Autonomic nervous system: physiology
Give an example of a cooperative effect of dual innervation
1. Parasympathetic innervation increase salivary serous cell secretion (watery component of saliva) 2. Sympathetic innervation increase salivary mucous cell secretion (mucus component of saliva)
What are some of the actions of the parasympathetic nervous system?
1. decrease in heart rate 2. decrease in pulmonary flow (bronchoconstriction) 3. redirect blood to digestive system & away from skeletal muscles etc 4. penile erection 5. increased glandular secretion (nasal, lacrimal, salivary) 6. increased peristalsis and digestive enzyme activity 7. relaxation of gut sphincters
Give an example of an antagonistic effect of dual innervation
1. exerted through dual innervation of same effector with differences in receptor type • heart rate decreases (parasympathetic) • heart rate increases (sympathetic) 2. exerted because each division innervates different cells of same organ also with different receptor types • pupillary dilator muscle (sympathetic) dilates pupil • constrictor pupillae (parasympathetic) constricts pupil
What are some of the actions of the sympathetic nervous system?
1. increased heart rate, 2. increased pulmonary airflow (bronchodilation) 3. redirection of blood to vital areas e.g. muscles & lungs (& away from intestines, skin etc) 4. inhibits digestive system (decreased peristalsis) 5. increased blood glucose concentration 6. increased metabolism
What neurotransmitter is used in a cholinergic neuron?
Acetylcholine (Ach)
What are the receptors for an adrenergic neurotransmitter?
Alpha receptors Beta receptors
What is the effect of a nicotinic receptor?
Always excitatory
How does the autonomic nervous system control many target organs using dual innervation ?
Antagonistic effects - Oppose each other Cooperative effects - 2 divisions act on slightly different effectors to produce a unified effect
How do nicotinic receptors work?
By opening ligand-gated ion channels
How is the autonomic nervous system influenced by spinal cord reflexes?
Defecation and micturition reflexes integrated in cord, brain can inhibit these responses consciously
How is the autonomic nervous system influenced by the cerebral cortex?
Emotions & sensory experiences
What sort of effect would an a1 alpha receptor have on blood vessels?
Excitatory, the blood vessel become smaller due to contraction of smooth muscle around the vessel.
What sort of effect would a b1 beta receptor have on the heart?
Excitatory, the heart rate would increase.
What is the effect of an a1 alpha receptor?
Generally excitatory
What is the effect of an b1 beta receptor?
Generally excitatory
What is the effect of an a2 alpha receptor?
Generally inhibitory
What is the effect of an b2 beta receptor?
Generally inhibitory
What sort of effect would a b2 beta receptor have on the lungs?
Inhibitory, the bronchioles of the lungs would dilate as the smooth muscle relaxes.
What is the effect of a muscarinic receptor?
May be excitatory (e.g. on smooth muscle or glands), or inhibitory (e.g. on heart)
Which synapses would excrete the neurotransmitter Norepinephrine?
Most post-ganglionic fibres of the sympathetic nervous system.
What are the receptors for a cholinergic neurotransmitter?
Nicotinic receptors Muscarinic receptors
What neurotransmitter is used in a adrenergic neuron?
Norepinephrine (NE)
How is the autonomic nervous system influenced by the midbrain, pons, and medulla oblongata?
Nuclei for cardiac and vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary changes
How is the autonomic nervous system influenced by the hypothalamus?
Nuclei for hunger, thirst, thermoregulation, sex drive
Where are muscarinic receptors found?
On all cardiac muscle, smooth muscle, and gland cells that receive cholinergic innervation
Muscarinic receptors are acted on by Ach from which neurons?
Postganglionic neurons
Nicotinic receptors are acted on by Ach from which neurons?
Preganglionic neurons
Where are nicotinic receptors found?
Somatic Nervous System - at the neuromuscular junction Autonomic Nervous System - in autonomic ganglia
Give an example of autonomic nervous system control in the absence of dual innervation?
Vasoconstriction/vasodialation Strong sympathetic tone (fast action potential) makes smooth muscle contract constricting the diameter of the blood vessel. Weak sympathetic tone (slow action potential) makes smooth muscle relax dilating the diameter of the blood vessel.
How autonomic nervous system control is exerted in the absence of dual innervation?
Without dual innervation, organs are regulated by the frequency of the action potentials, this is known as sympathetic tone.
Which synapses would excrete the neurotransmitter Acetylcholine?
• All pre-ganglionic fibres • Some post-ganglionic fibres (sweat glands and piloerector muscles) • All of the parasympathetic nervous system
