Organisation Of The Autonomic Nervous System - Lecture notes, lecture 12 PDF

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BMedSc Year 1; Module: Neuroscience 1 Lecture 12: Organisation of the Autonomic Nervous System Slide 4 (Autonomic Nervous System – Overview)     

It is involved in the ‘housekeeping’ of the body so it maintains an optimal internal environment – a lot of it is done without conscious thought For example if there is too little oxygen or too much carbon dioxide in the blood, the blood vessels work to counter-act these changes Its sensory input (distension) is taken in by chemoreceptors and osmoreceptors Its motor output goes to the smooth muscle, secretory glands and cardiac muscle, as examples It is autonomous (works on its own): it’s regulated largely through reflexes influenced by higher centres

Slide 5 (Autonomic Nervous System – Overview)      

It is made up of two divisions: the sympathetic nervous system and parasympathetic nervous system; they try to work together in equal measures The sympathetic nervous system is the ‘flight or fright’ system: so it is used for when we prepare for an emergency and uses energy for this ‘preparation’ For example, in the sympathetic nervous system, if we want to run away from a threat, we increase the amount of glucose to certain areas of the body The parasympathetic nervous system is the ‘rest and digest’ system: so it is used for when we want to regulate and maintain normal functions of the body and in this way we save energy, because no extra energy is needed For example, in the parasympathetic nervous system, since we do not need much energy than just maintaining the normal functions of the body, we decrease the amount of glucose Regulation of the autonomic nervous system depends on the co-ordination of these two sub-systems

Examples of Using the Sympathetic and Parasympathetic Nervous System at Particular Target Organs

Parasympathetic NS

Target Organ

Sympathetic Nervous System (What is needed in an emergency)

Decrease heart rate Dilate Constriction Erection Reduced

Heart Blood Vessels Bronchi GIT/Liver Penis Mental Activity

Increase heart rate and contractility Constrict Dilation Reduces and tightens + glucose release Ejaculation Increased

Slide 6 (Autonomic Nervous System – Organisation)     

Since the autonomic nervous system is concerned with getting substances to and from certain areas in the body, we obviously use the central nervous system, and then nerves go straight to the target organ If we are in the sympathetic nervous system, we start in the spinal cord and if we are in the parasympathetic nervous system, we have in the sacral spinal cord of the central nervous system or the brainstem So if we begin at our “starting point”, we then have pre-ganglion fibres – its cell body is in the brainstem or spinal cord, the axon is myelinated and it synapses in the ganglion The autonomic ganglion is a synapse for the pre-ganglion and post-ganglion fibres After a synapse in the ganglion, the post-ganglion fibre moves from its cell body which was in the ganglion and it synapses on its target; its axon is unmyelinated so it is vulnerable to trauma

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Slide 7  

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In a somatic motor fibre (voluntary), in the muscle we would have a sensory neuron entering the spinal cord, either going to inter-neurones or going to effector neurones and releasing Acetylcholine In an autonomic motor fibre (involuntary), in the target organ we would have a sensory neurone entering the spinal cord, either going to inter-neurones or going to effector neurones (here via using the pre-ganglionic fibre, synapse at the autonomic ganglion cell body and leave with a post-ganglionic fibre) and releasing Acetylcholine or Noradrenaline (if this was the heart, for example) again at the target organ Acetylcholine = Ach; Noradrenaline = NA

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Slide 8 (Sympathetic Division)   

Pre-ganglion fibres arise in the lateral horn of T1-L2 of the spinal cord (15 vertebrae) The autonomic (pre-vertebral) ganglia are close to the vertebral column; some of the autonomic ganglia in the sympathetic division are in their own sympathetic chain In the sympathetic division, there are short pre-ganglionic fibres and long post-ganglionic fibres

Slide 9 (Sympathetic Chain)     

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At any vertebra in the spinal cord, we have the posterior/dorsal area (where sensory input will be) and we have the anterior/ventral area (where motor output will be) Remember that just before a sensory neurone enters the spinal cord via its cell body ganglia or just after the motor neurone leaves the spinal cord to reach its destination, they came from/entered a bundle neurones These bundles of neurones are together in what are called rami/branches Therefore the sensory neurone comes through the dorsal ramus and the motor neurone leaves through the ventral ramus These rami are important in the autonomic nervous system because in a reflex, for example, when the pre-ganglionic fibre has left it the spinal cord, it arrives at certain areas called the rami – for example the ventral ramus, the ramus communicans or the white ramus communicans Then the pre-ganglionic fibre can go up or down (see next slide) to get to their ganglion to synapse at and then reach their target organ

Slide 10 (They do not all synapse at the same level)    

So not all sympathetic fibres immediately synapse at the same level (i.e. in the spinal cord) like they normally would in the peripheral or somatic nervous systems Instead, some of the neurones must first ascend the spinal cord and after leaving the spinal cord/sympathetic chain from their normal location, then they can synapse at the prevertebral (autonomic) ganglion This is the same thing for other neurones, but instead they need to first descend Some, however, just ‘pass through’ the spinal cord/sympathetic chain and then synapse a prevertebral ganglion

Slide 11 (Sympathetic Division)  

All pre-ganglionic fibres enter the sympathetic chain, after leaving the spinal cord, via the white rami communicans, at their own level The fate of the ganglion and what is does it now dependent on what level of the spinal cord you are in

If we takes T7 for example,    

If there is an immediate synapse, then the ganglion is at the same level, and the target will be the skin If there is a synapse by ascending the chain, there are 3 cervical regions where the ganglion is (superior, middle and inferior) and the target will be the head and neck region (or the eyes for the sympathetic NS) If there is a synapse by descending the chain, there are lumbar and sacral ganglions and the target will be the reproductive organs If we cross the chain and the ganglion are in the splanchnic nerves (pre-aortic plexus), then the target will be the stomach

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Slide 13 (Sympathetic Division)     

The pre-vertebral ganglion, in particular the pre-aortic plexi, is associated with the branches of the aorta Post-ganglion fibres are distributed to different blood vessels The greater splanchnic nerve (T6-T9) is connected to the coeliac ganglion/coeliac artery which supports the stomach and liver The lesser splanchnic nerve (T9, 10) is connected to the superior mesenteric (artery) which supports the Small and Large Intestine The least splanchnic nerve (T11, 12) is connected to the inferior mesenteric (artery) which supports the lower 2/3rds of the intestine and the rectum

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Slide 14 (Time for a Rest: Parasympathetic Division)    

All to do with the ‘rest and digest’ phase Pre-ganglionic fibres in the parasympathetic division arise in the BRAINSTEM and the SACRAL spinal cord The ganglia in this system are in/close to the target tissue in the parasympathetic system (than near the sympathetic column in the sympathetic system) It is made up of long pre-ganglionic fibres AND short post-ganglionic fibres

Slide 15 (Parasympathetic Division) Here are some examples with specific nuclei in the brain stem  

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The pre-ganglion cell body Edinger-Westphal is involved with Cranial Nerve 3, its ganglion is in the ciliary and the target is the pupillary constrictor, so the narrow can become narrower The superior salvatory cell body is involved with Cranial Nerve 7; its ganglion is in two places: the first is the ptergopalatine which targets the nose and eyes for hay-fever, and the second is the submandibular which targets the glands for salivation The inferior salviatory cell body is involved with Cranial Nerve 9; its ganglion is in the otic and the target is the parotid gland, which is involved with increasing salivation again The dorsal nucleus of X cell body is involved with Cranial Nerve 10 (Vagus Nerve) and its ganglion is in cardiac, pulmonary and enteric organs, which affects areas from the thorax to the abdomen S2-S4 of the sacral cord are involved with the renal and rectal part of the body

Slide 16 (Autonomic Afferents)     

In the sympathetic NS, sensory information goes through the sympathetic ganglion to the dorsal route ganglion In the parasympathetic NS, sensory information goes to the cranial nerve sensory nuclei (mostly), to the dorsal route ganglia to the dorsal horn Axons enter the spinal cord + brainstem via reflexes and these axons continue to higher centres if PAIN is involved Distension, hypoxia, hypercapnia and pH can cause diffusion and non-specific pain Sometimes we can get “referred pain” - for example, a heart attack can affect the C8 dermatome in the skin – organ pain is therefore often misinterpreted as skin pain (since people feel arm pain – it’s connected with the heart [attack] though)

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Slide 18 (Higher Control) Here are examples of higher control in the nervous system and example of their function in the body Spinal Cord

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Reflexes (eg. Peristalsis – two sets of muscles moving food down the gut)

Brainstem

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Cranial Nerve nuclei reflexes (eg. Sensitivity to light/blinking) Reticular formation ‘centres’ – if the body is low on oxygen, there is an increase in breathing capacity

Hypothalamus

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Integration (neural and endocrine)

Limbic System

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Emotion – fear and range (associated with the temporal lobe)

Cerebral Cortex

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Initiation – helps determine real or perceived stress

Slide 19 (Clinical Corrections)     

Chronic Stress can lead to hypertension, ulcers, constipation – autonomic nervous system drugs can be given Autonomic nervous system problems can also cause bladder infections or sexual dysfunction Raynaud’s Syndrome is the paradoxical constriction of peripheral blood vessels – when blood does not flow to the tips of fingers and the nerve frequency decreases, that tissue can die In Horner’s syndrome, there is a deficiency of sympathetic activity which can cause droopy eyelids and red, dry skin In Hirschsprung’s disease (to do with the megacolon), the abdomen cannot relax because there are no nerves present: so there is an increase in faeces, because of an obstruction

Slide 20 (Summary)      

We need a maintenance of an appropriate internal environment Pre-ganglionic (myelinated) fibres arise in the Central Nervous System Post-ganglion (non-myelinated) fibres are supplied to the target The sympathetic system is associated with urgent activities – motor fibres arise from T1-L2 The parasympathetic system is associated with quiet recuperative activity – motor fibres arise from the brainstem and S2-S4 Afferent fibres (sensory) – since they diffuse, they are poorly localised and so patients can poorly describe pain – known as referred pain

Lecture 12: Organisation of the Autonomic Nervous System Diagrams 4

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