autonomic nervous system & neurotransmitter in psychiatry

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INTRODUCTION:- The organs (the "viscera")

of our body, such as the heart, stomach and intestines, are regulated by a part of the nervous system called the autonomic nervous system (ANS). The ANS is part of the peripheral nervous system and it controls many organs and muscles within the body. In most situations, we are unaware of the workings of the ANS because it functions in an involuntary, reflexive manner. For example, we do not notice when blood vessels change size or when our heart beats faster.


The ANS is most important in two situations:

In emergencies that cause stress and require us to "fight" or take "flight" (run away)

and In nonemergencies that allow us to

"rest" and "digest."


The ANS regulates: Muscles

in the skin (around hair follicles; smooth muscle)

around blood vessels (smooth muscle) in the eye (the iris; smooth muscle) in the stomach, intestines and bladder

(smooth muscle) of the heart (cardiac muscle)

Glands The ANS is divided into two parts: 1.The sympathetic nervous system 2. The parasympathetic nervous system


1. Sympathetic Nervous System:- The sympathetic nervous system

originates in the spinal cord. Specifically, the cell bodies of the first neuron (the preganglionic neuron) are located in the thoracic and lumbar spinal cord. Axons from these neurons project to a chain of ganglia located near the spinal cord. In most cases, this neuron makes a synapse with another neuron (post-ganglionic neuron) in the ganglion. A few preganglionic neurons go to other ganglia outside of the sympathetic chain and synapse there. The post-ganglionic neuron then projects to the "target" - either a muscle or a gland.

http://faculty.washington.edu/chudler/synapse.html


2. Parasympathetic Nervous System:- The cell bodies of the

parasympathetic nervous system are located in the spinal cord (sacral region) and in the medulla. In the medulla, the cranial nerves III, VII, IX and X form the preganglionic parasympathetic fibers. The preganglionic fiber from the medulla or spinal cord projects to ganglia very close to the target organ and makes a synapse.

http://faculty.washington.edu/chudler/cranial.html


AUTONOMIC NERVOUS SYSTEMStructure Sympathetic Stimulation Parasympathetic

Stimulation

Iris (eye muscle)

Pupil dilation Pupil constriction

Salivary Glands

Saliva production reduced Saliva production increased

Oral/Nasal Mucosa

Mucus production reduced Mucus production increased

Heart Heart rate and force increased

Heart rate and force decreased

Lung Bronchial muscle relaxed Bronchial muscle contracted

Stomach Peristalsis reduced Gastric juice secreted; motility increased

Small Intestine

Motility reduced Digestion increased

Large Intestine

Motility reduced Secretions and motility increased

Liver Increased conversion ofglycogen to glucose

Kidney Decreased urine secretion Increased urine secretion

Adrenal medulla

Norepinephrine andepinephrine secreted

Bladder Wall relaxedSphincter closed

Wall contractedSphincter relaxed


NEUROTRANSMITTERS DEFINATION:- Neurotransmitters are chemicals located and

released in the brain to allow an impulse from one nerve cell to pass to another nerve cell.

DESCRIPTION:- There are approximately 50 neurotransmitters

identified. There are billions of nerve cells located in the brain, which do not directly touch each other. Nerve cells communicate messages by secreting neurotransmitters. Neurotransmitters can excite or inhibit neurons (nerve cells). Some common neurotransmitters are acetylcholine, norepinephrine, dopamine, serotonin and gamma aminobutyric acid (GABA). Acetylcholine and norepinephrine are excitatory neurotransmitters while dopamine, serotonin, and GABA are inhibitory. Each neurotransmitter can directly or indirectly influence neurons in a specific portion of the brain, thereby affecting behavior.


MECHANISM OF IMPULSE TRANSMISSION:-


A nerve impulse travels through a nerve in a long, slender cellular structure called an axon, and it eventually reaches a structure called the presynaptic membrane, which contains neurotransmitters to be released in a free space called the synaptic cleft. Freely flowing neurotransmitter molecules are picked up by receptors (structures that appear on cellular surfaces that pick up molecules that fit into them like a "lock and key") located

Neurotransmitters are chemicals that transmit messages from one nerve cell (neuron) to another. The nerve impulse travels from the first nerve cell through the axon—a single smooth body arising from the nerve cell— to the axon terminal and the synaptic knobs. Each synaptic knob communicates with a dendrite or cell body of another neuron, and the synaptic knobs contain neurovesicles that store and release neurotransmitters. The synapse lies between the synaptic knob and the next cell. For the impulse to continue traveling across the synapse to reach the next cell, the synaptic knobs release the neurotransmitter into that space, and the next nerve cell is stimulated to pick up the impulse and continue it.


NEUROTRANSMITTERS IN CNS:- I. Cholinergics :- a) Acetylcholine:- Function:- Acetylcholine are manifold

& include sleep, arousal, pain perception, modulation & coordination of movement, & memory acquisition & retention. Cholinergic mechanisms may have some role in certain disorders of motor behaviour & memory, such as Parkinson’s, Huntington’s, & Alzheimer’s diseases.


II. Monoamines:- a) Norepinephrine:- Functions:- It include the

regulation of mood, cognition, perception, locomotion, cardiovascular functioning, & sleep & arousal. The activity of norepinephrine also has been implicated in certain mood disorders such as depression & mania, in anxiety state & in schizophrenia.


b) Dopamine:- Functions:- It include regulation of

movement & coordination, emotions, voluntary decision-making ability. Increased levels of dopamine are associated with mania & schizophrenia.

c) Serotonin:- Functions:- It may play a role in sleep &

arousal, libido, appetite, mood, aggression, & pain perception. The serotoninergic system has been implicated in the etiology of certain psychopathological conditions including anxiety states, mood disorders, & schizophrenia.


d) Histamine:- The role of histamine in

mediating allergic & inflammatory reactions has been well documented. It’s role in the CNS as a neurotransmitter has only recently been confirmed, & the availability of information is limited. The highest concentrations of histamine are found within various regions of the hypothalamus. The exact processes mediated by histamine with the CNS are uncertain, some data suggest that histamine may play a role in the depressive illness.


III. Amino Acids:- a) Gamma-Aminobutyric Acid:- Function:- It prevent postsynaptic

excitation, interrupting the progression of the electrical impulse at the synaptic junction. This function is significant when slowdown of body activity is advantageous.

Alterations in the GABA system have been implicated in the etiology of anxiety disorders, movement disorders (eg: Huntington’s disease), & various forms of epilepsy.


b) Glycine:- The highest concentration of

glycine in the CNS are found in the spinal cord & brainstem. Glycine appears to be the neurotransmitter of recurrent inhibition of motor neurons within the spinal cord, & is possible involved in the regulation of spinal & brainstem reflexes. It has been implicated in the pathogenesis of certain types of spastic disorders & in “glycine encephalopathy”, which is known to occur with toxic accumulation of the neurotransmitter in the brain & cerebrospinal fluid.


c) Glutamate and Aspartate:- Functions:- Glutamate & aspartate

function in the relay sensory information & in the regulation of various motor & spinal reflexes.

-Alteration in this systems has been implicated in the etiology of certain neurodegenerative disorder, such as Huntington’s disease, temporal lobe epilepsy, & spinal cerebellar degeneration.


IV. Neuropeptides:- a.) Opioid Peptides:- Function:- Opioid pepties are thought to

have a role in pain modulation, which their natural morphine-like properties. They are released in response to painful stimuli, & may be responsible for producing the enalgesic effect following acupuncture.

Opioid peptides alter the release of dopamine & affect the spontaneous activity of the dopaminergic neurons. These finding may have some implication for opioid peptide-dopamine interaction in the etiology of schizophrenia.


b.) Substance P. :- Functions:- It has been found to be

highly concentrated in sensory fibers, & for this reason is thought to play a role in sensory transmission, particularly in the regulation of pain.

It has been associated with Huntington’s disease, dementia of the Alzheimer’s type & mood disorders.


c.) Somatostatin:- It (also called growth hormone-

inhibiting hormone) is found in the cerebral cortex, hippocampus, thalamus, basal ganglia, brainstem, & spinal cord & has multiple effect on the CNS. It exerts inhibitory effects on the release of norepinephrine & stimulatory effects on serotonine. It stimulates the turnover & release of dopamine in the basal ganglia & acetylcholine in the brainstem & hippocampus. Postmortem examinations have revealed high concentrations of somatostatin in brain specimens of clients with Huntington’s disease, & low concentrations in those with Alzheimer’s disease.

autonomic nervous system & neurotransmitter in psychiatry

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