Cells and tissues of the nervous system

Question 1

Describe the main components of the nervous system

Answer 1

• CNS
	• PNS
	• Efferent (sensory)
	• Afferent (motor)
	- Sympathetic
	- Parasympathetic
	• Neurons
	- Don’t stain well and so have to stain differently
	- Excitable
	• Glial cells (supporting cells)
	- Much smaller
	- More plentiful
	- Non-excitable

Question 2

Describe neurons

Answer 2

• Multiple dendrites and one axon and cell body
  
  • Impulses are generated by action potential and travel in one direction from the dendrites to the axon
  • Lots of cell organelles (RER, mitochondria, Golgi apparatus)
  • High metabolic rate
  • Needs a lot of proteins to secrete at synaptic terminals
  • Long lived and amitotic
  • Damage to the axon is reversible but to the cell body it is not
  • There is promising research into cell body repair

Question 3

Describe the axons and their envelope

Answer 3

• Schwann cells surround the cell membrane, wrapping round the axon multiple times to form a myelin sheath
  
  • Myelin sheaths allows saltatory conduction (jumping from node to node) which speeds up the rate of conduction
  • Non-myelinated cells also have Schwann cells surrounding the axon but it doesn’t wrap around it multiple times and so the myelin sheath is not formed

Question 4

Describe multi-polar neurons

Answer 4

• Motor neurons

- Interneurons

Question 5

Describe bipolar neurons

Answer 5

• Retinal nerve fibres

- Olfactory mucosa

Question 6

Describe psuedounipolar nerves

Answer 6

• Sensory

- Dorsal root ganglion is where the cell bodies of sensory neurons sit.

Question 7

Describe Glia cells

Answer 7

• Schwann cells (myelination)
• Satellite cells (surrounds neural cell bodies)
• Oligodendrocytes (myelination inside brain)
• Astrocytes (have feet that surround synapses and capillaries, help in K+ buffering (blood/brain barrier)
- Very common and very useful
• Microglia (phagocytosis, scar tissue formation inside the brain)
• Ependymal cells (lines verticals)
• It is important to understand glia cells as these are the cells that tumours most commonly affect

Question 8

Compare white and grey matter

Answer 8

• Grey matter: Cell bodies
- Collection of cell bodies inside the brain is called a nuclei
- Collection of cell bodies outside the brain is called a ganglion
• White matter: axons as they contain lipids and they are yellow/white
- Collection of axons is called a tract

Question 9

Explain hoe the CSF is circulated

Answer 9

• CSF is created in the choroid plexus of the ventricles (a thin, vascular, fragile structure in each of the ventricles)
  
  • It travels through all the ventricles and some continues on but most travels through one of the three holes in the roof of the 4th ventricle
  • Once they have travels through these holes they are now in the subarachnoid space and flow down the spinal cord and around the cerebrum
  • The CSF is reabsorbed in the arachnoid villi into the sagittal sinus
  • If you didn’t have CSF your brain would crush itself with its own weight

Question 10

Describe how the blood brain barrier works, and what it implies for drug therapy

Answer 10

• Formed by endothelial cells
  
  • Allows passage of water, some gases and lipid soluble molecules by diffusion
  • Selective transport of molecules such as amino acids and glucose happens as well
  • This all means it is really hard to get drugs to the brain

Question 11

Describe the different topographical features of the brain arise developmentally from different parts of the neural tube

Answer 11

• The prosencephalon (forebrain): gives rise to the cerebrum and the diencephalon  
	• The mesencephalon (midbrain): doesn't really grow much and just becomes the midbrain
The Rhombencephalon (hindbrain): forms the pond and medulla in the front and the cerebellum posteriorly

Question 12

Describe the location of the ventricles

Answer 12

• The lateral ventricles are within the cerebral hemispheres
  
  • The 3rd ventricle is between the diencephalon between the thalamus and hypothalamus
  • The cerebral aqueduct is within the midbrain
  • The 4th ventricle has the pons and medulla anterior to it and the cerebellum posterior to it

Question 13

Describe dural folds

Answer 13

• Falx cerebri
- Separates the two hemispheres of the cerebrum
• Tentorium cerebri
- Separates the cerebrum and the cerebellum
• Falx Cerebelli
- Separates the two left and right lobe of the cerebellum

Question 14

Describe the structure of the scalp

Answer 14

• Skin
  
  • Connective tissue (dense)
  • Aponeurosis (epicranial)
  • Loose connective tissue
  • Periostium

Question 15

Describe the structure of the skull bone

Answer 15

• The frontal bone
  
  • The parietal bones
  • The temporal bones
  • The occipital bone
  • The Zygomatic bone
  • The sphenoid bone

Question 16

Describe the meninges

Answer 16

• The pia matter (inside)
  
  • The arachnoid matter (middle)
  • The dura matter (outside)