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Lecture 15 – Ch.50: Sensory & Muscular I. Sensory Systems A. Sound B. Sight C. Taste/Smell II. Skeletal Muscles A. Structure B. Contraction C. Nerve Input III. Prep for final Sensory Input What is a Sensory Receptor? Specialized neurons that signal when stimulated Receptors named after stimuli they respond to: 1) Thermoreceptors: heat & cold 2) Mechanoreceptors: pressure/touch, stretch, motion, sound 3) Electromagnetic Receptors: light, electricity, magnetism 4) Chemoreceptors: 5) Nociceptors: osmolarity, gustation, olfaction pain – thermal, chemical, mechanical Sound: Sensory Input Sound waves are vibrations in fluid (air, water) Sensory Input Sound: Ear: Sound Electrical Signal Outer ear 1) Sound wave enters ear (auditory canal) Middle ear Inner ear Skull bone 2) Tympanic membrane vibrates Semicircular canals Auditory nerve to brain 3) Vibration passes to middle ear bones 4) Inner ear (cochlea) converts vibrations to electrical signal Cochlea Auditory canal Tympanic membrane Eustachian tube Sound: Sensory Input 5) Inside the cochlea, hair cells are between the basilar and tectorial membranes – vibrations cause the basilar membrane to vibrate, bending hairs against the tectorial membrane. Bone Auditory nerve Vestibular canal Cochlear duct Tympanic canal Tectorial membrane Hair cells Organ of Corti Basilar membrane To auditory Axons of nerve sensory neurons 5 Sensory Input Sound: 6) The basilar membrane varies in stiffness along its length – different regions vibrate in response to different frequencies. B C Stapes Vestibular canal A Cochlea Point B Tympanic membrane Basilar membrane Tympanic canal Relative motion of basilar membrane Axons of sensory neurons A 3 6,000 Hz Point C C 0 3 1,000 Hz 0 3 100 Hz 0 10 30 20 0 Distance from oval window (mm) Point A (a) B (b) What category of sensory receptors detect sound? Sensory Input Vision: Eye: Light Electrical Signal Some animals only sense light/dark Many arthropods have compound eyes; many images pieced together into a visual mosaic Compound eyes Vision: Sclera Sensory Input Retina Photoreceptors Fovea Neurons Rod Cone Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Central artery and vein of the retina Optic nerve fibers Pigmented epithelium 1) Light enters via cornea (transparent covering), through pupil (opening in center of iris - pigmented ring of muscle that controls light entry) 2) Light focused by lens on retina (sheet of photoreceptors) Vision: Sensory Input 3) Muscles attached to lens contract to change the lens shape and focus image on the fovea for any visual distance retina Distant object, lens thins to focus on retina. The blind spot is where the optic nerve connects to eyeball Close object, lens fattens to focus on retina. No photoreceptors, so images disappear Sensory Input Vision: 5) Light on the retina triggers receptors; optic nerve excited Rods: Dim-light vision (many but scattered) Cones: Color vision (Red/green/blue) CYTOSOL Rod Synaptic terminal Cell body Outer segment Disks Cone Rod Rhodopsin: Cone Retinal INSIDE OF DISK Opsin Sensory Input Odor/Taste: Papilla Nose / Tongue: Chemical Electrical Signal 1) Dissolved chemicals enter taste buds on tongue (via taste pore) Papillae Taste buds (a) Tongue 2) Chemicals bind with receptors; stimulate nerves 3) Tastants bind one of five types of receptor cells: Key Taste bud Sweet Salty Sour Bitter Umami Taste pore Sensory neuron • Olfaction enhances taste (b) Taste buds Sensory receptor cells Food molecules Sensory Input Odor/Taste: Brain potentials Odorants Nasal cavity Bone Epithelial cell Receptors for different odorants Chemoreceptor Plasma membrane Odorants 1) Chemicals enter nasal cavity; bind to receptors Cilia Mucus 2) Humans can detect more than 1000 different odorants due to different receptors Self-Check Sensation Type(s) of receptor; Description of sense Touch Sound Sight Taste Smell Pain 13 Some senses are unfamiliar to humans Other Senses: Sensory Input Electrolocation: Animal produces electrical field; interpret distortion in field Magnetic Field Detection: Echolocation: Animal emits pulse interprets returning signal Animals detect and orient based on earth’s magnetic field Muscular and skeletal systems Muscles power movement by contracting Bones provide framework for muscles Muscles Muscle Tissue (Muscle = “little mouse”): • Exerts force by contracting Movement due to actin microfilaments and myosin strands Slide past one another, change cell shape Transformation Chemical energy (ATP) Mechanical Energy Skeletal Muscles Muscle • Humans have > 700 unique skeletal muscles • Each muscle has multiple fibers – each fiber many muscle cells Bundle of muscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z lines Sarcomere Each muscle cell runs length of muscle - Multinucleate - Filled with myofibrils of contractile units = sarcomeres Skeletal Muscles Myofibrils of “thick” (myosin) and “thin” filaments (actin). Each filament is made of protein strands. Z lines Sarcomere Filaments arranged in sarcomeres Separated by Z-lines of fibrous protein Thick filaments (myosin) Thin filaments (actin) TEM M line Z line Sarcomere 0.5 m Z line Skeletal Muscles Each myofibril surrounded by sarcoplasmic reticulum - Fluid with high calcium levels - T-tubules in plasma membrane relay signals Synaptic terminal Axon of motor neuron T tubule Sarcoplasmic reticulum (SR) Mitochondrion Myofibril Plasma membrane of muscle fiber Sarcomere Ca2 released from SR Skeletal Muscles Neuromuscular junctions between axons and fibers All or nothing response: Skeletal muscle excited All sarcomeres of all cells respond axon of motor neuron synaptic terminal synaptic vesicles postsynaptic membrane Skeletal Muscles Action potential travels through T-tubules and opens Ca2+ channels in sarcoplasmic reticulum Ca2+ allows binding of thin and thick fibers Ca2+ is pumped back out after action potential ends Skeletal Muscles Strength of Muscle Contraction # of Fibers Stimulated Motor Unit: A single motor neuron and all the muscle fibers innervated by it Skeletal Muscles You cannot add fibers or muscle cells You can add more myofibrils Muscle muscle fibers Single muscle fiber (cell) Myofibril Things To Do After Lecture 15… Reading and Preparation: 1. Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. 2. Ch. 50 Self-Quiz: #1, 2, 3, 4, 5 (correct answers in back of book) 3. Read chapter 50, focus on material covered in lecture (terms, concepts, and figures!) 4. Prepare for final exam!!! “HOMEWORK” (NOT COLLECTED – but things to think about for studying): 1. Describe the types of sensory information processed by humans – which receptors are responsible for each type? 2. What is the problem in the eye of someone who is near-sighted versus someone who is far-sighted? How do corrective lens fix the problem? 3. Explain how a muscle contracts – include the units down to the sarcomere and their place in a muscle fiber.