Lecture Notes - Chapter 16 PDF

**[Lecture Notes - Chapter 16]** **Introduction** - **Efferent (Motor) Division of the Peripheral Nervous System** A. **Autonomic nervous system** (visceral motor system) -- The focus of this chapter - a. b. c. d. - - - - B. ***Somatic Nervous System** (SNS) -- Studied...

**[Lecture Notes - Chapter 16]** **Introduction** - **Efferent (Motor) Division of the Peripheral Nervous System** A. **Autonomic nervous system** (visceral motor system) -- The focus of this chapter - a. b. c. d. - - - - B. ***Somatic Nervous System** (SNS) -- Studied in Chapter 15* - - - **Higher-order functions** - Memory, states of consciousness, and age-related changes in the CNS **16-1 -- The Autonomic Nervous System** 1. - **Visceral motor** neurons originate in the hypothalamus and their axons extend to **autonomic nuclei** in the brain stem and/or the lateral gray horns of the spinal cord - These neurons are comparable to the upper motor neurons in somatic motor pathways 2. 3. - Has 2 main divisions and operates largely outside our awareness 1. **Sympathetic** **division (Thoracolumbar)** - *"Fight or flight" --* Prepares the body for stressful situations and emergencies - Increases alertness, metabolic rate, and muscular abilities 2. **Parasympathetic** **division (Craniosacral)** - *"Resting & digesting" -* Controls during resting conditions - Reduces metabolic rate and promotes digestion 1. **Enteric** **Nervous** **System** (**ENS**) - *"The Brain of the Gut"* - Consists of an extensive nerve networks in the walls of the digestive tract - ENS is influenced by the ANS but many complex visceral reflexes are coordinated locally and [operate without instructions from the CNS!] - Sympathetic vs. Parasympathetic Division - Most often, these two divisions have opposing effects - If the sympathetic division causes excitation, the parasympathetic causes inhibition - The two divisions may work together, with each controlling one stage of a complex process - The two divisions may also work independently with only one division innervates some structures **16-2 -- The Sympathetic Division** - The Sympathetic Division prepares the body for crisis, producing a "**fight or flight**" response - Major effects of the Sympathetic Division 1. Heightened mental alertness, euphoria 2. Increased metabolic rate and muscular tone 3. Reduced digestive and urinary functions 4. Liberation of energy reserves 5. Increased respiratory rate and respiratory passageways dilate 6. Increased heart rate and blood pressure 7. Sweat glands activated - **Preganglionic neurons of the Sympathetic Division** - Cell bodies originate in the lateral gray horns of spinal cord segments T~1~ through L~2~ - Called "**thoracolumbar flow**" - **Preganglionic fibers (axons)** - Pass though the - ventral root \> spinal nerve \> **white ramus** - The ramus is white because the preganglionic fibers are [ myelinated] - Synapse on **ganglionic neurons** located within an **autonomic ganglion** 1. **Sympathetic chain ganglia -- see below \*** - **Postganglionic fibers innervate structures in the head, neck, body wall, limbs, and the thoracic cavity** 2. **Collateral ganglia -- see below \*\*** - **Postganglionic fibers innervate structures in the abdominopelvic cavity** 3. **Adrenal medullae -- see below \*\*\*** - Ganglionic neurons are modified neuroendocrine cells that releases epinephrine and norepinephrine into the blood - Preganglionic fibers (axons) are **[short]** because autonomic ganglia are generally located close to the spinal cord *(adrenal medulla is the exception)* - **Ganglionic Neurons** of the Sympathetic NS - Cell bodies located in one of the three types of autonomic ganglia - **Postganglionic fibers** - **These are** **[long]** axons because they extend from the autonomic ganglia all the way to the effector/target organs - Sympathetic chains are found on both sides of vertebral column - Each sympathetic chain contains many ganglia: - 3 cervical ganglia - 10--12 thoracic ganglia - 4--5 lumbar ganglia - 4--5 sacral ganglia - 1 coccygeal ganglion - Each ganglion innervates a particular body segment(s) - What happens in a sympathetic chain ganglion? - It contains preganglionic fibers that synapse with ganglionic neurons - Where do the **postganglionic fibers** go? - It depends on where the motor command is going: A. - The **dorsal ramus** - Innervate effectors in the [back] - Sweat glands of the skin of the back - Smooth muscles in superficial blood vessels & arrector pili muscles in the skin of the back - The **ventral ramus** - Innervate effectors in the [body wall, head, neck or limbs] - Sweat glands of the skin of the body wall, head, neck or limbs - Smooth muscles in superficial blood vessels & arrector pili muscles in the skin of the body wall, head, neck or limbs A. A postganglionic fiber may leave the sympathetic chain ganglion and form bundles known as **sympathetic nerves** - Innervate organs in the thoracic cavity (heart and lungs) - **White rami only occur from levels T~1~ -- L~2~ but gray rami** occur at the level of every spinal nerve. Why is this? - Preganglionic neurons - Are only found in the lateral gray horns from **T~1~ -- L~2~** - May synapse in a ganglion at the same level they emerge OR - May go up and down the sympathetic chain to synapse in ganglia at different levels - *For example, a preganglionic fiber from T2 may ascend the trunk to synapse with a ganglionic neuron at level C3* - A single preganglionic fiber may synapse on many ganglionic neurons - How do sympathetic commands get to structures in the head - The come from the superior cervical ganglion - Are located anterior to the vertebrae - Innervate variety organs in the abdominopelvic cavity and contribute to: - A reduction of blood flow and energy by organs not vital to short-term survival - Release of stored energy reserves - **Preganglionic fibers that synapse in collateral ganglia** - Follow the same initial path as those that synapse in the sympathetic chain ganglia BUT pass through the sympathetic chain ganglia [w/o synapsing] - Once they pass through the sympathetic chain ganglia they are bundled into **splanchnic nerves** - Located in the posterior wall of abdominal cavity - Synapse in one of 3 **collateral ganglia**: A. **celiac ganglion** - Near the after the *celiac trunk* (an abdominal artery) - **Postganglionic fibers** innervate stomach, liver, gallbladder, pancreas, and spleen B. **superior messenteric ganglion** - Near base of *superior mesenteric artery* - Postganglionic fibers innervate small intestine and proximal 2/3 of large intestine C. **inferior messenteric ganglion** - Near base of *inferior mesenteric artery* - Postganglionic fibers innervate the large intestine, kidney, urinary bladder, sex organs - *The adrenal medulla is an exception to the rule: it has a long preganglionic fiber and a short postganglionic fiber.* - **Preganglionic fibers e**xtend all the way to the adrenal medulla, which is at the center of each adrenal gland - The **adrenal medulla** itself is a modified sympathetic ganglion - The preganglionic fibers synapse on modified ganglionic neurons called **neuroendocrine cells** - When stimulated, neuroendocrine cells release neurotransmitters into bloodstream rather than a synapse! - **Epinephrine** (75 -- 80% of output) - Also called *adrenaline* - **Norepinephrine** (20-25% of output) - Also called *noradrenaline* - Bloodstream carries neurotransmitters through body - Allows the neurotransmitters to function as hormones to affect target cells [throughout the body] - Causes **sympathetic activation** *"fight or flight"* - Controlled by sympathetic centers in hypothalamus - Cause changes in the metabolic activities of different cells, including cells that do not have direct sympathetic innervation **16-3 -- Neurotransmitters and Receptors in the Sympathetic Division** - Within sympathetic ganglia preganglionic fibers release **acetytlcholine** at their synapse with a ganglionic neuron - **Cholinergic** synapses use acetylcholine as a neurotransmitter - Binds to nicotinic **receptors** on the ganglionic neuron - Excites the ganglionic neuron - At the effector - Most postganglionic fibers release norepinephrine (NE) at their synapse with an effector - - - - - - Some postganglionic fibers release acetylcholine - **16-4 -- The Parasympathetic Division** - Parasympathetic Division Overview - The parasympathetic division stimulates food processing, nutrient absorption and storage, and promotes sedentary activities, producing a "**resting & digesting**" response - Major Effects of the Parasympathetic Division 1. Decreased metabolic rate 2. Decreases heart rate and blood pressure - Constriction of the respiratory passageways - Reduction in heart rate and in the force of contraction 3. Promotes digestion - Secretion by salivary and digestive glands - Increased motility and blood flow in digestive tract - Stimulation and coordination of defecation - Secretion of hormones that promote the absorption and utilization of nutrients by peripheral cells for growth and division 4. Stimulation and coordination of urination 5. Changes in blood flow and glandular activity associated with sexual arousal 6. Constriction of the pupils and focusing of the lens - Organization of the Parasympathetic Division - - - Called "**craniosacral flow**" - - Because ganglia of the parasympathetic division are located close to the target organ - A. ***Cranial parasympathetic outflow*** to visceral structures in head - *Preganglionic fibers travel through the **Oculomotor nerve (III)** &* - Synapse in the **ciliary ganglion** and postganglionic fibers extend to the [iris] and the [lens of the eye] - *Preganglionic fibers travel through the **Facial nerve (VII)** &* - Synapse in the pterygopalatine ganglion and postganglionic fibers extend to the [lacrimal gland] - Synapse in the Submandibular ganglion and postganglionic fibers extend to [salivary glands] - *Preganglionic fibers travel through the **Glossopharyngeal nerve (IX)** &* - Synapses in the Otic ganglion and postganglionic fibers extend to the [salivary glands] - *Preganglionic fibers travel through the **Vagus nerve** (X) &* - Provides parasympathetic innervation to structures in: - Neck, thoracic cavity, and abdominopelvic cavity - To areas as distant as the distal portion of large intestine - Provides 75 percent of all parasympathetic outflow! - Branches intermingle with fibers of the sympathetic division to form plexuses - Synapse in parasympathetic ganglia located close to (or within) target organs - **Terminal** **ganglion** -- paired and [located adjacent to] the target organ - Usually paired - **Intramural** **ganglion** - [embedded within] tissues of target organ B. - Preganglionic fibers carry sacral parasympathetic output do not join ventral roots of spinal nerves - Instead theyform **pelvic nerves** - **Preganglionic fibers synapse with a ganglionic neuron within an intramural ganglion** - Innervate kidneys, urinary bladder, portions of large intestine, and the sex organs - - - **16-5 -- Neurotransmitters and Receptors in the Parasympathetic Division** - All Parasympathetic neurons release Ach as a neurotransmitter. - Preganglionic cells of the Parasympathetic Division - Release Ach - Ach binds to **nicotinic** **receptors** on the post synaptic membrane of ganglionic neurons - Exposure to ACh causes excitation of ganglionic neuron or muscle fiber - Ganglionic neurons of the Parasympathetic Division also release Ach - Ach binds to **muscarinic** **receptors** at cholinergic neuromuscular junctions (neuron to muscle) or neuroglandular junctions (neuron to effector) - Can be excitatory or inhibitory **16-6 -- Sympathetic vs. Parasympathetic Effects** - Sympathetic Division - May innervate specific visceral structures via synapses or - May reach organs and tissues throughout the body via sympathetic activation - Neurotransmitters distributed into the blood has widespread effects - Parasympathetic Division - Only innervates specific visceral structures via synapses **16-7 -- Dual Innervation** - **Autonomic** **Tone** - Even without stimulation, ANS motor neurons show a resting level of spontaneous background activity - Allows nerves to increase activity - Or decrease activity - Most organs receive **Dual Innervation** - Instructions from both sympathetic and parasympathetic divisions - The divisions will have opposing effects - *Example: the heart* - Divisions have opposing effects on heart function - *Parasympathetic division* dominates at rest - Acetylcholine released by postganglionic fibers **slows heart rate** - *Sympathetic division* dominates during stress or crisis - NE released **accelerates heart rate** - Small amounts of Ach and NE are released continuously, producing autonomic tone - Some organs do not have Dual Innervation - Autonomic tone is even more important in these structures - *Example: sympathetic control of the smooth muscles controlling blood vessel diameter* - Sympathetic adrenergic fibers release NE at smooth muscle cells in blood vessel walls - Muscle cells remain [partially] contracted (blood flow somewhat restricted) - When more blood flow is needed, the sympathetic division: - Decreases the rate of NE release - Increases the release of Ach from sympathetic cholinergic fibers - Muscle cells relax and blood vessel dilates (blood flow increases) **16-8 Visceral Reflexes** - **Visceral** **Reflexes** - Provide automatic motor responses to visceral stimuli - Can be modified, facilitated, or inhibited by higher centers, especially the hypothalamus - All are polysynaptic reflexes A. Long reflexes - Autonomic equivalents of somatic polysynaptic reflexes - Typically control the activities of an entire organ - Visceral sensory neurons deliver information to CNS along dorsal roots of spinal nerves - ANS carries motor commands to visceral effectors B. Short reflexes - Provide most of the control and coordination in digestive tract and associated glands - Neurons involved form **enteric nervous system** - Capable of controlling digestive functions independent of CNS - Sensory neurons bypass CNS and instead synapse on interneurons in autonomic ganglia - Interneurons synapse on ganglionic neurons and distributes the motor command to a small area of a target organ for [localized] effects - **Visceral reflex arc** 1. Sensory receptor 2. Sensory neuron 3. Processing center (one or more interneurons) - May be in the CNS (long reflex) - May be in an autonomic ganglia (short reflex) 4. Visceral motor neurons - Preganglionic neuron (long reflex only) - Ganglionic neuron (long & short reflexes) 5. Peripheral effector - The hypothalamus - Can modify, facilitate, or inhibit visceral reflexes - *Example: consensual reflex* - Because the hypothalamus interacts with nearly all areas of the brain, including - the cerebral cortex (conscious awareness) - the limbic system (emotions) - activity in these areas can have a dramatic effect on ANS activity - The medulla oblongata - Coordinates complex sympathetic and parasympathetic reflexes - Respiration rate, heart rate, force of cardiac contractions - Salivation, swallowing, digestive secretions, peristalsis, and urinary function **16-9 Higher Order Functions** 1. Require the cerebral cortex 2. Involve conscious and unconscious information processing 3. Are not part of programmed "wiring" of brain - Can adjust over time - **Fact** **memories** - Are specific bits of information - *She wore a yellow dress* - *The scent of a particular perfume* - **Skill** **memories** - Learned motor behaviors - *How to light a match* - *Playing the piano* - With repetition, are incorporated at unconscious level - Two classes of memories are recognized: 4. **Short-term** **memories** - Do not last long, but while they persist the information can be recalled immediately - Contain small bits of information - *Such as a phone number* - Repeating the information can help to convert the short term memory into a long term memory - **Memory** **consolidation** is the conversion from short-term to long-term memory 5. **Long-term** **memories** - Last much longer than short-term memories - In some cases, they last a lifetime - Two types of long-term memory - *Secondary* *memories* fade over time and may require effort to recall - *Tertiary* *memories* are with you for life - Brain Regions Involved in Memory Consolidation/Access - **Amygdaloid body** & **hippocampus** - Components of the limbic system - Essential to memory consolidation - **Nucleus basalis** - **Cerebral cortex** - Stores long-term memories - Conscious motor and sensory memories are stored in the corresponding association area - *Example: Visual memories are stored in the visual association area, auditory memories are stored in the auditory association area, etc.* - Your degree of wakefulness indicates level of ongoing CNS activity - **Conscious** - Awareness of and attention to external events & stimuli - **Unconscious** - Sleep: may be awakened by normal stimuli - Anesthesia or coma: unresponsive to stimuli - Many degrees of conscious and unconscious states - *Example: Hypoactive delerium* - When CNS function is abnormal or depressed, the state of wakefulness is affected - **Deep** **sleep** - Also called *slow-wave or Non-REM* (*NREM*) sleep - Body completely relaxed - Cerebral cortex activity minimal - Heart rate, blood pressure, respiratory rate, and energy utilization decline up to 30 percent - **Rapid** **eye** **movement** (**REM**) **sleep** - Active dreaming occurs - Eyes move rapidly as dream events unfold - Changes in blood pressure & respiratory rate - EEG resembles the awake state - Muscle tone decreases markedly - Intense inhibition of somatic motor neurons prevents you from physically responding to your dreams - Nighttime sleep pattern begins in deep sleep then alternates between deep sleep & REM - Has important impact on CNS - Protein synthesis in neurons increases - Extended periods without sleep lead to disturbances in mental function - 25 percent of the U.S. population experiences *sleep disorders* - The **Reticular** **activating** **system** (**RAS**) - Extends from the medulla oblongata to the midbrain - RAS output from the midbrainprojects to thalamic nuclei that influence large areas of the cerebral cortex - When RAS is inactive so is the cerebral cortex - Any stimulus sufficient to activate the reticular formation or RAS produces widespread activation of the cerebral cortex or **arousal** - Causes you to wake up from sleep - Effects last only a minute - Remaining awake and maintaining consciousness depends on activity in the cerebral cortex, basal nuclei, and sensory and motor pathways continuing to stimulate RAS - Regulation of sleep--wake cycles - Involves interplay between brain stem nuclei - One group stimulates RAS with NE to maintain awake, alert state - Other group promotes deep sleep by depressing RAS activity with serotonin - After many hours, reticular formation becomes less responsive to stimulation and we becomes less alert and more lethargic **16-10 Age Related Changes to the Nervous System** - Effects of Aging - 85 percent of people over age 65 have changes in mental performance and CNS function - Anatomical and physiological changes begin after maturity (age 30) and accumulate over time 1. *Reduction in Brain Size and Weight* 2. *Reduction in Number of Neurons* 3. *Decrease in Blood Flow to Brain* - Fatty deposits build up in walls of blood vessels (arteriosclerosis) - Reduces blood flow through arteries - Increases chances of cerebrovascular accident (CVA), or stroke 4. *Changes in Synaptic Organization of Brain* - Synaptic connections are lost over time - Rate of neurotransmitter production declines 5. *Intracellular & Extracellular Changes in CNS Neurons* - Intracellular deposits - **Lipofuscin** - **Neurofibrillary tangles** - **Extracellular deposits** - **Plaques** - Plaques and tangles contain deposits of several peptides - Primarily two forms of **amyloid** (**A**) **protein** - Appear in brain regions associated with memory, emotions, and intellectual function - *Have a possible link to **Alzheimer's disease*** - A type of **senile dementia** (senility) that involves - Memory loss - Inability to make new memories - Emotional disturbances - **Alzheimer's disease** is most common - Anatomical changes lead to functional changes: - Memory consolidation comes more difficult - Secondary memories harder to access - Sensory Systems: Hearing, balance, vision, smell, & taste become less acute - Reflexes weaken or disappear - Motor Control: Precision decreases and reaction rates are slowed