structure of the ANS Flashcards
divisions of the nervous system:
what are the 3 step in function of somatic systems?
what are the 3 steps in function of autonomic (visceral) systems?
SOMATIC:
1) Upper motor neuron descends from motor cortex of brain
2) It synapses to lower motor neuron at the spinal cord
3) Lower motor neuron goes on to have its effect on skeletal muscle (through the dorsal root)
AUTONOMIC:
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
what is the enteric nervous system in control of?
the unconscious control of the gut
what are ganglions?
ganglions - a structure containing a number of nerve cell bodies, typically linked by synapses, and often forming a swelling on a nerve fibre.
where do pre-ganglionic fibres originate from?
where do post-ganglionic fibre originate from?
pre-ganglionic fibres originate from the CNS
post-ganglionic fibres originate from autonomic ganglia
where do pre-ganglionic fibres in the sypathetic system start?
where do post-ganglionic fibres in the sympathetic system start?
where do pre-ganglionic fibres in the parasympathetic system start?
where do post-ganglionic fibres in the parasympathetic system start?
what ANS system does the vagus nerve belong to?
what does the vagus nerve supply?
- Vagus nerve is parasympathetic (longer pre-ganglionic fibre and shorter post-synaptic fibre)
- 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
describe what the sympathetic system:
Sympathetic - leaving the organs (short presynaptic ganglion to the paravertebral sympathetic chain) and longer post-ganglion)
- Each sympathetic trunk extends as far as the atlas
- They all fuse with each other in the ganglion impar, which is opposite the coccyx
- There are superior, middle, and inferior cervical ganglion
- The latter often fuses with the T1 ganglion to from the stellate ganglion, that lies on the neck of the fist rib
- internal carotoid (sympathetic) plexus is sympathetic supply to organs in the head
what are the 3 fates of a pre-ganglionic sympathetic neuron after leaving the CNS?
1) Go up and synapse (ascend in the sympathetic chain)
2) Synapse at the same level
3) Go down and synapse (descend into the sympathetic chain)
4) Pass through without synapsing
when do autonomic motor/visceral reflexes occur?
why is this called visceral?
- 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
- It is called visceral, as it unconscious
- 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
visceral afferents and referred pain:
what does visceral pain tend to the follow the path of?
what do visceral reflex afferents follow the path of?
what is referred pain?
when does referred pain occur?
what does this result in?
- Visceral pain afferents tend to follow the path of sympathetic supply
- Visceral reflex afferents follow the path of parasympathetic supply
- Referred pain occurs when we get visceral pain heading back to the CNS
- Referred pain is 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
the target organs of the parasympathetic nervous system and sympathetic nervous system:
- Parasympathetic nervous supply is for rest and digest
- Sympathetic nervous supply is for fight or flight
how does the parasympathetic and sympathetic system affects the:
heart
digestive tract
lungs
urinary bladder
pupil of the eye
male sexual organs
blood vessels
salivary glands
sweat glands
liver
pilomotor
ANS and the eye:
what muscle does the sympathetic nervous system innervate?
what happens when the muscle constricts?
what muscle does the parasympathetic nervous system innervate?
what happens when the muscle contracts?
what structure is responsible for drainage in the eye?
what can drainage be stopped by?
what is the treatment to this?
- The sympathetic nervous system innervates the pupillary dilator muscle in the iris
- When this muscle constricts, It causes mydriasis (opening of the pupil) - d for dilate
- The parasympathetic nervous system innervates the pupillary constrict muscle in the iris
- When this muscle contracts, it causes miosis (closing of the pupil)
- 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
ANS and the urinary bladder:
when the bladder is filling, what control system dominates and what does it cause?
when the bladder is full, what control system dominates and what does it cause?
- When the bladder is filling, sympathetic control predominates
- Relaxation of detrusor muscle
- Contraction of internal sphincter muscle
- When the bladder is full, parasympathetic control predominates
- Contraction of detrusor muscle
- Relaxation of internal sphincter muscle
what is the purpose of variscosities?
- 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 innervation steps of the somatic efferent and parasympathetic 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
- 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
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
what are the 3 pathways of neurotransmitters within the ANS?
Neurotransmitters of the ANS
- 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
- Most post-ganglionic sympathetic neurons release noradrenaline, and some release ACh (e.g sweat glands)
