Tema 12

Question 1

Types of nervous fibres

Answer 1

Afferent: form sensory receptors to CNS
- Somatic: from esqueletos muscle, joints, skin and organs of special senses
- Visceral: from visceral organs, heart and glands

Efferent: from the CNS to peripheral organs.
- Motor: to esqueletal muscle
- Vegetative: to smooth muscle, heart and glands.

Nerves are formed of nerve fibres (axons with or without myelin) surrounded by layers of connective tissue
They conduce A.P to the SNC and viceversa
They are not the same; they have different velocity

Question 2

GENERAL CLASSIFICATION OF MOTOR AND SENSITIVE FIBRES

Answer 2

Type A:
-have myelin
-thickness of 2-20 μ
-velocity of 15-120m/seg
-Somatic nerves (sensitive and motor fibres)

Type B:
-have myelin
-thickness of 1-3 μ
-velocity of 3-15m/seg
-in preganglionar nerves (ANS)

Type C
-have NO myelin
-thickness of <1μ
-velocity of <2m/seg
- in postganglionar nerves (ANS) and 50% of sensitive fibre

Question 3

SUSCEPTIBILITY OF THE DIFFERENT TYPES OF NERVE FIBRES

Answer 3

HYPOXIA:
most susceptible: type B
intermediate: type A
least susceptible: type C

PRESSURE
most susceptible: type A
intermediate: type B
least susceptible: type C

LOCAL ANESTHESIA
most susceptible: type C
intermediate: type B
least susceptible: type A

Question 4

sensitive fibre classification

Answer 4

Ia: proprioception and streching
Ib: muscular tension + contraction strength
II: stretching, pressure of thin touch and vibration
III: thick touch, cold, acute pain
IV: heat, chronic pain, tickles

Question 5

AXONIC TRANSPORT

Answer 5

The axon has no ribosomes, so it can’t synthesise proteins
They are synthesised in the soma and transported quickly to the axon (anoxic transport)

Del soma a terminal axónico (anterógrado)
-transport of mitochondria and vesicles with NT, receptors, enzymes)
Mediated by kynesisns

Del terminal axónico al soma (retrógado)
-trasnport of waste products and non-functional mitochondria
- mediated by dyneins

Question 6

Neurogenesis in PNS

Answer 6

1. Growth cone goes near the myoblast and a functional primitive contact is stablished
2. There is an accumulation of synaptic vesicles in the anoxic terminal
3. Multiple axons converge in the same place
4. A neuromuscular junction matures and the rest of the axons are eliminated

Question 7

neurogenesis in CNS

Answer 7

In subventricular area: the new neurons migrate to the olfactory bulb, where they are functional
Subgranular area (hippocampus): new neurons help with learning

Question 8

neurogenesis in CNS

Answer 8

In subventricular area: the new neurons migrate to the olfactory bulb, where they are functional
Subgranular area (hippocampus): new neurons help with learning

Question 9

NEURONAL REGENERATION

Answer 9

In PNS
myelinated axons and dendrites can be repaired if:
-the soma is untouched
-schwann cells are still active

In CNS
very little or no reparation
the lack of regeneration is becase of:
- inhibitory influences of microglia, specially oligodendrocytes
- lack of signals that stimulate growth (only present in fetal development)

Question 10

NEUROTROPHINS

Answer 10

Proteins needed for growth and survival of neurons
They are products of muscles, other neurons and astrocytes
They are interiorised in the anoxic terminals and they are transported retrogrado to the soma.
In the soma they encourage the production of proteins related to the development, growth and survival of neurons.

Others are formed in the neuronal and are transported anterograde to the terminal.
They maintain the integration with the postsynaptic neuron