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Autonomic Nervous System
The AutonomicNervous System
Check out this link! Todays lecture made simple! The Autonomic Nervous System (Just ignore the Enteric System!)
The Autonomic Nervous System• Regulate activity of smooth muscle, cardiac muscle & certain glands
• Structures involved – general visceral afferent neurons – general visceral efferent neurons – integration center within the brain
•Receives input from limbic system and other regions of the cerebrum
Autonomic versus Somatic NS• Somatic nervous system – consciously perceived sensations – excitation of skeletal muscle – one neuron connects CNS to organ
• Autonomic nervous system – unconsciously perceived visceral sensations – involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion – two neurons needed to connect CNS to organ
• preganglionic and postganglionic neurons
-Autonomic motor neurons have cell bodies in the CNS and synapses with another neuron in an autonomic ganglion.
-a ganglion is a collection of cell bodies outside the CNS
-Thus, there is a preganglionic neuron and a postganglionic neuron
-it is the postganglionic neuron that synapses with the target tissue.
Autonomic system: has two divisions
1. Sympathetic-- fight or flight
2. Parasympathetic--rest and digest
These two often have opposite reactions. Cranial nerves and spinal nerves are part of the peripheral system.
Divisions of the PNS:
* Motor neurons of both divisions have the cell body in CNS(brain and spinal cord)
* Can be either somatic or autonomic
** Somatic motor neurons innervate skeletal muscles
** Autonomic neurons innervate organs we don't have conscious control over (cardiac muscle, smooth muscle, and glands)
Parasympathetic system: The main nerve is the Vagus nerve. It is involved in swallowing, speech, liver, spleen, small and large intestines, heart, etc.
• Notice that the ANS pathway is a 2 neuron pathway while the Somatic NS only contains one neuron.
ANS Neurotransmitters* Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released
| Adrenergic |
Acetylcholine (ACh)Acetylcholine is a primary neurotransmitter. - It is used by some neurons in the brain -It is used by ALL SOMATIC MOTOR NERVES OF THE PNS -It is used as the neurotransmitter by all preganglionic neurons of the ANS. -It is used by most postganglionic neurons of the Parasympathetic division of the ANS The contraction of a muscle uses Acetylcholine. ACh is an Excitatory (responds to nicotine) -when it binds to nicotine receptors and is sympathetic. ACh is an Inhibitory ( responds to muscarine )- when it binds to muscarinic receptors and is parasympathetic.
Examples of blocking ACh receptors are: The muscarinic effects of ACh are specifically inhibited the drug ATROPINE,
derived from the deadly nightshade plant ( Atropa belladonna ). Indeed, extracts of this plant were used by women during the Middle Ages to dilate their pupils ( atropine inhibits parasympathetic stimulation of the iris ). This was thought to enhance their beauty ( in Italian, bella means beautiful, donna means woman) Atropine is used clinically today to dilate the pupils during eye examinations.
The drug Curare- relaxes the muscle ( blocks the nicotinic receptors) and could cause you to die, however if you were given ventilation you would recover. It is a poison that belongs in the tomato family.
AChe is a nerve gas, your body will contract till you die.
Nerve gas- Inhibits ACHestaraes. You die from spastic paralysis, steady and prolonged involuntary contraction of the muscles contracted.
Cholinergic Neurons and Receptors
• Cholinergic neurons release acetylcholine from preganglionic neurons & from parasympathetic postganglionic neurons. • Excites or inhibits depending upon receptor type and organ involved Cholinergic receptors • Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells and at NMJ. Acetylcholine is excitatory when it bonds to these receptors. (also responds to Nicotine) • Muscarinic receptors are found on plasma membranes of all parasympathetic effectors. Acetylcholine is inhibitory when it binds to these receptors. (named because they also respond to muscarine, a drug from certain mushrooms)
Adrenergic Neurons and Receptors
Adrenergic Neurons and Receptors
• Adrenergic neurons release norepinephrine (NE)
What else is used as a transmitter?
*Post ganglionic sympathetic neurons release Norepinephrine as a neurotransmitter
*The receptors are termed "adrenegic"
*Norepinephrine released by sympathetic neurons, or epinephrine released by the adrenal medulla will stimulate the heart, dilate pupils and increase respiration
Reflex ArcThe reflex arc is a somatic motor neuron. Why? because is goes to a skeletal muscle. It has a cell body in the central nervous system, although it is part of the peripheral nervous system. The sensory neuron goes to a doral root ganglion which then goes to the cell body in the CNS and then goes to a motor neuron that goes straight to the target tissue.
The picture shows the central nerves system if you look on the left of the diagram you will see the Vagus nerve. The Vagus nerve is also called the pneumogastric nerve or the cranial nerve its the only nerve that starts in the Brain stem. the vagus nerve goes from the brain to the abdomen. All parts of the body controlled by the Vagus nerve are automatic nerves which we don't control, happens automatically like slow heart beat .
1. Where can you find muscarinic receptors?
a. on smooth muscles
b. on cardiac muscle cells
c. on glands
d. in parts of the brain
e. all of the above
2.Ganglia that can be seen alongside the spinal cord are not part of the sympathetic division?
3. The group of pharmaceutical chemists that made Viagra came from which country?
4. Somatic motor neurons have cell bodies located ____ the CNS that project axons only to ____; and are usually under ____ control.
a. outside; skeletal: involuntary
b. inside; the viscera; voluntary
c. inside; the viscera ; involuntary
d. inside; skeletal muscle; voluntary
5. Which of the following statements about parasympathetic neurons is true?
a. The nerve fibers are contained in spinal nerves.
b. They synapse in terminal ganglia, either next to or within the organs innervated.
c. They originate in thoracic and lumbar regions of the spinal cord.
d. Postganglionic fibers are usually longer than those of sympathetic neurons.
6. The drug muscarine, derived from some poisonous mushrooms stimulates all of the following cholinergic receptors, except those receptors in
|b.||the neuromuscular junction of skeletal muscle fibers.|
|c.||the digestive system.|
|d.|| most target organs of postganglionic parasympathetic nerve fibers.|
8. Which of the following target tissues receive acetylcholine when the sympathetic division is stimulated?
|c.||smooth muscle of the GI tract|
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