Anatomy Chapter 17: Autonomic Nervous System

3 Autonomic Nervous Systems

1. Sympathetic

2. Parasympathetic

3. Enteric

Characteristics of Autonomic Nervous System

Motor only and are all controlled subconsciously

Sympathetic division

fight or flight

Parasympathetic division

for resting situations

Certain organs are only

innervated by 1 division

Characteristics of autonomic pathways

1. No upper/lower motor neurons

2. 3 neurons total

3. Involve autonomic ganglia which exist in the periphery

Visceral Motor Neurons

Somas are in the nuclei of the brain and the axons travel down tracts and synapse with preganglionic neurons

Preganglionic neurons

Somas are in nuclei in the brain or spinal cord and send axons out of the CNS through the cranial or spinal nerves to synapse with postganglionic neurons

Postganglionic neurons

Somas are in autonomic ganglia and send axons out to effectors

Neural tube mantle cells become

preganglionic neurons

Neural crest cells become

postganglionic neurons

Clumps of neural crest cells will form

somas that will be found in future autonomic ganglia

Axons travel from ganglia

to effectors

Autonomic ganglia made up of

postganglionic somas that function in the sympathetic nervous system

Ganglia in sympathetic nervous system

1. Chain ganglia

2. Collateral ganglia

3. adrenal medulla

Chain ganglia

Sequence of sympathetic ganglia running parallel to spinal column on either side

Characteristics of chain ganglia

1. Run all the way from neck to coccyx

2. Connect with spinal nerves through rami communicans

3. Have their own nerves that exit the chain

nerves that exit the chain ganglia

Splanchic nerves

Collateral ganglia

Sympathetic ganglia in the abdominopelvic cavity

Examples of Collateral ganglia

1. Celiac

2. Superior mesenteric

3. inferior mesenteric

adrenal medulla

Deep part of adrenal glands

Preganglionic somas

are in nuclei of the spinal cord

Preganglionic axons

1. Exit spinal cord

2. Go through ventral root

3. through spinal nerve

4. into rami communicans

5. runs through white ramus

Sympathetic axons only travel through

Nerves T1-L2

After traveling through the white ramus, preganglionic axons will take

1 of 4 routes

1st route of preganglionic axons

Go into the chain and synapse with postganglionic soma in the first ganglion they encounter

2nd route of preganglionic axons

Go up/down the chain and synapse with postganglionic somas at a ganglion superior/inferior to where they came

3rd route of preganglionic axons

Exit the chain via the splanchnic nerves and travel to a collateral ganglion to synapse with post ganglionic somas there

4th route of preganglionic axons

Exit the chain via the splanchnic nerves and to the celiac ganglion. then they exit the ganglion travel through nerves to the adrenal medulla and synapse with chromaffin cells

Post ganglionic axons will

leave their ganglion

If the ganglion is in the chain, the axon of the post ganglionic axon will

go through the gray ramus of the rami communicans back to the spinal nerve and go to effectors

If the ganglion is collateral, the axon of the post ganglionic axon will

Go through nerves exiting the ganglion and travel to effectors throughout the body

If the ganglion is the adrenal medullae

there are no axons in chromaffin cells

The preganglionic neuron releases this neurotransmitter to the post ganglionic neuron

Acetylcholine

Type of receptors on the post ganglion neuron

Nicotinic receptor which acetylcholine binds to

Neurotransmitter released by post ganglion neuron to effectors

Norepinepherine

Receptors on effectors that bond to norepinephrine

Adrenergic receptors

Adrenergic receptors also bond to

epinephrine

Activation of adrnenal medulla

The preganglionic neuron synapses directly with the chromaffin cells

Nicotinic receptors on chromaffin cells

bond to acetylcholine

Chromaffin cells

no longer function like neurons

Chromaffin cells used to be

post ganglionic neurons but lost their axons so they do not synapse with anything

Chromaffin instead of synapsing

release norepinephrine into the blood where it travels to effectors

Adregenic receptors on the effector

respond to these chemicals exactly how they would if they were used as neurotransmitters

When your sympathetic nervous system becomes active

Both postganglionic neurons and chromaffin cells are releasing similar chemical signals at the same time

Since adregenic receptors on effectors will respond to both the neurotransmitter and endocrine signal

Effectors will get a double dose

Sympathetic responses are

immediate, systematic, and long lasting

Effects of sympathetic activation

1. Bronchodilation and higher breathing rate and depth

2. Increased heart rate and blood psi

3. Vasodilation of capillary beds in skin

4. Mobilization of stored energy and increased blood sugar

More effects of sympathetic activation

1. Elevated muscle tone

2. pupillary dilation

3. Increased alertness

4. Reduced perception of pain

5. inhibition of digestive and urinary system

Parasympathetic ganglia

Autonomic ganglia made up of postganglionic somas that function in the parasympathetic nervous system

Types of parasympathetic ganglia

1. Head and neck ganglia

2. Intramural ganglia

Head and neck ganglia

4 sets of ganglia connecting to the iris, tear gland, and salivary gland

Intramural ganglia

Ganglia found within the walls of many organs including heart, lungs, digestive, urinary, and reproductive organs and are not visible

Preganglionic axons of parasympathetic ns

1. Exit the cranium and travel through cranial nerves III, VII, IX, and X

2. Exit the spinal cord and go through the ventral root and nerves S2-S4

Parasympathetic post ganglionic neurons concerning head and neck ganglion

Axons will exit the ganglion and go to effectors in target organs through nerves

parasympathetic post ganglionic neurons concerning intramural ganglia

Axons are very short as they are already within their tragedy organs

Parasympathetic activation

1. Visceral motor neuron is stimulated

2. excite preganglionic neuron

3. Nicotinic receptors on post ganglionic neuron bond to acetylcholine

4. Synapses with effector

Effectors of parasympathetic activation

Muscarinic receptors bind to acetylcholine

When your parasympathetic NS becomes active

muscarinic receptors will receive neurotransmitter signals only from post ganglionic neurons

Parasympathetic responses are

immediate, acute, and short lasting

Effects of parasympathetic activation

1. Secretion of digestive enzymes

2. Secretion of hormones promoting nutrient absorption

3. Increased motility in digestive and urinary tract

4. Sexual arousal

More effects of parasympathetic activation

1. Bronchoconstriction and reduced breathing rate/depth

2. Decreased heart rate and blood pressure

3. Pupillary construction

Dual Innervation

Most organs receive innervation from both divisions

Effectors may have

both muscarinic and adrenergic receptors

Thoracic and abdominal regions have

numerous autonomic plexuses that consist of neurons from both divisions and go to most visceral organs

Visceral reflexes involve

either division of the autonomic NS

If a sensory neuron sends a signal to the CNS for processing

Both the preganglionic and post ganglionic neurons will be involved and is known as long visceral reflex

If the sensory neuron goes straight to the autonomic ganglion and synapses with the post ganglionic neuron

It skips the CNS and preganglionic neuron and is known as a short visceral reflex