Sensory and Motor Mechanisms

Sensory and Motor Mechanisms Chapter 49 Adrianna Wurster , Katrina Gladstone, Hannah Reed

Sensing and Acting • Origins of sensing can be traced back to the appearance, in prokaryotes, of cellular structures that sense pressure or chemicals in the environment and then direct movement • Detection and processing of sensory information and the generation of motor output provide the physiological basis for all animal behavior • When animals are in motion they are probing the environment through motion, sensing changes and anticipating the next action. This is a continuous cycle.

Sensory receptors • Sensory receptors- transduce stimulus energy and transmit signals to the central nervous system • info transmitted through the nervous system in the form of nerve impulses or action potentials, all or none events • what matters is where action potentials go, not what triggers them • sensations- action potentials that reach the brain via sensory neurons • perceptions- interpretation of senses by the brain • Sensations and perceptions begin with sensory reception which is the detection of a stimulus by a cell. Most are specialized epithelial cells. • Exteroreceptors- sensory receptors that detect stimuli coming from outside the body • Interoreceptors- detect stimuli coming from within the body, such as blood pressure and body position

Functions Performed by Sensory Receptors All stimuli represent forms of energy Four Functions: • sensory transduction • amplification • Transmission • integration

Sensory Transduction • sensory transduction- the conversion of stimulus energy to a change in the membrane potential of a sensory receptor • Receptor potential- change in membrane potential itself • receptor potentials result from opening or closing of ion channels in the sensory receptor plasma membrane caused by bending and stretching of the membrane by external stimuli • sensory receptors are extremely sensitive

Amplification • The strengthening of stimulus energy by cells in the sensory pathway • Some amplification occurs in sensory receptors and signal transduction pathways . • It can take place in accessory structures of complex organs

Transmission • transmission- energy stimulus has been transduced into a receptor potential, action potentials are transmitted to the central nervous system • if cell cannot generate action potentials themselves, these receptors release neurotransmitters at synapses with sensory neurons • receptors release an excitatory neurotransmitter, causing the sensory neuron to transmit action potentials to the central nervous system • magnification of a receptor potential affects the frequency of action potentials that travel as sensations to the central nervous system • many sensory neurons spontaneously generate action potentials at a low rate

Integration • process begins as soon as information is received • sensory adaptation- decrease in responsiveness during continued stimulation • integration occurs at all levels within the nervous system • complex sensory structures such as the eyes have higher levels of integration

Types of Sensory Receptors • Mechanoreceptors • Chemoreceptors • Electromagnetic receptors • Thermoreceptors • Pain Receptors

Mechanoreceptors • Mechanoreceptors- sense physical deformation caused by stimuli such as pressure, touch, stretch, motion, and sound (mechanical energy) • EX: crayfish stretch cell receptor and vertebrate hair cell are mechanoreceptors • Muscle Spindles- a mechanoreceptors stimulated by mechanical distortion • When muscle fibers are stretched, spindle fibers are stretched, depolarizing sensory neurons and triggering action potentials that are transmitted to the spinal chord • Mammalian sense of touch relies on mechanoreceptors, the dendrites of sensory neurons • Embedded in layers of connective tissue • Location of receptor depends on function

Chemoreceptors • Chemoreceptors- both general receptors that transmit information about the total solute concentration of a solution and specific receptors that respond to individual kinds of molecules • ex: osmorecpetors in the mammalian brain – detect solute concentration of the blood and stimulate thirst when osmolarity increases

Two of the most sensitive and specific Chemoreceptors known are in the antennae of the male silkworm moth

Electromagnetic receptors • detect various forms of electromagnetic energy, such as visible light, electricity, and magnetism • Photoreceptors detect the radiation of visible light • Snakes have sensitive inferred receptors that can detect the body heat of upcoming prey. • The platypus has electroreceptor on its bill that detect electric fields generated by the muscles of crustaceans. Snake vision

Thermoreceptors • respond to heat or cold, help regulate body temperature • There is controversy whether they are modified pressure receptors or if they are naked dendrites of certain sensory neurons

Pain Receptors • naked dendrites in the epidermis and dermis • Usually leads to defensive reaction • Different groups of pain receptors respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues • Prostaglandins increase pain by sensitizing receptors

Sensing gravity and sound in invertebrates • statocysts: sensory organs containing mechanoreceptors; function in sense of equilibrium • statoliths: dense granules surrounded by layer of ciliated receptor cells in a statocyst; moved by gravity and stimulates certain cells • indicate body position • insects have body hairs that vibrate in response to sound waves and localized “ears” (tympanic membrane stretched over air chamber

Hearing and equilibrium in mammals • hearing • tympanic membranebonesovalwindowcochleabasilarmembraneauditory nerve brain • sound is represented by changes in frequency sensations in auditory nerve • volume: amplitude • pitch: frequency

Equilibrium • utricle: detects body position/balance; hair cells and “ear stones” • saccule: detects body position/balance • clustered hair cells in gelatinous material with otoliths (ear stones, move with gravity); releases neurotransmitters interpreted by brain; disrupted during spinning

How the Cochlea distinguishes pitch: Variation in the width and stiffness of the basilar membrane (pink) tunes specific regions of the membrane to a specific frequency Different frequencies cause different places along the membrane to vibrate stimulating particular hair cells and sensory neurons.

Hearing and equilibrium in other vertebrates • have inner ears located near brain, saccule, utricle, semicircular canals, homologous structures to equilibrium sensors • no cochlea • otoliths in inner ear chamber stimulate sensory hairs • no eardrum – does not open outside body (vibrations in water from sound wavesskeletoninner earotoliths • lateral line system: along both sides of body, contain mechanoreceptors tht detect low frequency waves • neuromasts: hair cells embedded in cupula • helps perceive movement through water • terrestrial vertebrates: inner ear evolved

Sense of taste and smell are closely related in most animals • pheromones- chemical converstations • gestation (taste); olfaction (smell) • Taste in humans • receptor cells are modified epithelial cells organized into taste buds • sweet, sour, salty, bitter, umami – detected by chemoreceptors • Smell in humans • ciliaolfactory receptor cellolfactory bulb in brain • strong link to taste

Similar mechanisms underlie vision throughout the animal kingdom • all photoreceptors have light absorbing pigments and most are homologous • Vision in invertebrates • ocellus: detects light intensity and direction (eyespot/eyecup) • image forming eyes: • compound eyes; several thousand light detectors (ommatida) • single-lens eye: camera-like

The vertebrate visual system • camera-like • Structure of the eye • sclera: white, outer layer of connective tissue • choroid: thin, pigmented inner layer • conjunctiva: mucous membrane over sclera • cornea: fixed lens; lets light in • iris: color, regulates light entering pupil • pupil: hole in iris • retina: contains photoreceptors • rods and cones (no rods on fovea) • lens/ciliary body; divides cell into two cavities • accommodation: changing shape of lens to focus • aqueous humor: liquid filling anterior cavity • vitreous humor: jelly filling posterior cavity

Sensory transduction in the Eye • rhodospin: retinal (light absorbing molecule) bonded to ospin (protein) • photospins: three visual pigments of cones (red, green, blue)

Processing visual info • depolarized and hyperpolarized rods and cones release neurotransmitters (glutamate) at synapses • ganglion cells, horizontal cells, amacrine cells • lateral inhibition: sharpens edges and enhances contrast • optic chiasm: where two optic nerves meet near the center of the base of the cerebral cortex

Evolution of the Skeletal system • Dermoskeleton – the most primitive vertebrate system and the earliest to show mineralization within the vertebrate phylogeny • This early mineralized bone was known as “aspidin” . It is dominated by an organic matrix and collagen fibers • Ostostracans exhibited the first evidence of cellular bone • Placoderms are the earliest group to show systematic remodeling of the skeleton. • Cartilage and bone developed the endoskeleton separately from this evolutionary pattern and had an unmineralized origin. • Acraniate chordate Branchiostoma – cartilaginous elements used for support in hagfish, lamprey and some fins of early fish • Calcified cartilage arose from the neruocranium of primitive animals • cartilage template may undergo hypertrophy and eventually be replaced by bone, a process termed endochondral ossification.

Types of Skeletons and Their Functions • Functions: Support, Movement, Protection, homeostasis, storage • Support – without the structure of the skeletal system, humans would sag from the weight of their body • Protection – the skeleton protects soft tissues (organs) ex. ribs and sternum protect the heart and lungs, - skull protects the brain • Movement - give the muscles something to work against. skeletal muscle is attached to bone so it pulls on the bone when it contracts • Mineral homeostasis - stores calcium and phosphorus--minerals are released into the blood when needed • Blood cell production - red bone marrow produces red blood cells, white blood cells and other blood elements • Storage - storage of minerals and lipids(fats)---yellow marrow stores fat --(found in long bones)

Types of Skeletons • Hydrostatic skeletons • Exoskeletons • Endoskeletons

Hydrostatic Skeleton • Fluid held under pressure in a closed body compartment • Found in cold-blooded organisms • Dominant skeleton in cnidarians, flatworms, nematodes and annelids • Animals control their form and movement by using ,muscles and pressure to change the shape of the fluid filled compartments • EX: hydra can elongate by closing its mouth and using contractile cells in the body to constrict the gastrovascular cavity - it results in thrashing movements • The earthworm’s skeleton is the coelomic fluid . They use thir skeleton for peristalsis • It is a type of movement on land that produces rhythmic waves if muscle contractions from front to back • Hydrostatic skeletons are better suited for aquatic life because they cushion internal organs from shocks and provide support for crawling in terrestrial animals.

Exoskeleton • Hard encasement deposited on the surface of an animal • Have a calcareous shell - calcium carbonate shell • As an animal grows, it enlarges its shell by adding to the outer layers of the pre- existing shells • Ex. Mollusks • The jointed exoskeletons of arthropods is the cuticle> a nonliving coat secreted by the epidermis. • The cuticle is made up of chitin used for strength and flexibility. • It must be thin and flexible like leg joints for movement • Arthropods shed their exoskeleton (molt) to produce a larger one

Endoskeleton • Hard supporting elements (bones) buried within the soft tissues of animals • Sponges have hard spicules made of protein • Echinoderms have hard plates called ossicles under the skin • Chordates have a skeleton consisting of bone, cartilage, or a combination of the two • Mammalian skeleton consists of over 200 bones that can be fused together or connected by joints. • There are two parts of the skeleton: • Appendicular skeleton • Limb bones • Pectoral • Pelvic girdles • Anchor the appendages to the axial skeleton • Joints provide flexibility for body movement • Axial skeleton • Skull • Backbone • Ribcage

Head ofhumerus key Examplesof joints Axial skeleton Skull Appendicularskeleton Scapula 1 Clavicle Shouldergirdle Scapula Sternum 1Ball-and-socket joints, where the humerus contactsthe shoulder girdle and where the femur contacts thepelvic girdle, enable us to rotate our arms andlegs and move them in several planes. Rib 2 Humerus 3 Vertebra Radius Ulna Humerus Pelvicgirdle Carpals Ulna Phalanges 2Hinge joints, such as between the humerus andthe head of the ulna, restrict movement to a singleplane. Metacarpals Femur Patella Tibia Fibula Ulna Radius Tarsals 3Pivot joints allow us to rotate our forearm at theelbow and to move our head from side to side. Metatarsals Phalanges

Human Grasshopper Extensormusclerelaxes Bicepscontracts Tibiaflexes Flexormusclecontracts Tricepsrelaxes Forearmflexes Extensormusclecontracts Tibiaextends Bicepsrelaxes Forearmextends Flexormusclerelaxes Triceps contracts Muscles • In addition to the skeleton, muscles and tendons also support large land vertebrates • Animal movement is based on contractile systems that expend energy • The action of muscles is always to contract therefore the ability of muscles to move parts of the body in opposite directions requires them to be attached to the skeleton • Attached in antagonistic pairs where each member of one pair works against the other • EX: biceps and triceps

Types of Muscle • Skeletal muscle – attached to bones and causes movements of the body • Smooth Muscle – lines the walls of blood vessels and the digestive tract where it advances the movement of other objects through a slow process • Cardiac Muscle – responsible for rhythmic contractions of the heart. • Consists of cells with gap junctions to allow for electrical synapses

Vertebrate skeletal muscle • Skeletal muscle is responsible for movement and is characterized by a hierarchy of smaller and smaller units • A skeletal muscle consists of a bundle of long fibers • Running parallel to the length of the muscle • A muscle fiber • a bundle of smaller myofibrils arranged longitudinally • Composed of 2 types myofillaments • Thin Filaments - consisting of two strands of actin and one strand of regulatory protein • Thick Filaments - staggered arrays of myosin molecules • Skeletal muscle is also called striated muscle because the regular arrangement of the myofilaments creates a pattern of light and dark bands

Muscle Bundle ofmuscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Myofibril Z line Lightband Dark band Sarcomere TEM 0.5 m A band I band I band M line Thickfilaments(myosin) Thinfilaments(actin) H zone Z line Z line Sarcomere The repeating units are called sarcomeres which are the basic contractile unit of the muscle Sarcomeres are composed of long, fibrous proteins that slide past each other when the muscles contract and relax The borders of the sarcomere are called the z line

Z lines make up the border of sarcomeres > actin is attached here I band is the area near the end of the sarcomere where the thin actin filaments are located The A band is considered the length of the thick myosin fillaments During muscle contraction the length of the sarcomere is reduced- actin filaments slide over the myosin This is the sliding Filament model where the thick and thin filaments slide past each other so that the degree of overlap increases

The Neuromuscular Junction • A motor neuron will cause a muscle fiber to contract – the depolarization causes the neurotransmitters to be released into the synapse of the neuromuscular junction • 1. Action potential generates the release of acetylcholine • 2. The impulse is sent along sarcolemma and throughout the T tubules • The sarcolemma is the plasma membrane of the muscle call • The t tubules permeate the cell • 3. Sarcoplasmic reticulum releases Ca2+ • The sarcoplasm is the cytosol of the cell and holds the calcium- storing SR • 4. Myosin cross bridges form – the Ca2+ released binds with troponin to expose binding sites for myosin cross- bridge formation. • The availability of ATP begins the muscle contraction

Summation and Tetanus • A single action potential in a muscle will cause the muscle to contract for a few milliseconds and then relax • Called a twitch • If a second action potential comes before the first impulse is over the contraction will be larger • The summation effect • A series of overlapping action potentials creates a larger summation and therefore a larger contraction • If the rate of stimulation is fast enough, the twitches will become one smooth contraction called a tetanus (nothing to do with the shot) • A tetanus is what occurs when a large muscle (biceps) contract • The muscle will eventually fatigue after a period of prolonged contraction

Diseases Polymyositis • an uncommon connective tissue disease with muscle inflammation and skeletal muscle system weakness. • diagnosed most often in adults from 40 to 60 years of age or in children ages 5 to 15 years. . • signs and symptoms include: • Progressive muscle weakness • Difficulty swallowing (dysphagia) • Difficulty speaking • Mild joint or muscle tenderness • Fatigue • Shortness of breath • There is no exact cause of this disease but studies show that men are less likely to be affected than women. • Treatment: there is no known cure but the use of drugs and therapy can increase muscle strength • Corticosteroid - to reduce muscle inflamation

Diseases continued.. Stargardt’s Disease • juvenile macular degeneration, affects approximately one in 10,000 people and is characterized by central vision loss early in life • Causes • Stargardt's is an inherited disease passed along to children when both parents carry mutations of a gene associated with vitamin A processing in the eye. • Symptoms • Deterioration of vision as a child • Clouding of the cornea • Loss of color vision • Treatment and cures • Stem cell research to replace damaged tissue • Counter form of vitamin A to slow the formation of Vitamin A dimmers

Diseases continued.. • OtitisExterna the skin of the ear canal becomes inflamed. • Can result from • scratching the lining or your outer ear canal • a skin condition such as eczema, • fungal infection from swimming • Symptoms : • itchiness • watery discharge. • The discharge may dry overnight around the outside of the ear. • Little hearing loss • Treatments: • Antibiotics • Ear drops

Science, Technology, and Society • Hearing aid - a device typically worn inside or behind the ear that amplifies sound for use by people who cannot hear well. • Bionic Eye – in development by NASA. Used to repair damaged rods and cones with a ceramic implant detectors

Interdependence • Gas exchange – the muscles enable the diaphragm to move allowing air into the lungs • Digestion – bone and muscle move the jaw to break down the food • Nervous - involved in movement. Brain and nerves direct muscles to contract. Sensory organs are the first input of a stimulus • Cardiovascular – cardiac muscles contract to pump blood to the heart and around the body • Endocrine- hormones secreted directly correlate with muscle and bone growth

Works cited • Bentler, Ruth A."Hearing aid." World Book Advanced.World Book,2012.Web.20 April 2012. • Campbell, Neil A. and Reece Jane B . Biology “Seventh edition” .Pearson Education; Benjamin Cummings . New York: 2005. Print. • Columbia researchers work on preventing blindness from age-related macular degeneration and Stargardt's disease. Columbia University Medical Center. Press release. May 2011. • DenisonRH. 1963 “The Early History of the Vertebrate Calcified Skeleton”. Clin Orthopedics. Print. • Mayo clinic staff. “Polymyocitus” The Mayo Clinic. Mayo Foundation for Medical Education and Research (MFMER). 1998-2012. Web. 20 April 2012.

Sensory and Motor Mechanisms