Lecture 30 Flashcards
What are the major differences between the somatic and autonomic efferent pathways?
The somatic efferent pathways have a single neuron between the CNS and the effector, is always excitatory and only innervates skeletal muscle.
The autonomic efferent pathways instead have two neurons between the CNS and the effector, can be excitatory or inhibitory and innervates smooth and cardiac muscle, glands and the gastrointestinal tract neurons.
What does autonomic control act to maintain and what two opposing divisions does it use to do this?
The autonomic system acts to maintain homeostasis and does so by using the sympathetic (stimulating) and parasympathetic (restfulness) divisions to do so.
Where do the parasympathetic and sympathetic pre synaptic neurons emerge from and where are their ganglia relatively?
The sympathetic pre ganglionic neurons emerge from the thoracolumbar region (from T1 to L2) and have their ganglia in the sympathetic chain ganglia, which is located relatively close to the pre synaptic neurons.
The parasympathetic pre ganglionic neurons emerge from the craniosacral regions (sacrum and cranium ) and have their ganglia near or in the effector organs.
What are cholinergic and adrenergic neurons?
cholinergic neurons release ACh while adrenergic neurons release norepinephrine.
Describe the general structure of the two sympathetic neurons.
The preganglionic neuron is short and myelinated and releases ACh to nicotinic cholinergic receptors, the post ganglionic neuron is typically unmyelinated and usually releases norepinephrine which binds with alpha or beta adrenergic receptors but can sometimes (mainly in the skin e.g sweat glands or hair) release acetylcholine which will bind with muscarinic receptors.
Describe the general structure of the parasympaphetic neurons.
A cholinergic preganglionic neuron which is long and myelinated releases acetylcholine which binds with nicotinic cholinergic receptors on the postganglionic neuron, this second neuron is typically unmyelinated and will always release acetylcholine to muscarinic cholinergic receptors.
What are the ionotropic and metabotropic receptors? What seperates them?
Ionotropic receptors contain an ion channel, e.g the nicotinic cholinergic receptors, these will lead to depolarisation and hence excitation.
Metabotropic receptors are ones which are linked to messengers within the cell e.g the muscarinic cholinergic or alpha and beta adrenergic receptors, these can lead to depolarisation or hyperpolarisation and as such can be either excitatory or inhibitory.
What are the main effects of the parasympathetic and sympathetic systems?
The sympathetic is the fight or flight system, it prepares us for stress and effects include: increased heart rate and pupil size, contriction of blood vessels to allow more blood for muscles and decreases salivation and gastric motility.
The parasympathetic system is our rest and digest system and prepares us for rest. Effects include: decreased heart rate and pupil size and increased gastric motility and salivation.
Why does the sympathetic system decrease gastric motility and salivation?
Under situations where the sympathetic system is at full force all efforts need to be on surviving, hence our bodies don’t need to focus on tasks such as digestion or eating.
What parts of our body do not undergo dual innervation? What does this mean?
Our sweat glands, blood vessels, hairs and adrenal medulla are not dual innervated unlike most parts of our body. This means they are only controlled by the sympathetic division of our autonomic efferent system.
How does the sympathetic system regulate the effects on parts which are not dual innervated?
They are regulated by the amount of signal received, more signal means a stronger response.
What is weird about how the adrenal glands are activated? What does the adrenal gland do?
Our adrenal glands are innervated by the preganglionic neuron, there is no postganglionic neuron in this case. It acts to secrete epinephrine and norepinephrine into the blood as hormones, which will bind to the same adrenergic receptor types and activate cells more generally.
Where are the main centers for autonomic action?
The autonomic centers in the cerebral cortex and hypothalamus.
What role does the autonomic system play in our emotions? How can we attempt to control the autonomic system voluntarily?
The two divisions can control our physiological state because the sympathetic system stresses us out and the parasympathetic system makes us calm.
We can control it by regulating our emotional responses, e.g if always acting relaxed the parasympathetic neurons are more likely to be acting.
What two reflexes are the autonomic divisions involved in?
The light reflex whereby if less light is received the sympathetic fibers will cause adrenergic stimulation to widen the pupil and parasympathetic fibers will cause cholinergic stimulation to contract the pupil if there is too much light.
Also the baroreceptor reflex in the heart, whereby if the baroreceptors sense an increase in blood pressue it will activate the parasympathetic nerves, causing a heart rate decrease to lower the blood pressure.
