Nervous System 7 - Autonomic Nervous System

Question 1

What are the 3 main functional parts of the PNS?

Answer 1

Somatic nervous system (SNS)
Autonomic nervous system (ANS)
Enteric nervous system (ENS)

Question 2

What are the major differences between the somatic nervous system and the autonomic nervous system?

Answer 2

Sensory inputs
Target/effector organs
Pathways
Neurotransmitters
The responses of the target/effector organs to these neurotransmitters.

Question 3

Label and describe how the somatic nervous system detects and responds to stimuli?

Answer 3

Question 4

Label and describe how the autonomic nervous system detects and responds to stimuli?

Answer 4

Question 5

List the differences between the SNS and ANS?

Answer 5

Question 6

Identify the features of the SNS?

Neuron
Synapse

Answer 6

• One lower motor neuron.
• No synapse between neurons = no ganglia.
• The lower motor neuron originates in the ventral (anterior) horn of the spinal cord.

Question 7

Identify the features of the SNS?

Axon
Myelinated

Answer 7

• Long axon transmits nerve impulses from the spinal cord to the skeletal muscle it innervates via the neuromuscular junction.
• Lower motor neuron = highly myelinated (appears white) = rapid nerve impulse transmission from the spinal cord to the target/effector.

Question 8

Identify the features of the ANS?

Neuron
Synapse

Answer 8

• Two neurons in the pathway from the spinal cord to the target/effector.
• Synapse occurs at an autonomic ganglion.

Question 9

Explain the first and second order neuron in the autonomic nervous system?

Answer 9

First-order neuron:
- Called the preganglionic neuron.
- Its cell is located in the CNS.
- Contains preganglionic fibres (axon).

Second-order neuron:
- Called the postganglionic neuron
- Its cell is located in an autonomic ganglion outside the CNS.
- Contains postganglionic fibres (axon) = unmyelinated (appears grey).

Question 10

Explain the myelination in the autonomic nervous system and their effect?

Answer 10

Axons are either lightly myelinated (meaning a thin layer of myelin) or unmyelinated.

Effect:
Slower nerve impulse transmission compared to the SNS.

Question 11

Identify the features of the SNS and ANS?

Answer 11

Question 12

What is the main difference between the sympathetic & parasympathetic division in the autonomic nervous system?

Answer 12

Sympathetic division:
- Enables the body to cope with stress.
- Activated in conditions of ‘fight, flight or fright’.

Parasympathetic division:
- Referred to as being the ‘resting and digesting’ commander.
- Most active when an individual is calm and relaxed.

Question 13

Do both divisions of the ANS contain preganglionic & postganglionic neurons and explain how they are structured?

Answer 13

Both the divisions contain the first and second order neurons.

Preganglionic neuron:
- First neuron in the pathway.
- Runs from the spinal cord to an autonomic ganglion to synapse with the second neuron.

Postganglionic neuron:
- Second neuron in the pathway.
- Runs from the autonomic ganglion to the target/effector.

Question 14

What is dual innervation?

Answer 14

Most targets/effectors of the ANS receive dual innervation, meaning they receive innervation from both the parasympathetic and sympathetic divisions.

Question 15

Where are the cell bodies of the preganglionic neurons found in the sympathetic ANS and explain their structure?

Answer 15

Location:
Found only in the lateral horn of the spinal cord from segments T1 to L2 (or L3).

Structure:
- Short preganglionic fibres.
- Long postganglionic fibres.

Question 16

Where are the cell bodies of preganglionic neurons located in the sympathetic autonomic nervous system?

Answer 16

Located in the thoracic and upper lumbar segments of the spinal cord (T1-L3) = ‘thoracolumbar output’ to describe their site of origin.

Question 17

What is the location of the axons of preganglionic neurons in the sympathetic autonomic nervous system.

Answer 17

The axons of these neurons (preganglionic fibres) leave the spinal cord via the ventral roots of the spinal nerves and travel only a short distance to the sympathetic ganglia.

Question 18

What are ganglia and where are they located in the sympathetic autonomic nervous system?

Answer 18

Most ganglia are located along the vertebral column, in the two paravertebral chains (‘para’ = next to) called the right and left sympathetic chain (or sympathetic trunk).

Question 19

What are the names of the 3 adjacent ganglia in the cervical sympathetic trunk?

Answer 19

Superior cervical ganglion
Middle cervical ganglion
Inferior cervical ganglion.

Question 20

What is the function of rami communications?

Answer 20

Small branches that connect the sympathetic trunk and spinal nerves.

Question 21

Where do the preganglionic fibres that travel to the abdominal and pelvic organs synapse at & what are their nerves called?

Answer 21

These fibres travel to the prevertebral ganglia (‘pre’ = in front of) to synapse.

Splanchnic nerves (‘splanchnic’ = related to viscera).

Question 22

What do postganglionic fibres form & where are they located in the body?

Answer 22

Postganglionic fibres form multiple plexuses (webs of intertwining nerves) that are scattered throughout the body.

Question 23

What are the targets/effectors of the sympathetic nervous system and what are examples of organs?

Answer 23

Sympathetic nervous system = part of autonomic nervous system = its targets/effectors are involuntary organs and tissues.

Examples:
Smooth muscles in the walls of hollow organs, cardiac muscle and glands.

Question 24

Where are the cell bodies of preganglionic neurons located in the parasympathetic autonomic nervous system?

Answer 24

Located in the brainstem and the sacral spinal cord (S2-S4), so we can use the term
***aka = ‘craniosacral output’to describe their site of origin.

Question 25

How many cranial nerves contain parasympathetic fibres and which cranial nerves are these?

Answer 25

Oculomotor (CN III)
Facial (CN VII)
Glossopharyngeal (CN IX)
Vagus nerve (CN X)

Question 26

What is the name of the preganglionic neurons located in the sacrum, where do they originate from, and what is their function?

Answer 26

Name:
Pelvic splanchnic nerves

Origin:
Originate at the S2-S4 levels of the spinal cord.

Function:
Innervating pelvic organs and the distal aspect of the gastrointestinal tract.

Question 27

What are parsympathetic ganglia?

Answer 27

They are the locations of the cell bodies of the postganglionic neurons of the parasympathetic nervous system.

Question 28

What is the location of ganglia found in the parasympathetic autonomic nervous system?

Answer 28

Cranial nerves III, VII and IX:
In a few specific locations within the head.

Vagus (CN X) and pelvic splanchnic nerves:
Very close to, or inside the walls of, their targets/effectors.

Question 29

What is the function of postganglionic fibres & where are they located in the body?

Answer 29

Form multiple plexuses (webs of intertwining nerves) that are scattered throughout the body.

Question 30

What do most autonomic nerve plexuses contain?

Answer 30

End up containing both sympathetic and parasympathetic fibres.

Question 31

What are the targets/effectors of the parasympathetic nervous system and what are examples of organs?

Answer 31

Parasympathetic nervous system = part of the autonomic nervous system = its targets/effectors are involuntary organs and tissues.

Example:
Smooth muscle in the walls of hollow organs, cardiac muscle and glands.

Question 32

Why are the sympathetic & parasympathetic nervous system referred to as antagonistic?

Answer 32

They typically have opposite effects at their targets/effectors.

Question 33

What does it mean by targets/effectors of the ANS have dual innervation?

Answer 33

This means that they are supplied by both sympathetic and parasympathetic neurons.

Question 34

Describe the effects of the parasympathetic and sympathetic divisions on organs and body systems?

Answer 34

Question 35

What are visceral reflexes & what do they involve?

Answer 35

Visceral reflexes are unconscious, automatic, stereotyped responses to stimulation, involving visceral receptors and targets/effectors and somewhat slower responses.

Question 36

What is the process of the visceral reflex?

Answer 36

1. Receptors:
   Detect stretch, tissue damage, blood chemicals, body temperature and other internal stimuli.
2. Afferent neurons:
   Carry signals to the (CNS).
3. Efferent Parasympathetic Neurons:
   Carries motor signals away from the CNS to the target/receptor.
4. Target/Effector:
   Makes adjustments in response to innervation from the efferent parasympathetic neurons.

Question 37

What are the 2 roles of ANS?

Answer 37

1. Produces motor responses.
2. Responds to visceral sensory input.

Question 38

Complete the sentence:

Senses associated with the viscera are ___________.

Answer 38

Unconscious

Question 39

What is this phenomenon when strong visceral sensations rise to the level of conscious perception & provide an example?

Answer 39

Referred Pain:
When the sensations are often felt in unexpected places.

Example:
Strong visceral sensations from the heart will be felt as pain in the left shoulder and left arm.

Question 40

What is the broadly accepted theory of ‘referred pain?’

Answer 40

The visceral sensory fibres from the affected organ enter at the same level of the spinal cord as the somatosensory fibres from the referred pain location.