CH 15

Autonomic control by higher centres- Parasympathetic

(anterior and medial sections of hypothalamus) stimulation causes: - Decrease in heart rate and force of contraction and lowering of blood pressure - Constriction of pupils - Increased secretion and motility of GI tract.

Autonomic control by higher centres- Sympathetic

(posterior and lateral sections of hypothalamus) stimulation causes: - Increase in heart rate and force of contraction and rise in blood pressure (due to constriction of blood vessels) - Increase in body temperature and dilation of pupils - Inhibition of GI tract

Identify the adrenergic neurons, receptors, and neurotransmitters.

- neurons release norepinephrine (NE), also known as noradrenalin. Most sympathetic postganglionic neurons are adrenergic. Like ACh, NE is stored in synaptic vesicles and released by exocytosis. Molecules of NE diffuse across the synaptic cleft and bind to specific adrenergic receptors on the postsynaptic membrane, causing either excitation or inhibition of the effector cell. - Receptors that respond to Norepinephrine (NE) and Epinephrine (E) released by a sympathetic postganglionic neuron (NE) or as a hormone by chromaffin cells into the blood (NE and E) are called adrenergic receptors There are 2 subtypes found in the visceral effectors innervated by most sympathetic postganglionic axons and are based on the responses they elicit and their selective binding of drugs that activate or block them: 1. alpha receptors which are subdivided into alpha 1 (excitation) and alpha 2 (inhibition) 2. beta receptors which are subdivided into and beta 1 (excitation) and beta 2 (inhibition)

Identify the cholinergic neurons, receptors, and neurotransmitters.

- neurons release the neurotransmitter acetylcholine (ACh). In the ANS, the cholinergic neurons include (1) all sympathetic and parasympathetic preganglionic neurons, (2) sympathetic postganglionic neurons that innervate most sweat glands, and (3) all parasympathetic postganglionic neurons - ACh is stored in synaptic vesicles and released by exocytosis. It then diffuses across the synaptic cleft and binds with specific cholinergic receptors, integral membrane proteins in the postsynaptic plasma membrane. The two types of cholinergic receptors, both of which bind ACh, are nicotinic receptors and muscarinic receptors.

Visceral Effector (Glands)- Adipose tissue

- sympathetic = lipolysis and release of fatty acids

Identify certain cholinergic and adrenergic agonists and antagonists and their actions.

A large variety of drugs and natural products can selectively activate or block specific cholinergic or adrenergic receptors. An agonist is a substance that binds to and activates a receptor, in the process mimicking the effect of a natural neurotransmitter or hormone. Phenylephrine, an adrenergic agonist at α1 receptors, is a common ingredient in cold and sinus medications. Because it constricts blood vessels in the nasal mucosa, phenylephrine reduces production of mucus, thus relieving nasal congestion. An antagonist is a substance that binds to and blocks a receptor, thereby preventing a natural neurotransmitter or hormone from exerting its effect. For example, atropine blocks muscarinic ACh receptors, dilates the pupils, reduces glandular secretions, and relaxes smooth muscle in the gastrointestinal tract. As a result, it is used to dilate the pupils during eye examinations, in the treatment of smooth muscle disorders such as iritis and intestinal hypermotility, and as an antidote for chemical warfare agents that inactivate acetylcholinesterase.

Describe the effects of acetylcholine as a cholinergic neuron neurotransmitter.

Activation of nicotinic receptors by ACh causes depolarization and thus excitation of the postsynaptic cell, which can be a postganglionic neuron, an autonomic effector, or a skeletal muscle fiber. Activation of muscarinic receptors by ACh sometimes causes depolarization (excitation) and sometimes causes hyperpolarization (inhibition), depending on which particular cell bears the muscarinic receptors. For example, binding of ACh to muscarinic receptors inhibits (relaxes) smooth muscle sphincters in the gastrointestinal tract. By contrast, ACh excites muscarinic receptors in smooth muscle fibers in the circular muscles of the iris of the eye, causing them to contract. Because acetylcholine is quickly inactivated by the enzyme acetylcholinesterase (AChE), effects triggered by cholinergic neurons are brief.

Describe the components involved in an autonomic reflex.

Autonomic (visceral) reflexes are responses that occur when nerve impulses pass through the autonomic reflex arc. - A reflex arc is a neural pathway that controls a reflex. There are two types: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles) - Autonomic reflexes sometimes involve the spinal cord and some somatic reflexes are mediated more by the brain than the spinal cord. - Play a key role in regulating controlled conditions in the body e.g. blood pressure - by adjusting heart rate, ventricular contraction force, blood vessel diameter e.g. digestion - by adjusting motility and muscle tone of GI tract e.g. defecation and urination - by opening and closing sphincters

Identify the chemical nature of the autonomic neurotransmitter receptors and their location.

Based on the neurotransmitter they produce and release autonomic neurons are classified as either cholinergic or adrenergic. The receptors for the neurotransmitters are integral membrane proteins located in the plasma membrane of the postsynaptic neuron or effector cell.

Discuss the primary purpose of the sympathetic division responses

During physical or emotional stress, the sympathetic division dominates the parasympathetic division. High sympathetic tone favors body functions that can support vigorous physical activity and rapid production of ATP. At the same time, the sympathetic division reduces body functions that favor the storage of energy. Besides physical exertion, various emotions—such as fear, embarrassment, or rage—stimulate the sympathetic division. Visualizing body changes that occur during "E situations" such as exercise, emergency, excitement, and embarrassment will help you remember most of the sympathetic responses. Activation of the sympathetic division and release of hormones by the adrenal medullae set in motion a series of physiological responses collectively called the fight-or-flight response:

Illustrate and define the structures of ganglia along the path of sympathetic nerves from the CNS to their respective effectors.

Organization of Sympathetic Trunk Ganglia The paired sympathetic trunk ganglia are arranged anterior and lateral to the vertebral column, one on either side. Typically, there are 3 cervical, 11 or 12 thoracic, 4 or 5 lumbar, 4 or 5 sacral sympathetic trunk ganglia, and 1 coccygeal ganglion. The right and left coccygeal ganglia are fused together and usually lie at the midline. Although the sympathetic trunk ganglia extend inferiorly from the neck, chest, and abdomen to the coccyx, they receive preganglionic axons only from the thoracic and lumbar segments of the spinal cord

Illustrate and define the structures of rami along the path of sympathetic nerves from the CNS to their respective effectors.

Pathway from Spinal Cord to Sympathetic Trunk Ganglia Cell bodies of sympathetic preganglionic neurons are part of the lateral gray horns of all thoracic segments and of the first two lumbar segments of the spinal cord. The preganglionic axons leave the spinal cord along with the somatic motor neurons at the same segmental level. After exiting through the intervertebral foramina, the myelinated preganglionic sympathetic axons pass into the anterior root of a spinal nerve and enter a short pathway called a white ramus before passing to the nearest sympathetic trunk ganglion on the same side. Thus, white rami communicantes are structures containing sympathetic preganglionic axons that connect the anterior ramus of the spinal nerve with the ganglia of the sympathetic trunk. The "white" in their name indicates that they contain myelinated axons. Only the thoracic and first two or three lumbar nerves have white rami communicantes.

Illustrate and define the structures of cranial nerves and ganglia along the path of parasympathetic nerves from the CNS to their respective effectors.

The cranial parasympathetic outflow consists of preganglionic axons that extend from the brainstem in four cranial nerves. The sacral parasympathetic outflow consists of preganglionic axons in anterior roots of the second through fourth sacral spinal nerves. The preganglionic axons of both the cranial and sacral outflows end in terminal ganglia, where they synapse with postganglionic neurons. The cranial outflow has four pairs of ganglia and the ganglia associated with the vagus (X) nerve. The four pairs of cranial parasympathetic ganglia innervate structures in the head and are located close to the organs they innervate: 1.ciliary ganglia lie lateral to each optic (II) nerve near the posterior aspect of the orbit. Preganglionic axons pass with the oculomotor (III) nerves to the ciliary ganglia. Postganglionic axons from the ganglia innervate smooth muscle fibers in the eyeball. 2. pterygopalatine ganglia are located lateral to the sphenopalatine foramen, between the sphenoid and palatine bones. They receive preganglionic axons from the facial (VII) nerve and send postganglionic axons to the nasal mucosa, palate, pharynx, and lacrimal glands. 3.submandibular ganglia are found near the ducts of the submandibular salivary glands. They receive preganglionic axons from the facial nerves and send postganglionic axons to the submandibular and sublingual salivary glands. 4.otic ganglia are situated just inferior to each foramen ovale. They receive preganglionic axons from the glossopharyngeal (IX) nerves and send postganglionic axons to the parotid salivary glands.

Describe specific responses of effectors due to increased sympathetic stimulation.

The effects of sympathetic stimulation are longer lasting and more widespread than the effects of parasympathetic stimulation for three reasons: (1) Sympathetic postganglionic axons diverge more extensively; as a result, many tissues are activated simultaneously. (2) Acetylcholinesterase quickly inactivates acetylcholine, but norepinephrine lingers in the synaptic cleft for a longer period. (3) Epinephrine and norepinephrine secreted into the blood from the adrenal medullae intensify and prolong the responses caused by NE liberated from sympathetic postganglionic axons. These blood-borne hormones circulate throughout the body, affecting all tissues that have alpha and beta receptors. In time, blood-borne NE and epinephrine are destroyed by enzymes in the liver.

Components of the autonomic reflex arc: Sensory receptor -

distal end of the sensory neuron which responds to a stimulus and produces a change that will trigger a nerve impulse Usually associated with interoceptors which respond to internal stimuli like stretching of a visceral wall or chemical composition of body fluid)

The ANS is also comprised of a third division known as...

enteric nervous system (ENS). The ENS consists of millions of neurons in plexuses that extend most of the length of the gastrointestinal tract. Its operation is involuntary. Although the neurons of the ENS can function autonomously, they can also be regulated by the other divisions of the ANS. The ENS contains sensory neurons, interneurons, and motor neurons. Enteric sensory neurons monitor chemical changes within the GI tract as well as the stretching of its walls. Enteric interneurons integrate information from the sensory neurons and provide input to motor neurons. Enteric motor neurons govern contraction of GI tract smooth muscle and secretion of GI tract glands.

post-ganglionic neuron

has its cell bodies in the intermediate ganglion and its unmyelinated axon extending from the ganglion to the effector.

Explain the relationship of the hypothalamus, brain stem nuclei, limbic system, and cerebrum to the autonomic nervous system

hypothalamus is a major control and integration centre - Receives sensory input: from visceral functions, olfaction, gustation, changes in temperature, osmolarity and levels of substances in blood - Receives input from emotions (limbic system) Output from hypothalamus influences autonomic centres - In brainstem - CV, salivation, swallowing and vomiting centers - In spinal cord - defecation and urination in sacral spinal cord

Alpha 2 Receptors-

in smooth muscle of some blood vessels -cause inhibition (relaxation and vasodilation) cells of pancreas - cause decreased insulin secretion and inhibition of digestive hormone secretion platelets of blood - cause aggregation to form platelet plug

Beta 2 Receptors -

in smooth muscle of walls of airways, blood vessels that serve the heart, skeletal muscle adipose tissue, liver and walls of visceral organs like the urinary bladder - cause inhibition (relaxation and vasodilation, dilation of airways and relaxation of organ walls) - in ciliary muscles of the eye - cause inhibition (relaxation) - in hepatocytes in the liver - cause glycogenolysis

preganglionic neuron

in the autonomic nervous system of the PNS, a neuron that has its cell body located in the CNS and whose axon extends into the PNS to synapse with a second neuron at an autonomic ganglion (the second neuron's axon synapses with the target organ)

Define autonomic tone and emphasize that most organs receive innervation from both ANS divisions that have opposing and balancing effects, which depend on the neurotransmitter released and the particular receptor on the organ.

most body organs receive innervation from both divisions of the ANS, which typically work in opposition to one another. The balance between sympathetic and parasympathetic activity, called autonomic tone, is regulated by the hypothalamus. Typically, the hypothalamus turns up sympathetic tone at the same time it turns down parasympathetic tone, and vice versa. The two divisions can affect body organs differently because their postganglionic neurons release different neurotransmitters and because the effector organs possess different adrenergic and cholinergic receptors. A few structures receive only sympathetic innervation—sweat glands, arrector pili muscles attached to hair follicles in the skin, the kidneys, the spleen, most blood vessels, and the adrenal medullae. In these structures there is no opposition from the parasympathetic division. Still, an increase in sympathetic tone has one effect, and a decrease in sympathetic tone produces the opposite effect.

Structural and Functional of Autonomic Nervous System

regulates cardiac muscle, smooth muscle, and glands. These tissues are often referred to as visceral effectors because they are usually associated with the viscera (internal organs) of the body. - consists of neurons that regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac muscle, smooth muscle, and glands). Changes in the diameter of the pupils, dilation and constriction of blood vessels, and adjustment of the rate and force of the heartbeat are examples of autonomic motor responses. Unlike skeletal muscle, tissues innervated by the ANS often function to some extent even if their nerve supply is damaged. The heart continues to beat when it is removed for transplantation into another person, smooth muscle in the lining of the gastrointestinal tract contracts rhythmically on its own, and glands produce some secretions in the absence of ANS control. The ANS usually operates without conscious control. ex, can't voluntarily slow down your heart rate; instead, your heart rate is subconsciously regulated. The ANS can also receive sensory input from sensory neurons associated with interoceptors, sensory receptors located in blood vessels, visceral organs, muscles, and the nervous system that monitor conditions in the internal environment. Examples of interoceptors are chemoreceptors that monitor blood CO2 level and mechanoreceptors that detect the degree of stretch in the walls of organs or blood vessels. The ANS consists of two main division (branches): the sympathetic nervous system and the parasympathetic nervous system. Most organs receive nerves from both of these divisions, an arrangement known as dual innervation.

Visceral Effector (Glands) - Adrenal medulla -

sympathetic = secretion of epinephrine and norepinephrine (nicotinic ACh receptors)

Visceral Effector (Glands)- Kidneys

sympathetic = secretion of renin

Visceral Effector (Glands) - Lacrimal (tear) -

sympathetic = slight tears; parasympathetic = secretion of tears

Components of the autonomic reflex arc: Motor neurons -

two motor neuron pathway that conducts nerve impulse from integrating center out of CNS to the effector (pre- and postganglionic neurons)

Sympathetic Division(Thoracolumbar)

* Preganglionic neurons have cell bodies in lateral horns of grey matter in the 12 thoracic segments * Synapse to post ganglionic neuron: - in ganglion it first reaches - ascend or descend from entry level to synapse - pass through to synapse at prevertebral ganglion - extend through both to chromaffin cells

Discuss the primary purpose of the parasympathetic division and the general body functions it directs.

- Enhances rest and digest activities - High parasympathetic responses favours body functions that conserve and restore body energy during times of rest and recovery - Between times of exercise, parasympathetic dominates over sympathetic in sending impulses to the GI tract (digestive glands and smooth muscle) - Allows energy-supplying foods to be digested and absorbed - Reduces body functions that support physical activity

Visceral Effector: Smooth Muscle

- Lungs (bronchial muscles) - sympathetic = relaxation (airway dilation); parasympathetic = contraction (airway constriction) - Stomach and Intestines - sympathetic = decreased motility and tone, contraction of sphincters; parasympathetic = increased motility and tone, relaxation of sphincters - Urinary Bladder - sympathetic = relaxation of muscular wall, contraction of internal urethral sphincter; parasympathetic = contraction of muscular wall, relaxation of internal urethral sphincter

Parasympathetic Division(Craniosacral)

- Preganglionic neurons have cell bodies in the nuclei of cranial nerves (III, VII, IX and X) and lateral grey matter of the 2-4 sacral segments - Synapse with postganglionic neurons at terminal ganglia near or within an effector (with 4 or 5 post synaptic neurons supplying a single effector

SLUDD is as an acronym used to describe the responses of the parasympathetic nervous system:

- Salivation (increased) - Lacrimation (increased) - Urination (increased) - Digestion (increased) - Defecation (increased) ... and 3 decreases (in the rate of the heart beat (atrial), airway size and rate of breathing, and pupil size)

Visceral Effector: Cardiac Muscle

Cardiac Muscle - sympathetic = increased heart rate and force of atrial and ventricular contractions; parasympathetic = decreased heart rate and force of atrial contraction

mechanoreceptors

Examples of interoceptors that detect the degree of stretch in the walls of organs or blood vessels.

chemoreceptors

Examples of interoceptors that monitor blood CO2 level

nicotinic receptors

In plasma membrane of dendrites and cell bodies of sympathetic and parasympathetic postganglionic neurons, plasma membrane of chromaffin cells of the adrenal medulla and the motor end plate (of the NMJ)

Alpha 1 Receptors -

In smooth muscle of blood vessels of salivary glands, skin, mucosal membranes, kidneys, abdominal viscera and sphincters of the stomach and urinary bladder - cause excitation (contraction causing vasoconstriction and closing of sphincters) in salivary glands - cause secretion of potassium ions and water in sweat glands (palms and soles of feet) - cause increased sweating

Muscarinic receptors

In the plasma membrane of all effectors (smooth muscle, cardiac muscle and glands) innervated by parasympathetic postganglionic axons

Structural and Functional of Somatic Nervous System

When a somatic motor neuron stimulates a skeletal muscle, it contracts; the effect is always excitation. If somatic motor neurons cease to stimulate a skeletal muscle, the result is a paralyzed, limp muscle that has no muscle tone. The somatic nervous system usually operates under voluntary (conscious) control. Voluntary control of movement involves motor areas of the cerebral cortex that activate somatic motor neurons whenever you have a desire to move (kick a ball, turn a screwdriver, smile for a picture, etc.), neural pathways from the primary motor area of the cerebral cortex activate somatic motor neurons that cause the appropriate skeletal muscles to contract. The somatic nervous system is not always under voluntary control, however. The somatic motor neurons that innervate skeletal muscles involved in posture, balance, breathing, and somatic reflexes (such as the flexor reflex) are involuntarily controlled by integrating centers in the brainstem and spinal cord. The somatic nervous system can also receive sensory input from sensory neurons that convey information for somatic senses (tactile, thermal, pain, and proprioceptive sensations or the special senses (sight, hearing, taste, smell, and equilibrium. All of these sensations normally are consciously perceived. In response to this sensory information, somatic motor neurons cause the appropriate skeletal muscles of the body to contract.

Components of the autonomic reflex arc: Sensory neuron -

conducts nerve impulses from receptors to CNS

Discuss general body functions of sympathetic division responses

fight-or-flight response, which includes the following effects: - The pupils of the eyes dilate. - Heart rate, force of heart contraction, and blood pressure increase. - The airways dilate, allowing faster movement of air into and out of the lungs. - The blood vessels that supply the kidneys and gastrointestinal tract constrict, which decreases blood flow through these tissues. The result is a slowing of urine formation and digestive activities, which are not essential during exercise. - Blood vessels that supply organs involved in exercise or fighting off danger—skeletal muscles, cardiac muscle, liver, and adipose tissue—dilate, allowing greater blood flow through these tissues. - Liver cells perform glycogenolysis (breakdown of glycogen to glucose), and adipose tissue cells perform lipolysis (breakdown of triglycerides to fatty acids and glycerol). - Release of glucose by the liver increases blood glucose level. - Processes that are not essential for meeting the stressful situation are inhibited. For example, muscular movements of the gastrointestinal tract and digestive secretions slow down or even stop.

Beta 1 Receptors -

in cardiac muscle fibers - cause excitation (increased force and rate of contraction) - in juxtaglomerular cells of kidneys - cause secretion renin - in posterior pituitary - cause ADH secretion - in adipose cells - cause breakdown of triglycerides (release fatty acids into blood)

Components of the autonomic reflex arc: Integrating centre -

interneurons in CNS relay signals from sensory to motor neurons and main integrating centres for autonomic reflexes are in the hypothalamus and brainstem (some specific ones are in spinal cord)

Describe the effects of norepinephrine as an adrenergic neuron neurotransmitter.

is a neurotransmitter that is important for attentiveness, emotions, sleeping, dreaming, and learning. Norepinephrine is also released as a hormone into the blood, where it causes blood vessels to contract and heart rate to increase. Norepinephrine plays a role in mood disorders such as manic depression.

The anatomy of all autonomic motor pathways consist of two motor neurons in a series:

preganglionic neuron has its cell body in the central nervous system and the axon extends to an autonomic ganglion post-ganglionic neuron has its cell bodies in the intermediate ganglion and its unmyelinated axon extending from the ganglion to the effector.

Components of the autonomic reflex arc: Effector -

sooth muscle, cardiac muscle and glands

Visceral Effector (Glands)- Liver-

sympathetic = glycogenolysis, gluconeogenesis, decreased bile secretion; parasympathetic = glycogen synthesis and increased bile secretion

Visceral Effector (Glands)- Pineal-

sympathetic = increase synthesis and release of melatonin

Visceral Effector (Glands)- Sweat

sympathetic = increased sweating in most body regions

Visceral Effector (Glands)- Pancreas -

sympathetic = inhibits secretion of digestive enzymes and insulin while promoting secretion of glucagon; parasympathetic = secretion of digestive enzymes and insulin

Visceral Effector (Glands)- Posterior pituitary -

sympathetic = secretion of ADH