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

Chapter 33 Nervous System 33.1 Structure of the Nervous System Neurons Neurons are specialized nerve cells that help you gather information about your environment, interpret the information, and react to it. Neurons consist of three main regions: the dendrites, a cell body, and an axon.

The axon passes those impulses on to the other neurons or muscles. Chapter 33 Nervous System 33.1 Structure of the Nervous System Dendrites pass signals they receive on to the cell body in electrical impulses. The axon passes those impulses on to the other neurons or muscles.

Interneurons carry impulses to motor organs. Chapter 33 Nervous System 33.1 Structure of the Nervous System There are three kinds of neurons: sensory neurons, interneurons, and motor neurons. Sensory neurons send impulses from receptors in the skin and sense organs to the brain and spinal cord. Interneurons carry impulses to motor organs.

resulting in a secretion or movement. 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.

Neurons at rest do not conduct impulses. Chapter 33 Nervous System 33.1 Structure of the Nervous System A Nerve Impulse Neurons at rest do not conduct impulses. Sodium ions (Na+) collect on the outside of the cell membrane.

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

A nerve impulse is also known as an action potential. Chapter 33 Nervous System 33.1 Structure of the Nervous System An Action Potential 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.

33.1 Structure of the Nervous System Chapter 33 Nervous System 33.1 Structure of the Nervous System When a stimulus reaches threshold, channels open in the plasma membrane. Sodium ions are rapidly pumped through these channels causing a temporary change in the electrical charges. More positive charges are now inside the membrane.

The potassium restores the positive charge outside the cell. Chapter 33 Nervous System 33.1 Structure of the Nervous System The now positive charge inside the membrane causes other channels to open and the potassium is quickly pumped out of the cell. The potassium restores the positive charge outside the cell.

Chapter 33 Nervous System 33.1 Structure of the Nervous System This rapid positive to negative to positive charge reversal moves along the axon like a wave. The movement can be seen by finding the sodium-potassium reversal pattern in the three diagrams.

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

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

Chapter 33 Nervous System

Chapter 33 Nervous System 33.2 Organization of the Nervous System The nervous system consists of two major divisions: the central nervous system and the peripheral nervous system.

The Central Nervous System Chapter 33 Nervous System 33.2 Organization of the Nervous System The Central 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

The brain is sometimes called the control center of the entire body. Chapter 33 Nervous System 33.2 Organization of the Nervous System The Brain The brain is sometimes called the control center of the entire body. Divided into the cerebrum, the cerebellum, and the brain stem.

Chapter 33 Nervous System 33.2 Organization of the Nervous System The cerebrum is divided into two halves called the left and right hemispheres. The functions of the brain include thought processes (learning), memory, language, speech, voluntary body movements, and sensory perception.

The cerebellum controls balance, posture, and coordination. Chapter 33 Nervous System 33.2 Organization of the Nervous System The cerebellum controls balance, posture, and coordination. The skeletal muscles are controlled to make your motor skills coordinated and smooth.

The pons also aids in breathing. Chapter 33 Nervous System 33.2 Organization of the Nervous System The brain stem connects the brain and spinal cord and is composed of the medulla oblongata and the pons. The medulla oblongata helps control breathing rate, heart rate, and blood pressure. The pons also aids in breathing.

Regulates body temperature, thirst, appetite, and water balance. Chapter 33 Nervous System 33.2 Organization of the Nervous System The hypothalamus, located between the brain stem and the cerebrum, is essential for homeostasis. Regulates body temperature, thirst, appetite, and water balance.

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

The Peripheral Nervous System Chapter 33 Nervous System 33.2 Organization of the Nervous System The Peripheral 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.

The Somatic Nervous System Chapter 33 Nervous System 33.2 Organization of the Nervous System The Somatic 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.

The Autonomic Nervous System Chapter 33 Nervous System 33.2 Organization of the Nervous System The Autonomic 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.

There are two branches of the autonomic nervous system. Chapter 33 Nervous System 33.2 Organization of the Nervous System There are two branches of the autonomic 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.

Chapter 33 Nervous System

Chapter 33 Nervous System 33.3 The Senses Taste and Smell Specialized neurons in your body enable you to taste, smell, hear, see, and touch, and to detect motion and temperature. Taste buds detect combinations of chemicals that we identify as sweet, sour, salty, and bitter.

Signals from these receptors work together to create Chapter 33 Nervous System 33.3 The Senses Receptors associated with taste and smell are located in the mouth and nasal cavity. Signals from these receptors work together to create a combined effect in the brain.

Light travels through the cornea and the pupil to the lens. Chapter 33 Nervous System 33.3 The Senses Sight Light travels through the cornea and the pupil to the lens. The lens focuses the image on the retina. Rods and cones in the retina provide light-sensitivity and information about color.

Sound waves enter the auditory canal and cause a membrane, Chapter 33 Nervous System 33.3 The Senses Hearing Sound waves enter the auditory canal and cause a membrane, called the tympanum, at the end of the ear canal to vibrate. These vibrations cause the cochlea to generate nerve impulses that are interpreted by the brain.

Chapter 33 Nervous System 33.3 The Senses Balance The semicircular canals, located in the inner ear, transmit information about body position and balance to the brain.

Chapter 33 Nervous System 33.3 The Senses Touch Many types of sensory receptors that respond to temperature, pressure, and pain are found in the epidermis and dermis layers of the skin.

Chapter 33 Nervous System 33.4 Effects of Drugs How Drugs Work A drug is a substance, natural or artificial, that alters the function of the body.

Chapter 33 Nervous System

Some drugs affect the nervous system in the following ways: Chapter 33 Nervous System 33.4 Effects of Drugs Some drugs affect the nervous system in the following ways: can cause an increase in the amount of a neurotransmitter that is released into a synapse can block a receptor site on a dendrite, preventing a neurotransmitter from binding can prevent a neurotransmitter from leaving a synapse can imitate a neurotransmitter

Many drugs that affect the nervous system influence the level of Chapter 33 Nervous System 33.4 Effects of Drugs Many drugs that affect the nervous system influence the level of a neurotransmitter called dopamine. Normally, dopamine is removed from a synapse by being reabsorbed by the neuron that released it.

Classes of Commonly Abused Drugs Chapter 33 Nervous System 33.4 Effects of Drugs Classes of Commonly Abused Drugs Stimulants Drugs that increase alertness and physical activity Nicotine Caffeine

Drugs that tend to slow down the central nervous system Chapter 33 Nervous System 33.4 Effects of Drugs Depressants Drugs that tend to slow down the central nervous system Alcohol Inhalants Illegal drugs

Tolerance and Addiction Chapter 33 Nervous System 33.4 Effects of Drugs Tolerance and Addiction Tolerance occurs when a person needs more and more of the same drug to get the same effect. The psychological and/or physiological dependence on a drug is addiction.

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