Body and behavior task 2
How are neurons structured?
The Nervous System
Neurons = the basic information-processing and transmitting units of
the nervous system.
The nervous system is divided into:
o Central Nervous System (CNS): brain and spinal cord
o Peripheral Nervous System (PNS): nerves that connect the CNS
to the body
Neurons
Neuron structure
- Dendrites (input zone):
Branch-like structures that receive signals from other neurons
through synapses.
Function like antennas to pick up incoming messages.
- Soma/Cell Body (integration zone): the main part of the neuron that
contains the nucleus and most of the structures needed to keep the cell
alive and functioning. It performs essential metabolic and synthetic
(protein-making) activities for the neuron Main Internal Structures:
Cell Membrane: A double layer of lipids (lipid bilayer with embedded
proteins that control what enters and leaves the cell and help
transmit signal. Each phospholipid has:
o Hydrophilic head (water-loving) → faces outward toward water.
o Hydrophobic tails (water-fearing) → face inward, away from
water.
Forms a semipermeable barrier around the cell.
Cell membrane proteins:
o Channel proteins (PASSIVE): Form pores that allow specific ions or
molecules to pass through by diffusion; no energy required.
o Carrier proteins (PASSIVE or ACTIVE):
Passive carriers move substances down their concentration
gradient (no energy).
Active carriers (pumps) use energy (ATP) to move
substances against their gradient.
o Receptor proteins: detect external signals and trigger cellular
responses.
, Cytoplasm: A jellylike fluid that fills the cell and contains all the
organelles.
Cytoskeleton: A network of protein strands that gives the neuron its
shape and structure.
Nucleus: Contains the nucleolus (makes ribosomes) and
chromosomes (DNA), which hold genetic information.
o Transcription: DNA → messenger RNA (mRNA)
o Translation: mRNA → protein at ribosomes
Ribosomes: Small structures (some free-floating, some attached to
the rough ER) where proteins are built.
Endoplasmic Reticulum (ER):
o Rough ER: has ribosomes; makes proteins for export or for the
cell membrane.
o Smooth ER: makes lipids (fats) and forms channels for
transporting molecules.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for
secretion or delivery to other organelles (exocytosis)
Lysosomes: Small sacs containing enzymes that break down waste
or unwanted materials.
Mitochondria: The cell’s “power plants.” They extract energy from
nutrients to produce ATP, which fuels cell functions.
Axon hillock = the crucial, cone-shaped junction where a neuron's
cell body (soma) meets its axon the neuron's "decision-maker" to
initiate an action potential (nerve impulse) by summing up incoming
signals and firing if a threshold is reached, thanks to its high
concentration of voltage-gated sodium channels.
- Axon (conduction zone):
A long fiber that carries electrical impulses (action potentials) away
from the soma to terminal buttons.
Often covered by a myelin sheath, which speeds up signal
transmission.
Materials are moved along the axon by axoplasmic transport:
o Anterograde transport (kinesin): soma → terminal buttons
o Retrograde transport (dynein): terminal buttons → soma
- Terminal Buttons (output zone):
Small knobs at the end of axon branches.
How are neurons structured?
The Nervous System
Neurons = the basic information-processing and transmitting units of
the nervous system.
The nervous system is divided into:
o Central Nervous System (CNS): brain and spinal cord
o Peripheral Nervous System (PNS): nerves that connect the CNS
to the body
Neurons
Neuron structure
- Dendrites (input zone):
Branch-like structures that receive signals from other neurons
through synapses.
Function like antennas to pick up incoming messages.
- Soma/Cell Body (integration zone): the main part of the neuron that
contains the nucleus and most of the structures needed to keep the cell
alive and functioning. It performs essential metabolic and synthetic
(protein-making) activities for the neuron Main Internal Structures:
Cell Membrane: A double layer of lipids (lipid bilayer with embedded
proteins that control what enters and leaves the cell and help
transmit signal. Each phospholipid has:
o Hydrophilic head (water-loving) → faces outward toward water.
o Hydrophobic tails (water-fearing) → face inward, away from
water.
Forms a semipermeable barrier around the cell.
Cell membrane proteins:
o Channel proteins (PASSIVE): Form pores that allow specific ions or
molecules to pass through by diffusion; no energy required.
o Carrier proteins (PASSIVE or ACTIVE):
Passive carriers move substances down their concentration
gradient (no energy).
Active carriers (pumps) use energy (ATP) to move
substances against their gradient.
o Receptor proteins: detect external signals and trigger cellular
responses.
, Cytoplasm: A jellylike fluid that fills the cell and contains all the
organelles.
Cytoskeleton: A network of protein strands that gives the neuron its
shape and structure.
Nucleus: Contains the nucleolus (makes ribosomes) and
chromosomes (DNA), which hold genetic information.
o Transcription: DNA → messenger RNA (mRNA)
o Translation: mRNA → protein at ribosomes
Ribosomes: Small structures (some free-floating, some attached to
the rough ER) where proteins are built.
Endoplasmic Reticulum (ER):
o Rough ER: has ribosomes; makes proteins for export or for the
cell membrane.
o Smooth ER: makes lipids (fats) and forms channels for
transporting molecules.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for
secretion or delivery to other organelles (exocytosis)
Lysosomes: Small sacs containing enzymes that break down waste
or unwanted materials.
Mitochondria: The cell’s “power plants.” They extract energy from
nutrients to produce ATP, which fuels cell functions.
Axon hillock = the crucial, cone-shaped junction where a neuron's
cell body (soma) meets its axon the neuron's "decision-maker" to
initiate an action potential (nerve impulse) by summing up incoming
signals and firing if a threshold is reached, thanks to its high
concentration of voltage-gated sodium channels.
- Axon (conduction zone):
A long fiber that carries electrical impulses (action potentials) away
from the soma to terminal buttons.
Often covered by a myelin sheath, which speeds up signal
transmission.
Materials are moved along the axon by axoplasmic transport:
o Anterograde transport (kinesin): soma → terminal buttons
o Retrograde transport (dynein): terminal buttons → soma
- Terminal Buttons (output zone):
Small knobs at the end of axon branches.
