Sensory and Motor Mechanisms

 Being able to detect and respond to the environment is important for survival.  Systems involved include: nervous, skeletal, and muscle

 1. Sensory reception: detection of a stimulus by sensory cells (neurons, skin, ears, eyes, etc)  2. Transmission: an action potential is sent to the CNS  3. Perception: the brain processes the input into understandable images  4. Amplification and Adaptation: signals are increased or decreased based on importance

 1. Mechanoreceptors: sense physical changes caused by pressure, touch, stretch, motion, and sound. Often have hairs attached externally.  2. Chemoreceptors: detect changes in solute such as glucose, oxygen, carbon dioxide, amino acids. Can be internal (blood) or external (antennae)

 3. Electromagnetic receptors: detect light, electricity, and magnetism. Found in eyes, skull.  4. Thermoreceptors: detect heat and cold. Located in the skin.  5. Pain receptors: neurons that detect thermal, mechanical, or chemical stimuli

 Hearing: ears have tiny hairs that vibrate due to pressure waves and send signals to the brain  Equilibrium: These same hairs help orient your body, telling your brain the position of your head.

 Gustation (taste) and olfaction (smell) depend on chemoreceptors in the nose and mouth.

 Invertebrates have photoreceptors, which detect light.  Insects have compound eyes, made up to several thousand light detectors  Our eyes have photoreceptors called rods and cones that send information through the optical nerve to the brain.

 Smooth muscle: evolved first, non-striated, involuntary, digestive system, arteries, veins  Cardiac muscle: striated, in the heart, involuntary  Skeletal muscle: striated, multi-nucleated, voluntary, moves your body  Muscles are connected to the 206 bones in the body

 Muscles do work in pairs, one contracts and one extends ◦ Tendons connect bone to muscle ◦ Ligaments connect bone to bone

 Muscle cells are called muscle fibers, and are divided into sections called sarcomeres ◦ Made of bands of protein: thin (actin) & thick (myosin)

 Sarcoplasm ◦ muscle cell cytoplasm ◦ contains many mitochondria  Sarcoplasmic reticulum (SR) ◦ organelle similar to ER, it stores and releases Ca 2+ as needed Ca 2+ ATPase of SR

 Muscle movement is activated by the release of the neurotransmitter acetylcholine

 Nerve signal travels to muscles  Muscles release Ca 2+  This causes muscles to contract

 Slow twitch muscle fibers ◦ contract slowly, but keep going for a long time ◦ long distance runner ◦ “dark” meat = more blood vessels  Fast twitch muscle fibers ◦ contract quickly, but get tired rapidly ◦ sprinter ◦ “white” meat

 Muscle fatigue ◦ lack of sugar  lack of ATP to restore Ca 2+ gradient ◦ low O 2  lactic acid drops pH which interferes with protein function ◦ synaptic fatigue  loss of acetylcholine  Muscle cramps ◦ build up of lactic acid ◦ ATP depletion ◦ ion imbalance  massage or stretching increases circulation

 Some animals have exoskeletons made of chitin (arthropods and mollusks)  Internal skeletons are called endoskeletons.

 Muscles, skeletons, and the nervous system work together to produce movement, or locomotion, like:  Swimming (with flagella or a whole organism)  Walking, running, hopping, crawling, maintaining balance  Flying