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NEURON & NEURAL FIRING: �NEURAL COMMUNICATION & THE ENDOCRINE SYSTEM

Module 1.3a

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Learning Targets

LT 1.3-1

LT 1.3-2

LT 1.3-3

LT 1.3-4

Describe neurons, and explain how they transmit information.

Explain how nerve cells communicate with other nerve cells.

Explain how neurotransmitters influence behavior, and explain how drugs and other chemicals affect neurotransmission.

Explain how the endocrine system transmits information and interacts with the nervous system.

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Cell Body & Nucleus

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The Cell Body

round, centrally located structure
contains DNA
controls protein manufacturing
directs metabolism
no role in neural signaling

Contains the cell’s nucleus

Graphic from Hockenbury slides

Key words: Cell body; soma; cell nucleus

Interesting facts:

The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.)

The relative inability to grow new neurons leads to two interesting questions:

Q1: How do brain tumors (cancer) occur?

A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons.

Q2: If a person cannot grow new neurons, how does the brain change in order to accommodate new learning?

A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.

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Dendrites

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Dendrites

RECEIVE info/signals from other neurons
Inputs/receptor sites may number in thousands
If enough inputs received it may cause the cell’s axon to generate an electrical impulse (action potential)

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Dendritic Growth

As you learn, new dendrites can grow, creating more connections to other neurons
New connections are basis for learning
People with higher education have more dendritic connections than a high school dropout.

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Axon

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Axon

SENDS an electrical message when signaled by the dendrites

Where all the action is
Action Potential takes place

electrical charge is sent down the axon.

One axon per cell, 2 distinct parts

tube-like structure
branches at end (axon terminals) that branch out to dendrites of other cells

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Myelin Sheath & Nodes of Ranvier

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Myelin Sheath

White fatty casing on axon
Acts as an electrical insulator
Not present on all cells
When present, increases the speed of neural signals down the axon allowing the action potential to “jump” to each Node of Ranvier - like a paved highway (see video below to compare mylenated axons vs. non-mylenated axons
If this degenerates (dirt road), you have multiple sclerosis and can’t control your muscles.

Graphic from Hockenbury slides

Key words: myelin sheath; action potentials; axon

Interesting facts:

- The myelin sheath is NOT a part of the axon. The myelin sheath is actually formed of glial cells (oligodendricytes and Schwann cells) that wrap around the axon.

- You may have often heard the brain referred to as either white matter or gray matter. The myelin sheath appears white in nature. Hence, the term white matter refers to areas of the brain that are myelinated. Gray matter refers to areas of the brain that are unmyelinated.

- When you accidentally cut yourself, you often visually notice that you've cut yourself before you actually feel any pain from the cut. The reason for this is that visual information uses myelinated axons; whereas, pain information uses unmyelinated axons.

- The loss of myelin is a significant factor in the disease multiple sclerosis (MS). When myelin is lost, the high-speed transmission of information is slowed down or blocked completely, which could lead the person with the inability to walk, write or speak.

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Axon Terminal or Buttons

Axon Terminals

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Axon Terminal or Buttons

End of Axon where the electrical impulse triggers synaptic transmission sending message to the dendrites of a receiving neuron.
Let’s Review with this Quick Video.

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One Direction

Communication

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Glial Cells

They are the janitors of the neuron.
Support cells that provide neurons with structural support and nutrition.
They also remove cell wastes and enhance the speed of the neuron