Autonomic Nervous System Flashcards
What is the Autonomic Nervous System (ANS)?
Sub-division of the PNS
Not under conscious / voluntary control - involuntary, reflex responses to visceral stimuli
Not very involved with skeletal muscle (as that is more under conscious control), instead it mainly controls cardiac muscle, smooth muscle, internal organs and the skin
Rehulatory system that controls many of the body’s organ systems and homeostatic mechanisms
How does the ANS influence control?
- The hypothalamus in the brain constantly receiving sensory information via the visceral sensory pathway
- Via the afferent limb, the information travels through the PNS to the CNS (eventually to the hypothalamus)
- Hypothalamus then determines the level of response to follow
- Hypothalamus sends information via the CNS to the PNS, down the efferent limb of the ANS
- Motor visceral pathway carries out action via the sympathetic (S) or parasympathetic (P) route
Same tissues or different tissues?
What are the effects of the S and P branches of the ANS?
Which tissues do these branches innervate?
S - ‘Fight or flight’, leads to mobilisation and increased metabolism
P - ‘Rest and digest’, leads to routine maintenance
Often the same tissues, the different branches just have opposing / antagonistic effects
How do the S and P branches affect:
The heart
The stomach
The pupil
S - increases heart rate and contractility, decreases stomach activity / digestion, dilation of the pupil
P - decreases heart rate and contractility, increases stomach activity / digestion, constriction of the pupil
Fill in this diagram about the effects of the S and P branches on different areas of the body:
Do all tissues have an S and P branch innervating it? If not, give an example:
No
e.g. blood vessels, only innervated by sympathetic nerves - as they can both constrict and dilate the blood vessel
There are different receptors receiving the signal, so whilst one receptor type dilates the blood vessel, another constricts
What type of receptors and where are they found; to influence S / P control over heart rate?
Baroreceptors (pressure detector), found in the walls of major arteries, that feed sensory information back to the brain - this is done by their firing rate, the higher their firing rate the higher the BP
Too high BP influences P to decrease heart rate, or too low BP influences S to increase heart rate
This is because the baroreceptors and P are linked, the higher the firing rate of the baroreceptor, the greater the P activity and inhibition of S activity, and vice versa
How often in the information from the ANS being sent back to the brain?
How often is there a change between S or P control?
Information being detected and relayed back to the brain minute by minute
Physiologically, both these systems are permanently shifting
Where do the visceral motor nuclei originate?
Where do the motor neurons travel to / project to?
In the hypothalamus
To the brainstem or spinal cord, where they synapse with autonomic neurons (S and P)
What is a ganglion?
Autonomic neurons generally consist of how many neurons and what are they called?
A nerve cell cluster / group of nerve cell bodies
2 neurons - a pre-ganglionic neuron and a post-ganglionic neuron
What are the lengths and positions of the 2 neurons and ganglion that are part of the P branch of the ANS?
What are the lengths and positions of the 2 neurons and ganglion that are part of the P branch of the ANS?
Generally: long pre-ganglionic fibres, the ganglion is close to or embedded into the effector tissue, and short post-ganglionic fibres that produce the effect
Opposite! Generally: short pre-ganglionic fibres, the ganglion is close to the originating site of the pre-ganglionic neuron, and long post-ganglionic fibres that produce the effect
Many of the pre-ganglionic fibres synapse in the sympathetic trunks located parallel to either side of the spinal cord
Why are their anatomical differences in the lengths of the neurons and positions of the ganglions for the S and P branches?
S responses are often more co-ordinated, whereas a P effect is quite discrete e.g. the P nerve innervating the stomach is works fairly independently to the P nerve innervating the heart
S’s ‘fight or flight’ response requires rapid co-ordination, e.g. almost simulataneous increase in heart rate and blood flow to the brain and limbs, decreased digestion etc.
What is the exception to the 2 neuron arrangement of the ANS?
Adrenal gland - only one nerve to it
Which neurotransmitters are released at each of the S or P synapses? (between the pre- and post-ganglionic neurons, and the post-ganglionic neuron and effector organ)
Why is there a difference in the second set of NTs released by the 2 branches?
S - ACh (acetylecholine), then NA (noradrenaline)
P - ACh, then ACh
So the branches have opposing effects
What happens at the adrenal gland when it is stimulated by the S branch? How is it different to the post-ganglionic neurons stimulating the effector organs?
It secretes a hormone instead of a neurotransmitter - pre-dominantly adrenaline released (and some noradrenaline)
Secreted into the bloodstream, not a synapse
What is the micturition reflex? How is it innervated by the S and P branches?
Involves the bladder - the S and P branches innervate different muscles in the bladder
S - innervates the internal sphincter muscle (causes relaxation)
P - innervates the detrusor muscle (causes contraction), keeps urine retained within the bladder
What other nervous system supplies the internal sphincter muscle?
The SNS (somatic nervous system) - voluntary / conscious control over bladder so we can urinate when we want
What is the process of NT release in the synapse?
- Precursor usually comes from the diet and enters the nerve, where it is enzymatically modified into NTs
- It is packaged into vesicles, waiting for nerve depolarisation
- AP arrives, causing depolarisation and Ca2+ influx
- Exocytosis of the NTs from the vesicles
- NTs binds to the receptors, activating them
- Removal of NT from the synapse via reuptake into glial cells and pre-synaptic knob
Fill in the missing gaps in the diagram:
Why are ACh responses so rapidly produced and lost?
Due to the quick metabolism by acetylcholinesterase
Blocking acetylcholinesterase will cause a build up of acetylcholine in the synapse, leading to over-stimulation of the receptors
Fill in the missing gaps in the diagram:
Why is this more complicated than the ACh synaptic transmission?
Requires multiple steps to produce noradrenaline, tyrosine is aquired from the diet. Noradrenaline is not produced until inside the vesicles
How is adrenaline released from the adrenal gland? (Similar to noradrenaline, but what are the key differences?)
Fill in the missing gaps in the diagram:
Few more steps required to produce adrenaline
Adrenaline released directly into the bloodstream, no need for reuptake soon after
