Chapter 2 The Biology of Mind

Transcription

1 Chapter 2 The Biology of Mind PowerPoint Presentation by Jim Foley 2013 Worth Publishers

2 Surveying the Chapter: Overview What We Have in Mind Building blocks of the mind: neurons and how they communicate (neurotransmitters) Systems that build the mind: functions of the parts of the nervous system Supporting player: the slowercommunicating endocrine system (hormones) Star of the show: the brain and its structures

3 Searching for the biology of self Is our identity in the heart? In the brain? In the whole body? 3

4 Searching for the self by studying the body Phrenology Phrenology (developed by Franz Gall in the early 1800 s): the study of bumps on the skull and their relationship to mental abilities and character traits Phrenology yielded one big idea-- that the brain might have different areas that do different things (localization of function).

5 Today s search for the biology of the self: biological psychology Biological psychology includes neuroscience, behavior genetics, neuropsychology, and evolutionary psychology. All of these subspecialties explore different aspects of: how the nature of mind and behavior is rooted in our biological heritage. Our study of the biology of the mind begins with the atoms of the mind: neurons.

6 Neurons and Neuronal Communication: The Structure of a Neuron There are billions of neurons (nerve cells) throughout the body.

7 Action potential: a neural impulse that travels down an axon like a wave Just as the wave can flow to the right in a stadium even though the people only move up and down, a wave moves down an axon although it is only made up of ion exchanges moving in and out.

8 When does the cell send the action potential?... when it reaches a threshold The neuron receives signals from other neurons; some are telling it to fire and some are telling it not to fire. When the threshold is reached, the action potential starts moving. Like a gun, it either fires or it doesn t; more stimulation does nothing. This is known as the all-ornone response. How neurons communicate (with each other): The action potential travels down the axon from the cell body to the terminal branches. The signal is transmitted to another cell. However, the message must find a way to cross a gap between cells. This gap is also called the synapse. The threshold is reached when excitatory ( Fire! ) signals outweigh the inhibitory ( Don t fire! ) signals by a certain amount.

9 The synapse is a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The Synapse The synapse is also known as the synaptic junction or synaptic gap.

10 Neurotransmitters are chemicals used to send a signal across the synaptic gap. Neurotransmitters

11 Reuptake: Recycling Neurotransmitters [NTs] Reuptake: After the neurotransmitters stimulate the receptors on the receiving neuron, the chemicals are taken back up into the sending neuron to be used again.

12 Neural Communication: Seeing all the Steps Together

13 Roles of Different Neurotransmitters Some Neurotransmitters and Their Functions Neurotransmitter Function Problems Caused by Imbalances Serotonin Dopamine Acetylcholine (ACh) Norepinephrine GABA (gammaaminobutyric acid Glutamate Affects mood, hunger, sleep, and arousal Influences movement, learning, attention, and emotion Enables muscle action, learning, and memory Helps control alertness and arousal A major inhibitory neurotransmitter A major excitatory neurotransmitter; involved in memory Undersupply linked to depression; some antidepressant drugs raise serotonin levels Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility in Parkinson s disease and ADHD ACh-producing neurons deteriorate as Alzheimer s disease progresses Undersupply can depress mood and cause ADHD-like attention problems Undersupply linked to seizures, tremors, and insomnia Oversupply can overstimulate the brain, producing migraines or seizures; this is why some people avoid MSG (monosodium glutamate) in food

14 Serotonin pathways Networks of neurons that communicate with serotonin help regulate mood. Dopamine pathways Networks of neurons that communicate with dopamine are involved in focusing attention and controlling movement.

15 Hearing the message How Neurotransmitters Activate Receptors When the key fits, the site is opened.

16 Keys that almost fit: Agonist and Antagonist Molecules An agonist molecule fills the receptor site and activates it, acting like the neurotransmitter. An antagonist molecule fills the lock so that the neurotransmitter cannot get in and activate the receptor site.

17 The Inner and Outer Parts of the The central nervous system [CNS] consists of the brain and spinal cord. The CNS makes decisions for the body. Nervous System The peripheral nervous system [PNS] consists of the rest of the nervous system. The PNS gathers and sends information to and from the rest of the body.

18 Types of Neurons Sensory neurons carry messages IN from the body s tissues and sensory receptors to the CNS for processing. Motor neurons carry instructions OUT from the CNS out to the body s tissues. Interneurons (in the brain and spinal cord) process information between the sensory input and motor output.

19 The Nerves are not the same as neurons. Nerves consist of neural cables containing many axons. Nerves are part of the peripheral nervous system and connect muscles, glands, and sense organs to the central nervous system.

20 More Parts of the Nervous System

21 The Peripheral Nervous System

22 The Autonomic Nervous System: The sympathetic NS arouses (fight-or-flight) The parasympathetic NS calms (rest and digest)

23 The Central Nervous System The brain is a web of neural networks. The spinal cord is full of interneurons that sometimes have a mind of their own.

24 Neural Networks These complex webs of interconnected neurons form with experience. Remember: Neurons that fire together, wire together.

25 Interneurons in the Spine Your spine s interneurons trigger your hand to pull away from a fire before you can say OUCH! This is an example of a reflex action.

26 The Endocrine System The endocrine system refers to a set of glands that produce chemical messengers called hormones.

27 The Body s Slow but Sure Endocrine Message System The endocrine system sends molecules as messages, just like the nervous system, but it sends them through the bloodstream instead of across synapses. These molecules, called hormones, are produced in various glands around the body. The messages go to the brain and other tissues.

28 Adrenal Glands produce hormones such as adrenaline/epinephrine, noradrenaline/norepinephrine, and cortisol. Adrenal Glands Pancreas 1. The sympathetic fight or flight nervous system responds to stress by sending a message to adrenal glands to release the hormones listed above. 2. Effect: increased heart rate, blood pressure, and blood sugar. These provide ENERGY for the fight or flight!

29 The Pituitary Gland The pituitary gland is the master gland of the endocrine system. It is controlled through the nervous system by the nearby brain area--the hypothalamus. The pituitary gland produces hormones that regulate other glands such as the thyroid. It also produces growth hormone (especially during sleep) and oxytocin, the bonding hormone. Pituitary gland

30 The Brain What we ll discuss: how we learn about the brain the life-sustaining inner parts of the brain: the brainstem and limbic system the outer, wrinkled bark : the cortex left, right, and split brains Questions about parts of the brain: Do you think that the brain is the sum of its parts, or is the brain actually about the way they are connected? What do you think might happen if a particular area of the brain was stimulated? What do you think might happen if a particular area of the brain was damaged or not working well? Is it possible to understand the brain? If the human brain were so simple that we could understand it, we would be so simple that we couldn t. Emerson M. Pugh but we can try.

31 Investigating the Brain and Mind: How did we move beyond phrenology? How did we get inside the skull and under the bumps? by finding what happens when part of the brain is damaged or otherwise unable to work properly by looking at the structure and activity of the brain: CAT, MRI, fmri, and PET scans Strategies for finding out what is different about the mind when part of the brain isn t working normally: case studies of accidents (e.g. Phineas Gage) case studies of split-brain patients (corpus callosum cut to stop seizures) lesioning brain parts in animals to find out what happens chemically numbing, magnetically deactivating, or electrically stimulating parts of the brain

32 Studying cases of brain damage When a stroke or injury damages part of the brain, we have a chance to see the impact on the mind.

33 Intentional brain damage: Lesions (surgical destruction of brain tissue) performed on animals has yielded some insights, especially about less complex brain structures no longer necessary, as we now can chemically or magnetically deactivate brain areas to get similar information 33

34 Split-Brain Patients Split = surgery in which the connection between the brain hemispheres is cut in order to end severe full-brain seizures Study of split-brain patients has yielded insights discussed at the end of the chapter

35 We can stimulate parts of the brain to see what happens Parts of the brain, and even neurons, can be stimulated electrically, chemically, or magnetically. This can result in behaviors such as giggling, head turning, or simulated vivid recall. Researchers can see which neurons or neural networks fire in conjunction with certain mental experiences, and even specific concepts.

36 Monitoring activity in the brain Tools to read electrical, metabolic, and magnetic activity in the brain: EEG: electroencephalogram PET: positron emission tomography MRI: magnetic resonance imaging fmri: functional MRI

37 EEG: electroencephalogram An EEG (electroencephalogram) is a recording of the electrical waves sweeping across the brain s surface. An EEG is useful in studying seizures and sleep. 37

38 PET: positron emission tomography The PET scan allows us to see what part of the brain is active by tracing where a radioactive form of glucose goes while the brain performs a given task.

39 MRI: magnetic resonance imaging fmri: functional MRI MRI (magnetic resonance imaging) makes images from signals produced by brain tissue after magnets align the spin of atoms. The arrows below show ventricular enlargement in a schizophrenic patient (right). Functional MRI reveals brain activity and function rather than structures. Functional MRI compares successive MRI images taken a split second apart, and shows changes in the level of oxygen in bloodflow in the brain. 39

40 Areas of the brain and their functions The brainstem and cerebellum: coordinates the body The limbic (border) system: manages emotions, and connects thought to body The cortex (the outer covering): integrates information

41 The Brain: Less Complex Brain Structures Our tour of the brain begins with parts of the human brain found also in simpler animals; these parts generally deal with less complex functions: Brainstem (Pons and Medulla) Thalamus Reticular Formation Cerebellum Limbic System

42 The Brainstem: Pons and Medulla

43 The Base of the Brainstem: The Medulla The medulla controls the most basic functions such as heartbeat and breathing. Someone with total brain damage above the medulla could still breathe independently, but someone with damage in this area could not.

44 The Brainstem: The Pons The pons helps coordinate automatic and unconscious movements.

45 The Thalamus ( Inner Chamber ) The thalamus is the sensory switchboard or router. All sensory messages, except smell, are routed through the thalamus on the way to the cortex (higher, outer brain). The thalamus also sends messages from the cortex to the medulla and cerebellum.

46 Reticular ( Netlike ) Formation The reticular formation is a nerve network in the brainstem. It enables alertness, (arousal) from coma to wide awake (as demonstrated in the cat experiments). It also filters incoming sensory information.

47 Cerebellum ( little brain ) The cerebellum helps coordinate voluntary movement such as playing a sport. The cerebellum has many other functions, including enabling nonverbal learning and memory.

48 The Limbic ( Border ) System The limbic system coordinates: emotions such as fear and aggression. basic drives such as hunger and sex. the formation of episodic memories. The hippocampus ( seahorse ) processes conscious, episodic memories. works with the amygdala to form emotionally charged memories. The Amygdala ( almond ) consists of two lima beansized neural clusters. helps process emotions, especially fear and aggression.

49 Electrical stimulation of a cat s amygdala provokes aggressive reactions. If you move the electrode very slightly and cage the cat with a mouse, the cat will cower in terror. The Amygdala

50 The Hypothalamus: lies below ( hypo ) the thalamus. regulates body temperature and ensures adequate food and water intake (homeostasis), and is involved in sex drive. directs the endocrine system via messages to the pituitary gland. Thalamus The Hypothalamus as a Reward Center Riddle: Why did the rat cross the grid? Why did the rat want to get to the other side? Pushing the pedal that stimulated the electrode placed in the hypothalamus was much more rewarding than food pellets.

51 Review of Brain Structures

52 The Cerebral Cortex The lobes consist of: outer grey bark structure that is wrinkled in order to create more surface area for 20+ billion neurons. inner white stuff axons linking parts of the brain billion glial cells, which feed and protect neurons and assist neural transmission. 300 billion synaptic connections The brain has left and right hemispheres

53 The Lobes of the Cerebral Cortex: Preview Frontal Lobes Parietal Lobes Occipital Lobes Temporal Lobes involved in speaking and muscle movements and in making plans and judgments include the sensory cortex include the visual areas; they receive visual information from the opposite visual field include the auditory processing areas 53

54 Functions of the Brain: The Motor and Sensory Strips Output: Motor cortex (Left hemisphere section controls the body s right side) Input: Sensory cortex (Left hemisphere section receives input from the body s right side) Axons receiving motor signals FROM the cortex Axons sending sensory information TO the cortex

55 Using our knowledge of functions: Brain-computer interfaces and neural prosthetics Here, a robotic arm is operated through controls embedded in the motor strip of the cortex. We may soon be able to use computers to translate neural inputs into more commands and words than simply grabbing food.

56 Sensory Functions of the Cortex The sensory strip deals with information from touch stimuli. The occipital lobe deals with visual information. Auditory information is sent to the temporal lobe.

57 The Visual Cortex This fmri scan shows increased activity in the visual cortex when a person looks at a photograph.

58 Association function of the cortex More complex animals have more cortical space devoted to integrating/associating information

59 Association Areas: Frontal Lobes The frontal lobes are active in executive functions such as judgment, planning, and inhibition of impulses. The frontal lobes are also active in the use of working memory and the processing of new memories.

60 Phineas Gage ( ) Case study: In a work accident, a metal rod shot up through Phineas Gage s skull, destroying his eye and part of his frontal lobes. After healing, he was able to function in many ways, but his personality changed; he was rude, odd, irritable, and unpredictable. Possible explanation: Damage to the frontal lobes could result in loss of the ability to suppress impulses and to modulate emotions.

61 Parietal Lobe Association Areas This part of the brain has many functions in the association areas behind the sensory strip: managing input from multiple senses performing spatial and mathematical reasoning monitoring the sensation of movement

62 Temporal Lobe Association Areas Some abilities managed by association areas in this by the temples lobe: recognizing specific faces managing sensory input related to sound, which helps the understanding of spoken words

63 Whole-brain Association Activity Whole-brain association activity involves complex activities which require communication among association areas across the brain such as: memory language attention meditation and spirituality consciousness

64 Specialization and Integration Five steps in reading a word aloud:

65 Plasticity: The Brain is Flexible If the brain is damaged, especially in the general association areas of the cortex: the brain does not repair damaged neurons, BUT it can restore some functions it can form new connections, reassign existing networks, and insert new neurons, some grown from stem cells This 6-year-old had a hemispherectomy to end lifethreatening seizures; her remaining hemisphere compensated for the damage.

66 Our Two Hemispheres Lateralization ( going to one side ) The two hemispheres serve some different functions. How do we know about these differences? Brain damage studies revealed many functions of the left hemisphere. Brain scans and split brain studies show more about the functions of the two hemispheres, and how they coordinate with each other.

67 The intact but lateralized brain Right-Left Hemisphere Differences Left Hemisphere Thoughts and logic Details such as trees Language: words and definitions Linear and literal Calculation Pieces and details Right Hemisphere Feelings and intuition Big picture such as forest Language: tone, inflection, context Inferences and associations Perception Wholes, including the self

68 Split- Brain Studies To end severe whole-brain seizures, some people have had surgery to cut the corpus callosum, a band of axons connecting the hemispheres. Researchers have studied the impact of this surgery on patients functioning.

69 Separating the Hemispheres: Factors to Keep in Mind Each hemisphere controls the opposite side of the body AND is aware of the visual field on that opposite side. Without the corpus callosum, the halves of the body and the halves of the visual field do not work together. Only the left half of the brain has enough verbal ability to express its thoughts out loud.

70 Split visual field Each hemisphere does not perceive what each EYE sees. Instead, it perceives the half of the view in front of you that goes with the half of the body that is controlled by that hemisphere.

71 Divided Awareness in the Split Brain Try to explain the following result: 71

72 The divided brain in action Talent: people are able to follow two instructions and draw two different shapes simultaneously Drawback: people can be frustrated that the right and left sides do different things

73 The Future of Brain Research Can these questions be answered? Is every part of the mind s functioning going to be found someday on some brain scan? If so, have we found the mind, or is that still something separate from the brain?