2. Autonomic Nervous System
some typical responses of the Sympathetic division
"fight or flight" Increases heart rate. Increases blood pressure. Dilates bronchioles. Stimulates the adrenal medulla to release adrenaline. Mobilizes fat and glucose for energy.
some typical responses of the Parasympathetic division
"rest and digest" Decreases heart rate. Decreases blood pressure. Increases digestive activity.
On average, how many postganglionic neurons does a single preganglionic neuron synapse with?
8-9
Dual innervation
A large number of organs are innervated by both divisions of the ANS. These often have opposite effects The sympathetic division acts to mobilize the body during activity. The parasympathetic division promotes maintenance functions and conserves body energy.
Autonomic Nervous System
ANS part of the peripheral nervous system has both sensory (afferent) and motor (efferent) components Acts to regulate visceral functions that are largely outside of conscious control (automatic). It regulates cardiac function, digestion, respiration, salivation, sweating, pupil diameter, urination, and sexual arousal. made up of the... 1. Sympathetic Nervous System 2. Parasympathetic Nervous System
How is ANS activity controlled?
ANS activity is regulated by central nervous system (CNS) input from the... 1. cerebral cortex: overarching integration of ANS 2. hypothalamus: integrates cardiovascular, respiratory and swallowing function 3. brain stem: integrates urination, defecation, erection and ejaculation reflexes 4. spinal cord: acts at the subconscious level through the limbic system
What are the two divisions of the ANS and the general physiological roles of each?
ANS is divided in the sympathetic and parasympathetic divisions. the sympathetic division plays an important role in stressful situations as it prepares the body for fight or flight parasympathetic division has the maintenance function, important in rest-and-digest scenarios
Acetylcholine receptors
Acetylcholine binds to two types of ACh receptors: 1) Nicotinic receptors 2) Muscarinic receptors
Do the two divisions work together to achieve cooperative effects?
An example of the two divisions working cooperatively is in the external genitalia, specifically: Sympathetic stimulation causes ejaculation or reflex contractions of the vagina. Parasympathetic stimulation dilates blood vessels to produce an erect penis or clitoris
Anatomical organization
Autonomic pathways consist of two neurons in series: the preganglionic neuron and postganglionic neuron. These connect the central nervous system (CNS) and the effector via a ganglion. Note! the Sympathetic NS preganglion axons are shorter than parasympathetic nervous system. The opposite is true for the postganglionic axons where the Sympathetic are much longer than the parasympathetic system
Adrenergic receptors
Epinephrine and norepinephrine are both catecholamines that bind to two major types of receptors: 1) Alpha-adrenergic receptors (α adrenoceptors) of which there are two subtypes. 2) Beta-adrenergic receptors (β adrenoceptors) of which there are three subtypes. Adrenoceptors use G proteins and their associated signaling pathways to achieve their effects. Therefore, they are G protein-coupled receptors (GPCRs).
Muscarinic receptor subtypes are located in different regions of the body. What is the effect of parasympathetic stimulation on the following organs?
M1 = Parietal cells in the gastric epithelium, and neurons in the PNS and CNS = Stimulates gastric secretions and excitatory effects of acetylcholine in the nervous system. M2= The heart, and neurons in the PNS and CNS = Decrease in heart rate. Negative feedback loop to inhibit acetylcholine release. M3 = Smooth muscle of the GI, eye, glands (airways, salivary, gastric), and blood vessels = Increased gastrointestinal motility and gland secretions. Accommodation reflex in the eye. M4 and M5 = CNS = Not well defined.
Why were these ACh receptors given these names?
Nicotinic receptors also respond to nicotine. Muscarinic receptors also respond to muscarine, a toxic alkaloid found in mushrooms.
Parasympathetic innervation
One example of parasympathetic innervation is the accommodation reflex in the eye.
autonomic pathways: Sympathetic Nervous System
Pathways' point of origin: Thoracic and lumbar regions Preganglionic neuron length: Relatively short Ganglia location: In a chain alongside the spinal column Postganglionic neuron length: Relatively long
autonomic pathways: Parasympathetic Nervous System
Pathways' point of origin: Brain stem and sacral regions Preganglionic neuron length:Relatively long Ganglia location: Near or in target organs Postganglionic neuron length: Relatively short
Parasympathetic blockade
People can mistakenly eat the poisonous berries of the Atropa belladonna plant. These contain atropine and scopolamine, which block parasympathetic activity. If you ingested Atropa belladonna berries, what symptoms would you exhibit?
What sensory neurons are there, and what physiological parameters do they monitor?
Sensory neurons are found throughout the peripheral nervous system and monitor the following physiological parameters: Composition of the blood (oxygen and carbon dioxide) Arterial blood pressure Contents of the stomach and intestines Degree of stretch of the lungs Volume of extracellular fluid
Preganglionic transmission
Sympathetic preganglionic neurons and parasympathetic preganglionic neurons both release acetylcholine (ACh). These neurons are said to be "cholinergic". Released ACh diffuses across the synaptic cleft and binds to nicotinic ACh receptors. --> This opens the ligand-gated ion channel and allows ions to flow into the cell, which depolarizes the postganglionic neuron.
ANS divisions
Sympathetic system: the "fight or flight" division Parasympathetic system: the "rest and digest" division
enteric nervous system (ENS)
The ENS is found in the wall of the gastrointestinal tract from the esophagus to the distal colon. Neurons that innervate the ENS are collected into two plexuses: The myenteric plexus is found between the longitudinal and circular smooth muscle layers. The submucosal plexus is found in the submucosa. These plexuses receive input from sensory receptors which are supplied by both sympathetic and parasympathetic fibers. These fibers also directly supply smooth muscle, glands, and blood vessels in the abdomen. The neurons in the gut nerve plexuses regulate and coordinate local gut activity using a variety of neurotransmitters. Parasympathetic input enhances digestive activity and sympathetic input inhibits digestive activity.
Sympathetic innervation: Adrenal medulla innervation
The adrenal glands sit on top of the kidneys. They are innervated by the sympathetic nervous system. Adrenal medulla cells synthesize epinephrine and norepinephrine. These hormones are secreted directly into the bloodstream by chromaffin cells (postganglionic sympathetic neurons that lack axons).
Postganglionic transmission
The depolarized postganglionic neurons release different neurotransmitters. Parasympathetic postganglionic neurons--> always release ACh, which binds to muscarinic receptors on effector cells. These neurons are said to be "cholinergic". Most sympathetic postganglionic neurons--> release norepinephrine, which binds to adrenergic receptors (adrenoceptors) on effector cells. These neurons are said to be "adrenergic".
Sympathetic innervation
The following effectors are only innervated by sympathetic fibers: Adrenal medulla Sweat glands Arrector pili muscles of the skin Kidneys Most blood vessels
Parasympathetic innervation: accommodation reflex
The purpose of changing the shape of the lens is that the increased curvature helps to bend light, and bring it into focus on the retina When we focus on a distant object, the ciliary body relaxes and tension on the lens suspensory ligaments pulls the lens flat. When we focus on a near object, the ciliary body contracts and the tension on the lens suspensory ligaments is relieved. This allows the lens to become rounder in shape and refract light at a higher angle. Ciliary body muscle fibers are supplied solely by the parasympathetic nervous system.
Muscarinic receptors
are GPCRs which have both stimulatory and inhibitory roles depending on which α-subunits are bound to the complex.
name the different spinal regions? (top to bottom)
cervical thoracic lumbar sacral coccygeal
What is the difference between cholinergic and adrenergic nerve fibers? How do neurotransmitters released by these neurons interact with specific cholinergic and adrenergic receptor subtypes?
cholinergic fibers release acetylcholine which then acts on nicotinic or muscarinic receptors. nicotinic receptor activation results in synaptic transmission, while muscarinic receptor activation results in either simulatory or inhibitory roles, depending on which alpha-subunits are bound to the GPCR complex adrenergic fibers release epinephrine or norepinephrine what the act on alpha or beta adrenoreceptors: alpha1 activation results in muscle contraction alpha2 activation results in the inhibition of smooth muscle relaxation beta activation results in muscle relaxation
What are examples of effectors innervated by both branches of the ANS? Describe the major effects of each branch on these effectors.
heart, lungs (bronchioles) and gi tract (digestive system) are examples of organs innervated by both divisions ofANS. symp system stimulates the heart to increase rate and force of contraction, while parasym stimulation decreases heart rate. symp stimulation of lungs dilates bronchioles but parasympathetic stimulation constricts them. sympathetic stimulation decreases digestive system activity while parasympathetic stimulation increases digestive activity
How does the location of the ganglia explain the length of the preganglionic neurons and postganglionic neurons?
in the sympathetic division, the ganglia chain is located alongside the spinal column. consequently, the preganglionic neuron only needs to travel a relatively short distance. this mean the postganglionic neuron needs to travel a longer distance to reach the effector on the parasympathetic division, the ganglia is located near or in the effector organ. means the preganglionic neurons need to travel a long distance. consequently the postganglionic neurons needs to travel only a very short distance
What is a visceral reflex arc? Include structural and functional details of sensory and motor components.
its a type of autonomic reflex that occurs when a stimulus is sensed by a receptor in the viscera (internal organs in the main cavities of the body, especially those in the abdomen) information regarding this stimulus is relayed via sensory neurons to an integration center. the integration center may be preganglionic neuron or a neuron within the walls of the GI tract. a signal is sent via motor neurons to produce a response
In assessing autonomic nervous system function in a healthy person, which of the following may occur with a change from a supine to a standing posture?
little change in systolic blood pressure after 3 mins
Why is the adrenal medulla described as a modified sympathetic ganglion?
neural crest cells generate many different cells and tissue types during development. the cells of the adrenal medulla arise from the embryonic neural crest and are thus really modified neurons. we can regard them as comparable to postganglionic neurons supplied by preganglionic sympathetic neurons
How does the anatomy of the parasympathetic and sympathetic systems differ? Include these details in your answer: CNS outflow locations, ganglia locations, preganglionic and postganglionic neuron relative lengths, and ganglionic and effector neurotransmitters.
neurons of the sympathetic nervous system originate from the lumbar and thoracic region of the spinal cord. the ganglia chain is located alongside the spinal column so the preganglionic neuron is relatively short while the postganglionic neuron is relatively long to reach the target organ neurons of the parasympathetic division originate from the brainstem and sacral region of the spinal cord. the ganglia are located near or on the effector organ, so the preganglionic neurons are relatively long and the postganglionic neurons are relatively short. the preganglionic neurons of both autonomic divisions release the neurotransmitter acetylcholine (ACh). the sympathetic postgang neurons release norepinephrine, and the parasypmathetic postgang neurons release acetylcholine
In assessing autonomic nervous system function, which of the following is true for heart rate variability (HRV)?
normally heart rates varies from beat to beat as a consequence of changes in the parasympathetic (vagus nerve) and sympathetic nerve activity
Neurons of the ENS
play an important role in visceral reflex arcs within the GI tract. Sensory neurons, interneurons, and motor neurons participate in both short reflex arcs and long reflex arcs to regulate digestive system activity Short reflexes: mediated entirely by the ENS neurons in response to stimuli within the GI tract. Long reflexes: mediated by both the CNS and the ENS. External stimuli (for example, exercise or stress) are processed in the CNS, which influences ENS activity via the sympathetic and parasympathetic systems. This allows the CNS to increase or decrease GI activity, and coordinate GI activity with other systems.
What are some examples of effectors innervated by only one branch of the ANS?
sweat glands, arrector pilli muscles of the skin, kidneys, most blood vessels and adrenal medulla are only innervated by the sympathetic system. epinephrine is released when we are stressed. explains why in these situations we may sweat ciliary muscles in the eye are only innervated by the parasympathetic division. explains accommodation reflex when a person is resting and digesting
How does sympathetic innervation of the adrenal gland compare with sympathetic innervation of other effectors?
the preganglionic neuron synapses directly with cells of the adrenal medulla, this is why the adrenal medulla is often referred to as a modified sympathetic ganglion. there are no postganglionic neurons present but chromaffin cells release epinephrine directly into the bloodstream
Binding of a catecholamine to G protein-coupled receptors (GPCRs) results in the following...
α1 adrenoceptor: the αq subunit activates the enzyme phospholipase C causing an increase in calcium ion (Ca2+) levels. In smooth muscle this results in muscle contraction. α2 adrenoceptor: the αi/o subunit inhibits the adenylate cyclase enzyme. This causes intracellular cyclic adenosine monophaste (cAMP) levels to decrease. In smooth muscle this inhibits muscle relaxation. β adrenoceptor: the stimulatory G protein (Gs) activates adenylate cyclase. This causes intracellular cAMP levels to increase. In smooth muscle this results in muscle relaxation. SUMMARY: Therefore in smooth muscle, downstream signaling events result in either contraction or relaxation.
