Nervous System

Question 1

Information coming out of the central nervous system is transmitted along….. neurons.

Answer 1

Efferent

Question 2

The multiple thin, branched structures on a neuron whose main function is to receive incoming signals are the …..

Answer 2

Dendrites

Question 3

The RMP most closely reflects the equilibrium potential of ………., meaning that,………

Answer 3

Potassium ions, meaning that substantial amounts move out of a cell, rendering it slightly negative internally.

Question 4

What is true about the cell membrane charge

Answer 4

Cells generally carry a slight negative charge, which exists internally, and is localized at the cell membrane.

Question 5

What does RMP stand for?

Answer 5

It is the RESTING MEMBRANE POTENTIAL and is the electrical gradient across the cell membrane value of 70 mV

Question 6

How does RMP happens in the cell ?

Answer 6

K + ions contribute to the resting membrane potential
* in electrical equilibrium and chemical disequilibrium.
*membrane is more permeable to k+ ions
*k+ excess-ve charge buildup inside the cell as Pr- cannot cross the membrane. An electrical gradient is formed.
*The- negative charges attract k+ ions back into the cell down the electrical gradient.
*Net movement of k+ stops. The membrane potential at which the electrical gradient opposes the chemical gradient known as the equilibrium potential E. Ek= -90 mV

Question 7

What is the value in mV in the Resting membrane

Answer 7

If we consider the contribution of Na+ alone the resting membrane potential would be +60 Ena. However, K+ is 40 times more permeable in the cell. Ek Would be -90 if it is taken alone. But in real cell because a small amount of Na leaking into the cell the value is -70mV

Question 8

What is the Nerst equation?

Answer 8

This equation refers to the equilibrium potential. Derived under resting membrane conditions when the works required to move an ion across the membrane (up its concentration gradient) equals the electrical work required to move an ion against a voltage gradient.

Question 9

What is hyperkalemia ?

Answer 9

Is when the concentration of potassium in the body is higher than the normal parameters. Therefore, the kidneys are not able to get rid of it and potassium build up in the blood. Potassium helps for muscles to work including heartbeat and respiration. High levels can lead to heart failure.

Question 10

If Na+ gates in cell membranes were to open, what could happen to na+ and to the charge across the membrane, and why?

Answer 10

Na+ is in higher concentration outside the membrane
* The inside of the membrane is negatively charge with respect to the outside.
This create an electrochemical gradient for Na+
*Na+ ions carry in positive charges, causing the interior of the cell to become more positive.
* If the membrane potential is changed to the threshold level. an action potential will be generated ( all or none/ nothing principle.

Question 11

There are three main types of gated channels (related to the nature of the stimulus each responds to) - What are these and how do they work?

Answer 11

MECHANICAL CHANNEL: *Respond to mechanical stimuli e.g. pressure or sound waves.
*All of these stimuli channels the conformation of the channel protein and open up the channel.
VOLTAGE GATED CHANNEL:
*Open when the membrane potential changes to a particular value.
CHEMICAL GATED CHANNEL:= ligand-gated= receptor-mediated
*Open when a chemical molecule e.g. neurotransmitter binds .

Question 12

In terms of neural signalling, what does the “all or nothing” rule refer to ?

Answer 12

An action potential will happen only when the membrane of an excitable cell is stimulated to a particular threshold value.
Once is reached, depolarisation and the formation of an action potential must happen.

Question 13

Describe how the voltage gated sodium channel, once activated, initiates electrochemical changes across the membrane, and how these sodium gates determine the absolute refractory period.

Answer 13

When a membrane is depolarised to the threshcold by a stimulus, the voltage change across the membrane is enough to open Na+ channel activation gates.
*Na+ ions flood into the neurone, carrying positive charges. The more positive the inside of the cell becomes, the more Na+ gates open .
*This change in membrane potential from negative to positive inside depolarises the membrane to a maximum of about 30mV.
*The influx of Na+ is stopped when the inactivation gate closes.
*For short time period, the gates on the Na+ channels have not been reset, and another stimulus of the same size cannot stimulate the formation of another action potential. This short period of time is called the absolute refractory period.

Question 14

In terms of generating AP’ what is the functional difference between the absolute and relative refractory period.

Answer 14

ABSOLUTE REFRACTORY PERIOD:
*No furtheraction potential can be stimulated, no matter how strong the stimulus
*Na+ channel gated have not yet been reset.
RELATIVE REFRACTORY PERIOD:
* A large suprathreshold graded potential can start a second AP by activating Na+ channels which have been reset.
*Refractory periods limit the rate at which signals can be transmitted down a neuron.
*Absolute refractory period prevent reverse propagation of action potential (Action potential travels in only one direction)

Question 15

What constitutes a myelinated axon?

Answer 15

*Myelin is a fatty coating around the axons of some neurones.
*Laid down by oligodendrocytes in the CNS and Schwann cells in the PNS.
*Interrupted at intervals
*Allows more rapid action potential by saltatory conduction.

Question 16

How does the chart of action potential works?

Answer 16

1.Depolarization: Na+ enters
2. Repolarization : K+ leaves
3. Hypolarization after- -70 mV
4. the membrane potential unit is millivolts
5. Ant time is measured in milliseconds

Question 17

Which of the following does not influence the time necessary for the nerve impulse to be conveyed by a particular neuron.

Answer 17

• Length of the axon
  *Presence or absence of myelin sheath
  *Diameter of the axon
  *Presence or absence of nodes of ranvier
  Correct answer: Whether the axon is sensory or motor.

Question 18

Voltage-gated sodium channels in the neurons provide for movement of Na+ intro or out of cells ? And this movement is due to?

Answer 18

Into cells, due to an electrochemical gradient

Question 19

High extracellular levels of potassium ions will…

Answer 19

Reduce the RMP to zero.

Question 20

One of the folloing concerning sub-thresholds potentials is incorrect- Which is it?

Answer 20

A) These occur on the membranes of the cell body and axon hillock
B)The move along axons to trigger pre-synaptic events.INCORRECT
C)They mey summate to produce an action potential.
D) They are activated by chemically- gated channels.
E)They are not activate(usually) by voltage- gated channel.

Question 21

What role does the sodium inactivation gate play in action potential(AP) propagation in nerve cells?

Answer 21

It prevents Na+ from entering the cell, and so determines the absolute refractory period.

Question 22

Which cell or cells provide for myelination of neural axons and to what effect?

Answer 22

Oligodendrocytes, to allow for rapid transmission of action potential in the CNS and Schwann cells, to allow for rapid transmission of action potentials PNS

Question 23

If a neuron has a resting RMP of -70, and it becomes hyperpolarized, the membrane potential is likely to be approximately……….. and the nerve is ………..

Answer 23

-85 mV………. Less likely to fire

Question 24

Tetrodotoxin is a toxin that blocks voltage gated sodium channels. What effect does this substance have on the function of neurons?

Answer 24

The neuron is not able to propagate action potential.

Question 25

Conotoxins are produced by fish- hunting snails and block voltage- gated calcium channels. Therefore, what effects would conotoxins have on synapse function?

Answer 25

*The release of neurotransmitter from nerve terminals is dependent on the entry Ca2+ through voltage-gated Ca2+ channels.
If these channelos were inhibited from opening by conotoxin, neurotransmitter would not be released——- no neurotransmitter across the synapse——– no postsynaptic potentials —- no action potential stimulated in postsynaptic neuron ot the muscle sarcolemma— no muscle contraction.

Question 26

What do SNARE proteins control? What are v- and t- SNARES and how do they interact?

Answer 26

SNARE protein (Soulable NSF attachment protein Receptor proteins) or the fusion of vesicles with the plasma membrane (exocytosis) or the membrane of internal organelle e.g. lysosomes
*Vesicle or v-SNAREs are incorporated into the membranes of transport vesicles during budding.
*Target or t-SNARE are located in the membranes target compartments.
*During membrane fusin, the SNARE proteins involved combine to form a SNARE complex
*The influx of calcium into the cell triggers the completion of assembly reaction.

Question 27

Direct transfer of electrical signals occur between nerve or muscle cells- explain how, and what the strengths and limitations of this signaling mechanism are ….

Answer 27

Action potential pass bidirectionally between cells at gap junction (cardiac and smooth muscle cell, some neurons). Ions can flow directly from neuron to neuron or muscle to muscle cell.
Benefits :
-Gap junctions provide a means to synchronise activity e.g. brain and retinal neurons, cardiac and smooth muscle cell intestine, ureter, uterus, embryological development. There is no deley.
Limitations:
-All electrical synapses are excitatory i.e. the presynaptic action potential cannot be converted into an IPSP
Electrical synapses cannot integrate information and make decisions.
-Electrical synapses can travel in either direction, so there is no way of directing signals from a specific origin to specific destination.
Signals cannot be amplified
-Signals cannot be modified.

Question 28

Write a short account of Myasthenia gravis, its causes, consequences and why acetylcholine-esterase inhibitors may be used to treat it.

Answer 28

-Autoimmune disease
- Antibodies to acetylcholine (ACh) nicotinic postsynaptic receptors at the postsynaptic muscle membrane.
*Fewer endplate potential will be produced, and they may fall below the threshold value of generation of an action potential. The end result of this process inefficient neuromuscular transmission.
-Progressively reduced muscle strength with repeated use and recovery of muscle strength after a period of rest.
-Acetylcholinesterase inhibitors reduce the destruction of ACh in the synapse, increasing the chance of activating the acetylcholine receptors.

Question 29

Neural signalling: Describe what happens when an AP arrives at the terminus ( at the presynaptic region of the neuron)

Answer 29

1) action potential arrives at axon terminal.
2) Voltage gated channels open and CA enters to the axon terminal.
3) Ca2+ entry causes neurotransmitter- containing synaptic vesicles to release their contents by exocytosis.

Question 30

why might a child liberally covered in insect repellent show muscle tremor? Remember that insect repellants commonly contain acetylcholine esterase inhibitors.

Answer 30

Normally, after the appropriate response is accomplished, acetylcholinesterase is released which breaks down the acetylcholine terminating the stimulation of the muscle.
-Acetylcholinesterase is unable to breakdown or remove acetylcholine, the muscle can continue to move uncontrollably-
-Repeated and unchecked firing of electrical signals can cause uncontrolled, rapid twitching of some muscle, paralysed breathing, convulsions, and in extreme cases, death.

Question 31

If several subthreshold graded potential originating at different location reach the trigger zone and at the same time to produce a suprathreshold potential

Answer 31

an action potential is initiated as a consequence of just spatial summation.

Question 32

What are the two types of summation and their definition.

Answer 32

-Temporal: two excitatory signals overlapping in time.
-Spatial: Signals are coming from different parts.

Question 33

A synapse must include: 1. axon; 2 presynaptic cell membrane; 3 synaptic cleft; 4 postsynaptic cell membrane; 5 Cell body. Which one of the following combination is correct.

Answer 33

2 presynaptic cell membrane
3 synaptic cleft
4 postsynaptic cell membrane

Question 34

Explain the EPSP and IPSP and how they relate to thresholds and firing action potentials.

Answer 34

The EPSP’s (Excitatory postsynaptic potential) will function to bring the postsynaptic cell closer to an Action potential, while an IPSP (Inhibitory postsynaptic potential) less likely to occur.

The axon hillock is the integrator of all the EPSP and IPSP (they are summed or added up here) that generated on the post synaptic membrane.

EPSP+ IPSP less than -55mV =No action potential

EPSP+ IPSP more than -55mV =Action potential

Question 35

If a stimulus to a nerve fails to reach threshold …….

Answer 35

A graded potential will likely occur.

Question 36

When more action potential arrive at the axon terminal, how are neurotransmitters affected?

Answer 36

More molecules are released into the synapse.

Question 37

Inhibitory postsynaptic potentials IPSP

Answer 37

Result in local hyperpolarizations

Question 38

Steroid hormones exert their action by …..

Answer 38

diffuses through the plasma membrane and bind an intracellular receptor.
by inducing changes in gene expression. They do this by binding cytoplasmic receptors in cells.

Question 39

What, in simple terms, defines a hormone?

Answer 39

Chemical substances (mostly amino acids based) secreted into the interstitial fluid/blood in very small amounts by specialised cells or glands and carried by the bloodstream to other parts of the body where they interact with specific receptors in the target tissue to produce a particular response

Question 40

Describe the similarities, and the major differences, between neural and endocrine signals.

Answer 40

Nervous system:
Electrochemical impulses delivered by hormones, rapid and precise.
Chemical neurotransmitters carry the signals the signal from a neuron to another neuron, a muscle, or a gland
(wired)

Endocrine system:
-Hormonal signals- chemical messengers
-Duration not speed-slower to start, last longer
-E.g. regulation of H2O and electrolyte balance, stress reaction, growth, reproduction, and so on
-Works with CNS to control of circulation, digestion , metabolism, mobilisation of defences.

Question 41

What does the term paracrine refer to?

Answer 41

Pararines: locally acting chemicals which affect nerby cells. Diffuse limited distances and are rapidly inactivated and include histamines, prostaglandins, nitric oxide, growth factors, and blood coagulation factors.

Question 42

What does the term autocrine mean?

Answer 42

Are chemicals which exert effects on the same cells which secrete them
e.g. growth factors to promote proliferation of the cell type-such as cytokines and interleukins used by some white cells involved in immune response.

Question 43

What does the term Endocrine mean?

Answer 43

They are released into the blood and lymph and distributed to the whole body, but act only on tissues which have a specific receptors for them.

Question 44

What are cytokines?

Answer 44

Cytokines are signalling molecules which allow signalling between cells to the immune system
Cytokines can act as paracrine, autocrine or endocrine molecules.

Question 45

Describe how water soluble hormones elicit intracellular in their target cells.-

Answer 45

-water soluble hormones bind to cell-surface and initiate a rely of second messenger signalling in the cell.
e.g. Cause an increase in the cellular concentration of cAMP, which leads to phosphorylation of cellular proteins.
e.g. enzymes , or cause a release of intracellular calcium stores

Question 46

Describe how lipid soluble hormones elicit intracellular changes in their target cells.

Answer 46

Steroid and thyroid hormones are lipid soluble and therefore able to diffuse through the plasma membrane
-Have cytoplasmic or nuclear receptors held inactive bound by chaperones.
-Hormones binds to its receptor and chaperones separates
-Hormone receptor complex binds to hormone response element of a gene.
-Activates or represses transcription and then mRNA
-mRNA translated to protein which brings about the cellular effect.
-The cellular effect develops more slowly that with second messenger systems.

Question 47

Distinguish between agonist and antagonist, permissiveness and synergic effects.

Answer 47

*Permissiveness
One hormone cannot exert its effects without another hormone being present.
E.g. Thyroid hormone “permits” for hypothalamic, pituitary and gonadal hormones to stimulate sexual development.

*Antagonism
One hormone or more hormones opposes the action of another hormone.
e.g. induline/glucagon, the first lowers blood glucose ,the second raises it.

*Synergism
More than one hormone produces the same effects on target cells, but the combined effect is grates than the sum of individual effects

*Agonists- activate a response from the receptor. The agonist can be a primary ligand which has a physiological role on the receptor. Or a drug molecule which has a similarly shaped receptor binding site and mimics the action of the primary ligand.

Question 48

Describe what vascular tone is , how is it achieved and the functional importance of it?

Answer 48

Vascular tone is the degree of contraction that is presented in smooth muscle associated with the vasculature. It is maintained primarily by noradrenaline released from the SNS (sympathetic nervous system) and enables the vessels to rapidly change in diameter either larger or smaller.

Question 49

With release of noradrenaline, some blood vessels constrict and others will dilatate- explain these phenomena in terms of receptors.

Answer 49

-Vessels that have smooth muscle cells with alpha receptors will constrict when noradrenaline binds to alpha receptors.
-Vessels that have smooth muscle cells with beta receptors will dilate when noradrenaline binds.
- These receptors are found in different parts of the body, alpha receptors in non-essential organs and beta receptors in coronary blood vessels and skeletal muscle vessels.
-You can therefore have different responses to the same hormone in different parts of the body.

Question 50

What might someone suffering an asthma attack be treated with beta agonist, and if this is a non-selective agonist, what might happen to their heart rate?

Answer 50

You would give someone beta agonist because you want to dilate the airways and activation of beta receptors will cause this .
However, if you gave them a non-selective agonist it will activate both beta 1 and beta 2 receptores. activation of beta 1 receptors will cause the heart to beat faster and increase blood pressure which you generally don’t want to do.

Question 51

An agent that is introduces to bind to cell receptors and elicit a response (i.e to activate receptors) is a/ an

Answer 51

Agonist

Question 52

An external agent that is introduced into the body and binds to a cell receptor to prevent it from responding is a/an

Answer 52

antagonist

Question 53

Which hormone would bind to receptors in the cell or in the nuclei of a cell to affect DNA expression?

Answer 53

any steroid

Question 54

If glucagon acting alone can maximally increases blood sugar to 100mg/ml, and adrenaline aline increased blood sugar to 50 mg/ml, but in combination these hormones increased blood sugar to 180 mg/ml, these two hormones are said to be

Answer 54

Synergic

Question 55

Only one of these endocrine organs is derives from neural tissue and release catecholamines upon SNS stimulation.

Answer 55

Adrenal medulla

Question 56

Airways usually hace a responderance of beta 2 receptors, and the heart beta 1 receptors, and many blood vessels have alpha receptors. These all bind to noraderalin. during an acute asthma attack, the sufferer is likely to benefit most from a

Answer 56

Beta 2 agonist

Question 57

what causes repolarization

Answer 57

k goes out of the cell

Question 58

A neuronal circuit where large number of presynaptic neurons provide input to one postsynaptic neuron is called…

Answer 58

convergence