Chapter 3

• Of which 2 types of nerve cells does brain tissue consist of?

  Neurons -> information processing

  Glial cells -> support cells
• How can we count nerve cells?

  brain soup
• Cerebral cortex

  • 82% brain mass
  • ~ 16 billion neurons (19% brain neurons)!
  • ~ 61 billion glial cells
• Cerebellum

  • 10% brain mass
  • ~ 69 billion neurons (80% brain neurons)
  • ~ 16 billion glial cells
• Rest of brain (without cerebral cortex & cerebellum)

  • 8% brain mass
  • ~ 1 billion neurons (1% brain neurons)
  • ~ 8 billion glial cells
• What are the 3 parts of neurons (basic structure)?

  dendrites -> no. many -> collect information (input) from other neurons

  cell body (soma) -> no. 1 -> integrates information

  axon -> no. 1 -> sends information (output) branches at the end
• Neuron - basic structure

  first: Dendrites

  middle: cell body

  last: axon

  
• Neurons -flow of information

  1. input (Dendrites)
  2. Integration (cell body)
  3. Output (Axon)

  
• What are 3 major types of neurons?

  1. sensory neurons (Input; Afferent)
  2. interneurons (Association)
  3. motor neurons (Output; Efferent)
• Sensory neurons

  = input (Afferent); bring info to the CNS

  • long Dendrites
  • short Axons
  • dendrites + cell body outside of CNS (cell body in dorsal root ganglion)
  • axon inside CNS

  
• Interneurons

  = association; associate sensory & motor activity in CNS

  • short dendrites
  • short axons
  • dendrites, cell body & axon inside CNS (in brain + spinal cord)

  
• Motor neurons

  = output (efferent); send signals from brain & spinal cord to muscles

  • short dendrites
  • long axons
  • dendrites + cell body inside CNS (in lower brainstem + spinal cord)
  • axon outside CNS

  
• Dorsal root location

  
• Sympathetic division (stimulation)

  1. Cranial 2. Cervical 3. Thoracic 4. Lumbar 5. Sacral

  
• Glial cells

  = support cells

  What do they do?

  Aid neurons in processing information by providing:

  • physical support, protection
  • nutrients
  • increase conduction (lit. glue neurons together)
  • !!! DO NOT transmit info by themselves
• Glial cell - image

  
• What are the 5 major types of glial cells?

  Astrocytes, oligodendroglia, microglia, ependymal cells, Schwann cells
• What are the features & functions of glial cell: Ependymal cell?

  • small, ovoid
  • secretes cerebrospinal fluid (CSF)
  • Appearance:

  
• What are the features and function of the glial cell: Astrocyte?

  • star-shaped, symmetrical
  • nutritive & support function
  • Appearance:

  
• What are the features and function of the glial cell: Microglial cell?

  • small, mesodermally derived
  • defensive function
  • appearance:

  
• What are the features & function of the glial cell: Oligodendroglial cell?

  • asymetrical
  • forms myelin aroung axons in brain & spinal cord
  • appearance:

  
• What are the features & function of the glial cell: Schwann cell?

  • asymetrical
  • wraps around peripheral nerves to form myelin
  • appearance:

  
• Types of glial cells- table overview

  
• Glial cells-– Ependymal cells (CSF)

  What is the normal brain & ventricles and what is the Hydrocephalus brain?

  red: normal brain & ventricles

  orange: ventricles

  yellow: Hydrocephalus brain

  green: swollen ventricles

  
• What do the glial cells Astrocytes do?

  • structural support to the CNS (scaffold cells)
  • Move nutrients & chemicals between blood vessels & neurons
  • Enhance brain activity by contributing to increased blood flow
  • Stimulate repair of damaged brain tissue (scarring)
  • enable tight bond between blood-vessel cells & neurons -> blood-brain barrier
• Astrocyte-glial cell image:

  1. Astrocyte 2. blood vessel 3. blood-vessel cells 4. astrocyte end feet 5. tight junctions 6. myelinated axon 7. Neuron

  
• Glial cells – Microglia

  • only glial cell originating in blood as offshoot of immune system (type of macrophage) & migrate throughout nervous system (all other glial cells originate in the brain)
  • Identify & attack foreign tissue (defense cells)
  • Invade areas with damaged cells + provide growth factors to aid in repair
  • Consume dead & inflamed brain cells (plaques, Alzheimer)
• What do Glial cells – Oligodendroglia and Schwann cells do?

  Myelinate neurons to enhance neural transmission speed (insulate axons)

  • Oligodendroglia (inside CNS)
  • Schwann cells (outside CNS)
• Glial cells - Oligodendroglia (inside CNS)- image

  1. Oligodendrocytes 2. Dendrite 3. Neuron 4. Myelin sheath 5. Axon 6. Synapse 7. Nucleus

  
• Glial cell - Schwann cells (outside CNS)- image

  1. Node of Ranvier 2. Nucleus 3. Schwann cells

  
• Glial cells- Neuron repair

  Which glial cell encourages neuronal repair?

  Schwann cells (PNS) -> cells in the PNS can be repaired after damage
• Glial cells- Neuron repair

  Which glial cells DO NOT encourage neuronal repair?

  Oligodendrocytes (CNS) -> cells in the CNS cannot be repaired (yet)
• Glial cells – Neuron Repair

  How does it work/ look like?

  image:

  
• Histology of Glial cells- How do we know all this information?


  traditional staining

  now: imaging techniques in living tissue (in vivo) -> DTI: Diffusion Tensor Imaging

  traditional staining- image:

  
• What are the main disadvantages of staining?

  only works in fixed brain tissue (ex vivo, in vitro, post-mortem)
• What is the internal structure of a typical (nerve) cell?

  cell membrane, Nucleus, Nuclear membrane, Endoplasmic reticulum, Golgi bodies, Microtubules, (also 3 others but not part of exam so left out)
• What is the cell membrane?

  membrane surrounding the cell
• What is the nucleus?

  cell core, contains chromosomes and genes
• What is the nuclear membrane?

  surrounds nucleus
• What does the Endoplasmic reticulum do?

  assembles proteins