Intro to Cognitive Science

Transcription

1 Intro to Cognitive Science Jamuna Subramaniam Department of Biological Sciences and Bioengineering Indian Institute of Technology Kanpur

2 Higher order brain functions Language Learning and memory Thought Emotion

3 Parts of the brain

4 Diseases led to the discovery of the regions involved in specific functions.

5 Brain imaging EEG collecting the peripheral brain electrical activity PET positron emission tomography radioactive tracers in the water deutrium more active areas more blood flow increased radiotracer signal Individual neurotransmitters radiotracers receptor binding,occupancy and turnover molecular level studies possible at the systems level in humans. MRI&fMRI Based on bloodflow paramagnetic property of hemoglobi Active brain regions oxygen bound blood flow will be higher.

6 MRI

7 Human brain

8 The nervous system of a vertebrate

9 Structure and functional areas of the cerebrum

10 Brain regions involved in language Left lobe Wernicke s area Auditory input understanding speech Broca s area Motor output Indelligible speech

11 Areas active during different language tasks

12 Language learning disability Dyslexia

13 Molecular and cellular network level understanding!!!!!!

14 NERVOUS SYSTEMS Three overlapping functions sensory input integration motor output Interconnected network of neurons

15 Overview of a vertebrate nervous system

16 Networks of neurons with intricate connections form nervous systems Neuron Structure and Synapses. The neuron is the structural and functional unit of the nervous system. Nerve impulses are conducted along a neuron. Dendrite cell body axon hillock axon Some axons are insulated by a myelin sheath.

17 Axon endings are called synaptic terminals. They contain neurotransmitters which conduct a signal across a synapse. A synapse is the junction between a presynaptic and postsynaptic cell.

18 Aplysia neuron

19 Types of Nerve Circuits. Single presynaptic neuron several postsynaptic neurons. Several presynaptic neurons single postsynaptic neuron. Circular paths. Presynaptic neurons muscles neuromuscular junctions

20 Types of neurotransmission 1. Electrical 2. Chemical

21 Every cell has a voltage, or membrane potential, across its plasma membrane A membrane potential is a localized electrical gradient across the membrane. Anions are more concentrated within a cell. Cations are more concentrated in the extracellular fluid. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

22 Measuring Membrane Potentials. Fig. 48.6a An unstimulated cell usually have a resting potential of 70mV. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

23 How a Cell Maintains a Membrane Potential? Cations K+ is the principal intracellular cation. Na+ is the principal extracellular cation. Anions Proteins, amino acids, sulfate, and phosphate are the principal intracellular anions. Cl is the principal extracellular anion. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

24 The basis of the membrane potential Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

25 Types of gated ion channels Chemically gated ion channels open or close in response to a chemical stimulus. Voltage gated ion channels open or close in response to a change in membrane potential. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

26 Graded Potentials: Hyperpolarization and Depolarization Graded potentials are changes in membrane potential Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

27 Hyperpolarization Gated K+ channels open K+ diffuses out of the cell the membrane potential becomes more negative. Fig. 48.8a Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

28 Depolarization Gated Na+ channels open Na+ diffuses into the cell the membrane potential becomes less negative. Fig. 48.8b Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

29 The Action Potential: All or Nothing Depolarization If graded potentials sum to 55mV a threshold potential is achieved. This triggers an action potential. Axons only. Fig. 48.8c Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

30 Step 1: Resting State. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

31 Step 2: Threshold. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

32 Step 3: Depolarization phase of the action potential. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

33 Step 4: Repolarizing phase of the action potential. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

34 Step 5: Undershoot. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

35 Propagation of the action potential Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

36 Chemical or electrical communication between cells occurs at synapses Electrical Synapses Action potentials travel directly from the presynaptic to the postsynaptic cells via gap junctions. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

37 Chemical Synapses More common than electrical synapses. Postsynaptic chemically gated channels exist for ions such as Na+, K+, and Cl. Depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize. Brought about by binding of neurotransmitters released from the presynaptic terminal to the postsynaptically localized chemically gated channels Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

38 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

39 Fundamental currencies of the living cell DNA/RNA string of nucleotides nitrogenous base (four different bases pentose sugar and phosphate) Protein : string of amino acids (20 different amino acids) secondary, tertiary and quarternary structures DNA RNA Protein R NH2 (CH)n COOH

40 Excitatory neurotransmission Positive event brings about membrane depolarization action potential generation an action happening Major excitatory neurotransmitter in the CNS: glutamate Glutamate receptors : Ionotrophic (Na+ channel coupled) functional receptor complex is multimeric Three different types: Kainate, AMPA and NMDA receptors Diseases : conitnous firing excitotoxicity neuronal death in stroke, epilepsy

41 Inhibitory neurotransmission Hyperpolarization modulates no action potential generation Inhibitory anion : Cl Inhibitory neurotransmitter : GABA gamma aminobutyric acid GABAA receptor complex pentameric several types of subunits: alpha, beta, gamma, delta and rho subunit subtypes. Have modulatory sites anesthetics, antianxiety drugs

42 In vitro patch clamp recording Nobel Price: Neher and Sakmann, 1991

43 The Major Known Neurotransmitters

44 Integration of multiple synaptic inputs

45 Summation: graded potentials (EPSPs and IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron. Fig Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

46 Cellular communication at synapse Summation of input Action potential generation Output action

47 Biological clock Emotions Learning and memory

48 Human brain

49 The Hypothalamus and Circadian Rhythms The biological clock is the internal timekeeper. The clock s rhythm usually does not exactly match environmental events. Experiments in which humans have been deprived of external cues have shown that biological clock has a period of about 25 hours. In mammals, the hypothalamic suprachiasmatic nuclei (SCN) function as a biological clock. Produce proteins in response to light/dark cycles. This, and other biological clocks, may be responsive to hormonal release, hunger, and various external stimuli. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

50 The limbic system (emotions)

51 Learning and memory Short term memory stored in the frontal lobes. The establishment of long term memory involves the hippocampus. The transfer of information from short term to long term memory is enhanced by repetition (remember that when you are preparing for an exam). Influenced by emotional states mediated by the amygdala. Influenced by association with previously stored information.

52 Synaptic signaling 1. Fast neurotransmission 2. Slow neurotransmission

53 Signal transduction: Mode of regulation Phosphorylation dephosporylation Second messenger : camp, calcium, IP3, cgmp

54 Figure 11.5 Overview of cell signaling (Layer 3) Overview of cell signaling (Layer 3)

55 Figure The specificity of cell signaling

56 Cross talk between different signal cascades

57 Signal amplification

58

59 Learning and memory A Nobel laureate s perspective Eric Kandel

60 Selection of the problem: Learning and behavior easily tractable

61 Selection of the organism: less complicated easy to observe behavior and molecular events Selection of behavior: Memory storage behavior

62 Memory storage behavior Neural circuit Critical neurons Cellular and molecular changes in specific neurons

63 Aplasia marine snail

64 Model behavior Gill and siphon withdrawal upon tactile stimuli Aplasia neuron visible to naked eye

65 Types of memory Short term: lasts only minutes Long term: lasts for days By practice (timed repetition) Short term memory Long term memory

66 Behavior taught learned fear Sensitization shock in the tail, withdrawal of siphon and gill

67 Neuronal circuit in gill withdrawal 24 mechanosensory neurons integrate siphon skin 6 monosynaptic connection to gill motor neuron

68 Neurons in in vitro culture

69 Injection of signal cascade components

70 Molecular events Serotonin, dopamine Involvement of camp cascade Serotonin, dopamine camp levels Modulatory pathway involves camp cascade Sensory neurons release glutamate memory facilitation

71 Synaptic plasticity Increase in strength. Increase in synapse number.

72 Behavior : Spatial memory

73 Hippocampal activation

74 Diseases of Cognition Dementia Loss of memory Alzheimer s disease Cerebral cortex and hippocampus; Amyloid plague accumulation. Most prevalent Complex neurodegenerative disease defects in the neurotransmitter acetylcholine and glutamate! Huntington s disease

75 Diseases of the thought process Psychiatirc diseases Schizophrenia delusions, hallucinations Too much of dopamine neurotransmitter signaling.

76 Spinal cord injury

77 THANK YOU