Sensory and Motor Mechanisms Chapter 50 Campbell Biology

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

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 bind 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)