CNS - Neurocytology

Question 1

List the three Nervous Systems in the human body.

Answer 1

Nervous systems

1. Central nervous system (CNS)

– brain and spinal cord.

2. Peripheral nervous system (PNS)

– cranial nerves, spinal nerves and ganglia.

3. Enteric nervous system (ENS)

Question 2

Describe the general division of PNS.

Answer 2

Peripheral Nervous System

1. Somatic nervous system (SNS):
   - The part that is controlled by the free will.
2. Autonomic nervous system (ANS):
   - Not controlled by free will, e.g., heart, glands, bowel.

Usually devided in:

• Sympathic
• Parasymphatic

Question 3

List the main cells that are included in the Nervous System?

Answer 3

The nervous system consists of several different types of cells:

1. Neurons = nerve cells (100 billions)
2. Glial cells = supportive function (1000 billions)
   
   • Astrocytes
   • Oligodendrocytes
   • Schwann cells
   • Mikroglia

Question 4

Explain a fundamental difference between grey and white brain matter.

Answer 4

Brain

1. Grey matter
   - bodies of nerve cells.
2. White matter
   - nerve fibers.

Question 5

What is a nerve cell called?

Answer 5

Neuron = nerve cell

A large number of neurons together form a nerve. I.e

N. Ischiadicus (Sciatic nerve)

Question 6

Explain MR Tractography.

Answer 6

MR Tractography

In neuroscience, tractography is a 3D modeling technique used to visually represent neural tracts using data collected by Difusion Weighted images (DWI). It uses special techniques of magnetic resonance imaging (MRI), and computer-based image analysis. The results are presented in two- and three-dimensional images.

Question 7

What role does Myelin play in the Nervous Systems?

Answer 7

Myelin

• Insulation – speed up signal transmission
  
  • Oligodendrocytes - CNS
  • Schwann cells - PNS

Question 8

Describe Astrocytes.

Answer 8

Astrocytes

• Most common cell type in CNS
• Blood Brain Barrier
• Provision of nutrients
• Nervous repair
• Astrocytoma grade I-IV
  
  • Astrocytomas are tumors that arise from astrocytes—star-shaped cells that make up the “glue-like” or supportive tissue of the brain.

Question 9

Explain Oligodendrocytes.

Answer 9

Oligodendrocytes

• Support and insulation
• Myelin of the CNS
• Brain and spinal cord
• Oligodendroglioma
  
  • Oligodendrogliomas (tumors) come from oligodendrocytes, one of the types of cells that make up the supportive, or glial, tissue of the brain. They can be low-grade (grade II) or high-grade (grade III, or anaplastic).

Question 10

Explain Schwann cells

Answer 10

Schwann cells

• Myelin of PNS
• Acoustic schwannoma
  
  • A vestibular schwannoma (also known as acoustic neuroma, acoustic neurinoma, or acoustic neurilemoma) is a benign, usually slow-growing tumor that develops from the balance and hearing nerves supplying the inner ear. The tumor comes from an overproduction of Schwann cells—the cells that normally wrap around nerve fibers like onion skin to help support and insulate nerves.

Question 11

Explain Microglia cells.

Answer 11

Microglia

Microglia are a type of glial cell located throughout the brain and spinal cord. Microglia account for 10–15% of all cells found within the brain. As the resident macrophage cells, they act as the first and main form of active immune defense in the central nervous system (CNS).

BBB

Question 12

Explain Membrane Potential.

Answer 12

Membrane potential

• Current = movement of charged particles
  
  • The direction of current is that of positive charged ions (e.g Na+, K+, Ca2+) moving
• Voltage = difference in electric potential

Question 13

Explain Resting membrane potential

Answer 13

Resting membrane potential

Over the nerve cell membrane there is an electric potential (same as a battery)

• On the inside of the cell membrane: surplus of negative charges
• On the outside of the cell membrane: surplus of positive charges

This gives a -70 mV difference in potential between the out- och inside of the cell in resting state

Question 14

How is resting membrane potential achieved?

Answer 14

The concentration of ions within and outside of the nerve cell is different:

Concentration gradients:

• Extracellular the sodium (Na+) concentration is high and the potassium (K+) concentration low
• Intracellular the Na+ concentration is low and the K+ concentration high

Question 15

Explain Action Potential.

Answer 15

Action potential

“The electric communication between nerve cells”

A small membrane potential exists in the resting neuron (70 mV) due to uneven distribution of ions. Sodium (Na+) at the outside and potassium (K+) at the inside.

A stimulus, e.g., at the synaps, affects the resting membrane potential, depolarize the membrane to a threshold level. Sodium ions will start to rush into the cell through voltage-gated channels because nature wants to “even out” the concentration gradients – depolarization.

This leads to the opening of potassium channels, potassium ions flow out.

Refractory period – ions are actively pumped back.

Question 16

Describe the velocity of Action Potential.

Answer 16

The velocity of the action potential

Faster in thick than in thin fibers

• Thick myelinated fibres 10-130 m/s (e.g touch, sharp pain)
• Thin myelinated fibers 0.5-2 m/s (e.g. Dull pain)
• Because pain is transmitted in both fast and slow fibers a painful stimuli can be felt as two ”phases” ;

One early (transmitted in fast fibers) and one late

(transmitted in slow fibers)

This is called ”first och second pain”

Question 17

Give examples when the action potential may be disrupted.

Answer 17

Examples when the action potential is disrupted:

• In multipel Sclerosis (MS) the myelin is damaged =>impairment of transmission
• Local anesthetic (e.g. Xylocain): blockage of Voltage-gated Na+-channels. Pain impulses are not transmitted.

Question 18

How can compression affect the transmission of the NS?

Answer 18

Compression

Mechanical compression blocks transmission

Exampels:

When the arm ”goes numb”

or

”Saturday night palsy”

(N. radialis)

Question 19

Give examples of some neurotransmitters.

Answer 19

Neurotransmitter:

• Glutamate
• Dopamine
• Acetylcholine
• GABA
• Serotonine

Question 20

Give examples of diseases related to synaptic transmission

Answer 20

Diseases and drugs related to synaptic transmission

• Parkinson disease
  
  • Lack of dopamin
  • Treatment – increase amount of dopamin
• Schizofrenia
  
  • Excessive amount of dopamin
  • Treatment – inhibit dopamin
• Myasthenia Gravis
  
  • Receptors for neurotransmittor Acetylcholine is blocked by antibodies at the neuromuscular junction

Question 21

Give examples of drugs acting in neuromuscular junction.

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Answer 21

Drugs acting in neuromuscular junction

• Curare (arrow poison) blocks ACh-receptors in

muscles causing palsy

• Anesthetic drug Pavulon has the same effect – used

for muscle relaxation in surgey

• Neostigmin stops the degradation of ACH and is used to reverse muscle relaxation efter operation. Can cause cramps - Sarin gas!
• Botulinum toxin (from the bacteria Clostridie Botulinum) – most potent toxin known. Blockage of ” exocytos” av ACh-vesikler – no transmission at the NMJ
• Cocain inhibit the uptake of noradrenalin precursor of adrenaline.
• Depression – lack of serotonin ”tricyclic anti-depressive and ”selective serotonin reuptake inhibitors” (SSRI – e.g. Prozac) inhibit the uptake of serotonin.

Question 22

Explain Plasticity.

Answer 22

Plasticity

How to develop and adapt to a changing environment and body.

Behavior – result of interaction between genes and environment

Experiences form behavior through lerning and memories

What are the molecular/morfological causes in the CNS for these changes?

Question 23

Does the memory lie in the synapses?

Answer 23

Research suggest that neurons can learn and remember activity patterns that results in behavior

Aplysia californica

Nobel prize winner year 2000 - Eric Kandel has studied the plasticity in the withdrawal reflex in this snail. Repeated not tissue-damaging stimulation resulted in habituation – a decrease in response after repeated stimulation.

When mechanical stimulation was together with electric Stimulation in tail the withdrawal reflex is ”sensitized”. Sensititation - increase in behavior after repeated stimulation

Question 24

Explain habituation/sensitiation.

Answer 24

1. The number of synapses is up-/downregulated after habituation/sensititation
2. The strenght of the synaps - the amount of transmittors released from presynaptic terminal
3. Number and type of receptors in the postsynaptic membrane
4. The receptors ”probability of activation” and conductivity

Lasting changes found after stimulation protocols are called:

Long Term Potentiation (LTP = When the synapse gets stronger).

Long Term Depression (LTD = When the synapse gets weaker).

These phenomenon are believed to be the neuronal mechanism of memories..!