AP class notes

1. Sensory & Motor Mechanisms Chapter 50

2. Sensory receptors transduce stimulus energy and transmit signals to the CNS Stimuli = forms of energy Sensation involves converting energy into a change in the membrane potential of sensory receptors Sensations are action potentials that reach the brain via sensory neurons The brain interprets sensations, giving the perception of stimuli

3. Sensory pathway Fig. 50-2 Weakreceptorpotential Action potentials –50 Membranepotential (mV) Membranepotential (mV) 0 –70 –70 Slight bend:weakstimulus 1 2 3 4 5 6 7 0 Brain perceivesslight bend. Dendrites Time (sec) Stretchreceptor 2 4 1 Axon 3 Brain Muscle Brain perceiveslarge bend. Action potentials Large bend:strongstimulus 0 Membranepotential (mV) Strong receptorpotential –50 Membranepotential (mV) –70 Reception 1 1 2 3 4 5 6 7 0 –70 Time (sec) Transduction Transmission Perception 2 3 4

4. Sensory Reception Detection of stimulus Sensory receptors Detect heat, light, pressure, chemicals Blood pressure, body position Sensory transduction Conversion of stimulus to change in membrane potential Charge difference in membrane due to ions

5. Transmission Passage of nerve impulse along axons and across synapses Sensory cells without axons release neurotransmitters at synapses with sensory neurons Larger receptor potentials generate more rapid action potentials Integration of sensory information begins when information is received

6. Perception Interpretation of sensory system input by brain Ex: colors, smells, sounds, tastes Is there a sound if a tree falls and no one is around to hear it? Action potentials = all or none!!

7. Modification of stimuli Amplification Strengthening of stimulus energy During transduction Produces many product molecules by one enzyme Adaptation Decrease in responsiveness Allows you to filter stimulus

8. Types of Sensory Receptors Mechanoreceptors Sense physical deformation Pressure, touch, stretch, motion, sound Chemoreceptors Both general and specific General = total solute concentration Specific = chemicals that attach to specific receptor proteins Electromagnetic receptors Detect electromagnetic radiation Light, electricity, magnetism

9. Types of Sensory Receptors Thermoreceptors Detect heat and cold Pain receptors Extreme pressure or temperature Nocireceptors Detect noxious conditions

10. Ex: Hearing & Equilibrium Mechanoreceptors produce receptor potentials settling particles or moving fluid cause deflection of cell surface structures Hairs Different stiffness and lengths Cause vibrations of different frequencies Statocysts Sense gravity & maintain equilibrium Grains of sands Gravity settles sand to bottom stimulates receptor

11. Hearing in mammals Ear converts energy of pressure waves to nerve impulses Mechanoreceptor = hair cells Signal is amplified before it reaches the hair cell

12. Hearing in mammals (cont) 1. Moving air causes tympanic membrane to vibrate 2. 3 bones transmit vibrations to oval window – membrane on cochlea’s surface 3. when bone vibrates on oval window, pressure waves created in fluid 4. in vestibular canal, pressure causes hairs to vibrate up and down 5. mechanoreceptors open or close ion channels in membrane

13. Fig. 50-8 Middleear Outer ear Inner ear Stapes Skullbone Semicircularcanals Incus Malleus Auditory nerveto brain Bone Cochlearduct Auditorynerve Vestibularcanal Tympaniccanal Cochlea Ovalwindow Eustachiantube Pinna Auditorycanal Organ of Corti Roundwindow Tympanicmembrane Tectorialmembrane Hair cells Hair cell bundle froma bullfrog; the longestcilia shown areabout 8 µm (SEM). Axons ofsensory neurons To auditorynerve Basilarmembrane

14. Sound variables Volume Determined by amplitude of sound wave Larger volume = greater bending of hairs Pitch Determined by sound wave’s frequency High frequency = high pitch

15. Equilibrium in mammals Inner ear detects movement, position and balance Utricle & Saccule Chambers located behind oval window Sheet of hair cells that go into a gelatinous material Contains otoliths Semicircular canals Connected to utricle Detect turning of the head

16. Muscle Contraction Skeletal muscle Striated Connected to bones Thick filaments Staggered arrays of myosin Thin filaments 2 strands of actin and 2 strands of a regulatory protein coiled

17. Skeletal muscle Sarcomere Repeating unit Z lines M lines Fig. 50-25b TEM 0.5 µm M line Thickfilaments(myosin) Thinfilaments(actin) Z line Z line Sarcomere

18. Sliding Filament Model Thin and thick filaments slide past each other increasing the overlap of the fibers Head of myosin Binds ATP to provide energy for muscle contraction Tail of myosin Adheres to other tails of myosin to form the thick filament

19. Muscle fiber contraction Myosin head is bound to ATP (low energy)

20. Muscle Fiber Contraction Myosin hydrolyzes ATP to ADP now in high E

21. Muscle Fiber Contraction Myosin head binds to actin = cross-bridge

22. Muscle Fiber Contraction ADP is released, myosin returns to low E, thin filament slides