The Nervous System: Chapter 35-2 Neurons and The Reflex Arc Science Standards: 9b and 9e

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1 The Nervous System: Chapter 35-2 Neurons and The Reflex Arc Science Standards: 9b and 9e Ms. Y. Martinez LSHS

2 Science Standards you will learn: 9b: how the nervous system mediates communication between different parts of the body and the body s interactions with the environment. 9e: the roles of sensory neurons, interneurons, and motor neurons in sensation, thought, and response.

3 The Nervous System In your body, the job of receiving and sending messages is done by your nervous system. The Nervous System allows us to run, write, see, talk, breath, etc. The basic cell of the Nervous System is the neuron. The Nervous System controls and coordinates functions throughout the body and responds to internal and external stimuli.

4 Neurons The nervous system is composed of nerve cells, or neurons. Neurons, the basic cells of the Nervous System, are cells that transmit impulses. Impulses are messages in the form of electrical signals.

5 E. Axon Terminal D. Myelin Sheath F. Cell Body B. Nucleus A. Axon C. Dendrites

6 Although neurons come in all shapes and sizes, they have certain features in common.

7 The largest part of a typical neuron is the cell body. The cell body contains the nucleus and much of the cytoplasm. Cytoplasm Nucleus

8 Spreading out from the cell body are short, branched extensions called dendrites. Dendrites provide a large surface area for connecting with other neurons, and carry nerve impulses towards the cell body.

9 The long fiber that carries impulses away from the cell body is called the axon. A single long axon carries the nerve impulse away from the cell body. The axon ends in a series of small swellings called axon terminals.

10 Most neurons have many companion cells called Schwann cells. Schwann cells wrap their cell membrane around the axon many times in a spiral to form a thick insulating lipid layer called the myelin sheath. As an impulse moves along the axon, it jumps between each Schwann cell, which increases the speed at which the impulse can travel.

11 A nerve is a discrete bundle of several thousand neuron axons.

12 Neuron Types Neurons can be classified into three types according to the direction in which an impulse travels. There are three types of neurons: Sensory Neuron Motor Neuron Interneuron

13 Sensory Neuron Sensory Neuron: carry impulses from the sense organs to the spinal cord and brain.

14 Motor Neuron Motor Neuron: carry impulses from the brain and the spinal cord to muscles and glands.

15 Interneuron Interneuron: Make up the brain and spinal cord connect sensory and motor neurons and carry impulses between them.

16 Name the Neuron: A. Sensory Neuron C. Interneuron Spinal Cord B. Motor Neuron

17 Divisions of the Nervous System The human nervous system is separated into two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

18 Central Nervous System The CNS relays messages, processes information, and analyzes information. It is the control center of the body. It includes the brain and spinal cord.

19 The Brain The brain is composed of three major parts: Cerebrum - largest part; controls senses, memory, intelligence Cerebellum - coordinates voluntary muscle movement Brain Stem - controls the body's involuntary actions

20 Peripheral Nervous System The PNS lies outside of the central nervous system. It receives information from the environment and relays commands from the central nervous system to organs and glands.

21 The Reflex Arc A reflex arc is the pathway along the central nervous system where an impulse must travel to bring about a reflex. A reflex arc is how neurons work together. It is how a stimulus elicits a response from your body without thinking. Examples include coughing and sneezing.

22 You need to keep the conditions inside your body constant. Doing this is called homeostasis. You need to detect a change in the environment (a stimulus) and react to the change (a response) in a way that maintains homeostasis. When you do this without thinking, it is called a reflex.

23 An example What is the stimulus? -The hammer hits the tendon. What is the response? -The muscle contracts, causing the foot to jerk upward.

24 Other Reflexes: Stimulus The aroma of your favorite food A nasty odor A bright light shining in your eye An insect flying towards your eye Response Salivation Nausea Pupils get smaller Blinking

25 Consider the following situation:

26 How it works: A reflex arc includes a sensory receptor, sensory neuron, an interneuron, motor neuron, and effector. An effector is a bodily organ (as a gland or muscle) that becomes active in response to stimulation. Salivary Gland

27 When you step on a tack, sensory receptors stimulate a sensory neuron. The sensory neuron relays the signal to an interneuron within the spinal cord. The signal is then sent to a motor neuron The motor neuron stimulates a muscle in your leg to lift your leg.

28 Reflex Arc Pathway: B. Receptor A. Stimulus C. Sensory Neuron D. Interneuron G. Response F. Effector E. Motor Neuron

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