3.2 Autonomic Nervous System

Question 2

What is the advantage of the two-neuron chain in the autonomic nervous system (rather than the single neuron from CNS to effector in somatic)?

Answer 2

More junctions are possible; greater connectivity

Question 3

Sympathetic pathways consist of a pre- and post-ganglionic neuron. What is the exception to this?

Answer 3

When the preganglionic neuron synapses with the adrenal medulla

Question 4

Describe the length of the pre/post ganglionic fibres in para vs sympathetic

Answer 4

Para: Long pre, short post
Sympa: Short pre, long post

Question 5

What neurotransmitters are released by para/sympathetic neurons?

Answer 5

Para: Ach in both
Sympa: Ach, then noradrenaline

Question 6

Which neurotransmitter do somatic neurons release at their synapse with effector organs?

Answer 6

ACh

Question 7

Which arm of the autonomic nervous system innervates more structures?

Answer 7

Sympathetic

Question 8

How can the sympathetic nervous system cause dilation AND constriction in different structures, despite a single neurotransmitter (e.g. blood vessels vs bronchioles)

Answer 8

Different expression of receptors

Question 9

Describe the responses of the different kinds of alpha and beta receptors to stimulation

Answer 9

Alpha 1/2: smooth muscle contraction

B1: Cardiac muscle contraction

B2/B2: Smooth muscle relaxation

Question 10

Which is the only case where the sympathetic nervous system does NOT use NA? What receptor is involved, and where?

Answer 10

• Sweat glands
• ACh
• Muscarinic receptors

(no sympa. innervation)

Question 11

What receptors does ACh from the para. nervous system bind to?

Answer 11

Muscarinic (M1-M5)

Question 12

Within what vertebral levels are the cell bodies of sympathetic nerves found?

Answer 12

T1-L2 (sympa = together)

Question 13

What are the two kinds of sympathetic ganglia?

Answer 13

• Paravertebral
• Prevertebral

Question 14

All sympa. preganglionic fibres synapse within a paravertebral ganglion in the sympathetic chain, except…

Answer 14

Those that innervate the adrenal glands or the abdomen

Question 15

Describe a sympathetic nerve pathway from pre/post ganglionic through the sympathetic trunk

Answer 15

• Preganglionic fibre arises from lateral horn, and travels out through spinal nerve
• Exits spinal nerve, ad enters sympathetic trunk
• Can travel up, down, or stay at same level
• Synapses on post-synaptic in a ganglion, and heads out to effector through spinal nerve
• OR: Becomes splanchnic nerve -> Purely atonomic nerves that head into abdominal viscera

Question 16

True or false: splanchnic nerves contain autonomic and somatic fibres

Answer 16

• False
• Only autonomic, unlike spinal nerves

Question 17

What can happen to sympathetic fibres after they leave the sympathetic chain?

Answer 17

• Rejoin spinal nerves to innervates sweat glands, erector pili, blood vessels
• Or: become splanchnic nerves, and supply viscera

Question 18

What are the four prevertebral sympathetic ganglia?

Answer 18

• Coeliac
• Aorticorenal
• Superior mesenteric
• Inferior mesenteric

Question 19

How do preganglionic sympathetic fibres reach the prevertebral ganglia?

Answer 19

Through the abdominopelvic splanchnic nerves

Question 20

Which cells within the adrenals do sympathetic fibres innervate?

Answer 20

Chromaffin cells

Question 21

Where does the parasympathetic nervous system arise?

Answer 21

• Brainstem (CNs)
• Sacral, from S2-S4

Question 22

What does the parasympathetic nervous system supply?

Answer 22

Organs of Head, neck, trunk, and external genitalia

Question 23

Do parasympathetic fibres synapse near/far from effectors?

Answer 23

Near (long pre, short post)

Question 24

The filum terminale is an extension of which meningeal layer?

Answer 24

Pia mater

Question 25

Which brain area is considered the "boss" of the autonomic nervous system?

Answer 25

The hypothalamus

Question 26

What is the role of the spinal cord in controlling the autonomic nervous system?

Answer 26

Controlling sympathetic visceral reflexes and parasympathetic visceral reflexes (depending on area of spinal cord)

Question 27

What are some autonomic processes that the hypothalamus mediates?

Answer 27

- Temperature - Sex drive - Hunger - Circadian rhythms

Question 28

Autonomic nervous system maintains physiological parameters within an optimal range by means of...

Answer 28

Feedback loops

Question 29

Where does the solitary nucleus receive input from?

Answer 29

- All chemo/baroreceptors - Visceral sensory input from thorax and adbomen (by CN X, VII, IX)

Question 30

Where does the solitary nucleus send output to (up and down)?

Answer 30

Within brainstem: Para. preganglionic neurons, sympa. control centres, resp. neurons. Up: Hypothalamus, amygdala, thalamus

Question 31

What are the functions of autonomic brainstem nuclei?

Answer 31

- Mediate autonomic reflexes - Control specific autonomic functions - Modulate global autonomic tone

Question 32

Where does the hypothalamus receive input from in terms of autonomic regulation?

Answer 32

- Spinal cord/brainstem nuclei - Limbic system

Question 33

The hypothalamus doesn't just maintain a stable internal environment by modulating our autonomic tone. It also alters our...

Answer 33

Behaviour

Question 34

Is the autonomic nervous system purely driven by REACTIVE feedback loops?

Answer 34

- No; it can also be proactive (e.g. increased ventilation before exercise) - This is in response to higher order thinking

Question 35

What are the two muscles of the iris; which is controlled by which arm of the ANS, and which does what?

Answer 35

- Pupillary sphincter (para., inner, constricts pupil) - Pupillary dilator (sympa., outer, dilates pupil)

Question 36

Which arm of the ANS is involved in near/far vision, and what are the corresponding lens changes

Answer 36

- Near: lens bulges, para. - Far: lens tightened, sympa.

Question 37

Which muscle/ligament attaches to the lenses of the eye and controls near/far vision? What is the relationship between muscle contraction and ligament tension?

Answer 37

- Ciliary muscle - Suspensory ligament - When the muscle contracts, the ligament is loosened (myopia)

Question 38

Which muscle receives sympathetic innervation that keeps the eyelid open when contracted? What larger muscle is it a part of?

Answer 38

Superior TAsal muscle. TAgs along as part of levator palpebrae superioris.

Question 39

What causes Horner's Syndrome? From this, derive the three signs

Answer 39

Caused by lost sympathetic nerve supply to the eye: 1. Drooping eyelid (partial ptosis) 2. Constricted pupil (miosis) 3. Bilateral anhidrosis

Question 40

Describe parasympathetic innervation of the pupil (fully)

Answer 40

- Occulomotor nucleus in brainstem - Synapses in ciliary ganglion - Heads out to muscarinic receptors in pupillary sphincter

Question 41

Describe sympathetic innervation of the pupil (fully)

Answer 41

- First order neuron runs from hypothalamus to upper thoracic region (T1-T6) - Second order neuron runs up sympa. chain to superior cervical ganglion, and synapses - Third order neuron travels with internal carotid artery before entering superior orbital fissure

Question 42

In terms of autonomic innervation, which receptors can be found in the bladder, and where?

Answer 42

- Detrusor: muscarinic (P), and B2 (S) - Internal urethral sphincter: alpha 1 (S)

Question 43

True or false: the internal urethral sphincter has parasympathetic innervation

Answer 43

- False - We simply mediate the amount of sympathetic input (like regenerative braking)

Question 44

Why doesn't everyone piss themselves all the time?

Answer 44

Because we have top-down cortical inhibition of the pontine micturition center, which prevents contraction of the destrusor muscle via local, spinal reflexes.

Question 45

How is a suprapontine lesion likely to influence micturition (assuming it does in some way)?

Answer 45

Hyperreflexia -> loss of top down inhibition

Question 46

How is a suprasacral spinal lesion likely to influence micturition (assuming it does in some way)?

Answer 46

Detrustor-sphincter dyssynergia; detrusor overactivity

Question 47

How is a sacral spinal lesion likely to influence micturition (assuming it does in some way)?

Answer 47

Hypocontractile/acrontractile detrusor (failure of fundamental reflex pathway)