Human Nervous System

What is a homunculus?

A model of what the body would look like if the actual body parts were in the same proportion as the parts of the brain dedicated to the sense. You can see that the hands, lips, and tongue have relatively much larger areas of the brain dedicated to the touch response than the legs or feet.

What are neurons?

A neuron is a single cell consisting of an axon, a cell body, and dendrites. A nerve is a bundle of axons wrapped together like wires in a cable.

Describe reflexes:

A reflex is a reaction that occurs without the intervention of the whole central nervous system. In the case of the knee jerk, the signal goes from your leg to your spinal cord and immediately back again to your leg. Your knee jerks without requiring the help of your brain.

Describe the brain:

Did you ever wonder where your feelings come from? Many people refer to feelings from the heart, but the heart has nothing to do with emotions. Feelings actually occur in the brain. In addition to feelings are your thoughts and your ability to acquire knowledge. Your brain also monitors and directs the functioning of all of the physical functions of your entire body.

What are somatic and autonomic nervous systems?

For every muscle you control, for every sensation you are aware of, there are many other sources of stimuli you are not conscious of. Blinking involves muscles. Generally, you don't think about doing it; it just happens. Breathing is a response to needing oxygen, but you don't have to coordinate each breath. When you eat, you don't tell your stomach to start digesting your food. Those actions don't just happen. Sensory receptors inside your body pick up information from the organs and send it to the brain, and the brain directs these things to go on. So, the motor division has two parts: The somatic nervous system receives messages from motor neurons that govern activities you control consciously. The autonomic nervous system receives messages from motor neurons that govern activities you do not control consciously.

Describe the motor division:

Once the brain has processed information from the sensory division of the PNS, it sends out its responses via the motor division. Neurons in the motor division are motor neurons, and they carry signals from the CNS to the PNS. Every muscle you move—the muscles in your typing fingers, running legs, and smiling face—receives messages from motor neurons that stimulate those muscles to contract.

Describe sensory receptors:

Sensory receptors are structures that are capable of detecting stimuli. They are located at the end of special neurons called sensory neurons. The body has five basic types of sensory receptors. Each type of receptor detects different forms of stimuli.

Describe the brain stem:

The brain stem regulates breathing, heart rhythms, digestion, and other basic life-support functions.

Describe the central nervous system:

The central nervous system (CNS) consists of the brain and spinal cord, and is responsible for processing information and sending out responses to the information it receives.

Describe the cerebellum:

The cerebellum governs motor activity and plays an important role in the perception of sensory stimuli. Coordination, balance, and posture are all governed by the cerebellum.

Describe the cerebrum:

The cerebrum is responsible for voluntary movement and conscious thought. The abilities to speak, understand language, remember things, respond emotionally, and smell odors are all centered in the cerebrum.

What is the nervous system?

The nervous system is a network that connects all parts of the body. The nervous system tells every part of your body what to do based on analysis of the information it receives. Just as blood vessels form a network throughout the body, the nerves make up a network, too. The best way to picture the nervous system is as a branching complex of wires (nerves) connected to one main computer (brain). Except for initiating certain reflex responses (such as jerking your hand away from a hot stove), the nervous system works like this: Nerves pick up information. Information moves to the brain for processing. The brain processes the information and sends out a response to the body. The body responds. Neurons carry the information from one part of the body to another to make the process happen.

Nervous system review:

The nervous system takes in, processes, and responds to information through the actions of billions of networked neurons. The nervous system plays many different roles. It responds to stimuli and changes inside and outside the body. It processes the information and responds to it in a way that is beneficial to the organism. It sends messages directing the body to do what the brain has determined should be done. It allows communication throughout the entire body. It allows humans and many other organisms to think, learn, and feel.

Describe the peripheral nervous system:

The peripheral nervous system (PNS) consists of all of the nerves of the body. The nerves take in information and deliver messages to and from the CNS. The PNS sends information to the CNS, which sends a response back through the PNS, so the flow of information in response to stimuli is most often like this: PNS→CNS→PNS

What are the two divisions of the PNS?

The second major division of the nervous system is the PNS. Remember, the CNS comprises the brain and the spinal cord. Every other area of the nervous system is part of the PNS. You can think of the PNS as consisting of two divisions: The sensory division of the PNS brings information from the body to the CNS. The motor division of the PNS brings information from the CNS to the body.

Describe the spinal cord:

The spinal cord is a thick, ropelike bunch of nerve tissues. Branching out from the spinal cord are 31 pairs of nerves that start the network of billions of neurons that communicate with all body parts. The main function of the spinal cord is to link the CNS to the PNS, so it is extremely vital to the entire body. It is the only pathway through which messages can travel to the brain. Your backbone, which is a column of bones called vertebrae, helps protect your spinal cord from damage, but injury can still occur. If the connection between the body and brain is lost, the affected body parts may be unable to move, which is what happens to a person who is paralyzed. In that case, somehow the spinal cord has been damaged, and the communication between certain parts of the body and brain has been lost.

Spinal cord:

You can think of the brain as the boss of a company and the spinal cord as the boss's personal assistant. The brain is the manager of everything the body does. Based on the information the brain receives, it orders every part of the body to deal with stimuli and respond in ways that maintain homeostasis. Some actions are under conscious control, while others, such as heart rate and digestion, are not. Like the boss's personal assistant, the spinal cord handles the billions of messages coming in from the PNS and makes sure they get to the brain. The spinal cord also directs messages coming from the brain, and sends them along the right pathway of nerves to reach their intended destinations.

The autonomic nervous system consists of the parasympathetic and sympathetic divisions:

You remember homeostasis—the balance of systems your body maintains. As you know, your body doesn't always exist in perfect balance. It must be constantly returned to that state. For example, one minute you are in homeostasis, but after an intense workout, your cells are deficient in oxygen. Then, your heart rate increases to pump more oxygen to your cells. Two divisions of the autonomic system—parasympathetic and sympathetic—work together to keep your body balanced, and at the same time allow it to respond to stimuli as needed. These two divisions counter each other's efforts to restore balance to the body. The parasympathetic division works mostly when the body is in a calm or resting state. It sends messages that keep your body working normally, such as keeping your breathing calm or keeping your blood pressure even. The sympathetic division sends messages to body parts during times of intense activity or stress. That stress could be either physical or emotional, but in both cases, a response is activated because of something unusual that is going on.

What are the nervous systems main subsystems?

the central nervous system and the peripheral nervous system.