Lecture 3

Question 1

How is the nervous system organized (different parts) ?

Answer 1

1) CNS : brain (surrounded by cerebrospinal fluid) and spinal cord -> sensory processing and voluntary motor activity

2) PNS : all other neuronal tissue -> relays info to CNS (afferent) and conducts info from CNS to body (efferent). Origin = cranial nerves and spinal nerves

PNS into :
- somatic (voluntary) : sensory and motor (skeletal muscles)
- vegetative (autonomic) : visceral sensory and visceral motor

Question 2

What are the cells present in nervous system tissue ?

Answer 2

• Neurons
  Glial cells :
• microglia = immune cells
• ependymal cells = line membranes
• oligodendrocytes (CNS) = myelin sheets
• astrocytes : connection between neurons and blood vessels -> gives glucose to neuron depending on energy demand, also takes up potassium (for membrane potential)

Question 3

4 types of neurons

Answer 3

1) multipolar (many dendrites)
2) bipolar (rare sensory neurons)
3) pseudo-unipolar : dendrite and axon joinded before cell body
4) unipolar (no dendrite)

Question 4

Some differences between post synaptic potential and action potential

Answer 4

• input signal VS regenerating conduction signal (regenerated at every Ranvier node with same amplitude)
• different channels VS only voltage gated
• Na+, K+, Ca2+ VS K+, Na+
• AP is only depolarizing
• can VS cannot be summed
• AP has a refractory period

Question 5

two types of channels that create postsynaptic potentials

Answer 5

1) chemically gated ion channel
2) GPCR system : pathway alters the state of ion channels

Both are ligand gated.

Question 6

ions involved in EPSP and IPSP

Answer 6

EPSP : Na+ comes IN
IPSP : K+ out (GPCR) or Cl- in

Question 7

How do the ions reach axon hillock ? What are some losses ?

Answer 7

Diffusion along concentration gradient.
Loss : leakage current (K+ go out from the permanently opened channels) and cytoplasmic resistance (slows down flow)

-> strength of signal decreases over distance

Question 8

steps of action potential

Answer 8

1) stimulus
2) Na+ enters -> depolarizes cell
3) potential goes from -70 to +30 (threshold is -55)
4) Na+ channels close and voltage gated K+ channels open
5) K+ leaves cell to repolarize, but even hyperpolarizes
6) voltage gated K+ close, cell returns to normal potential through Na/K pump

Question 9

model of the NaV gated channel in the AP

Answer 9

1) resting potential : channel is closed, but can be activated
2) at threshold, potential sensor is driven towards extracellular space -> activation gate is opened -> depolarization
3) at max, inactivation gate (ball) closes, stopping the Na+ flow -> channe in closed and inactivable
4) during repolarization, the activation gate closses and inactivation gate opens -> channel is closed but can be activated