Autonomic Nervous System

Autonomic Nervous System

                                                                                                                                                                                                R.Sayan {256-Eng}

Autonomic Nervous System

The autonomic nervous system (ANS) is a regulatory branch of the central nervous system that helps people adapt to changes in their environment. It adjusts or modifies some functions in response to stress. The ANS helps regulate...

Blood vessels' size and blood pressure

The heart's electrical activity and ability to contract

The bronchium's (BRON'ke-um) diameter (and thus air flow) in the lungs

The ANS also regulates the movement and work of the stomach, intestine and salivary glands, the secretion of insulin and the urinary and sexual functions. The ANS acts through a balance of its two components, the sympathetic nervous system and parasympathetic nervous system.

Ø  Autonomic nervous system (ANS):

v  Innervates organs whose functions are not usually under voluntary control.

v  Effectors include cardiac and smooth muscles and glands.

·         Effectors are part of visceral organs and blood vessels.

Autonomic Neurons

·         2 neurons in the efferent pathway.

·         1^st neuron has its cell body in gray matter of brain or spinal cord.

o   Preganglionic neuron.

·         Synapses with 2^nd neuron within an autonomic ganglion.

o   Postganglionic neuron.

·         Autonomic ganglion has axon which extends to synapse

 with target tissue.

·         Preganglionic autonomic fibers originate in midbrain, hindbrain, and upper thoracic to 4^th sacral levels of the spinal cord.

·         Autonomic ganglia are located in the head, neck, and abdomen.

·         Presynaptic neuron is myelinated and postsynaptic neuron is unmyelinated.

·         Autonomic nerves release NT that may be stimulatory or inhibitory.

Visceral Effector Organs

·         Involuntary effectors are somewhat independent of their innervation.

o   Smooth muscles maintain resting tone in absence of nerve stimulation.

Denervation hypersensitivity:

Damage to autonomic nerve makes its target tissue more sensitive than normal to stimulating agents.

o   Cardiac and many smooth muscles can contract rhythmically in absence of nerve stimulation.

Divisions of the ANS

Ø  Sympathetic nervous system and para-sympathetic nervous system:

·         Both have preganglionic neurons that originate in CNS.

·         Both have postganglionic neurons that originate outside of the CNS in ganglia.

Sympathetic Division

·         Myelinated preganglionic fibers exit spinal cord in ventral roots from T1 to L2 levels.

·         Most sympathetic nerve fibers separate from somatic motor fibers and synapse with postganglionic neurons within paravertebral ganglia.

o   Ganglia within each row are interconnected, forming a chain of ganglia that parallels spinal cord to synapse       with postganglionic neurons.

·         Divergence:

o   Preganglionic fibers branch to synapse with # of postganglionic neurons.

·         Convergence:

o   Postganglionic neuron receives synaptic input from large # of preganglionic fibers.

 

Sympathetic Division

·         Myelinated preganglionic fibers exit spinal cord in ventral roots from T1 to L2 levels.

·         Most sympathetic nerve fibers separate from somatic motor fibers and synapse with postganglionic neurons within paravertebral ganglia.

o   Ganglia within each row are interconnected, forming a chain of ganglia that parallels spinal cord to synapse with postganglionic neurons.

·         Divergence:

o   Preganglionic fibers branch to synapse with # of postganglionic neurons.

·         Convergence:

o   Postganglionic neuron receives synaptic input from large # of preganglionic fibers.

Ø  Mass activation:

§  Divergence and convergence cause the

SNS to be activated as a unit.

Ø  Axons of postganglionic neurons are

unmyelinated to the effector organ. 

Adrenal Glands

Ø  Adrenal medulla secretes epinephrine (Epi) and norepinephrine (NE) when stimulated by the sympathetic nervous system.

Ø  Modified sympathetic ganglion:

o   Its cells are derived form the same embryonic tissue that forms postganglionic sympathetic neurons.

Ø  Sympathoadrenal system:

o   Stimulated by mass activation of the sympathetic nervous system.

o   Innervated by preganglionic sympathetic fibers.

Parasympathetic Division

·         Preganglionic fibers originate in midbrain, medulla, pons; and in the 2-4 sacral levels of the spinal column.

·         Preganglionic fibers synapse in terminal ganglia located next to or within organs innervated.

·         Most parasympathetic fibers do not travel within spinal nerves.

o   Do not innervate blood vessels, sweat glands, and arrector pili muscles.

·         4 of the 12 pairs of cranial nerves (III, VII, X, XI) contain preganglionic parasympathetic fibers.

·         III, VII, XI synapse in ganglia located in the head.

·         X synapses in terminal ganglia located in widespread regions of the body.

·         Vagus (X):

o   Innervates heart, lungs esophagus, stomach, pancreas, liver, small intestine and upper half of the large intestine.

·         Preganglionic fibers from the sacral level innervate the lower half of large intestine, the rectum, urinary and reproductive systems.

Sympathetic Effects

§  Fight or flight response.

§  Release of norepinephrine (NT) from postganglionic fibers and epinephrine (NT) from adrenal medulla.

§  Mass activation prepares for intense activity.

§  Heart rate (HR) increases.

§  Bronchioles dilate.

§  Blood [glucose] increases.

Parasympathetic Effects

·         Normally not activated as a whole.

o   Stimulation of separate parasympathetic nerves.

·         Release ACh as NT.

·         Relaxing effects:

o   Decreases HR.

o   Dilates visceral blood vessels.

o   Increases digestive activity.

Adrenergic and Cholinergic Synaptic Transmission

·         ACh is NT for all preganglionic fibers of both sympathetic and parasympathetic nervous systems.

·         Transmission at these synapses is termed cholinergic:

o   ACh is NT released by most postganglionic parasympathetic fibers at synapse with effector.

·         Axons of postganglionic neurons have numerous varicosities along the axon that contain NT.

·         Transmission at these synapses is called adrenergic:

o   NT released by most postganglionic sympathetic nerve fibers is NE.

o   Epi, released by the adrenal medulla is synthesized from the same precursor as NE.

·         Collectively called catecholamines.

·          

Responses to Adrenergic Stimulation

·         Beta adrenergic receptors:

o   Produce their effects by stimulating  production of cAMP.

o   NE binds to receptor.

o   G-protein dissociates into a subunit or bg-  complex.

o   Depending upon tissue, either a subunit or bg-complex produces the effects.

o   Alpha subunit activates adenylate cyclase, producing cAMP.

o   cAMP activates protein kinase, opening ion channels.

·         Alpha₁ adrenergic receptors:

o   Produce their effects by the production of Ca²⁺.

o   Epi binds to receptor.

o   Ca²⁺ binds to calmodulin.

o   Calmodulin activates protein kinase, modifying enzyme action.

·         Alpha₂ adrenergic receptors:

o   Located on presynaptic terminal.

§  Decreases release of NE.

·         Negative feedback control.

o   Located on postsynaptic membrane.

§  When activated, produces vasoconstriction.

·         Has both excitatory and inhibitory effects.

·         Responses due to different membrane receptor proteins.

o   a₁ : constricts visceral smooth muscles.

o   a₂  : contraction of smooth muscle. 

o   b₁  : increases HR and force of contraction.

o   b₂  : relaxes bronchial smooth muscles.

o   b3: adipose tissue, function unknown.

Responses to Cholinergic Stimulation

·         All somatic motor neurons, all preganglionic and most postganglionic parasympathetic neurons are cholinergic.

o   Release ACh as NT.

o   Somatic motor neurons and all preganglionic autonomic neurons are excitatory.

o   Postganglionic axons, may be excitatory or inhibitory.

·         Muscarinic receptors:

o   Ach binds to receptor.

o   Requires the mediation of G-proteins.

o   bg-complex affects opening or closing a channel, or activating enzymes.

·         Nicotinic receptors (ligand-gated):

o   ACh binds to 2 nicotinic receptor binding sites.

o   Causes ion channel to open within the receptor protein.

o   Opens a Na⁺ channel.

·         Always excitatory.

Other Autonomic NTs

·         Certain nonadrenergic, noncholinergic postganglionic autonomic axons produce their effects through other NTs.

o   ATP.

o   VIP.

o   NO.

Organs With Dual Innervation

·         Most visceral organs receive dual innervation (innervation by both sympathetic and parasympathetic fibers).

·         Antagonistic effects:

o   Sympathetic and parasympathetic fibers innervate the same cells.

o   Actions counteract each other.

o   Heart rate.

·         Complementary:

o   Sympathetic and parasympathetic stimulation produces similar effects.

o   Salivary gland secretion.

·         Cooperative:

o   Sympathetic and parasympathetic stimulation produce different effects that work together to produce desired effect.

o   Micturition.

Organs Without Dual Innervation

·         Regulation achieved by increasing or decreasing firing rate.

·         Adrenal medulla, arrector pili muscle, sweat glands, and most blood vessels receive only sympathetic innervation.

o   Nonshivering thermogenesis.

Control of the ANS by Higher Brain Centers

• Sensory input transmitted to brain centers that integrate information.
• Can modify activity of preganglionic autonomic neurons.
• Medulla:
• Most directly controls activity of autonomic system.
• Location of centers for control of cardiovascular, pulmonary, urinary, reproductive and digestive systems.
• Hypothalamus:
• Regulates medulla.
• Cerebral cortex and limbic system:
• Responsible for visceral responses that are characteristic of emotional states.

Physiology

Report Title - Autonomic Nervous System

By – Ramakirushnan Sayan   - Group - 256

Brain Anatomy and Function

Parietal Lobes The parietal lobes can be divided into two functional regions. One involves sensation and perception and the other is concerned with integrating sensory input, primarily with the visual system. The first function integrates sensory information to form a single perception (cognition). The second function constructs a spatial coordinate system to represent the world around us. Individuals with damage to the parietal lobes often show striking deficits, such as abnormalities in body image and spatial relations (Kandel, Schwartz & Jessel, 1991). Functions: Location for visual attention. Location for touch perception. Goal directed voluntary movements. Manipulation of objects. Integration of different senses that allows for understanding a single concept. Observed Problems: Inability to attend to more than one object at a time. Inability to name an object (Anomia). Inability to locate the words for writing (Agraphia). Problems with reading (Alexia). Difficulty with drawing objects. Difficulty in distinguishing left from right. Difficulty with doing mathematics (Dyscalculia). Lack of awareness of certain body parts and/or surrounding space (Apraxia) that leads to difficulties in self-care. Inability to focus visual attention. Difficulties with eye and hand coordination. Temporal Lobes Kolb & Wishaw (1990) have identified eight principle symptoms of temporal lobe damage: 1) disturbance of auditory sensation and perception, 2) disturbance of selective attention of auditory and visual input, 3) disorders of visual perception, 4) impaired organization and categorization of verbal material, 5) disturbance of language comprehension, 6) impaired long-term memory, 7) altered personality and affective behavior, 8) altered sexual behavior. Functions: Hearing ability Memory aquisition Some visual perceptions Catagorization of objects. Observed Problems: Difficulty in recognizing faces (Prosopagnosia). Difficulty in understanding spoken words (Wernicke's Aphasia). Disturbance with selective attention to what we see and hear. Difficulty with identification of, and verbalization about objects. Short-term memory loss. Interference with long-term memory Increased or decreased interest in sexual behavior. Inability to catagorize objects (Catagorization). Right lobe damage can cause persistant talking. Increased aggressive behavior. Occipital Lobes The occipital lobes are the center of our visual perception system. They are not particularly vulnerable to injury because of their location at the back of the brain, although any significant trauma to the brain could produce subtle changes to our visual-perceptual system, such as visual field defects and scotomas. Functions: Vision Observed Problems: Defects in vision (Visual Field Cuts). Difficulty with locating objects in environment. Difficulty with identifying colors (Color Agnosia). Production of hallucinations Visual illusions - inaccurately seeing objects. Word blindness - inability to recognize words. Difficulty in recognizing drawn objects. Inability to recognize the movement of an object (Movement Agnosia). Difficulties with reading and writing. Cerebellum The cerebellum is involved in the coordination of voluntary motor movement, balance and equilibrium and muscle tone. It is located just above the brain stem and toward the back of the brain. It is relatively well protected from trauma compared to the frontal and temporal lobes and brain stem. Functions: Coordination of voluntary movement Balance and equilibrium Some memory for reflex motor acts. Observed Problems: Loss of ability to coordinate fine movements. Loss of ability to walk. Inability to reach out and grab objects. Tremors. Dizziness (Vertigo). Slurred Speech (Scanning Speech). Inability to make rapid movements. Brain Stem The brain stem plays a vital role in basic attention, arousal, and consciousness. All information to and from our body passes through the brain stem on the way to or from the brain. Like the frontal and temporal lobes, the brain stem is located in an area near bony protrusions making it vulnerable to damage during trauma. Functions: Breathing Heart Rate Swallowing Reflexes to seeing and hearing (Startle Response). Controls sweating, blood pressure, digestion, temperature (Autonomic Nervous System). Affects level of alertness. Ability to sleep. Sense of balance (Vestibular Function). Observed Problems: Decreased vital capacity in breathing, important for speech. Swallowing food and water (Dysphagia). Difficulty with organization/perception of the environment. Problems with balance and movement. Dizziness and nausea (Vertigo). Sleeping difficulties (Insomnia, sleep apnea).

Anatomy Of Brain video lecture

Cyanobacteria (blue-green algae)

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Cyanobacteria (blue-green algae)

Cyanobacteria, also known as blue-green algae, grow in any type of water and are photosynthetic (use sunlight to create food and support life). Cyanobacteria live in terrestrial, fresh, brackish, or marine water. They usually are too small to be seen, but sometimes can form visible colonies, called an algal bloom. Cyanobacteria have been found among the oldest fossils on earth and are one of the largest groups of bacteria. Cyanobacteria have been linked to human and animal illnesses around the world, including North and South America, Africa, Australia, Europe, Scandinavia, and China.

yanobacterial blooms and how they form

Cyanobacterial blooms (a kind of algal bloom) occur when organisms that are normally present grow exuberantly. Within a few days, an bloom of cyanobacteria can cause clear water to become cloudy. The blooms usually float to the surface and can be many inches thick, especially near the shoreline. Cyanobacterial blooms can form in warm, slow-moving waters that are rich in nutrients such as fertilizer runoff or septic tank overflows. Blooms can occur at any time, but most often occur in late summer or early fall.
They can occur in marine, estuarine, and fresh waters, but the blooms of greatest concern are the ones that occur in fresh water, such as drinking water reservoirs or recreational waters.

What a cyanobacterial bloom looks like

Some cyanobacterial blooms can look like foam, scum, or mats on the surface of fresh water lakes and ponds. The blooms can be blue, bright green, brown, or red and may look like paint floating on the water. Some blooms may not affect the appearance of the water. As algae in a cyanobacterial bloom die, the water may smell bad.

Cyanobacterial harmful algal blooms (CyanoHABs)

CyanoHABs are algae blooms that threaten people, animals, or the environment. They are dangerous for many reasons:

• Dense CyanoHABs can block sunlight and use up all the oxygen in the water, killing other plants and animals.
• Some cyanobacteria that can form CyanoHABs produce toxins that are among the most powerful natural poisons known. These toxins have no known antidotes.
• CyanoHABs can make people, their pets, and other animals sick. Often, the first sign that an HAB exists is a sick dog that has been swimming in an algae-filled pond.
• Children are at higher risk than adults for illness from CyanoHABs because they weigh less and can get a relatively larger dose of toxin.

Other effects of fresh-water CyanoHABs

• CyanoHABs can make drinking water smell and taste bad.
• They can make recreational areas unpleasant.

 

Species of cyanobacteria that form CyanoHABs in fresh water

• Microcystis aeruginosa
• Anabaena circinalis
• Anabaena flos-aquae
• Aphanizomenon flos-aquae
• Cylindrospermopsis raciborskii.

Cyanotoxins

Cyanotoxins are a diverse group of chemical substances that are categorized by their specific toxic effects as follows:

• Neurotoxins affect the nervous system.
• Anatoxin-a
• Anatoxin-a(s)
• Saxitoxin
• Neosaxitoxin
• Hepatotoxins affect the liver.
• Microcystins
• Nodularins
• Cylindrospermopsin
• Tumor promoters are chemicals that can increase tumor growth.
• Microcystins
• Lipopolysaccharides are chemicals that can affect the gastrointestinal system.

]for a list of cyanotoxins and their specific toxic mechanisms, their effects, the symptoms they cause, and treatments for poisoning.

How you could be exposed to CyanoHABs and cyanotoxins

• Drinking water that comes from a lake or reservoir with a CyanoHAB.
• Drinking untreated water.
• Engaging in recreational activities in waters with CyanoHABs.
• Inhaling aerosols from water-related activities such as jet-skiing or boating.
• Inhaling aerosols when watering lawns, irrigating golf-courses, etc. with pond water.
• Using cyanobacteria-based dietary supplements that are contaminated with microcystins.
• Receiving dialysis (this has been documented only in Brazil).

Types of illnesses people and animals can get from exposure to CyanoHABs

• Getting it on the skin may give people a rash, hives, or skin blisters (especially on the lips and under swimsuits).
• Inhaling water droplets from irrigation or water-related recreational activities can cause runny eyes and nose, a sore throat, asthma-like symptoms, or allergic reactions.
• Swallowing water that has cyanobacterial toxins in it can cause
• Acute, severe gastroenteritis (including diarrhea and vomiting).
• Liver toxicity (i.e., increased serum levels of liver enzymes). Symptoms of liver poisoning may takes hours or days to show up in people or animals. Symptoms include abdominal pain, diarrhea, and vomiting.
• Kidney toxicity.
• Neurotoxicity. These symptoms can appear within 15 to 20 minutes after exposure. In dogs, the neurotoxins can cause salivation and other neurologic symptoms, including weakness, staggering, difficulty breathing, convulsions, and death. People may have numb lips, tingling fingers and toes, or they may feel dizzy.

Testing for cyanobacterial toxins

• Most of the toxins require specialized testing that can take weeks.
• Some kits are available to test for microcystins on site.

How to protect yourself, your family, and your pets from exposure to CyanoHABs

• Don’t swim, water ski, or boat in areas where the water is discolored or where you see foam, scum, or mats of algae on the water.
• If you do swim in water that might have a CyanoHAB, rinse off with fresh water as soon as possible.
• Don’t let pets or livestock swim in or drink from areas where the water is discolored or where you see foam, scum, or mats of algae on the water.
• If pets (especially dogs) swim in scummy water, rinse them off immediately—do not let them lick the algae (and toxins) off their fur.
• Don’t irrigate lawns or golf courses with pond water that looks scummy or smells bad.
• Report any "musty" smell or taste in your drinking water to your local water utility.
• Respect any water-body closures announced by local public health authorities.

How to treat people or animals that have been exposed to cyanobacterial toxins

• Get medical treatment right away if you think you, your pet, or your livestock might have been poisoned by cyanobacterial toxins.
• Remove people from exposure and give them supportive treatment.

How to help reduce the occurrence of CyanoHABs

• Reduce nutrient loading of local ponds and lakes by using only the recommended amounts of fertilizers and pesticides on your yard.
• Properly maintain your household septic system.
• Maintain a buffer of natural vegetation around ponds and lakes to filter incoming water.

How to get more information about cyanobacteria

Federal

• Centers for Disease Control and Prevention (CDC)
   
• Harmful Algal Blooms (HABs) site
  This site defines HABs; describes CDC’s HABs-related activities; and provides links to data, publications, and other HABs resources.
   
• Cyanobacteria site
  This site defines cyanobacteria; describes CDC’s cyanobacteria-related activities; and provides links to data, publications, and other cyanobacteria resources.
   
• Environmental Protection Agency (EPA)
   
• Drinking Water Contaminant Candidate List site[
  This site provides information about EPA’s list of contaminants that are not regulated, occur in public water systems, and may require regulation under the Safe Drinking Water Act. Algae that can be harmful are on this list.