The Autonomic Nervous System Flashcards
What are the functions of the autonomic nervous system?
Concerned with control of internal environment - works together with the endocrine system -Homeostasis
Controls important functions not under voluntary control. ie. autonomous
What are the divisions of the autonomic NS?
Sympathetic – “fight, flight, or fright”
Activated during exercise, excitement, and emergencies
Parasympathetic – “rest and digest”
Concerned with conserving energy
What are the major components of the ANS?
- Spinal outflow
- Cranial sacral outflow= parasympathetic
- Thoraco-lumbar outflow= sympathetic
- Viscera that is innervated
- Hypothalamus, limbic system, brainstem= higher order control centres
What is the enteric nervous system?
Intrinsic collections of neurones within the wall of the digestive tract, and can function independently of the CNS or PNS
Describe the basic organisation of the sympathetic division
- Tissues from T1-L2
- Preganglionic fibers from the lateral gray horn
- Supplies visceral organs and structures of superficial body regions
- Contains more ganglia than the parasympathetic division
Where are the sympathetic trunk ganglia?
Located on both sides of the vertebral column
Linked by short nerves into sympathetic trunks
Joined to ventral rami by white and gray rami communicantes
Fusion of ganglia fewer ganglia than spinal nerves
What are the pre-vertebral ganglia?
Not all sympathetic fibres coming from spinal cord (T1-L2) will synapse with second neurone in sympathetic chain. Some will run through sympathetic chain without synapsing to prevertebral ganglia.
Prevertebral ganglia occur only in abdomen and pelvis
They lie anterior to the vertebral column
Main ganglia include: Coeliac, superior mesenteric, inferior mesenteric, inferior hypogastric ganglia
Describe the chain of events in the sympathetic NS
- Sympathetic fibres at T1 to L2
- White and gray ramus communicantes
- Sympathetic chain
- Synapse with second neurone to viscera
- Some fibres pass straight through to pre-vertebral ganglia
- Aorta
Alpha 1 sympathetic pharmacology
located most smooth muscle in arterioles causing vasoconstriction
Alpha 2 sympathetic pharmacology
located on coronary arteries causing vasodilatation
Beta 1 sympathetic pharmacology
located on cardiac muscle causing increased contractility
Beta 2 sympathetic pharmacology
found in sino-atrial node to increase heart rate, in some smooth muscle in arterioles (esp. skeletal muscle ) causing vasodilation and in smooth muscle of bronchi causing bronchodilation
Describe the cranial-sacral outflow of the parasympathetic division
Cranial outflow
Comes from the brain
Innervates organs of the head, neck, thorax, and abdomen
Sacral outflow
Supplies remaining abdominal and pelvic organs
What are the cranial outflow nerves?
Preganglionic fibers run via: Oculomotor nerve (III) Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X)
Cell bodies located in cranial nerve nuclei in the brain stem
Describe the outflow vis the vagus nerve
Fibers innervate visceral organs of the thorax and abdomen
Stimulates - digestion, reduction in heart rate and blood pressure
Preganglionic cell bodies
Located in dorsal motor nucleus in the medulla
Ganglionic neurons
Confined within the walls of organs being innervated
Describe the sacral outflow of the parasympathetic NS
Emerges from S2-S4
Innervates organs of the pelvis and lower abdomen
Preganglionic cell bodies
Located in visceral motor region of spinal gray matter
Form splanchnic nerves
Pharmacology of the parasympathetic system
Nicotinic and muscarinic receptors
Bind ACh
What are the sensory functions of the ANS neurones?
- Sympathetic and parasympathetic afferents very similar to somatic sensory pathways.
- Mostly free nerve endings in viscera, axons passing to ganglion (dorsal root ganglion or cranial nerve sensory ganglion). 2nd order neuronal cell body found in dorsal grey matter of spinal cord.
Describe the sensory innervation of viscera
- Usually not consciously perceived (except hunger, fullness)
- Visceral reflexes (coughing, vomiting, swallowing etc)
- In pathological conditions may result in pain and nausea- referred pain
Compare somatic and autonomic systems
-Somatic= corticospinal pathways in LMN, One motor neuron extends from the CNS to skeletal muscle
Axons are well myelinated, conduct rapidly
-Autonomic= Chain of two motor neurons
Preganglionic neuron
Postganglionic neuron
Conduction is slower due to thinly or unmyelinated axons
What are the anatomical differences in Sympathetic and Parasympathetic Divisions?
-Arise from different regions of the CNS= S: thoracolumbar, P \: cranio-sacral -Length of postganglionic fibers Sympathetic – long postganglionic fibers Parasympathetic – short postganglionic fibers -Branching of axons Sympathetic axons – highly branched Influences many organs Parasympathetic axons – few branches Localised effect
What are the neurotransmitters released by preganglionic axons?
Acetylcholine for both branches (cholinergic – nicotinic receptors)
What are the neurotransmitters released by postganglionic axons?
Sympathetic – most release noradrenaline (adrenergic)
Parasympathetic – release acetylcholine (muscarinic receptors)
What are the roles of the adrenal medulla in the sympathetic division?
Major organ of the sympathetic nervous system
Secretes great quantities adrenaline (some NA)
Stimulated to secrete by pre-ganglionic sympathetic fibers
How is the adrenal medulla innervated?
- Pre-ganglionic fibres into peripheral nerve through sympathetic chain
- Thoracic splanchnic
- Direct innervation
- Adrenaline and noradrenaline release
What is the Central Control of the ANS?
Control by the brain stem and spinal cord
Reticular formation exerts most direct influence
Medulla oblongata
Periaqueductal gray matter
Control by the hypothalamus and amygdala
Hypothalamus – the main integration center of the ANS
Amygdala – main limbic region for emotions
Control by the cerebral cortex
What are the clinical manifestations of autonomic dysfunction?
- Diabetes
- Dizziness
- Dry mouth/ eyes
- Fatigue
- Gastric disturbance
- Micturition issues
- Incontinence
- Constipation/ diarrhoea
What is Horner’s syndrome?
Miosis (small pupil)
Ptosis (drooping eyelid)
Loss of sweating same side of face
Redness of conjunctiva
May result from interruption of sympathetic fibres centrally (anywhere between hypothalamus and upper thoracic level of spinal cord) or peripherally (cervical sympathetic chain)
Causes include:
Carotid artery dissection, brainstem stroke, syringomyelia
What is syncope?
Vasovagal syncope: simple faint, seen commonly in young people with no underlying illness
Sudden vasodilatation occurs often caused by strong emotion.
Peripheral resistance decreases in arterioles and blood pressure falls. Cardiac rate fails to increase. Vagal stimulation may then occur leading to further bradycardia and to perspiration, increased peristalsis, yawning, nausea, pallor and salivation
What is orthostatic hypotension?
Like vasovagal syncope but brought on by getting up from reclined position or standing still for long period
Often person stands up and then has steady fall in blood pressure but without compensatory rise in HR. Mild staggering or falling may precede loss of consciousness
Describe problems with bladder control
Prime example of autonomic dysfunction.
Common symptom of Multiple sclerosis patients.(75% of MS patients)
Main symptoms are urgency, frequency and urge incontinence.
Main cause is overactivity of detrusor muscle. Involuntary bladder contraction gives rise to feeling of need to void immediately despite bladder volume being low.
What tests are used for abnormality of the ANS?
Pupil reactions
Postural blood pressure response.
By bedside -a fall >30mmhg systolic and >15mmhg diastolic is abnormal.
Variation of HR with deep breathing (sinus arrhythmia).
Lacrimal function
