BISC 421 1st Edition Lecture 13 Outline of Current LectureI. Synaptc Plastcity II Current LectureI. Spinal Cord and Motor CortexSpinal Cord and Motor CortexLocomotion •Famous for two things: 1. Coming up with an electronic tming device to take photos of subjects-‐ able to capture movement by having this device-‐can measure precisely these movements 2. Shooting wife’s boyfriend •Images that Muybridge took during moton•Understanding diferent movements•What youre able to do because of your spinal cordMotor Pathways•Just know the positons of the motor neurons upper and lower•Involvement of the brain stem and motor cortex•The basal ganglia and cerebellum•All of these components are going to project to local circuit neurons in the spinal cord and motor neurons•Upper motor neurons are in the brain stem and the cortex and these neurons will send signals about moton but they will not synapse onto muscles themselves but actually other neurons that will then project to neurons•Know diference between upper and lower neuron * key point•Secton taken through the spinal cord-‐ coronal slice•Cell bodies are pale and the white mater stained dark•Cord divided into two divisions-‐ dorsal and ventral horn•Dorsal horn-‐ receives input from sensory cells and local circuit neurons•When sensory informaton is coming in it is called aferent pathway•Eferent means away•Ventral horn-‐ cell bodies of lower motor neurons•Ventral roots-‐ eferent pathway (traveling out-‐ exit)•Look at the mnemonic at botom•Upper = cervical column•Along chest = thoracic•Lower back = lumbar•Lowest part = sacralSo many different types of fibers•When it exits the cord and enters the muscle it synapses on many muscle fibers-‐ known as the motor unit-‐ group of muscle fbers that receive input from a single motor neuron•A single acton potental will afect all of these muscle fibers•Arrangement is somatotopic in lower motor neurons•Central means closer to midline•Lateral means further from midline•Discovered this by injectng dye and labelingDifferent types of motor neuron innervate different types of muscle fibers•There are diferent kinds of muscles•Diferent types of motor neurons innervate diferent types of muscles•Slow small: innervate muscle fbers that have slow but sustained contractions•Large fatgable: larger groups of muscles that generate larger forces (when you jump)•Intermediate not fatgable: muscles used to stand for example•Motor pool: group of motor neurons that innervate a single muscle-‐ diferent kindsof alpha motor neurons to innervate a single muscle•The motor unit is one motor neuron and all the muscle fbers it contacts. This is the opposite-‐many motor neurons synapsing onto one motor•There are some slow fbers as well as FF fbers and FR fbers in one single muscleOne muscle in depthMuscle involved in spinal reflexes•Muscle spindles: send signals about the state of the muscles – how relaxed or contracted it is•Striated muscle in the picture – in the middle is the muscle spindle•Spindles- fusiform- spindle shaped. Intrafusal fbers (inside muscle spindle) arranged in parallel with extrafusal fbers•Inside the muscle spindle there are two types of intrafusal fbers – 1.Nuclear bag fbers (group 1a) 2. Nuclear chain fbers (group II)• The motor neurons tug on the sides to regulate the tension that the bag and chain fbers are under•Other kind of sensory organ in the muscle is the golgi tendon organ•Signal informaton about force- don't want to rip muscle, prevents this from happening•Next: animaton posted on blackboard-WATCH•Summary at the botom of the slide•monosynaptc stretch reflex- classic hammer to knee reflex•alpha motor neurons can only excite but the only way to relax a muscle is by inhibiton of presynaptc motor neuron, there are not inhibitory motor neurons•golgi tension reflex regulates via negatve feedback•regulate the gain on your contracton- the more it stretches it leads to less stretch- work against contracton•top down control- have upper motor neurons that innervate lower motor neurons on opposite side on the bodyBrainstem to Spinal Cord•two regions: primary motor cortex and premotor cortex•premotor cortex- movement planning•primary motor cortex- movement executon•map of body in the motor cortex•the muscles controlling our faces are heavily innervated – huge representaton of face but not as many upper neurons devoted to other areas of the body•These two regions look diferent•Most gigantc cells in the cortex are in the motor cortex- upper motor neurons called betz cells- highly specialized and can conduct quickly•Pay atenton to bolded regions only•Cross from brain to body•But need bilateral control for postureFunctonal Organizaton of Motor Cortex•If stck an electrode in motor cortex- arranged according to movement•Map of movement in the motor
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