nerve cells and nerve impulses

nerve cells

The Building Blocks of the Nervous System

1. neurons

2. glia

2 types of cells in the nervous system

neurons

The primary signaling units, responsible for transmitting information via electrical and chemical signals.

100 billion to 1 trillion

neurons are around —

glia

Non-neuronal cells that support and protect neurons, performing various functions like myelination and nutrient supply

9x

glia are around — more than neurons

Santiago Ramon y Cajal

• Pioneer of Neuron Doctrine

• — revolutionized our understanding of the nervous system by demonstrating that neurons are distinct, individual cells, not a continuous network

Golgi staining technique

Santiago Cajal’s meticulous drawings of brain tissue, using the —-, revealed the intricate structure of neurons and their connections.

astrocytes

Star-shaped cells in the central nervous system, they provide structural support, regulate blood flow, and contribute to the blood-brain barrier

oligodendrocytes

Found in the central nervous system, they produce myelin, a fatty substance that insulates axons, speeding up nerve impulse transmission

schwann cells

located in the peripheral nervous system (PNS), they also produce myelin, wrapping around axon to insulate them

radial glia

Found during development, they guide migrating neurons to their correct positions in the brain

cellular membrane

The outer boundary of the neuron, regulating the passage of substances in and out.

nucleus

Contains the neuron's genetic material (DNA) and controls cellular activity.

mitochondria

The "powerhouses" of the cell, responsible for energy production

ribosomes

Sites of protein synthesis, essential for building and maintaining the neuron

endoplasmic reticulum

A network of membranes involved in protein synthesis and transport.

dendrites

Branching extensions that receive signals from other neurons

axon

A long, slender projection that transmits signals away from the cell body

cell body

The central part of the neuron, containing the nucleus and other organelles

myelin sheath

A fatty covering that insulates the axon, increasing the speed of nerve impulse transmission

presynaptic terminals

Specialized endings of the axon that release neurotransmitters, chemical messengers that communicate with other neurons

dendritic spines

• are small, tree-like protrusions found on dendrites, which are the branching extensions of neurons. These tiny structures play a crucial role in the complex process of neural communication.

• are highly dynamic, changing shape and size in response to experience, contributing to learning and memory

afferent neurons (sensory neurons)

Carry sensory information from the body to the CNS.

efferent neurons (motor neurons)

Carry motor commands from the CNS to muscles and glands

interneurons

Connect neurons within the CNS, mediating complex neural circuits and processing information.

blood-brain barrier

A highly selective barrier that prevents most chemicals and pathogens from entering the brain.

endothelial cells

Tightly joined cells lining the blood vessels in the brain, forming the physical barrier.

active transport system

Specialized proteins that actively pump essential nutrients and remove waste products across the blood-brain barrier

resting potential

is a fundamental concept in neuroscience that refers to the difference in electrical charge between the inside and outside of a neuron when it's not actively sending or receiving signals.

polarized

The cell is — during resting state

negatively charged

The inside of a neuron is typically more — than the outside, due to the presence of negatively charged proteins and other molecules within the cell.

-70 millivolts (mV)

During at rest, a neuron usually contains about — inside relative to the outside

Microelectrode

— A thin device used to measure resting potential; Is inserted into the cell body

selective permeability

refers to the ability of a cell membrane to allow certain substances to pass through while restricting others. In the case of neurons, the cell membrane is more permeable to potassium ions (K+) than sodium ions (Na+).

electrical gradient

• Negative Interior: The inside of a neuron is typically more negatively charged than the outside.

• Attraction: This negative charge attracts positively charged sodium ions, causing them to move inward.

Concentration Gradient

• Higher Outside: Sodium ions are more concentrated outside the cell than inside.

• Diffusion: This concentration difference drives sodium ions to diffuse inward, following a natural tendency to move from areas of higher concentration to lower concentration.

action potentials

• are the electrical signals that neurons use to communicate with each other.

• occur when sodium ions rapidly enter the cell

• If the depolarization reaches a critical threshold (usually around -55 to -65 mV), an —- will occur.

all-or-none law

No action potential if the threshold isn’t reached.

reversed polarity

Cell charge goes from negative to positive

depolarization

Na⁺ channels open, making inside more positive

repolarization

Na⁺ channels close, K⁺ channels open, restoring negative charge.

hypolarization

• occurs as potassium ions flow out, making the membrane potential more negative

• Membrane potential briefly becomes more negative than resting.

axon hillock

Action potential starts at the — and travels down with constant intensity.

back-propagation

The action potential can move back into the cell body and dendrites.

passive-propagation

Cell body and dendrites passively detect the electrical event; they don't conduct action potentials.

myelin

• Insulating material made of fats and proteins.

• Facilitates fast signal transmission along an axon.

myelinated axons

• Found only in vertebrates.

  • Signals are interrupted by nodes of Ranvier.

nodes of ranvier

• High density of voltage-gated channels.

• Enhances transmission of action potential

saltatory conduction

• Action potential jumps from one node of Ranvier to another.

• Energy efficient, using sodium only at nodes.

refractory period

The state after which an action potential has been fired.

1. absolute refractory period

2. relative refractory period

2 types of refractory period

absolute refractory period

No action potential can be produced regardless of stimulation; Happens during the start of the depolarization phase to the repolarization phase

relative refractory period

Requires stronger-than-usual stimulation to produce another action potential; Occurs during the hyperpolarization phase

typical neuron

• Projection Neurons

• Has axons.

• Follow the allor-none law.

• Produces Action Potential.

• Potential stays the same as it travels

local neurons

• Interneurons

• Has no axons.

• Do not follow the all-ornone law.

• Produces Graded Potential.

• Potential gradually decays as it travels.

local neurons

• Influences the exhibitory or inhibitory activity of other neurons.

• Crucial in maintaining balance.

• Difficult to study due to its nature of being small and limitations of electrode size making the —- susceptible to damage.