Autonomic Nervous System

Question 1

What is the role of the ANS?

Answer 1

It regulates all visceral activities in the body, regulating background functions that dont need voluntary action - these are vital to life

Question 2

What do the actions controlled by the ANS aim to do?

Answer 2

Maintain homeostasis - constantly adjust to maintain a constant internal environment
Respond to changes in the environment - perform the appropriate response to avoid harm and facilitate survival

Question 3

How is the ANS still linked to the brain?

Answer 3

Signals from the cortex, especially the limbic system relay to the hypothalamus (integrating control station), and to the ANS via brain stem and spinal cord

Question 4

How are organs innervated by the ANS?

Answer 4

Many organs are innervated by both sympathetic and parasympathetic nervous systems. When this happens, it’s called dual innervation and they work in unison to achieve the appropriate effect on the organ.

Question 5

Which parts of the spinal cord does parasympathetic innervation come from?

Answer 5

Cranial and sacral ie. uppermost and lowermost regions

Question 6

Which parts of the spinal cord does sympathetic innervation come from?

Answer 6

Thoracic and lumbar T1-L3 ie. middle regions

Question 7

How can effector organs not receive dual innervation but still act in sympathetic and parasympathetic ways?

Answer 7

Certain effector organs do not receive any parasympathetic innervation, however when the sympathetic stimulation subsides, the effects fade

Question 8

Describe the organisation of the sympathetic division of the nervous system

Answer 8

The sympathetic division emerges from the thoracolumbar region of the spinal cord. Preganglionic neuron soma are in the lateral horn of grey matter. These fibres exit from the ventral root of the corresponding spinal and synapse in ganglia alongside vertebral column (sympathetic chain). The chain runs the whole length of the column because some nerves go in both directions. The nerves go to the skin and organs.

Question 9

Where do the nerves of the viscera synapse?

Answer 9

They synapse in collateral ganglia and go to viscera and reproductive organs

Question 10

Where are the collateral ganglia found?

Answer 10

AKA prevertebral ganglia. Found in the thorax and abdomen, next to some of the major blood vessels.

Question 11

How do nerves travel from the spinal cord to the skin?

Answer 11

The axons exit the spinal cord at the lateral horn, into the ventral root, emerging as a mixed spinal nerve. The axons then enter the sympathetic trunk ganglia via the white ramus communicans. They synapse in the ganglion, exit via the grey ramus communicans, and go to the skin. They can also run up or down the sympathetic trunk to reach their targets.

Question 12

How do nerves travel from the spinal cord to target organs in the abdomen?

Answer 12

They exit the lateral horn, enter the sympathetic chain via the white ramus, pass through the ganglia, and travel to the collateral ganglia as a splachnic nerve. They synapse in the collateral ganglia or the adrenal meddula. The post ganglionic neurons then travel to the target visceral organs. Plexuses surround the collateral ganglia to diffuse the sympathetic output.

Question 13

Where are the soma of the pre ganglionic neurons of the parasympathetic neurons that emerge from the cranial level of the spinal cord

Answer 13

The pre ganglionic soma of neurons at the cranial level in PSNS are in the 4 nuclei of the cranial nerves in the brainstem.

Question 14

Where are the ganglia of the parasympathetic nervous system?

Answer 14

Near or in the target organs, so the preganglionic neurons are long and myelinated, and the post ganglionic neurons are short and unmyelinated

Question 15

Where are the soma of the pre ganglionic neurons of the parasympathetic neurons that emerge from the sacral region of the spinal cord

Answer 15

In the lateral horn of the spinal horn. They synapse in the ganglia within the walls of the pelvic organs.

Question 16

Describe the neurotransmitters used in the somatic nervous system

Answer 16

Achetylcholine, with nicotinic receptors at the neuromuscular junction

Question 17

Describe the neurotransmitters used in the sympathetic nervous system

Answer 17

Acetylcholine, with nicotinic receptors at the ganglion for the preganglionic neurons. The post ganglionic neurons are adrenergic. On sympathetic stimulation, the adrenal medulla releases adrenaline into the circulation.

Question 18

Describe the neurotransmitters used in the parasympathetic nervous system

Answer 18

Preganglionic neurons use acetylcholine with nicotinic receptors at the ganglion. Post ganglionic neurons are cholinergic but the target organ receptors are muscarinic.

Question 19

What is the purpose of autonomic reflexes?

Answer 19

To maintain homeostasis

Question 20

What is a general reflex arc?

Answer 20

Sensor - registers the change
Sensory neuron - afferent
Integrating centre - usually in spinal cord or medulla
Pre ganglionic axon
Autonomic ganglion
Post ganglionic axon - efferent
Effector - restores change back to ideal level

Question 21

What are the receptors for visceral sensation and what do they sense?

Answer 21

Chemoreceptors - carotid bodies, aortic bodies (blood O2, cO2, pH)
Central chemoreceptors - medulla oblongata (CSF pH)
Baroreceptors - aortic arch, carotid sinuses, large veins, heart right atrium (blood pressure)
Mechano/Thermoreceptors - visceral pain, inflammation, stretch, obstruction)

Question 22

Which pathway do afferent neurons from receptors in reflex arcs travel in?

Answer 22

They travel in the same pathway as sympathetic efferents (spinal nerves), they enter the spinal cord through white rami and dorsal roots, and connect to the efferent branch of the reflex arc via interneurons. They send collaterals to the brain for consciousness of pain

Question 23

Why is it important that the ANS regulates blood pressure?

Answer 23

When we stand up quick to keep blood pressure up

Question 24

Describe the baroreceptor reflex

Answer 24

Blood vessels have a sympathetic tone (constantly constricted). Baroreceptors in aortic arch and carotid sinus keep sympathetic stimulation under control by tonic inhibition. Decreased BP -> less stretch -> less inhibition -> increased SNS output -> increased vasoconstriction. If blood pressure increases, the opposite happens, and also sympathetic stimulation of the heart decreases, as well as PSNS (vagus nerve) activated to slow HR

Question 25

How is the pupil reflex used in diagnostics and clinical settings?

Answer 25

The reflex reveals sensory/motor legions and their location, and also assess brainstem death or inhibition by drugs eg. barbituates. Eyedrops in exams are muscarinic antagonists, inhibiting neurotransmission between PS post ganglionic neuron and muscle, inhibiting dilation. Stimulants like cocaine potentiate noradrenaline (SNS) which leads to dilation of the pupils.

Question 26

How does the sympathetic nervous system induce an acute stress response?

Answer 26

The sympathetic nervous system stimulates the adrenal medulla with acetylcholine via splanchnic nerves. Chromaffin cells release adrenaline into the circulation rather than at a synapse - activating every tissue with adrenergic receptors, with the same effects as nor adrenaline from sympaethic nerve terminals. Adrenaline and noradrenaline act as hormones and neurotransmitters

Question 27

What is dysautonomia?

Answer 27

Autonomic dysfunction, which has devastating effects due to the ANS’ control of vital functions. It is often caused by other conditions such as diabetic neuropathy, alcoholism, autoimmune disease (Guillan-Barre syndrome), MS. Or can be primary. Many causes have unknown cause. Can be SNS and/or PSNS failure/overactivity

Question 28

What is primary autonomic failure?

Answer 28

Mostly chronic involving sympathetic and parasympathetic divisions. The signs and symptoms include an inability to maintain BP when upright (orthostatic hypotension), inability to sweat, constrict pupils, empty bladder and bowels, sexual dysfunction.