Coordination and Control – Nerve Conduction Assignment
Task 1 – How Hormones Bind To Receptors
Throughout our bodies there are many processes happening every hour of the day. Our human nervous system will therefore have to start to detect and respond to these changes. There are two methods in which our bodies can respond to these responses. These are through the nervous system and are hormonal system. This process happens when the nervous system starts sending electrical messages along our nerves which then go onto reach different parts of our bodies. Another way is by the hormonal system this system starts to send chemical messages around our bodies in the blood. These electrical and chemical messages will tell our bodies what to do next.
The diagram demonstrates below how the hormone process works in three simple steps:
3714750121920Gland starts to produce chemical messengers
Chemical messages travel in the blood towards the whole of the body
Now starts to have effects at the target organs
Hormones have now been received and produced
Hormones are often “defined as a chemical messenger which is carried in the blood, which helps to regulate homeostasis, growth and reproduction and helps the body cope with stress.” (Dixon V 2018)
The structures which will respond to these hormones are called the target cells often referred to as target tissues or organs.
How Hormones Work and Bind To Target Cells
When a hormone starts to arrive at its target cell, the hormone will start to bind to a specific receptor, these acts as a switch which influences chemical or metabolic reactions inside the cell. “Receptors for peptide hormones are situated on the cell membrane and those for lipid-based hormones are located inside the cells”. (Grant, A, Waugh A 2010)
The level of hormones within the blood will be variable these can also be self regulating within its normal range. “A hormone is released in response to a specific stimulus and usually its action reverses or negates stimulus through a negative”. (Grant, A, Waugh A 2010)
In every second of our daily lives, there are hormone messengers working in order to keep our bodies on track. “These powerful endocrine system signalers start to regulate a variety of our cell processes”. (Tultane University 2004) They also have a role in stimulating cells in order to release chemicals, send electrical or chemical signals, or to grow or produce proteins.
This process always starts with a hormone starting to bind to a specific hormone receptor either one which is embedded in the cells outer surface membrane or one which is floating inside the cell cytoplasm or nucleus.
“There are three different ways in which a hormone can affect cell function.” (Dixon V 2018)
In some cases hormones can be affected by the permeability of the cell membrane. This happens when hormones starts to bind to a receptor on the actual membrane, this as a result the causes it to become activated which now acts a transporter which allows substances now to be able to enter and leave the cell. An example of this is when glucose uptake will be stimulated by insulin. Insulin will start to increase the absorption of glucose, this happens when it starts to trigger a membrane carrier mechanism. Without insulin are bodies would have to produce insulin blood glucose at 10-20 times higher than the normal rate for it to be able to work properly. It is particularly important for the brain. Blood glucose is filtered out of the blood by the kidneys. A process called active transport in the tubules start to return the glucose back to the blood in order to remain normal levels and make sure that none of this becomes excreted.
Some hormones will release what is called a second messenger, which is found inside the cell. This process happens when the hormones bind to a receptor on the membrane, this then goes onto activate an enzyme in the membrane, this now catalyses the production of a chemical which is found in the cytoplasm this can affect various aspects of the cell. For example, adrenalin stimulates the breakdown of glycogen. Adrenalin is commonly known to help with the fight or flight process. This prepares us to face any kind of danger which could be a threat to us it gears the body up to produce more adrenaline in order for us to deal with this situation and fastens the heart rate in order for us to become prepared to face these challenges and be able to fight or run away from situations. For example when we face danger our adrenaline is used in order to prepare us the fasten heart rate is one of the main symptoms the body faces this helps to prepare the body for extensive exercise e.g. running away from danger this process will start to cool off after the fight or flight process and the human experiencing this has calmed down.
39598601315720Finally the last type of hormone is called steroids. Steroid hormones are lipid soluble this means that they can easily pass through membranes by the process of diffusion. They will start to diffuse into the nucleus, where they go onto bind to a receptor, this then activates and is used for protein synthesis. An example of this is testosterone which stimulates sperm production. The male reproductive system produces the amount of testosterone required to be able to produces sperm to fertilise a female egg when this process works the female egg becomes fertilised and produces an egg which goes onto produce a foetus in the womb.
“Usually the hormone does not enter the cell. Its effect is determined not by the hormone itself, but by the receptor in the actual target cell.” (Dixon V 2018)
Therefore the same hormone can result in having different effects in different target cells overall.
Task 2 – Nerve Impulses Are Imitated and Transmitted
Nerve impulses start off from the function of neurones which are nerve cells and it is the transmission of signals from the sense organs such as; the skin and eyes within the central nervous system which controls the brain and spinal cord and from the central nervous system effectors organs. Each neuron will be made up of a cell body form which small projects which are called dendrites start to protrude.
“The cytoplasmic extensions transmit nerve impulses in one direction.” (Dixon V 2018)
The messages that the nerves carry are called nerve impulses, they will carry electrical signals. They will pass through very quickly along the axon of the neuron and then an impulse will travel along the axon similar to a train which is moving along a train track.
Each one will be separate from the next one. They will start to travel one after the other and some have fatty sheaths around them. This helps to insulate the axon and will as a result make the impulse travel in a faster way.
All are reactions within the body happen in the same. They are either one of the three: a stimuli, effectors or receptors. The stimuli are changes that can become detected. Receptors will detect change and effectors will bring out the responses.
A nerve impulse is initiated by the stimulation of sensory nerves endings or by the passage of an impulse which is from another nerve. Transmission of the impulse or action potential is mainly due to the movement of ions which are found across the nerve cell membrane. When it is in a resting state the nerve cell membrane becomes polarised. This is due to the differences in the concentrations of the actual ions which are across the plasma membrane. This therefore means that there will be a difference in the electrical charge on each side of the cell membrane. This term is often referred to as the resting membrane potential. When it is at rest the charge which is outside will be positive and the inside will therefore be negative. The main principle ions which are involved within this process are: Sodium (Na+ ) this is referred to as the main extracellular cation and Potassium (K+) and is referred to as the main intercellular cation.
In its resting state there will be a continual tendency for these types of ions to start to diffuse alongside their concentration gradients. For example, potassium will be outwards and sodium will be into the cells. When they become stimulated the permeability of the nerve cell membrane to those ions starts to change. Initially sodium floods into the neurone from the extracellular fluid which causes depolarisation, which then goes onto create a nerve impulse resulting in actual potential. Depolarisation is a very fast process which enables the conduction of nerve impulses along the length of a neurone within a few milliseconds. This will pass through the point of stimulation in one direction which is towards the area of resting potential. This one way type of direction enables transmission becomes ensured this happens due to the following depolarisation and therefore takes time for the repolarisation happen. Almost immediately after following the entry of the sodium and potassium this starts to flood out of the neurone and the movement of these ions will now start to return the membranes potential to its actual resting rate. This process is called the refractory period during which restimulation cannot occur as this would be impossible. The action of the sodium-potassium pump expels out sodium from the cell in exchange for potassium then goes onto return the levels of sodium and potassium to their original resting state, repolarising the neurone.
-476252577465In myelintaed neurones the insulin properties which the myelin sheath have prevents the actual movement of any form of ions. Therefore as a result any electrical changes which happen across the membrane can now only occur at the gaps in the myelin sheath. For example, at the nodes of the Ranvier. When an impulse happens at one of these nodes the depolarisation will start to pass along the myelin sheath towards the next node this is so that the flow of the current begins to appear and starts to leap from one node to another this process is called saltatory conduction. The actual speed of this conduction will depend on the diameter of the neurone. Therefore the larger the diameter the faster the conduction will be. In addition to this myelinated fibres will conduct impulses much faster than unmyelinated fibres this is because, salatory conduction is much faster than continuous conduction which is often referred to as simple propagation. The fastest fibres can conduct impulses to the skeletal muscles at a rate of 130 metres per second while the slowest impulses can only travel at a speed of 0.5 metres per second.
Summation Of Post Synaptic Potential
The Effect of Action Potential
There are many effects of action potential some of the common ones are that it opens up the sodium and calcium channels. The calcium inflow causes the docking of the vesicles at the presynaptic membrane. As a result to this the vesicles and membrane start to fuse together and a transmitter now becomes released into the cleft. Transmitter molecules open the sodium channels in the postsynaptic membrane
The Synapse and Neurotransmitters
The end of one actual neuron will be connected to the next one. There will always be a small gap in between the two. When an impulse reaches the end of an axon, a chemical will be produced. The chemical will now diffuse across the gap and starts off the impulse which is in the next neuron. Only at the end of a neuron will be able to make this kind of chemical. Therefore this is the main reason in which synapses make sure that an impulse can only travel in one direction.
Synapses have two main functions these are to act as resistor this is where the impulses will take a number of types before there is enough chemical produced in order to start the impulse into the next neuron. They also act as a form of junction box where one neuron can pass through on its own impulse to a number of neurons.
These synapses can easily be affected by the use of drugs; some drugs as a result can block them. Others can make them start to work in a rapid way which is now too quickly. Alcohol is known to be a trigger to causes affects in the brain. As a result this can slow down people’s reactions.
There will always be more than one neurone which is involved with the process of transmission of a nerve impulse from its main origin to its destination whether it is a sensory or a motor nerve. There will be no physical contact between the two neurones. The point in where the nerve impulse starts to pass through from the presypnatic neurone to the postsynaptic neurone is the synapse. At its free end, the axon of the presynaptic neurone breaks up into minute branches these then go onto terminate into small swellings which are called terminal boutons. These will be in a close proximity to the dendrites and the cell body of the postsynaptic neurone. The space which is now between them is called the synaptic cleft. “Synaptic knobs contain spherical membrane bound sypnatic vesicles” (Grant, A, Waugh A, 2010) these store a chemical the neuron transmitter which is now released into the synaptic cleft. Neurotransmitters are synthesised by nerve cell bodies, which are actively transported along the axons and are then stored in the synaptic vesicles. They are released by exocytosis this is in response to the actual potential and this starts the process of diffusing across the synaptic cleft. They will act only onto specific receptor sites on the postsynaptic membrane. However their action very short lived this is mainly due to the fact that they have immediately acted on the postsynaptic cell such as; the muscle fibre and they are either inactivated by the enzymes or they are therefore taken back to the synaptic knob.
However some types of important drugs which are used will start to mimic, neutralise (antagonise) or start to prolong neurotransmitter activity. Neurotransmitters will usually have an excitatory effect on postsynaptic receptors however these can sometimes become inhibitory.
There are also more than 50 different types of neurotransmitters which are found in the brain and spinal cord, some of these include; noradrenalin, adrenaline, dopamine, histamine and serotonin to name a few. Other substances such as: endorphins will have specialised roles in the transmissions of pain signals.
Somatic nerves will carry impulses directly to the synapses to the skeletal muscle, the neuromuscular junctions which stimulate contraction. In the automatic nervous system, efferent impulses will travel along two neurones (the preganglionic and postganglionic) and across two synapses towards the effector tissue for example, the cardiac muscle, smooth muscle and glands, in both the sympnatic abd parasympathetic divisions.
Adaptation Of The Synapse
If the stimulus is maintained there will become more generator potential which gradually lessons over time and the action potential can now stop.
Temporary adaptation occurs when the frequency of action potential is very high, this makes the transmitter secrete faster than it can be recycled. This can lead to temporary failure to be able to send action potentials in order to protect the body from continuous and possibly unpleasant stimuli.
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