Biological Processes. Neurons - how do they work? Nervous system: communication system of your body and brain

Transcription

1 Biological Processes Overview: The Nervous System: s Anatomy, communication, networks CNS/PNS The Brain Anatomy, localization of function Methods to study the brain (Dr. Heidenreich) Nervous system: communication system of your body and brain The basic unit of the nervous system is a neuron The nervous system contains over 1000 billion individual neurons Your brain alone consists of about 100 billion neurons s have both chemical and electrical processes s how do they work? (1) Your brain is almost entirely made up of neurons, specialized for different behaviors (2) s are complex cells that communicate by means of an electrochemical language (3) Activity in the neurons gets passed from one to another in a network (4) Chemicals stimulate the cell to transmit an electrical impulse. When the impulse reaches the end of the cell, chemicals are released which are picked up by neighboring cells which stimulate those cells 1

2 s have three basic parts Dendrites (1) Receives chemicals called neurotransmitters from neighboring cells and starts the electrical signal Axon (2) Transmits the electrical impulse down the length of the cell Terminal buttons (3) Releases chemical neurotransmitters to neighboring cells How neurons communicate Step1: chemicals (neurotransmitters) enter through the dendrites dendrites +++ Different neurotransmitters have different effects on the neuron. Some will make it more likely to fire. Others will make it less likely to fire. Step2: Action potential If enough of the excitatory (++) chemicals enter the dendrites, the neuron will transmit an electrical signal down the length of the axon Resting potential = Axon (1) Fluid inside the neuron is negatively charged (2) Fluid outside has positive and negative ions When the message is positive, + ions flow into cell and an electrical charge travels down the neuron This impulse is called an action potential 2

3 If enough of the inhibitory ( ) chemicals enter the dendrites, the neuron is less likely to have an action potential Resting potential = (1) Fluid inside the neuron is negatively charged (2) Fluid outside has positive and negative ions When the message is negative, ions flow into cell making the inside more negative than the resting potential and the cell is less likely to fire Step3: Neurotransmitter release Sacs of chemicals (called neurotransmitters) sit in the terminal endings. terminal buttons When the electrical signal makes its way down the axon. neurotransmitters are released into the space between nerve cells (the synapse) Synapse and are are picked up by the dendrites of neighboring neurons How are neurotransmitters relevant to real world behavior? Certain psychological and neurological disorders may be linked to abnormal levels of certain neurotransmitters Depression may be linked to abnormally low levels of serotonin Alzheimer s disease may be linked to abnormally low levels of acetylcholine Parkinson s disease may be linked to abnormally high levels of dopamine 3

4 The neurons in your brain are highly interconnected. It is really a communication network. The networks are called neural nets. They consist of as many as 1,000 billion neurons and 100,000 billion connections among neurons The connections between neurons are key in many experiences and behaviors. For example, learning serves to change the connections and makes the network store information. Action potentials only travel in one direction. Each neuron is like an on and off switch. It either fires or it doesn t. Each neuron connection carries information about experience or behavior (pleasure, pain, hunger, thirst, movements of your body, etc.) but what is most important is a pattern of activity across groups of neurons Your experiences and behaviors are a consequence of complex patterns of activity in groups of neurons in your brain The 100 billion neurons in the brain can be thought of as 100 billion onoff switches Each onoff pattern means something different to the brain

5 Your experiences and behaviors are a consequence of complex patterns of activity in groups of neurons in your brain The 100 billion neurons in the brain can be thought of as 100 billion onoff switches Each onoff pattern means something different to the brain Your experiences and behaviors are a consequence of complex patterns of activity in groups of neurons in your brain Brain images show these onoff patterns on a much larger scale How do these ideas help us learn about human behaviors? McClelland s work video What about neurons outside of the brain? The central nervous system (CNS)consists of the brain and spinal cord 5

6 What about neurons outside of the brain? The peripheral nervous system consists of all the other nerve cells of the body The PNS and CNS work together to process and react to stimuli in the environment. What about neurons outside of the brain? Sensory neurons take signals from the PNS and send them to CNS. Motor neurons take signals from CNS and send them to the PNS. interneurons This is known as a reflex or a reflex arc ANATOMY OF THE BRAIN The brain is organized into two hemispheres. Each hemisphere has four lobes. Parietal Lobe Left Hemisphere Right Hemisphere Occipital Lobe Temporal Lobe Frontal Lobe Top View Right View: Right Cerebral Hemisphere 6

7 Localization of function: DIFFERENT PARTS OF THE BRAIN SEEM TO DO DIFFERENT THINGS There are frontback differences RECEPTION perceptions, interpretations Back Front EXPRESSION actions, plans More Localization of function THE BRAIN IS ORGANIZED INTO FOUR LOBES Vision Touch/Movement Parietal Lobe Occipital Lobe Frontal Lobe Temporal Lobe Cognitive Functions Right View: Right Cerebral Hemisphere Language & Hearing Even more localization of function THE BRAIN IS ORGANIZED INTO PROJECTION AREAS AND ASSOCIATION AREAS somatosensory motor Impulses from the sense organs are sent to the primary sensory areas visual auditory Association Area organizes and integrates information across projection areas Impulses from the primary motor area are sent to the rest of the body An important lesson: Equal areas of body do not receive equal brain space 7

8 Different parts of the somatosensory cortex receive nerve impulses from different parts of the body. foot knee chest hand face What do you notice about how the somatosensory cortex is organized? Why do you think the hands have so many cells devoted to them? Different parts of the motor cortex send out nerve impulses to different parts of the body. foot knee chest hand face The motor cortex is organized the same way as the sensory cortex in an adjacent area of the brain. Brain function is also lateralized Lateralization of function: DIFFERENT HALVES OF THE BRAIN SEEM TO DO DIFFERENT THINGS Damage to the left hemisphere leads to difficulties in language tasks Damage to the right hemisphere leads to difficulty in spatial tasks LANGUAGE (like producing and understanding words) SPATIAL ABILITIES (like reading maps) Top View 8

9 It is important that the two hemispheres of the brain receive and process the same information about the world The corpus callosum is a band of tissue that connects the two hemispheres of the brain. It allows for fast and efficient sharing of information. LANGUAGE (like producing and understanding words) SPATIAL ABILITIES (like reading maps) but what would happen if someone did not have a corpus callosum? Would one hemisphere of the brain know something that the other did not? How could we find out? We would need to find people without a corpus collosum (such people exist) and present them with information so that only one hemisphere of their brain received it. The organization of the visual system provides one way for us to do this Vision is not divided by eye. Instead it is divided by visual field. Left Field Right Field Left Cortex Right Cortex When stimulation occurs in only ONE visual field ONLY the OPPOSITE visual cortex receives the image In order to do this, the participant is instructed to stare straight ahead and the image is flashed very briefly Left Field Right Field Why does it have to be flashed so quickly? Left Cortex Right Cortex 9

10 Let s say we briefly flash an image in the RIGHT visual field... What did you see? In this case the image goes to the LEFT HEMISPHERE, which has access to the words to describe what is being seen. A bird LANGUAGE SPATIAL ABILITIES Let s say we briefly flash an image in the LEFT visual field... What did you see? In this case the image goes to the RIGHT HEMISPHERE, which DOES NOT have access to the words to describe what is being seen. I don t know LANGUAGE SPATIAL ABILITIES Lateralization of function: motor control LEFT HEMISPHERE Controls movement of and processes stimulation from the RIGHT SIDE of the body Contralateral control RIGHT HEMISPHERE Controls movement of and processes stimulation from the LEFT SIDE of the body 10

11 This is what happened to Phineas Gage... Notice what part of the brain is injured... Excerpts from Descartes Error: Emotion, Reason, and the Human Brain, By Antonio Damasio The rod enters his left cheek, pierces the base of the skull, traverses the front of the brain, and exits at high speed through the top of the head. The rod has landed more than a hundred feet away, covered in blood and brains What happened to Gage after the accident? After being transported to a nearby doctor, Gage got out of the cart himself, with a little assistance from his men However he was somehow different. Before the accident Gage was: wellbalanced, a shrewd businessman, controlled, considerate, and soft spoken.. After the accident he was: fitful, irreverent, profane, irritable, demanding, and unable to plan for the future According to his doctor the equilibrium or balance between his intellectual faculty and his animal propensities has been destroyed He could no longer function as a foreman of the railroad site. 11

12 What can we (as scientists interested in the influence of the brain on behavior) learn from this? Two key questions: What part of the brain did he injure? How did it affect his behavior? Conclusion: This part of the brain (the frontal lobe) has something to do with decision making, planning, social interaction, personality, etc. Summary of Biological Processes: (1) fires through electrical and chemical processes (2) Action potential starts process for sending info to other neurons (3) Activity of neurons across the network = behavior (4) Brain function localized and lateralized lobes/hemispheres (5) Brain function studied by clinical cases, brain recordings, and experimental methods 12