The Biological Basis of Behavior

1. The Biological Basis of Behavior Chapter 2

2. Neurons: The Messengers • About 100 billion neurons (nerve cells) in the human brain • Neurons have many of the same features as other cells • Nucleus • Cytoplasm • Cell membrane • What makes neurons unique is their shape and function

3. Structure of Neurons • Dendrites • Carry information to the cell body from other neurons • Cell Body (Soma) • Contains nucleus • Axon • Carries information to the next cell • Myelin Sheath • Insulates the axon and speeds up the neural impulse

4. Types of Neurons • Sensory neurons • Carry information from sensory systems to the brain • Also referred to as afferent • Motor neurons • Carry information from the brain to muscles and glands • Also referred to as efferent • Interneurons • Carry information between other neurons

5. Glial Cells • Cells that insulate and support neurons • Create the myelin sheath • Remove waste products • Provide nourishment • Prevent harmful substances from entering the brain

6. The Neural Impulse

7. The Neural Impulse • Ions • Charged molecules • Resting Potential • When more negative ions are inside the neuron than outside • Charge is approximately -70mV • Neuron is not transmitting information

8. The Neural Impulse • Polarization • When the electrical charge of a cell moves away from zero • Depolarization • When the electrical charge of a cell moves toward zero

9. The Neural Impulse • Action Potential • Sudden, massive change in charge in the neuron • Occurs when depolarization reaches the threshold of excitation • Ions flow across cell membrane

10. The Neural Impulse • Graded Potentials • Subthreshold depolarization • Many subthreshold depolarizations are added together to produce an action potential (a process known as summation)

11. The Neural Impulse • All-or-None Law • A neuron either fires or it does not • When it does fire, it will always produce an impulse of the same strength • Intensity of a stimulus is coded by the frequency of action potentials

12. The Neural Impulse • Absolute refractory period • Period immediately after an action potential when another action potential cannot occur • Relative refractory period • Period following absolute refractory period when a neuron will only respond to a stronger than normal impulse

13. The Synapse • Synaptic space (synaptic cleft) • Tiny gap between neurons • Terminal button • Enlarged area at the end of an axon • The synapse • Composed of the terminal button of one neuron, the synaptic space, and the dendrites or cell body of the receiving neuron

14. Transmission Between Neurons • Synaptic vesicles • Sacs in terminal button that release chemicals into synaptic space • Neurotransmitters • Chemicals released by synaptic vesicles • Receptor sites • Location on receptor neuron for specific neurotransmitter

15. Some Well-Known Neurotransmitters • Acetylcholine (ACh) • Released at the neuromuscular junction • Plays an important role in arousal and attention • Loss of ACh producing cells is linked to Alzheimer’s Disease • Dopamine • Affects neurons associated with voluntary movement • Plays a role in learning, memory, and emotions • Loss of dopamine-producing cells causes symptoms of Parkinson’s Disease

16. Some Well-Known Neurotransmitters • Serotonin • Found throughout the brain • Appears to sets an “emotional tone” • Low serotonin levels are implicated in depression • Endorphins • Reduce pain by inhibiting or “turning down” neurons that transmit pain information

17. Psychopharmacology • Most psychoactive drugs (and toxins) work by blocking or enhancing synaptic transmission • Botulism • Blocks release of ACh at the neuromuscular junction, causing paralysis • “Botox” is botulism toxin used to prevent facial muscles from making wrinkles

18. Psychopharmacology • Curare • Can stun or kill prey quickly • Blocks ACh receptors causing paralysis • Antipsychotic medications • Block dopamine receptors • Reduces schizophrenic hallucinations • Caffeine • Increases the release of excitatory neurotransmitters by blocking the inhibitory neurotransmitter adenosine

19. Psychopharmacology • Cocaine • Prevents reabsorption of dopamine • Leads to heightened arousal of entire nervous system

20. Neural Plasticity • The brain can be changed, both structurally and chemically, by experience • Rat studies show that an “enriched” environment leads to larger neurons with more connections • Has also been shown in humans • Recent research has uncovered evidence of neurogenesis, or the production of new brain cells, in human brains

21. Nervous System Organization • Central nervous system (CNS) • Consists of the brain and spinal cord • Peripheral nervous system • Connects the CNS to the rest of the body • Somatic nervous system • Autonomic nervous system

22. Central Nervous System

23. The Brain – The Central Core • Medulla • Controls breathing, heart rate, and blood pressure • Pons • Maintains the sleep-wake cycle • Cerebellum • Coordinates body’s movements

24. The Brain – The Central Core • Thalamus • Relays information from sensory receptors to the brain • Hypothalamus • Influences motivated behavior • Regulates hunger, thirst, body temperature, and sexual drive. • Directly involved in emotional behavior

25. The Brain – The Central Core • Reticular formation • Network of neurons found throughout the brain • Serves to alert and arouse higher brain in response to incoming information

26. The Brain – The Limbic System • Ring of structures located between the central core and the cerebral hemispheres • Important to learning and emotional behavior • Hippocampus essential in formation of new memories • Amygdala, together with the hippocampus, is important for regulating emotions

27. The Cerebral Cortex • Occipital lobe • Receives and processes visual information • Temporal lobe • Complex visual tasks such as face recognition • Receives and processed auditory information • Involved in balance, some emotions and motivations • Some language processing

28. The Cerebral Cortex • Parietal lobe • Receives sensory information from body • Involved in spatial abilities • Frontal lobe • Coordinated information from other lobes • Controls voluntary movement, attention, setting goals, and expression of appropriate emotions

29. Hemispheric Specialization • Corpus Callosum • Fibers that connect the two hemispheres • Allow close communication between left and right hemishphere • Each hemisphere appears to specialize in certain functions

30. Split-Brain Research • Much information about functions of each hemisphere has come from studying split-brain patients

31. Tools for Studying the Nervous System

32. Microelectrode Techniques • Very small electrodes inserted into individual neurons • Used to study activity of a single neuron

33. Macroelectrode Techniques • Used to get a picture of overall activity in the brain • An example is an EEG, which uses electrodes placed on a person’s scalp to measure brain activity

34. Structural Imaging • Computerized Axial Tomography (CT-scan) • Uses X-rays to create a 3-dimensional image of the brain • Magnetic Resonance Imaging (MRI) • Uses a magnetic field and radio waves to produce images

35. Functional Imaging • EEG imaging • electrical activity on the scalp from millions of neurons is used to produce a continuous picture of activity in the brain • Magentoencephalography (MEG) and Magnetic source imaging (MSI) • Can localize activity more precisely than EEG

36. Functional Imaging • Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) • Use radioactive glucose to determine location of greatest brain activity • Functional Magnetic Resonance Imaging (fMRI) • Shows function and structure by measuring movement of blood molecules within the brain

37. The Spinal Cord

38. The Spinal Cord • Complex cable of nerves that connects brain to rest of the body • Carries motor impulses from the brain to internal organs and muscles • Carries sensory information from extremities and internal organs to the brain

39. The Spinal Cord • The spinal cord controls some protective reflex movements without any input from the brain

40. The Peripheral Nervous System

41. The Somatic Nervous System • Consists of neurons that communicate between the body and the brain • Afferent neurons • Neurons that carry messages from sense organs to spinal cord • Efferent neurons • Neurons that carry messages from the spinal cord or brain to muscles and glands

42. The Autonomic Nervous System • Sympathetic division • Most active when you are angry, afraid, or aroused • Fight-or-flight response • Increases heart rate and breathing • Stops digestion

43. The Autonomic Nervous System • Parasympathetic division • Calms body • Produces effects opposite to those of the sympathetic division • Reduces heart rate and breathing • Restores digestion

44. The Endocrine System

45. The Endocrine System • Helps coordinate and integrate complex psychological reactions • Endocrine glands secrete hormones into the bloodstream • Hormones serve to organize the nervous system and body • Hormones also activate behavior, such as sexual behavior

46. The Endocrine System • Thyroid gland • Secretes hormones (primarily thyroxin) that control metabolism • Parathyroid glands • Control levels of calcium and phosphate which in turn controls levels of excitability

47. The Endocrine System • Pineal gland • Secretes melatonin which regulates the sleep-wake cycle • Pancreas • Regulates blood-sugar levels • Secretes insulin and glucagon

48. The Endocrine System • Pituitary gland • Referred to as the “master gland” because it regulates many other glands • Gonads • Ovaries and testes secrete estrogens and androgens • Adrenal glands • Secretes hormones in reaction to stress

49. Genes, Evolution, and Behavior

50. Genetics • Heredity - transmission of trait from one generation to next • Chromosomes • Pairs of thread like bodies that contain genes • Deoxyribonucleic acid (DNA) • Organic molecule arranged in a double-helix • Contains the “code of life”