Sensory and Motor Mechanisms

1. Sensory and Motor Mechanisms Chapter 49 LAST SET OF NOTES EVER IN AP BIO!!!

2. Sensations and Perceptions • Begin with sensory reception, the detection of stimuli by sensory receptors • Exteroreceptors • Detect stimuli coming from the outside of the body • Interoreceptors • Detect internal stimuli • Sensory receptors perform four functions • Sensory transduction, amplification, transmission, and integration

3. Fluid moving inone direction Fluid moving in other direction No fluidmovement “Hairs” ofhair cell Neuro-trans-mitter at synapse Moreneuro-trans-mitter Lessneuro-trans-mitter –50 –50 Axon –50 Receptor potential –70 –70 –70 Membranepotential (mV) Membranepotential (mV) Membranepotential (mV) Action potentials 0 0 0 –70 –70 –70 5 6 7 1 2 3 4 0 0 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Time (sec) Time (sec) Time (sec) (b) Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when sur-rounding fluid moves. Each hair cell releases an excitatory neurotransmitter at a synapse with a sensory neuron, which conducts action potentials to the CNS. Bending in one direction depolarizes the hair cell, causing it to release more neurotransmitter and increasing frequency Figure 49.2b Sensory Receptors • Changing energy in membrane potential leads to a change in frequency of action potentials

4. Sensory Transduction • Sensory transduction is the conversion of stimulus energy • Into a change in the membrane potential of a sensory receptor • This change in the membrane potential • Is known as a receptor potential • Many sensory receptors are extremely sensitive • With the ability to detect the smallest physical unit of stimulus possible

5. Amplification • Amplification is the strengthening of stimulus energy • By cells in sensory pathways • Ex. Human Eye • Few photons of light triggers about 100,000 times more energy • From eye to brain

6. Transmission • After energy in a stimulus has been transduced into a receptor potential • Some sensory cells generate action potentials, which are transmitted to the CNS • Sensory cells without axons • Release neurotransmitters at synapses with sensory neurons

7. Integration • The integration of sensory information • Begins as soon as the information is received • Occurs at all levels of the nervous system • Some receptor potentials • Are integrated through summation • Another type of integration is sensory adaptation • A decrease in responsiveness during continued stimulation

8. Types of Sensory Receptors • Based on the energy they transduce, sensory receptors fall into five categories • Mechanoreceptors • Chemoreceptors • Electromagnetic receptors • Thermoreceptors • Pain receptors

9. Cold Light touch Pain Hair Heat Epidermis Dermis Hair movement Nerve Strong pressure Connective tissue Mechanoreceptors • Mechanoreceptors sense physical deformation • Caused by stimuli such as pressure, stretch, motion, and sound • The mammalian sense of touch • Relies on mechanoreceptors that are the dendrites of sensory neurons

10. 0.1 mm Chemoreceptors • Chemoreceptors include • General receptors that transmit information about the total solute concentration of a solution • Specific receptors that respond to individual kinds of molecules

11. Electromagnetic • Electromagnetic receptors detect various forms of electromagnetic energy • Such as visible light, electricity, and magnetism

12. Thermoreceptors • Thermoreceptors, which respond to heat or cold • Help regulate body temperature by signaling both surface and body core temperature

13. Pain Receptors • In humans, pain receptors, also called nociceptors • Are a class of naked dendrites in the epidermis • Respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues

14. Overview of ear structure The middle ear and inner ear 1 2 Incus Semicircularcanals Skullbones Stapes Middleear Outer ear Inner ear Malleus Auditory nerve,to brain Pinna Tympanicmembrane Cochlea Eustachian tube Auditory canal Ovalwindow Eustachian tube Tympanicmembrane Tectorialmembrane Hair cells Roundwindow Cochlear duct Bone Vestibular canal Auditory nerve Axons of sensory neurons Basilarmembrane To auditorynerve Tympanic canal Organ of Corti The organ of Corti The cochlea 4 3 Hearing and Equilibrium

15. Taste and Smell • Taste in Humans • The receptor cells for taste in humans • Are modified epithelial cells organized into taste buds • Five taste perceptions involve several signal transduction mechanisms • Sweet, sour, salty, bitter, and umami (elicited by glutamate)

16. Taste pore Sugar molecule Sensoryreceptorcells Taste bud Sensoryneuron Tongue Sugar Sugarreceptor Adenylyl cyclase G protein ATP cAMP Proteinkinase A SENSORYRECEPTORCELL K+ Synapticvesicle —Ca2+ Neurotransmitter Sensory neuron 2Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. 3Activated protein kinase A closes K+ channels in the membrane. 4 The decrease in the membrane’s permeability to K+ depolarizes the membrane. 5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell. 6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter.

17. Smell in Humans • Olfactory receptor cells • Are neurons that line the upper portion of the nasal cavity • When odorant molecules bind to specific receptors • A signal transduction pathway is triggered, sending action potentials to the brain

18. Vision • The main parts of the vertebrate eye are • The sclera, which includes the cornea • The choroid, a pigmented layer • The conjunctiva, that covers the outer surface of the sclera • The iris, which regulates the pupil • The retina, which contains photoreceptors • The lens, which focuses light on the retina

19. Sclera Choroid Retina Ciliary body Fovea (centerof visual field) Suspensoryligament Cornea Iris Opticnerve Pupil Aqueoushumor Lens Vitreous humor Central artery and vein of the retina Optic disk(blind spot)

20. Sight • 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

21. Mechanical Movements • The various types of animal movements • All result from muscles working against some type of skeleton • The mammalian skeleton is built from more than 200 bones • Some fused together and others connected at joints by ligaments that allow freedom of movement

22. 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 Skeleton

23. Human Grasshopper Extensormusclerelaxes Bicepscontracts Tibiaflexes Flexormusclecontracts Tricepsrelaxes Forearmflexes Extensormusclecontracts Tibiaextends Bicepsrelaxes Forearmextends Flexormusclerelaxes Triceps contracts • Skeletal muscles are attached to the skeleton in antagonistic pairs • With each member of the pair working against each other

24. Muscle Bundle ofmuscle fibers Nuclei Single muscle fiber (cell) Plasma membrane Z line Myofibril Lightband Dark band Sarcomere TEM 0.5 m Thickfilaments(myosin) A band I band I band M line Thinfilaments(actin) Z line Z line H zone Sarcomere • Vertebrate skeletal muscle • Is characterized by a hierarchy of smaller and smaller units

25. Muscle • A skeletal muscle consists of a bundle of long fibers • Running parallel to the length of the muscle • A muscle fiber • Is itself a bundle of smaller myofibrils arranged longitudinally • The myofibrils are composed to two kinds of myofilaments • Thin filaments, consisting of two strands of actin and one strand of regulatory protein • Thick filaments, staggered arrays of myosin molecules

26. Skeletal Muscle • Skeletal muscle is also called striated muscle • Because the regular arrangement of the myofilaments creates a pattern of light and dark bands • Each repeating unit is a sarcomere • Bordered by Z lines • The areas that contain the myofilments • Are the I band, A band, and H zone

27. Sliding-Filament Theory • According to the sliding-filament model of muscle contraction • The filaments slide past each other longitudinally, producing more overlap between the thin and thick filaments • The sliding of filaments is based on • The interaction between the actin and myosin molecules of the thick and thin filaments • The “head” of a myosin molecule binds to an actin filament • Forming a cross-bridge and pulling the thin filament toward the center of the sarcomere

28. Tropomyosin Ca2+-binding sites Actin Troponin complex (a) Myosin-binding sites blocked Contraction • A skeletal muscle fiber contracts • Only when stimulated by a motor neuron • When a muscle is at rest • The myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin

29. Contraction • For a muscle fiber to contract • The myosin-binding sites must be uncovered • This occurs when calcium ions (Ca2+) • Bind to another set of regulatory proteins, the troponin complex • The stimulus leading to the contraction of a skeletal muscle fiber • Is an action potential in a motor neuron that makes a synapse with the muscle fiber

30. Cardiac Muscle • Cardiac muscle, found only in the heart • Consists of striated cells that are electrically connected by intercalated discs • Can generate action potentials without neural input

31. Smooth Muscle • In smooth muscle, found mainly in the walls of hollow organs • The contractions are relatively slow and may be initiated by the muscles themselves • In addition, contractions may be caused by • Stimulation from neurons in the autonomic nervous system