PCOM Anatomy 3; Autonomic Nervous System

What are three possible actions of the pre-ganglionic fiber when it reaches the ganglion?

1. It can synapse within the trunk ganglion with a post-synaptic sympathetic neuron. 2. It can ascend or descend through the sympathetic trunk to synapse in another trunk ganglion. (The sympathetic trunk consists of these fibers traveling from 1 ganglion to another). 3. It can pass through the trunk (chain) ganglion and emerge from the trunk without synapsing. This way is responsible for the formation of the splanchnic nerves that synapse in collateral ganglia that occur only in the abdomen and pelvis.

What is the Autonomic Nervous System or ANS?

A system of motor neurons innervating smooth muscle, cardiac muscle and glands (effector organs). It is involuntary.

What does the ANS use to reach its effector organ?

A two-neuron chain.

Explain the actions of the two divisions of the ANS.

Both serve the same effector organs. They have opposite effects - the sympathetic division mobilizes the body (fight and flight) and the parasympathetic divisions promotes maintenance and conserves energy (rest and digest).

Where are sympathetic ganglia located?

Close to the spinal cord.

How do the effector organs respond to the neurotransmitters.

Depending on the type of receptor on the effector organ, the response can be excitatory or inhibitory.

What are the 3 D's (clues) of the Parasympathetic division?

Digestion, defecation and diuresis.

Where are most parasympathetic autonomic ganglia located?

Either in or very close to the effector organ.

Regarding the Sympathetic division; what are the 4 E's (clues)?

Exercise, excitement, emergency, embarrassment.

Where do pre-ganglionic fibers of CN VII (facial) originate?

From both the lacrimal nuclei of the pons (stimulate nasal and lacrimal glands) and the superior salivatory nuclei of the pons (stimulate the submandibular and sublingual glands). Thus = tears and saliva - which is why someone inflicted by Bells Palsy may lack tears and saliva.

Where do the sympathetic chain ganglia run?

From occiput to sacrum but the pre-ganglionic sympathetic nerve fibers arise only from T1 - L2 spinal cord levels.

How is that sympathetic nerve flow can reach every part of the body?

Gray rami carrying post-ganglionic axons are associated with every trunk (chain) ganglion from cervical to sacral region.

Where do sympathetic pre-ganglionic fibers originate?

In the thoracic lumbar region of the spinal cord (T1 - L2) and specifically in the lateral horns (gray matter).

What is the name of this first neuron of the ANS chain? What is its axon called?

It is called the preganglionic neuron. The axon is called the preganglionic axon.

Where is the cell body of the first neuron located?

It is located in the brain or spinal cord.

Postganglionic fibers release what kind of chemical?

Neurotransmitters - acetycholine by parasympathetic fibers and norepinephrine by sympathetic fibers.

What are the 2 divisions of the ANS?

Parasympathetic and Sympathetic

What do the post-ganglionic fibers of CN III innervate?

Post-ganglionic fibers innervate the smooth muscles of the iris causing pupillary constriction (the sphincter pupillae muscle) needed for close vision. They also innervate the ciliary muscles of the eye which are important in controling lens shape. In this case, causing contration and allowing the lens to bulge - needed for focus on near objects. (Parasympathetic is responsible for near vision and sympathetic for distance).

Where in the CN III (oculomotor) do pre-ganglionic fibers originate. Where do they synapse?

Pre-ganglionic fibers originate from the Edinger-Westphal nuclei in the midbrain and synapse in the ciliary ganglia within the eye orbit.

CN X (vagus) fibers?

Pre-ganglionic fibers originate from the dorsal motor nuclei of the medulla. Provides nerve fibers to various nerve plexuses that innervate thoracic and abdominal structures such as the heart, lungs and esophagus.

Where do the pre and post-ganglionic fibers of CNIX (glossopharyngeal) originate? Functions?

Pre-ganglionic fibers originate from the inferior salivatory nuclei of the medulla. Post-ganglionic fibers to the parotid glands.

What is the craniosacral division?

Pre-ganglionic neurons that emerge from the brain and spinal cord.

What are some of the symptoms experienced during flight or fight?

Rapidly pounding heart, increased respiratory rate/depth, dry mouth, cold sweaty skin, dilated pupils.

The ANS is a division of what nervous system?

The PNS or Peripheral Nervous System.

What happens if a synapse occurs in a trunk ganglion?

The post-ganglion fibers enter the ventral or dorsal rami via the gray rami communicans and from there they travel to their effectory organs.

What innervates the effector organ?

The postganglionic axon innervates the effector organ.

What is the 2nd motor neuron is called? What is its axon called?

The postganglionic neuron and the postganglionic axon.

In which nerves do the parasympathetic pre-ganglionic fibers run?

The pre-ganglionic fibers in the cranial division run in CN III, CN VII, CN IX, CN X. The sacral division originates from spinal cord segments S2, S3, S4 and their pre-ganglionic fibers form the pelvic splanchnic nerves.

Describe the action of sympathetic pre-ganglionic axons?

They leave the spinal cord via the ventral root and travel within the white ramus communicans to enter the sympathetic trunk (or chain) ganglia.

What is the autonomic ganglion?

This is where the preganglionic axon synapses with the 2nd motor neuron outside of the CNS.