Lecture 2: The Microstructure of the Brain Flashcards
(25 cards)
What are neurons, and what role do they play in the nervous system?
- Neurons, also known as nerve cells, are the basic units of the nervous system.
- Neurons transmit electrical and chemical signals between each other, allowing for the rapid communication needed for various functions within the body. (collect, conduct, and transmit information)
How many neurons are present in the human brain?
The human brain contains a large number of neurons, ranging from approximately 100 to 200 billion neurons (about 1-2 x 10¹¹ neurons).
How do neurons differ from other cells in the body?
Subtypes: There are thousands of different types of neurons, each differing in their location, appearance, connections, physiological characteristics, and functions.
Terminal Differentiation: They lose the ability to reproduce themselves, unlike other cells that can regenerate.
Oxygen Sensitivity: Neurons are highly sensitive to a lack of oxygen. If deprived of oxygen for just a few minutes, they lose viability
What are the main components of the nervous system?
Neurons: Responsible for the transmission of information through electrical and chemical signals.
Glial Cells (Glia): These cells support neurons. There are about ten times more glial cells than neurons in the brain.
What is the primary function of neurons in the nervous system?
Neurons are primarily responsible for conveying information within the nervous system.
- They do this through electrical and chemical signals, allowing for rapid communication between neurons.
What is the function of glial cells in the nervous system?
Primarily involved in supporting and maintaining the environment for neurons, assisting in the protection and insulation of neurons, and regulating the extracellular environment.
How do neurons transmit information between each other?
Neurons transmit information through a combination of electrical and chemical signals.
- Electrical signals are used to propagate the information within a single neuron
- Chemical signals (in the form of neurotransmitters) are used to carry information from one neuron to another at synapses.
What are the four morphologically defined regions of a neuron?
- Cell Body (Soma or Perikaryon): The metabolic and genomic hub of the neuron.
- Dendrites: Branching processes that receive information from other neurons.
- Axon: A long cylindrical process that propagates information away from the cell body.
- Presynaptic Terminals (Synaptic Boutons): Specialized enlarged regions at the end of the axon that terminate near the dendrites or cell body of another neuron
What does the nucleus contain, and what is its function?
- Contains 46 chromosomes
- It carries the instructions for producing proteins vital for neuron function.
What is the function of the plasma membrane?
It is thin, around 10 nm in thickness, and highly organized to regulate what enters and exits the cell.
What are key organelles?
- mitochondria (for ATP production)
- lysosomes (for cellular digestion) - Golgi apparatus (for processing proteins)
- endoplasmic reticulum (ER)
- ribosomes (for protein synthesis)
What are Nissl bodies (Nissl substances)
Concentrated areas of rough ER and ribosomes within the soma and dendrites, crucial for synthesizing proteins.
- They are absent in the axon and axon hillock.
What colours and metals are found in some neurons
Pigments:
dopamine (substantia nigra) or norepinephrine (locus ceruleus)
Metals:
zinc, copper, and iron
What are dendrites, and their functions?
Branched, tree-like extensions from the soma and serve as the primary receptive areas for receiving signals from other neurons.
- Contains Nissl bodies to engage in protein synthesis
What is the dendrite tree?
The main dendrite (called a primary dendrite or 1st order dendrite) extends from the soma, and this can branch further into 2nd, 3rd, 4th, and even 5th order dendrites
- increases the surface area of the neuron, which is critical for making synaptic connections.
What are dendrite spines and their functions?
- small protrusions on dendrites, increase the surface area further.
- These spines are dynamic and respond to neuronal activity (like glutamate signaling) by changing shape or size, which is believed to be the structural basis of learning and memory.
What happens when dendrites are impaired or cannot change?
ex: Down’s syndrome
What are axons and their functions?
- long, cylindrical process that conducts electrical impulses (action potentials) away from the soma to communicate with other neurons or target tissues
- The axon does not contain ribosomes and relies on the soma to produce proteins and other molecules required for axonal function.
What are the types of myelination in the different nervous systems?
CNS: Axons are often myelinated by oligodendrocytes in the central nervous system (CNS)
PNS: Schwann cells in the peripheral nervous system (PNS)
What is the myelin sheath?
A lipid-rich covering that increases the speed of action potential conduction.
It acts as an insulator and enables saltatory conduction (action potentials jump between nodes of Ranvier, gaps in myelin).
What is the cytoskeleton and its function?
- a complex network of filamentous protein polymers (microtubules, neurofibrils, actin microfilaments)
- helps maintain the axon’s shape and enables it to change dynamically in response to developmental and injury signals.
What are axon terminals (Presynaptic Terminals) and their function?
- synaptic boutons
- the endings of the axon and are specialized for releasing neurotransmitters into synapses
- contain synaptic vesicles filled with neurotransmitters, which are released into the synaptic cleft when an action potential reaches the terminal
How is communication possible from the axon terminals?
The synaptic cleft is the narrow gap (10–20 nm) separating the presynaptic and postsynaptic membranes. It is where neurotransmitters are released to transmit signals.
The release of neurotransmitters across the synaptic cleft allows for communication with the postsynaptic neuron or cell, resulting in an excitatory or inhibitory response.
What are the different types of synapses?
Axodendritic (axon to dendrite)
Axosomatic (axon to cell body)
Axoaxonic (axon to axon).
