Co-ordination and Response شرح للثانوية الأجنبية ,, شرح مفصل
اللهم صل علي النبي
Co-ordination and Response
You have previously learned that one of the 7 characteristics of living organism is irritability or sensitivity. And this is the ability to detect a change in the outer environment and respond to it. A change in the environment is also called a stimulus (plural stimuli). Actions taken by the body in order to co-operate with a stimuli are called responses. The body detects a stimulus by parts in the body called receptors and is able to respond to it through other parts called effectors. Two organ systems are continuously working to detect and respond to stimuli, these organ system are called the nervous system and the endocrine system.
The Nervous System:
The nervous system is a system of organs working together to detect and respond to stimuli. The nervous system is made up of two systems, the Central Nervous System (C.N.S) and the Peripheral Nervous System (P.N.S) the peripheral nervous system connects the central nervous system to the other parts of the body.
Central Nervous System (CNS):
The central nervous system is made up of the brain and the spinal cord. The spinal cord is basically a big bundle of nerve cells running through a tunnel inside the backbone which protects it while the brain is protected by the skull. The central nervous system is what gives out orders to other parts of the body to perform certain jobs.
The Peripheral Nervous System PNS:
The peripheral nervous system is the other part of the nervous system. The main job of the PNS is to detect stimuli and send impulses to the CNS according to the stimuli. The PNS is made of receptors and nerves that carry the impulses.
Receptor cells are ones whose function is to detect something about its environment. There are many receptors in the body that are able to detect many changes like temperature, touch, light, sound and chemicals. There are some organs in the body that are there to detect just one stimulus, like the eye for example. These are called sensory organs and they can be defined as a group of receptor cells responding to specific stimuli.
Effectors are the opposite of receptors. Receptors are two detect the stimuli while effectors are two respond to it. Effectors are usually muscles and glands.
Neurons (Nerve Cells):
Neurones are one of the most important structures of the nervous systems. Neurones act as a wire that transmits electrical impulses all over the body. Like a cable that consists of many wires, a bundle of neurones is called a nerve. There are 3 types of neurones, each type is to transmit electrical impulses from a specific place to another.
Motor Neurone: This is a neurone that transmits electrical impulses from the Central nervous system to the effectors.
This neurone is made up of three segments; the cell body which is the start of the motor neurone and is in the CNS, axon which stretches out from the cell body all the way to end of the neuron, and the motor plate which is the end of the neurone and is in the effector muscle.
Neurones have features that are common between most animal cells like a nucleus, cymiddlelasm and cell surface membrane, but they also have some exclusive features like the axon. The axon is an extended cymiddlelasm thread along which electrical impulses travel. Some motor neurones have axons of length 1 metre. Axons are coated by a layer of myelin called myelin sheath, this is an electrically insulating layer which is essential for the proper functioning of the nervous system.
Another exclusive feature of neurones is dendrites, these are several short threads of cymiddlelasm coming out of the cell body. Their function is to pick up electrical impulses from other cells.
The last exclusive feature of motor neurones only is motor end plate. This is just the end of the axon which is in the muscle. It passes the electrical impulses from the neurone to the muscle fibres.
Sensory Neurones: like other neurones, sensory neurones carry electrical impulses from one place to another. But sensory neurones carry electrical impulses in the direction different to that of motor neurones, from the receptors to the CNS.
The sensory neurone’s shape is unique. This is because it is made of a cell body, with two arms extending out of it. The first arm is the axon which’s other end is in the CNS. The second arm is dendrite which’s other end is in the receptor. The dendrite is similar in structure to the axon except that it joins the receptor with the cell body. The electrical impulses of the sensory neurone flow from the receptor, through the dendrite to the cell body, then from the cell body to the CNS through the axon.
Relay Neurone: Relay neurones are located in the CNS. Their job is to pass electrical impulses from the sensory neurone onto the motor neurone, so it acts like a diversion.
Where neurones meet, they are not actually touching each other. Instead there is a gap called synapse or junction box. When the electrical impulses reach the end of a neurone, the neurone secretes a chemical transmitter which passes by diffusion to the other neurone causing the impulses to be carried from the first neurone to the second.
Reflex Arc (Nervous System in Action):
If your finger touches a hot surface, receptor cells in the skin of your finger detect a stimulus, which is a sudden rise in the temperature. The receptor uses the energy of the stimulus to generate electrical impulses. These impulses are then carried by the axons of the dendrites of the sensory neurone through cell body to axon and from the axon to the CNS. At the CNS the electrical impulses travel through the synapse to the relay neurone, which passes it onto the motor neurone. The nerve impulses are transmitted through the axon of the motor neurone to the targeted muscle which contracts when electrical impulses reach it, resulting in your finger being pulled away from the hot surface. This pathway is called the reflex arc and happens in about a fraction of a second.
Reflex Arc: RECEPTOR → Sensory Neurone → CNS → Motor Neurone → EFFECTOR
[IMG]Voluntary and Involuntary Actions: The reflex arc is a reflex action. Reflex means it is automatically done without your choice. This is because when the electrical impulses reach the relay neurone in the CNS from the receptors, some impulses are carried by other neurones to the brain, and some impulses are passes onto the motor neurone to the effector muscle and the response takes place. The electrical impulses going to your brain are much slower that the ones going to the effector muscle directly. This is why the reflex action takes place before you realise it, it is uncontrollable. Reflex actions are said to be involuntary actions. Involuntary actions start at the sense organ heading to the effector. They are extremely quick. Voluntary actions are the ones that you make the choice to do. Like picking up a bag from the floor for example. Your brain sends electrical impulses to the effector muscles ordering them to contract so you could pick the bag up. Voluntary actions are slower than involuntary actions and they start at the brain. The Human Eye: The human eye is a sensory organ. This means it is an organ of tissues working together to detect and respond to a specific stimulus, which is light.[/IMG]
Features of the Human Eye:
Lens: changes shape to focus light on retina
Ciliary muscles: contracts and relaxes to adjust thickness of the lens
Suspensory ligaments: loosens and tightens to adjust thickness of lens
Iris: widens and narrows to control amount of light entering the eye depending on light intensity
Choroid: middle layer surrounding the eye. It contains many blood vessels
Sclera: outer most tough, protective layer of the eye.
Retina: inner most layer. It is sensitive to light and it is where the fovea is and it has rods and cons
Fovea: very light sensitive spot
Blind spot: Where the optic nerve touches the eye. No light sensitive cells in this area.
How We See:
When the light hits an object, it is reflected in all directions. When a light ray reflected from the object hits your eye you see that object. At the back of your eye, there is a spot on the retina called the fovea (blind spot). This spot is full of light sensitive cells. When the light ray falls on the fovea, the light sensitive cells generate electrical impulses that travel through the optic nerve to brain. When the electrical impulses reach the brain, the brain generates the image you see. This all happens in less than a fraction of a second.
But this is the general idea only. Light rays enter the eye from every direction. If they are not focused on the fovea, they will most probably not hit it and we won’t see. Here comes the role of the front part of the eye. When the light ray hits the eye at an angle, it first has to penetrate the cornea which refracts (bends) the light ray inwards. The cornea acts as a converging (convex) lens. Then the light penetrates the lens which refracts the ray a little more inwards focusing the light ray on the fovea. And thus the light ray is focused on the retina. When the ray hits the retina, the closer to the fovea the sharper the image is.
Accommodation:
The angle at which the light ray hits the hits the eye depends on the distance of the object. Every light ray that hits the eye needs a certain amount of refraction in order to be directed to the fovea. This is why the lens has the ability to widen and narrow according to the distant of the object you’re looking at in order to make the light ray hit the retina at the right spot. This is called accommodation. Light rays refracted from close objects are diverging (spreading out), they need to be refracted inwards to be focused on the fovea. When you look at a close object, it takes some time till the vision becomes clear. This is because at first, the light ray is not correctly refracted, so it hits the retina away from the fovea. The electrical impulses are generated and sent to the brain which realises that the image is not clear. The brain then sends electrical impulses to the ciliary muscles making them contract. When the ciliary muscles contract the suspensory ligaments become loose, this makes the lens become thicker and rounder for more refraction of the light rays. Now the light rays are correctly refracted and hit the retina at the fovea, the image becomes clear.
[IMG]For far visions it is the exact opposite. The rays reflected from far objects are almost parallel. Very little refraction should be done. The brain sends electrical impulses to ciliary muscles making them relax, the suspensory ligaments now tighten up and pull the lens which become narrow.[/IMG]
Rods and Cones:
The retina is full of light sensitive cells called photoreceptors. There are two types photoreceptors, they are rods and cones. Rods and cones are specialised types of neurons. They look alike but they are a little different in function.
Rods are sensitive to dim light. At night or in dark places, most light detection electrical impulses transmission is done by rods. Vitamin A is essential for proper functioning of rods, if Vitamin A lacks it can lead to night blindness. Rods are spread all over the retina.
Cones are sensitive to bright and coloured light. All cones are packed in one area, the fovea.
The Pupil:
The pupil of the eye is the dark round area in the centre of it. It is surrounded by a coloured ring structure called the iris. The pupil and the together play a big role in protecting the eye from damage by limiting the amount of light entering the eye. If too much light fall on the retina, the rods and cones get damaged. The iris and pupil change their size to smiddle that happening. The iris contains two sets of muscles; Circular and Radial muscles. Circular muscles run around the iris and radial muscles run from the centre to the outside. When circular muscles contract they make the pupil smaller. When the radial muscles contract the stretch the pupil outwards making it wider.
In bright light, too much light starts entering the eye, which is dangerous for the rods and cones, which detect the high light intensity. The rods and cones start a reflex arc by sending electrical impulses to the brain via sensory neurone. The brain responds by sending electrical impulses to the muscles of the iris via motor neurone. These impulses make the circular muscles contract and the radial muscles relax limiting the amount of light entering the eye, thus protecting the rods and cones from damage.
If you walk into a dark room, the rods and cones sense the little amount of light. They start another reflex arc and send electrical impulses to the brain which responds by sending electrical impulses the muscles of the iris. The radial muscles contract and the circular muscles relax widening the pupil to let more light in
Antagonistic Muscles:
You have just learned that in order for the pupil to get narrower or wider, two muscles work simultaneously, when one contracts the other relaxes. Pairs of muscles like that are called antagonistic muscles.
The most known antagonistic muscle pair is the biceps and triceps of the arm. The bi and the tri for short, they are what causes the movement of the arm. They work simultaneously to bend or straighten the arm. The biceps is located in front of the humerus bone of the upper arm. The biceps is joined to the radius bone of the lower arm and the triceps is joined to the ulna bone of the lower arm. Muscles are attached to bones by strong fibres called tendons.
When you want to bend your arm the brain send two electrical impulses, one to the bi making it contract and one to the tri telling it to relax. When the bi contracts, it becomes shorter pulling the bones to which it is attached close and bending the arm. This causes the fibres of the tri to stretch while they are relaxed.
To straighten your arm, the brain send electrical impulses to both muscles making the bi relax in order to leave the muscle it is attached to free. The tri contracts and becomes shorter pulling the muscle it is attached to into place and straightening the arm.
The biceps can be called a flexor because it flexes (bends) the arm. The triceps can be called an extensor because it extends (straightens) the arm.
Co-ordination and Response
You have previously learned that one of the 7 characteristics of living organism is irritability or sensitivity. And this is the ability to detect a change in the outer environment and respond to it. A change in the environment is also called a stimulus (plural stimuli). Actions taken by the body in order to co-operate with a stimuli are called responses. The body detects a stimulus by parts in the body called receptors and is able to respond to it through other parts called effectors. Two organ systems are continuously working to detect and respond to stimuli, these organ system are called the nervous system and the endocrine system.
The Nervous System:
The nervous system is a system of organs working together to detect and respond to stimuli. The nervous system is made up of two systems, the Central Nervous System (C.N.S) and the Peripheral Nervous System (P.N.S) the peripheral nervous system connects the central nervous system to the other parts of the body.
Central Nervous System (CNS):
The central nervous system is made up of the brain and the spinal cord. The spinal cord is basically a big bundle of nerve cells running through a tunnel inside the backbone which protects it while the brain is protected by the skull. The central nervous system is what gives out orders to other parts of the body to perform certain jobs.
The Peripheral Nervous System PNS:
The peripheral nervous system is the other part of the nervous system. The main job of the PNS is to detect stimuli and send impulses to the CNS according to the stimuli. The PNS is made of receptors and nerves that carry the impulses.
Receptor cells are ones whose function is to detect something about its environment. There are many receptors in the body that are able to detect many changes like temperature, touch, light, sound and chemicals. There are some organs in the body that are there to detect just one stimulus, like the eye for example. These are called sensory organs and they can be defined as a group of receptor cells responding to specific stimuli.
Effectors are the opposite of receptors. Receptors are two detect the stimuli while effectors are two respond to it. Effectors are usually muscles and glands.
Neurons (Nerve Cells):
Neurones are one of the most important structures of the nervous systems. Neurones act as a wire that transmits electrical impulses all over the body. Like a cable that consists of many wires, a bundle of neurones is called a nerve. There are 3 types of neurones, each type is to transmit electrical impulses from a specific place to another.
Motor Neurone: This is a neurone that transmits electrical impulses from the Central nervous system to the effectors.
This neurone is made up of three segments; the cell body which is the start of the motor neurone and is in the CNS, axon which stretches out from the cell body all the way to end of the neuron, and the motor plate which is the end of the neurone and is in the effector muscle.
Neurones have features that are common between most animal cells like a nucleus, cymiddlelasm and cell surface membrane, but they also have some exclusive features like the axon. The axon is an extended cymiddlelasm thread along which electrical impulses travel. Some motor neurones have axons of length 1 metre. Axons are coated by a layer of myelin called myelin sheath, this is an electrically insulating layer which is essential for the proper functioning of the nervous system.
Another exclusive feature of neurones is dendrites, these are several short threads of cymiddlelasm coming out of the cell body. Their function is to pick up electrical impulses from other cells.
The last exclusive feature of motor neurones only is motor end plate. This is just the end of the axon which is in the muscle. It passes the electrical impulses from the neurone to the muscle fibres.
Sensory Neurones: like other neurones, sensory neurones carry electrical impulses from one place to another. But sensory neurones carry electrical impulses in the direction different to that of motor neurones, from the receptors to the CNS.
The sensory neurone’s shape is unique. This is because it is made of a cell body, with two arms extending out of it. The first arm is the axon which’s other end is in the CNS. The second arm is dendrite which’s other end is in the receptor. The dendrite is similar in structure to the axon except that it joins the receptor with the cell body. The electrical impulses of the sensory neurone flow from the receptor, through the dendrite to the cell body, then from the cell body to the CNS through the axon.
Relay Neurone: Relay neurones are located in the CNS. Their job is to pass electrical impulses from the sensory neurone onto the motor neurone, so it acts like a diversion.
Where neurones meet, they are not actually touching each other. Instead there is a gap called synapse or junction box. When the electrical impulses reach the end of a neurone, the neurone secretes a chemical transmitter which passes by diffusion to the other neurone causing the impulses to be carried from the first neurone to the second.
Reflex Arc (Nervous System in Action):
If your finger touches a hot surface, receptor cells in the skin of your finger detect a stimulus, which is a sudden rise in the temperature. The receptor uses the energy of the stimulus to generate electrical impulses. These impulses are then carried by the axons of the dendrites of the sensory neurone through cell body to axon and from the axon to the CNS. At the CNS the electrical impulses travel through the synapse to the relay neurone, which passes it onto the motor neurone. The nerve impulses are transmitted through the axon of the motor neurone to the targeted muscle which contracts when electrical impulses reach it, resulting in your finger being pulled away from the hot surface. This pathway is called the reflex arc and happens in about a fraction of a second.
Reflex Arc: RECEPTOR → Sensory Neurone → CNS → Motor Neurone → EFFECTOR
[IMG]Voluntary and Involuntary Actions: The reflex arc is a reflex action. Reflex means it is automatically done without your choice. This is because when the electrical impulses reach the relay neurone in the CNS from the receptors, some impulses are carried by other neurones to the brain, and some impulses are passes onto the motor neurone to the effector muscle and the response takes place. The electrical impulses going to your brain are much slower that the ones going to the effector muscle directly. This is why the reflex action takes place before you realise it, it is uncontrollable. Reflex actions are said to be involuntary actions. Involuntary actions start at the sense organ heading to the effector. They are extremely quick. Voluntary actions are the ones that you make the choice to do. Like picking up a bag from the floor for example. Your brain sends electrical impulses to the effector muscles ordering them to contract so you could pick the bag up. Voluntary actions are slower than involuntary actions and they start at the brain. The Human Eye: The human eye is a sensory organ. This means it is an organ of tissues working together to detect and respond to a specific stimulus, which is light.[/IMG]
Features of the Human Eye:
Lens: changes shape to focus light on retina
Ciliary muscles: contracts and relaxes to adjust thickness of the lens
Suspensory ligaments: loosens and tightens to adjust thickness of lens
Iris: widens and narrows to control amount of light entering the eye depending on light intensity
Choroid: middle layer surrounding the eye. It contains many blood vessels
Sclera: outer most tough, protective layer of the eye.
Retina: inner most layer. It is sensitive to light and it is where the fovea is and it has rods and cons
Fovea: very light sensitive spot
Blind spot: Where the optic nerve touches the eye. No light sensitive cells in this area.
How We See:
When the light hits an object, it is reflected in all directions. When a light ray reflected from the object hits your eye you see that object. At the back of your eye, there is a spot on the retina called the fovea (blind spot). This spot is full of light sensitive cells. When the light ray falls on the fovea, the light sensitive cells generate electrical impulses that travel through the optic nerve to brain. When the electrical impulses reach the brain, the brain generates the image you see. This all happens in less than a fraction of a second.
But this is the general idea only. Light rays enter the eye from every direction. If they are not focused on the fovea, they will most probably not hit it and we won’t see. Here comes the role of the front part of the eye. When the light ray hits the eye at an angle, it first has to penetrate the cornea which refracts (bends) the light ray inwards. The cornea acts as a converging (convex) lens. Then the light penetrates the lens which refracts the ray a little more inwards focusing the light ray on the fovea. And thus the light ray is focused on the retina. When the ray hits the retina, the closer to the fovea the sharper the image is.
Accommodation:
The angle at which the light ray hits the hits the eye depends on the distance of the object. Every light ray that hits the eye needs a certain amount of refraction in order to be directed to the fovea. This is why the lens has the ability to widen and narrow according to the distant of the object you’re looking at in order to make the light ray hit the retina at the right spot. This is called accommodation. Light rays refracted from close objects are diverging (spreading out), they need to be refracted inwards to be focused on the fovea. When you look at a close object, it takes some time till the vision becomes clear. This is because at first, the light ray is not correctly refracted, so it hits the retina away from the fovea. The electrical impulses are generated and sent to the brain which realises that the image is not clear. The brain then sends electrical impulses to the ciliary muscles making them contract. When the ciliary muscles contract the suspensory ligaments become loose, this makes the lens become thicker and rounder for more refraction of the light rays. Now the light rays are correctly refracted and hit the retina at the fovea, the image becomes clear.
[IMG]For far visions it is the exact opposite. The rays reflected from far objects are almost parallel. Very little refraction should be done. The brain sends electrical impulses to ciliary muscles making them relax, the suspensory ligaments now tighten up and pull the lens which become narrow.[/IMG]
Rods and Cones:
The retina is full of light sensitive cells called photoreceptors. There are two types photoreceptors, they are rods and cones. Rods and cones are specialised types of neurons. They look alike but they are a little different in function.
Rods are sensitive to dim light. At night or in dark places, most light detection electrical impulses transmission is done by rods. Vitamin A is essential for proper functioning of rods, if Vitamin A lacks it can lead to night blindness. Rods are spread all over the retina.
Cones are sensitive to bright and coloured light. All cones are packed in one area, the fovea.
The Pupil:
The pupil of the eye is the dark round area in the centre of it. It is surrounded by a coloured ring structure called the iris. The pupil and the together play a big role in protecting the eye from damage by limiting the amount of light entering the eye. If too much light fall on the retina, the rods and cones get damaged. The iris and pupil change their size to smiddle that happening. The iris contains two sets of muscles; Circular and Radial muscles. Circular muscles run around the iris and radial muscles run from the centre to the outside. When circular muscles contract they make the pupil smaller. When the radial muscles contract the stretch the pupil outwards making it wider.
In bright light, too much light starts entering the eye, which is dangerous for the rods and cones, which detect the high light intensity. The rods and cones start a reflex arc by sending electrical impulses to the brain via sensory neurone. The brain responds by sending electrical impulses to the muscles of the iris via motor neurone. These impulses make the circular muscles contract and the radial muscles relax limiting the amount of light entering the eye, thus protecting the rods and cones from damage.
If you walk into a dark room, the rods and cones sense the little amount of light. They start another reflex arc and send electrical impulses to the brain which responds by sending electrical impulses the muscles of the iris. The radial muscles contract and the circular muscles relax widening the pupil to let more light in
Antagonistic Muscles:
You have just learned that in order for the pupil to get narrower or wider, two muscles work simultaneously, when one contracts the other relaxes. Pairs of muscles like that are called antagonistic muscles.
The most known antagonistic muscle pair is the biceps and triceps of the arm. The bi and the tri for short, they are what causes the movement of the arm. They work simultaneously to bend or straighten the arm. The biceps is located in front of the humerus bone of the upper arm. The biceps is joined to the radius bone of the lower arm and the triceps is joined to the ulna bone of the lower arm. Muscles are attached to bones by strong fibres called tendons.
When you want to bend your arm the brain send two electrical impulses, one to the bi making it contract and one to the tri telling it to relax. When the bi contracts, it becomes shorter pulling the bones to which it is attached close and bending the arm. This causes the fibres of the tri to stretch while they are relaxed.
To straighten your arm, the brain send electrical impulses to both muscles making the bi relax in order to leave the muscle it is attached to free. The tri contracts and becomes shorter pulling the muscle it is attached to into place and straightening the arm.
The biceps can be called a flexor because it flexes (bends) the arm. The triceps can be called an extensor because it extends (straightens) the arm.
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رد: Co-ordination and Response شرح للثانوية الأجنبية ,, شرح مفصل
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رد: Co-ordination and Response شرح للثانوية الأجنبية ,, شرح مفصل
منوره حبيبتي
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