15-1: How the Nervous System Works. 7 th Grade Life Science

Transcription

1 7 th Grade Life Science

2 Purpose Students will be able to: 1. Identify the functions of the nervous system. 2. Describe the structure of a neuron and the kinds of neurons found in the body. 3. Explain how nerve impulses travel from one neuron to another.

3 Functions of the Nervous System Functions of the nervous system include: 1. Receives info about what is happening inside and outside the body. 2. It directs the way your body responds. 3. It helps maintain homeostasis.

4 Functions of the Nervous System Receives info The nervous system allows you to see a fly buzzing around, smell food cooking, hear the birds. It also checks your blood pressure and blood sugar levels.

5 Functions of the Nervous System Responds to info The nervous system responds to what it receives. You may swat the buzzing fly or smile at the sound of the birds. The smell of food may cause your mouth to water.

6 Functions of the Nervous System Anything in an environment that can cause an organism to react is called a stimulus. What an organism does with a stimulus is called a response.

7 Functions of the Nervous System Swatting a fly and smiling are examples of voluntary responses. But when your mouth waters after smelling food, that is an involuntary response.

8 Functions of the Nervous System Heart beating, food digesting, and hormones being released are more examples of involuntary responses to a stimulus. DON T COPY Question: What stimulus causes insulin to be released as an involuntary response in your bloodstream?

9 Functions of the Nervous System Keeping homeostasis The nervous system receives a stimulus indicating you need nutrients. The body s response is to make you feel hungry.

10 What is a Neuron? The cells that carry information through the nervous system are called neurons or nerve cells. The message carried by a neuron is called a nerve impulse.

11 Neuron Structure A neuron has a large cell body containing a nucleus, threadlike extensions called dendrites, and an axon. Dendrites carry impulses toward the cell body.

12 Neuron Structure Axons carry the impulses away from the cell body. There are many dendrites, but only one axon per neuron. Axons can have more than one tip sending signals to more than one other neuron.

13 Neuron Structure Bundles of neuron axons get grouped together by connective tissue. A bundle of these nerve fibers is called a nerve.

14 Kinds of Neurons There are three kinds of neurons, the sensory neuron, interneuron, and motor neuron. Sensory neurons pick up stimuli from external and internal environments and convert it to a nerve impulse.

15 Kinds of Neurons The impulse travels along the neuron until it reaches an interneuron in the spinal chord or the brain. Interneurons carry impulses from one neuron to another.

16 Kinds of Neurons The pulse may then transfer to a motor neuron. Motor neurons send an impulse to a muscle or gland, which responds to the impulse.

17 How Impulses Travel Nerve impulses begin in the dendrites of a neuron. Then quickly (120 meters per second) travel to the neuron body and down the axon to the axon tip.

18 What happens at the synapse? At the axon tip, the impulse can jump to another structure across a gap called a synapse. Examples of other structures include another dendrite, a sweat gland, or a muscle.

19 How a Synapse Works For an impulse to cross the synapse (the gap), a chemical is released, which crosses over the gap and triggers the impulse in the adjacent neuron or structure.

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21 Billions of Neurons in your brain!!

22 Summary Neurons in your body receive a stimulus which your body responds to. Neurons are made of dendrites, a cell body, and axons. Bundles of neuron fibers are called nerves. Nerve impulses jump over gaps between neurons called synapses.