerebellum

(Hypothalamus tells medulla what to do but medulla has more direct contact/control over the body)

Question 10

Discuss organs WITHOUT dual innervation.

Answer 10

• Only innervated by simp division:
• So they are regulated by increase or decrease of symp nerve activity
• Important for body temp regulation.

Other examples:

• Adrenal medulla
• Arrector pili muscles
• Sweat glands in skin
• Most blood vessels