Week 3 Module 1: Neurons and Glial cells

What is the average number of cerebral cortical neurons?

100 billion

Up to what speed can signals in the brain travel?

268 MPH

What is the size range of most cells?

0.01-0.05 mm

What are the two types of the cells in the nervous system?

Neurons

Glial cells

What are neurons?

Cells that sense change and communicate to other neurons

What are the basic functions of a neuron?

Reception, transmission, and transfer of information

What are glial cells?

Cells that insulate, support, and nourish neighboring neurons

How are neurons categorized?

Sensory

Motor

Interneuron

What is a sensory neuron?

A neuron that detects changes in the external or internal environment and sends information about these changes to the CNS

What is a motor neuron?

A neuron located within the CNS that controls the contraction of muscle or the secretion of glands

What is a interneuron?

Communicates only to other neurons and provides connections between sensory and motor neurons

What is the soma?

The cell body that contains the nucleus- it is the metabolic center of the neuron and contains chromosomes and DNA

What is a dendrite?

Structures attached to the soma of a neuron and receives information from the terminal bouton of an adjacent neuron

What is the myelin sheath?

A protective sheath that is made out of fat and protein; it insulates the axon and prevents the spreading of messages between axons, it also increases the speed of transmission

What is the node of ranvier?

The naked portion of a myelinated axon between adjacent oligodendroglia or Schwann cells, these allow action potentials to quickly jump from node to node

What is a synapse?

A junction between terminal bouton of an axon and the membrane of another neuron, neurotransmitters act as chemical signals and are passed between neurons in the synapse

What is an axon?

A long, thin, cylindrical structure that conveys information from the soma of a neuron to its terminal bouton

When is an axon considered myelinated?

When the myelin sheath completely wraps around the axon (usually several times)

When is an axon considered non-myelinated?

When the axon is not or is partially covered by myelin

What is a terminal bouton?

The bud at the end of an axon, it forms synapses with another neuron and sends information to that neuron

What is a neurotransmitter?

A chemical released by a terminal bouton, it can be excitatory or inhibitory when effecting another neuron

What is indicated by A?

Dendrite

What is indicated by B?

Soma/cell body

What is indicated by C?

Axon hillock

What is indicated by D?

Myelin sheath

What is indicated by E?

Node of ranvier

What is indicated by F?

Terminal bouton

What is housed in the cell membrane?

I on channels that allow ions in and out of the cell

What happens when the ion channels are open?

Ions such as Na+, K+, Cl-, and Ca2+ can enter the cell

Once ions begin crossing the cell membrane through the ion channel, what happens?

Depolarization occurs, rapidly changing the electrical charge of the inside of the cell, as the electrical potential between the positive outside of the cell and negative inside of the cell causes a transfer in ions

How do neurons communicate?

By undergoing rapid changes in electrical potential across the cell membrane

What is resting potential?

The resting state of a neuron when it is not transmitting information, the inside of the neuron contains more negative charge than the outside

What is the typical resting potential of a neuron?

-70 mV

What does it mean when the membrane depolarized?

The potential becomes less negative than the resting potential (through depolarization) resulting in excitatory reaction that increases the likelihood that the neuron will generate a transmittable electrical signal

What happens when the membrane is hyperpolarized?

The potential becomes more negative than the resting potential (hypopolarization), inhibiting and decreasing the ability of the neuron to generate an electrical signal

What is action potential?

An positive ions enter through ion channels the charge inside of the cell changes to a positive charge, this triggers a signal to travel down the nerve’s axon

The response of an action potential is…

All-or-nothing, if the electrical change does not reach a certain amount the action potential will not be triggered

Ion channels are specific and open for…

Specific ions ex: a Na+ ion channel will only let Na+ through even though other ions are present

What is the threshold value that must be met or passed for the action potential to be triggered?

-55 mV

What is the hyperpolarization that occurs after the action potential is triggered?

To correct the large change in charges the cell will begin the hyperpolarization process to return the cell’s interior to its resting state, it works too well resulting in a more negative charge on the inside of the cell than its normal resting state

What are the stages or steps of the triggering of the action potential? (For example a sodium ion channel and potassium ion channel)

The cell is in its negative resting stat until a Na+ ion channel opens and lets in the positive ions which results in the inside of the cell becoming more positive

The K+ ions within the cell are pushed out through their respective K+ ion channels

The Na+ ion channel letting in positive Na ions becomes refractory and prevents more Na+ ions from entering the cell

K+ ions continue to leave the cell through their respective ion channel to slowly return the cell to its resting state

The K+ ion channel that was allowing K+ ions to leave the cell close and the Na+ ion channel resets

The extra K+ outside the cell diffuses away

What is the sequence of events following the stimulation of a sensory receptor?

1. A receptor potential is generated by mechanical change (pressure) of the end-receptor

2. An action potential propagates along the axon of the sensory neuron from the periphery to the spinal cord

3. Release of chemical transmitters at the synapse with the second neuron generates a synaptic potential in the second neuron

4. Of sufficient stimuli are received by the second neuron, an action potential is generated in this neuron

5. The action potential propagates along the axon

6. When the action potential reaches the axon terminal, a chemical transmitters is released from the terminal

7. The transmitter then binds to receptors on the membrane of the third neuron, and opening of membrane channels generates synaptic potentials

What are the steps involved in information being sent across synapse?

1. Action potential arrives at axon terminal

2. Voltage-gated CA2+ channels open

3. Ca2+ enters the presynaptic neuron

4. Ca2+ signals to neurotransmitter vesicles

5. Vesicles move to the membrane and dock

6. Neurotransmitters released via exocytosis

7. Neurotransmitters bind to receptors

8. Signal initiated in postsynaptic cell

What is exocytosis?

The membrane of the neurotransmitter is removed so that its contents can be released

What leads to the change in graded potential?

Once the neurotransmitter binds to its receptors

What are the 6 vital functions of glial cells?

Direct neurons

Produce myelin

Remove debris

Gather neurotransmitters

Provide nourishment

Form the blood brain barrier

What do astrocytes do?

Provides support for neurons of the central nervous system

Provides nutrients and other substances (neurotransmitter, growth factors, etc.)

Regulates chemical composition of extra cellular fluid (ion concentrations)

Blood flow in the brain (vasodilation/constriction)

What are the two main subtypes of glial cells?

Microglia

Macroglia

What are microglia?

The smallest glial cells that protect the brain from invading microorganisms

What are phagocytes (phagocytosis)?

The process of cells engulfing and digesting other cells or debris caused by cellular degeneration

When are microglia activated?

During nervous system development and following injury, infection, and/or disease

In conditions such as Alzheimer’s, Parkinson’s, MS, and ALS the microglia…

Become overly active and leads to neural damage

What are Macroglia?

The larger support neurons such as astrocytes, oligodendrocytes, and Schwann cells

How do microglia cells help during nervous system development?

Many neurons that do not make strong synapses die, and as neural cells die the microglia are lured to them due to the secretion of protein, the microglia the clean up and remove the dying cells

What are oligodendrocytes?

Cells that form myelin sheaths in the CNS

How much myelin sheaths are made from oligodendrocytes?

15-30 sheaths per cell

What are Schwann cells?

Cells that form myelin sheaths in the PNS

How much myelin is made by Schwann cells?

1 sheath per cell as the Schwann cell itself wraps around the axon