Lecture 5 : The Autonomic Nervous System Flashcards
Tuesday 14th January 2025
Is the autonomic nervous system the involuntary system?
Yes, under unconscious control
What are the functions of the autonomic nervous system?
- Contraction/ relaxation of smooth muscle (heart)
- Exocrine and endocrine secretion
- Control of the heartbeat
- Steps in intermediary metabolism
Does the autonomic nervous system have an additional synapse to the somatic nervous system?
Yes
What are the 2 types of neurone found in the autonomic nervous system?
Preganglionic neuron (CNS → Autonomic Ganglion)
Postganglionic neuron (Ganglion → Effector organ)
Where does the additional synapse occur?
Occurs in an autonomic ganglion, where the preganglionic neuron synapses with the postganglionic neuron.
Is the autonomic ganglion a cluster of neuronal cell bodies?
Yes
What do neruones in an autonominc ganglion have?
Dendrites. However, those in a sensory ganglion are unipolar and so only have an axon
Is conduction in the autonomic nervous system a simple relay?
No, integration occurs
Do autonomic ganglion contain many postganglionic cell bodies?
Yes
Is the adrenal medulla a special case with the sympathetic nervous system, as there’s no post ganglionic neurone?
- Yes. Instead, the preganglionic neuron synapses directly on chromaffin cells in the adrenal medulla.
- Chromaffin cells function like postganglionic neurons but release hormones (mainly epinephrine) into the blood, not to a specific organ
- This allows for a fats and widespread ‘fight or flight’ response
What are the 2 branches of the autonomic nervous system?
Sympathetic and parasympathetic
What is the preganglionic transmitter in the sympathetic branch?
acetylcholine
What is the postganglionic transmitter in the sympathetic branch?
noradrenaline
What is a varicosity?
A varicosity is a swelling or bulge along the axon of a postganglionic neuron.
Unlike a traditional synapse, varicosities are spread out along the axon and release neurotransmitters over a wider area.
This allows for diffuse communication with smooth muscle, cardiac muscle, or glands — the typical autonomic targets.
Why is the use of varicosities by the autonomic nervous system important?
This setup is great for modulating large areas, like blood vessels or the gut wall, where precise point-to-point control isn’t necessary.
It also helps explain how autonomic control is slower and more widespread than somatic motor control (which uses neuromuscular junctions).
Where in the spinal cord is the pre ganglionic neurone of the synpathetic nervous system found?
In the lateral horn
Where in the spinal cord is the pre ganglionic neurone of the parasynpathetic nervous system found?
Brainstem
What is the function of the sympathetic nervous system?
Activates the body during stress (e.g., increases heart rate, dilates pupils, inhibits digestion).
What is the preganglionic transmitter in the parasympathetic nervous system?
acetylcholine
What is the postganglionic transmitter in the parasympathetic nervous system?
acetylcholine
What are the differences and similarities between receptors in the sympathetic and parasympathetic nervous system?
- Preganglionic neurones both release acetylcholine
-The first synapse (at the autonomic ganglion) uses nicotinic acetylcholine (ACh) receptors in both systems.
- They both have different post-ganglionic neurotransmitters. Sympathetic system: Releases noradrenaline (norepinephrine) at the target organ, which binds to α (alpha) and β (beta) adrenoceptors in the target organs (e.g., heart, lungs, muscles). Whilst Parasympathetic system: Releases acetylcholine (ACh) at the target organ, which binds to muscarinic ACh receptors.
What are some examples of channel-linked receptors (ionotropic)?
Nitotinic Ach receptor
What is an example of a G-protein coupled receptor? (metabotropic)
Muscarininc Ach receptor
What is an example of a kinase-linked receptor?
Insulin receptor
What is an example of a receptor linked to gene transcription? (nuclear receptor)
Oestrogen receptor
What is the function of the autonomic nervous sytem?
Rest and digest (satiation and repose)
Is it true that the parasympathetic and sympathetic nervous systems sometimes have opposing actions?
Yes, but not all the time
What happens to the eyes in the sympathetic nervous system?
Pupils dilate and the ciliary muscles relax
What happens to the salivary glands in the sympathetic nervous system?
They secrete more saliva
What happens to the sweat glands in the sympathetic nervous system?
They secrete more sweat
What happens to the hair follicles in the sympathetic nervous system?
They undergo piloerection (stand up)
What happens to the heart in the sympathetic nervous system?
It increases in rate and force
What happens to the hair follicles in the sympathetic nervous system?
What happens to the Layrnx, trachea, bronchi and lungs in the sympathetic nervous system?
little effect
What happens to the Oesphagus, stomach, intestines in the sympathetic nervous system?
They decrease their motility and constrict their sphincters
What happens to the liver in the sympathetic nervous system?
increase glycogenolysis, secrete more glucose into the bloodstream
What happens to the kidney in the sympathetic nervous system?
Secretes resin
What happens to the blood vessels in the sympathetic nervous system?
constrict (except in muscles) to redirect blood to where it’s needed the most
What happens to the reproductive organs in the sympathetic nervous system?
They undergo ejaculation
What are the 2 main outflows of the parasympathetic nervous system?
The cranial outflow and the sacral outflow
Describe the cranial outflow
- Originates from the brainstem and includes cranial nerves.
- Controls head and upper body
Describe the sacral outflow
- Originates from the sacral region of the spinal cord.
- Controls the lower body i.e the bladder
What is the vagus nerve
- The most important nerve of the parasympathetic system.
- Extends from the brainstem and innervates many organs: Heart, lungs, etc
What happens to the eye in the parasympathetic nervous system?
- pupil constricts and ciliary muscle constricts
What happens to the salivary glands in the parasympathetic nervous system?
- Secretes saliva as normal
What happens to the sweat glands and the hair muscles in the parasympathetic nervous system?
There is no effect
What happens to the heart in the parasympathetic nervous system?
Decreases in rate
What happens to the Layrnx, trachea, bronchi and lung in the parasympathetic nervous system?
constriction, increase secretion
What happens to the oesophagus, stomach and intestines in the parasympathetic nervous system?
increase motility, relax sphincters, increase secretion
Is there any effect on the liver, kidney, or blood vessels in the parasympathetic nervous system?
No
What is the effect of the parasympathetic nervous system on the reproductive organs?
Erection
Does the parasympathetic nervous system have shorter post-ganglionic neurones than the sympathetic nervous system?
Yes
Are both the sympathetic and parasympathetic systems active at all times?
Yes
What is autonomic tone…
The idea that most tissues receive a basal level of autonomic activity at all times
What reflexes is the autonomic system controlled by?
Visceral reflexes
Describe the control of the autonomic nervous system
Autonomic (visceral) reflexes
Sensory fibres (visceral afferents)
l
Interneurons (in neural circuits in hypothalamus,
brainstem/spinal cord)
l
Sympathetic and parasymapathetic pre/postganglionic
neurones
l
Effector organ i.e. eye, heart etc.
Give some examples of autonomic reflexes
- Baroreceptor reflex
- Lung inflation reflex
- Salivary
- Vomiting
- Defecation
- Micturition
- Defence reflex (fight or flight response)
- All of these reflexes result in: Increase heart rate, cardiac output and blood pressure, increased blood flow to muscles
What controls autonomic reflexes?
The hypothalmus
Which systems control the eye?
Both the sympathetic and parasympathetic nervous systems
What system controls the pupillary light reflex?
Parasympathetic
Nervous system
What is the pupillary light reflex
- The pupillary light reflex is an involuntary reflex that controls the size of the pupil in response to light.
- It helps regulate the amount of light entering the eye to protect the retina and optimize vision.
What is Presbyopia
loss of near vision as lens becomes less elastic
Does the Micturition
Reflex include conscious control?
No
What is the Micturition
Reflex
It’s the reflex that controls the emptying of the bladder.
What are some examples of when things go wrong with the autonomic nervous system?
dizziness, fatigue, blackouts, postural hypotension, Neurodegenerative disease, Horner’s syndrome
What is Horner syndrome
Horner syndrome is caused by damage to the sympathetic nerve pathway that runs from the brain to the eye and face. This disruption can occur at any point along its three-neuron route, leading to characteristic symptoms on the affected side.
