Biological Psychology: Neurons, Neurotransmission, and Brain Structure

Biological Psychology

Neurons: The Brain's Communicators

Neurons are specialized nerve cells responsible for communication within the nervous system. They are the fundamental building blocks of the nervous system and transmit information via electrical signals known as action potentials.

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

• Dendrites: Branch-like structures that receive information from other neurons.

• Axon: Long fiber that transmits information away from the cell body.

• Axon terminals: End of the axon where neurotransmitters are released.

• Synapse: Junction between neurons where neurotransmitters are released to communicate with other neurons.

Glial cells: Support neurons, provide nutrients, and protect them. "Glial" means glue.

Myelin Sheath and Multiple Sclerosis

The myelin sheath is a fatty layer that insulates axons, speeding up neural transmission. Loss of myelin, as seen in multiple sclerosis (MS), causes erratic signals and impaired neural communication.

How Does a Neuron Fire?

An electrical impulse called the action potential enables neurons to communicate. The process involves several steps:

1. Resting potential: The neuron is polarized (negative inside, positive outside). Sodium ions (Na+) cannot pass through the membrane due to selective permeability.

2. Action potential: A brief electrical charge travels down the axon, transmitting neural messages.

3. Repolarization: Potassium ions (K+) flow out, restoring the resting state.

4. Return to resting potential: The neuron resets its electrical state.

5. Refractory period: A short period during which the neuron cannot fire again, regardless of stimulation.

Electrochemical Communication

When an action potential reaches the end of an axon, it triggers the release of neurotransmitters into the synapse. These chemical messengers bind to receptors on the receiving neuron's dendrites, transmitting the signal.

• Excitatory neurotransmitters: Increase the likelihood that the neuron will fire.

• Inhibitory neurotransmitters: Decrease the likelihood that the neuron will fire.

Neurotransmission: Fate of Neurotransmitters

After neurotransmitters are released:

• Release: Action potential triggers neurotransmitter release into the synaptic cleft.

• Binding: Neurotransmitters bind to receptors on the postsynaptic neuron (lock and key mechanism).

• Reuptake: Excess neurotransmitters are removed by drifting away, being broken down, or reabsorbed. Reuptake involves neurotransmitters being taken back into the presynaptic neuron for recycling. Some drugs (e.g., cocaine) block reuptake, prolonging neurotransmitter effects.

Major Neurotransmitters

• Glutamate: Most common excitatory neurotransmitter in the CNS. Associated with learning and memory. Excessive glutamate is toxic and may contribute to schizophrenia and other mental disorders.

• GABA (gamma-aminobutyric acid): Main inhibitory neurotransmitter. Dampens neural activity, leading to less brain activity.

• Acetylcholine: Involved in arousal, selective attention, memory, and sleep. Anticholinergic drugs (e.g., Benadryl) can increase risk of dementia.

• Dopamine: Associated with pleasure, reward, voluntary movement, and attention. Deficits linked to Parkinson's disease; excess linked to schizophrenia.

• Serotonin: Made from tryptophan. Found in brain, gut, and blood platelets. Regulates mood, sleep-wake cycles, appetite, cognition, and pain perception. Low levels associated with depression and anxiety.

Agonists and Antagonists

• Agonists: Substances that enhance or mimic neurotransmitter effects. They may increase neurotransmitter release, block reuptake, or directly bind to receptors. Example: Nicotine is an acetylcholine agonist; Xanax is a GABA agonist.

• Antagonists: Substances that inhibit neurotransmitter effects. They block neurotransmitter release, break down neurotransmitters, or bind to receptors to prevent activation. Example: Botox blocks acetylcholine, causing muscle paralysis.

The Nervous System: An Overview

• Neurons are the building blocks; action potentials travel down axons.

• Glial cells support, nourish, and protect neurons.

• Neurons meet at synapses and communicate via neurotransmission.

The Brain: Structure and Function

• Major divisions: Forebrain, midbrain, hindbrain.

• Cerebral cortex: Outer layer, divided into four major lobes. Handles higher-order thinking and voluntary action.

• Subcortical structures: Located beneath the cortex (e.g., limbic system).

Neural Plasticity

The brain is adaptable and can change:

• Myelination: Increases speed and efficiency of neural transmission.

• Pruning: Removal of unnecessary synaptic connections to improve efficiency.

• Plasticity: The ability of the brain to reorganize and adapt; decreases with age.

Hindbrain

The hindbrain is the primitive part of the brain, controlling basic functions such as eating and sleeping.

• Medulla: Controls vital functions (heartbeat, breathing, swallowing).

• Pons: Involved in sleep and arousal.

• Cerebellum: Coordinates motor movements.

• Reticular Activating System: Key in arousal and alertness.

Midbrain and Forebrain

• Midbrain: Controls movement and transmits sensory information (seeing, hearing).

• Forebrain: Responsible for complex behaviors, emotions, and higher mental processes.

Cerebral Cortex

• Higher mental processes: Sense of self, reasoning, planning.

• Consists of two cerebral hemispheres (left and right), connected by the corpus callosum.

• Contralateral control: Each hemisphere controls the opposite side of the body.

Cerebral Cortex Lobes

• Frontal lobe: Planning, decision making, voluntary movement.

• Parietal lobe: Sensation (somatosensory).

• Temporal lobe: Auditory processing.

• Occipital lobe: Visual processing.

Lateralization

Cognitive functions may rely more on one hemisphere than the other.

• Left hemisphere: Language skills, speech comprehension, production.

• Right hemisphere: Spatial abilities, face recognition, music.

Split-Brain Surgery

A procedure that severs the corpus callosum to reduce the spread of epileptic seizures. This can affect communication between the hemispheres.

Frontal Lobes: Planning and Personality

The frontal lobes are crucial for planning, decision making, and personality. Damage to this area (e.g., Phineas Gage case) can result in significant changes in behavior and personality.

Table: Major Neurotransmitters and Their Functions

Neurotransmitter	Main Function	Associated Disorders
Glutamate	Excitatory; learning and memory	Schizophrenia, neurotoxicity
GABA	Inhibitory; reduces neural activity	Anxiety, epilepsy
Acetylcholine	Movement, attention, memory	Alzheimer's disease
Dopamine	Pleasure, reward, movement	Parkinson's, schizophrenia
Serotonin	Mood, sleep, appetite	Depression, anxiety

Table: Brain Lobes and Functions

Lobe	Main Function
Frontal	Planning, decision making, movement
Parietal	Sensation, spatial awareness
Temporal	Auditory processing, memory
Occipital	Vision

Example: Phineas Gage

Phineas Gage suffered a traumatic brain injury in Vermont when a tamping iron destroyed much of his left frontal lobe, resulting in dramatic changes to his personality and behavior. This case illustrates the role of the frontal lobes in personality and executive function.

Additional info:

• Neural plasticity is essential for learning and recovery from brain injury.

• Agonists and antagonists are important in pharmacology and the treatment of neurological and psychiatric disorders.