- James Stenson
Neurons are small in size, microscopic. They consist normally with a cell body, dendrites and an axon. However they are all differentiated in structure as they are related to their function.
Sensory Neurons - They are called afferent neurons. This means an impulse moving towards a point or the central anxious system. As the name advises they obtain their information from our sensory receptors. For instance our eye, ears, tongue and epidermis. The stimuli's information is then passed onto the control centre of the cell. It then undergoes the axon, till the finish of the neuron is come to at the axon terminals. These electric powered impulses that travel through the neuron can only flow in a single way. The composition of sensory neurons include the cell body and dendrons (single dendrite) being located outside of the spinal cord found in your arms, feet and torso. Axons inside a sensory neuron are brief contrasting to the dendrites(extensions that do impulses) that happen to be long. (WESTONE, 2015)
Diagram of the Sensory Nueron(Above) (WESTONE, 2015)
Motor Neurons - They are called efferent neurons. This implies an impulse leaving a point or to the central anxious system. This allows for responses from the brain to be sent to muscles or organs (effectors). The information first enters the motor neuron through the dendrites which is then handed onto the cell body (control centre). The impulse is then directed down although axon until it reaches the end of the neuron called the axon terminals. The axon terminals are called electric motor end plates whenever a motor neuron connects to a muscle. Contrastingly from sensory neurons the dendrites are brief and axons are normally long. The mind formulates the mandatory response and directs a series of electron impulses through the motor neurons to the effectors to offer an appropriate response. (WESTONE, 2015)
Diagram of your Motor Nueron (still left) (WESTONE, 2015)
The Myelin Sheath - These are a framework that is situated within many neurons beyond the central anxious system. Specialised skin cells known as Schwann skin cells myelinate skin cells by securely wrapping a sheath throughout the axon within a neuron. Myelin is abundant with fat and helps to create insulation for electrical activity. This insulation is exactly what helps the impulses to visit faster. (KENT, Michael, 2000) (WESTONE, 2015)
The Axon Terminals - They are found at the end associated with an axon. This structure allows the transfer of impulses in one neuron to another, without the neurons ever coming into physical connection with one another. The gap between the two neurons is known as a synapse. An electrical impulse will reach the end of the axon and this causes the release of neurotransmitter chemicals (stored in vesicles). The neurotransmitter chemicals cross the synaptic difference between your axons and invite the impulse to be continued. (KENT, Michael, 2000) (WESTONE, 2015)
Role IN A Reflex Arc - A reflex arc is a neural pathway that control buttons an action reflex. Most sensory neurons do not pass information directly to the mind, but instead to the synapse in the spinal cord. This enables reflex actions that occurs quickly using the spinal motor neurons minus the delay of experiencing to wait for an impulse from the brain. However the brain will still have the sensory type but this will be whilst the reflex action occurs. A good example of this is when you touch something hot, the skins sensory neurons take the stimuli and using a relay neurone send the impulse to a motor neurone for an instant reflex action. The mind shortly later on will be alerted to the stimuli after the reflex action has occurred. (KENT, Michael, 2000) (BBC BITESIZE, 2015)
The Framework and Function of the Individual Eye
|
Part of Eye |
Description and Function |
|
Aqueous Humour |
This is a watery smooth that fills a chamber of the attention called the anterior chamber. It is located behind the cornea and before the lens. The liquid is a salt solution (alkaline) including sodium and chloride ions. It retains the intraocular pressure. Provides nutrition for ocular tissues. Helps the refractive index. Immunoglobulins can be found which indicate a job within the immune system. |
|
Choroid |
A level of the eyeball between the retina and sclera. It really is a quite slender and very vascularised membrane. Its function is to help prevent blurred vision due to extra light on the retina. It achieves this by its dark brown colouring and pigment which helps to absorb the excess light. |
|
Ciliary Muscle |
This is located within your eyes and is also area of the ciliary body. It is a ring formed muscle that contracts and relaxes to alter the curvature of the lens of the eye. For instance when the ciliary muscle relaxes the lens is allowed to be chiseled, this permits us to focus on distant things. Conversely when the ciliary muscle is contracted the lens is permitted to be round, this permits us to concentrate on things that are near to us. |
|
Cornea |
The corneas function is to donate to image processing by refracting light as it enters the eye. It can be a strong, transparent bulge located at the front of the attention. It has a radius of ~8mm and it is a non vascular structure. It is very sensitive as it has a great great quantity of nerves. |
|
Fovea |
This is a small melancholy within the retina behind each eyesight. Large ammounts of photo-detector skin cells known as cones are located within the spot of the Fovea. It has a somewhat yellow appearance to it and is also the area of greatest acuity of perspective. Its function is high resolution imagery allowing us to focus on details. |
|
Hyaloid |
The Hyaloid membrane is clear and its function is to separate the retina from the vitreous humour. |
|
Iris |
This is the colored part of our eye and it is completely variable in size. This allows the iris to modify its size and so the pupils size to regulate the quantity of light entering the eye. |
|
Lens |
The lens refracts light moving through the attention. The light will already have been refracted once by the cornea. However it will concentrate the light into the retina. The lens can change condition according to the distance an thing being focused on is. That is known as accommodation and the ciliary muscles contracting and calming help to achieve these modifications and allow us to give attention to objects both near and way. |
|
Optic Nerve |
The optic nerve function is to provide the brain with sensory information for control within the brain. An optic nerve is connected to each eyes and is the second cranial nerve. Each optic nerve is made up of about one million fibres, these fibres are what permit the nerve to relay all the information obtained by the eye. |
|
Papilla |
This is where in fact the optic nerve leaves the attention to spread information to the brain. It is known as the blind spot of the eye. |
|
Pupil |
The pupil exists within both of our eyes and located within the centre. The pupil really helps to determine how much light gets into the eye. It achieves this by the pupilary reflex. When encountered by glowing light the nerves send information to the iris leading to a muscular contraction that reduces the size of the pupil. Less light is then able to enter the attention, the contrary happens when there is not enough light. The muscles in the iris will relax allowing the pupil to increase in size. This would then allow more light to get into the attention. |
|
Retina |
The retina is situated behind the eye and could it be a surface or display that allows a graphic to be created. It also gathers information and transmits it to the mind. The retina has photosenstive skin cells known as rods and cones enabling information to be changed into nerve impulses that can then be sent via the optic nerve to the brain. |
|
Sclera |
The sclera comprises of white fibrous tissue and elastic fibres. It is sometimes called the whites of your sight. It is a significant tough substance and its own firm fibrous materials helps keep up with the shape of the eye. It is very good thicker into the posterior of the eye. |
|
Vitreous Humour |
This a translucent element that fills the chamber behind the lens of the eye. It is a jelly like substance and it is quite thin. It really is enclosed by the hyaloid membrane. It's function is to keep carefully the structure and helps to keep the retina in place by pressing it up against the choroid. |
|
Zonules |
The Zonules function is to attach the lens to the ciliary muscles. Largely made of fibrillin (connective tissue). |
(IVY ROSES, 2015) (KENT, Michael, 2000)
3. 5
There are two types of photoreceptor cells, rods and cones, they both provide different functions.
|
Rods |
Cones |
|
The outer segment is rod formed. |
The outer section is cone shaped. |
|
Rods are sent out throughout the retina, there are roughly 109 rod cells per eye. Due to the quantity of rods they are used for peripheral vision. |
Cones are mainly found within the fovea of the eye. Which means that only images in the centre of the retina can be diagnosed. There are roughly 106 rod cells per eye which is a third less than rod skin cells. |
|
Rod skin cells offer good level of sensitivity and can detect an individual photon of light. This makes them very helpful for vision at night and in the dark. |
Cones contrastingly offer quite poor awareness and require dazzling light to function. As a result they are just practical in well lit surroundings or your day time. |
|
Rods have only one type, therefore they can only just offer monochromatic perspective. |
Whereas Cones have three types, red green and blue, as a result they are accountable for allowing us to see shades and have colour vision. |
|
Multiple rods are just connected to one bipolar cell. This means that this leads to poor acuity. Rods are not effective at resolving fine detail of things in emphasis. |
Conversely each cone is normally connected to one bipolar cell. This results very good acuity. The cones can be utilized for resolving details and focusing objects in high res detail. |
(BIOLOGY MAD, 2015)
Visual acuity is what level of details can be seen, for example reading would require word on a full page would require high acuity. For an activity such as reading the cones would be accountable for the high res focus required. Even though we have way fewer cones than fishing rod, we prioritise using cones as they enable this fine detail target and their perception of colorings. We're constantly moving our eyes so that images can be centered on a small area of the retina called fovea. It may appear that we can read many words at once but in certainty we only read one expression at a time. But to pay because of this our eyes move rapidly and present us the impression that we can read more. Cones offer a lot more clarity than rods this is because of the actual fact they are very densely crammed at 160, 000 cones per mm2. This when compared to family pets such as Hawks is suprisingly low as they may have 1 million cones per mm2. Hence the expressions "You see like a hawk" "Hawkeye" etc.
Cones are also accountable for colour vision. As humans we've three varieties of rhodopsin that are sensitive to various areas of the visual light spectrum. Ten percent of the cones are delicate towards red. Whereas renewable and blue cones are forty-five percent. This is mainly due to our evolution, having the ability to identify predators covering within long grasses and jungle surroundings. The brain steps the light from the result of each one of these three cones. It will compare the nerve impulses and it allows the brain to detect any shade (That we're in a position to see).
In other animals notable examples include dogs, that have two different types of cones. Green and blue. This allows canines to see blue, inexperienced and yellows. Whereas Butterflies have five cones and can see colours that we as humans don't know exist. One of the most impressive exemplory case of colour vision in the pet kingdom is the mantis shrimp. It has sixteen shade receptive cones. To place that into point of view, rainbows are made of three colours (RGB), you can only imagine just what a rainbow must may actually a mantis shrimp. (BIOLOGY MAD, 2015)
Accommodation of the Eye
Accommodation is the ability of the eye to alter concentrate in response to both near and far things. To achieve this the eyes alter the form of the lens. The cornea is in charge of the primary concentrate and the lens is for adjustments. To regulate the lenses shape the suspensory ligaments and ciliary muscles must action upon it.
The image left is of a distant object. The zoom lens must be thin and have a long focal length. That is attained by the ciliary muscles relaxing and allowing the suspensory ligaments to pull the lens out. This makes the zoom lens thinner and we can focus on things in the distance.
The second image left is of the eye concentrating on an object up close. The lens is required to be thick and also have a short focal length. To achieve this the ciliary muscles agreement. This creates a tiny ring and needs the tension away from the suspensory ligaments. This makes the zoom lens into this solid, smaller form allowing us to see things strongly in hi-def. (BIOLOGY MAD, 2015)
Corneal Reflex
Also known as the blink reflex, this is the involuntary blinking of the eyelids scheduled to a stimulus of the cornea. This can appear from light, touching, or probably a overseas body trying to enter. This is a very fast response which occurs at 0. 1 of a second. Its only purpose is the safeguard of the eye. That is a brain stem reflex, a stimulus will impact the cornea and the nerves connected to the cornea as a sensory neurone. This information is then relayed to a motor neurone which causes the involuntary action of blinking or shutting of the eyelid.
Reflexes are involuntary and most importantly rapid activities. Nervous cells is far better suited to reflexes rather than hormones because of many reasons.
Type of sign, hormones are blood-borne impulses where as nervous tissues transmits through electric powered impulses across synapses. Hormones actions on the body are long lasting compared to the short lived nervous system response for a reflex. For example, holding your hand onto something hot would result in a sensory neurone to send information to a relay neurone and onto a engine neurone and the mind causing an instant muscle contraction, leading to you moving your arm. Evaluating this to the hormone Adrenaline which would offer you that attack or flight increase increasing your heart rate, levels of sugar in bloodstream, diverting blood vessels to muscles and brain and allows you to definitely quickly move your palm. However the destruction may have already happened to your hand before you'd time to respond. This is because the velocity of transmission of an hormone is relatively slower than the very fast and immediate stressed system. The control of a hormone is indirect as it impacts the bloodstream where as the stressed system is immediately controlling as it can control and switch on muscles and glands. Human hormones are also very wide-spread that affect various parts of your body, where as nervous cells is very localised. A good example of this might be insulin and glucagon.
This is produced within the beta cells of the pancreas this can be a peptide hormone. It regulates our blood sugar by using two hormones, insulin and glucagon. The pancreas is monitoring our bodies blood sugar levels constantly so when it picks up a spike, for example after consuming it will encourage the beta cells to produce insulin. The insulin assists the sugar absorption rate into cells where it can be used for cellular respiration. But when there exists too much sugar it will positively convert glucose into glycogen which is how the body stores energy. This process is known as gluconeogenisis.
But this is far too standard for a reflex to make use of. This process takes time to detect, for the hormones to be secreted into the blood stream and take time to get to areas that want remedy. That is why the swift characteristics of neurones is much better suitable for reflexes.
(KENT, Michael, 2000)
Bibliography
BBC BITESIZE. 2015. BBC. [online]. Available from INTERNET: <http://www. bbc. co. uk/schools/gcsebitesize/science/add_ocr_pre_2011/brain_mind/reflexactionsrev1. shtml>
BIOLOGY MAD. 2015. Eye - Cones, Rods. [online]. Available from World Wide Web: <http://www. biologymad. com/nervoussystem/eyenotes. htm#rodscones>
IVY ROSES. 2015. Anatomy of Human Eye. [online]. Available from INTERNET: <http://www. ivyroses. com/HumanBody/Eye/Anatomy_Eye. php>
KENT, Michael. 2000. Advanced Biology. Oxford, pp. 182-183.
WESTONE. 2015. Framework of Neurons. [online]. Available from INTERNET: <http://tle. westone. wa. gov. au/content/record/969144ed-0d3b-fa04-2e88-8b23de2a630c/1/human_bio_science_3b. zip/content/002_stressed_control/page_03. htm>
Word Count: 1628 (not including dining tables nor diagram annotations)
