Brain Cells

Question 1

Neurons

Answer 1

• Cells of the nervous system that conducts nerve impulses; consisting of an axon and several dendrites
• Electrically active
• Function: information processing
• ~ 85 billion

Question 2

Glial cells

Answer 2

• Cells in the nervous system that support and protect neurons:
  
  • regulating the chemical environment
  • enhancing electrical signalling of neurons
  • removing debris left by dead neurons
  • role in brain signalling
• ~85 billion

Question 3

Neuron structure

Answer 3

Soma + dendrites + axon

Question 4

Soma

Answer 4

• Metabolic centre of the neuron
• Composed of:
  
  • Cytosol: intracellular fluid inside a cell (salty, potassium rich solution)
  • Cytoplasm: everything within the cell membrane, including organelles, but excluding the nucleus
  • Organelles: same as found in other eukaryotic animal cells
    
    • nucleus
    • mitochondria
    • rough endoplasmic reticulum
    • smooth endoplasmic reticulum
• ~20 μm (10-6 m)

Question 5

Mitochondria

Answer 5

• Cellular respiration – generates adenosine triphosphate (ATP)
• ATP = energy currency of the cell

Question 6

Cytoskeleton

Answer 6

• “Cell skeleton” = cell shape → correct positioning of organelles and racks for in cell transportation
• Consists of:
  
  • Microtubule - 20 nm - tubulin molecule
  • Neurofilament - 10 nm
  • Microfilament - 5 nm - actin molecule

Question 7

Neuronal membrane

Answer 7

• Barrier to enclose the cytoplasm inside the neuron
• Protein composition varies depending on the location (soma, axon, dendrites).
• CRITICAL for the function of neurons – electrical activity of neurons is dependent on the membrane

Question 8

Axon

Answer 8

• A tube-like structure that propagates the integrated signal from the axon hillock to specialized endings called axon terminals
• Only found in neurons
• Each neuron has only one axon
• Highly specialized for information transfer (electrical signals) over distances (“electrical cables”)
• Axons can extend < 1mm to 1 m long.
• Axon hillock: region where the axon originates.
  
  • Integrates signals from multiple synapses and serves as a junction between the cell body and an axon
  • The neurofilaments in the axon hillock become clustered together as fascicles.

Question 9

Axon terminal

Answer 9

• Region where the axon contacts with other neurons
• Terminal arbor – short branches at the end of the axon
• Synaptic vesicles – that contain important chemicals for communication (neurotransmitters)
• Numerous mitochondria → high energy demand
• Synapse – point of contact between an axon and other neuron

Question 10

Dendrite

Answer 10

• Branched projections of a neuron that conduct the impulses received from other neural cells to the cell body
• Dendritic tree – collection of dendrites from a neuron, a branch is called dendritic branch
• “antennas of the neuron” / “receiving ends” → lots of synapses
• Dendritic spines increase possible synaptic contact sites between neurons.
  
  • Very effective synapses that can quickly change in appearance
  • Important for plasticity and learning (new spines can grow, existing spines can become larger or smaller, or disappear)
  • Ribosomes can be found in spines → protein synthesis for quick structural change of spines

Question 11

Pyramidal cell

Answer 11

Question 12

Purkineje cell

Answer 12

Question 13

Spindle-shaped cell

Answer 13

Question 14

Classification of neurons

Answer 14

• Based on number of neurites (axons and dendrites):
  
  • Unipolar: only 1 neurite is attached to cell body (soma); no dendrite at soma, only axon!
  • Bipolar: 2 neurites (1 dendrite + 1 axon) are attached to soma
  • Multipolar: many neurites (many dendrites + 1 axon) are attached to soma
    
    • Taking up only a very small amount of information can lead to greater precision → uni and bipolar neurons are most often sensory neurons
    • Multipolar neurons can be found in the central nervous system (brain and spinal cord)
• Based on dendrites: classification is often unique to a particular part of the brain
  
  • e.g. stellate cells have a very tight network of dendrites → perfect for interconnection and information exchange between neighbouring neurons; whereas pyramidal cells are perfect for transferring information over long distances (e.g. from brain to spinal cord)

Question 15

Types of neuroglia

Answer 15

• Central nervous system
  
  • Ependymal cells
  • Oligodendrocytes
  • Astrocytes
  • Microglia
• Peripheral nervous system
  
  • Satellite cells
  • Schwann cells

Question 16

Astrocytes

Answer 16

• In the CNS astrocytes provide nutrients to neurons, give synapses structural support, and block toxic substances from entering the brain;
• ”star-like”
• Most numerous glia in the brain
• In the gaps between neurons
• Influence neurite growth
• Regulation of chemical content in extracellular space (potassium K+)
• Restricting spread of neurotransmitters from synaptic cleft
• Active removal of neurotransmitters from synaptic clef

Question 17

Satellite glia

Answer 17

Provide nutrients and structural support for neurons in the PNS

Question 18

Myelinating glia

Answer 18

Oligodendrocytes (CNS) and Schwann cells (PNS): insulation of axons by supplying a myelin sheath around axon → increases conduction speed

Question 19

Myelination disorder

Answer 19

Multiple sclerosis

Question 20

Microglia

Answer 20

• Microglia scavenge and degrade dead cells, protecting the brain from invading microorganisms.
• ~ 10% of the cells in the brain
• Continually survey their local environment
• Remove dead or degenerated neurons and glia → the “immune cells of the brain”
• Developmental synaptic pruning → get rid of week, extra synapses
• Synaptic plasticity in the adult → learning and memory

Question 21

Microglia dysfunction

Answer 21

• Autism spectrum disorder
• Alzheimer’s disease

Question 22

Special properties of the neuronal membrane

Answer 22

• Phospholipid bilayer: one layer is hydrophilic (attracts water), the other is hydrophobic (rejects water) → helps to protect cell contents
• Proteins: ion channels selective for different ions → enables communication with the exterior
• Membrane potential: at rest, the inside of the neuronal membrane is electrically negative relative to the outside (resting potential) → Vm = -65 mV
• Potassium channel

Question 23

Concentration gradient

Answer 23

Particles move from an area of high concentration to an area of low concentration