The Central Nervous System and Behavior Prof. Dr. Ali Çayköylü

1. The Central NervousSystem and Behavior Prof. Dr. Ali Çayköylü Republic of Turkey YıldırımBeyazıt University Ankara Atatürk Training and Research Hospital Department of Psychiatry 22.11.2012

2. THEME: Brain activity is the sourceof human consciousness, intelligence, and behavior.

3. Key Questions How do nerve cells operate ancommunicate? What are the major parts of the nervoussystem? How is the brain studied? Why is the human cerebral cortex so important, and what are its parts?

4. How do nerve cells operate and communicate? Neurons carry information from the senses to the brain They also activate muscles and glands A single neuron is not very smart — it would take many just to make you blink Millions of neurons must send messages at the same time to produce even the most fleeting thought. Each neuron receives messages from many others and sends its own message on.

5. Everything you think, feel, or do can be traced back to electrical impulses flashing through spidery networks of neurons. When neurons form vast networks, they produce intelligence and consciousness. Let’s see how neurons operate and how the nervous system is “wired.”

6. What does a neuron look like? What are its main parts? No two neurons are exactly alike, but most have 4 basic parts. The dendrites, which look like tree roots, receive messages from other neurons. The soma does the same. In addition, the soma(cell body)sends messages of its own down a thin fiber called the axon. Axonal transport conveysallthecellularelementsnecessaryforsynaptictansmissionstotheAxonterminals,

7. What does a neuron look like? What are its main parts?

8. Like miniature cables, axons carry messages through the brain and nervous system. Altogether, your brain contains about 3 million miles of axons. Now let’s summarize with a metaphor

9. . Imagine that you are standing in a long line of people who are holding hands. A person on the far right end of the line wants to silently send a message to the person on the left end. She does this by pressing the hand of the person to her left, who presses the hand of the person to his left, and so on. The message arrives at your right hand (your dendrites). You decide whether to pass it on. (You are the soma.) The message goes out through your left arm (the axon). With your left hand (the axon terminals), you squeeze the hand of the person to your left, and the message moves on.

10. SynapsesandNeurotransmitters How does information move from one neuron to another? The nerve impulse is primarily electrical. That’s why electrically stimulating the brain affects behavior. In contrast to the nerve impulse, communication between neurons is chemical. The microscopic space between two neurons, over which messages pass, is called a synapse. When an action potential reaches the tips of the axon terminals, neurotransmitters are released into the synaptic gap. Neurotransmitters are chemicals that alter activity in neurons.

11. Let’s return to our metaphor of people standing in a line. To be more accurate, you and the others shouldn’t be holding hands. Instead, each person should have a squirt gun in his or her left hand. To pass along a message, you would squirt the right hand of the person to your left. When that person notices this “message,” he or she would squirt the right hand of the person to the left, and so on.

12. When chemical molecules cross over a synapse, they attach to special receiving areas on the next neuron. These tiny receptor sites on the cell membrane are sensitive toneurotransmitters. The sites are found in large numbers on nerve cell bodies and dendrites. Muscles and glands have receptor sites, too.

15. Do neurotransmitters always trigger an action potential in the next neuron? No, but they do change the likelihood of an action potential in the next neuron. Some transmitters excite the next neuron (move it closer to firing). Others inhibit it (make firing less likely).

16. Neurotransmitters SerotoninSleep, appetite, sensory perception, temperature regulation, pain suppression, and mood DopamineVoluntary movement, learning, memory, and emotion AcetylcholineMuscle action, cognitive functioning, memory, and emotion NorepinephrineIncreased heart rate and the slowing of intestinal activity during stress, learning, memory, dreaming, waking from sleep, and emotion GABA(gama-aminobutyic acid)The major inhibitory neurotransmitter in the brain

17. How Drugs and Other Chemicals Alter Neurotransmitters? The agonist molecule excites. It mimics the effects of a neurotransmitter on the receiving neuron. Morphine mimics the action of neurotransmitters by stimulating receptors in the brain involved in mood and pain sensation. The antagonist molecule inhibits by blocking the neurotransmitters or by diminishing their release. Botulin poison causes paralysis by blocking receptors for acetylcholine (a neurotransmitter that produces muscle movement)

18. Neural Network Let’s put together what we now know about the nerve impulse and synaptic transmission to see how neural networks process information in our brains. Five neurons synapse with a single neuron that, in turn, connects with three more neurons. At the point in time depicted in the diagram, the single neuron is receiving one stronger and two weaker excitatory messages as well as two inhibitory ones. Does it fire an impulse?

20. It depends: If enough “exciting” messages arrive close in time, the neuron will fire — but only if it doesn’t get too many “inhibiting” messages that push it away from its trigger point. In this way, messages are combined before a neuron “decides” to fire its all-or-nothing action potential.

21. Let’s try another metaphor. You are out shopping for new jeans with five friends. Three of them think you should buy the jeans (your best friend is especially positive) and two think you shouldn’t. Because, on balance, their input is positive, you go ahead and buy the jeans. Maybe you even tell some other friends they should buy those jeans as well. Similarly, any single neuron in a neural network “listens” to the neurons that synapse with it and combines that input into an output. At any instant, a single neuron may weigh hundreds or thousands of inputs to produce an outgoing message. After the neuron recovers from the resulting action potential, it again combines the inputs, which may have changed in the meantime, into another output, and another, and another.

22. In this way, each neuron in your brain functions as a tiny computer. Compared with the average laptop computer, a neuron is terribly simple and slow. But multiply these events by 100 billion neurons and 100 trillion synapses, all operating at the same time, and you have an amazing computer — one that could easily fit inside a shoebox.

23. Neuroplasticity The neural networks in your brain constantly change. The term neuroplasticityrefers to the capacity of our brains to change in response to experience. New synapses may form between neurons or synaptic connections may grow stronger. Other synaptic connections may weaken and might even die. Every new experience you have is reflected in changes in your brain. For example, rats raised in a complex environment have more synapses and longer dendrites in their brains than rats raised in a simpler environment.

24. Arda and Emre are playing catch with a football. This may look fairly simple. However, to merely toss the football or catch it, a huge amount of information must be sensed, interpreted, and directed to countless muscle fibers. As they play, Arda and Emre’s neural circuits are ablaze with activity.

25. Let’s explore the “wiring diagram” that makes their game of catch possible. The central nervous system (CNS) consists of the brain and spinal cord. The brain carries out most of the “computing” in the nervous system. Arda must use his brain to anticipate when and where the football will arrive. Arda’s brain communicates with the rest of his body through a large “cable” called the spinal cord. From there, messages flow through the peripheral nervous system (PNS). This intricate network of nerves carries information to and from the CNS.

28. The Spinal Cord Spinal Nerves: 31 of them; carry sensory and motor messages to and from the spinal cord Cranial Nerves: 12 pairs that leave the brain directly; also work to communicate messages

29. How is the Spinal Cord Related to Behavior? Reflex Arc: Simplest behavioral pattern; occurs when a stimulus provokes an automatic response Sensory Neuron: Nerve cell that carries messages from the senses toward the CNS Connector Neuron: Nerve cell that links two others Motor Neuron: Cell that carries commands from the CNS to muscles and glands Effector Cells: Cells capable of producing a response

31. Peripheral Nervous System • Somatic NS Consists of nerves connected to sensory receptors and skeletal musclesPermits voluntary action (writing your name) • Autonomic NS Permits the involuntary functioning of blood vessels, glands, and internal organs such as the bladder, stomach and heart

32. Peripheral Nervous System • Sensory Nerves (to the brain) Carry messages from special reporters in the skin, muscles, and other internal and external sense organs to the spinal cord and then to the brain • Motor Nerves (from the brain) Carry orders from CNS to muscles, glands to contract and produce chemical messengers

33. Sympathetic NSand Emotion You perceive the sensory stimulus. The adrenal gland sends two hormones: epinephrine and norepinephrine. They activate the sympathetic nervous system. That produces a state of arousal or alertness that provides the body with the energy to act (the pupils dilate, the heart beats faster, and breathing speeds up).

35. The Forebrain The Cerebrum Higher forms of thinking take place in it It is divided into two halves called the cerebral hemispheres that are connected by a large band of fibers called the corpus callosum They have different tasks (lateralization)

36. The Forebrain The Cerebral Cortex The cerebrum is covered by several thin layers of densely packed cells known as the cerebral cortex On each cerebral hemisphere, deep fissures divide the cortex into 4 lobes

37. The Hindbrain Medulla – breathing, heart rate Pons – sleeping, walking, dreaming Riticular Activating System – alertness, attention Cerebellum – balance, coordination for the muscles

38. The Forebrain Thalamus Direct sensory messages to higher centers in the brain The sight of sunset is directed to a visual area The only sense that completely bypasses the thalamus is the sense of smell, which has its private switching station, the olfactory bulb

39. The Forebrain The Limbic System The Amygdala Responsible for evaluating sensory information It determines its emotional importance It makes the decision to approach or to withdraw Its initial response may be overridden by the appraisal of the cerebral cortex The Hippocampus The gate way to memory The Hypothalamus It is involved with drives associated with survival such as hunger, thirst, emotion, sex, and reproduction

40. The ForebrainThe Limbic System

41. How is the brain studied? Biopsychology is the study of how biological processes, and especially those of the nervous system, relate to behavior. In their research, many biopsychologists try to relate specific parts of the brain to the control of particular cognitive or behavioral functions, such as being able to recognize faces or move your hands. That is, they try to learn where functions are localized (located) in the brain. Many techniques have been developed to help identify brain structures and the functions they control.

42. How does the brain allow us to think, feel, perceive, or act? To answer questions like these, we must localize function by linking these psychological or behavioral capacities with particular brain structures. In many instances, this has been done through clinical case studies. Such studies examine changes in personality, behavior, or sensory capacity caused by brain diseases or injuries. If damage to a particular part of the brain consistently leads to a particular loss of function, then we say the function is localized in that structure. Presumably, that part of the brain controls the same function in all of us.

43. Why is the human cerebral cortex so important, and what are its parts? In many ways we are pretty unimpressive creatures. Animals surpass humans in almost every category of strength, speed, and sensory sensitivity. However, we do excel in intelligence.

44. Does that mean humans have the largest brains? Surprisingly, no. Elephant brains weigh 13 pounds, and whale brains, 19 pounds. At 3 pounds, the human brain seems puny — until we compare brain weight to body weight. We then find that An elephant’s brain is 1/1,000 of its weight; the ratio for sperm whales is 1 to 10,000. The ratio for humans is 1 to 60. If someone tells you that you have a “whale of a brain”be sure to find out if they mean size or ratio!

45. So having a larger brain doesn’t necessarily make a person smarter? That’s right. While a small positive correlation exists between intelligence and brain size, overall size alone does not determine human intelligence . In fact, many parts of your brain are surprisingly similar to corresponding brain areas in lower animals, such as lizards. It is your larger cerebral cortex that sets you apart.

46. The cerebral cortex, which looks a little like a giant, wrinkled walnut, consists of the two large hemispheres that cover the upper part of the brain. The two hemispheres are divided into smaller areas known as lobes. Parts of various lobes are responsible for the ability to see, hear, move, think, and speak. Thus, a map of the cerebral cortex is in some ways like a map of human behavior, as we shall see.

47. The cortex is composed of two sides, or cerebral hemispheres (half-globes), connected by a thick band of fibers called the corpus callosum. The left side of the brain mainly controls the right side of the body. Likewise, the right brain mainly controls left body areas. Right and left brain hemispheres perform differently on tests of language, perception, music, and other capabilities.

48. RightBrain/LeftBrain The brain divides its work in interesting ways. Roughly 95 percent of us use our left brain for language (speaking, writing, and understanding). In addition, the left hemisphere is superior at math, judging time and rhythm, and coordinating the order of complex movements, such as those needed for speech. In contrast, the right hemisphere can produce only the simplest language and numbers. Working with the right brain is like talking to a child who can say only a dozen words or so.

49. Although it is poor at producing language, the right brain is especially good at perceptual skills, such as recognizing patterns, faces, and melodies; putting together a puzzle; or drawing a picture. It is also helps you express emotions and detect the emotions that other people are feeling. Even though the right hemisphere is nearly “speechless,” it is superior at some aspects of understanding language. If the right side of the brain is damaged, people lose their ability to understand jokes, irony, sarcasm, implications, and other nuances oflanguage. Basically, the right hemisphere helps us see the overall context in which something is said.

50. In general, the left hemisphere is mainly involved with analysis(breaking information into parts). It also processes information sequentially (in order, one item after the next). The right hemisphere appears to process information simultaneously and holistically (all at once). To summarize further, you could say that the right hemisphere is better at assembling pieces of the world into a coherent picture; it sees overall patterns and general connections. The left brainfocuses on small details.The right brain sees the wide-angle view; the left zooms in on specifics. The focus of the left brain is local, the right is global.