Chapter 3

Neuron

The basic functional unit of the nervous system, neurons are specialized cells that transmit information throughout the body via electrical and chemical signals, playing a crucial role in processing and communicating sensory and motor information.

Dendrites

Branch-like extensions of neurons that receive incoming signals from other neurons or sensory cells, playing a vital role in determining whether the neuron will generate an electrical response.

Axon

A long, slender projection of a neuron that conducts electrical impulses away from the cell body and towards other neurons or muscles, often covered by a myelin sheath to enhance transmission speed.

Glial Cells

Non-neuronal cells in the nervous system that provide structural support, nourishment, and protection to neurons while also aiding in the maintenance of homeostasis and forming myelin.

Myelin Sheath

A fatty layer encasing axons that significantly increases the speed at which electrical impulses are transmitted along the neuron, facilitating efficient communication within the nervous system.

Synapse

The specialized junction between two neurons, where the transmission of signals occurs through the release of neurotransmitters from the presynaptic neuron to bind with receptors on the postsynaptic neuron.

Sensory Neurons

A type of neuron responsible for transmitting sensory information from the peripheral nervous system to the central nervous system, allowing us to perceive our environment.

Motor Neurons

Neurons that carry signals from the central nervous system to muscles and glands, enabling actions and responses to stimuli, such as movement.

Action Potential

A rapid and temporary fluctuation in the electrical potential of a neuron’s membrane that occurs when a stimulus reaches a certain threshold, leading to the transmission of an electrical signal along the axon.

Resting Potential

The stable, negative charge (-70mV) that exists across the neuronal membrane when the neuron is not actively transmitting a signal, maintained by ion channels and pumps.

Reuptake

The process by which neurotransmitters are reabsorbed into the presynaptic neuron after they have activated receptors on the postsynaptic neuron, effectively terminating the neurotransmitter's action.

Transduction

The process through which sensory receptors convert physical energy (such as light, sound, or pressure) from stimuli into electrical signals that can be interpreted by the nervous system.

Absolute Threshold

The minimal level of stimulus intensity that is required for a sensory system to detect a stimulus 50% of the time, establishing sensitivity baselines for sensory modalities.

Just Noticeable Difference (JND)

The smallest difference in stimulus intensity that a person can detect at least 50% of the time, which is governed by the principle that differences are proportionate to the initial stimulus intensity.

Weber's Law

The principle stating that the just noticeable difference between stimuli is a constant ratio of the original stimulus intensity, implying that larger stimuli require larger differences to notice a change.

Signal Detection Theory

A theoretical framework that explains how individuals discern between signal presence and noise in uncertain conditions, accounting for the influence of motivation and expectations.

Sensory Adaptation

A phenomenon where prolonged exposure to a stimulus results in a diminished sensitivity, allowing individuals to focus on changes in their environment rather than constant stimuli.

Receptors

Molecular structures located on the surface of neurons that bind to specific neurotransmitters, initiating a response in the receiving neuron.

Action Potentials vs. Graded Potentials

Action potentials are all-or-nothing responses that occur when a neuron fires, while graded potentials are smaller, variable changes in membrane potential that can summate to trigger an action potential.

Nervous System

The complex network of neurons and glial cells that coordinates the body's actions and sensory information processing, integral to maintaining homeostasis and responding to stimuli.

Central Nervous System (CNS)

Comprising the brain and spinal cord, the CNS is responsible for processing sensory information, integrating data, and coordinating responses.

Peripheral Nervous System (PNS)

The part of the nervous system outside the CNS that connects it to the limbs and organs, encompassing both sensory and motor neurons.

Excitatory Neurotransmitters

Chemicals that increase the likelihood of the firing of action potentials in receiving neurons by depolarizing their membranes.

Inhibitory Neurotransmitters

Chemicals that decrease the likelihood of action potentials occurring in receiving neurons by hyperpolarizing their membranes.

Neuroplasticity

The remarkable ability of the brain to reorganize itself by forming new neural connections throughout life, influenced by experience, learning, and environmental changes.

Cerebral Cortex

The outermost layer of the brain, crucial for higher-order functions such as perception, cognition, reasoning, decision-making, and voluntary motor activity.

Somatic Nervous System

The component of the peripheral nervous system responsible for voluntary muscle movements and transmitting sensory information to the central nervous system.

Autonomic Nervous System

The division of the peripheral nervous system that manages involuntary bodily functions, including heart rate, respiration, and digestion.

Sympathetic Nervous System

The part of the autonomic nervous system that initiates the body's 'fight or flight' response, preparing the body to respond to perceived threats.

Parasympathetic Nervous System

The branch of the autonomic nervous system that conserves energy and promotes 'rest and digest' functions following stress responses.

Reflex Arc

The neural pathway that mediates reflex actions, consisting of a sensory neuron, an interneuron (in some cases), and a motor neuron, allowing for rapid responses to stimuli.

Brainstem

The structural base of the brain that regulates fundamental life functions such as breathing, heart rate, and blood pressure, acting as a communication center between the brain and spinal cord.

Limbic System

A complex set of brain structures that support functions such as emotion, memory, and motivation; it includes the hippocampus, amygdala, and other associated areas.