WEEK 2 NERVE CELLS AND NERVE IMPULSES

Nervous System

composed of two fundamental cell types: neurons and glial cells, each with specialized roles that work together to support the brain and body's complex functions. Understanding these cells is critical for appreciating how the nervous system processes and transmits information.

Neurons Primary Function

Neurons are the functional units of the nervous system responsible for transmitting electrical signals (nerve impulses) and chemical signals (neurotransmitters) between different parts of the body.

Neuron Excitability

Neurons can generate and propagate electrical signals in response to stimuli.

Neuron Specificity

Each neuron connects with specific target cells (other neurons, muscles, or glands) to ensure precise communication.

Sensory Neurons

Transmit information from sensory organs (e.g., eyes, skin) to the central nervous system (CNS).

Motor Neurons

Carry signals from the CNS to muscles or glands to elicit responses.

Interneurons

Facilitate communication between sensory and motor neurons, often within the brain or spinal cord.

Dendrite Function

Dendrites are branched, tree-like structures extending from the cell body (soma) that receive signals from other neurons or sensory receptors and transmit them toward the soma.

Dendrite Importance

They increase the surface area of the neuron, allowing it to communicate with multiple neurons.

Soma Function

The soma contains the nucleus, maintains metabolic activities, integrates incoming signals, and generates outgoing signals if the threshold is reached.

Soma Components

Contains organelles like mitochondria for energy production and ribosomes for protein synthesis.

Axon Function

The axon is a long, thin structure that carries electrical impulses away from the soma to other neurons or muscles.

Axon Structure

Axons vary in length from micrometers to meters, such as in motor neurons.

Node of Ranvier Function

Gaps in the myelin sheath that facilitate saltatory conduction by allowing impulses to jump between nodes.

Node of Ranvier Importance

Essential for efficient and rapid signal transmission.

Axon Terminal Function

Axon terminals release neurotransmitters into the synapse to communicate with the next neuron or effector.

Synaptic Connection

Axon terminals convert electrical signals into chemical messages.

Schwann Cell Function

Schwann cells produce the myelin sheath in the peripheral nervous system and insulate axons.

Schwann Cell Role in Repair

Aid in the repair and regeneration of damaged neurons.

Myelin Sheath Function

A fatty layer formed by Schwann cells that insulates axons and enhances nerve impulse conduction speed.

Myelin Sheath Disease Association

Damage to the myelin sheath such as in multiple sclerosis slows signal transmission or causes loss of function.

Nucleus Function

Contains the neuron’s genetic material and regulates protein synthesis and cell maintenance.

Summary of Neuron Signal Flow

Dendrites receive signals, soma integrates them, axon generates and transmits an action potential, myelin sheath and nodes of Ranvier accelerate transmission, axon terminals release neurotransmitters.

Glial Cells Definition

Glial cells outnumber neurons and provide structural and functional support essential for neuron survival.

Astrocytes Structure

Star-shaped glial cells located primarily in the CNS.

Astrocytes Functions

Maintain extracellular environment, form part of the blood-brain barrier, and provide metabolic support.

Astrocyte Example

Clear glutamate after synaptic transmission to prevent excitotoxicity.

Oligodendrocytes and Schwann Cells Function

Produce myelin sheath that insulates axons and increases action potential conduction speed.

CNS vs PNS Myelination

Oligodendrocytes myelinate CNS axons while Schwann cells myelinate PNS axons.

Microglia Structure

Small mobile glial cells that act as immune defense in the CNS.

Microglia Function

Engulf debris, respond to pathogens, and modulate inflammation.

Ependymal Cells Function

Produce and circulate cerebrospinal fluid that cushions the brain and spinal cord.

Neuron vs Glia Primary Function

Neurons transmit signals while glia support, maintain, and provide immune response.

Neuron Ability to Divide

Neurons rarely divide except in some areas.

Glia Ability to Divide

Glial cells can divide and proliferate.

Blood Brain Barrier Definition

A selective and protective barrier that shields the brain from harmful substances while allowing essential nutrients and gases to pass.

BBB Endothelial Cells

Tightly packed cells with tight junctions preventing harmful substances from entering brain tissue.

BBB Astrocytes

Extend end-feet around capillaries and regulate BBB formation and maintenance.

BBB Basement Membrane

Provides structural support and additional filtration.

BBB Pericytes

Regulate blood flow, vessel stability, and permeability.

BBB Selective Permeability

Allows small nonpolar lipid-soluble molecules while restricting large or polar molecules.

BBB Drug Delivery Challenge

Many therapeutic drugs cannot cross the BBB, complicating treatment of neurological diseases.

Resting Potential Definition

Electrical charge difference across neuronal membrane when neuron is not transmitting.

Resting Potential Value

Approximately -70 millivolts in most neurons.

Resting Potential Cause

Unequal ion distribution with more sodium outside and more potassium inside.

Sodium Potassium Pump Function

Uses ATP to pump 3 sodium ions out and 2 potassium ions into the cell.

Depolarization

Voltage-gated sodium channels open allowing sodium ions to enter and raise membrane potential.

Repolarization

Potassium channels open allowing potassium ions to exit and restore negative charge.

Hyperpolarization

Membrane potential drops below resting potential due to prolonged potassium channel opening.

All or None Law Definition

An action potential either occurs fully or not at all if threshold is reached.

Saltatory Conduction Definition

Action potential jumps between nodes of Ranvier increasing transmission speed.

Epilepsy Cause

Mutations in sodium, potassium, or calcium channels causing excessive neuronal firing.

Multiple Sclerosis Cause

Autoimmune attack on oligodendrocytes leading to demyelination.

Synapse Definition

A junction with a minute gap separating two neurons or a neuron and muscle or gland.

Synapse Coined By

Charles Sherrington in 1897.

Chemical Synaptic Transmission

Neurotransmitters are released from presynaptic neuron and bind to postsynaptic receptors.

Drugs and Synapses

Drugs influence neurotransmitter release, receptor activity, or reuptake.