Neurons and Synaptic Transmission

This section explores Neurons and Synaptic Transmission for Psychology. Neurons are specialised cells in the nervous system responsible for transmitting information throughout the body. They play a key role in interpreting sensory data, coordinating motor functions, and facilitating complex processes like thought and emotion. There are three primary types of neurons in the body:

• Sensory Neurons
• Relay Neurons
• Motor Neurons

Additionally, the communication between neurons occurs through a process known as synaptic transmission, which involves neurotransmitters, as well as excitatory and inhibitory processes.

Types of Neurons: Structure and Function

Sensory Neurons

Function: Sensory neurons are responsible for carrying information from sensory receptors (like those in the skin, eyes, ears) towards the Central Nervous System (CNS).

Structure: Sensory neurons have a unique structure with a long dendrite and a short axon. This design allows them to receive sensory information quickly and efficiently pass it to the CNS for processing.

Role: These neurons are crucial for our ability to perceive environmental stimuli (e.g., pain, temperature, sound) and respond accordingly. When they detect a stimulus, they generate an electrical impulse that travels to the brain or spinal cord for processing.

Relay Neurons (Interneurons)

Function: Relay neurons act as connectors, facilitating communication between sensory and motor neurons within the CNS. They do not have direct connections to muscles or sensory receptors.

Structure: Relay neurons are often found entirely within the CNS, with short dendrites and either short or long axons, depending on their role and location.

Role: These neurons are vital for processing and interpreting sensory information within the CNS and play a key role in reflexes and higher-order functions, such as decision-making and learning.

Motor Neurons

Function: Motor neurons transmit commands from the CNS to effectors, such as muscles and glands, to generate a response or action.

Structure: Motor neurons have short dendrites and a long axon that extends from the CNS to muscles or glands.

Role: Motor neurons enable voluntary and involuntary movements by causing muscles to contract or glands to secrete. For example, if a person touches a hot surface, motor neurons will convey signals to the arm muscles to pull away from the heat source.

Synaptic Transmission

Synaptic transmission is the process by which information is passed from one neuron to another across a small gap known as the synapse. Neurons communicate via electrochemical signals, and this communication occurs at the synapse, where neurotransmitters are released and influence the receiving (postsynaptic) neuron.

Key Steps in Synaptic Transmission

Action Potential Arrival: When an electrical impulse (action potential) reaches the end of the presynaptic neuron (the sending neuron), it triggers the release of neurotransmitters.

Neurotransmitter Release: Neurotransmitters are stored in small sacs called vesicles at the end of the presynaptic neuron. Upon the arrival of the action potential, these vesicles fuse with the membrane of the presynaptic neuron, releasing the neurotransmitters into the synaptic cleft (the gap between neurons).

Binding to Receptors: The neurotransmitters diffuse across the synaptic cleft and bind to specific receptor sites on the postsynaptic neuron (the receiving neuron). This binding causes changes in the postsynaptic neuron, potentially leading to an action potential if the signal is strong enough.

Excitatory or Inhibitory Effects: Once the neurotransmitters bind to receptors, they have either an excitatory or inhibitory effect on the postsynaptic neuron.

Excitatory Neurotransmitters: These increase the likelihood that the postsynaptic neuron will fire an action potential. For example, glutamate is a common excitatory neurotransmitter that depolarises the postsynaptic cell, making it more likely to respond.

Inhibitory Neurotransmitters: These decrease the likelihood that the postsynaptic neuron will fire. GABA (gamma-aminobutyric acid) is a common inhibitory neurotransmitter that hyperpolarises the postsynaptic neuron, making it less likely to fire.

Termination of the Signal: After the neurotransmitters have exerted their effect, they are either broken down by enzymes, reabsorbed into the presynaptic neuron through a process called reuptake, or diffused away from the synapse. This ends the signal and resets the synapse for the next transmission.

Neurotransmitters, Excitation, and Inhibition

Neurotransmitters are chemical messengers that influence whether a neuron will generate an action potential.

Excitation occurs when a neurotransmitter, such as glutamate, binds to the postsynaptic neuron and makes it more likely to fire.

Inhibition occurs when a neurotransmitter, like GABA, binds to the postsynaptic neuron and makes it less likely to fire.

The balance between excitatory and inhibitory signals is crucial for normal brain function. An imbalance may lead to disorders such as anxiety, depression, or epilepsy.

Summary

Neurons:

• Sensory neurons transmit sensory information to the CNS.
• Relay neurons facilitate communication within the CNS.
• Motor neurons carry signals from the CNS to muscles and glands.

Synaptic Transmission:

• An action potential triggers the release of neurotransmitters from the presynaptic neuron into the synaptic cleft.
• Neurotransmitters bind to receptors on the postsynaptic neuron, causing excitatory or inhibitory effects.
• After the message is transmitted, neurotransmitters are broken down or reabsorbed, ending the signal.

Synaptic transmission enables the brain and body to communicate, coordinating responses and regulating both conscious and unconscious processes.