HSS 391 Ch. 17 Autonomic Nervous System

Somatic nervous system

Includes processes that are perceived or controlled consciously

Autonomic nervous system

Aka the “visceral motor system”; involves processes and commands that are controlled below the level of consciousness; system seeks to maintain body homeostasis and to regulate processes that keep the body alive

• It responds to visceral sensory input — detects stimuli associated with blood vessels and internal organs

• It is a two-neuron system

Preganglionic neuron

First-order neuron with cell body located in the spinal cord or brainstem (CNS); carries motor information away from the CNS and synapses on postganglionic neuron in the periphery

Postganglionic neuron

Second-order neuron with cell body located in a ganglia (PNS); carries motor information to the effector (target organ) to elicit autonomic effects

What structures regulate the ANS?

• Hypothalamus

• Brainstem

• Spinal cord

Hypothalamus regulation of ANS

Serves as an integration & command center; involved in emotional & physiological processing

Midbrain regulation of ANS

Nuclei regulate visceral reflexes (BP, HR, blood vessel diameter, pupil size, digestion, etc.)

Spinal cord regulation of ANS

Reflexive control of urination & defecation in children (before they are able to consciously control the tone of external sphincters)

What are the divisions of the ANS?

• Parasympathetic

• Sympathetic

Parasympathetic division

Maintains homeostasis when the body is at REST (“rest & digest”); conserves energy & maintains energy stores

Sympathetic division

Maintains homeostasis when the body is ACTIVE during exercise, excitement, and emergencies (“fight or flight”); ensures that adequate nutrients are released from stores for use during times of stress

The parasympathetic division is also known as the _____ divsion.

craniosacral

The sympathetic division is also known as the _____ divsion.

thoracolumbar

Where is the preganglionic cell located in the parasympathetic division?

Brainstem & lateral horn of sacral spinal cord from S2-S4

Where is the preganglionic cell located in the sympathetic division?

Lateral horn of the thoracic & lumbar spinal cord from T1-L2

Where is the postganglionic cell located in the parasympathetic division?

Terminal (periphery close to target organ) or intramural (within wall of target organ) ganglia

Where is the postganglionic cell located in the sympathetic division?

Sympathetic trunk/chain ganglia or prevertebral ganglia (far from target organs)

What nerves carry preganglionic axons in the parasympathetic division?

Mostly cranial nerves

What nerves carry preganglionic axons in the sympathetic division?

Spinal nerves

Typically, in the parasympathetic division, the length of the preganglionic axon is _____ and the length of the postganglionic axon is _____.

long; short

Typically, in the sympathetic division, the length of the preganglionic axon is _____ and the length of the postganglionic axon is _____.

short; long

Exceptions to the general rule in sympathetic fibers…

Sympathetic fibers innervating the GUT do not follow the general sympathetic rules and are anatomically arranged more like parasympathetic fibers

• Preganglionic axons bypass the paravertebral/sympathetic chain ganglia to synapse onto postganglionic neurons in prevertebral ganglia locaed close to the target organ

• Therefore, preganglionic axons are LONG

Pathway associated with ciliary ganglia

Parasympathetic ganglia

• Source: CN III

• Nucleus: Edinger-Westphal

• Target organ (function): contraction of sphincter pupillae (pupil constriction) and ciliary muscle (accommodation, close vision)

Pathway associated with pterygopalatine ganglia

Parasympathetic ganglia

• Source: CN VII

• Nucleus: superior salivatory

• Target organ (function): lacrimal gland

Pathway associated with submandibular ganglia

Parasympathetic ganglia

• Source: CN VII

• Nucleus: superior salivatory

• Target organ (function): submandibular and sublingual glands

Pathway associated with otic ganglia

Parasympathetic ganglia

• Source: CN IX

• Nucleus: inferior salivatory

• Target organ (function): parotid gland

Pathway associated with visceral plexuses

Parasympathetic ganglia

• Source: CN X

• Nucleus: dorsal motor

• Target organ (function): cardiac, abdominal aortic, esophageal, & pulmonary plexuses

Pathway associated with hypogastric plexus

Parasympathetic ganglia

• Source: S2-S4

• Nucleus: N/A

• Target organ (function): urogenital viscera (bladder, rectum, penis, vagina, uterus, descending colon)

Pathway associated with celiac ganglia

Sympathetic ganglia

• Source: T5-T9

• Target organ (function): foregut via greater splanchnic nerve (esophagus, stomach, proximal ½ duodenum, liver, gallbladder, pancreas, & spleen)

Pathway of superior mesenteric ganglia

Sympathetic ganglia

• Source: T10-T12

• Target organ (function): midgut via lesser splanchnic nerve (distal ½ duodenum, small intestine up to transverse colon)

Pathway of inferior mesenteric ganglia

Sympathetic ganglia

• Source: T11-L2

• Target organ (function): hindgut via least splanchnic nerve (distal transverse colon, sigmoid colon, rectum)

Reflexive control of pupillary constriction

Parasympathetic stimulation of pupillary constrictor muscles → decreased diameter of the pupil

• Protective in that it limits the amount of light entering the eye

Reflexive control of pupillary dilation

Sympathetic stimulation of the dilator pupillae muscles results in a wider pupil

• Allows more light to enter the eye to stimulate photoreceptors

Pathway for pupillary constriction

1. Photoreceptors collect light in retina → transfer to brain via optic nerve (CN II)

2. Information passes through optic chiasm, then optic tract

3. Synapse onto neurons in the ipsilateral pretectal nucleus

4. Project bilaterally to Edinger-Westphal nuclei

5. Project to ipsilateral ciliary ganglia

6. Project to ipsilateral pupillary constrictor muscles via oculomotor nerve (CN III)

Result of the pathway for pupillary constriction

• Direct response: constriction in stimulated eye

• Commissural response: constriction in opposite eye (due to decussation & bilateral projections)

What response to the pupillary light reflex would occur if there is damage to the optic nerve (CN II)?

No pupillary response

What response to the pupillary light reflex would occur if there is damage to the optic chiasm?

Both a direct and commissural response

What response to the pupillary light reflex would occur if there is damage to one optic tract?

Both a direct and commissural response

What response to the pupillary light reflex would occur if there is damage to one pretectal nucleus?

Both a direct and commissural response

What response to the pupillary light reflex would occur if there is damage to the contralateral Edinger-Westphal nucleus?

Direct response only