The Autonomic Nervous System Flashcards
What is the ANS ?
The autonomic nervous system (ANS) is largely involuntary and regulates physiologic processes
Where does the ANS originate?
Just above the spinal cord in a region of the brain stem called the Medulla
What are the two main divisions of the ANS ?
It has two main divisions:
Sympathetic and Parasympathetic. These divisions have opposite effects and work reciprocally
What do all homeostatic behaviours arise from ? and mediated by ?
All homeostatic behaviour arises from neural modulation of organ systems, which is mediated by hypothalamic control of the autonomic and the endocrine system
What do the physiological responses of the body need to be ?
Co-ordinated. The fight and flight response: - Heart pounding; increase in rate of the heartbeat and force of contraction - Breath becomes rapid and shallow - Dry mouth - Sweaty palms - Muscles tense
When does the activity in the Sympathetic Division increase?
- Rest&Digestion to Fight&Flight
This is when the body is under stress so sympathetic activation causes an increased heart rate, the force of contraction, and rate of conduction, allowing for increased cardiac output to supply the body with oxygenated blood
When does the activity in the Parasympathetic Division increase?
- Fight&Flight to Rest&Digestion
The parasympathetic nervous system is responsible for the body’s rest and digestion response when the body is relaxed, resting, or feeding. It basically undoes the work of sympathetic division after a stressful situation. The parasympathetic nervous system decreases respiration and heart rate and increases digestion
What are within the cell bodies and what do they do?
Within the medulla are nerve cell bodies that
spontaneously fire action potentials, e.g.
cell bodies of parasympathetic vagus nerves
and also cells that regulate sympathetic
activity
What is the activity within the ANS regulated by ?
- Sensory receptors in the body that monitor physiological function and respond to mechanical, chemical or thermal stimuli. e.g. baroreceptors, in blood vessels and heart respond to stretching with increased activity and send response to NTS (nucleus
tractus solitarius) in medulla to stimulate parasympathetic (vagal) activity and reduce sympathetic output. - In this way ANS responds to changes in pressure within the cardiovascular system
Explain the Baroreceptor Reflex ?
- Baroreceptors detect changes in arterial pressure
- Signals sent to the medulla of the brain stem
- Heart rate adjusted
What’s one thing that the autonomic regions of medulla receive ?
Inputs from hypothalamus. This is involved, for example, in how the body responds to exercise and thermal stress with changes to cardiac and vascular function
What’s another thing that the autonomic regions of medulla receive ?
Input from higher brain regions such as the cortex. This is involved in body’s response to fear and stress.
Where do the cell bodies of the two divisions of the ANS originate ?
- Thoracic and lumbar regions for sympathetic pre-ganglionic
fibres - Medulla and Sacral regions for the parasympathetic pre-ganglionic fibres
Where is the location of the autonomic ganglia in the Sympathetic chain located ?
- In close proximity to the spinal cord and the Celiac and
Mesenteric ganglion for
pathways innervating GI
tract and reproductive
organs - Pre-ganglionic fibres are generally short
Where is the location of the autonomic ganglia in the Parasympathetic division located ?
- The ganglia lie
close to the target
tissues so pre-ganglionic fibres are long and post-
ganglionic fibres are short.
What are some of the main effects of the Parasympathetic division ?
- constricts pupils
- increases saliva production
- reduces the heart rate
- constricts bronchia
- stimulates the activity of the digestive organs
- stimulates the activity of the pancreas
- stimulates the gall bladder
- constricts urinary bladder
- stimulates erection of genitals of man and woman
What are some of the main effects of the Sympathetic division ?
- dilates pupils
- inhibits saliva production
- dilates bronchia
- rises the heart rate
- inhibits the activity of the digestive organs
- inhibits the activity of the pancreas
- inhibits the gallbladder
- stimulates the adrenal medulla to release adrenaline and noradrenaline
- relaxes urinary bladder
- stimulates orgasm in genitals of man and woman
What is the response to direct excitation of the adrenal medulla by sympathetic pre-ganglionic neurons ?
The adrenal medulla secretes adrenaline in the blood stream. Circulating adrenaline acts on the same receptors as noradrenaline
So, what is the sympathetic response caused by ?
Noradrenaline released at synapses acting upon receptors at the synapse, combined with the actions of adrenaline
What are the receptors for adrenaline and noradrenaline?
- Adrenoreceptors, which are a class of GPCRs
- α1a, α1b, α1d
- α2a, α2b, α2c
- β1, β2, β3
What effect does the β1 receptor have on the heart ?
- Increase in rate and force leading to increased
cardiac output and oxygen consumption
What effect does the α1 receptor have on the blood vessels ?
Constriction of vascular smooth muscle
What effects does the β2 receptor have in the skeletal muscle ?
Relaxation of vascular smooth muscle
What effect does the β2 receptor have on the bronchi?
Relaxation smooth muscle of air ways
What effect do alpha 1 and beta 2 receptors in the liver ?
- Glycogenolysis
- Gluconeogenesis
How do we target these receptors pharmacologically for therapeutic benefit?
- Noradrenaline
- Adrenaline
- Isoprenaline
- Salbutamol
Beside Asthma, what else can salbutamol be used as a treatment for ?
- Treatment of premature labour
- Relaxes the muscles in the uterus and stops contractions due to labour during this stage of pregnancy
What do adrenergic agonist increase ? and used to treat?
- Increase heart rate and force, and increase peripheral vascular resistance
- Used to treat shock and anaphylactic shock
What is Propranolol commonly used for ?
Commonly used ‘β blocker’ used to prevent feeling of heart pounding when anxious and also used to treat hypertension
What are the side effects of Propranolol ?
Side effects include
bronchoconstriction and hence not recommended for asthmatics
What is the advantage of Atenolol ?
Atenolol has the advantage of being selective for β1
What does atenolol reduce in regards to heart rate and arterial pressure ?
Reduces the effect of exercise
and excitement on heart rate and arterial pressure
Where are catecholamine neurotransmitters also found in?
Catecholamine neurotransmitters are
also in the CNS
Drugs targeting noradrenergic transmission in the periphery to treat high blood pressure can have undesirable effects in? and cause ?
the CNS, and cause depression
What are some side effects of anti-depressants ?
Raising blood pressure and causing hypertension
