Biological psychology

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How the Nervous System Works: Cells and Neurotransmitters

Overview of the Nervous System

The nervous system plays a crucial role in coordinating all bodily functions, from movement to sensation and cognition. Neurons and neurotransmitters are the primary components responsible for communication within the nervous system.

Neurons: Specialized cells that transmit information throughout the body.
Neurotransmitters: Chemical messengers that facilitate communication between neurons.

Neural Communication

Psychologists focus on neurons, which are responsible for sending and receiving messages throughout the body. Neurons are highly specialized for communication and are the fundamental units of the nervous system.

Purpose: Receive input, process information, and transmit signals to other neurons or effectors.
Specialization: Neurons are specialized for rapid and efficient communication.

Parts of a Neuron

Cell Body (Soma): Contains the nucleus and genetic material; synthesizes proteins and chemicals for neuron function.
Dendrites: Branch-like structures that receive information from other neurons.
Axon: Long, tail-like structure that transmits electrical impulses away from the cell body.
Axon Terminal: End of the axon; contains synaptic vesicles filled with neurotransmitters.
Synapse: The gap between neurons where neurotransmitters are released to transmit signals.

Types of Neurons

Sensory Neurons: Carry information from sensory receptors to the brain and spinal cord.
Motor Neurons: Transmit signals from the brain and spinal cord to muscles and glands.
Interneurons: Connect sensory and motor neurons within the central nervous system.

Glial Cells

Glial cells provide support, nourishment, and protection for neurons. They also play a role in insulating neurons and facilitating neural communication.

Act as the 'glue' of the nervous system.
Form myelin sheaths to insulate axons and speed up neural impulses.
Remove waste and synchronize neural activity.
Damage to glial cells can lead to neurological diseases (e.g., multiple sclerosis).

Neurons' Electrical System

Action Potential

Neural activity is based on changes in the concentration of charged atoms (ions) inside and outside the neuron. The action potential is the electrical impulse that travels down the axon.

Resting Potential: The neuron is negatively charged inside relative to outside.
Action Potential: Triggered when the neuron is stimulated, causing a rapid change in charge.
Refractory Period: The neuron must reset before it can fire again.

Equation:

Step-by-Step: Action Potential

Neuron at rest: Negative charge inside, positive outside.
Stimulation: Sodium channels open, sodium ions rush in, depolarizing the membrane.
Action potential travels down the axon.
Potassium channels open, potassium flows out, repolarizing the membrane.
Returns to resting potential (refractory period).

Neurotransmitters and Hormones

Electrochemical Communication

When an action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synapse. These chemicals bind to receptors on the next neuron, transmitting the signal.

Excitatory Neurotransmitters: Increase the likelihood of the next neuron firing.
Inhibitory Neurotransmitters: Decrease the likelihood of the next neuron firing.

Types of Neurotransmitters

Acetylcholine: Involved in muscle movement, attention, memory, and sleep.
Dopamine: Influences movement, motivation, reward, and emotion.
Serotonin: Regulates mood, appetite, and sleep.
GABA (gamma-aminobutyric acid): Main inhibitory neurotransmitter; reduces neural activity.
Glutamate: Main excitatory neurotransmitter; involved in learning and memory.
Norepinephrine: Involved in arousal and alertness.

Neurotransmitter Release and Reuptake

After neurotransmitters are released, they bind to receptors and then are either broken down, reabsorbed (reuptake), or drift away.
Reuptake inhibitors (e.g., SSRIs) block the reabsorption of neurotransmitters, increasing their availability.

Neurotransmitter Agonists and Antagonists

Agonists: Enhance the effect of neurotransmitters (e.g., cocaine is a dopamine agonist).
Antagonists: Block the effect of neurotransmitters (e.g., beta blockers block norepinephrine).

Examples

Alcohol increases GABA and decreases glutamate, leading to sedation.
Anti-anxiety medications often enhance GABA activity.

The Brain: Structure and Function

Major Divisions of the Brain

Hindbrain: Oldest part; controls basic life functions (e.g., heartbeat, breathing).
Midbrain: Connects sensory information between brain, eyes, and ears.
Forebrain: Manages complex cognitive activities; includes the cerebral cortex and limbic system.

Hindbrain Components

Medulla: Controls heartbeat, breathing, blood pressure.
Pons: Sleep and arousal.
Cerebellum: Motor coordination.
Reticular Activating System: Regulates arousal and attention.

Forebrain Components

Cerebral Cortex: Higher mental processes (reasoning, perception, language).
Thalamus: Sensory relay station.
Hypothalamus: Regulates hunger, thirst, temperature, and hormones.
Limbic System: Emotion and memory (includes amygdala and hippocampus).

Cerebral Cortex

Divided into two hemispheres, connected by the corpus callosum.
Each hemisphere has four lobes: frontal, parietal, temporal, occipital.

Functions of the Lobes

Frontal Lobe: Planning, decision-making, movement, language (Broca's area).
Parietal Lobe: Sensory processing, spatial orientation.
Temporal Lobe: Hearing, language comprehension (Wernicke's area), memory.
Occipital Lobe: Visual processing.

Hemispheric Specialization

Left Hemisphere: Language, fine motor skills, logic.
Right Hemisphere: Spatial abilities, facial recognition, simple language skills.

Neural Plasticity and Intergenerational Trauma

Neural Plasticity

The brain's ability to adapt and change in response to experience. Includes myelination (insulation of axons), pruning (removal of unused connections), and reorganization after injury.

Plasticity decreases with age but remains possible throughout life.
Example: London taxi drivers have larger hippocampi due to extensive spatial navigation.

Intergenerational Trauma

Trauma can be passed down through both environmental and genetic factors, making future generations more vulnerable to stress and mental health issues.

Observed in children of Holocaust survivors, war veterans, and those exposed to significant trauma.
PTSD can be associated with changes in brain structure and function.

Summary Table: Major Neurotransmitters

Neurotransmitter	Main Functions	Associated Disorders
Acetylcholine	Muscle movement, attention, memory, sleep	Alzheimer's disease (deficiency)
Dopamine	Movement, motivation, reward, emotion	Parkinson's disease (deficiency), schizophrenia (excess)
Serotonin	Mood, appetite, sleep	Depression (deficiency)
GABA	Main inhibitory neurotransmitter	Anxiety, seizures (deficiency)
Glutamate	Main excitatory neurotransmitter, learning, memory	Excitotoxicity (excess)
Norepinephrine	Arousal, alertness	Depression (deficiency)

Key Terms

Neuron: Nerve cell; basic unit of the nervous system.
Neurotransmitter: Chemical messenger between neurons.
Action Potential: Electrical impulse traveling down the axon.
Synapse: Gap between neurons where neurotransmitters are released.
Glial Cell: Support cell in the nervous system.
Plasticity: Brain's ability to change and adapt.