40 Questions
Where are the cell bodies of the parasympathetic preganglionic neurons located?
In the brain stem and sacral spinal cord (S2 and S3)
What type of axons do the postganglionic neurons usually have?
Slow conducting unmyelinated axons
What is the function of the preganglionic neuron in the ANS?
To connect the CNS with the target organ through a postganglionic neuron
What is the characteristic of the sympathetic trunk?
A fusion of sympathetic ganglia
What type of tissue do the postganglionic neurons innervate?
Smooth muscle, cardiac muscle, and glandular tissue
Where are the cell bodies of the sympathetic preganglionic neurons located?
In the spinal cord segments T1-L3
What is the characteristic of the synaptic buttons of the postganglionic neurons?
They are distributed along the length of the branches
What is the difference between the sympathetic and parasympathetic systems in terms of their effect on target organs?
One must understand all separate functions in each organ to determine the effect of sympathetic or parasympathetic system
What is the primary function of the sympathetic system in regards to physical activity?
To enable vigorous physical activity with rapid production of energy
What is the primary function of the enzyme choline acetyltransferase in the synthesis of acetylcholine?
To convert acetyl-CoA and choline into acetylcholine
Which part of the spinal cord is the anatomical origin of the sympathetic system?
Thoracolumbar spinal cord
What is the effect of the sympathetic system on pupil size?
Dilation
What is the final step in the synthesis of norepinephrine from tyrosine?
Hydroxylation of dopamine to form norepinephrine
Which of the following is NOT a function of the sympathetic system?
Stimulation of stomach activity
What is the function of acetylcholinesterase in the cholinergic system?
To convert acetylcholine into an acetate ion and choline
Where does the conversion of norepinephrine into epinephrine take place?
In the adrenal gland
How do the sympathetic and parasympathetic systems interact?
They work together in an antagonistic fashion
What type of receptor is nicotinic receptor?
Ligand-gated ion channel
What is the primary control center of the autonomic nervous system?
Hypothalamus
Which system is the hypothalamus a part of?
Limbic system
What is the role of the choline in the synthesis of acetylcholine?
To combine with acetyl-CoA to form acetylcholine
What type of input does the hypothalamus receive directly or indirectly?
Both somatic and visceral sensory input
Where is acetylcholine synthesized in the cholinergic nerve fibers?
In the terminal endings of the nerve fibers
What is the result of the binding of acetylcholine to cholinergic receptors?
Activation of the postsynaptic neuron
Which type of receptor binding results in the release of calcium from the ER?
Alfa1 receptors
What is the effect of NE binding to Beta1 receptors in the heart?
Increase heart rate and contraction force
What is the effect of dopamine on renal vascular smooth muscle?
Sympathetic impact
What is the result of NE or EPI binding to Beta receptors?
Activation of adenylate cyclase
What is the effect of Beta2 receptors on respiratory passages?
Relaxation of smooth muscle
What is the effect of dopamine on sweat glands?
Sympathetic impact
What is the result of NE binding to Alfa2 receptors?
Reduce cAMP levels
What is the effect of Beta3 receptors on adipose tissue?
Release of fatty acids
Which type of receptors are found at the neuromuscular junction in skeletal muscles?
NM (Muscle) receptors
What is the result of acetylcholine binding to a nAChR?
Opening of sodium channels
Which type of receptors are GPCRs?
Muscarinic receptors
What is the effect of M2 and M4 muscarinic receptors?
Generation of IPSPs
Which of the following is an example of the effect of M3 muscarinic receptors?
Contraction of bronchioles
What is the effect of the activation of muscarinic receptors?
Results in EPSPs or IPSPs, depending on the receptor subtype
Which type of receptors are located at the synapses between peripheral target tissues and sympathetic postganglionic neurons?
Adrenergic receptors
What is the subtype of alfa receptors that signals through Gq?
Alfa1
Study Notes
Sympathetic System
- Enables vigorous physical activity with rapid production of energy (ATP)
- Increases heart rate, respiration, and blood flow to active muscles
- Causes pupil dilation for increased vision
- Anatomically arises from the thoracolumbar spinal cord, known as the thoracolumbar system
Functions of Sympathetic System
- Dilates pupils
- Inhibits salivation, stomach activity, gallbladder, and intestinal activity
- Increases heartbeat
- Relaxes airways and bladder
- Stimulates release of glucose
- Secretes epinephrine and norepinephrine
- Promotes ejaculation and vaginal contraction
Autonomic Nervous System (ANS)
- Under the control of the hypothalamus, which acts as an integrator
- Afferent and efferent fibers of the ANS travel via the spinal cord and cranial nerves to connect between the CNS and target organs
- Hypothalamic control is made by the brainstem (reticular formation) with some influence by the cerebral cortex
- The hypothalamus is part of the limbic system, which generates autonomic emotional response
Preganglionic Neurons
- In the ANS, a preganglionic and postganglionic neuron, in series, connects the CNS with the target organ
- The somatic motor system has only one lower motor neuron (LMN) connecting the skeletal muscle and the spinal cord
- The ANS preganglionic neuron has its cell body within the CNS, while its synapse is with the postganglionic neuron in the peripheral ganglion
- Both sympathetic and parasympathetic system cells bodies of the preganglionic neurons are located in the CNS
Sympathetic Preganglionic Neurons
- Cell bodies are located in the intermediolateral nucleus of the spinal cord segments T1-L3
Parasympathetic Preganglionic Neurons
- Cell bodies are located in the brain stem and sacral spinal cord (S2 and S3)
Postganglionic Neurons
- Cell body is in the peripheral ganglion in the PNS
- The sympathetic system forms the sympathetic trunk, which is a fusion of several sympathetic ganglia in a chain-like form, on each side of the vertebral column
- Postganglionic neurons usually have slow conducting unmyelinated axons
- They innervate smooth muscle, cardiac muscle, and glandular tissue
- They can excite or inhibit the target tissue
ANS Neurotransmitters
Acetylcholine Mechanism
- Synthesized in the terminal endings and varicosities of the cholinergic nerve fibers
- Steps: choline acetyltransferase converts acetyl-CoA and choline into acetylcholine, stored in a vesicle, released, and then converted into an acetate ion and choline by acetylcholinesterase, and recycled
Norepinephrine Mechanism
- Synthesized in the axoplasm of the varicosities and stored at secretory vessels
- Steps: tyrosine is converted into Dopa, then dopamine, then stored in vesicles, and then converted into norepinephrine, and finally converted into epinephrine in the adrenal gland
Postsynaptic Receptors
Cholinergic Receptors
- Bind to acetylcholine and are classified into two types: nicotinic and muscarinic
- Nicotinic receptors are ligand-gated ion channels found in the autonomic ganglia of both sympathetic and parasympathetic systems
- Muscarinic receptors are GPCRs found on all effector cells that are stimulated by postganglionic cholinergic neurons
- There are five subtypes of muscarinic receptors: M1, M2, M3, M4, M5, which signal through Gi or Gq (family of G proteins)
Postsynaptic Receptors: Adrenergic
- Located at the synapses between the peripheral target tissues and sympathetic postganglionic neurons that release norepinephrine
- Adrenergic receptors are also stimulated by the release of catecholamines from the adrenal glands
- Adrenergic receptors are GPCRs, and can be further divided into alpha and beta receptors
- Alpha receptors have the subtypes: alpha1 (Gq) and alpha2 (Gi), which induce vasoconstriction of most blood vessels, raising blood pressure
- Beta receptors have the subtypes: beta1, beta2, beta3 (Gs), which increase heart rate and contraction force, relax smooth muscle, and release fatty acids
Postsynaptic Receptors: Dopamine
- Mediates numerous physiological effects in the CNS and at the peripheral target organs
- Dopamine is released by some postganglionic sympathetic neurons synapsing with specific organs, like renal vessels
- Dopamine binds to dopaminergic receptors (which are GPCRs), and this binding will activate different cellular processes, resulting in EPSPs or IPSPs
Learn about the functions of the sympathetic nervous system, including its role in physical activity, heart rate, and other bodily functions. Understand how it stimulates and inhibits various bodily responses.
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