Biology Cell Notes

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Dana Ballout Biology Notes May 5, 2012
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...
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