Neurons and Synapses Key words: Types of neurons; sensory neurons; motor neurons; interneurons; afferent nerves; efferent nerves

Cells in the brain 2 types: Neurons – communication specialists Glia or Glial cells – make up 90% of the brain’s cellls cells that support, nurture, and insulate neurons, clean up dead cells, and modify neural functioning The uses & functions of glial cells not yet fully understood Used to think glial cells were scaffolding (greek for “glue) for the brain, but more recent studies indicate a more important role in thinking: memory, learning, etc. May facilitate creation or maintenance of neural pathways. Interesting facts: The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.) The relative inability to grow new neurons leads to two interesting questions: Q1: How do brain tumors (cancer) occur? A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons. Q2: If a person cannot grow new neurons, how does the brain change in order to accomodate new learning? A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.

Neurons Basic building Blocks of the Nervous System Body’s communication wiring Transmit messages from one part of the body to another 3 different types we need to know Afferent neurons, efferent neurons, interneurons Some neurons go all the way down your spinal column Interesting facts: The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.) The relative inability to grow new neurons leads to two interesting questions: Q1: How do brain tumors (cancer) occur? A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons. Q2: If a person cannot grow new neurons, how does the brain change in order to accomodate new learning? A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.

Soma - the cell body Contains the cell’s Nucleus Round, centrally located structure Contains DNA Maintains the cell No role in neural signaling Key words: Cell body; soma; cell nucleus Interesting facts: The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.) The relative inability to grow new neurons leads to two interesting questions: Q1: How do brain tumors (cancer) occur? A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons. Q2: If a person cannot grow new neurons, how does the brain change in order to accomodate new learning? A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.

Dendrites Information collectors; neurotransmitter receivers Receive inputs from neighboring neurons Inputs may number in thousands If enough inputs are received, the cell’s AXON may generate an output Interesting facts: - The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons: 1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree. 2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.

Dendritic Growth Mature neurons generally can’t divide But new dendrites can grow Provides room for more connections to other neurons New connections are the basis for learning Interesting facts: - The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons: 1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree. 2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.

Axon The cell’s output structure One axon per cell, 2 distinct parts tubelike structure branches at end that connect to dendrites of other cells Interesting facts: - The diameter of an axon may vary from approximately 1mm-20mm. - An axon may travel long distances to reach it's destination (longest axon is approximately 3 feet in humans and 10 feet in giraffes).

Terminal Buttons (Axon terminals) Swellings at the ends of axons Store and release neurotransmitters Messages are sent to neighboring neurons

Myelin sheath White fatty casing on axon which acts as an electrical insulator Not present on all cells When present increases the speed of neural signals down the axon Divided by Nodes of Ranvier Myelin Sheath Interesting facts: - The myelin sheath is NOT a part of the axon. The myelin sheath is actually formed of glial cells (oligodendricytes and Schwann cells) that wrap around the axon. - You may have often heard the brain referred to as either white matter or gray matter. The myelin sheath appears white in nature. Hence, the term white matter refers to areas of the brain that are myelinated. Gray matter refers to areas of the brain that are unmyelinated. - When you accidentally cut yourself, you often visually notice that you've cut yourself before you actually feel any pain from the cut. The reason for this is that visual information uses myelinated axons; whereas, pain information uses unmyelinated axons. - The loss of myelin is a significant factor in the disease multiple sclerosis (MS). When myelin is lost, the high-speed transmission of information is slowed down or blocked completely, which could lead the person with the inability to walk, write or speak.