Nervous+System

The Nervous System

Our nervous system //__receives__//, //__interprets__// (or understands), and //__responds__// to information from inside and outside our body. The signals that our body responds to are called **stimuli**.

Parts of the nervous system
**1. BRAIN**

>> the largest part of the brain; it is responsible for learning, memory and your senses the back of the brain that is responsible for coordinating your muscles and your balance 3. **medulla:** the "stem" of your brain that is responsible for vital body functions - things your body has to do to stay healthy and are done automatically
 * the MAIN organ of the nervous system
 * the brain receives messages, interprets what the message is saying, and then makes a response.
 * has three parts:
 * 1) **cerebrum:**
 * 1) **cerebellum:**



**2. SPINAL CORD**

**3. NEURONS**
 * A thick bundle of nerves that runs from the base of the brain down the back. The spinal cord sends the response for a reflex

Reflexes and ordinary nerve impulses __//Ordinary Nerve// Impulses__ __//Reflexes//__
 * single cells that carry **impulses** (or messages) to and from the brain
 * neurons have these parts[[image:http://webspace.ship.edu/cgboer/neuron.gif width="264" height="195"]]
 * 1) **dendrites** - receive the message from another neuron
 * 2) **cell body/nucleus** - the center of the neuron
 * 3) **axon** - carries the impulse away from the cell body toward the next neuron
 * The space in between neurons is called the **synapse**. Impulses have to cross this synapse to the dendrites on the next neuron.
 * There are 3 kinds of neurons:
 * 1) **sensory neurons** - carry information TO the brain from our senses (ears, eyes, nose, tongue and skin)
 * 2) **interneuron** - neurons found in the brain and spinal cord; they connect to sensory neurons
 * 3) **motor neurons** - carry information FROM the brain to the muscles of the body - they causes our muscles to move!
 * Impulses for everyday kinds of actions
 * are responded to by the brain
 * are voluntary impulses - we can control them!
 * Impulses to protect the body from harm
 * are responded to by the spinal cord
 * are involuntary impulses - we cannot control them

Reviewed by: Elana Pearl Ben-Joseph, MDDate Reviewed: August 2004
 * What are Reflexes? **

Have you ever wondered why your leg kicks when the doctor taps your knee with that rubber hammer? It's because of your reflex.

A **reflex** is an involuntary, or automatic, action that your body does in response to something- without you even having to think about it. You don't decide to kick your leg, it just kicks. There are many types of reflexes and every healthy person has them. In fact, we're born with most of them.

Reflexes protect your body from things that can harm it. For example, if you put your hand on a hot stove, a reflex causes you to immediately remove your hand before the message, "Hey, this is hot!" even gets to your brain.

Other examples of protective reflexes are blinking when something flies toward your eyes or raising your arm if a ball is thrown your way. Even coughing and sneezing are reflexes. They clear the airways of irritating things.
 * Blinking and Sneezing**

The reflex that the doctor checks by tapping your knee is called the patellar, or knee jerk, reflex. It is also known as a deep tendon reflex (DTR) because the doctor is actually tapping on a tendon called the **patellar tendon**. This tap stretches the tendon and the muscle in the thigh that connects to it. A message then gets sent to the spinal cord that the muscle has been stretched.

The spinal cord very quickly sends a message back to the muscle telling it to contract. The contraction of the muscle causes your lower leg to kick out. You might be wondering why such a reflex exists. This type of reflex is important in keeping your balance. When you're standing up, gravity might cause your knee to bend slightly, and this could make you fall if you didn't have the protective DTR to straighten that knee and keep you standing upright.

A doctor often checks for DTRs to make sure that the nervous system is working properly. Aside from the knee, they can also be checked along the outside of the elbows, in the crooks of the arm, and at the wrists and ankles.

So the next time your doctor taps you with that little rubber hammer, say, "Hey doc, how are my DTRs?"

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