Nervous System Notes & Summary PDF

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Notes and Summary for the Nervous System....

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Nervous System Notes & Summary

The Structure of the Nervous System: 1. Neurons:  Neurons are specialized nerve cells that help you gather information about your environment, interpret the information, and react to it. 

Dendrites receive signals called impulses from other neurons and conduct the impulses to the cell body.

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The axon carries the nerve impulse from the cell body to other neurons and muscles. An image of the nerve cell (Neuron):

The Three Kinds of Neurons: 1. Sensory neurons:  Send impulses from receptors in the skin and sense organs to the brain and spinal cord. 2. Interneurons/ Relay neurons:  They receive the signals sent by the sensory neurons. Interneurons also send signals to the motor neurons.  Located in the brain and spinal cord. 3. Motor neurons:  Carry impulses away from the brain and spinal cord to a gland or muscles, which results in response.

A Nerve Impulse:

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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. Negatively charged proteins actively transport sodium ions out of the cell and potassium ions into the cell.

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. 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. 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. 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:  

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.

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.

The Organization of the nervous system:

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The nervous system consists of two major divisions: the central nervous system and the peripheral 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 central nervous system includes the brain and the spinal cord.

1. The Brain:  The brain is sometimes called the control center of the entire body.  Divided into the cerebrum, the cerebellum, and the brain stem.  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.  The skeletal muscles are controlled to make your motor skills coordinated and smooth.  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.  The hypothalamus, located between the brain stem and the cerebrum, is essential for homeostasis.  Regulates body temperature, thirst, appetite, and water balance.

2. The Spinal Cord  Nerve column that extends from the brain to the lower back.  Protected by the vertebrae  Processes reflexes

The Peripheral Nervous System:

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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 peripheral nervous system is divided into somatic nervous system, and the autonomic nervous system.

1. 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.

2. 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.  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.

The Senses: 1. 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.  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. 2. 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.

3. Hearing:

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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.

4. Balance:  The semicircular canals, located in the inner ear, transmit information about body position and balance to the brain.

5. Touch:  Many types of sensory receptors that respond to temperature, pressure, and pain are found in the epidermis and dermis layers of the skin.

The effects of drugs on the nervous system:  

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A drug is a substance, natural or artificial, that alters the function of the body. 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 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: 1. Stimulants:  Drugs that increase alertness and physical activity such as nicotine and caffeine. 2. Depressants:  Drugs that tend to slow down the central nervous system such as alcohol, inhalants, and illegal drugs.

Tolerance and Addiction:

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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....