FIRST MIDTERM EXAM October 18, 2011 BILD2

Transcription

1 FIRST MIDTERM EXAM October 18, 2011 BILD2 WRITE YOUR NAME ON ALL 6 PAGES. ANSWER ALL 10 QUESTIONS (100 POINTS). CONFINE YOUR ANSWERS TO THE SPACE ALLOWED. If you would like to write on the back of the exam ask to have a TA initial that page. Pen or pencil is acceptable, but answers must be legible to be corrected. Answer only the exact questions asked, but provide all the detail possible in those cases (be sure to use the correct vocabulary, describing by name the key players, structures, and processes). SAM 1. (10 points) JOSHUA 2. (10 points) JOSHUA 3. (5 points) NASHA 4. (10 points) MARY 5. (10 points) KAIVAN 6. (20 points) HIEN 7. (10 points) HIEN 8. (10 points) AIVI 9. (5 points) AIVI 10. (10 points) 100 total TOTAL POINTS By signing this waiver I give permission for this exam to be left for me to pick up in the boxes outside the elevators on the third floor of Pacific Hall. I realize that this procedure may expose my grade to public scrutiny. If I do not sign this waiver, I acknowledge that my exam will be available for pick up only between 8:00 and 11:00 AM, Monday-Friday in 3100E Pacific Hall. Signature Date 1 P age

2 1. (10 points) List the five different categories of Glia present in the vertebrate CNS and briefly describe their function. Must give one function for each cell for full points Ependymal cells- line the ventricles and have cilia that promote circulation of the cereprospinal fluid. Microglia- protect the nervous system from invading microorganisms. Oligodendrocytes- function in axon myelination Astrocytes- ( any one of the following) structural support, regulate extracellular concentrations of ions and neurotransmitters, dilate nearby blood vessels to support neurons with increased oxygen or glucose, contribute to the formation of the blood brain barrier, can facilitate activity at the synapse by releasing neurotransmitter. Radial glia-forms a scaffold for new neurons to migrate on during the development of the CNS. Could as add serves as a stem cell for additional neurons and glia. [Schwann cell is not an acceptable answer, they are only in the PNS, remove point if listed] 2. (10 points) State whether the movement of an action potential along an axon is bidirectional or unidirectional. Explain why. Unidirectional. The refractory period, when sodium inactivation gates are still closed underlies this function. The action potential moves along the axon in one direction as a depolarization wave. Depolarization at one site on the membrane spreads to the adjacent neighboring region reinitiating the action potential there. The original site is undergoing repolarization when the new region depolarizes. Voltage gated sodium channels are shut and cannot open for a distinct period of time (refractory period) making depolarization in the opposite direction impossible. 3. (5 points) The activation of what channel in the presynaptic membrane responds to the arriving action potential and causes the docking of synaptic vesicles into the synaptic cleft? voltage-gated Ca2+ channels ( can explain further if complete name not listed: AP depolarizes the synaptic membrane which opens Ca2+ channels. Ca2+ enters the synapse and causes the synaptic vesicles to fuse with the presynaptic membrane.) 2 P age

3 4. (10 points) Distinguish between: a) Statocyst and Organ of Corti: Statocyst is the organ for equilibrium in most invertebrates. Contains hair cells to sense position and gravity. The organ of Corti is the structure in the mammalian inner ear that houses the hair cells that sense pressure waves that are perceived as sound. b): NMDA receptor and AMPA receptor: Both are receptors important for long-term potentiation that bind glutamate and are found at the postsynaptic membrane. NMDA is critical to start LTP, AMPA receptors are inserted in the membrane to continue supporting LTP. (other possibilities exist, NMDA allows Ca2+, AMPA allows Na+ when bound to glu, NMDA has Mg+ block, need one difference listed) c): Rhodopsin and Photopsin: Both are visual pigments composed of retinal bound to opsin that sense light. Rhodopsin is found in rods and senses light or dark. Photopsin is found in cones and different photopsins respond to different wavelengths of light (red, blue or green) d): Chemical synapse and electrical synapse: In an electrical synapse the electrical current flows from one neuron to another through gap junctions. At chemical synapses a chemical neurotransmitter carries the information across the synaptic cleft. 5. (10 points) Describe the role of the sodium-potassium pump in establishing a cell s membrane potential. What ion permeabilities determine the resting potential of the membrane, and why is it usually around -60 to -80 mv? NA/K pump is responsible for maintaining the steep gradients of higher K+ concentration inside the cell and higher Na+ concentration outside the cell. Uses ATP to transport these ions against their concentration gradient. The resting potential is determined mostly by potassium with an EK of about -90 mv, but also slightly from sodium with an ENa of about +55mV. The weighted average of the two yields the resting potential of around -60 to -70 mv usually. The EK plays a stronger role because there are more selectively permeable K+ channels in the membrane then Na+ (hence more K+ outflux), therefore driving the potential toward EK. 3 P age

4 6. (20 points) A schematic of a section of the mammalian retina is shown below. Label the key structures and cell types indicated. Select a sensory receptor and describe what it detects and how. Next define lateral inhibition and list the cells that perform this function. See figure in your text (Choriod, cone, rod, horizontal cell, bipolar cell, amacrine cell, ganglion cell, optic nerve) Rods detect light and dark because rhodopsin is located in the membrane of its outer segment. Rhodopsin is made of a light absorbing molecule retinal, which switches between isomers depending on whether light is present. This change in retinal causes a change in the opsin receptor it is bound to and causes rhodopsin (retinal + opsin) to become active. Lateral inhibition is a form of contrast enhancement performed by horizontal and amacrine cells. (can also describe cellular process of lateral inhibition in place of an exact definition) 4 P age

5 7. (10 Points) Match the left column with the best choice in the right column a) Occipital lobe g Somatosensory cortex b) Equilibrium Potential of K + f Long-term potentiation c) Hand-eye coordination j Motor cortex d) Sensory information relay i +62mV e) Reticular formation h Corpus Callosum f) NMDA receptor e Brainstem g)parietal lobe c Cerebellum h)band of Axons b -90 mv i) Equilibrium Potential of Na + d Thalamus j)frontal lobe a Vision 8. (10 Points) Two excitatory post synaptic potentials (EPSPs) occur at the same time at two different synapses of the same postsynaptic neuron. Explain how these events could lead to an action potential. In your explanation describe the state of the membrane potential at rest prior to the EPSPs and leading to the action potential. Account for the contribution of the various membrane bound channels involved. How would the neuronal response differ if one of the simultaneous inputs was an inhibitory PSP rather than an excitatory one? At rest the membrane potential is negative (between -60mV and -80mV). When an AP is sent from a presynaptic neuron, NT will be released and will bind to ligand-gated ion channels at the postsynaptic neuron. Bound NT causes these channels to open and if these channels allow K+ and Na+ ions to diffuse the membrane potential will approach values btw the E K and E Na which is more positive then resting potential resulting in an excitatory postsynaptic potential (EPSP) which causes the membrane potential to depolarize. If two EPSPs occur at the same time their effects can add together and cause a greater depolarization of the membrane and if the summation of the resulting depolarization from both inputs reaches -55mV the postsynaptic neuron will generate an AP. If an inhibitory PSP is generated instead of an excitatory one, no AP will be generated. An IPSP is formed when channels open that hyperpolarize the membrane.the IPSP (hyperpolarization) will counter the effect of the concurrent EPSP (depolarization). The membrane potential will not increase and threshold will not be reached, no AP. 5 P age

6 9. (5 points) If the binding of a neurotransmitter to its receptor opens Cl- channels, what would be the effect on the postsynaptic cell? (Cl- is in higher concentration outside the cell.) It would hyperpolarize the membrane, producing an IPSP 10. (10 points) Name the specific type of mechanoreceptor responsible for sending information for hearing and balance in mammals. Explain how vibration of the basilar membrane in the cochlea conveys information about the volume of sound. (Make sure to explain changes that take place in and are modulated by the sensory cell listed) Hair cell. When the hairs of the hair cell are not bent it releases neurotransmitter and the sensory neuron fires action potentials at a certain frequency. The bending of the hairs in different directions causes the hair cells to either depolarize or hyperpolarize and release more or less NT. This results in a change in the frequency of the sensory neurons AP. Sounds waves are converted to pressure waves that cause the basilar membrane to move or vibrate and hairs on the attached hair cells hit the tectorial membrane. Volume is a function of the amplitude of sound. High amplitude sound causes more vigorous vibration (larger amplitude), which causes greater bending of the hairs on the hair cells, and more action potentials in the sensory neuron. 6 P age