Introduction to Cognitive Neuroscience

Topic 2: The Nervous System

Neurons: The rock stars of the nervous system Santiago Ramon y Cajal The father of modern neuroscience Did extensive study of neuronal structures

Neurons: the rock stars of the nervous system 2 types of nerve cells

Neurons (transmit signals) Glia (provide support and structure; repair

2 types of “brain matter” Grey matter – neuronal bodies (soma) White matter - axons

Neuron Structures Soma = body Nucleus (all cells have it) inside soma Axon Terminal Bouton (axon terminal) Dendrites Myelin Sheath (composed of

Schwann cells)

How do neurons communicate? Axon meets dendrite

The space between the axon and dendrite is called the SYNAPSE

The neuron SENDING information is called the presynaptic neuron (because it is BEFORE the synapse)

The neuron RECEIVING information is called the postsynaptic neuron (because it is AFTER the synapse)

How do neurons communicate? Electrical signals

Action potential

Chemical signals Neurotransmitters

How do neurons communicate? The lipid bilayer Vesicles

Vesicles bind to the terminal bouton (the axon terminal) and NTs are released into the synapse

The NTs are taken up by receptors on the postsynaptic neuron – they tell the next neuron what to do

How do neurons communicate? Action potentials

Electrical signals that travel down the axon to stimulate the release of NTs

When a neuron is not sending a signal, it is “at rest.” This is called the resting potential. Resting potential is at about -70 mV (millivolts)

Action potentials are caused when different ions permeate the cell membrane Na+ Cl- and K+

How do neurons communicate? The process of an action potential

1. Stimulus – may be chemical or electrical2. Ion pumps open and change the polarization of the

cell3. The cell hyperpolarizes past the threshold level

(typically around +30 - +40 mV4. This causes a wave of hyperpolarization down the cell

(through the myelin sheath; nodes of Ranvier)5. When the AP reaches the axon hillock, NTs are

stimulated to be released6. NTs travel to post-synaptic cell; depending on the

type they may stimulate or suppress another AP

How to neurons communicate? The myelin sheath

Composed of Schwann Cells A special type of Glial cell, primarily located in the

PNS These coat the axon and allow potentiation to

“jump” down the axon The un-myelinated regions are called the Nodes of

Ranvier

Demyelination is thought to be a primary contributor to dementia (Alzheimer’s disease) and Multiple Sclerosis (MS)