Biological Psychology: Neurons, Glial Cells, and Neural Communication

Topic 3: Biological Psychology

Neurons: The Brain’s Communicators

Neurons are the fundamental units of the nervous system, specialized for communication. They transmit information using electrical signals known as action potentials.

• Nerve cells are specialized for communication with each other.

• Neurons are the building blocks of the nervous system.

• They transmit information in the form of electrical signals (action potentials).

• Neurons trigger each other with neurotransmitters such as dopamine.

Neural Components

Neurons have distinct structural components that enable their function.

• Cell body (soma): Contains the nucleus and builds new cell components.

• Dendrites: Branchlike extensions that receive information from other neurons.

• Axon: Long tail-like structure that transmits information away from the cell body.

• Axon terminal: Knob at the end of the axon containing synaptic vesicles filled with neurotransmitters.

• Synapse: The space between neurons where neurotransmitters are released and received.

• Myelin sheath: Fatty insulation from glial cells that makes signal transmission faster and smoother.

Glial Cells

Glial cells are non-neuronal cells that provide support and protection for neurons.

• Glial means "glue"; these cells are plentiful in the brain.

• They play a support role in psychological functioning, such as making myelin.

• Glial cells feed and protect neurons, acting as bodyguards.

• Myelin sheath: Fatty insulation from glial cells surrounding the axon.

• Multiple sclerosis (MS): Loss of myelin causes erratic signals and impaired neural communication.

How Does a Neuron Fire?

Neural firing involves a sequence of electrical and chemical events.

1. Resting potential: The neuron is polarized (negative inside, positive outside). The membrane is selectively permeable, preventing sodium ions (Na+) from entering.

2. Action potential: A brief electrical charge travels down the axon, transmitting neural messages. When stimulated, the neuron depolarizes (gates open, Na+ rushes in).

   • All-or-none law: The neuron either fires completely or not at all.

   • Frequency = intensity: The strength of the stimulus is encoded by the frequency of action potentials.

3. Repolarization: Potassium ions (K+) flow out, repolarizing the axon.

4. Return to resting potential: The neuron restores its original state.

5. Refractory period: A brief period during which the neuron cannot fire again, allowing recovery and recharge.

   • Analogy: Like flushing a toilet, you must wait before it can be flushed again.

Action Potential Equation

The change in membrane potential during an action potential can be described by the Nernst equation:

$E = \frac{RT}{zF} \ln \left( \frac{[\text{ion outside}]}{[\text{ion inside}]} \right)$

Electrochemical Communication

Neurons communicate via both electrical and chemical signals.

• When an electrical signal reaches the end of an axon, it triggers the release of neurotransmitters into the synapse.

• Neurotransmitters bind to receptors on the receiving neuron's dendrites, transmitting the signal.

• Excitatory messages: Increase the likelihood that a neuron will fire.

• Inhibitory messages: Decrease the likelihood that a neuron will fire.

Summary Table: Neural Components

Component	Function
Cell body (soma)	Contains nucleus, builds cell components
Dendrites	Receive information
Axon	Transmits information
Axon terminal	Releases neurotransmitters
Myelin sheath	Insulates axon, speeds transmission
Synapse	Site of neurotransmitter release

Example: Multiple Sclerosis

In multiple sclerosis, the immune system attacks the myelin sheath, leading to erratic neural signals and impaired movement or sensation.

Additional info:

• Neurotransmitters such as dopamine, serotonin, and acetylcholine play key roles in mood, movement, and cognition.

• Glial cells are involved in psychological functioning beyond support, including modulating synaptic activity and responding to injury.