Description and explanation of how caffeine, barbiturates and opiates affect the various parts of the nervous system

The most widely used stimulants are

• caffeine (in coffee, tea, and cola beverages)

• nicotine (in cigarettes)

• amphetamines

• cocaine

All of these drugs mimic the stimulation provided by the sympathetic nervous system.  ACh is a neurotransmitter at synapses early in the pathways of sympathetic stimulation. Although a weak drug in one sense, nicotine is strongly addictive. The use of chewing gum and skin patches containing nicotine is designed to satisfy the craving for nicotine while avoiding the serious health effects of other ingredients in the item.
The effects of drug abuse vary from person to person, particularly when individuals just start consuming certain drugs. However, after long periods of continued use, the majority of individuals who take both  recreational and prescription drugs have a high likelihood of becoming addicted. Drug abuse and addiction can change a person's entire life within a very short time period. As a person begins to form a physical and emotional dependency on a particular drug, he or she feels a powerful urge to consume the drug regularly. The extent of an individuals vulnerability to his or her drug addiction depends on a wide variety of factors, including the person's genes, mental health, physical health, and environment. A person who is addicted to drugs will also have to deal with the physical drug addiction effects they will ultimately experience as a result of being addicted to drugs.
Different drugs affect the body in different ways, but all drugs chemically alter the brain. The drug effects that occur in individuals who consume drugs depend on how the brain processes the chemicals in each drug. The amount of drugs needed to cause certain effects vary as well. All of an individuals perceptions are controlled by the brain; therefore, the brain dictates the effects of drug abuse in individuals. What a person feels, hears, smells, tastes, thinks, and sees depends on what the brain is communicating to the individuals body. The brain and body have normal functioning patterns and operate according to very specific patterns when a person does not consume substances that cause any type of chemical disruption. However, when chemicals are introduced to the brain, the chemical messengers in the brain are altered, causing the brain to transfer a different set of signals to the body. Chemicals can cause individuals to see, think, and act very differently than they normally would, which is why drug abuse affects individuals and the world around them.

Description of the nervous pathway of a reflex arc

A reflex arc starts off with receptors being excited. They then send signals along a sensory neuron to your spinal cord, where the signals are passed on to a motor neuron. As a result, one of your muscles or glands is stimulated.Knee-jerk reflexThe knee-jerk reflex involves a sudden kicking movement of your lower leg after the tendon just below your kneecap has been tapped. Doctors often trigger this reflex to test the function of your nervous system. If the reaction is exaggerated or absent, it may indicate a damage to the central nervous system.Autonomic reflexesMost reflexes go completely unnoticed because they don't involve a visible and sudden movement. Body functions such as digestion or blood pressure, for example, are all regulated by reflexes. These reflexes are known as autonomic reflexes.

What synapses are and how impulses travel across them

A synapse is a gap between neourons, signals go in only one direction so there is a pre-synaptic neuron and a post-synaptic neuron. The signal originates near the cell body of the pre-synaptic neuron. It travels via action potential down the axon to what is called the  terminal button , which forms one part of the synapse. The terminal button contains neurotransmitters stored in vesicles. When the signal reaches the end of the axon, these vesicles fuse with the cell membrane and the neurotransmitters are dumped outside of the cell a  process called exocytosis into the synapse.

There are two main types of neurons:
Sensory neurons carry signals from the outer parts of your body (periphery) into the central nervous system.
Motor neurons (motoneurons) carry signals from the central nervous system to the outer parts (muscles, skin, glands) of your body
The motor neurons are specified to send messages away from the Central Nervous System. The sensory neurons are specified in the senses of taste, touch, hearing, smell, and sight. They send messages from the sensory receptors to the Central Nervous System.

the sensory neuron has sensory skin cell at the end of it, it is liked by a dendrom and then a celll body and axon.

while the motor neurns has dendrites to collect impulse from others, it has a cell body and a axon that passes the impulses to affected cell.

Sense organs, their receptors and the stimulus they respond to.

The five sense organs and the receptor it contains are:
• touch-skin, pressure , pain and temperature
• smell- nose, smell receptors near the olfactory nerve.
• Taste- Tongue, ( taste receptors  sweet, sour, salt and bitter)
• Hearing- ears, ear doom
• Sight- retina, eyes
Stimulus is a thing or event that triggers a specific functional reaction in an organ or tissue: "areas of the brain which respond to auditory stimuli
A receptor is an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve

Description of the main parts of the nervous system

nervous system

The nervous system is the control and communication system of the body. Its job is to send and receive messages. Your nervous system controls all your thoughts and movements.
Neurons
The cells that make up the nervous system are calledneurons. Long, stringy neurons are perfect for carrying the electrical messages that are the "language" of the nervous system. 
Brain 
The brain is the command center of our entire body. The brain is the body's main information center. It is made of billions of neurons. The brain helps the body respond to the information it receives from the senses. The brain also processes thoughts. When you think, neurons in your brain are working.
The brain has three main parts. The largest is the cerebrum, which controls vision, touch, and other senses.  Thinking takes place in the cerebrum. 
The cerebellum is another section of the brain. The cerebellum helps control balance and coordination. 
Another part of the brain is called the brain stem. The brain stem is the link to the spinal cord and it also controls digestion, breathing, and heartbeat.
Spinal
The spinal cord is a tube of neurons that runs up the spine and attaches to the brain stem. Information from nerves that branch out to the rest of the body goes to the spinal cord. Some messages are processed by the spinal cord but most information is sent on to the brain.