Nervous System I Chapter 11

Nervous System  The nervous system is the master controlling and communicating system of the body  Every thought, action, and emotion reflects its activity.  Three overlapping functions  Millions of sensory receptors to monitor changes occurring both inside and outside the body. (called sensory input)  It processes and interprets sensory input and decides what should be done at each moment  It causes a response (called motor output), by activating effector organs  This next slide is on pg 389 in your book!

Nervous System

Central Nervous System and Peripheral Nervous System.  Central Nervous System (CNS) composed of the brain and spinal cord  Peripheral nervous system (PNS) composed of the nervous (cranial and spinal) that connects the CNS to other body parts.  Together these systems provide three general functions sensory, integrative and motor.

Autonomic and Somatic Nervous Systems  Autonomic: Portion of the nervous system that controls the actions of the viscera. (such as heart, stomach, intestines, and various glands)  Somatic: Portion of the nervous system that controls skin and skeletal muscles.

Two Divisions of Autonomic Nervous Systems  Sympathetic Division: Mobilizes body systems. Arises from the thoracic and lumbar regions of the spinal cord.  Parasympathetic Division: Conserves energy and promotes housekeeping functions during rest. Arises from the brain and sacral regions of the spinal cord.

 The nervous system is composed predominantly of neural tissue.  It also includes some blood vessels and connective tissue.  Neural Tissue consists of two cell types  Nerve cells called Neurons  Neurogilia or glial cells Nervous System

Neurons and Neuroglial Cells  Neurons- A nerve cell that consists of a cell body and its processes.  Neuroglial- specialized cell that produces myelin, communicates between cells, and maintains the ionic environment, as well as other functions.

 They are specialized to react to physical and chemical changes in their surroundings.  While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages away from the cell body. Dendritescell bodyaxonDendritescell bodyaxon  The information is in the form of of bioelectric signals called nerve impulses.  Nerves are bundles of axons. Neurons

Neurons

 You need to use a plain white sheet of paper and properly draw, color, and label a neuron.  You may use the drawing in this PowerPoint or on pg 392 in your book. Draw, Color and Label

 Neurons vary in size and shape, and in function.  Structure is different.  Bipolar- a cell body with two processes, one axon and one dentrite. (Specialized parts of eyes, nose and ears.)  Unipolor- Cell body with a single process that divides into two branches and functions as an axon.(cell body in ganglion outside the brain or spinal cord)  Multipolar- Cell body with many processes, one of which is an axon, the rest dendrites.( Most common type of neuron in the brain and spinal cord) Classification of Neurons

 When function is different…  Sensory neuron conducts nerve impulses from receptors in peripheral body parts into the brain or spinal cord  Interneuron-Transmits nerve impulses between neurons within the brain and spinal cord  Motor Neurons- conduct nerve impulses from the brain or spinal cord out to effectors- muscle or glands. Classification of Neurons

The Synapse  The operation of the nervous system depends on the flow of information through chains of neurons functionally connected by synapses.  The synapse is a junction between two cells.  A synaptic cleft is the gap between parts of the two cells at a synapse.  Synapse can occur between two neurons, a receptor cell and a neuron, or a neuron and an effector.

 Between adjacent neurons, there is a microscopic gap called the synaptic cleft.  However small, the electrical signal carrying a message cannot bridge the synaptic cleft as it is. The Synapse Transmission

The Synapse  The neuron conducting impulses toward the synapse is the presynaptic neuron  The neuron transmitting the electrical signal away from the synapse is the postsynaptic neuron.  There are two varieties of synapses:  Electrical  Chemical

The Electrical Synapse  Less common variety.  They intimately connect the cytoplasm of adjacent neurons and allow ions and small molecules to flow directly from one neuron to the next.  Found in regions of the brain responsible for certain stereotyped movements.  Jerking of the eyes  Involved in emotions and memory.  Abundant in embryonic nervous tissue.

 The chemical synapse are specialized for release and reception of chemical neurotransmitters.  The solution to this is the synapse, an elegant way of bridging the gap chemically. The electrical impulse triggers the release of certain chemical substances into the gap. These substances are called neurotransmitters and are carried over the small synaptic cleft by diffusion. The Chemical Synapse

 Once on the other side of the cleft, the neurotransmitters bind to certain proteins, called receptors, that are attached to the cell surface of the receiving cell. The binding of the transmitter to the receptor leads to the generation of a new electrical impulse. The gap has been bridged! The Synapse Transmission

 The SynapseNerve Signaling – An Introduction Nerve Signaling – An IntroductionNerve Signaling – An Introduction

Synapse Transmission  Impulses usual travel from dendrite or cell body, then along the axon to a synapse.  Axons have synaptic knobs at their distal ends that secrete neurotransmitters.  The neurotransmitter is released when a nerve impulse reaches the end of an axon, this opens two channels Na + and Ca 2+  This surge of Ca 2+ acts as a messenger, directing synaptic vesicles to empty contents.  Then the neurotransmitter diffuses across the synaptic cleft  A neurotransmitter reaching the dendrite or cell body on the distal side of the cleft triggers a nerve impulse. The Synapse Transmission

Neurotransmitter  Different neurotransmitters are being released on different occasions. The intensity and strength of the electrical impulse will decide which neurotransmitter to be released. Neurotransmitters

Neurotransmitter  Not all neurotransmitters are known, but among the more profoundly mapped  Some medical disorders are caused by the dysfunction of neurotransmission in the central nervous system, for example lack of certain neurotransmitters.  One such disorder is Parkinson's disease. Neurotransmitters