7. The Automatic Nervous System Flashcards
What are the 3 divisions of the automatic nervous system?
Sympathetic nervous system
Parasympathetic nervous system
Enteric nervous system
What are the functions of the ANS?
Motor system providing control over visceral functions essential to homeostasis
Coordinated cardiovascular resp, digestive, urinary and reproductive functions
Some metabolic functions
Visceral sensory fibres
ANS controls visceral reflexes
What does the ANS extrinsically regulate?
Cardiac muscle
Smooth muscle
Glandular secretions
What is a ganglion?
A congregation of synapses
What is the anatomy of the neurones?
Preganglionic neurones have cell bodies within the CNS that send axons to peripheral ganglia and they synapse to postganglionic neurones where the cells then innervate various target organs
Where are the preganglionic neurones of the sympathetic neurones found?
Found between T1 and L2 of spinal cord
Where are the postganglionic sympathetic neurones found?
Sympathetic chain ganglia
Collateral ganglia
Adrenal medulla
What are the features of the neuroeffector junction?
Postsynaptic nerve terminals different from neuromusuclar junction
No synaptic knobs
Terminal portions branch and form network over surface & may penetrate outer layer
Each branch may have many varicosities
Chains of varicosities pass near to tissue surface
No specialized postsynaptic surface membranes
Receptors all over tissue surface - intra-junctional and extra junctional receptors
What are the general functions of PNS?
Pupillary constriction & eye near-focusing
↑’s secretion form digestive glands (salivary, gastric, duodenal & intestinal glands, pancreas & liver)
↑’s smooth muscle activity in GI tract
↑’s secretion of hormones that promote absorption & utilization of nutrients in peripheral tissues (eg. insulin)
Participates in defecation
Constricts bronchioles
↓’s heart rate & myocardial contractility
participates in sexual arousal & stimulation of sexual gland secretions in both genders
What are the two major receptor subtypes?
Nicotinic receptors and muscarinic receptors
What is meant by the term autonomic tone?
Describes resting spontaneous level of activity in autonomic nerves in absence of stimuli
What is the relationship between blood vessels and sympathetic activity?
constrict with ↑’d sympathetic activity
dilate with ↓’d sympathetic activity
What is the enteric nervous system?
The nervous system to control the GI tract
Where is the enteric nervous system located?
Oesophagus to anus
What are the two plexuses of the enteric nervous system?
Myenteric plexus between circular and longitudinal
Mainly controls GI movements
What are the two plexuses of the enteric nervous system?
Myenteric plexus between circular and longitudinal
Mainly controls GI movements
Submucosal plexus in submucosa
-mainly controls mucosal secretion and local blood flow
What nerves provide extrinsic innervation?
Sympathetic nerves
Parasympathetic nerves
What do the sympathetic nerves do?
Slows down contractions, secretions and blood flow
What do the parasympathetic nerves do?
Speeds things up
Where do sensory nerves from the gut and and walls travel to?
Collateral ganglia
Spinal cord
Brain via vagus
What does extrinsic innervation allow?
GI tract to function independently, modified by CNS and allows fine reflex control
What is the fight or flight response and what mediates it?
A coordinated response involving parasympathetic nerves, sympathetic nerves and adrenal medullae
Hypothalmus
What happens during the fight/flight response?
↑’d heart rate and contractility
↑’d vasoconstriction in skin, gut, kidney, etc
↑’d BP
↓’d vasoconstriction & ↑’d rate & depth of breathing
relaxed accommodation & pupil dilation
↑’d mental alertness (reticular formation threshold lowered)
↓’d sensitivity to pain
↑’d plasma & FFA concentrations
↑’muscle glycolysis
What do baroreceptors do?
Act as short-term buffers to BP fluctuations
What does an acute rise in BP cause?
Increased receptor discharge
What does an acute rise in BP cause?
Increased receptor discharge
Polysynaptic pathways will alter autonomic outflow
Decreased sympathetic activity to arterial blood vessels and decreased TPR
Decreased sympathetic activity to venous blood vessels Decreased venous return to heart and cardiac output
What is the response to a sharp BP fall?
A decreased receptor discharge results in
increased sympathetic activity to heart
decreased parasympathetic activity to heart
increased HR
Increasedd myocardial contractility
increased sympathetic vasoconstriction
Increased sympathetic venoconstriction
