Question

1a. Distinguish between sensory neurons, motor neurons, and association neurons in terms of structure, location, and function.

1b. Describe the structure of the sheath of Schwann, or neurilemma, and explain how it promotes nerve regeneration. Explain how a myelin sheath is formed in the PNS.

1c. Explain how myelin sheaths are formed in the CNS. How does the presence or absence of myelin sheaths in the CNS determine the color of this tissue?

1d. Define the terms depolarization and repolarization, and illustrate these processes graphically.

1e. Describe how the permeability of the axon membrane to Na 1 and K 1 is regulated and how changes in permeability to these ions affect the membrane potential.

1f. Describe how gating of Na 1 and K 1 in the axon membrane results in the production of an action potential.

1g. Explain the all-or-none law of action potentials, and describe the effect of increased stimulus strength on action potential production. How do the refractory periods affect the frequency of action potential production?

1h. Describe how action potentials are conducted by unmyelinated nerve fibers. Why is saltatory conduction in myelinated fibers more rapid?

1i. Describe the location of neurotransmitters within an axon and explain the relationship between presynaptic axon activity and the amount of neurotransmitters released.

1j. Describe the sequence of events by which action potentials stimulate the release of neurotransmitters from presynaptic axons.

1k. Explain how chemically regulated channels differ from voltage-regulated channels and the nature of excitatory and inhibitory postsynaptic potentials.

1l. Explain how ligand-gated channels are opened, using nicotinic ACh receptors as an example.

1m. Explain how ligand-gated channels operate, using muscarinic ACh receptors as an example.

1n. Describe where stimulatory and inhibitory effects of muscarinic ACh receptors occur and how these effects are produced.

1o. Compare the properties of EPSPs and action potentials, identify where in a neuron these are

1p. Explain the significance of glutamate in the brain and of NMDA receptors.

1q. Describe the mechanism of action of glycine and GABA as neurotransmitters, and discuss their significance.

1r. Explain how nitric acid is produced in the body, and describe its functions.

1s. Define spatial summation and temporal summation, and explain their functional importance.

1t. Explain how postsynaptic inhibition is produced and how IPSPs and EPSPs can interact.

1u. Describe the mechanism of presynaptic inhibition.produced.

Answer 1

1a. Motor neurons have short dendrites , cell body and long axon. Sensory neurons have cell body, long dendrites and short axon. Associated neurons have all structures within CNS.

Motor neurons located outside CNS. Associated neurons located inside CNS and sensory neurons located both.

Sensory neurons transmit signals from periphery to CNS and motor neurons carry signals from the central nervous system to the outer parts. Interneurons play role in interconnecting within the brain and spinal cord.

1.b. Neurilemma also called as sheath of Schwann is the outermost lining of Schwann cells which is a nucleated cytoplasmic later surrounding axon of the neuron. Nerve fibers are able to regenerate only when the soma is not damaged and also the neurilemma must remain intact which creates the tube called as regenration tube inside that the growing axon re-establishes its original connection. Schwann cells are responsible for myelin sheath around axons in PNS. Axon is spiral wrapped around by myelin which is usually an expanded glial plasma membrane that then compacts.

1c. Oligodendrocytes are responsible for myelin sheath in CNS by concentric wrapping process around the axon. Myelin sheath is primarily made up of protein and fatty substances which enable faster transmission of electrical impulses efficiently along the axon. White matter of brain/SC contains axons with myelin sheaths which give characteristic white coloration. Grey matter of CNS has high concentrations of cell bodies and dendrites thata re devoid oflack myelin sheaths.

1d. Depolarization adn repolarization are phases of action potential. During depoalrization, the internal charge of the cell becomes less negative or more positive whereas, in repolarization, internal charge returns to a more negative value to attain the restin steady state.