Introduction to Cognitive Science Lecture 4: Neuroscienc e: An

Overview

Neuroscience: Neuroscience: An OverviewAn Overview

September 17, 2009

A Quick Tour of Neuroscience

The Nervous System

The Neuron

The Action Potential

Synaptic Transmission

Methods of Studying Neuronal Activity

Basic Neuroanatomy

The Nervous SystemCentral & Peripheral

Nervous Systems

Unconscious, e.g., heart rate, sweating

PNS: nervous system outside CNS

SUBDIVISIONS:•Somatic: nerves innervate skin, joints, and muscles (axons in PNS while somas in CNS)•Autonomic

Autonomic Nervous System (part of PNS)CNS:

brain & Spinal Cord

The Neuron:Basic Structure

Santiago Ramón y Cajal (1852-1934)“The Neuron Doctrine”

Neurons are the most basic functional units in the brain which communicate with one another via contact and not continuity.

Basic Structure of a Neuron

Nucleus:Cellular organelle that contains DNA

Soma: Cell Body

Collateral Axon

Schwann Cells:

Make myelin

Myelin Sheath:Membraneous wrapping around axons made by Schwann cells (PNS) or oligodendroglia (CNS)

Dendrites:Receive signals from other neurons (sometimes the same neuron!)

Node of Ranvier:Space between two myelin-sheaths where axon is exposed

Axon

Terminal Arbor:Branches at end of the axon that terminate in the same region of the nervous system

Saltatory Conduction:

In myelinated neurons, the action potential skips along the nodes of Ranvier resulting in faster conduction

Axon Hillock: Electrical trigger zone at the beginning of the axon

Ways of Describing Neurons

By Neurite Shape or Number (axons and dendrites)

BipolarBipolar UnipolarUnipolar Multi-polarMulti-polar PyramidalPyramidal

By Connections

• Primary Sensory Neurons: receive information from neurites in sensory surfaces such as skin or retina

• Motor Neurons: send messages from central nervous system to other areas

• Interneurons: neurons that are neither sensory or motor neuron; can also describe CNS neurons whose axons do not leave the structure in which they reside

By Neurotransmitter

Neurotransmitter:A chemical released by a presynaptic area at axon terminii upon stimulation and activates post-synaptic dendrites

•Amino Acids: e.g. glutamate, Gamma-Amino Acids: e.g. glutamate, Gamma-aminobutyric acid (GABA)aminobutyric acid (GABA)

•Monoamines: e.g.Monoamines: e.g.

Serotonin:Serotonin:

AcetylcholineAcetylcholine

Epinephrine (Adrenaline)Epinephrine (Adrenaline)

Norepinephrine (Nor-Adrenaline)Norepinephrine (Nor-Adrenaline)•Others:Others:

AcetylcholineAcetylcholine

AdenosineAdenosine

Nitric OxideNitric Oxide

PeptidesPeptides

AND LOADS MORE!!AND LOADS MORE!!

The Action Potential

A Brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels.

Action potentials sweep down axons to transfer information from one place to another in the nervous system.

Neuronal Firing Patterns

• Tonic: some neurons are always active and fire constantly

• Phasic: neurons fire in bursts

Synaptic Transmission

Methods for Studying Neurons

Neuronal Firing: Intracellular Recordings Neuronal Firing: Intracellular Recordings • Impale neuron or axon with a microelectrode (very Impale neuron or axon with a microelectrode (very

challenging)challenging)• Measure potential difference between the tip of the Measure potential difference between the tip of the

intracellular electrode and another electrode in the intracellular electrode and another electrode in the solution bathing the neuron.solution bathing the neuron.

• Intracellular electrode is filled with KCl salt solution which Intracellular electrode is filled with KCl salt solution which has high electrical conductivityhas high electrical conductivity

• Electrode connected to an amplifier; can view potential Electrode connected to an amplifier; can view potential differences on an oscilloscope (voltmeter). Voltage differences on an oscilloscope (voltmeter). Voltage changes can be heard as a popping sound.changes can be heard as a popping sound.

Movie:Movie:

http://www.youtube.com/watch?v=IgUMdwa1_Ushttp://www.youtube.com/watch?v=IgUMdwa1_Us

Fluorescent Proteins:Study Neuron Shape & Development• Get neurons to express Green Get neurons to express Green

Fluorescent protein (GFP) as a Fluorescent protein (GFP) as a markermarker

• Can study neuron shape and Can study neuron shape and growthgrowth

• If GFP is spliced (entered) into If GFP is spliced (entered) into DNA near where a specific gene DNA near where a specific gene of interest resides:of interest resides:

Both the gene product and GFP Both the gene product and GFP are expressed togetherare expressed together

Electroencephalogram (EEG)Electroencephalography (EEG) is a Electroencephalography (EEG) is a non-invasive technique for detecting non-invasive technique for detecting and localizing electrical activities of the and localizing electrical activities of the central nervous system. EEG systems central nervous system. EEG systems measure the electric potentials induced measure the electric potentials induced on the surface of the scalp using on the surface of the scalp using electrodes.electrodes.

USESUSES

•Clinical: localization of focal epilepsy Clinical: localization of focal epilepsy sources, psychiatrysources, psychiatry

•Research: to analyze sensorimotor or Research: to analyze sensorimotor or cognitive functions of the brain.cognitive functions of the brain.

Functional Magnetic Imaging (fMRI)• Type of MRI that studies blood flow

responses to neuronal activity

• Can study responses to specific visual or auditory stimuli or performance of a cognitive task.

• Here are areas where neural activation was greater when listening to sentences using incorrect syntax vs correct syntax (blue)

• And when the auditory recordings were intelligible vs untintelligible

Obesler, et. Al. Obesler, et. Al. Disentangling Syntax and Intelligibility in AuditoryDisentangling Syntax and Intelligibility in Auditory

Language Comprehension, Human Brain Mapping (2009)Language Comprehension, Human Brain Mapping (2009)

Major Brain Regions

Left and Right HemispheresLeft and Right Hemispheres

The human brain consists of two hemispheres that The human brain consists of two hemispheres that are more or less mirror images of each other in are more or less mirror images of each other in terms of their physical shape.terms of their physical shape.

Functionally, however, there are some symmetries Functionally, however, there are some symmetries but also asymmetries.but also asymmetries.

Symmetries exist in the processing of low-level Symmetries exist in the processing of low-level sensory input and motor control, where the left sensory input and motor control, where the left hemisphere is responsible for the right half of the hemisphere is responsible for the right half of the body and vice versa.body and vice versa.

One striking asymmetry is that the ability to One striking asymmetry is that the ability to understand and produce language is much more understand and produce language is much more pronounced in the left than in the right hemisphere.pronounced in the left than in the right hemisphere.

Left and Right HemispheresLeft and Right Hemispheres

Decades ago, a common treatment of epilepsy was Decades ago, a common treatment of epilepsy was to cut the corpus callosum, which is the main to cut the corpus callosum, which is the main connection between the hemispheres, in order to connection between the hemispheres, in order to limit the spreading of epileptic activity. limit the spreading of epileptic activity.

These split-brain patients typically behaved and felt These split-brain patients typically behaved and felt like healthy people in everyday life situations.like healthy people in everyday life situations.

In laboratory experiments, however, the In laboratory experiments, however, the consequences of the functional separation of their consequences of the functional separation of their hemispheres can be demonstrated.hemispheres can be demonstrated.

Split-Brain PatientsSplit-Brain Patients

If the image of an object is presented in their left If the image of an object is presented in their left visual field, they cannot tell the experimenter the visual field, they cannot tell the experimenter the identity of the object.identity of the object.

This is because this visual information is processed This is because this visual information is processed only in the right hemisphere, which cannot produce only in the right hemisphere, which cannot produce language.language.

They could pick that object from a set of items They could pick that object from a set of items placed outside their visual field using their left hand placed outside their visual field using their left hand (controlled by the right hemisphere) but not their (controlled by the right hemisphere) but not their right one.right one.

Patients can name objects presented in their right Patients can name objects presented in their right visual field and pick them with their right hand, but visual field and pick them with their right hand, but not with their left one. not with their left one.