Neurons

Question 1

What are nerve cells?

Answer 1

Cells that form nervous system and quickly carry signals along their membranes in the form of NERVE IMPULSES or ACTION POTENTIALS.

Question 2

What do nerve cells allows?

Answer 2

They allow for rapid communication between one part of the body and another

Question 3

What are the 2 main neurons for communication?

Afferent arrives, efferent exits - CNS

Answer 3

AFFERENT neurons take signals from PERIPHERAL TISSUES TO CENTRAL NERVOUS SYSTEM (CNS)
EFFERENT neurons take signals from CNS to PERIPHERAL TISSUES.

Question 4

What needs to be delivered to nerves?

Answer 4

Have high rate of metabolism and require a continuous delivery of O2 and GLUCOSE.

Can have extreme longevity (given optimum conditions, some can function for a lifetime).

Once formed and functioning they lose their ability to divide (amitotic).

Question 5

What are the main features of a nerve?

Answer 5

Neurons are often large, complex cells and they all feature a cell body.
Also feature:
A respective (input) region
A conducting component
A secretory (output) region

Question 6

Name the structure of the neuron

Answer 6

Cell Body (perikaryon/soma): The biosynthetic center of the neuron and contains the usual organelles (except centrioles).

Denetrites provide a LARGE SURFACE AREA to receive input.

Axon, arises from axon hillock, can be very short or long depending on neuron. Towards end, branches forming TELODENDRIA, the ending known as terminals, synaptic knobs or boutons.

Question 7

What are the 4 different structures of the neuron?

Answer 7

MULTIPOLAR NEURON (motor neuron in CNS)
BIPOLAR NEURON (in the eye)
PSEUDO-UNIPOLAR NEURON
UNIPOLAR NEURON

Question 8

What do dendrites (UNIPOLAR) receive?

Answer 8

Receive signal inputs which then get converted into charges of membrane voltage (Vm).

These electrical signals are not action potentials, but are short distance graded potential, which then spread.

Integration of Vm changes occur,

THIS ALL RESUTS IN AN AVERAGE Vm CHANGE REACING THE SOMA.

Question 9

What can be found in the cell body?

Answer 9

Consists of a large nucleus with a noticeable nucleolus surrounded by glandular cytoplasm (owls eye)

Mitochondria are found throughout cell body.

Microtubules and microfilaments also seen and are important in intercellular transport and in maintaining CELL SHAPE.

Proteins and some neurotransmitters are produced here.

Also aggregates all the inputs from the dendritic tree.

Then changes in Vm(membrane voltage) get transferred to the axon hillock.

Question 10

What does the axon hillock (UNIPOLAR) generate - can be found in the retina?

Answer 10

1st part of output pathway of neuron.

Generates action potential if receiving enough stimulation from cell body.

Expresses the ion channels that are needed for action potentials.

Question 11

What does the axon allow for?

Answer 11

Each neuron has a single axon arising from the axon hillock.

Different axon can vary in their diameter, which will reflect in their conduction speeds.

Individual axons retain a uniform diameter along their length.

Axons may occasionally have branches coming off, called AXON COLLATERALS.

Axons allow for action protein propagation towards targets.

Axons also allow for (axoplasmic) transport of molecules to nerve terminals.

Question 12

What is the membrane channel like at rest?

Answer 12

At rest the membranes of cells are electrically charged (POLARISED) with + change on the outside and - change on the inside.

Question 13

What is the membrane channel like when depolarisation occurs?

Answer 13

When nerve has be simulated, an action potential flows down the axon as membrane DEPOLARISATION is occurring.

DEPOLARISATION means that the + and - charges SWAP themselves across the membrane.

Nerves are REUSABLE, so after nerve has carried an action potential, its membrane will be RECAHREGED (known as REPOLARISATION). Nerve is now ready to function again.

Question 14

What does a plasma membrane do?

Answer 14

The plasma membrane of cell provides a barrier between the intercellular and extracellular environments.

Question 15

Name examples of a hydrophilic substances

Answer 15

HYDROPHILIC SUBSTANCES such as Na+, K+, Ca2+, Cl- ions and glucose are unable to simply diffuse in and out through cell membranes.

Question 16

What are membranes made up of?

Answer 16

Membranes are made up of PHOSPHOLIPID MOLECULES, which are AMPHIPATHIC and readily form BILAYERS.

Question 17

What is the voltage for many cells, skeletal muscles and the neurons?

Answer 17

For many cell types this is around -50 mV.
For resting skeletal muscle cells it is ~ -90 mV
For neurons the Vm is around -65 to -70 mV.

Question 18

What are the 2 things that contribute to a difference in voltage charge?

Answer 18

Plasma membrane forming a barrier against the SIMPLE DIFFUSION of ionic species.

Na+/K+ ATPase pump found in plasma membranes.

Question 19

What are ionic gradients generated by?

Answer 19

Ionic gradients are generated by Na+/K+ ATPase pumps

Question 20

What are the 3 things that K+ does for cells?

Answer 20

1) Controls cell volume
2) Renders nerve and muscle cells electrically excitable
3) Drives the active transport of sugars of amino acids.

Question 21

How much does K+/Na+ pump each?

Answer 21

Na+/K+ ATPase pumps helps POLARISE MEMEBRANES.

With each turn the pumps, pump out 3 Na+ ions but not let 2 K+ ions enter the cell.

Question 22

What charge does inside the cell lose and what does the charge of the outside gain?

Answer 22

Inside cell always LOSING + CHARGE, outside always GAINING + CHARGE.

Question 23

What are the 2 things channels can be?

Answer 23

LIGAND OPERATED (IONICTROPIC - without charges)
VOLTAGE OPERATED

Question 24

What kind of chain is Na+ channel and what does it contain?

Answer 24

Na+ channel is a single polypeptide chain with 4 repeating units (I-IV). The + helix contains many lysine and arginine residues and is probably involved with voltage gating.

The + charges maybe paired with - charges on other helices.
Membrane depolarisation shifts the position of helices, so opening the ion channel.

Question 25

What happens to the Na+ channels when anaesthsia is applied?

Answer 25

Voltage gated Na+ channels major role in normal nerve conduction. Local anasehetics e.g. LIDOCAINE , interfere with function to inhibit conduction.
Local anasehetics molecules diffuse in axons and begin BLOCKING Na+ CHANNELS.

Eventually many channels become in activated that an action potential can neither be SUBSTAINED NOR GENERATED.
Never block and so analgesia now occurs.

Local anasehetics are ‘use dependent’ meaning that degree of block PROPORTIONAL to the rate of nerve stimulation.

Indicated these drugs are better able to block open Na+ channels. So, nociceptive neurons may become affected before somatic nerves.

Question 26

What are the types of drugs that affect Na+ channel?

Answer 26

channel blockers:
- tetrodotoxin
- saxitoxin
- conotoxins
- local anaesthetics
- antiepilepitcs
- antidysrhythmics

block of inactivation:
- veratridine
- batrachotoxin
- scorpion toxin
- DDT
- pyrethroids

Question 27

What is the relative refractory period?

Answer 27

During interval when a second action potential can be generated, but initiation will require a stronger stimulus. The membrane will be hyperpolarised, so will need the bigger stimulus.

Question 28

What is the absolute refractory period?

Answer 28

When a neuron can’t carry another action potential. Ion channels close but are in a deactivated state and so can’t open again.

Question 29

What happens during the rate of AP propagation in a normal diameter?

Answer 29

Same diameter axons have a high resistance so slower conduction speeds

Question 30

What happens during the rate of AP propagation in a large diameter?

Answer 30

Large diameter axons have low resistance, so faster conduction speeds

Question 31

What is the function of the myelin sheath?

Answer 31

Some nerves surrounded by a whitish segmented covering known as myelin sheath. myelin good electrical conductor.
Periphery - these formed by Schwann cells, wrap themselves around an axon

Question 32

How does an action potential conduct in myelinated and unmyelinated axons?

Answer 32

Myelinated nerve fibre conduct action potential rapidly when compared to unmyelinated axons

Question 33

What part of the nerve cell is always unmyelinated?

Answer 33

Dendrites always UNMYELINATED

Question 34

What is a saltatory conduction?

Answer 34

Gaps between Schwann cells cause action potential to jump from node to node which greatly increases conduction speeds for a given axon diameter.

Question 35

List the axon classification of myelinated, diameters of axon and unmyelinated?

Answer 35

A = Myelinated axon
a, b, y and delta = diameters of axon
C = unmyelinated axon

Question 36

What is the function of a synapse?

Answer 36

Nerve terminals do not physically touch the cells they are innervating. Instead synapses occur at these points.

Synapses are minute gaps between neurons that are in communication with other cells (sometimes less than the diameter of vesicle).

Signal contained within an action potential, when it reaches the terminal of a neuron, has to jump across synaptic cleft and affects the next cell.

Question 37

How are neurotransmitters involved with the synapse?

Answer 37

As neurotransmitters are released from a nerve terminal and rapidly diffuse across the tiny synapse to stimulate receptors on the next cell.

Question 38

What happens when somatic motor neuron releases a neurotransmitter Ach?

Answer 38

somatic motor neurons release the neurotransmitter Ach in neuromuscular junctions, which binds to and simulates nicotinic receptors. If the level of stimulation reaches threshold, this has a EXCITATORY EFFECT and skeletal muscle fibers CONTRACT.

Question 39

What happens at preganglionic fibres - 4 steps?

Answer 39

1) Preganglionic fibres for both PARASYMPATHETIC and SYMPATHETIC nervous systems and release Ach that binds to nicotinic receptors.

2) All parasympathetic postganglionic fibres release Ach but here muscarinic receptors are stimulated.

3)Most sympathetic postganglionic fibres release noradrenaline (NA), which bind to adrenergic receptors.

4) Sympathetic postganglionic fibres that innervate sweat glands release Ach, which binds to muscarinic receptors.

Question 40

What did Dale suggest in 1910?

Answer 40

1910: Dale suggested noradrenaline mimicked sympathetic nerve stimulation more closely than adrenaline.

Question 41

What did Dale discovered in 1914?

Answer 41

1914: Dale discovered Ach has 2 types of activity. Muscarinic action of Ach can be reproduced by muscarine, which can be extracted from AMANITA MUSCARIA/FLY AGARIC. These effects can be BLOCKED using ATROPINE (extracted from atropa belladonna/deadly nightshade), to leave Ach nicotinic effects, which can be reproduced using nicotine (nicotiana tabacum/tobacco). Ach or ‘cholinergic’ receptors named after muscarine and nicotine.

Question 42

What happens when the neurotransmitter will diffuse across the synapse?

Answer 42

Released neurotransmitter will diffuse across the tiny synapse and bind to receptors on the post synaptic membrane.

Question 43

What happens at ligand gated ion receptors?

Answer 43

Ligand gated ion (ionotropic) receptors are often rapid acting, but have short lasting effects.
Receptor complex has ligand binding capabilities that controls its ion channel.

Answer 44

G-Protein Coupled Receptors (metabotropic) are SLOW ACTING, but have LONGER LASTING EFFECTS.

Have 7 transmembrane spanning regions and are not directly coupled to their targets.

Question 45

How are G-Proteins used as?

Answer 45

Have to use G-Proteins to act as ‘go-betweens’ so their responses take longer to occur.

Question 46

The responses for G-Protein would involve ion channels and what are the products formed by enzymes known as?

Answer 46

Responses may involve ion channels or affect secondary activation or inhibition of an intracellular enzyme e.g. adenylate cyclase (ATP - cAMP), phospholipase C (PIP2 - IP3 + DAG).
Products formed by these enzymes are known as SECOND MESSENGERS.
Second messengers form part of a cascade of intracellular events, leads to cell response.

Question 47

Why are G-Proteins called G-proteins?

Answer 47

G - Proteins are so called cus of ability of their a-subunits to bind the guanine nucleotides GDP and GTP.
At rest, they bind to GDP, but when stimulated bind to GTP.
G-Proteins are made up of a, B and Y subunits.

Question 48

How to switch off a synapse?

Answer 48

Action potential propagation and neuro transmitter release ceases.

Neurotransmitter is removed from the synaptic cleft by wither: BREAKDOWN OR REUPTAKE.

Question 49

What are the 2 driving forces of ions?

Answer 49

1) Conc gradient
2) Electrical charge

Question 50

what is nernst’s equation?

Answer 50

E ion = RT/zF in ([ion]o / [ion]i )

Question 51

Goldman Equation (Goldman Hodgkin Katz equation):