FEM 4100 BRAIN & HUMAN BEHAVIOR

1. 0 FEM 4100 BRAIN & HUMAN BEHAVIOR

2. 0 Topic 3 Neurotransmission: Sending & Receiving Messages

3. The basic unit of the nervous system • A specialized cell that conducts impulses through the nervous system and contains three major parts—a cell body, dendrites, and an axon • Receives signals from neurons or sensory organs • Processes information • Sends signals to other neurons, muscles, or organs • The brain contains an average of one hundred billion neurons (50b – 300b) The Neuron 0

4. Afferent neurons relay messages from the sense organs and receptors—eyes, ears, nose, mouth, and skin—to the brain or spinal cord • Efferent neurons convey signals from the central nervous system to the glands and the muscles, enabling the body to move The Neuron 0

5. There are three general types of neurons • Sensory neuron • A neuron that detects changes in the external or internal environment and sends information about these changes to the central nervous system. • Motor neuron • A neuron located within the central nervous system that controls the contraction of a muscle or the secretion of a gland. • Interneuron • A neuron located entirely within the central nervous system. • Interneurons carry information between neurons in the brain and between neurons in the spinal cord Cells of the Nervous System 0

6. Three classifications of neurons • Multipolar neurons • A neuron with one axon and many dendrites. • Bipolar neurons • A neuron with one axon and one dendrite attached to its soma. • Unipolar neurons • A neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system. Cells of the Nervous System 0

7. Three classifications of neurons 0

8. Neuron Basic Structure 0

9. Cells of the Nervous System • Neuron Basic Structure • Soma or “cell body” • The part of the neuron that contains the nucleus and carries out the neuron’s metabolic functions • Dendrite • A branched treelike structure attached to the soma of a neuron; • Receives signals / information from the terminal button of other neurons. • Back propagating - when dendrites relay messages from the cell body to their own branches • Axon • The long, slender, tail-like extension of the neuron that transmits signals / conveys information from the soma of a neuron to its terminal button, to be received by the dendrites or cell body of the other neurons or to muscles or glands 0

10. Neuron Basic Structure

11. Neuron Basic Structure • Synapse • A junction where the terminal button of a sending axon communicates with a receiving neuron across the synaptic cleft • Terminal button • The bud at the end of a branch of an axon; forms synapses with another neuron; sends information to that neuron.

14. Neuron Basic Structure • Neurotransmitter • Chemical messengers that relay neural messages across the synapse • A chemical that is released into the synaptic cleft from a terminal button (axon) of a sending neuron, crosses a synapse, and binds to appropriate receptor sites on the dendrites or cell body of a receiving neuron, influencing the cell either to fire or not to fire; • Has an excitatory or inhibitory effect on another neuron. • Receptors • Protein molecules on the dendrite or cell body of a neuron that will interact only with specific neurotransmitters • Action of neurotransmitters • Excitatory • Influencing the neurons to fire • Inhibitory • Influencing neurons not to fire

15. Cells of the Nervous System • Internal structure • Membrane • A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles. • Cytoplasm • The viscous, semi-liquid substance contained in the interior of a cell. • Mitochondria • An organelle that is responsible for extracting energy from nutrients.

16. Internal Structure

17. Internal structure • Adenosine triphosphate (ATP) • A molecule of prime importance to cellular energy metabolism; its breakdown liberates energy. • Nucleus • A structure in the central region of a cell, containing the nucleolus and chromosomes. • Chromosome • A strand of DNA, with associated proteins, found in the nucleus; carries genetic information.

18. Internal structure • Deoxyribonucleic acid (DNA) • A long complex macromolecule consisting of two interconnected helical strands; along with associated proteins, strands of DNA constitute the chromosomes. • Gene • The functional unit of the chromosome, which directs synthesis of one or more proteins. • Cytoskeleton • Formed of microtubules and other protein fibers, linked to each other and forming a cohesive mass that gives a cell its shape.

19. Internal structure • Enzyme • A molecule that controls a chemical reaction, combining two substances or breaking a substance into two parts. • Microtubule • A long strand of bundles of protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within the cell. • Axoplasmic transport • An active process by which substances are propelled along microtubules that run the length of the axon.

20. Cells of the Nervous System • Supporting Cells • Glial cells • Also known as neuroglia or “neural glue”. • The supporting cells of the central nervous system. • Fills the gaps between neurons • Supports and feeds neurons • 10 times more glial cells than neurons • Gial cells help to make the brain more efficient by holding neurons together, removing waste products such as dead neurons, making the myelin coating for the axons, and performing other manufacturing, nourishing, and cleanup tasks • Myelin producers • Oligodendrocytes (CNS) • Schwann cells (PNS) • Astrocytes – largest glia, many functions • Microglia – involved in response to injury or disease

21. Cells of the Nervous System • Glial cells • Astrocyte or “star cell” • A glial cell that provides support to neurons of the central nervous system, provides nutrients and other substances, and regulates the chemical composition of the extracellular fluid. • Phagocytosis • The process by which cells engulf and digest other cells or debris caused by cellular degeneration. • Oligodendrocyte • A type of glial cell in the central nervous system that forms myelin sheaths

23. Supporting cells • Myelin sheath • A white, fatty coating wrapped around axons • Acts as an insulator, preventing messages from spreading between adjacent axons. • Enables impulses to travel much faster and more efficiently • Multiple Sclerosis (MS) involves deterioration of the myelin sheath • Node of Ranvier • A naked portion of a myelinated axon, between adjacent oligodendrocytes or Schwann cells. • Microglia • The smallest glial cells; act as phagocytes and protect the brain from invading microorganisms. • Schwann cell • A cell in the peripheral nervous system that is wrapped around a myelinated axon, providing one segment of its myelin sheath.

27. Terminology

28. The Blood-Brain Barrier (BBB) • Features of the blood-brain barrier • Regulates the chemicals that can enter the CNS from the blood. • Helps the CNS maintain the proper composition of fluids inside and outside the neurons. • Blood-brain barrier • A semipermeable barrier between the blood and the brain produced by cells in the walls of the brain’s capillaries. • Area postrema • A region of the medulla where the blood-brain barrier is weak; poisons can be detected there and can initiate vomiting.

30. Neural impulse –Brief electric surge that carries the neuron’s message • Ions –Charged particles that are moved across the cell membrane The Neural Impulse

31. Measuring electrical potentials (Neural Impulses) of axons • Axons have two basic electrical potentials • Resting membrane potential • Action potential • The membrane potential can change • Depolarization • Hyperpolarization • Threshold of excitation • Electrode • A conductive medium that can be used to apply electrical stimulation and record electrical potentials. Communication Within a Neuron

32. Measuring electrical potentials of axons • Microelectrode • A very fine electrode, generally used to record activity of individual neurons. • Membrane potential • The electrical charge across a cell membrane; the difference in electrical potential inside and outside the cell. • Oscilloscope • A laboratory instrument that is capable of displaying a graph of voltage as a function of time on the face of a cathode ray tube.

34. Measuring electrical potentials of axons • Resting membrane potential • Inside of the neuron is negative with respect to the outside • Resting membrane potential is approximately -70 mV in the giant squid axon. • Membrane is polarized, it carries a charge • The membrane potential of a neuron at rest, about 270 millivolts • The resting membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials; • Depolarization • Reduction (toward zero) of the membrane potential of a cell from its normal resting potential. • Hyperpolarization • An increase in the membrane potential of a cell, relative to the normal resting potential.

35. Ionic Basis of the Resting Potential • Ions, charged particles, are unevenly distributed • Factors contributing to uneven distribution • Homogenizing • Random motion – particles tend to move down their concentration gradient • Electrostatic pressure – like repels like, opposites attract • Membrane is selectively permeable • Sodium-potassium pumps

36. Ions Contributing to Resting Potential • Sodium (Na+) • Chloride (Cl-) • Potassium (K+) • Negatively charged proteins (A-) • synthesized within the neuron • found primarily within the neuron • The Neuron at Rest • Ions move in and out through ion-specific channels • K+ and Cl- pass readily • Little movement of Na+ • A- don’t move at all, trapped inside

37. Equilibrium Potential • The potential at which there is no net movement of an ion – the potential it will move to achieve when allowed to move freely • Na+ = 120mV • K+ = -90mV • Cl- = -70mV (same as resting potential) • The Neuron at Rest • Na+ is driven in by both electrostatic forces and its concentration gradient • K+ is driven in by electrostatic forces and out by its concentration gradient • Cl- is at equilibrium • Sodium-potassium pump – active force that exchanges 3 Na+ inside for 2K+ outside

38. The Ionic Basis of Action Potentials • When summation at the axon hillock results in the threshold of excitation (-65mV) being reached, voltage-activated Na+ channels open and sodium rushes in. • Remember, all forces were acting to move Na+ into the cell. • Membrane potential moves from -70 to +50mV.

39. Measuring electrical potentials of axons • Action potential • The brief electrical impulse that provides the basis for conduction of information along an axon. • The sudden reversal of the resting potential, which initiates the firing of a neuron • Threshold of excitation • The value of the membrane potential that must be reached to produce an action potential.

40. Difference between a strong and weak stimulus • A weak stimulus may cause few neurons to fire and at a slow rate • A strong stimulus may cause thousands of neurons to fire at the same time and at hundreds of times per second

43. The force of diffusion • Diffusion • Movement of molecules from a region of high concentration to regions of low concentration. Communication Within a Neuron

44. The force of electrostatic pressure • Electrolyte • An aqueous solution of a material that ionizes a soluble acid, base, or salt. • Ion • A charged molecule. • Cations are positively charged, and anions are negatively charged. • Electrostatic pressure • The attractive force between atomic particles charged with opposite signs or the repulsive force between two atomic particles charged with the same sign. Communication Within a Neuron

46. Ions in the extracellular and intracellular fluid • Intracellular fluid • The fluid contained within cells. • Extracellular fluid • Body fluids located outside cells. • Sodium-potassium transporter • A protein found in the membrane of all cells that extrudes sodium ions. Communication Within a Neuron

49. The action potential • Ion channel • A specialized protein molecule that permits specific ions to enter or leave the cell. • Voltage-dependent ion channel • An ion channel that opens or closes according to the value of the membrane potential. Communication Within a Neuron

50. The Ionic Basis of Action Potentials • Rising phase: Na+ moves membrane potential from -70 to +50mV. • End of rising phase: After about 1 millisec, Na+ channels close. • Change in membrane potential opens voltage-activated K+ channels. • Repolarization: Concentration gradient and change in charge leads to efflux of K+. • Hyperpolaization: Channels close slowly - K+ efflux leads to membrane potential <-70mV. Communication Within a Neuron