Biological Bases of Behavior

1. Biological Bases of Behavior Unit III

2. Neural processing and the endocrine system

3. Neurons: The Origin of Behavior • Neurons: cells in the nervous system that communicate with one another to perform information-processing tasks • Components of neurons: • Cell body – coordinates information-processing tasks and keeps the cell alive • Dendrites – receive information from other neurons • Axon – transmits information to the other neurons, muscles and glands

5. Glialcells – support cells found in the nervous system • Some digest parts of dead neurons • Some provide physical and nutritional support for neurons • Myelin sheaths – an insulating layer of fatty material around the axons of some neurons • Formed by some glial cells • Synapse: junction or region between the axon of one neuron and the dendrites or cell body of another

6. The synapse

7. Types of Neurons • Sensory neurons – receive information from the external world and convey it to the brain via the spinal cord • Motor neurons – carry signals from the spinal cord to the muscles to produce movement • Interneurons – connect sensory neurons, motor neurons and other interneurons • Most common

8. Communicating information within a neuron • Communication happens in two stages: • Conduction of an electric signal over relatively long distances within neurons • Transmission of electric signals between neurons over the synapse

9. Communication -cont- • Neuron’s cell membrane is porous and allows ions (small electrically charged molecules ) to flow in and out of the cell • When at rest, channels that allow small, positively charged potassium ions (K+) to pass are open • Channels that allow the flow of other molecules are normally closed • There are more potassium ions inside the neuron, so some K+ ions flow out leaving the neuron with fewer positively charged molecules on the inside relative to the outside • Resting potential – difference in electric charge between the inside and outside of a neuron’s cell membrane

10. Communication -cont- • Action potential – electric signal that is conducted along the length of a neuron’s axon to the synapse • Occurs only when an electric shock reaches a certain level, or threshold • When an electric charge is raised to the threshold value, the K+ channels briefly shut down and other channels that allow the flow of sodium (Na+), another positively charged ion, are opened • When an electric current passes down the length of a myelinated axon, the charge “jumps” from node to node instead of travelling down the entire axon

11. Refractory period – time following an action potential during which a new action potential can’t be initiated • After action potential reaches it’s maximum, K+ flows out until the axon returns to resting potential • Eventually an active chemical “pump” in the cell membrane moves Na+ back outside the axon and K+ inside

12. Action Potential

13. The Action Potential

14. Synaptic transmission between neurons • Terminal buttons – knoblike structures that branch out from most axons • When the action potential reaches the terminal button, it stimulates the release of neurotransmitters – chemicals that transmit information across the synapse to a receiving neuron’s dendrites • Neurotransmitters float across the synapse and bind to sites on the dendrites of the receiving neuron called receptors – parts of the cell membrane that receive the neurotransmitter and initiate a new electric signal • Activation of receptors on the receiving neuron can cause a new electric potential to be initiated, called synaptic transmission

15. Neurotransmitters left in the synapse are cleared up through one of three processes: • Reuptake – neurotransmitters are reabsorbed by the terminal buttons of the presynaptic neuron’s axon • Enzyme deactivation – specific enzymes break down and destroy specific neurotransmitters • Autoreceptors – detect how much of a neurotransmitter has been released into a synapse and signal the neuron to stop releasing the neurotransmitter when too much is present

16. Synaptic Transmission

17. Types of Neurotransmitters

18. How Drugs Mimic Neurotransmitters • Agonists – drugs that increase the action of a neurotransmitter • Prozac blocks reuptake of serotonin

19. Antagonists – drugs that block the function of a neurotransmitter

20. The Organization of the Nervous System

21. Nervous system – interactive network of neurons that conveys electrochemical information throughout the body • Made up of two divisions: • Central nervous system (CNS) – brain and the spinal cord • Peripheral nervous system (PNS) – connects the CNS to the body’s organs and muscles • Also composed of two parts:

22. Somatic nervous system – set of nerves that conveys information into and out of the CNS • Autonomic nervous system (ANS) – set of nerves that carries involuntary and automatic commands that control blood vessels, body organs and glands • Sympathetic nervous system – set of nerves that prepares the body for action in threatening situations • Parasympathetic nervous system – helps the body return to a normal resting state

23. The Human Nervous System

24. Sympathetic and parasympathetic systems

25. Components of the CNS: The Spinal Cord • Some behaviors do not require input from the brain to the spinal cord • Spinal reflexes – simple pathways in the nervous system that quickly generate muscle contractions

26. Components of the CNS:The Brain

27. The Hindbrain • Hindbrain – area of the brain that coordinates information coming into and out of the spinal cord • Sometimes called the brain stem – includes: • Medulla – extension of the spinal cord into the skull that coordinates heart rate, circulation and respiration • Reticular formation – brain structure that regulates sleep, wakefulness and levels of arousal • Cerebellum – large structure that controls fine motor skills • Thalamus – directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla • Pons – relays information from the cerebellum to the rest of the brain

28. The Hindbrain

29. The MIdbrain

30. The forebrain • Highest level of the brain • Controls complex cognitive, emotional, sensory and motor functions • Divided into two main parts: • Cerebral cortex – outermost layer of the brain • Subcortical structures – areas of the forebrain housed under the cerebral cortex near the center of the brain

31. Subcortical structures • Limbic system – located below the cerebral hemispheres • Associated with emotions and drives • Amygdala – involved in many emotional processes, particularly the formation of emotional memories • Hippocampus – plays a role in the storage of memories

32. Subcortical structures -cont- • Thalamus – sits on top of the brain stem and serves as a relay station • Like a server in a computer network • Hypothalamus– regulates body temperature, hunger, thirst and sexual behavior • Basal ganglia – large neuron clusters that work with the cerebellum and cerebral cortex to control and coordinate voluntary movements

34. The forebrain

35. The cerebral cortex • Divided into two hemispheres • Each controls the opposite side of the body • Corpus callosum – thick band of nerve fibers that connects large areas of the cerebral cortex on each side of the brain and supports communication of information across the hemispheres • Hemispheres are subdivided into four areas/lobes • Occipital lobe – processes visual information • Parietal lobe – processes information about touch • Temporal lobe – hearing and language • Frontal lobe – has specialized areas for movement, abstract thinking, planning, memory and judgment

37. Motor cortex – area at the back of the frontal lobe that controls voluntary movements • Sensory cortex – area at the front of the parietal lobes that registers and processes body touch and movement sensations • Association areas – areas of the cerebral cortex that are composed of neurons that help provide sense and meaning to information registered in the cortex • Are usually less specialized and more flexible than neurons in the primary areas

38. The brain and language • Aphasia – impairment of language, usually caused by left hemisphere damage either to Broca’s area or to Wernicke’s area • Broca’s area – controls language and expression • Usually in the left frontal lobe • Directs muscle movements involved in speech • Wernicke’s area – controls language reception • Usually in left temporal lobe

39. Plasticity – the brain’s ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience

40. Our divided brain • Split brain – results from surgery that isolates the brain’s two hemispheres by cutting the fibers connecting them

41. Some things to remember about the brain’s hemispheres: • There is no activity to which only one hemisphere makes a contribution • Logic is not confined to the left hemisphere and creativity and intuition are not exclusive properties of the right hempishere • It is impossible to educate one hemisphere at a time • There is no evidence that people are purely “left-brained” or “right-brained”

42. How we study the brain • Brain lesioning – abnormal disruption in the tissue of the brain resulting from injury or disease • Is done with laboratory animals to determine the function of different parts of the brain • Strokes and brain injuries create lesioned areas in the brain

43. Electrical activity within the brain is measured with an electroencephalogram (EEG) • Multiple electrodes are attached to the outside of the head • Advantages: • Can detect very rapid changes in electrical activity, allowing analysis of stages of cognitive activity • Disadvantages: • Provides poor spatial reasoning of the source (cells, brain region) of electrical activity

44. Neuroimaging techniques • PET (positron mission tomography) scan–indicates specific changes in neuronal activity by detecting where a radioactive form of glucose goes while the brain performs a given task • Advantage – provides visual image corresponding to anatomy • Disadvantages: • Requires exposure to low levels of radioactivity • Not as clear as an MRI • Cannot follow changes faster than 30 seconds

45. CT (computed tomography) scan – series of X-rays taken from different angles and combined by computer into a composite representation of a slice through the body • MRI (magnetic resonance imaging) – show brain anatomy • fMRI (functional MRI) – can reveal brain’s functioning and structure

46. fMRI scan of a concussion

47. Genetics, evolutionary psychology and behavior

48. Behavior genetics • Chromosome – strands of DNA wound around each other in a double-helix configuration • DNA – complex molecule containing the genetic information that makes up the chromosomes • Genes – biochemical units of heredity that make up the chromosomes

49. Twin and adoption studies • Identical twins – develop from a single fertilized egg that splits in two • Also called monozygotic twins • Share 100% of their genes • Fraternal twins – develop from separate fertilized eggs • Also called dizygotic twins • Share about 50% of their genes • Likelihood increases with use of fertility treatments and genes