Neural Tissue

Question 1

Some neurons have as many as _____ dendrites

a) 5,000 b) 40,000 c) 100,000 d) 400,000

Answer 1

400,000

Question 2

What is the region called that an an action potential arises?

Answer 2

Axon hillock (initial segment)

Question 3

What happens at the axon hillock?

Answer 3

The axon hillock (initial segment) is the ‘trigger zone’ where propagated electrical signals are generated

Question 4

What is the name given to axon branches?

Answer 4

Collaterals

Question 5

Neurotransmitters can be released at the terminal axon and at a series of bulging areas known as….

Answer 5

Varicosities

Question 6

Which cells produce myelin in the CNS

Answer 6

Oligodendrocytes

Question 7

What are the differences between oligodendrocytes and Schwaan cells?

Answer 7

Schwaan cells: -Single myelin segment for a single axon -Surrounded by a basal lamina -Node of Ranvier covered by Schwaan cell processes Oligodendrocytes: -myelinate up to 60 axons -Bare node of Ranvier

Question 8

What is a nuclei?

Answer 8

Groups of nerve cell bodies with similar anatomical connections

Question 9

How is information passed between neurons?

Answer 9

At synapses by release of neurotransmitters from presynaptic terminals These act on receptors on the post synaptic membrane to cause depolarisation or hyper polarisation

Question 10

What does the PNS consist of?

Answer 10

Cranial nerves Spinal nerves Their ramifications

Question 11

Where are bipolar neurons found?

Answer 11

The afferent pathways of the visual, auditory and vestibular systems

Question 12

Nissl bodies a) What are they? b) Where are they found?

Answer 12

Nissl bodies are large granular bodies found in neurons that contain RER; ribosomes. They are the sites of protein synthesis. - easily seen with basophilic dyes - nerve cells are highly metabolically active.

Question 13

Which of the 2 are the motor proteins involved in the anterograde and retrograde movement of substances? a) Actin b) Kinesin c) Dynein d) Tubulin

Answer 13

Kinesin & Dyein -Anterograte = away from soma -Reterograde = back towards soma

Question 14

Neuromelanin, a brown-black pigment, is a by-product of the synthesis of catecholamines. Where is this noticeable found?

Answer 14

-Cell groups that use catecholamines as their neurotransmitter -Pars compact of the substantia nigra

Question 15

Give examples of when acetylcholine is the neurotransmitter

Answer 15

• Neuro (striated) muscular junction - Autonomic ganglia - Postganglionic sympathetic neurons

Question 16

What are the 3 types of neurotransmitters and give examples?

Answer 16

Amino acids - Glutamate &; GABA (excitatory & inhibitory respectifully in the CNS)

Monoamines - Dopamine, adrenaline &; noradrenaline

Peptides - Somatostatin & opiod receptors

Question 17

What are the 5 fundamental processes of synaptic transmission?

Answer 17

1 - Manufacture 2 - Storage 3 - Release 4 - Interact with post-synaptic receptors 5 - Inactivation

Question 18

What is neuromodulation?

Answer 18

Neuromodulators secreted by a small number of neurons that diffuse over a large area to regulate a diverse population of neurons.

Question 19

Give the 2 factors which determine the resting membrane potential

Answer 19

1. Differences in the specific ion concentrations of the intra and extracellular fluids
2. Differences in membrane permeabilities to the different ions

Question 20

Why is the Na+/K+ATPase pump an electrogenic pump?

Answer 20

It moves 3Na+ out of the cell for every 2K+ in

Net removal of charge from the cell which contributes to the membrane potential.

(Electrogenic contribution is small but it maintains concentration gradients which also affect the membrane potential)

Question 21

How is a resting membrane potential established?

Answer 21

Partially permeable membrane

Na+/K+ATPase pumps on membrane

3Na+ out for every 2K+ in

Creates an chemical gradient

Membrane more permeable to K+

K+ diffuse out along electrochemical gradient

Less positive charge on the inside

Some K+ diffuses back

Equilibrium established closer to K+ at about 70mV

Question 22

Describe the events which lead to an action potential

Answer 22

Neurotransmitters activate receptors on dendrites/soma

Receptors open Na+ ion channels

Influx of Na+ into cell

Change in membrane potential opens more voltage gated channels

If the potential changes felt in the axon hillock are positive & large enough, an action potential is triggered.

Question 23

What are graded potentials?

Answer 23

Changes in membrane potential that are confined to a relatively small region of the plasma membrane.

Produced when a specific change in the cells environment acts on a specific part of the membrane.

‘A potential change of variable amplitude and duration that is conducted decrementally; it has no threshold or refractory period’

Question 24

Define: pacemaker potential

Answer 24

A spontaneously occuring graded potential change that occurs in certain specialised cells

Question 25

What are the 2 main differences between Na+ and K+ channels?

Answer 25

1. Na+ channels are much faster
2. Na+ channels have an inactivation gate (ball and chain mechanism that limits the flux of sodium ions by blocking the channel shortly after depolarization opens it)

Question 26

How is one way propagation of action potentials established?

Answer 26

Change in the membrane potential has a positive feedback on Na+ channels close by to reach a threshold potential.

Generates a new threshold while the initial site is repolarising and then undergoes the refractory period.

Local current cannot generate a second action potential in initial site but ‘sets off’ an action potential in the region ahead.

Question 27

Explain why myleinated axons are more metabolically efficient than unmyleinated axons

Answer 27

1. Faster conduction speeds: Saltatory conduction between nodes of Ranvier. Less leakage of charge, charge arrives quicker and an AP is generated sooner
2. Reduces metabolic cost as fewer membrane pumps are needed to restore ions
3. Saves room - axons can be thinner

Question 28

Why does the break down of mylein affect the transmission of messages?

Answer 28

Degeneration of myelin and development of scar tissue disrupts and eventually blocks neurotransmission along myelinated axons

Question 29

Name the afferent fibers from left to right.

Is the speed of conduction increasing/decreasing from left to right?

Answer 29

Decreasing.

A alpha have a large diameter and are myleinated (80-120 m/s)

C fibres are small and unmyelinated (0.5 - 2.0 m/s)

Question 30

What do A delta and C afferent fibers have in common?

Answer 30

• Associated with nocieption
• Substantia gelatinosa (tip of dorsal horn)
• Excitatory
• Use glutamic acid and peptide substance P for neurotransmitters