Physiology of ANS Lecture 1 by Dr. Mudassar Ali Roomi
Post on 15-Apr-2017
234 Views
Preview:
Transcript
U N I T XI
Textbook of Medical Physiology, 11th edition
GUYTON & HALL
Chapter 60: lecture 1The Autonomic Nervous System (ANS);
The Adrenal Medulla
ByDr. Mudassar Ali Roomi (MBBS, M.Phil)
Assistant Professor Physiology
Autonomic Nervous System (ANS)
• It is motor system for visceral organs, blood vessels and secretory glands
• This system helps to control:– arterial pressure, – gastrointestinal motility,– gastrointestinal secretion, – urinary bladder emptying,– sweating, – body temperature, – and many other activities,
• One of the most striking characteristics of the autonomic nervous system is the rapidity and intensity with which it can change visceral functions.
Why is ANS called so?
• The name was given as it was thought that this system is independent of CNS.
• But it is controlled by many parts of CNS and these centers are present in the :– medulla oblangata,– pons– mid brain,– hypothalamus,– portion of limbic system – cerebral cortex.– Spinal cord
CNS centres for control of ANS
Sympathetic Nervous System
• It consists of the thoraco lumbar outflow.
• The lateral horns of spinal segments T1-L2 contain cell bodies of the pre-ganglionic sympathetic neuron.
• Sympathetic ganglia can be divided into 2 groups.
1)Paravertebral ganglia (which make the sympathetic chain)
2)Pre-vertebral ganglia which include celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion.
visceral motor neuron located in the intermediolateral horn of the spinal cord from T-1 to L-2 (thoracolumbar outflow) Axons can take 1 of 3 paths
1. enter the sympathetic chain via the white ramus and terminate there
2. enter the sympathetic chain via the white ramus and ascend or descend a few segments before terminating
3. enter via the white ramus and exit via a splanchnic nerve and terminate in a prevertebral ganglia
Figure 60-2; Guyton & Hall
Physiologic Anatomy of the sympathetic Nervous System
Segmental Distribution of the Sympathetic Nerve Fibers
• the sympathetic fibers from cord segment T-1 generally pass up the sympathetic chain to terminate in the head;
• from T-2 to terminate in the neck; • from T-3, T-4, T-5, and T-6 into
the thorax; • from T-7, T-8, T-9, T-10, and T-11
into the abdomen; • and from T-12, L-1, and L-2 into
the legs.
Special Nature of the Sympathetic Nerve Endings in the Adrenal Medullae
• Adrenal medulla is a part of the sympathetic nervous system
• Adrenal medulla cells are embryologicaly post-ganglionic sympathetic neuron lost their N.fibers to become secretory.
• Instead of giving post ganglionic symp N.fiber these secrete catacholamines (adrenaline & nor-adrenaline).
Physiologic Anatomy of the Parasympathetic Nervous System
• Visceral motor neurons are located in discrete brain stem nuclei and in sacral segments (S2-4). It is also called as craniosaccral outflow.
• Parasympathetic nerves originate from cranial nerves III, VII, IX, and X and the sacral spinal cord.
– occulomotor nerve - fibers to the pupillary sphincters and ciliary muscle
– facial nerve - fibers to nasal, lacrimal and submandibular gland
– glossopharyngeal nerve - fibers to parotid gland
– vagus nerve - motor inputs to visceral organs
– sacral segments - fibers to descending colon, rectum, bladder and genitalia
Neurotransmitters in ANS
• sympathetic nerves release norepinephrine at their nerve endings
– these nerves are call adrenergic nerves• parasympathetic nerves release acetylcholine
at their nerve endings– these nerves are called cholinergic
nerves• All preganglionic sympathetic and
parasympathetic nerves release acetylcholine.• All postganglionic parasympathetic nerves
release acetylcholine. • almost all postganglionic sympathetic nerves
release norepinephrine– except for sweat glands, piloerector
muscles and select blood vessels which release Ach ******
Mechanisms of Transmitter Secretion andSubsequent Removal of the Transmitterat cholinergic neuro-effector junction
Mechanisms of Transmitter Secretion andSubsequent Removal of the Transmitterat the adrenergic neuro-effector junction
Receptors of the Autonomic Nervous System
•Cholinergic receptors1. Muscarinic receptors
(M1, M2, M3)2. Nicotinic receptors
a. Nnb. Nm
•Adrenergic receptors1. Alpha 1,22. Beta 1,2
top related