Biology 223- Unit 5 PDF

Spinal Nerves and Plexuses Three Connective Tissue Layers of Spinal Nerves 1. Epineurium Outer layer Dense network of collagen fibers 2. Perineurium Middle layer Divides nerve into fascicles (axon bundles) 3. Endoneuriu...

Spinal Nerves and Plexuses Three Connective Tissue Layers of Spinal Nerves 1. Epineurium Outer layer Dense network of collagen fibers 2. Perineurium Middle layer Divides nerve into fascicles (axon bundles) 3. Endoneurium Inner layer Surrounds individual axons  Figure 13-6 A Peripheral Nerve Blood vessels Connective Tissue Layers Epineurium covering spinal nerve Perineurium (around one fascicle) Endoneurium Myelinated axon Fascicle Schwann cell  Spinal Nerves and Plexuses Peripheral Distribution of Spinal Nerves – Spinal nerves Where dorsal and ventral roots unite Then branch and form pathways to destination  Spinal Nerves and Plexuses Nerve Plexuses – Complex, interwoven networks of nerve fibers – Control skeletal muscles of the neck and limbs  Spinal Nerves and Plexuses The Four Major Plexuses 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus  Figure 13-10 Peripheral Nerves and Nerve Plexuses C Lesser occipital nerve C1 Great auricular nerve Cervical C2 plexus C3 Transverse cervical nerve C4 Supraclavicular nerve C5 Brachial C6 Phrenic nerve plexus C7 T 8 T1 T2 Axillary T3 nerve T4 T5 T6 Musculocuta T7 neous 8 nerve T Thoracic nerves 9 T 10 T 11  Figure 13-10 Peripheral Nerves and Nerve Plexuses T 1 2L Radial nerve 1 Lumbar L plexus 2 Ulnar nerve L L3 Median nerve 4L S5 Iliohypogastric Sacral 1 nerve plexus S 2S 3S Ilioinguinal 4S nerve C5 Lateral femoral o cutaneous nerve 1 Genitofemoral nerve Femoral nerve Obturator nerve Superior Gluteal nerves Inferior Pudendal nerve Saphenous nerve Sciatic nerve  Reflexes Reflexes – Automatic responses coordinated within spinal cord – Through interconnected sensory neurons, motor neurons, and interneurons – Produce simple and complex reflexes  Reflexes Neural Reflexes – Rapid, automatic responses to specific stimuli – Basic building blocks of neural function – One neural reflex produces one motor response – Reflex arc The wiring of a single reflex Beginning at receptor Ending at peripheral effector Generally opposes original stimulus (negative feedback)  Reflexes Five Steps in a Neural Reflex – Step 1: Arrival of stimulus, activation of receptor Physical or chemical changes – Step 2: Activation of sensory neuron Graded depolarization – Step 3: Information processing by postsynaptic cell Triggered by neurotransmitters – Step 4: Activation of motor neuron Action potential – Step 5: Response of peripheral effector Triggered by neurotransmitters  Figure 13-15 Events in a Neural Reflex Dorsal Sensation Arrival of stimulus and Activation of a root activation of receptor sensory neuron relayed to the brain by axon collaterals Information processing REFLEX in the CNS ARC Receptor Stimulus Response by effector Effector Ventral root KEY Sensory neuron Activation of a (stimulated) motor neuron Excitatory interneuron Motor neuron (stimulated)  Reflexes Four Classifications of Reflexes 1. By early development 2. By type of motor response 3. By complexity of neural circuit 4. By site of information processing  Reflexes Development of Reflexes – Innate reflexes Basic neural reflexes Formed before birth – Acquired reflexes Rapid, automatic Learned motor patterns  Reflexes Motor Response – Nature of resulting motor response Somatic reflexes – Involuntary control of nervous system » Superficial reflexes of skin, mucous membranes » Stretch or deep tendon reflexes (e.g., patellar, or “knee- jerk,” reflex) Visceral reflexes (autonomic reflexes) – Control systems other than muscular system  Reflexes Complexity of Neural Circuit – Monosynaptic reflex Sensory neuron synapses directly onto motor neuron – Polysynaptic reflex At least one interneuron between sensory neuron and motor neuron  Reflexes Site of Information Processing – Spinal reflexes Occur in spinal cord – Cranial reflexes Occur in brain  Figure 13-16 The Classification of Reflexes Reflexes can be classified by development response complexity processing of circuit site Innate Somatic Monosynaptic Spinal Reflexes Reflexes Reflexes Genetically Control skeletal One synapse Processing in determined contractions muscle the spinal cord Include superficial and stretch reflexes Acquired Visceral (Autonomic) Reflexes Polysynaptic Cranial Reflexes Reflexes Learned Control actions Multiple Processing in ofcardiac smoothmuscles, and glands, and (two to several synapse the brain adipose tissue hundred)  Spinal Reflexes Spinal Reflexes – Range in increasing order of complexity Monosynaptic reflexes Polysynaptic reflexes Intersegmental reflex arcs – Many segments interact – Produce highly variable motor response  Spinal Reflexes Monosynaptic Reflexes – A stretch reflex – Have least delay between sensory input and motor output For example, stretch reflex (such as patellar reflex) – Completed in 20–40 msec – Receptor is muscle spindle  Figure 13-17 A Stretch Reflex Receptor (muscle spindle) Spinal cord Stretch REFLE X Stimulu ARC s Effector Contraction KEY Sensory neuron (stimulated) Motor neuron (stimulated) Response  Spinal Reflexes Postural reflexes – Stretch reflexes – Maintain normal upright posture – Stretched muscle responds by contracting Automatically maintain balance  Spinal Reflexes Polysynaptic Reflexes – More complicated than monosynaptic reflexes – Interneurons control more than one muscle group – Produce either EPSPs or IPSPs  Spinal Reflexes The Tendon Reflex – Prevents skeletal muscles from: Developing too much tension Tearing or breaking tendons – Sensory receptors unlike muscle spindles or proprioceptors  Spinal Reflexes Withdrawal Reflexes – Move body part away from stimulus (pain or pressure) For example, flexor reflex – Pulls hand away from hot stove – Strength and extent of response Depend on intensity and location of stimulus  Figure 13-19 A Flexor Reflex Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors KEY inhibited Sensory neuron Motor (stimulated) neuron (inhibited) Excitatory Inhibitory interneuron interneuron Motor neuron (stimulated)  Somatic Nervous System Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings  Nervous System Two Divisions of the Nervous System Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Cranial Nerves and Spinal Nerves Two Divisions of PNS: 1. Somatic Nervous System SNS Skeletal Muscle Control (Conscious or voluntary)efferent Sensory Division(afferent) 2. Autonomic Nervous System ANS Control of cardiac and smooth muscle, glands and adipose tissue (Unconscious control or involuntary. Two divisions: 1. Sympathetic Parasympathetic  Comparison of SNS and ANS SNS uses both somatic sensory and somatic motor neurons. A somatic sensory neuron conducts stimulus information (such as a tactile receptor in the skin) Somatic motor neurons innervate skeletal muscle fibers. ANS also utilizes sensory and motor neurons. Visceral sensory neurons provide input to activate the ANS. Visceral motor neurons innervate skeletal, cardiac and smooth muscle, glands and adipose tissue 18-3 Fig. 12.2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central nervous system Peripheral nervous system cranial and spinal nerves Spinal Sensor Motor Brai y Division cord n Division efferent afferent Visceral Somatic Visceral Somatic motor motor sensory sensory Division Division division division autonomic Skeletal muscle Sympatheti Parasympatheti c c division division  An Introduction to Sensory Pathways and the Somatic Nervous System An Introduction to: Sensory receptors Sensory processing Conscious and subconscious motor functions  ANS & PNS Rely on receptors Receptor: Dendrites or specialized cells that transmits action potentials from the body and external environment to the CNS. Sensation: the arriving information to CNS Perception: Conscious awareness of a sensation Projection: The area where the CNS makes you perceive that the sensation started  The Senses 1. Special Senses: found in special sense organs 2. General Senses: scattered throughout body. a. Somatic Senses b. Visceral Sense  Sensory Receptors Special Senses Olfaction (smell) -Chemoreceptor Vision (sight)-Photoreceptor (Rods-dim light & Cones-high light(red, green, blue)) Gustation (taste) Equilibrium (balance) -Mechanical receptor Hearing  Sensory Receptors General Senses Describe our sensitivity to: Temperature Pain All Mechanical Receptors Touch Pressure Vibration Proprioception  Detecting Stimuli -All receptors have receptor specificity -Receptive Field  Sensory Receptors Adaptation Reduction in sensitivity of a constant stimulus Your nervous system quickly adapts to stimuli that are painless and constant  Sensory Receptors Adaptation Tonic receptors Are always active Show little peripheral adaptation Are slow-adapting receptors Remind you of an injury long after the initial damage has occurred  Sensory Receptors Adaptation Phasic receptors Are normally inactive Become active for a short time whenever a change occurs Provide information about the intensity and rate of change of a stimulus Are fast-adapting receptors  Receptor Activity 1. Information arrives at receptor 2. Receptor Potential Local Potential 3. Generator Potential Action Potential 4. Transduction  Classifying Sensory Receptors -Classify receptors based on: 1. Location of Sensation 2. Type of Sensation Location of Sensation Interoceptors: Monitor visceral organs and function Exteroceptors: Monitor external environment Proprioceptors: Monitor positions of skeletal muscles and joints No proprioceptors are found in the thoracic and abdominopelvic cavities.  Type of Sensation 1. Nociceptors 2. Thermoreceptors 3. Mechanoreceptors 4. Chemoreceptors  Nociceptors Location: common Skin joint capsules blood vessel walls Periostea around bones Sensitive to: Temperature extremes Mechanical damage Chemicals  Nociceptors free nerve endings with large receptive fields Branching tips of dendrites Not protected by accessory structures Two types of axons will transmit pain sensations: – Type A fibers -Small diameter Type B fibers -Myelinated -Medium diameter – Type C fibers -Myelinated -Small diameter -Unmyelinated  Classifying Sensory Receptors Nociceptors Myelinated Type A fibers Carry sensations of fast pain, or prickling pain, such as that caused by an injection or a deep cut Sensations reach the CNS quickly and often trigger somatic reflexes Relayed to the primary sensory cortex and receive conscious attention  Classifying Sensory Receptors Nociceptors Type C fibers Carry sensations of slow pain, or burning and aching pain Cause a generalized activation of the reticular formation and thalamus You become aware of the pain but only have a general idea of the area affected  Thermoreceptors Thermoreceptors Also called temperature receptors Are free nerve endings located in The dermis Skeletal muscles The liver The hypothalamus  Thermoreceptors Thermoreceptors Two types of thermoreceptors: 1. Warm Receptors 2. Cold Receptors Temperature sensations Conducted along the same pathways that carry pain sensations  Mechanoreceptors Mechanoreceptors Sensitive to stimuli that distort their plasma membranes Contain mechanically gated ion channels whose gates open or close in response to Stretching Compression Twisting Other distortions of the membrane  Mechanoreceptors Three Classes: 1. Tactile Receptors Touch 2. Baroreceptors Pressure 3. Proprioceptors Body Position  Tactile Receptors Mechanoreceptors: Tactile Receptors Provide the sensations of touch, pressure, and vibration – Touch sensations provide information about shape or texture – Pressure sensations indicate degree of mechanical distortion – Vibration sensations indicate pulsing or oscillating pressure  Classes of Tactile Receptor 1. Free Nerve Endings 2. Root Hair Plexus 3. Merkel Discs 4. Meissner’s Corpuscles 5. Pacinian Corpuscle 6. Ruffini Receptors  Classifying Sensory Receptors 1. Free nerve endings Sensitive to touch and pressure Situated between epidermal cells Free nerve endings providing touch sensations are tonic receptors with small receptive fields  Classifying Sensory Receptors 1. Root hair plexus nerve endings Monitor distortions and movements across the body surface wherever hairs are located Adapt rapidly, so are best at detecting initial contact and subsequent movements  Classifying Sensory Receptors 1. Tactile discs Also called Merkel discs Fine touch and pressure receptors Extremely sensitive to tonic receptors Have very small receptive fields  Classifying Sensory Receptors 1. Tactile corpuscles Also called Meissner’s corpuscles Perceive sensations of fine touch, pressure, and low-frequency vibration Adapt to stimulation within 1 second after contact Fairly large structures Most abundant in the eyelids, lips, fingertips, nipples, and external genitalia  Tactile corpuscl e Epidermis Capsule Dendrite s Dermi s Sensory nerve fiber Tactile corpuscle Tactile LM 330 corpuscle  Classifying Sensory Receptors 1. Lamellated corpuscles Also called Pacinian corpuscles Sensitive to deep pressure Fast-adapting receptors Most sensitive to pulsing or high-frequency vibrating stimuli  Dermis Dendritic process Accessory cells (specialized fibroblasts) Concentric layers (lamellae) of collagen fibers separated by fluid Lamellated LM 125 Lamellated corpuscle corpuscle (cross section)  Classifying Sensory Receptors Ruffini corpuscles Also sensitive to pressure and distortion of the skin Located in the reticular (deep) dermis Tonic receptors that show little if any adaptation  Baroreceptors Monitor change in pressure Consist of free nerve endings that branch within elastic tissues In wall of distensible organ (such as a blood vessel) Respond immediately to a change in pressure, but adapt rapidly  Proprioceptors Three Major Groups of Proprioceptors 1. Muscle spindles – Monitor skeletal muscle length – Trigger stretch reflexes 2. Golgi tendon organs – Located at the junction between skeletal muscle and its tendon – Stimulated by tension in tendon – Monitor external tension developed during muscle contraction 3. Receptors in joint capsules – Free nerve endings detect pressure, tension, movement at the joint  Chemoreceptors Chemoreceptors Respond only to water-soluble and lipid-soluble substances dissolved in surrounding fluid Receptors exhibit peripheral adaptation over period of seconds; central adaptation may also occur  Chemoreceptors Chemoreceptors Located in the Carotid bodies Aortic bodies Receptors monitor pH, carbon dioxide, and oxygen levels in arterial blood  Sensory Pathways Somatic Sensory Pathways Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs Three major somatic sensory pathways 1. The spinothalamic pathway 2. The posterior column pathway 3. The spinocerebellar pathway  Sensory Pathways The Spinothalamic Pathway Provides conscious sensations of poorly localized (“crude”) touch, pressure, pain, and temperature Posterior Column Pathway Carries sensations of highly localized (“fine”) touch, pressure, vibration, and proprioception The Spinocerebellar Pathway Cerebellum receives proprioceptive information about position of, Skeletal muscles, Tendons and Joints Somatic Sensory Pathways Somatic Sensory Pathways -As the information travels towards the brain it will cross over -the crossing over occurs somewhere in the spinal cord  Somatic Sensory Pathways Feeling Pain 1. Referred Pain 2. Phantom Pain 3. Chronic Pain  ANS divisions Three ANS divisions 1. Sympathetic (or thoracolumbar) division Axons emerge from thoracic and superior lumbar segments of spinal cord Innervate ganglia relatively close to spinal cord “Kicks in” only during periods of exertion, stress, or emergency 2. Parasympathetic (or craniosacral) division Axons emerge from brain stem and sacral spinal segments Innervate ganglia very close (or within) target organs © 2011 Pearson Education, Inc.  Divisions of the ANS Sympathetic Division “Kicks in” only during exertion, stress, or emergency “Fight or flight” Parasympathetic Division Controls during resting conditions “Rest and digest” © 2011 Pearson Education, Inc.  Divisions of the ANS Sympathetic and Parasympathetic Division 1. Most often, these two divisions have opposing effects If the sympathetic division causes excitation, the parasympathetic causes inhibition 2. The two divisions may also work independently Only one division innervates some structures 3. The two divisions may work together, with each controlling one stage of a complex process © 2011 Pearson Education, Inc.  Autonomic Nervous System Sympathetic Division Parasympathetic Division In the sympathetic division, or thoracolumbar In the parasympathetic division, or cranio- (thor-a-kō-LUM-bar) division, axons emerge sacral (krā-nē-ō-SĀ-krul) divions, axons from emerge from the brain stem and the sacral the thoracic and superior lumbar segments of segments of the spinal cord, and they innervate the ganglia very close to (or within) target organs. spinal cord and innervate ganglia relatively close to the spinal cord. Cranial nerves (III, VII, IX, and X) T1 T2 T3 T4 The two main divisions T5 of the ANS: the T6 sympathetic Thoracic T7 and parasympathetic nerves T8 divisions T9 T1 T1 0 1 T1 2 L1 Lumbar nerves L2 (L1, L2 only) S2 Sacral nerves S3 S4 (S2, S3, S4 only) Figure 14.1 1 © 2011 Pearson Education, Inc.  Autonomic ganglia Autonomic ganglia Sympathetic division Preganglionic fibers (neurons) are relatively short while postganglionic fibers (neurons) are relatively long Accordingly, sympathetic ganglia (where these fibers synapse) are relatively near spinal cord Specific ganglia 1. Sympathetic chain (on either side of spinal cord) Innervates visceral effectors in thoracic cavity, head, body wall, and limbs © 2011 Pearson Education, Inc.  Autonomic ganglia 2. Collateral ganglia (within abdominopelvic cavity) Includes celiac, superior, and inferior mesenteric ganglia Innervates visceral effectors in abdominopelvic cavity 1. Adrenal medulla Center of adrenal gland Acts as endocrine gland Targets organs and systems throughout body © 2011 Pearson Education, Inc.  Autonomic ganglia Sympathetic division Prepares body for heightened levels of somatic activity Known as “fight or flight” division Typical responses 1. Heightened mental alertness 2. Increased metabolic rate 3. Reduced digestive and urinary functions 4. Activation of energy reserves 5. Increased respiratory rate and dilation of passageways 6. Elevated heart rate and blood pressure 7. Activation of sweat glands © 2011 Pearson Education, Inc.  Divisions of the ANS Parasympathetic Division Preganglionic fibers originate in brain stem and sacral segments of spinal cord; craniosacral Synapse in ganglia close to (or within) target organs Preganglionic fibers are long Postganglionic fibers are short Parasympathetic division stimulates visceral activity Conserves energy and promotes sedentary activities © 2011 Pearson Education, Inc.  The Parasympathetic Division Also termed the craniosacral division. Primarily concerned with conserving energy and replenishing nutrient stores. Is most active when the body is at rest or digesting a meal. nicknamed the “rest-and-digest” division Participates along with the sympathetic division in maintaining homeostasis (a constant internal environment). 18-0 © 2011 Pearson Education, Inc.  Divisions of the ANS Five Responses to Increased Parasympathetic Activity 1. Decreased metabolic rate 2. Decreased heart rate and blood pressure 3. Increased secretion by salivary and digestive glands 4. Increased motility and blood flow in digestive tract 5. Urination and defecation stimulation © 2011 Pearson Education, Inc.  Anatomic Differences Divisions are distinguished by several anatomic differences. Preganglionic neuron cell bodies are housed in different regions of the CNS. Parasympathetic preganglionic neurons originate in either the brainstem or the lateral gray matter of the S2–S4 spinal cord regions. Sympathetic preganglionic neurons originate in the lateral horns of the T1–L2 spinal cord regions 18-0 © 2011 Pearson Education, Inc.  0 © 2011 Pearson Education, Inc.  Anatomic Differences Parasympathetic division is structurally more simple than the sympathetic division. Parasympathetic division is also termed the craniosacral division because its preganglionic neurons are housed within nuclei in the brainstem and within the lateral gray regions of the S2–S4 spinal cord segments. Ganglionic neurons in the parasympathetic division are found in either terminal ganglia, which are located close to the target organ, or intramural ganglia, which are located within the wall of the target organ 18-0 © 2011 Pearson Education, Inc.  Autonomic innervation patterns Parasympathetic division Vagus nerve (X) alone provides ~75% of all parasympathetic outflow Numerous vagus nerve branches intermingle with sympathetic fibers forming nerve plexuses Preganglionic fibers in sacral spinal cord segments form distinct pelvic nerves Innervate intramural ganglia in kidneys, bladder, terminal portions of large intestine, and sex organs © 2011 Pearson Education, Inc.  Effects and General Functions of the Parasympathetic Division Parasympathetic division is most active during times when the body must process nutrients and conserve energy. Lack of extensive divergence in preganglionic axons prevents the mass activation seen in the sympathetic division. Effects of the parasympathetic nervous system tend to be discrete and localized. Parasympathetic activity can affect one group of organs without necessarily having to “turn on” all other organs. 18-0 © 2011 Pearson Education, Inc.  Organization and Anatomy of the Sympathetic Division Much more complex than the parasympathetic division, both anatomically and functionally. Sympathetic preganglionic neuron cell bodies are housed in the lateral horn of the T1–L2 regions of the spinal cord. Preganglionic sympathetic axons travel with somatic motor neuron axons to exit the spinal cord and enter first the anterior roots and then the T1–L2 spinal nerves. Preganglionic sympathetic axons remain with the spinal nerve for merely a short distance before they branch off and leave the spinal nerve. 18-0 © 2011 Pearson Education, Inc.  Left and Right Sympathetic Trunks Immediately anterior to the paired spinal nerves are the left and right sympathetic trunks. Each is located immediately lateral to the vertebral column. A sympathetic trunk looks much like a pearl necklace. the “string” of the “necklace” is composed of bundles of axons the “pearls” are the sympathetic trunk (or paravertebral) ganglia, which house sympathetic ganglionic neuron cell bodies 18-0 © 2011 Pearson Education, Inc.  Fight-or-Flight Function of the ANS May involve a single effector or many effectors. In mass activation, a large number of ganglionic neurons activate many effector organs. causes a heightened sense of alertness due to stimulation of the reticular activation system 18-0 © 2011 Pearson Education, Inc.  Dual Innervation by the Parasympathetic and Sympathetic Divisions of the ANS Innervate organs through specific axon bundles called autonomic plexuses. Communication by chemical messengers, called neurotransmitters. specific in each division of the autonomic nervous system Usually all organs are innervated by both divisions of the autonomic nervous system. Maintains homeostasis through autonomic reflexes that occur in the innervated organs. 18-0 © 2011 Pearson Education, Inc.  Neurotransmitters and Receptors Two neurotransmitters are used in the ANS. acetylcholine (ACh) norepinephrine (NE) Neurotransmitters are released by the presynaptic cell. Bind to specific receptors in the postsynaptic cell membrane. Binding has either an excitatory or an inhibitory effect on the effector, depending on the specific receptor. 18-0 © 2011 Pearson Education, Inc.  Acetylcholine Ach is secreted by all preganglionic neurons in both the parasympathetic and sympathetic neurons. Called cholinergic fibers Any receptor that binds Ach is called a cholinergic receptor © 2011 Pearson Education, Inc.  Cholinergic Receptors Two types of cholinergic receptors 1. Muscarinic receptors All cardiac muscle, smooth muscle and gland cells that have a muscarinic receptor Either excitatory or inhibitory due to subclasses of the muscarinic receptor © 2011 Pearson Education, Inc.  Cholinergic Receptors 1. Nicotinic Receptors On all ANS postganglionic neurons, in the adrenal medulla and at neuromuscular junctions of skeletal muscles Excitatory when Ach binding receptors © 2011 Pearson Education, Inc.  Norepinephrine (NE) Is secreted by nearly all postganglionic sympathetic neurons. Called adrenegic fibers Several types of adrenegic receptors Alpha-adrenergic Beta-adrenergic © 2011 Pearson Education, Inc.  Autonomic neurotransmitters and receptors Autonomic neurotransmitters and receptors Sympathetic division Adrenergic receptors (bind “adrenaline”) Located in plasma membranes of target cells Binding of epinephrine (E) or norepinephrine (NE) activates enzymes (2nd messenger system) within cell Two classes 1. Alpha receptors (generally stimulated by NE & E) α1 receptors – generally excitatory α2 receptors – generally inhibitory © 2011 Pearson Education, Inc.  Autonomic neurotransmitters and receptors Sympathetic division (continued) Adrenergic receptors (continued) Two classes (continued) 1. Beta receptors (generally stimulated by E) β1 receptors – cardiac muscle stimulation and increased tissue metabolism β2 receptors – relaxation of respiratory passage and blood vessel smooth muscle β3 receptors – release of fatty acids from adipose tissue for metabolic use in other tissues © 2011 Pearson Education, Inc.  Autonomic neurotransmitters and receptors Sympathetic division (continued) Neurotransmitter release Epinephrine (E) and norepinephrine (NE) can be released Locally, involving more norepinephrine Effects last a few seconds Generally, from adrenal medulla 3× more epinephrine than norepinephrine More beta receptors activated Effects may last several minutes © 2011 Pearson Education, Inc.  Parasympathetic Neurotransmitters Both the preganglionic and postganglionic axons in the parasympathetic division release acetylcholine and thus are called cholinergic. The preganglionic axon and a few postganglionic axons in the sympathetic division are also cholinergic. 18-0 © 2011 Pearson Education, Inc.  Autonomic neurotransmitters and receptors Parasympathetic division Receptors (all bind ACh) 1. Nicotinic receptors (also bind nicotine) Located on ganglion cell surfaces Also on sympathetic ganglion cells and at SNS neuromuscular junctions Always excitatory 2. Muscarinic receptors (also bind muscarine toxin) Located at cholinergic neuromuscular and neuroglandular junctions as well as some sympathetic cholinergic junctions Can be excitatory or inhibitory © 2011 Pearson Education, Inc.  A summary of the anatomical characteristics of the sympathetic division of the ANS (left) and of the parasympathetic division of the ANS (right) A summary of the anatomical characteristics A summary of the anatomical characteristics of the sympathetic division of the ANS of the parasympathetic division of the ANS Sympathetic Parasympatheti c CNS Preganglionic Preganglionic CNS neuron neuron PNS PNS Preganglionic Preganglionic fiber fiber Adrenal Sympathetic medulla or ganglion Ganglionic Ganglionic neurons neurons Postganglioni c Parasympathetic Bloodstream fiber Postganglionic ganglion KEY fiber Neurotransmitter s Acetylcholne Norepinephrine Epinephrine TARGET TARGET Figure 14.5 2 – 3 © 2011 Pearson Education, Inc.