Click on a lesson name to select. Chapter 33 Nervous System Section 1: Structure of the Nervous System Section 2: Organization of the Nervous System Section 3: The Senses Section 4: Effects of Drugs

Neurons  Neurons are specialized nerve cells that help you gather information about your environment, interpret the information, and react to it Structure of the Nervous System Nervous System  Neurons consist of three main regions: the dendrites, a cell body, and an axon. Chapter 33

 Dendrites pass signals they receive on to the cell body in electrical impulses. Nervous System  The axon passes those impulses on to the other neurons or muscles Structure of the Nervous System Chapter 33

 There are three kinds of neurons: sensory neurons, interneurons, and motor neurons. Nervous System  Sensory neurons send impulses from receptors in the skin and sense organs to the brain and spinal cord.  Interneurons carry impulses to motor neurons Structure of the Nervous System Chapter 33

Nervous System 33.1 Structure of the Nervous System  Motor neurons carry impulses away from the brain and spinal cord to a gland or muscles, resulting in a secretion or movement.  The nerve impulse completes a reflex arc, or a nerve pathway that consists of a sensory neuron, an interneuron, and a motor neuron. Chapter 33

Nervous System Chapter 33

A Nerve Impulse Nervous System  Neurons at rest do not conduct impulses.  Sodium ions (Na + ) collect on the outside of the cell membrane Structure of the Nervous System Chapter 33

 Potassium ions (K+) collect on the inside of the cell membrane. Nervous System 33.1 Structure of the Nervous System  Negatively charged proteins actively transport sodium ions out of the cell and potassium ions into the cell. Chapter 33

An Action Potential Nervous System  A nerve impulse is also known as an action potential.  The minimum stimulus to cause an action potential to be produced is called a threshold Structure of the Nervous System Chapter 33

1. When a stimulus reaches threshold, channels open in the plasma membrane. Nervous System 2. Sodium ions are rapidly pumped through these channels causing a temporary change in the electrical charges.  More positive charges are now inside the membrane Structure of the Nervous System Chapter 33 Impulse Transmission Steps

3.The now positive charge inside the membrane causes other channels to open and the potassium is quickly pumped out of the cell. Nervous System 4. The potassium restores the positive charge outside the cell Structure of the Nervous System Chapter 33

 This rapid positive to negative to positive charge reversal moves along the axon like a wave. Nervous System  The movement can be seen by finding the sodium-potassium reversal pattern in the three diagrams Structure of the Nervous System Chapter 33

Nervous System Chapter 33

 Nodes along the axon allow ions to pass through the myelin layer to the plasma membrane. Nervous System  The ions jump from node to node and increase the speed of the impulse. Speed of an Action Potential 33.1 Structure of the Nervous System Visualizing Action Potential Chapter 33

 The small gap between the axon of one neuron and the dendrite of another neuron is called a synapse. Nervous System  An action potential is carried across these gaps by neurotransmitters. The Synapse 33.1 Structure of the Nervous System Chapter 33

 The nervous system consists of two major divisions: the central nervous system and the peripheral nervous system Organization of the Nervous System Nervous System Chapter 33

The Central Nervous System Functions Nervous System  The central nervous system (CNS) is made up mostly of interneurons.  Coordinates all of the body’s activities  Relays messages, processes information, and analyzes responses 33.2 Organization of the Nervous System Chapter 33

The Brain Nervous System  The brain is sometimes called the control center of the entire body.  Divided into the cerebrum, the cerebellum, and the brain stem Organization of the Nervous System Chapter 33

 The cerebrum is divided into two halves called the left and right hemispheres. Nervous System  The functions of the brain include thought processes (learning), memory, language, speech, voluntary body movements, and sensory perception Organization of the Nervous System Chapter 33

 The cerebellum controls balance, posture, and coordination. Nervous System  The skeletal muscles are controlled to make your motor skills coordinated and smooth Organization of the Nervous System Chapter 33

 The brain stem connects the brain and spinal cord and is composed of the medulla oblongata and the pons. Nervous System  The medulla oblongata helps control breathing rate, heart rate, and blood pressure.  The pons also aids in breathing Organization of the Nervous System Chapter 33

 The hypothalamus, located between the brain stem and the cerebrum, is essential for homeostasis. Nervous System  The hypothalamus regulates body temperature, thirst, appetite, and water balance Organization of the Nervous System Chapter 33

The Spinal Cord Nervous System  Nerve column that extends from the brain to the lower back.  Protected by the vertebrae  Processes reflexes 33.2 Organization of the Nervous System Chapter 33

The Peripheral Nervous System Nervous System  A nerve is a bundle of axons and may contain sensory and motor neurons.  The peripheral nervous system (PNS) contains all the neurons that are not part of the central nervous system Organization of the Nervous System Chapter 33

The Somatic Nervous System Nervous System  Nerves in the somatic nervous system relay information from external sensory receptors to the central nervous system, and motor nerves relay information from the central nervous system to skeletal muscles.  Voluntary movements and reflexes are a part of the somatic nervous system Organization of the Nervous System Chapter 33

The Autonomic Nervous System Nervous System  The autonomic nervous system carries impulses from the central nervous system to the heart and other internal organs.  The body responds involuntarily, not under conscious control Organization of the Nervous System Chapter 33

 There are two branches of the autonomic nervous system. Nervous System  The sympathetic nervous system is most active in times of emergency or stress when the heart rate and breathing rate increase.  The parasympathetic nervous system is most active when the body is relaxed Organization of the Nervous System Chapter 33

Nervous System Chapter 33

Taste and Smell  Specialized neurons in your body enable you to taste, smell, hear, see, and touch, and to detect motion and temperature The Senses Nervous System Chapter 33