Sensory system

Question 1

How is the spinal cord divided?

Answer 1

Cervical nerves (8 pairs)
Thoracic nerves (12 pairs)
Lumbar nerves (5 pairs)
Sacral nerves (5 pairs)
Coccygeal nerv (1 pair)

Question 2

What are the stages of development of the fetus

Answer 2

1. Ovum
2. Ball of cells
3. Balstocyst (week 1)
4. Blastocyst (week 3) — embyonic disk – Neural plate
   Neural plate will form Neural groove which will for Neural tube
5. Neural tube in the Neural plate (week 4)

Question 3

At what week does the Neural tube starts to form?
What does it become?

Answer 3

week 4
Becomes the CNS and part of the PNS

Question 4

What are the different parts of the Neural plate?

Answer 4

Ectotderm (become neural system and skin)
Mesoderm (become muscles and bones)
Endoderm (respiratory and digestive systems)

Question 5

What do the Forebrain, Midbrain and Hindbrain become?

Answer 5

Forebrain becomes cerebral hemispheres
Midbrain becomes midbrain
Hindbrain becomes Pons, Medulla, Cerebellum
Cavities become, ventricles and central canal

Question 6

What is the Law of specific nerve energies?

What is the Law of projection?

Answer 6

Law of specific nerve energies = Regardless of how a sensory receptor activated, sensation = the one for which the receptor is specialized
ex: rubbing your eyes makes you see light

Law of projection = Wherever in the brain you stimulate a sensory pathway, sensation always felts at the receptors location
ex: Phantom limb pain

Question 7

Which receptors are responsible for touch?

Answer 7

Mechanoreceptors!!
Superficial layer:
- Meissner’s corpuscule: rapidly ad, fluttering
- Merkel’s disk: slowly ad, pressure and texture

Deep layer:
- Pacinian corpuscule: rapidly ad, strong vibrations
- Ruffini endings: slowly ad, shape of object, stretch of skin

Question 8

What is referred pain?

Answer 8

Visceral and somatic pain afferents commonly synapse on same neurons in the spinal cord