Elaborate communication system that contains more than 100 billion nerve cells in the brain alone Control the actions of the body Makes adjustments to regulate the body and keep it within safe limits Two main divisions: 1. Central Nervous System (CNS) 2. Peripheral Nervous System (PNS) Consists of the nerves of the brain and spinal cord and acts as a coordinating centre for incoming and outgoing information Consists of nerves that carry information between the organs of the body and the central nervous system Further divided into Somatic and Autonomic nerves Part of the PNS Controls skeletal muscle, bone, and skin Under conscious control (lifting weights) Sensory somatic nerves relay information about the environment to the CNS Motor somatic nerves initiate an appropriate response Part of the PNS Contains special motor nerves that control the internal organs of the body Controls unconscious, life sustaining activities (breathing) Two divisions: Sympathetic nervous system prepares the body for stress Parasympathetic nervous system returns the body to a resting state Divisions of the Nervous System Two types of nerve cells: Glial Cells nonconducting cells important for structural support and metabolism of the nerve cells Neurons functional units of the nervous system, conduct nerve impulses Three groups: 1. Sensory Neurons sense and relay information from the environment to the central nervous system (afferent neurons). Located in clusters called ganglia located outside the spinal cord. Ex: chemoreceptors on your tongue 2. Interneurons link neurons within the body. Found predominantly in the brain and spinal cord. Integrate and interpret the sensory information and connect sensory neurons to outgoing motor neurons 3. Motor Neurons also known as efferent neurons. Relay information to effectors (muscles, organs, and glands) which produce responses All neurons contain dendrites, cell bodies, and axons End Plate of Axon Dendrites - Receive information from either sensory receptors or interneurons Cell body contains the nucleus of the cell Axon Extension of cytoplasm that carries nerve impulses away from the cell body and towards other neurons or effectors Many axons are covered with a white coat of protein called the myelin sheath This sheath acts as insulation for the neuron allowing nerve impulses to travel more quickly than in unmyelenated axons Myelin prevents the loss of charged ions from the nerve cell Myelin is made by specialized cells called Schwann cells The areas between the sections of myelin sheath are known as the nodes of Ranvier An electrochemical message created by the movement of ions through the nerve cell An electrical signal travels along the axon of a nerve cell away from the dendrite This signal must then be passed on to another nerve cell The small space between two neurons is called a synapse In a synapse, small vesicles containing chemicals called neurotransmitters are located in the end plates of neurons Once the nerve impulses reaches the end plate, neurotransmitters are released The neurotransmitters are released from the presynaptic neuron and diffuse across the synaptic cleft The neurotransmitters in the synaptic cleft then act on the dendrites of the postsynaptic neuron and the nerve impulse is carried along the axon This allows the signal to be passed on between separate neurons Therefore the electrochemical signal can be broken down Electrical along the neuron/axon Chemical in the synapse