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The Neuron

Structure and Function of Neurons

Neurons are the fundamental units of the nervous system, responsible for transmitting information throughout the body. Their structure enables efficient communication via electrical and chemical signals.

  • Cell body (soma): Contains the nucleus and organelles; integrates incoming signals.

  • Dendrites: Branch-like extensions that receive signals from other neurons.

  • Axon: Long projection that transmits electrical impulses away from the cell body.

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

  • Myelin sheath: Insulating layer that increases the speed of signal transmission.

Major types of neurons:

  1. Sensory neurons: Transmit sensory information to the CNS.

  2. Motor neurons: Carry signals from the CNS to muscles and glands.

  3. Interneurons: Connect neurons within the CNS.

Glial Cells

Glial cells support and protect neurons, playing roles in homeostasis, myelination, and immune defense.

  • Provide structural support

  • Form myelin

  • Remove waste

  • Regulate the environment around neurons

Neuronal Communication

How Neurons Communicate

Neurons communicate via electrical and chemical signals, primarily through action potentials and synapses.

  • Action potential: A rapid electrical signal that travels along the axon.

  • Synapse: The junction between two neurons where neurotransmitters are released.

Resting Potential

The resting potential is the difference in electrical charge across the neuron's membrane when it is not actively transmitting a signal.

  • Membrane potential: Difference in charge between inside and outside of the cell.

  • Resting potential: Typically around -70mV (inside is more negative than outside).

Formula:

Concentration Gradient

Ions move from areas of high concentration to low concentration, creating electrical gradients across the membrane.

  • Selective permeability of the membrane

  • Ions such as Na+, K+, Cl- move through channels

Action Potential

An action potential is an all-or-none electrical signal conducted along the axon to the synapse.

  • Occurs when membrane potential reaches threshold

  • Key terms: Refractory period (time after an action potential when a neuron cannot fire again)

Synaptic Transmission

Synapse Structure and Function

Synapses are specialized junctions where neurons communicate via neurotransmitters.

  • Pre-synaptic neuron: Releases neurotransmitter

  • Post-synaptic neuron: Receives neurotransmitter

  • Concentration of neurotransmitter regulated by auto-receptors and reuptake mechanisms

Neurotransmission

Chemical communication between neurons occurs when neurotransmitters cross the synaptic cleft and bind to receptors on the post-synaptic neuron.

EPSP & IPSP

Post-synaptic potentials determine whether a neuron will fire an action potential.

  • EPSP (Excitatory Post-Synaptic Potential): Depolarizes the membrane, increasing likelihood of firing.

  • IPSP (Inhibitory Post-Synaptic Potential): Hyperpolarizes the membrane, decreasing likelihood of firing.

Example: EPSP: From -70mV to -60mV; IPSP: From -70mV to -80mV

Post-Synaptic Potentials to Action Potentials

If the sum of EPSPs and IPSPs reaches threshold, the neuron will fire an action potential.

Neurotransmitters

Chemical Communication

Neurotransmitters are chemicals that transmit signals across synapses. Different neurotransmitters have specific functions and are found in particular regions of the brain.

Major Neurotransmitters

  • Glutamate: Main excitatory neurotransmitter; involved in learning and memory.

  • GABA (gamma-aminobutyric acid): Main inhibitory neurotransmitter; regulates anxiety and motor control.

  • Acetylcholine: Involved in muscle contraction and memory.

  • Dopamine: Associated with motivation, pleasure, and motor behavior.

  • Serotonin: Regulates mood, sleep, and arousal.

  • Endorphins: Act within pain pathways; reduce pain and elevate mood.

Drugs & Synaptic Transmission

Effects of Drugs on Neurotransmission

Drugs can impact synaptic transmission by influencing the concentration or activity of neurotransmitters in the synaptic cleft.

  • Agonists: Enhance neurotransmitter action.

  • Antagonists: Inhibit neurotransmitter action.

The Nervous System

Organization of the Nervous System

The nervous system is divided into central and peripheral components, each with specialized functions.

  • Central Nervous System (CNS): Brain and spinal cord; processes and integrates information.

  • Peripheral Nervous System (PNS): Connects CNS to the rest of the body; includes somatic and autonomic divisions.

Division

Main Components

Function

CNS

Brain, Spinal Cord

Integration and processing of information

PNS

Somatic, Autonomic

Connects CNS to limbs and organs

Somatic

Motor and sensory nerves

Voluntary movement

Autonomic

Sympathetic, Parasympathetic

Involuntary functions (e.g., heart rate, digestion)

The Brain

Forebrain

The forebrain is responsible for complex cognitive, emotional, sensory, and motor functions.

  • Cerebral cortex: Outer layer; involved in perception, emotion, movement, and thought.

  • Lobes:

    • Occipital: Visual processing

    • Temporal: Auditory processing, language

    • Parietal: Somatosensory information

    • Frontal: Abstract thinking, planning, movement

    • Insular: Taste, perception, compassion

  • Basal ganglia: Intentional movement

  • Limbic system: Emotion, motivation, memory (includes hippocampus, amygdala, thalamus)

  • Hippocampus: Memory formation

  • Amygdala: Emotional processing

  • Thalamus: Sensory relay

  • Hypothalamus: Regulates homeostasis

  • Pituitary gland: Hormone release

Midbrain and Hindbrain

  • Midbrain: Orientation and movement

  • Reticular formation: Arousal and sleep

  • Medulla: Heart rate, circulation, respiration

  • Cerebellum: Motor coordination, balance

  • Pons: Relays information, sleep and dreaming

Brain Lateralization

Right/Left Brained People?

Brain lateralization refers to the specialization of certain functions in either the left or right hemisphere.

  • Left hemisphere: Logical, analytical

  • Right hemisphere: Creative, intuitive

  • Most functions are not strictly lateralized

Corpus Callosum & Optic Chiasm

  • Corpus callosum: Connects the two hemispheres

  • Optic chiasm: Point where optic nerves cross

Genes and Heritability

Chromosomes and Genes

Genetic information is carried on chromosomes, which consist of DNA. Genes are segments of DNA that code for specific traits.

  • Chromosomes: 23 pairs in humans

  • Genes: Basic units of heredity

  • Genotype: Genetic makeup

  • Phenotype: Observable traits

Monogenic vs. Polygenic Inheritance

  • Monogenic: Trait determined by a single gene pair

  • Polygenic: Trait determined by multiple gene pairs

Heritability

Heritability is the extent to which genetic factors contribute to differences in a trait among individuals.

  • Formula:

  • Ranges from 0 to 1

  • Heritability applies to populations, not individuals

Nature vs. Nurture

The nature vs. nurture debate concerns the relative contributions of genetics (nature) and environment (nurture) to behavior and traits.

  • Genes and environment interact to shape development

Gene x Environment Interactions

Phenotype is determined by the interaction between genes and environment.

  • Some genetic effects only appear in specific environments

Epigenetics

Epigenetics refers to heritable changes in gene expression that do not involve changes to the DNA sequence.

  • Environmental factors can influence gene expression

Additional info:

  • Some content inferred for completeness, such as definitions and examples of neurotransmitters and brain regions.

  • Tables and formulas have been expanded for clarity and academic context.

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