Nervous System. Chapter Structure of the Nervous System. Neurons

Transcription

1 33.1 Structure of the 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.

2 33.1 Structure of the 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.

3 33.1 Structure of the 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.

4 33.1 Structure of the 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.

5 33.1 Structure of the A Nerve Impulse Neurons at rest do not conduct impulses. Sodium ions (Na + ) collect on the outside of the cell membrane.

6 33.1 Structure of the 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.

7 33.1 Structure of the 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.

8 33.1 Structure of the 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.

9 33.1 Structure of the 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.

10 33.1 Structure of the 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.

11 33.1 Structure of the 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.

12 33.1 Structure of the 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.

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14 33.2 Organization of the The nervous system consists of two major divisions: the central nervous system and the peripheral nervous system.

15 33.2 Organization of the The Central 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

16 33.2 Organization of the The Brain The brain is sometimes called the control center of the entire body. Divided into the cerebrum, the cerebellum, and the brain stem.

17 33.2 Organization of the 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.

18 33.2 Organization of the The cerebellum controls balance, posture, and coordination. The skeletal muscles are controlled to make your motor skills coordinated and smooth.

19 33.2 Organization of the 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.

20 33.2 Organization of the The hypothalamus, located between the brain stem and the cerebrum, is essential for homeostasis. Regulates body temperature, thirst, appetite, and water balance.

21 33.2 Organization of the The Spinal Cord Nerve column that extends from the brain to the lower back. Protected by the vertebrae Processes reflexes

22 33.2 Organization of the The Peripheral 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.

23 33.2 Organization of the The Somatic 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.

24 33.2 Organization of the The Autonomic 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.

25 33.2 Organization of the 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.

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27 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.

28 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.

29 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.

30 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.

31 33.3 The Senses Balance The semicircular canals, located in the inner ear, transmit information about body position and balance to the brain.

32 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.

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

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35 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

36 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.

37 33.4 Effects of Drugs Classes of Commonly Abused Drugs Stimulants Drugs that increase alertness and physical activity Nicotine Caffeine

38 33.4 Effects of Drugs Depressants Drugs that tend to slow down the central nervous system Alcohol Inhalants Illegal drugs

39 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.