EXS 207 Topic 9: Peripheral Nervous System PDF

11/28/2023 EXS 207 Topic 9: Peripheral Nervous System 1 Three Key Components of the PNS CNS #1 #3 Sensory Motor Receptors Endings 2 1 ...

11/28/2023 EXS 207 Topic 9: Peripheral Nervous System 1 Three Key Components of the PNS CNS #1 #3 Sensory Motor Receptors Endings 2 1  11/28/2023 SENSORY RECEPTORS 3 Sensory Receptors Respond to changes in their environment (stimuli) Activation results in graded potentials that MAY trigger nerve impulses Classified by: – Stimulus type (modality) – Location – Structure (we will not discuss this at this time) 4 2  11/28/2023 Classification by Stimulus Type Receptor Stimulus Type Mechanoreceptors Touch, pressure, vibration, stretch Thermoreceptors Change in temperature Photoreceptors Light energy Chemicals (taste/smell molecules, changes in Chemoreceptors blood chemistry) Potentially damaging stimuli (extreme Nociceptors heat/cold, excessive pressure, inflammatory chemicals) What about itch receptors – which category? 5 Itch Receptors Histamine sensitive C-fibers Also sensitive to heat and capsaicin Not identified until 1997! Why had these receptors escaped detection? Very thin axons Animal model limitations Had been focused on mechanical stimuli Schmelz M, et al. (1997). Specific C-receptors for itch in human skin. J Neurosci. 17(20): 8003-8 6 3  11/28/2023 Classification by Location 1. Exteroceptors – stimuli from outside body – Skin receptors for touch, pressure, pain, temperature – Most special sense organs – vision, hearing, smell 2. Interoceptors (visceroceptors) – stimuli from internal viscera and blood vessels – Chemical changes – Tissue stretch – Temperature changes 7 Classification by Location 3. Proprioceptors – Respond to stretch in: Skeletal muscles Tendons Joints Ligaments Connective tissue coverings of bones and muscles – Inform the brain of one’s movements 8 4  11/28/2023 Sensation (awareness of stimulus) and perception (interpretation of stimulus meaning) are vital to survival and occur exclusively in the brain. How do we get there? That is, how does sensory integration occur? 9 We will talk about processing of sensory information at three levels: 1. Receptor level: sensory receptors 2. Circuit level: processing in ascending pathways 3. Perceptual level: processing in cortical sensory areas 10 5  11/28/2023 Processing at the receptor level Regardless of the stimulus type (heat, pressure, light, etc.) it must be converted into electrical energy – transduction. Information about the stimulus (strength, duration, pattern) is encoded by the frequency of nerve impulses. What happens in response to a constant stimulus? Adaptation! 11 Receptor level processing: Adaptation Change in sensitivity in presence of constant stimulus Receptor membrane becomes less responsive Graded potentials decline in frequency or stop Phasic Receptors Adapt rapidly Photoreceptors, Meissner’s corpuscles Tonic Receptors Adapt slowly, or not at all Nociceptors, most proprioceptors 12 6  11/28/2023 Processing at the circuit level Ascending pathways carry impulses toward the cerebral cortex Thalamus ensures that info reaches correct region of cerebral cortex We have crude sensation once signal reaches thalamus (specific localization and discrimination occurs in cerebral cortex) 13 Processing at the perceptual level Perception of the sensory stimulus occurs Aspects of sensory perception: – Perceptual detection – Magnitude estimation – Spatial discrimination – Feature abstraction – Quality discrimination – Pattern recognition 14 7  11/28/2023 Perceptual Detection: ability to detect that a stimulus has occurred (requires input from multiple receptors) Magnitude Estimation: ability to detect how intense the stimulus is (frequency coding) Spatial Discrimination: identifying site or pattern of stimulation (2-point discrimination test) 15 Feature Abstraction: identification of more complex aspects and several stimulus properties Velvet is warm, compressible, and smooth but not completely continuous Marble is cool, hard, and smooth but continuous Quality Discrimination: ability to identify submodalities of a sensation (taste for example) Pattern Recognition: recognition of familiar or significant patterns in stimuli 16 8  11/28/2023 http://www.sussexpostcards.info/index.php?page=3 17 18 9  11/28/2023 19 20 10  11/28/2023 21 22 11  11/28/2023 http://www.youtube.com/watch?v=DDMvvel PXj0 23 24 12  11/28/2023 NERVES 25 Nerve Structure https://openstax.org/books/anatomy-and- physiology/pages/13-4-the-peripheral-nervous-system A nerve is a bundle of PNS axons enclosed by connective tissue. Same structure is called a tract in the CNS. Endoneurium surrounds each axon Perineurium surrounds bundles of axons (fascicles) Epineurium surrounds entire nerve 26 13  11/28/2023 https://openstax.org/books/anatomy-and- physiology/pages/13-4-the-peripheral-nervous-system 27 Nerve Classification Direction of Impulse Transmission Origin Sensory (afferent) Cranial Motor (efferent) Spinal Mixed 28 14  11/28/2023 Cranial Nerves https://openstax.org/books/anatomy-and-physiology/pages/13-4-the-peripheral-nervous-system 29 Cranial nerves are mostly named for the structure they serve or their function. # Name Type Function I Olfactory Sensory Smell II Optic Sensory Sight III Oculomotor Motor Eye movement IV Trochlear Motor Eye movement V Trigeminal Both M – chewing S – sensation from face VI Abducens Motor Eye movement VII Facial Both M – facial expression S – taste VIII Vestibulocochlear Sensory Hearing & balance IX Glossopharyngeal Both M – secretion of saliva, swallowing S - taste X Vagus Both M – visceral muscle movement S – visceral organ sensation XI Accessory Motor Swallowing & head movement XII Hypoglossal Motor Movement of tongue during speech, swallowing 30 15  11/28/2023 Cranial Nerve Mnemonics Names On occasion, our trusty truck acts funny; very good vehicle any how. Olfactory optic, oculomotor trochlear trigeminal abducens facial; vestibulocochlear glossopharyngeal vagus accessory hypoglossal. Functions Some say marry money, but my brother says big brains matter more. Sensory sensory motor motor, both motor both sensory both both motor motor. 31 Spinal Nerves Named for where they emerge – Cervical: C1-C8 – Thoracic: T1-T12 – Lumbar: L1-L5 – Sacral: S1-S5 – Coccygeal: C0 All are mixed nerves Do not directly attach to spinal cord 32 16  11/28/2023 Spinal Nerves Exits vertebral column through intervertebral foramina https://commons.wikimedia.org/ wiki/File:Spinal_nerve.svg Spinal Nerve (Mixed) 33 MOTOR ENDINGS 34 17  11/28/2023 Somatic Motor Endings: Skeletal Muscle Innervation Somatic motor neurons innervate voluntary muscles via NMJs ACh opens chemically-gated ion channels https://openstax.org/books/anatomy -and-physiology/pages/10-2- skeletal-muscle 35 Autonomic Motor Endings: Visceral muscle and gland innervation https://openstax.org/books/anatomy-and-physiology/pages/15-1-divisions-of- the-autonomic-nervous-system Autonomic motor fibers do not form discrete junctions with effector cells Neurotransmitter (ACh or norepinephrine) is released from swellings (varicosities) along the length of the axon Call these synapse en passant – “synapses in passing” 36 18  11/28/2023 REFLEXES 37 Inborn vs. Learned Reflexes Inborn (intrinsic) reflex: rapid, involuntary, predictable motor response to a stimulus Learned (acquired) reflexes: result from practice and/or repetition (e.g. driving a car) 38 19  11/28/2023 Components of a Reflex Arc https://commons.wikimedia.org/wiki/File:I mgnotra%C3%A7at_arc_reflex_eng.svg 1. Receptor: site of stimulus action 2. Sensory neuron: transmits afferent impulses to CNS 3. Integration center: monosynaptic or polysynaptic region within CNS 4. Motor neuron: conducts efferent impulses from integration center to effector organ 5. Effector: muscle fiber or gland cell that responds to efferent impulses by contracting or secreting 39 Reflex Types Cranial reflexes: integration center in Spinal reflexes: integration center in brain; utilizes cranial nerves spinal cord; utilizes spinal nerves Autonomic (visceral) reflexes: Somatic Reflexes: stimulate skeletal activate smooth muscles, cardiac muscle muscle, glands Monosynaptic: one synapse in Polysnaptic: more than one synapse integration center (sensory neuron in integration center (interneurons communicates directly with motor) used) 40 20