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Sensory and Motor Mechanisms Chapter 50 Campbell Biology – 9 th Edition
You must know The location and function of several types of sensory receptors How skeletal muscles contract Cellular events that lead to muscle contraction
Sensory Receptors Mechanoreceptors: physical stimuli – pressure, touch, stretch, motion, sound Thermoreceptors: detect heat/cold Chemoreceptors: transmit solute conc. info – taste (gustatory), smell (olfactory) Electromagnetic receptors: detect EM energy – light (photoreceptors), electricity, magnetism Pain receptors: respond to excess heat, pressure, chemicals
Chemoreceptors: antennae of male silkworm moth have hairs sensitive to sex phermones released by the female Eye Infrared receptor This rattlesnake and other pit vipers have a pair of infrared receptors, one between each eye and nostril. The organs are sensitive enough to detect the infrared radiation emitted by a warm mouse a meter away. Some migrating animals, such as these beluga whales, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation.
Reception: Reception receptor detects a stimulus Sensation = action potentials reach brain via sensory neurons Perception: Perception information processed in brain
Middle ear Inner ear Outer ear Structure of the Human Ear Stapes Middle ear Incus Semicircular canals Skull bones Auditory nerve, to brain Malleus Pinna Tympanic Auditory membrane canal Eustachian tube Tympanic membrane Oval window Cochlea Round window Eustachian tube Tectorial membrane Hair cells Bone Cochlea duct Vestibular canal Basilar membrane Axons of To auditory sensory neurons nerve Auditory nerve Tympanic canal Organ of Corti
Equilibrium in the inner ear: Semicircular canals (fluid -filled chambers) detect head movements through hairs of receptor cells Semicircular canals Ampulla Flow of endolymph Vestibular nerve Cupula Hairs Hair cell Vestibule Utricle Saccule Nerve fibers Body movement
Structure of the Vertebrate Eye (also some invertebrates) Sclera Choroid Retina Ciliary body Fovea (center of visual field) Suspensory ligament Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Central artery and vein of the retina Optic disk (blind spot)
Retina Optic nerve Vision Compound eyes: several thousand ommatidia (light detectors) with its own lens; insects & crustaceans Vertebrates: Rods: sense light Cones: color vision Rhodopsin: light-absorbing pigment that triggers signal transduction pathway that leads to sight To brain Retina Photoreceptors Neurons Amacrine cell Optic nerve Ganglion fibers cell Cone Rod Horizontal cell Bipolar cell Pigmented epithelium
Types of Skeletons Hydrostatic: fluid held under pressure in closed body compartment Hydra, nematodes, annelids Exoskeletons: hard encasements on surface of animal Insects, mollusks, crustaceans Endoskeleton: hard supporting elements buried within soft tissues Human bony skeleton
Key Axial skeleton Appendicular skeleton Shoulder girdle Sternum Rib Humerus Vertebra Radius Ulna Skull Examples of joints Head of humerus Scapula Clavicle Scapula Ball-and-socket joints, where the humerus contacts the shoulder girdle and where the femur contacts the pelvic girdle, enable us to rotate our arms and legs and move them in several planes. Humerus Pelvic girdle Carpals Ulna Phalanges Metacarpals Femur Hinge joints, such as between the humerus and the head of the ulna, restrict movement to a single plane. Patella Tibia Fibula Ulna Tarsals Metatarsals Phalanges Radius Pivot joints allow us to rotate our forearm at the elbow and to move our head from side to side.
Muscles always contract Muscles work in antagonistic pairs to move parts of body Human Grasshopper Extensor muscle relaxes Biceps contracts Biceps relaxes Triceps contracts Flexor muscle contracts Forearm flexes Triceps relaxes Tibia flexes Extensor muscle contracts Forearm extends Tibia extends Flexor muscle relaxes
Skeletal Muscle Structure Muscle Bundle of muscle fibers Single muscle fiber (cell) Attached to bones by tendons Types of muscle: Nuclei Plasma membrane smooth (internal organs) Myofibril Light Z line band Dark band cardiac (heart) Skeletal (striated) Sarcomere 1 long fiber = single muscle cell Each muscle fiber = bundle of myofibrils, composed of: ▪ Actin: thin filaments ▪ Myosin: thick filaments TEM I band Thick filaments (myosin) A band M line 0. 5 µm I band Thin filaments (actin) Z line H zone Sarcomere Z line
0. 5 µm Z H A Sarcomere Relaxed muscle fiber I Contracting muscle fiber Fully contracted muscle fiber Sarcomere: basic contractile unit of the muscle Z lines – border I band – thin actin filaments A band – thick myosin filaments
Muscle Contraction: 0. 5 µm Sarcomere relaxed: actin & myosin overlap 2. Contracting: Muscle fiber stimulated by motor neuron Length of sarcomere is reduced Actin slides over myosin 3. Fully contracted: actin & myosin completely overlap 1. Z H A Sarcomere Relaxed muscle fiber I Contracting muscle fiber Fully contracted muscle fiber Sliding-filament model: thick & thin filaments slide past each other to increase overlap (Note: Filaments do NOT shorten!)
Muscle fibers only contract when stimulated by a motor neuron Motor neuron axon Mitochondrion Synaptic terminal T tubule Sarcoplasmic reticulum Myofibril Plasma membrane of muscle fiber Ca 2+ released from sarcoplasmic reticulum Sarcomere
Synaptic terminal of motor neuron Synaptic cleft T TUBULE PLASMA MEMBRANE SR ACh Ca 2+ CYTOSOL Ca 2+
Depolarization of muscle cell releases Ca 2+ ions binds to troponin expose myosin sites on actin Tropomyosin Ca 2+-binding sites Actin Troponin complex Myosin-binding sites blocked. Ca 2+ Myosinbinding site Myosin-binding sites exposed.
Hydrolysis of ATP by myosin cross-bridge formed thin filament pulled toward center of sarcomere Thick filament Thin filaments Thin filament Myosin head (low-energy configuration) Thick filament Thin filament moves toward center of sacomere. Actin Myosin head (lowenergy configuration) Cross-bridge binding site Myosin head (highenergy configuration) Cross-bridge
Speed of muscle contraction: • Fast fibers – brief, rapid, powerful contractions • Slow fibers – sustain long contractions (posture)
Problems ALS (Lou Gehrig’s disease): degeneration of motor neurons, muscle fibers atrophy Botulism: block release of acetylcholine, paralyzes muscles Myasthenia gravis: autoimmune disorder, produce antibodies to acetylcholine Calcium deficiency: muscle spasms and cramps Rigor mortis (after death): no ATP to break actin/myosin bonds; sustained muscle contraction until breakdown (decomposition)