Nervous System, Cells, and Channels

Cell body

function: where the nucleus and other important organelles will be stored. Important for survival of the neurons. Also referred to as the soma.

What are the separations of nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS)

Describe the function of the nervous system

1. Respond to external stimuli

2. Respond to internal stimuli

3. Coordination

4. Higher functions

Dendrite

function: receive a signal, these signals can be in the form of an action potential, or even a stimuli. They are responsible for receiving that particular signal.

Axon hillock

function: most proximal part of the axon, where we generate an action potential, the action potential starts here.

Axon

function: transmits the action potential. We are going to take the action potential from axon hillock and transmit the action potential over the last structure, referred to as the synaptic knob.

Synaptic knobs

function: convert an electrical nerve impulse into a chemical signal and transmit it to a neighboring cell. Perform exocytosis.

Myelin sheath

• Function: insulation of the axon by covering it with lipids to have the AP travel quickly along the axon. A lot of neurons that are responsible for bringing information quickly have to be myelinated

• There are no channels underneath the myelin sheath

Node of ranvier

Function: regions that are not myelinated and they will regenerate the action potential

Gray Matter

Will not have a lot of myelination. The reason being is because there’s a lot of dendrites, lots of cell bodies, so there is no need to have myelination. 

White Matter

• A structure that has a lot of mylonation, myelinated axons within white matter. White matter is important for signal transmission. 

• Looks lighter in color, has a lot of adipose CT due to myelination

Nerve

• Collection of axons in the peripheral nervous system 

• In central nervous system, a collection of axons

Nucleus

A collection of neural cell bodies in the central nervous system

Ganglion

Collection of neural cell bodies in peripheral nervous system  

Nerve Plexus

A collection of nerves 

Sensory Neuron

Allow us to send sensory information from peripheral to central nervous system

Motor Neuron

Efferent neuron (to leave) effectors like muscles and glands. Take info from
CNS to outer periphery

What are the basic neuron types? Remember: structure determines function

• Bipolar (interneuron) - takes information from one cell to many different cells 

• Unipolar (sensory neuron)  - carry from skin to CNS

• Multipolar (motor neuron) - carry information from NS to a muscle, the ones we typically see

• Pyramidal cell 

What are the 3 shared functions of a neuron?

1. Receive signal

2. Transmit signal

3. To affect another cell

What are the functions of the brain?

1. localization of function

2. integration of function

3. contralateral function

Localization of function

1. Referring to location, where on the brain are we looking at. 

2. Different parts of brain will do different things

Integration of Function

1. Different parts of your brain need to talk to each other to do basic behavior 

2. The recruiters to coordinate

Contralateral Function

1. Sensory info from one side goes to the opposite side of the brain 

2. Left arm to right brain, right left to left brain, etc.

Which side of the brain has the language center?

the left side of the brain

What is the corpus callosum made of?

structure made of white matter

What is the function of the corpus callosum?

allows electrical signals, action potentials, to travel from one side of the brain to the other.

Why would someone want to sever their corpus callosum?

Epileptic seizures, occur on the left side of the brain, can be one reason to sever this region of the brain. We want to prevent that seizure traveling to the right side of the brain.

Explain what a severed corpus callosum would do to a person peripheral vision and language center?

Individuals with severed corpus callosum left and right brain will not communicate with one another, if they have an object on the left peripheral vision they will not be able to verbally communicate what that is due to the right side of the brain NOT having a language center, that is on the left side.

What function of the brain would the severed corpus callosum effect?

the contralateral function

List the types of glia cells

1. Oligodendrocytes

2. Schwann Cells 

3. Astrocyte

4. Microglia

How much of the cells are glia cells within our nervous system?

90% are glia cells with only less than 10% being neurons

Oligodendrocytes

• cell that looks like it has a few branches

• function: of forming myelin sheath around axons of neurons, found specfically in the central nervous system

Schwann Cells

1. Will only myelinate one region

2. They will myelinate axons in the periphereal system

Astrocyte

Function: cells that support neurons by nourishing them and forming the blood brain barrier (BBB). Capable of taking appropriate nutrients from capillary and taking it over to the neuron.

Why do we want the blood brain barrier?

the brain is an important organ, we need to ensure that things that are harmful to it wont be allowed to get to it. It allows us to filter things and making sure that the brain is only getting what is needs.

Can all medicines cross the blood brain barrier?

no, some medications cannot cross it therefore we need to find those that can for patients that need it.

Microglia

• Very small glia cells

• These are macrophages

What does it mean when we say an ion wants to follow their concentration gradient?

It means they’re going to go to the side with less concentration

What are the three shared functions of neurons?

1. Receive a signal 

   1. Keeping it general with type of signal 

2. Transmit a signal 

   1. Take signal and transport it from one cell to another point 

3. To affect another cell 

   1. To be able to ‘talk’ to another cell, gland, muscle or something else. 

What is the importance of diffusion?

allows movement across spaces, in cases of sodium and potassium to diffuse across the inter/extercellular spaces

Which side of the cell is more positively charged?

the outside of the cell

Which side of the cell is more negatively charged in comparison?

the inside of the cell is more negatively charged, relative to the outside of the cell

Where is sodium more concentrated?

Tends to be more concentrated on the outside of the cell than compared to the inside of the cell.

Where is potassium more concentrated?

Tends to be more concentrated on the inside of the cell than compared to outside of the cell

What does it mean when we say they are going against their concentration gradient?

it means they are going to the side where we have more of those ions.

What are the two protein channels called?

1. sodium channels

2. potassium channels

How do voltage gated channels activate?

they activate due to changes in voltage

Describe sodium channels

• They activate due to changes in voltage 

• Only allow sodium to pass through

• wave of depolarization occurs

Describe potassium channels

• Only allow potassium to pass through

• Potassium channels tend to open a little bit slower

• Wave of re-polarization occurs

Describe wave of depolarization

1. When we see sodium coming into the cell we call this the wave of depolarization

2. The axon flips in polarity, wave traveling together along the axon

Describe wave of repolarization

1. If potassium leaves the cell we get the original charge we started with, it will go back to being negatively charged. Because we are losing positively charged ions. 

2. The axon flips in polarity again

Describe sodium qualities in relation to our nervous system

• has a positive charge (+1 charge) 

• Na = natrium (latin)

• Tends to be more concentrated on the outside of the cell than compared to the inside of the cell. 

• Remember: There is more of this ion than there is potassium. In total, both the inside and the outside of the cell, there is more sodium than compared to potassium

Describe potassium qualities in relation to our nervous system

• Potassium is an ion that has a positive charge (+1 charge) 

• Kalium = potassium (latin)

• Tends to be more concentrated on the inside of the cell than compared to outside of the cell

How do we describe an action potential?

When we have both the wave of depolarization and repolarization occurring in tandem

Where does the action potential get to?

the synaptic knob

When we see sodium coming into the cell we call this the wave of —?

depolarization

The axon flips in polarity again, potassium leaves the cell this is called the wave of —?

Repolarization

What is the function of myelin sheath?

insulation of the axon by covering it with lipids to have the AP travel quickly along the axon

What is nodes of ranvier?

regions that are not myelinated and they will regenerate the action potential

Do all axons need to be myelinated?

no, some neurons are not myelinated that do not need to send signals very quickly. Ex; the neuron that is responsible for bringing in information on how much food you have within your stomach.

Will there be channels underneath the myelin sheath?

no

What is saltatory conduction?

if we have an myelinated axon, we propagate the action potential by this conduction, hopping from one node to another node, speeds up the action potential

What is continuous conduction?

if we have an unmyelinated axon, we have this conduction. no myelination will result in needing to hit every single voltage channel in order to get to the synaptic knob. It will take more time for this reason

Define synapse

the structure that allows us to communicate between a neuron to another cell

Function of presynaptic neuron

fires an action potential and reached the synaptic knob of that neuron

Function of synaptic vesicles

hold chemicals known as neurotransmitters, they are held by vesicles.

What are presynaptic vesicles

after the neuron fires, the AP will come down and need to stimulate the release certain chemicals. This is what these chemicals are.

Function of presynaptic vesicles

vessels to hold the chemicals we call neurotransmitters

Define exocytosis in relation to neurons

this is going to allow the vesicles to release their neurotransmitters into a space known as synaptic cleft

Function of a synaptic cleft

the neurotransmitters will diffuse across it and need to interact with certain channels that are found on the postsynaptic cell. We have to use specific types of channels.