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Sensory and Motor Mechanisms

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1 Sensory and Motor Mechanisms
Samaneh Bolourchi, Jennifer Tszeng & Athena Zeng

2 Introduction: Sensory Pathways
Sensory receptors transduce stimulus energy & transmit signals to CNS (central nervous system) Reception: detection via exteroreceptors or interoreceptors Transduction: stimulus energy converted into ∆ in membrane potential of sensory receptor (receptor potential) Amplification: stimulus energy strengthens in cells in pathways Adaptation: decrease in responsiveness Transmission: action potentials transmitted to the CNS Perception: constructions formed in brain (ie color, smell, sounds)

3 Introduction: Types of Receptors
Sensory receptors are specialized neurons or epithelial cells that exist singly or in groups with other cell types in sensory organs, such as eyes or ears. Mechanoreceptors sense physical deformation cause by forms of mechanical energy such as pressure, touch, etc. Chemoreceptors respond to chemical stimuli. Electromagnetic receptors respond to various forms of electromagnetic energy such as visible light, electricity, and magnetism. Thermoreceptors respond to heat or cold and help regulate body temperature by signaling surface and body core temperature. Pain receptors, or nociceptors, are a class of naked dendrites in the epidermis.

4 Mechanoreceptors Detect mechanical energy
typically consist of ion channels linked to external cell structures (ie hairs) & internal structures (ie cytoskeleton) Bending/stretching plasma membrane changes permeability to sodium & potassium ions Type of mechanoreceptor varies greatly between organisms Crustaceans - vertebrate stretch receptors Mammals - dendrites of sensory neurons

5 Introduction: Sound & Balance
Ear receives vibrations of moving air and converts into what the mind perceives as sound Also detects body movement, position & balance Structures vary between organisms Terrestrial vertebrates: inner ear is main organ of hearing & equilibrium Fish/Amphibians: lack certain parts but also contain homologous structures Invertebrates - statocysts

6 Sound in Humans: Structure of Human Ear
Outer ear Pinna Tympanic membrane Middle ear Malleus, incus, stapes Oval window Eustachian tube Inner ear Fluid-filled chambers ie semicircular canals & cochlea

7 Sensory Reception: Hair Cells
Rod-shaped hairs in corti Vibration of basilar membrane bends hairs against surrounding fluid & tectorial membrane Bundle direction affects reception Activates mechanoreceptors 1093; base explanation on 1094; use 1094 diagram

8 Balance in Humans: Utricle & Saccule

9 Sound & Balance: Variation in Organisms
Terrestrial vertebrates: ear has = main organ of hearing & equilibrium Fish/Amphibians - similar to mammalian ears; lack several structures Frogs/toads - single middle bone (stapes) Frogs: small side pocket in saccule - basis for evolution of mammalian cochlea Birds - cochlea; single middle bone (stapes)

10 Sound & Balance: Fish/Amphibians
lateral line system have ears outside of body; no eardrum or cochlea; air-filled swim bladder also vibrates in response to sound

11 Sound & Balance in Invertebrates

12 Thermoreceptors Detect heat Located in skin and anterior hypothalamus
Mammals contain a range of thermoreceptor types for particular temperature ranges Receptor proteins open a calcium channel upon binding certain products At least five different types of thermoreceptors belong to the transient receptor potential (TRP) family of channel proteins

13 Pain Receptors Nociceptors detect noxious conditions
Essential - stimulus prompts defensive reaction Animals also produce chemicals to enhance pain perception

14 Touch Receptors usually on skin
Humans contain naked dendrites to detect noxious thermal, mechanical & chemical stimuli Epidermis, dermis, hypodermis * structure of connective tissue & location of receptors dramatically affect the type of mechanical energy that best stimulates them

15 Human Integumentary System
Heat Light touch Pain Cold Hair Nerve Connective tissue Hair movement Strong pressure Dermis Epidermis

16 Chemoreceptors The most sensitive chemoreceptors
are on sensory hairs of the male silkworm which detect sex pheromones. 0.1 mm

17 Gustation In mammals, taste receptors are located in taste buds, most of which are on the surface of the tongue Each taste receptor responds to a wide array of chemicals, but is most responsive to a particular type of substance. It is the pattern of taste receptor response that determines perceived flavor. Transduction in taste receptors occurs by several mechanisms.


19 Olfaction In mammals, olfactory receptors line the upper portion of the nasal cavity. The receptive ends of the cells contain cilia that extend into the layer of mucus coating the nasal cavity. Each olfactory receptor cell expresses only one or a few odorant receptor genes.


21 Electromagnetic Receptors
Respond to various forms of electromagnetic energy such as visible light, electricity, and magnetism. Photoreceptors detect energy in form of light Examples: Snakes—body heat of prey. Fish—electric currents—prey. Animals—earths magnetic field. (birds)

22 Types of Eyes the simplest is the eye cup of planarians
In invertebrates, there are compound eyes and single-lens eyes: Compound: in crustaceans , insects, etc. (have several thousand facets called ommatidia) Single-lens: jellies, spiders, etc (single lens that focuses light) In vertebrates Evolved independently and differ from the single-lens eyes of invertebrates

23 Eye Structure

24 Sensory Transduction The human retina contains two types of photoreceptors Rods are sensitive to light but do not distinguish colors Cones distinguish colors but are not as sensitive Each rod or cone in the vertebrate retina contains visual pigments consisting of light-absorbing molecules called retinal bonded to membrane proteins called opsin Rhodopsin (retinal + opsin) is the visual pigment of rods. Absorption of light by retinal triggers a signal transduction pathway!

25 Signal Transduction cont.
EXTRACELLULAR FLUID Membrane potential (mV) – 40 – 70 Dark Light – Hyper- polarization Time Na+ cGMP CYTOSOL GMP Plasma membrane INSIDE OF DISK PDE Active rhodopsin Light Inactive rhodopsin Transducin Disk membrane 2 Active rhodopsin in turn activates a G protein called transducin. 3 Transducin activates the enzyme phos-phodiesterae(PDE). 4 Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na+ channels in the plasma membrane by hydrolyzing cGMP to GMP. 5 The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes. 1 Light isomerizes retinal, which activates rhodopsin.

26 Signal Transduction (cont.)
Three other types of neurons contribute to information processing in the retina Ganglion cells, horizontal cells, and amacrine cells Signals from rods and cones travel from bipolar cells to ganglion cells, which then transmit info to brain by optic nerve (axon of ganglion) Horizontal cells and amacrine cells function in neural pathways that integrate visual info before sent to brain. Lateral inhibition causes a greater contrast b/n light and dark (as the horizontal cells inhibit more distant photoreceptors) and this enhances the image, and sharpens its edges.

27 Synaptic activity of rod cells in light and dark
Dark Responses Rhodopsin inactive Na+ channels open Rod depolarized Glutamate released Bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors Light Responses Rhodopsin active Na+ channels closed Rod hyperpolarized No glutamate hyperpolarized or depolarized, depending on glutamate receptors

28 Evolution of Visual Perception
All photoreceptors contain similar pigment molecules that absorb light (despite diversity) Genetic underpinnings of all photoreceptors evolved in the earliest bilateral animals.

29 Vertebrate Skeletal Muscle
Myofibrils consist of: Thin filaments: two strands of actin and two strands of a regulatory protein Thick filaments: staggered arrays of myosin molecules Striated Muscle: regular arrangement of filaments create light/dark band pattern Sarcomere: basic contractile unit between Z- lines



32 Types of Muscle Skeletal Muscle Voluntary movements Attatched to bones
Cardiac muscle is similar to skeletal muscle with striations. Smooth muscle lacks striations lines walls of blood vessels and digestive system organs.

33 Skeletal Systems Support, protection, and movement
Hydrostatic Skeleton – consists of fluid held under pressure in a closed body compartment. Form and movement are controlled by changing the shape of this compartment. Examples: Flatworms, Nematodes, Annelids, Jellyfish Exoskeleton – encasement deposited on the surface of an animal. -> chitinous or made from calcium salts, etc. Examples: Insects, Crustaceans, Mollusks Endoskeleton – Interior skeleton within muscles and skin. Act as levers when the muscles contract to allow the organism to move. Examples: Mammals, Birds, Reptiles, Fish, Sponges

34 Locomotion Requires energy to overcome friction & gravity
Swim: friction is major issue; gravity is minor Land: requires self-support & movement against gravity Flight: requires wings developed enough to lift & overcome gravity

35 Diseases: Color Blindness
Color-Blindness: due to alterations in the genes for one or more photopsin proteins. There are different types: No color vision deficiencies. with protanopia. with deuteranopia. with tritanopia.

36 Diseases (Cont.) \ALS, amyotrophic lateral sclerosis, or Lou Gehrig’s
Myasthenia gravis

37 Bibliography Pictures:
Information: "color blindness." Encyclopedia Britannica Encyclopedia Britannica Online. 09 Apr < A. Campbell, Neil, and Jane B. Reece. Biology. San Francisco: Pearson Education, Inc., 05 Jan. 2009 "mechanoreceptor." Encyclopedia Britannica Encyclopedia Britannica Online. 09 Apr < "inner ear." Encyclopedia Britannica Encyclopedia Britannica Online. 09 Apr < Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 3, 1997, ISBN Bejan, Adrian; Marden, James H. (2006), "Constructing Animal Locomotion from New Thermodynamics Theory", American Scientist 94 (4): 342–349

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