3.2 Autonomic Nervous System Flashcards
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)?
More junctions are possible; greater connectivity
Sympathetic pathways consist of a pre- and post-ganglionic neuron. What is the exception to this?
When the preganglionic neuron synapses with the adrenal medulla
Describe the length of the pre/post ganglionic fibres in para vs sympathetic
Para: Long pre, short post
Sympa: Short pre, long post
What neurotransmitters are released by para/sympathetic neurons?
Para: Ach in both
Sympa: Ach, then noradrenaline
Which neurotransmitter do somatic neurons release at their synapse with effector organs?
ACh
Which arm of the autonomic nervous system innervates more structures?
Sympathetic
How can the sympathetic nervous system cause dilation AND constriction in different structures, despite a single neurotransmitter (e.g. blood vessels vs bronchioles)
Different expression of receptors
Describe the responses of the different kinds of alpha and beta receptors to stimulation
Alpha 1/2: smooth muscle contraction
B1: Cardiac muscle contraction
B2/B2: Smooth muscle relaxation
Which is the only case where the sympathetic nervous system does NOT use NA? What receptor is involved, and where?
- Sweat glands
- ACh
- Muscarinic receptors
(no sympa. innervation)
What receptors does ACh from the para. nervous system bind to?
Muscarinic (M1-M5)
Within what vertebral levels are the cell bodies of sympathetic nerves found?
T1-L2 (sympa = together)
What are the two kinds of sympathetic ganglia?
- Paravertebral
- Prevertebral
All sympa. preganglionic fibres synapse within a paravertebral ganglion in the sympathetic chain, except…
Those that innervate the adrenal glands or the abdomen
Describe a sympathetic nerve pathway from pre/post ganglionic through the sympathetic trunk
- 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
True or false: splanchnic nerves contain autonomic and somatic fibres
- False
- Only autonomic, unlike spinal nerves
What can happen to sympathetic fibres after they leave the sympathetic chain?
- Rejoin spinal nerves to innervates sweat glands, erector pili, blood vessels
- Or: become splanchnic nerves, and supply viscera
What are the four prevertebral sympathetic ganglia?
- Coeliac
- Aorticorenal
- Superior mesenteric
- Inferior mesenteric
How do preganglionic sympathetic fibres reach the prevertebral ganglia?
Through the abdominopelvic splanchnic nerves
Which cells within the adrenals do sympathetic fibres innervate?
Chromaffin cells
Where does the parasympathetic nervous system arise?
- Brainstem (CNs)
- Sacral, from S2-S4
What does the parasympathetic nervous system supply?
Organs of Head, neck, trunk, and external genitalia
Do parasympathetic fibres synapse near/far from effectors?
Near (long pre, short post)
The filum terminale is an extension of which meningeal layer?
Pia mater
Which brain area is considered the “boss” of the autonomic nervous system?
The hypothalamus
What is the role of the spinal cord in controlling the autonomic nervous system?
Controlling sympathetic visceral reflexes and parasympathetic visceral reflexes (depending on area of spinal cord)
What are some autonomic processes that the hypothalamus mediates?
- Temperature
- Sex drive
- Hunger
- Circadian rhythms
Autonomic nervous system maintains physiological parameters within an optimal range by means of…
Feedback loops
Where does the solitary nucleus receive input from?
- All chemo/baroreceptors
- Visceral sensory input from thorax and adbomen (by CN X, VII, IX)
Where does the solitary nucleus send output to (up and down)?
Within brainstem: Para. preganglionic neurons, sympa. control centres, resp. neurons.
Up: Hypothalamus, amygdala, thalamus
What are the functions of autonomic brainstem nuclei?
- Mediate autonomic reflexes
- Control specific autonomic functions
- Modulate global autonomic tone
Where does the hypothalamus receive input from in terms of autonomic regulation?
- Spinal cord/brainstem nuclei
- Limbic system
The hypothalamus doesn’t just maintain a stable internal environment by modulating our autonomic tone. It also alters our…
Behaviour
Is the autonomic nervous system purely driven by REACTIVE feedback loops?
- No; it can also be proactive (e.g. increased ventilation before exercise)
- This is in response to higher order thinking
What are the two muscles of the iris; which is controlled by which arm of the ANS, and which does what?
- Pupillary sphincter (para., inner, constricts pupil)
- Pupillary dilator (sympa., outer, dilates pupil)
Which arm of the ANS is involved in near/far vision, and what are the corresponding lens changes
- Near: lens bulges, para.
- Far: lens tightened, sympa.
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?
- Ciliary muscle
- Suspensory ligament
- When the muscle contracts, the ligament is loosened (myopia)
Which muscle receives sympathetic innervation that keeps the eyelid open when contracted? What larger muscle is it a part of?
Superior TAsal muscle. TAgs along as part of levator palpebrae superioris.
What causes Horner’s Syndrome? From this, derive the three signs
Caused by lost sympathetic nerve supply to the eye:
- Drooping eyelid (partial ptosis)
- Constricted pupil (miosis)
- Bilateral anhidrosis
Describe parasympathetic innervation of the pupil (fully)
- Occulomotor nucleus in brainstem
- Synapses in ciliary ganglion
- Heads out to muscarinic receptors in pupillary sphincter
Describe sympathetic innervation of the pupil (fully)
- 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
In terms of autonomic innervation, which receptors can be found in the bladder, and where?
- Detrusor: muscarinic (P), and B2 (S)
- Internal urethral sphincter: alpha 1 (S)
True or false: the internal urethral sphincter has parasympathetic innervation
- False
- We simply mediate the amount of sympathetic input (like regenerative braking)
Why doesn’t everyone piss themselves all the time?
Because we have top-down cortical inhibition of the pontine micturition center, which prevents contraction of the destrusor muscle via local, spinal reflexes.
How is a suprapontine lesion likely to influence micturition (assuming it does in some way)?
Hyperreflexia -> loss of top down inhibition
How is a suprasacral spinal lesion likely to influence micturition (assuming it does in some way)?
Detrustor-sphincter dyssynergia; detrusor overactivity
How is a sacral spinal lesion likely to influence micturition (assuming it does in some way)?
Hypocontractile/acrontractile detrusor (failure of fundamental reflex pathway)
