THE_NERVOUS_SYSTEM

Nervous System

Nervous System

The network of nerve cells and fibers that transmits nerve impulses between parts of the body.

Neurons

Basic functional units of the nervous system that can generate action potentials and transmit signals to other cells.

Central Nervous System (CNS)

Consists of the brain and spinal cord, processes and coordinates information.

Peripheral Nervous System (PNS)

Includes all neural tissue outside the CNS, delivers sensory information to the CNS and carries motor commands to peripheral tissues.

Afferent Division

Carries sensory information from PNS receptors to the CNS.

Efferent Division

Carries motor commands from the CNS to PNS muscles and glands.

Autonomic Nervous System (ANS)

Controls subconscious actions, smooth muscle contractions, and glandular secretions.

Synapse

Area where a neuron communicates with another cell.

Axon

Long process that carries electrical signals or action potentials to a target.

Neurotransmitter

Chemical messengers released at the presynaptic membrane affecting receptors of the postsynaptic membrane.

Sensory Neurons

Neurons that are afferent in function, bringing input from receptors to the central nervous system (CNS). They have unipolar cell bodies located in the dorsal root ganglia outside the spinal cord. They monitor both the internal and external environments.

Motor Neurons

Neurons that carry signals with instructions to muscles and glands via efferent fibers (axons). They are divided into somatic motor neurons of the somatic nervous system (SNS) and visceral motor neurons of the autonomic nervous system (ANS).

Interneurons

Also known as association neurons, these neurons are found in the brain, spinal cord, and autonomic ganglia. They relay information between different areas of the CNS and are responsible for the distribution of sensory information and coordination of motor activity. They are involved in higher functions like memory, planning, and learning.

Astrocytes

Neuroglial cells in the CNS that provide structural support for neurons, maintain the blood-brain barrier, regulate the interstitial environment, and guide neuron development.

Oligodendrocytes

Cells in the CNS with processes that form myelin around axons, contributing to the white matter of the spinal cord and brain.

Microglia

The smallest glial cells in the CNS that act as phagocytes to remove debris, waste products, and pathogens.

Ependymal Cells

Cells lining the ventricles of the brain and the central canal of the spinal cord, assisting in the circulation of cerebrospinal fluid (CSF). Specialized ependymal cells in the choroid plexus aid in the production of CSF.

Schwann Cells

Neuroglial cells in the PNS that form myelin sheaths around axons, participating in the myelination of peripheral axons and the repair process after injury.

Nodes of Ranvier

Unmyelinated spaces between Schwann cells along axons in the PNS.

Satellite Cells

Also known as amphycytes, these cells surround neuron cell bodies in the PNS ganglia, regulating the environment around the neurons.

Regeneration of Peripheral Nerves

The process by which damaged nerves in the peripheral nervous system recover and regrow, involving Schwann cells and axon regeneration.

Wallerian Regeneration

The process of nerve regeneration in which the axon distal to the injury degenerates, Schwann cells proliferate, and a new myelin sheath is formed.

Membrane Potentials

Electrical signals produced by ion movements through membrane channels in cell membranes.

Resting Potential

The membrane potential of a cell at rest, resulting from the unequal distribution of ions inside and outside the cell.

Graded Potential

Temporary, localized changes in the resting potential caused by a stimulus. Local changes in membrane potential due to the opening of chemically gated channels, affecting a limited area around the stimulus. Changes in membrane potential that can be excitatory (EPSP) or inhibitory (IPSP) and depend on the intensity of the stimulus. Changes in membrane potential that vary in size, as opposed to action potentials which are all-or-none responses.

Action Potential

An electrical impulse produced by a graded potential that propagates along the axon to the synapse. A rapid change in the membrane potential of a cell, especially a neuron, that involves a depolarization followed by repolarization.

Sodium-Potassium Pump

Active transport process that moves 3 Na+ out of the cell and 2 K+ into the cell, helping maintain the resting membrane potential.

Resting Membrane Potential

The electrical charge difference across the plasma membrane of a cell when it is at rest, typically around -70 mV.

Electrochemical Gradient

The combined influence of the electrical gradient and the concentration gradient on the movement of ions across a membrane.

Potassium Ion

Positively charged potassium ion (K+) involved in generating the resting membrane potential.

Sodium Ion

Positively charged sodium ion (Na+) involved in the electrochemical gradients across the plasma membrane.

Membrane Channels

Proteins in the cell membrane that regulate the flow of ions, influencing the membrane potential.

Chemically Gated Channels

Membrane channels that open in response to specific molecules binding to receptors, such as neurotransmitters.

Voltage-Gated Channels

Membrane channels that respond to changes in membrane potential, opening or closing based on the electrical charge.Channels in the axolemma that open and close in response to changes in membrane potential, such as sodium and potassium channels.

Mechanically Gated Channels

Membrane channels that open in response to physical distortion of the membrane, such as touch or pressure.

Depolarization

Shift in membrane potential towards zero or a more positive value, often caused by the influx of sodium ions.

Hyperpolarizing

Change in membrane potential towards a more negative value, often due to the efflux of positive ions like potassium.

Repolarization

Return of the membrane potential to its resting state after a stimulus is removed.

Depolarization

Phase in which the membrane potential becomes less negative, reaches zero, and then becomes positive during an action potential.

Hyperpolarization

Phase in which the membrane potential becomes more negative than the resting membrane potential during an action potential.

Threshold

Level of membrane potential (-55 mV) that must be reached to initiate an action potential.

All-or-none Principle

Concept stating that an action potential either occurs completely if the threshold is reached or does not occur at all if the threshold is not reached.

Repolarization

Phase in which the membrane potential is restored to the resting state after depolarization during an action potential.

Axon Hillock

Area where the initial stimulus for an action potential must be large enough to reach the threshold level to initiate the action potential.

Sodium Ion Channels

Channels in the axolemma that open during depolarization, allowing sodium ions to rush into the cell.

Potassium Ion Channels

Channels in the axolemma that open during repolarization, allowing potassium ions to move out of the cell.

Voltage-gated sodium channels

Channels that remain inactivated until the membrane repolarizes to near threshold levels, at which point they become closed but capable of opening.

Voltage-gated potassium channels

Channels that begin closing as the membrane reaches the normal resting potential, causing potassium ions to continue leaving the cell and producing a brief hyperpolarization.

Refractory period

The time period from the beginning of an action potential to the return to the resting state, during which the membrane does not respond normally to another stimulus.

Absolute Refractory Period

The time period when sodium channels are open or inactivated, and no action potential is possible.

Relative Refractory Period

The period when the membrane potential is almost normal, and a very large stimulus can initiate an action potential.

Propagation of Action Potentials

The movement of action potentials generated in the axon hillock along the entire length of the axon, with two types being continuous propagation in unmyelinated axons and saltatory propagation in myelinated axons.

Type A Fibers

Myelinated fibers with a larger diameter that carry important information at high speeds to and from the central nervous system.

Type B Fibers

Myelinated fibers with a medium diameter that carry intermediate signals at medium speeds, such as sensory information and peripheral effectors.

Type C Fibers

Unmyelinated fibers with a small diameter that carry slower information at small speeds, such as involuntary muscle and gland control.

Synapse

The junction between two neurons or a neuron and a target cell where communication occurs.

Electrical Synapse

A type of synapse where ions flow directly between cells through gap junctions, allowing for rapid communication.

Chemical Synapse

A type of synapse where neurotransmitters are released into a synaptic cleft to communicate between cells.

Postsynaptic Potential

Changes in membrane potential of the postsynaptic cell in response to neurotransmitters released from the presynaptic cell.

Neurotransmitter

Chemical compounds released by neurons that transmit signals across synapses to target cells.

Cholinergic Synapse

Synapses that use acetylcholine as the neurotransmitter, found in neuromuscular junctions and various parts of the nervous system.

Acetylcholine (ACh)

A neurotransmitter that diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane, leading to depolarization.

Acetylcholinesterase (AChE)

An enzyme that breaks down acetylcholine into acetate and choline, ending depolarization at the synapse.

Biogenic Amines

Organic molecules that act as neurotransmitters, including norepinephrine, epinephrine, dopamine, and serotonin.

Inhibitory Neurotransmitters

Neurotransmitters that open chloride channels, causing hyperpolarization and making it harder to generate an action potential, such as GABA and glycine.

Neuromodulators

Compounds that influence the release of transmitters or affect the action of neurotransmitters on the postsynaptic membrane, often neuropeptides like opioids.

Direct Action

When a neurotransmitter attaches to proteins, opening chemically gated channels and allowing ion flow across the membrane.