| HUMAN SYSTEMS: The Nervous System
ACT #1: Introduction to the Nervous System All areas of the skin are not equally sensitive to all stimuli. In any given skin area there are certain positions, often close together, than can recognize only one kind of sensation: A) Pinch the skin at your elbow, earlobe, cheek, and the inside of your forearm. Describe any differences in sensation. B) What is a sensation? (Use your Lion textbook for a definition.) C) There is another interesting characteristic of skin receptors. The degree to which you can recognize 2 distinct sensations when your skin is stimulated at two points varies with the area of the skin. In areas where the touch receptors are close together, you will feel two sensations. For areas where the receptors are far apart 2 sensations will feel like one. 1. Get the needle apparatus from the teacher. You will need to work with a partner for this. 2. Have the partner look away. Set the needles 8 cm apart. Making sure the points touch the skin at exactly the same time, touch the inner surface of the arm. Raise the needles and repeat several times, moving them closer and farther apart. Ask your partner if he or she feels one or two needles. 3. How far apart where the needles when s/he recognized the sensations as one? 4. Try this with the palm of your hand. How far apart? 5. Try this with the inner surface of the index finger. How far apart? 6. Be careful with this one: try this with the bottom of your neck. How far apart? 7. In which area of the skin do receptors seem to be the farthest apart? Closest together? D) What does this activity tell you about the spacing of nerve cells on/underneath your skin? ACT #2: The highly specialized Neuron The nervous system consists of lots of nerve cells or NEURONS. There are three types of neurons: (Take Notes) Sensory Neurons: these neurons carry messages TO the brain and spinal cord. Motor Neurons: these neurons carry messages FROM the brain and spinal cord. Interneurons: these neurons connect sensory and motor neurons. 1) Draw a picture of a typical neuron pg. 876 Fig. 29.3 or insert the picture that you copied down from my notes in class. Label the dendrites, cell body, axon, and axon endings. 2) The dendrites carry impulses toward the cell body and the axons carry impulses away from the cell body. So, in addition to the labeling, draw a large arrow on top of your diagram of the neuron showing the DIRECTION of the nerve impulse ACT #3: Transmission and Directionality of Nerve Impulses pg. 876-879 text. Nerve impulses travel in one direction. Neurons never touch each other directly. (A) How do nerve impulses transmit ALONG a fiber? Draw these (1 & 2) diagrams and explain what�s happening. (1) + + + + + + + + + + (2) + + + - - - + + + + - - - - - - - - - - - - - + + + - - - - - - - - - - - - - - - - - + + + - - - - + + + + + + + + + + + + + - - - + + + + (B) What�s going on with the plasma membrane of the neuron in the resting membrane stage or resting potential? Which ions are pumped into the cell what ions are pumped out of the cell? What are sodium-potassium pumps? What do sodium-potassium pumps do? Diagram (1). (C) What is an action potential? Which ions rush into the neuron during the action potential? Diagram (2). (D) What is the All-or-Nothing response? (E) How does the impulse travel along the neuron? (F) Why doesn�t the impulse travel backwards? (G) How does the plasma membrane go back to the resting stage? ACT #4: Chemical synapse Because neurons never physically touch, nerve impulse must jump a gap called the SYNAPSE. (A) What is a CHEMICAL SYNAPSE? (B) What are NEUROTRANSMITTERS? Are there different kinds of neurotransmitters? How are they different? (C) How are neurotransmitters removed from the synaptic cleft? (D) What can happen if neurotransmitter uptake is slowed or blocked (in the case of a person taking drugs)? ] READ THIS: Takifugu is a genus of pufferfish. The fish is highly toxic, but despite this � or perhaps because of it � it is considered a delicacy in Japan. The fish contains lethal amounts of the poison tetrodotoxin in the internal organs, especially the liver and the ovaries, but also in the skin and the testes. Tetrodotoxin blocks the transmission of action potentials by binding to the pores of sodium channels on the membrane of neurons. (E) Play doctor for a second. What do you think could happen to someone who has swallowed a piece of sushi containing this toxin? |