Nerves

Question 1

What are cells of NS?

Answer 1

Neurons
receive and transmit information to other cells
Adult brain: ~100 billion neurons

Glia
many functions, support neurons in their functions

Question 2

What’s the structure of a neuron?

Answer 2

Soma (cell body)
- Contains nucleus, ribosomes, mitochondria etc.

Dendrites
•Branching fibres
•Receive info via synaptic receptors

Axon
•Thin fibre of constant diameter
•Information sender of the neuron

Myelin sheath
•Insulates the axon
•Nodes of Ranvier: interruptions in the myelin sheath

Presynaptic terminal (end bulb, bouton)
•Point from which axon transmits information

Question 3

What’s the difference between afferent and efferent axons?

Answer 3

Afferent axon: brings info to a structure

Efferent axon: carries info away from a structure

• Sensory neuron: afferent to the rest of the nervous system
• Motor neuron: efferent from the nervous system
• Within the nervous system axon can either be afferent or efferent

Question 4

What’s the structure of Glia?

Answer 4

Smaller but more numerous than neurons (1:10), many supportive functions
Do not transmit information across long distances

Astrocytes
•Help synchronize the activity of neurons
•Remove waste materials

Microglia
•Remove waste materials and microorganisms (viruses, fungi)

Oligodendrocytes and Schwann cells
•Build the myelin sheaths

Radial glia
•Guide the migration of neurons and the growth of their axons

Question 5

What protects the NS?

Answer 5

Skull (brain), backbone (spinal cord), meninges (membranes surrounding brain and spinal cord)

Blood-brain barrier
- Prevents viruses, bacteria, harmful chemicals from entering the brain
- Depends on the endothelial cells that form the walls of the capillaries
- Cells closely spaced, nothing passes between them
- To cross the barrier, chemicals need to cross the cell’s membrane

Question 6

What’s stops and passes the barrier?

Answer 6

Most viruses, bacteria, toxins
Large molecules, electrically charged molecules

Passively (no expenditure of energy)
Small uncharged molecules (O2, CO2)
Water
Fat-soluble molecules (vitamins A and D, various drugs)
Actively (expenditure of energy)
Glucose
Amino acids
Certain vitamins

Question 7

What’s nerve impulse?

Answer 7

Neurons conduct information via electrical impulses

Speed: < 1 meter/second (unmyelinated axon) to 100 m/s (myelinated axon)

Conduction of impulses depends on the resting potential and the action potential

Question 8

What’s resting potential?

Answer 8

At rest, neurons are more negative inside than outside
- Voltage difference called the resting potential
- Typical resting potential -70 millivolts (mV)

Results from an unequal distribution of negatively and positively charged particles

Question 9

How is resting potential maintained?

Answer 9

Concentration gradients
- Ions are in random motion
- Move from areas of high concentration to areas of low concentration

Electrical gradient
- Accumulation of charges repels like charges and attracts unlike charges
- (+ repels +, - repels -, + attracts -)

Membrane permeability at rest
- CL- and K+ pass
- Na+ pass with difficulty
- Protein ions do not pass

Sodium-potassium pump
- Transports Na+ out and K+ in
- Requires energy

Question 10

What’s action potential?

Answer 10

Action potential (AP) - response of a neuron to stimulation above a certain threshold
RP prepares the neuron to respond quickly to a stimulus with an AP
Stimulation results in depolarization – the neuron becomes less negative