Structure of the ANS Flashcards
What are the three steps in function of a somatic system
Steps in the function of somatic systems
1) Upper motor neuron descends from motor cortex of brain
2) It synapses to lower motor neuron int eh brain stem or spinal cord
3) Lower motor neuron goes on to have its effect on skeletal muscle
What are the 3 steps in function of autonomic (visceral) systems
- Steps in the function of autonomic (visceral) systems
1) Hypothalamus sends neurons down to nuclei in the brainstem or spinal cord
2) From the spinal cord, there is a pre-ganglionic neuron, that synapses in a ganglion
3) A post-synaptic ganglion then goes to an effector
Where do pre-ganglionic fibres of the ANS originate from?
Pre-ganglionic fibres originate from the CNS
Where do post-ganglionic fibres of the ANS originate from
Post-ganglionic fibres of the ANS originate from autonomic ganglia
What is the length of pre and post- ganglionic fibres in the sympathetic nervous system
The sympathetic nervous system has short pre-ganglionic and long post-ganglionic neurons
What is the length of pre and post ganglionic fibres in the parasympathetic nevous system
The parasympathetic nervous system has long pre ganglionic and short post-ganglionic neurons
Where do Sympathetic pre-ganglionic fibres originate
thoracolumbar origin
Where do Sympathetic post-ganglionic fibres originate
paravertebral chain/prevertebral ganglia origin
Where do parasympathetic pre-ganglionic fibres orginate
brainstem and sacral spinal cord (craniosacral origin)
Where do parasympathetic pre-ganglionic fibres originate
origin in or near the target organ
What does the vagus nerve supply? what does this include?
The vagus nerve (cranial nerve 10) supplies pre-ganglionic innervation everything outside the neck, all the way down to 2/3rds of the way around the transverse colon
This includes the heart, lungs and upper GI tract
What happens to the pre-ganglionic neurons of the sympathetic nervous system?
Pre-ganglionic fibres of the sympathetic nervous system emerge, and very quickly enter the paravertebral chain of connected ganglion
Here, they synapse with post-ganglionic fibres, which will go on to have their effects on viscera
What structures connect ganglia to spinal nerves?
What can happen to nerves emerge that emerge anteriorly?
Rami communicans connect ganglia to spinal nerves
Nerves that emerge anteriorly can go to synapse on pre-vertebral ganglia
Where does each sympathetic trunk extends as far as?
As the atlas
Where do all the sympathetic trunks fuse with each other
They all fuse with each other in the ganglion impar, which is opposite the coccyx
What are the 3 different types of cervical ganglion?
- Superior
- Middle
- Inferior
What does the inferior cervical ganglion Fuse?
It fuses with the T1 ganglion to from the stellate ganglion, that lies on the neck of the first rib
What are the options in what a pre-ganglionic sympathetic neuron does when it leaves the CNS?
Options in what a pre-ganglionic sympathetic neuron does:
1) Go up and synapse
* It can leave the CNS and enter the sympathetic chain via white rami communicans
* It can then ascend to the sympathetic chain towards the cervical ganglia
* In cervical region, it can synapse and become a post-ganglionic neuron
2) Synapse at the same level
* A pre-synaptic neuron can leave the CNS and go into the synaptic chain and synapse at the level it comes out
* E.g Comes out in T2 of the spinal cord and synapses in T2 ganglion, and the post-synaptic neuron will pass back into the spinal nerve, then off into its distribution of T2 (around the upper thorax and armpit)
* There are cardiopulmonary splanchnic nerves controlling the heart and lungs
* These tend to come out in the cervical chain, an come down outside of its chain
3) Go down and synapse
* Enters the synaptic chain, and instead of synapsing, we descend to a lower level
* E.g coming out of T12, descending through the sympathetic chain to synapse in sympathetic ganglion around L4, then traveling back out of the L4 neuron to supply sweat glands
4) Pass through without synapsing
* Pre-synaptic neuron leaves the CNS, and enters the sympathetic chain, but doesn’t synapse
* Instead, we pass straight out of he front of the sympathetic ganglion in a thoracic splanchnic nerve
* We then come down to the abdomen, where we synapse onto a preaortic or prevertebral ganglion
* The post-ganglionic neuron then goes out to supply the gut tube
How do autonomic visceral reflexes occur?
Autonomic visceral reflexes occur when visceral afferents travel back to the CNS carrying information in order to initiate a response e.g heart rate and blood pH
Why is called visceral?
As it is unconscious
How do autonomic motor reflexes occur?
In autonomic motor reflexes, neurons will follow back along their path of parasympathetic innervation
E.g upper part of gut tube, sensory afferents will travel back along the same direction the vagus nerve came in
What do visceral pain afferents follow vs visceral reflex afferents?
Visceral pain afferents tend to follow the path of sympathetic supply
Whereas visceral reflex afferents follow the path of parasympathetic supply
When does referred pain occur?
Referred pain occurs when we get visceral pain heading back to the CNS
What is referred pain?
when our visceral pain afferent synapses onto the same second order sensor neurone as a somatic afferent. This results in pain being felt in the skin
e.g visceral pain being felt as somatic pain in the skin due to referred pain
What do the parasympathetic and sympathetic nerves innervate?
- Pupils
- Salivary glands
- Heart
- Bronchi of lungs
- Liver
- Stomach/small intestine
- Large intestine/rectum
- Bladder
- genitals
What is the parasympathetic nervous system for?
Rest and digest
What is the sympathetic nervous system for?
Fight or flight
What effects do parasympathetic and sympathetic innervation have on heart tissue?
Parasympathetic: Decrease heart rate
Sympathetic: Increase heart rate and force of contraction
What effects do parasympathetic and sympathetic innervation have on digestive tract?
Parasympathetic: Increase motility and secretion
Sympathetic: Decrease motility and secretion
What effects do parasympathetic and sympathetic innervation have on lungs?
Parasympathetic: Bronchoconstriction
Sympathetic: Bronchodilation
What effects do parasympathetic and sympathetic innervation have on Urinary Bladder?
Parasympathetic: Release of urine
Sympathetic: Urinary retention
What effects do parasympathetic and sympathetic innervation have on Pupil of the eye?
Parasympathetic: Constricts
Sympathetic: Dilates
What effects do parasympathetic and sympathetic innervation have on Male sexual organs?
Parasympathetic: Erection
Sympathetic: Ejaculation
What effects do parasympathetic and sympathetic innervation have on Blood Vessels?
Parasympathetic: No effect
Sympathetic: Constriction
What effects do parasympathetic and sympathetic innervation have on salivary glands?
Parasympathetic & Sympathetic: increased secretion
What effects do parasympathetic and sympathetic innervation have on sweat glands?
Parasympathetic: No effect
Sympathetic: Increased secretion
What effects do parasympathetic and sympathetic innervation have on the liver?
Parasympathetic: No effect
Sympathetic: Glycogenolysis and Gluconeogenesis
What effects do parasympathetic and sympathetic innervation have on the pilomotor?
Parasympathetic: No effect
Sympathetic: Piloerecrection
What is the sympathetic innervation in the eye
- The sympathetic nervous system innervates the pupillary dilator muscle in the iris
- When this muscle constricts it causes mydriasis (opening of the pupil)
What are the parasympathetic innervation in the eye?
The parasympathetic nervous system innervates the pupillary constrict muscle in the iris
When this muscle contracts, it causes miosis (closing of the pupil)
What regions are responsible for drainage in the eye? How can this be stopped and treated?
Canals of Schlemm are responsible for drainage in the eye
Drainage can be stopped by overreactive dilator muscles
To treat this, stimulating the eye with sympathetic antagonists can prevent the problem
What part of the ANS predominates when the bladder is fiiling?
- sympathetic control predominates
- Relaxation of detrusor muscle
- Contraction of internal sphincter muscle
What part of the ANS predominates when the bladder is full?
When the bladder is full, parasympathetic control predominates
Contraction of detrusor muscle
Relaxation of internal sphincter muscle
What do autonomic reflex arcs exist for
Visceral control
What explains referred pain
Path of afferent fibres can explain referred pain
Where do varicosities exist in the ANS? What occurs here?
Chain like networks of varicosities exist where neurotransmitters are released onto the surface of smooth muscle cells
Here, there is synapse between post-ganglionic fibres and target tissues
Describe the 3 steps in the neuron network in the somatic efferent system
In the somatic efferent system:
1) a single neuron extends from the CNS that synapses on a skeletal muscle fibre
2) This acts on a Nicotinic ACh receptor
3) This causes the contraction of the muscle
What is unique about the stimulation of the adrenal medulla in the sympathetic system?
Stimulation of the adrenal medulla is done by a long pre-ganglionic fibre that releases ACh, which stimulates release of adrenaline into circulation, which travels around the body and effects tissues
Describe the 3 steps in the neuron network in the parasympathetic system?
1) Pre-ganglionic fibres release ACh as a NT
2) This binds to ACh receptor on the postganglionic cell, causing depolarisation and an action potential to go down the post-ganglionic fibre
3) Post-ganglionic fibres also release ACh as a NT onto the target organ, which acts on muscarinic ACh receptors
Where do pre-ganglionic fibres synapse on the adrenal medulla?
On the adrenal medulla, sympathetic fibres synapse on chromaffin cells
What do chromaffin cells release?
Chromaffin cells release adrenaline and noradrenaline into systemic circulation
What pre and post-ganglionic neurotransmitters are used in the ANS? What receptors do they act on?
All pre-ganglionic neurons in the parasympathetic and sympathetic nervous system release ACh, which acts on nicotinic receptors
All post-ganglionic parasympathetic neurons release ACh, which acts on muscarinic receptors
