Neurophysiology

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

Glia and neurons

Glia

Cells that support the activities of neurons

Macroglia types

• astrocytes

• Ependymal cells

• Oligodendrocytes

• Schwann cells

Neurons

Information processing and communication

What is one of the most important glial cell types and why?

Astrocytes because they have large amount of functions

Astrocytes functions

• tentacles help form blood brain barrier

• Connect to neurons to provide nourishment and remove toxins from neurons back into blood

Ependymal cells

Have fine cilia that move the cerebrospinal fluid

Where are Ependymal cells located?

Line the ventricles and the central canal of the spinal cord

Oligodendroctyes

Responsible for forming myelin

Myelin

A fatty sheath that surrounds the axon and allows faster communication thru axon

Where are oligodendroctyes located?

In the central nervous system

One oligodendrocyte supports ____ axon(s)

Multiple

Schwann cells

Provide electrically insulating myelin in the peripheral nervous system

Schwann cells only form _____ segment of myelin

One

Neural membrane

Phospholipid bilayer membrane that acts as a wall to keep things out

Ion channels

Proteins embedded in neural membrane that act as a door and open under specific circumstances

Neural cytoskeleton

Inner skeleton that provides a way for things to get from one end to the other

The neurofilaments in the neural cytoskeleton are for?

Support

The microtubules in the neural cytoskeleton are for?

Transport

Tau

A microtubule associated protein that connects microtubules and holds them in place

Tau dysregulation in Alzheimer’s

• certain enzymes cause molecules of phosphate to be added to tau

• Disconnected tau forms neurofibrillary tangles

• No tau to hold microtubules in place —> microtubules separate and collapse

• Neural death

In the neural cell body, the DNA cannot leave the _____

Nucleus

What feature of neurons make them unique from other cells?

Dendrites

Dendrite function

Receive signals from adjacent neurons

Dendritic spines

Increase surface area and allow for more connections to be made

Hillock

• area where axons start

• Directly adjoined to cell body

Axon function

Transmit signals

T/F Myelin sheath is often but not always present in axons

True

Node of ranvier

Little gap in the myelin sheath

Axon terminal

• end of axon

• Site where message is sent to dendrite

Synapse

Where axon meets dendrite and message is sent across via chemicals

Inside the axon messages are ______, while outside the axon message are _____

Electric, chemical

Unipolar neuron

Single branch extending from the cell body

Bipolar neuron

Two branches extending from the neural cell body; one axon and one dendrite

Multipolar neuron

Many branches extending from the cell body, usually one axon and numerous dendrites

Purkinje cells are a type of?

Multipolar neuron

Sensory neurons

Specialized to receive information from outside world and from within our bodies

Motor neurons

Transmit commands from the CNS directly to muscles and glands

Interneurons

Act as bridges between sensory and motor systems

Action potential

Electricity that is generated in the hillock

Action potential is driven by different chemicals coming out that have positive or negative charges, known as

Ionic composition

Difference in ion concentrations inside vs outside the cell provides the neuron with ____ for electrical signaling

A source of energy

_____ and ____ levels are higher in the extracellular fluid outside the neuron

Sodium and chloride

_____ levels are higher in the intracellular fluid inside the neuron

Potassium

The inside of the neuron is resting at a _____ state

Slightly negative

Potassium stays inside of cell because of

Slightly negative charge inside the cell

What are the two different driving forces for sodium to go inside the neural cell?

• the inside of the cell is negative and sodium is positive

• There is much more sodium outside the cell

The resting potential of neurons was found by?

• using giant squid axon

• One prob in seawater, one prob in axon —> measured the difference in electricity between then

T/F The giant squid axon is visible with the naked eye

True

Diffusion

Molecules move from areas of high concentration to areas of low concentration along a concentration gradient

Electrostatic pressure

• like signed ions repel each other

• Opposite signed ones move toward each other

Proteins are ____ charged

Negatively

T/F Proteins are too big to fit through the ion channel

True

The resting neural membrane is permeable to

Potassium

Resting potential

-70 mV

In the resting state of the neuron, some potassium leaks out and some sodium leaks in

Action potential is a sudden surge of ____ that goes through the neuron

Positivity

Membrane potential must reach a threshold of about ____ to produce an action potential

-65 mV

At _____, voltage gated sodium ion channels open to allow sodium to flow into the neuron

-65 mV

t/f Voltage gated potassium ion channels open near the peak of the action potential to allow potassium to flow out of the cell

True

At the conclusion of an action potential the membrane

Hyperpolarizes

Hyperpolarized

• below -70mV

• An still fire an action potential at this point but it’s harder to go from -80 mV to -65 mV

T/F Action potentials are “all or none”

True

Action potential - sequence of events

1. At resting potential (-70mV), a little bit of sodium comes in and makes the cell more positive

2. When inside cell hits -65 mV sodium doors start to open, sodium rushes in and causes cell to jump to 40 mV

3. Now that cell is positive inside potassium leaves, which causes inside of cell to go back to negative in order to fire another action potential

Absolute refractory period

Nothing you can do to fire a 2nd action potential, its impossible

Relative refractory period

Can fire a second action potential but its hard because when K+ leaves the cell the mV can reach -80 to -85

Action potential propagation

The action potential reproduces itself down the length of the axon

Propagation in unmyelinated axon

• requires reproduction of the action potential at each successive atonal segment

• AP moves slowly from one door to another

Propagation in myelinated axons

• requires reproduction of the action potential in the nodes of ranvier

Saltatory conduction

The propagation of action potentials along myelinated axons from one node of ranvier to the next

Why is myelin important in the propagation of action potential

It allows the action potential to jump between uninsulated gaps in the myelin sheath

Multiple sclerosis is the body’s attack of the ____ system

Myelin

T/F The surge of electricity in AP is critical for to neurons to communicate

True

What are the two forms of synapses

Gap junctions and chemical synapses

Gap junctions

Incredibly thin; instant electrical communication; door to door

Most synapses are?

Chemical

Chemical synapses

Release of neurotransmitters that cause either excitatory or inhibitory messages to be shared

Neurotransmitters are related from the _____ cell in chemical synapses

Presynaptic

Neurotransmitters bind to _____ receptor cites in chemical synapses

Postsynaptic

____ is necessary to release neurotransmitters in chemical synapses

Action potential

Synaptic vesicles

Balls filled with neurotransmitters

Neurochemical release steps

1. When electricity reaches end of axon, the surge of electricity allows for special calcium ion channels to open that only open when electricity is nearby

2. Calcium enters cell and helps the synaptic vesicles relapse it’s neurotransmitters by disconnecting vesicles from microtubules

3. Vesicles are recycled: return to neuron cell body for repair or are refilled

Ionotropic receptors

Fast message sent by neurotransmitter; a change in electricity by allowing ions in and changing the potential of the next neuron

The first spike of electricity in an action potential comes from

Ionotropic receptors

What are the three ways that neurotransmitters are terminated

• reuptake

• Diffusion

• Deactivating enzymes

Reuptake

Reabsorption of NT to be used later

Diffusion (neurotransmitter termination)

NT leaves and tends to go into surrounding astrocytes

Deactivating enzymes (NT termination)

Break up and break down neurotransmitters

_____ receptors either send excitatory or inhibitory message to start or stop an action potential in next neuron

Ionotropic

T/F Excitatory messages dont have a long effect

True

T/F A single Ionotropic excitatory message is not enough to cause an action potential to be sent

True

What are the two ways that messages can be received in neural integration

Spatial summation and temporal summation

Spatial summation

Simultaneous stimulation of many presynaptic terminals

Temporal summation

Repeated stimulation of one presynaptic terminal

Metabotropic receptors

Slow messages sent by neurotransmitters that are more important

Metabotropic receptors use

G proteins

Metabotropic receptors guide

Tolerance and withdrawal