Review: What makes up the Nervous System? • The brain • Spinal cord • Nerves • 2 types of cells: • neurons: send and receive signals • glial cells: protect, support, and insulate neurons
Review: What are the two types of neurons? • Sensory neurons • What do sensory neurons do? • Cells that monitor stimuli and send signals to the spinal cord or brain. • Motor neurons • What do motor neurons do? • Cells that carry impulses from the brain or spinal cord to muscles, glands, or other neurons
Let’s take a closer look at a neuron. • Dendrites-branchlike structures on the cell body that receive the signal • Cell body-Central part of the neuron that contains the cell nucleus • Axon-rod-like extension off of cell body which conducts signal through neuron • On your diagram, label dendrite, cell body, cell nucleus, and axon.
A Neuron Glial cell
How are neurons organized? • Each neuron connects to 100’s of thousands of other neurons.
How is a signal sent? • First, a stimulus happens. A stimulus is any incoming information that causes a response. • The signal moves from the • stimulus dendrites cell body axon another neuron. • Sensory neurons detect the stimulus, and begin to send an electrical signal that passes through several neurons. • The signal then starts all over in another neuron.
Is it that easy? • No. • When the signal gets to the end of a neuron, it comes to a synapse, or a small space between the neurons.
What happens at the synapse? In order to transmit the signal from one neuron to another across the synapse, the neuron releases a chemical called a neurotransmitter. Neurotransmitters act as chemical messengers from one neuron to another.
Neurotransmitters and Disease • Dopamine is a neurotransmitter related to muscular function • Serotonin is a neurotransmitter that is associated with “happy” nerve signals
Once a signal is sent through the neurons, where does it go? • It is usually sent to the brain, processed, and then another signal is sent through the motor neurons to induce movement or give a response.
Think about when you touch a hot object. • You withdraw your hand without having to think at all. • Your brain processes it later. • This quick response to a stimulus that does not require a trip to the brain is called a reflex arc.
The brain is not involved in a reflex arc. Look at the picture describe where the signal is sent and how it is returned.
Ms. Plecki’s Biology Class Proudly Presents…. A Biodrama on The Nervous System
Motor Neurons • Left hand= dendrite • Body= cell body • Right hand= axon