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Unformatted text preview: PSYC 401 LAB MANUAL LAB 2 - STRETCH REFLEX PAGE 1 Core Questions • What are motor units? • How do muscles increase their strength and speed of contraction? • What are proprioceptors and what do they do? • What is a re¡ex, speci¢cally a stretch re¡ex? • What is electromyography and how do you do it? • How can you measure aggregate conduction velocity? • How do you do 2- channel, triggered recording with CHART? Muscle control A simple neural circuit that helps control body position The gymnast is controlling the position of his arms and legs with considerable strength and extreme precision. To do this, he uses proprioceptors, sensory organs that continuously monitor the strength of muscle contraction along with the position and movement of body parts. He constantly adjusts the force each muscle group generates so he can offset tiny changes in position. Neural circuits that make this possible are some of the simplest in the body and are based on proprioceptors. Not just gymnastics, but routine skills like walking and other coordinated movement in the real world would be impossible without these systems. WHAT ARE WE GOING TO DO? We will Frst study the way we regulate the strength of muscle contraction. You will quantify motor unit recruitment and contrast fast and slow contraction strategies. Then you will then study the activity and function of a proprioceptor-based re¡ex circuit that has both simple and complex components. Measuring aggregate conduction velocity will provide clues to the structure of the circuit. Web resources: PSYC 401 LAB MANUAL LAB 2 - STRETCH REFLEX PAGE 2 THE BASIC IDEA A motor unit (MU) is one alpha motor neuron and all the muscle fbers it synapses with (innervates). An action potential in the motor neuron causes simultaneous APs in all the fbers oF its motor unit. Motor unit size varies tremendously. Eye muscles must produce extremely precise movements, but don’t need much Force: MU is 1:3. Hand muscles must do precise movements with some Force: MU is 1:100. The gastrocnemius (calF muscle) requires no precision, but immense strength: MU 1:1800. The Force generated by a muscle is determined in part by the contribution oF each muscle fber, but more importantly by the number oF fbers active. To increase the Force oF contraction, you recruit more motor units, hence more fbers. The contraction oF a muscle can be ‘dynamic’ - lots oF movement, little tension - or ‘isometric’ - no movement, lots oF tension. To study muscle contraction regulation, we will Focus on a relatively small muscle, the frst dorsal interosseus muscle oF the hand and the large biceps muscle oF the upper arm. You will use surFace EMG recording. This means an electrode on the skin picks up the action potentials in the muscle fbers below it. The signals tend to be quite large, especially over large bulky muscles. When Few MUs are active, you can see action potentials From individual MUs. As more MUs are recruited, however, most oF what you see will be the sum oF hundreds or...
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- Spring '11
- stretch reflex