The Nervous System

Question 1

Functions of the Nervous System?

Answer 1

1)Sensation (info from outside world - ex: vision)
2)Integration (positive or negative info)
3)Initiation of motor activity (towards positive sensation, away from negative sensation
=turning sensation into action potentials)

Question 2

What are the 2 major sub-divisions of the NS? their functions?

Answer 2

-Central Nervous System
=brain + spinal cord (receives sensory info, integrates, generates motor activity, controls consciousness and perception)
-Peripheral Nervous System
=all nerves + glia outside the CNS (carries sensory info from periphery to to CNS via AFFERENT nerves
+ carries motor info from CNS to periphery via EFFERENT nerves)

Question 3

What are glia vs nerves?

Answer 3

• nerves = bundles of axons

- glia = clusters of cell bodies of sensory neurons

Question 4

What are the different functional divisions of PNS?

Answer 4

1) Sensory = afferent
-somatosensory (skeletal muscle and skin)
-viscerosensory (viscera/organs - ex: gut, bladder…)
-special sensory (ears, eyes, nose)
2) Motor = efferent
-somatomotor (skeletal muscle, voluntary)
-autonomic (smooth muscle, involuntary):
-parasympathetic/sympathetic (homeostatic control of
body)
-enteric (‘second brain’, gastrointestinal tract)

Question 5

Describe spinal nerves

Answer 5

-31 pairs, supply trunk and limbs
(8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal)
-spinal nerves contain both sensory and motor axons (=mixed)

Question 6

Describe cranial nerves

Answer 6

• 12 pairs, innervate head and neck
• control many head/neck functions
• some nerves purely motor, some purely sensory, some mixed sensory and motor

Question 7

Describe differences between grey vs white matter in spinal cord

Answer 7

• grey matter: in centre, contains cell bodies, roughly the same along spinal cord
• white matter: on outside, contains axon tracts, more white matter in neck than tail (axons taking info up along spinal cord)

Question 8

What is the brain comprised of?

Answer 8

-central core + 2 cerebral hemispheres

Question 9

What is the sympathetic nervous system?

Answer 9

• part of autonomic nervous system (itself part of PNS)

- “fight or flight”

Question 10

What is the parasympathetic nervous system?

Answer 10

• part of autonomic nervous system (itself part of PNS)

- “rest and digest”

Question 11

What is meant by laminar organisation of the grey matter in spinal chord?

Answer 11

• neurons with similar functions located in similar positions
• 9 distinct layers in spinal chord
• distinct positions in dorsal-ventral axis:
  1) neurons receiving pain/touch info
  2) interneurons relaying info to other neurons
  3) motor neurons

Question 12

What are the stages of neuron generation?

Answer 12

From multipotent ectodermal cells to neurals:

1) Competence (become progenitors)
2) Specification (stay or leave progenitor characteristics, reversible)
3) Commitment (neuronal subtype has been selected)
4) Differentiation (exit cell cycle and express neuronal genes)

Question 13

What is a totipotent cell?

Answer 13

totipotent: can give rise to all embryonic and extraembryonic tissue

Question 14

What is a pluripotent stem cell?

Answer 14

pluripotent: can give rise to all embryonic tissue

Question 15

What is a multipotent stem cell?

Answer 15

multipotent: can give rise to many different types of cells (but not all)

Question 16

What is a progenitor cell?

Answer 16

progenitor: can give rise to small number of cell types (final ones)

Question 17

What is a differentiated cell?

Answer 17

differentiated: leaves cell cycle (no longer divides), takes on characteristics of tissue it will form

Question 18

What is a morphogen?

Answer 18

morphogen: protein that gives positional info to cells via a concentration gradient and alters cell fates

Question 19

What is induction?

Answer 19

induction: instructing the development of cells through the local communication amongst embryonic cells

Question 20

What are organising centres?

Answer 20

organising centres: groups of inducing cells, secrete signals

Question 21

How do morphogens provide positional information?

Answer 21

-morphogens indicate to cells how close or far away they are from source of morphogen
-cells can thus locate themselves in tissue and relative to other cells
=differentiation accordingly

Question 22

What morphogen is responsible for the generation of distinct neural subtypes at distinct positions in dorsal-ventral axis of neural tube?

Answer 22

• Sonic Hedgehog (Shh)
• expressed by notochord and floorplate
• notochord induces floorplate which then induces motor neurons
• example:
  
  • high concentration = floorplate cells (closest to ventral notochord)
  • lower concentration = motor neurons
• continuous gradient of Shh is read out to give rise to different progenitor cells which will themselves give rise to differentiated cells

Question 23

How do neural crest cells differentiate?

Answer 23

NCCs come into contact with different inducing signals as they migrate to different parts of embryo

Question 24

What are the fates of NCCs in the trunk (in order)?

Answer 24

• sensory (dorsal) + sympathetic ganglia
• andrenomedullary cells (linked to NS)
• schwann cells
• melanocytes

Question 25

What NC populations are dorsal root ganglia comprised of?

Answer 25

DRGs formed by 3 NC pops:

• 1 from NC opposite anterior part of somite
• 2 from each adjacent region opposite posterior part of somite

Question 26

Describe the developmental potency of NCCs in trunk

Answer 26

-NCCs initially multipotent
=can differentiate depending on signals in different locations
-multipotency more restricted as NC ages
-later NC differentiates into melanocytes (less important in embryo/for development)

Question 27

What parts of the nervous system do NCCs give rise to?

Answer 27

NCCs give rise to large part of PNS:
-sensory neurons
-autonomic neurons
(-Schwann cells around axons)

Question 28

What is the function of Schwann cells in the PNS?

Answer 28

-Schwann cells are glial cells which wrap around axons of motor + sensory neurons of PNS
-they are support cells
-regulate speed of action potentials as they travel down axons
-heavy myelinating Schwann cells
=fast action potential conduction velocity
-non-myelinating Schwann cells
=reduction of action potential conduction velocity

Question 29

Give an example of heavily + poorly myelinated neurons

Answer 29

-sensory + motor neurons involved in knee jerk reflex
=heavy myelinated
-those involved in pain = less myelinated (slower signals)

Question 30

When do NCCs differentiate into Schwann cells?

When do they become melanocytes?

Answer 30

-NCCs only differentiate into Schwann cells once neural component has been fully formed
-contact of NCCs with axon of neuron = lineage restriction into glial cells (Schwann cells)
-axon produces signals:
once axon completely covered in glial cells, no more signal (signal hidden)
=NCCs become melanocytes instead of glial cells

Question 31

Describe the three-neuron sensory pathways

Answer 31

Most somatic and visceral sensor systems are three-neuron pathways:

1) primary afferent/sensory neuron conveys info from periphery to spinal chord
2) secondary neuron ascends up spinal chord to thalamus
3) tertiary neuron projects from thalamus to appropriate region of sensory cortex