CAPS 301 5 Introduction to PNS (HUYNH) (1) 2 PDF

© Barry Mason 2014. Not for use or reproduction without permission. CAPS 301 Components of Peripheral Nervous System Dr. Frank Huynh...

© Barry Mason 2014. Not for use or reproduction without permission. CAPS 301 Components of Peripheral Nervous System Dr. Frank Huynh Department of Cellular and Physiological Sciences University of British Columbia © Barry Mason 2014. Not for use or reproduction without permission. Objectives By the end of this lecture you should be able to: 1) describe the general organization of the nervous system – organizational hierarchy of the nervous system – the general structure of a nerve 2) compare and contrast the structure and function of the two branches of the autonomic nervous system - sympathetic - parasympathetic 3) describe the locations and target effectors of major nerves - cranial nerves - spinal nerves © Barry Mason 2014. Not for use or reproduction without permission. © Barry Mason 2014. Not for use or reproduction without permission. PERIPHERAL NERVOUS SYSTEM Peripheral nerves are composed of bundles of axons sensory (afferent) – towards CNS motor (efferent) – away from CNS autonomic – (involved in functions that are NOT under voluntary control). © Barry Mason 2014. Not for use or reproduction without permission. Fig. 5.2 © Barry Mason 2014. Not for use or reproduction without permission. PERIPHERAL NERVOUS SYSTEM Sensory neurons – cell body outside the CNS in sensory ganglia. “ganglion” denotes a collection of neuronal cell bodies in the PNS. © Barry Mason 2014. Not for use or reproduction without permission. PERIPHERAL NERVOUS SYSTEM Motor neurons – innervate striated muscle fibres – cell body (soma) in the CNS – release acetylcholine - acts via nicotinic receptors at the neuromuscular junction (NMJ). © Barry Mason 2014. Not for use or reproduction without permission. Objectives By the end of this lecture you should be able to: 1) describe the general organization of the nervous system – organizational hierarchy of the nervous system – the general structure of a nerve 2) compare and contrast the structure and function of the two branches of the autonomic nervous system - sympathetic - parasympathetic 3) describe the locations and target effectors of major nerves - cranial nerves - spinal nerves © Barry Mason 2014. Not for use or reproduction without permission. ANS Functions There are two branches in the ANS: sympathetic and parasympathetic nervous systems Functions: Homeostasis – maintaining a stable internal environment Controls vegetative systems (life support) – semi-autonomously – coordinates with endocrine systems Blood pressure – HR, Stroke Volume, total peripheral resistance GI motility Salt/water balance Pupillary reflexes Sexual function © Barry Mason 2014. Not for use or reproduction without permission. ANS Afferents Send information into control centres: Baroreceptors in aortic arch, carotid sinus monitor blood pressure Osmoreceptors-regulation of plasma ions Thermal (hot and cold) sensors in skin, CNS for regulating body temperature. Cutaneous receptors detect sexual stimuli Pain fibres in viscera Stretch receptors monitor distension in lungs, bladder, stomach, bowel © Barry Mason 2014. Not for use or reproduction without permission. Control of ANS – Higher Centres ANS coordinated via: Some reflexes at spinal cord level Medulla – within the brainstem Hypothalamus Prefrontal cortex – emotional states © Barry Mason 2014. Not for use or reproduction without permission. Autonomic neurons – There are 2 neurons in the efferent pathway from the CNS to the peripheral organ. The 1st neuron (preganglionic) has its cell body in the CNS. The 2nd neuron (postganglionic) in an autonomic ganglion in the periphery. Ganglion is close to the CNS in the sympathetic system Ganglion is close to, or actually within, the target organ in the parasympathetic system. © Barry Mason 2014. Not for use or reproduction without permission. © Barry Mason 2014. Not for use or reproduction without permission. Autonomic Neurons Similar to axon terminals but release NTs over a large area, rather than just on single cells © Barry Mason 2014. Not for use or reproduction without permission. CATABOLIC Effects of Sympathetic Nervous System Increased Heart Rate, Stroke Volume and Blood Pressure Increased blood flow to skeletal muscle Decreased blood flow to skin Fight or Flight response: – Release of epinephrine/norepinephrine from adrenal medulla stimulates skeletal muscle glycogenolysis © Barry Mason 2014. Not for use or reproduction without permission. ANABOLIC Effects of Parasympathetic Nervous System Decreased Heart Rate, Stroke Volume and Blood Pressure Increased G.I. tract motility and secretions Relaxation of sphincters in esophagus, stomach, bladder Rest and Digest response Paradoxical Co-activation: – Both sympathetic and parasympathetic systems activated during intense conflict situations © Barry Mason 2014. Not for use or reproduction without permission. Distinguishing features of the SNS and PNS Sherwood, 5th Canadian Ed. © Barry Mason 2014. Not for use or reproduction without permission. Distinguishing features of the SNS and PNS Sherwood, 5th Canadian Ed. © Barry Mason 2014. Not for use or reproduction without permission. Objectives By the end of this lecture you should be able to: 1) describe the general organization of the nervous system – organizational hierarchy of the nervous system – the general structure of a nerve 2) compare and contrast the structure and function of the two branches of the autonomic nervous system - sympathetic - parasympathetic 3) describe the locations and target effectors of major nerves - cranial nerves - spinal nerves © Barry Mason 2014. Not for use or reproduction without permission. PNS Nerves – Cranial Nerves Originate inside cranium and proximal spinal cord Can carry: – Afferent information (fibres) – Efferent fibres – ANS fibres © Barry Mason 2014. Not for use or reproduction without permission. Note: Some CN are composed of just sensory fibres, some just motor, some are mixed © Barry Mason 2014. Not for use or reproduction without permission. CRANIAL NERVES (See Fig 3-18) There are 12 pairs (please note Roman numerals) I. OLFACTORY – sensory - sense of smell. II. OPTIC – sensory - vision. III. OCULOMOTOR motor, voluntary – moves eyeball medially (towards midline) motor, autonomic (parasympathetic) – constricts pupil and thickens lens. © Barry Mason 2014. Not for use or reproduction without permission. CRANIAL NERVES IV. TROCHLEAR – motor, voluntary – moves eyeball. V. TRIGEMINAL – motor, voluntary – mastication. – sensory, touch, temperature, pain etc from face, head and mouth. VI. ABDUCENS – motor – moves eyeball laterally. * Note, opposite to III. * III and VI must work together when we are looking right or left. This is coordinated by information carried in the MLF (medial longitudinal fasciculus). This is a tract connecting III nerve nucleus to VI nerve nucleus. © Barry Mason 2014. Not for use or reproduction without permission. CRANIAL NERVES VII. FACIAL motor, voluntary – muscles of facial expression. motor, autonomic (parasympathetic) – lacrimal and salivary glands. sensory, taste – tastebuds of (anterior 2/3 of the tongue). VIII. VESTIBULOCOCHLEAR (Auditory) sensory, from cochlea – hearing sensory, from vestibular apparatus – gravity, motion and position of head. IX. GLOSSOPHARYNGEAL motor, voluntary – pharynx swallowing motor, autonomic (parasympathetic) – salivary glands. sensory, taste – tastebuds (posterior 1/3 of tongue). sensory, - carotid sinus baroreceptors - monitors pressure of arterial blood - Important in reflex regulation of heart rate and BP. sensory, - carotid body chemoreceptors – monitors CO2, O2 in arterial blood - Important in control of breathing. © Barry Mason 2014. Not for use or reproduction without permission. CRANIAL NERVES X. VAGUS motor, voluntary – pharynx swallowing; larynx phonation. motor, autonomic (parasympathetic) to heart (slows heart rate), to abdominal organs – controls secretion and motility. sensory, from aortic baroreceptors and chemoreceptors sensory, from GI tract. XI. ACCESSORY motor, voluntary – swallowing motor, voluntary – shoulder shrugging XII. HYPOGLOSSAL motor, voluntary – tongue. * Please note, IX, X, and XI all involved in swallowing. Vagus (X) is the most important. © Barry Mason 2014. Not for use or reproduction without permission. SPINAL NERVES 31 pairs: 8 cervical (C.1 - C.8) 12 thoracic (T.1 - T.12) 5 lumbar (L.1 – L.5) 5 sacral (S.1 – S.5) 1 coccygeal All have voluntary motor function. All (except C. 1) have sensory fibres. © Barry Mason 2014. Not for use or reproduction without permission. © Barry Mason 2014. Not for use or reproduction without permission. AUTONOMIC SYSTEM SYMPATHETIC Preganglionics arise from all thoracic and the 1st and 2nd lumbar segments. T.1 - L.2. PARASYMPATHETIC Parasympathetics are carried in Cranial nerves III, VII, IX and X, and Sacral 2, 3 and 4. – Preganglionics arise from Sacral segments S.2, S.3 and S.4. * Please note: none of the cranial nerves carry sympathetic fibres. The sympathetic innervation of the head comes from the upper thoracic spinal nerves. © Barry Mason 2014. Not for use or reproduction without permission. AUTONOMIC SYSTEM Sherwood, 5th Canadian Ed. © Barry Mason 2014. Not for use or reproduction without permission. Objectives By the end of this lecture you should be able to: 1) describe the general organization of the nervous system – organizational hierarchy of the nervous system – the general structure of a nerve 2) compare and contrast the structure and function of the two branches of the autonomic nervous system - sympathetic - parasympathetic 3) describe the locations and target effectors of major nerves - cranial nerves - spinal nerves © Barry Mason 2014. Not for use or reproduction without permission. Principles of Sensory Physiology copyright © Dennis Kunkel Dr. Frank Huynh Department of Cellular and Physiological Sciences University of British Columbia © Barry Mason 2014. Not for use or reproduction without permission. Objectives By the end of this lecture you should be able to: 1) define a sensory receptor 2) identify some sensory receptors and what they detect 3) understand the general mechanisms of how sensory receptors relay signals to the CNS, including how sensory intensities are coded 4) describe two different types of receptor adaptation PRINCIPLES OF SENSORY PHYSIOLOGY SPECIAL AND GENERAL SENSES The special senses are modalities carried by cranial nerves They are: – Olfaction – Cr. I – Vision – Cr. II – Taste – Cr. VII and Cr. IX – Hearing and balance (equilibrium) – Cr. VIII The general or somatic senses (somatosensory) – Detected from all parts of the body (and head) and transmitted to CNS via: – Cr. V (trigeminal) – All spinal nerves except C.1  DEFINITION AND CLASSIFICATION OF SENSORY RECEPTORS Sensory receptors are transducers – devices that convert one form of energy into another form. – They detect various stimuli and convert them into action potentials. They include, with reference to the modality being detected: Photoreceptors – light: rods and cones of the retina. Thermoreceptors – changes in temperature, central (hypothalamus) and peripheral (skin) Nociceptors – pain Mechanoceptors – mechanical stimuli – can be subdivided into: – exteroceptors – respond to stimuli from outside the body eg. touch receptors – proprioceptors – give information about position of the body, or its parts eg. muscle spindles.  Classes of Sensory Receptors Mechanoreceptors: tactile Light touch, vibrations, surrounded by connective tissue, rapidly adapt Touch and deep pressure, rough Most sensitive to surfaces, vibrations and touch, vibrations, rapid slow to adapt adaptation, Stretch (deformation), torque surrounded by (rotational force), detect connective tissue deformation in joints, slow to adapt  Objectives By the end of this lecture you should be able to: 1) define a sensory receptor 2) identify some sensory receptors and what they detect 3) understand the general mechanisms of how sensory receptors relay signals to the CNS, including how sensory intensities are coded 4) describe two different types of receptor adaptation  THE SENSORY RECEPTOR RECEPTOR AND GENERATOR POTENTIALS The membrane must be depolarized to a threshold level to generate an action potential (AP) – Remember – AP needs open voltage-gated Na+ channels. The generator potential (GP) is a depolarization of the peripheral, receptive portion of the sensory axon. – caused by sensory stimulus – exception: in rods and cones, the GP is a hyperpolarization If the GP is big enough to reach threshold, action potentials will be produced. – APs propagate to the CNS. In myelinated sensory axons, the action potential is initiated at the 1st node of Ranvier.  (First node of Ranvier in myelinated axons) (axon hillock) (axon hillock)  THE SENSORY RECEPTOR The GP is similar to the EPSP in that it: Compare to action potentials which:  THE SENSORY RECEPTOR The GP is similar to the EPSP in that it: – can be graded in amplitude, i.e. the bigger the stimulus, the bigger the GP – does NOT cause the membrane to be refractory – is NOT actively propagated. Compare to action potentials which:  THE SENSORY RECEPTOR The GP is similar to the EPSP in that it: – can be graded in amplitude, i.e. the bigger the stimulus, the bigger the GP – does NOT cause the membrane to be refractory – is NOT actively propagated. Compare to action potentials which: – are all or none. – cause the membrane to be come refractory. – are actively propagated by regenerating themselves all along the axonal membrane.  THE SENSORY RECEPTOR The mechanism responsible for the GP depends on the type of receptor: – In all cases is due to the opening or closing of ion channels – Result is depolarization (except in photoreceptors) The GP of somatosensory mechanoreceptors – direct effect of mechanical stimuli on stretch-sensitive channels. Non-selective and allow both Na+ and K+ to pass. Net result is depolarization due to greater driving force for Na+. The GP of nociceptors, photoreceptors, and chemoreceptors – Separate cells or G-protein-coupled mechanisms that influence channels indirectly.  Receptor Potential in Specialized Afferent Ending Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Specialized Afferent Ending Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Specialized Afferent Ending Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Separate Cell Ending Ex. auditory, photoreceptors Fig. 5-2b Sherwood, 5th Cdn Ed.  Receptor Potential in Separate Cell Ending Ex. auditory, photoreceptors Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Separate Cell Ending Ex. auditory, photoreceptors Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Separate Cell Ending Ex. auditory, photoreceptors Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Separate Cell Ending Ex. auditory, photoreceptors Fig. 5-2a Sherwood, 5th Cdn Ed.  Receptor Potential in Separate Cell Ending Ex. auditory, photoreceptors Fig. 5-2a Sherwood, 5th Cdn Ed.  HOW IS STIMULUS INTENSITY CODED? How are different intensities of stimuli translated into neural activity? Two coding strategies: 1. Frequency coding – Greater the intensity – greater the frequency of action potentials in individual axons. – NOT A LINEAR FUNCTION 2. Population coding – With increased intensity, more individual receptors are recruited.  Stimulus strength Increased stimulus strength leads to increased graded potential Fig. 6-3, Sherwood 9th Ed.  Stimulus strength Increased stimulus strength leads to increased action potential frequency along afferent neuron Fig. 6-3, Sherwood 9th Ed.  Stimulus strength Increased stimulus strength leads to increased action potential frequency along afferent neuron and greater quantity of neurotransmitter release from afferent Fig. 6-3, terminals Sherwood 9th Ed.  Stimulus strength Is this frequency coding or population coding? Fig. 6-3, Sherwood 9th Ed.  Stimulus strength Is this frequency coding or population coding? How do you get population coding? Fig. 6-3, Sherwood 9th Ed.  Objectives By the end of this lecture you should be able to: 1) define a sensory receptor 2) identify some sensory receptors and what they detect 3) understand the general mechanisms of how sensory receptors relay signals to the CNS, including how sensory intensities are coded 4) describe two different types of receptor adaptation  Receptor Adaptation Most sensory receptors have the property of adapation. Decreased depolarization despite sustained stimulus strength Tonic receptors – adapt slowly or not at all – Continue to generate AP and relay info to CNS Ex. Muscle stretch receptors (which monitor muscle length) or joint proprioceptors (which monitor degree of joint flexion) CNS must get this continuous info to maintain posture and balance.  Receptor Adaptation Phasic receptors – adapt rapidly – No longer responds to maintained stimulus Ex. Touch receptors on skin that signal change in pressure Think of putting clothes or accessories on. You quickly forget that you are wearing them. When you take them off though, you are aware of it (ie. the “off response”) Speed of Adaptation Off response is depolarization seen when stimulus is removed Fig. 6-4  Objectives By the end of this lecture you should be able to: 1) define a sensory receptor 2) identify some sensory receptors and what they detect 3) understand the general mechanisms of how sensory receptors relay signals to the CNS, including how sensory intensities are coded 4) describe two different types of receptor adaptation CLASSIFICATION OF PERIPHERAL NERVE FIBRES copyright © Dennis Kunkel Dr. Frank Huynh Department of Cellular and Physiological Sciences University of British Columbia  Objectives By the end of this lecture you should be able to: 1) classify nerve fibres by the letter or Roman numeral classification system 2) characterize each type of nerve fibre by fibre type (afferent vs. efferent), diameter, myelination status, and conduction velocity. 3) identify some structure types that are innervated by each fibre type  CLASSIFICATION OF PERIPHERAL NERVE FIBRES There are 2 classification schemes The first is based on conduction velocity and uses A,B,C designation. – Group A have fastest conduction velocity (large diameter; myelinated) – Group B, are smaller, but still myelinated – Group C, smallest, non-myelinated – A fibres usually subdivided into A, A, A, A. – Usually, this scheme is used for motor fibres –hence -motor neurones and - motor neurones. * Note the “A” is dropped.  CLASSIFICATION OF PERIPHERAL NERVE FIBRES The other scheme is based on measurements of diameter and uses Roman numerals: – I, II, III, and IV – This scheme is used exclusively for sensory axons. * note that some authors refer to unmyelinated axons as C- fibres, others as group IV fibres.  CLASSIFICATION OF PERIPHERAL NERVE FIBRES Roman numeral Letter Conduction Types of structures Classification Classification Diameter Myelinated velocity innervated (sensory) (motor) Ia - 12-20 µm 70-120 m/sec Yes Muscle spindle primary endings (intrafusal fibres) Ib - 12-20 µm 70-120 m/sec Yes Golgi tendon organs (detect muscle tension) - A 12-20 µm 70-120 m/sec Yes Efferents to extrafusal muscle fibres II A 6-12+ µm 30-70 m/sec Yes Other encapsulated endings and endings with accessory structures: Meissner corpuscles, Merkel endings, muscle spindle secondary endings, etc - Aγ 2-10 µm 10-50 m/sec Yes Efferents to intrafusal muscle fibres  CLASSIFICATION OF PERIPHERAL NERVE FIBRES Roman numeral Letter Diameter Conduction Myelinated Types of structures classification classification velocity innervated (sensory) (motor) III A 1-6 µm 5-30 m/sec Yes Some nociceptors (sharp pain) Cold receptors Most hair receptors Some visceral receptors Some efferents to intrafusal muscle fibres - B