SHS 280 Exam 2

Neurons are the

Basic information processing unit of the nervous system

There are 15-20 billion neurons in the central nervous system making trillions of connections

Cell body

Neurons are cells and the cell body has the same structures found in other types of cells

Dendrites

Where most signals are received

They contain receptors that receive the neurotransmitter (chemical signal) sent by nearby neurons

They can have very simple or very complex morphologies

Dendrites allow for

Greater integration of signals from multiple neurons

Signals can be received other places

Cell body

Axons

Axons

Axons are responsible for sending signals to other neurons

Action potential (Axons)

Once a strong enough electrical signal reaches the axon it continues at full strength to the end of the axon

This all-or-nothing signal is called an action potential

Axon hillock

This is where action potentials are generated

Nodes of Ranvier

Where action potentials are regenerated

Neurotransmitters

Synapse

End of axon where neurotransmitter is released (presynaptic terminal)

Portion of dendrite where neurotransmitter is received (postsynaptic dendrite)

Space between the presynaptic terminal and postsynaptic dendrite (synaptic cleft)

Presynaptic terminal

End of axon where neurotransmitter is released

Postsynaptic dendrite

Portion of dendrite where neurotransmitter is received

Synaptic cleft

Space between the presynaptic terminal and postsynaptic dendrite

Neuronal signals are

electrical and chemical signals

Within the neuron the signal is transmitted from the

dendrites to the axons via an electrical signal

Signals are sent between neurons via a

chemical signal

Endogenous

originating or produced from within an organism, tissue, or cell

Neurotransmitters are __________ to the neuron

Endogenous

Neurotransmitters are Released by a neuron in response to _______

Stimulation

Affects the activity of the

Postsynaptic neuron

After the neurotransmitter is released, the neurotransmitter is

Removed or inactivated

When directly applied to the postsynaptic membrane, must have the

Same effect as when released by the presynaptic neuron

Excitatory Neurotransmitters

They can help cause the postsynaptic neuron to fire

Inhibitory Neurotransmitters

They can help prevent the postsynaptic neuron from firing

Glial cells play an important support role in the

Nervous system and impact neuronal functions

Glial cells

Form myelin sheaths around neurons

Myelin

Insulates and protects the nerve fibers

Myelin prevents the ____ of ______ and ______ __ the ______ _______ ____ the ____

Myelin prevents the loss of current and speeds up the signal passing down the axon

Not all axons in humans have

Myelin

Not all species have

Myelin (have wider axons to speed up the signals)

Neuron communication

A) Electric -> Chemical

Dendrite to Cell Body (Passive Flow)

When a chemical hits the dendrite, it creates a small electrical wave. This wave flows passively down the branch like water rippling across a pond until it collects in the main cell body.

Cell Body to Axon Hillock (The Funnel)

The cell body funnels down into a small, V-shaped neck called the axon hillock.

All the loose electrical ripples from different dendrites gather together here. The axon hillock acts like a calculator—it adds all the charges together. If the charge hits a specific threshold, it triggers a massive electrical spike (an action potential).

Axon Hillock to Axon (The Highway)

How they connect: The axon hillock is the physical root or starting gate of the long axon cable.

Passing the step: Once the spike is triggered at the hillock, it gets pushed down the axon. Because the axon is wrapped in insulated myelin, the electrical signal doesn't leak out; instead, it rapidly hops across the gaps (Nodes of Ranvier) like a stone skipping across water

Axon to Terminal Boutons (The End Zone)

How they connect: At its very end, the axon splits into tiny branches that tip into little bulbs called terminal boutons (knobs).

Passing the step: The electrical wave travels all the way down the axon cable until it slams into these terminal knobs.

Terminal Boutons ➔ Synaptic Cleft (The Chemical Release)

How they connect: The terminal boutons (axon tips) form the presynaptic membrane. This membrane contains specialized docking zones that hold storage bubbles (synaptic vesicles) right up against the edge of the open synaptic cleft.

Passing the step: The electrical action potential reaches the bouton and opens voltage-gated calcium channels. Calcium rushes into the cell, signaling the vesicles to fuse with the membrane (exocytosis). The vesicles pop open, dumping neurotransmitters directly into the cleft.

Synaptic Cleft ➔ Next Dendrite (The Chemical Bridge)

How they connect: The synaptic cleft is a narrow, 20-nanometer fluid-filled space. It completely separates the sending bouton from the receiving postsynaptic density (the receptor-rich surface of the next dendrite).

Passing the step: The neurotransmitters passively float (diffuse) across the fluid-filled gap. When they reach the other side, they bind to specific ligand-gated receptors on the dendrite. This binding opens ion channels, generating a new electrical wave in the next neuron.

Neurons are principally

Electrical systems

Ions

Signals coming in are _________ to _______ which passes to the ____ ____ and down the ____

This electrical current is mediated by

Signals coming in are converted to current which passes to the cell body and down the axon

Ions

Ions are _________ and ________ charged particles

Negatively and Positively

Main ions involved in neurons are

•Potassium (K+)

•Sodium (Na+)

•Calcium (Ca 2+)

•Chloride (Cl-)

Ion channels serve two purposes

Maintain the cell at a specific resting state membrane potential

Cause electrical changes in the cell to temporarily change the membrane potential

Types of ion channels

•Leak channels

•Voltage-gated

•Ligand-gated

•Mechanosensitive

•Light-gated

•Temperature-gated

Leak channels

letting things continuously leak in and out

Voltage-gated

It only opens when it senses a specific electrical charge (voltage change)

Ligand-gated

It requires a specific chemical "key" (a ligand like a neurotransmitter) to physically bind and unlock it.

Mechanosensitive

It opens when it senses physical pressure, stretch, or mechanical force

Light-gated

It only opens when light hits its sensors

Temperature-gated

It automatically pops open when things get too hot or cold.

Ion channels are generally ________ for only one __________ ___

Ion channels are generally selective for only one particular ion

Ion channels change

–They can open or close

–This controls the electrical charge of a segment of the neuron