Zoology 120 (Lec) Topic 3B - Whole-Body Control Systems Peripheral Nervous System PDF

20373-X: ZOOLOGY 120 ANIMAL PHYSIOLOGY | LECTURE PERIPHERAL NERVOUS SYSTEM LECTURER: BRIAN ALLISON MARTOS DATE OF LECTURE: MARCH 19, & APRIL 11, 2024 2024 II. I. Perineurium Efferent Nervous System A. Efferent Division B. Autonomic Nervous System C. Somatic Nervous System Afferent Nervous System A....

20373-X: ZOOLOGY 120 ANIMAL PHYSIOLOGY | LECTURE PERIPHERAL NERVOUS SYSTEM LECTURER: BRIAN ALLISON MARTOS DATE OF LECTURE: MARCH 19, & APRIL 11, 2024 2024 II. I. Perineurium Efferent Nervous System A. Efferent Division B. Autonomic Nervous System C. Somatic Nervous System Afferent Nervous System A. Subtopic 1 Association of Afferent and Efferent A. Organization of the Vertebrate Nervous System Peripheral Nervous System surrounds bundles of axons (fascicles) ○ fascicles— a bundle of nerve or muscle fibers Groups of axons with their endoneurium are arranged in bundles contains flat fibrocytes with their edges sealed by tight junctions meaning it won’t allow the passage of molecules → constitute the blood nerve barrier cells comprise the blood nerve barrier which maintain fiber’s environment Endoneurium Central Nervous System: brain and spinal cord Components of PNS ○ Nerves— bundles of axons/nerve fibers; the classifications depend whether they will be coming from/innervating the brain or spinal cord Cranial nerve— any nerve fiber innervates/ come from the brain Spinal nerve— any nerve fiber innervates/ come from the spinal cord ○ Ganglia— made up of the cell bodies of the nerve fibers; where cell bodies of neurons outside CNS are stored; 3 classifications Terminal— Collateral— Ganglion chain— surrounds individual axons ○ remember, sometimes there are axons that may be covered by myelin sheath → endoneurium will cover myelin sheath before it covers the axons contains reticular fibers, scattered fibroblasts, capillaries, and occasional mast cells and macrophages. ○ mast cell and macrophages– function for immunity; kill any microorganism that will enter the axons A N G EL IK A 2023-2024 A N TO N IO OUTLINE Organization of the III. Vertebrate Nervous System A. Peripheral Nervous System B. Organization of Nerves IV. C. Ganglia Functional Classification V. of Neurons A. Classes of Neurons I. 2ND SEMESTER Figure 2. Transverse section showing the coverings of a spinal nerve. Epineurium— outermost covering; also has the blood vessels ○ Dense superficial region → more loose, deeper region where veins and arteries are found Veins— more flat Arteries— more circular Presence of blood vessels means there is epineurium Each fascicle has capillary (at least one capillary in fascicle) for transport of gasses JA N A H Figure 1. The general organization of the nervous system. Nerves are classified either cranial or spinal, but the functional organization of the nerves will be the same. Organization of Nerves Epineurium outermost covering of the nerve made of dense irregular connective tissue with occasional associated adipose tissue covers the entire nerve Figure 3. Micrograph of nerve fibers. TRANSCRIBED BY: JANAH ANGELIKA R. ANTONIO | BIOLOGY 1 LECTURE 2B - PERIPHERAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY location. have a receptor on the periphery to receive the stimulus either inside or outside the organisms body ○ This receptor will trigger the formation of action potential(1st set) → AP will travel through axon/afferent fiber Peripheral afferent axon— “afferent fiber” that extends from the receptor going towards the cell body Central afferent axon— cell body to the CNS Cell body of the afferent neurons does not have dendrites. Interneurons— found entirely within CNS; dendrites and cell bodies are innervated by the axon terminal of the afferent neurons ○ Transmission of signal from the axon terminal to the interneuron is through synapses Neurotransmitters are released by the axon terminals and then will bind to the receptors in the dendrites or cell body of the interneurons ○ Responsible for: Integrating afferent information and formulating an efferent response based on the stimulus to transmit it to the efferent neuron Higher mental functions associated with the “mind” Efferent neurons— carry instructions from CNS to effector organs – muscles and glands ○ Axon terminal will release neurotransmitters that will bind to the receptors in the dendrites and cell body of the efferent neurons → trigger the formation of graded potentials → passive flow of current to the axon hillock → … → axon terminals → terminate at the effector organ(muscle or gland) Figure 4. SEM of transverse section of 12 nerve fascicles. Ganglia JA N A H collection of cell bodies surrounded by satellite cells which serve as relay stations. Sensory Ganglia— has outer connective tissue capsule that serves as a covering; have fibers; cell body of sensory neurons ○ pseudounipolar neurons ○ distinct connective tissue capsule ○ cranial ○ spinal Figure 5A: cell bodies need to be connected to an axon; each nerve fibers will have corresponding cell body in the ganglion ○ F: fascicles or nerve fibers ○ G: autonomic ganglion ○ C: connective tissue Figure 5B: locate the cell body of neurons ○ satellite glial cells— small circular structures that surround neurons; form cytoplasmic extensions that completely covers the cell body of the neuron Some would say that these glial cells air for nutrition of neurons Figure 5C: lipofuscin— pigmentation; lipid-containing residues of lysosomal digestion; consistent with age-related cytological changes ○ more lipofuscin = older cell Autonomic Ganglia— cell body of efferent neuron ○ multipolar neurons ○ less distinct capsule A N G EL IK A A N TO N IO ○ Figure 5. Structure and location of the three functional classes of neurons. *Efferent autonomic nerve pathways consist of a two-neuron chain between the CNS and the effector organ. III. Efferent Nervous System Efferent Division II. Functional Classification of Neurons Aside from somatic and autonomic nervous system, some references would say that there is a third division of the efferent division → Enteric Nervous System Classes of Neurons Afferent neurons— inform CNS about conditions in both the external and internal environment ○ part of PNS; can receive either a sensory(outside) or visceral(inside) stimuli depending on the CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 2 LECTURE 2B - PERIPHERAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY Most visceral organs are innervated by both sympathetic and parasympathetic fibers. Dual innervation of organs by both branches of ANS allows precise control over organ’s activity. In general, it produces opposite effects in a particular organ (antagonistic) Sympathetic Nervous System dominates in emergency or stressful (“fight-or-flight”) situations promotes responses that prepare body for strenuous physical activity *sweat glands are only innervated by the sympathetic nervous system inhibit actions that will delay the movement of organism A N TO N IO Parasympathetic Nervous System Figure 6. Organization of the vertebrate nervous system. Afferent fibers travel within the same nerves as efferent fibers but in the opposite direction. The enteric nervous system lies entirely within the wall of the digestive tract. EFFERENT DIVISION: communication link by which CNS controls activities of muscles and glands Deliver the response that was given by the CNS TWO DIVISIONS OF EFFERENT DIVISION OF NERVOUS SYSTEM 1. Autonomic Nervous System 2. Somatic Nervous System Autonomic Nervous System JA N A H Involuntary branch of PNS Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue Autonomic Nerve Pathway: extends from CNS to an innervated organ Two-neuron chain: CNS will formulate an appropriate response that will travel through these neurons ○ Preganglionic fiber— synapses with cell body of second neuron found on the CNS; terminates on a ganglion ○ Postganglionic fiber— innervates effector organ It is in this ganglion that we can see the cell bodies Preganglionic neuron will release neurotransmitters in the ganglion → receptors from postganglionic cell will receive the neurotransmitters → graded potential → action potential → travel along the postganglionic fiber → reach axon terminal → release of neurotransmitters → bind to the receptors of the effector organ ○ *Note: PNS will still have their own neurons that contains cell bodies contained in the ganglion A N G EL IK A dominates in quiet, relaxed (“rest-and-digest”) situations; peace promotes body-maintenance activities such as digestion Figure 7. Autonomic nerve pathway. Two Subdivisions that have contrasting effects ○ Sympathetic Nervous System: Thoracic and lumbar nerves ○ Parasympathetic Nervous System: Cervical and sacral nerves CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 3 LECTURE 2B - PERIPHERAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY Table 2. Effects of the Autonomic Nervous System on Various Organs. Figure 8. Schematic representation of the structures innervated by the mammalian sympathetic and parasympathetic nervous systems. Parasympathetic Nervous System Fibers originate in the thoracic and lumbar regions of the spinal cord. Fibers originate from cranial and sacral areas of CNS. Most preganglionic fibers are short (ganglions determines the length of these fibers) Preganglionic fibers are longer Long postganglionic fibers Very short postganglionic fibers Preganglionic fibers release Acetylcholine Most postganglionic fibers release noradrenaline (norepinephrine) Preganglionic fibers release Acetylcholine Postganglionic fibers release Acetylcholine Collateral ganglion JA N A H Adrenal Medulla EXCEPTION ON AUTONOMIC NERVOUS SYSTEM Exceptions to general rule of dual reciprocal innervation by the two branches of autonomic nervous system ○ Most arterioles and veins receive only sympathetic nerve fibers (arteries and capillaries are not innervated) → constrict Arteries and the capillaries will have no innervations because: The flow of blood in the arteries is dependent on the pumping of the heart Capillaries are found in the arterioles and veins. Since arterioles are already innervated by the sympathetic nervous system, the flow of blood in the capillaries will be dependent on the flow of blood from the arterioles. Blood → arteries → arterioles → capillaries → travel through the veins(needs innervation to bring back blood to heat) When these are stimulated, they will constrict Most sweat glands are innervated only by sympathetic nerves During stressful situations, the organism panics so there is an increase in production of heat. This will be counteracted by sweat to cool down the body. Salivary glands are innervated by both ANS divisions but activity is not antagonistic – both stimulate salivary secretion; but what happens during: Sympathetic(inhibit): tonic control will be decreased Parasympathetic(stimulate): tonic control will be increased A N G EL IK A Sympathetic Nervous System A N TO N IO Table 1. Difference of sympathetic and parasympathetic nervous systems. CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 4 LECTURE 2B - PERIPHERAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY Figure 10. Schematic representation of the structures innervated by the mammalian sympathetic and parasympathetic nervous systems. Adrenal Gland — composed of cortex and adrenal medulla ○ Adrenal Medulla — modified sympathetic ganglion that does not have postganglionic fiber; releases NE and E ○ Adrenal cortex — secretes glucocorticoids that are essential for glucose, protein and fat metabolism A N G EL IK A A N TO N IO found on effector cell membranes Cardiac muscles, smooth muscles and glands Adrenergic Receptors — for NE and E ○ Receptors G protein coupled mechanism Alpha (α) receptors — cause muscle contraction and vasoconstriction in certain body parts α1 receptors — mainly found in the arterioles; constriction; activate Phospholipase C(cleave phospholipids just before the phosphate group) α2 receptors — block cAMP messenger system; found mainly in the smooth muscles of the digestive tract → decreased contraction Beta (β) receptors — cause muscle relaxation and vasodilation in other areas β1 receptors — uses cAMP messenger system; mainly found in the heart ○ Increased heart rate and contractility β2 receptors — mainly found in the bronchioles which causes it to dilate *1 subscripts are excitatory; 2 subscripts are inhibitory Sensitivity of receptors ○ α and β neurotransmitters respond to NE ○ α receptors have greater sensitivity towards NE ○ β1 receptors have almost equal affinity to both NE and E ○ β2 receptors mainly respond to E JA N A H Figure 11. Adrenals: cortex and medulla. Figure 13. Title. Figure 12. Sites of release for Acetylcholine and Norepinephrine. Autonomic Neurotransmitter Receptors Cholinergic Receptors — nicotinic and muscarinic receptors may function as external agents(agonists and antagonists); for ACh ○ Nicotinic Receptors — activated by nicotine; found on postganglionic cell bodies of all autonomic ganglia; adrenal medulla ○ Muscarinic Receptors — activated by muscarin; ALPHA RECEPTORS ○ Alpha receptor(adrenergic) that responds to NE ○ When NE binds to a receptor, it will activate Phospholipase C ○ Phospholipase C cleaves PIP2 to IP3 Phosphatidylinositol-4,5-bisphosphate (PIP2) — found in the cell membrane Inositol-1,4,5-triphosphate (IP3) and diacylglycerol (DAG) ○ IP3 will bind to a receptor in the sarcoplasmic reticulum ○ Binding results to the receptors opening the Ca2+ channel exit of Ca2+ ions ○ Exit of Ca2+ ions will cause cascade of reactions along with the activation of certain proteins by the protein kinase(phosphorylate) Elicit a response to the cell → constriction of CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 5 LECTURE 2B - PERIPHERAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY the arterioles ○ A N TO N IO ○ particularly in the heart and salivary glands; (normally parasympathetic; decreased rate or decreased force of contraction); antagonist MECHANISM: ACh will not bind → decrease the effect of parasympathetic → sympathetic will dominate → increased rate or contraction of the heart used to treat some types of slow heart rate diseases; used to decrease the secretion of saliva during operations Salbutamol: activates β2-adrenergic receptors; agonist dilation of bronchioles → increase in airflow Metoprolol: blocks β1-adrenergic receptors; antagonist lowers blood pressure and heart rate Somatic Nervous System Figure 14. Life cycle of receptors. BETA RECEPTORS ○ Binding of NE to β1 adrenergic receptor(found in heart) G coupled mechanism ○ Activation of adenylyl cyclase ○ Conversion of ATP to cAMP ○ Activation of protein kinase → phosphorylation ○ Entry of Ca2+ ions ○ Phosphorylation of sarcoplasmic reticulum Contains Ca2+ ions receptors ○ Further increase of Ca2+ ions coming from the SR(since SR releases Ca2+ ions) ○ Ca2+ ions will bind to troponin ○ Enhanced actin-myosin interaction ○ ↑ cardiac contractile force and velocity A N G EL IK A innervates skeletal muscle(motor neurons) subject to voluntary control consists of axons of motor neurons that originate in the spinal cord or brain stem and end on skeletal muscle. Motor neuron releases neurotransmitter, ACh, which stimulates muscle contraction. Motor neurons are the final common pathway by which various regions of CNS exert control over skeletal muscle activity. ○ These areas of CNS include spinal cord, motor regions of cortex, basal nuclei, cerebellum, and brain stem. Neuromuscular Junctions Motor end plate has no threshold potential JA N A H Figure 16. Title. Clinical Correlations ○ Poliovirus — selective destruction of the motor neurons particularly the cell bodies ○ Amyotrophic Lateral Sclerosis (ALS) — Lou Gehrig's disease; progressive degeneration of motor neurons Figure 15. β adrenergic receptor. Autonomic Agonists and Antagonists ○ Agonists — mimic the response ○ Antagonists — block the response Examples: ○ Atropine: binds to muscarinic receptors only, CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 6 LECTURE 2B - PERIPHERAL NERVOUS SYSTEM | ANIMAL PHYSIOLOGY IV. Afferent Nervous System Afferent Division Sends information from internal and external environment to CNS ○ Visceral afferent— incoming pathway for information from internal viscera (organs in body cavities) ○ Sensory afferent— somatic (body sense) sensation, external environment Somatic: sensation arising from body surface and proprioception Special senses » Vision, hearing, taste, smell Afferent and Efferent Association A N TO N IO 12 Cranial Nerves I. Olfactory – mucosa in the nasal cavity II. Optic – III. Oculomotor – IV. Trigeminal – V. Trochlear – VI. Abducens – VII. Facial – VIII. Vestibulocochlear – IX. Glossopharyngeal – X. Vagus – XI. Accessory – XII. Hypogolossal – JA N A H A N G EL IK A Figure 17. Composition of Cranial Nerves. ▢ ▢ xxx xxx References CDC UNIVERSITY OF THE PHILIPPINES BAGUI O 7