Nerve Cells: Structure and Function : Nerve Cells: Structure and Function By: Katherine Napolitano Mrs. Williams Period G Nerve Cell Overview: Nerve Cell Overview Function of Nerve Cells : Function of Nerve Cells The most basic function of nerve cells is to transmit information. At this time there about 28 billion nerve cells, also known as neurons, penetrating body tissue. Nerve cells vary in shape and size, however all have very similar structure. Nerve Cells are part of the nervous tissue that senses stimuli and transmits signals from one part of a person to another. Function of Nerve Cells:: Function of Nerve Cells: As stated the main function of nerve cells or neurons is to send information from the outside world to the brain and have the brain interpret it. Example: When a young child places their hand on a hot surface, the nerve cell that is on the tip of the child’s finger to their spine sends a report to the child’s brain by electricity and after the electric information is shared with another nerve cell and it is changed to chemical energy and is then changed back to electricity by the new cell. After all this occurs the information about the heat is sent to another nerve cell in the spinal cord that tells your muscles in your arm to pull it away from the heat. Neurons and Their Connection to the Senses: Neurons and Their Connection to the Senses The neuron is the main integral element of the senses and other physical senses such as physical, regulatory, as well as memory and consciousness. Neurons receive nerve signals or action potentials, integrate action potentials, and then transmit these signals to other neurons and effector organs like glands or muscles. Sensory Neurons : Sensory Neurons Sensory Neurons are required for the simplest of movements of reflexes. Sensory Neurons receive information from a sensory receptor, or stretch receptors that detect a sudden stretch, usually about a change in a stimulus. Changes in Stimuli Include: Light Pressure Sound Then the information is passed onto a motor neuron. Motor Neurons : Motor Neurons These specific type of neurons transmit Messages from the brain to muscles or glands. Motor neurons signal an effector cell. This is Muscle or gland that actually carries out the response. These neurons are also known as motoneurons. These motoneurons are mainly responsible for either Directly or indirectly controlling the contraction or relaxing of muscles. In many cases it leads to a movement. Interneurons : Interneurons Interneurons are found mainly in the spinal cord. Interneurons often times inhibit motor neurons to flexor muscles preventing them from contracting. This type of neuron is constantly active and are basically “talking” to each other. This helps to direct an appropriate action in response to everything. A More In depth Look: : A More In depth Look: http://www.brightstorm.com/science/biology/the-human-body/neurons Connecting It All Together : Connecting It All Together The 7 Steps of the Knee-Jerk Reflex: 1.) The jerking of the knee is caused by tapping the tendon that is connected to the quadriceps muscle. This jerk is also known as a patellar. 2.) Sensory or Stretch receptors then detect the sudden extension in the quadriceps muscles in the thigh. 3.) Next, sensory neurons convey the all the information in the spinal cord. 4.) The information travels through synapses between sensory neurons and motor neurons, all of this takes place in the spinal cord. 5.) Then the motor neurons convey signals to the quadriceps muscle to contract which in turn jerks the lower leg forward. 6.) Two major kinds of neurons mediate the actual reflex action however the sensory neurons also communicate with the interneurons in the spinal cord. 7.) Lastly, the interneurons inhibit certain motor neurons and the inhibition prevents the flexors from contracting. Visually Seeing the Connection:: Visually Seeing the Connection: Structural Diversity of Neurons: : Structural Diversity of Neurons: 3 Main Types: 1.) Vertebrate Sensory Neurons: The multi-branched dendrites communicate with the sensory receptor cells, and consists of a long axon and conveys signals from the dendrites to synapses with neurons. 2.) Vertebrate Interneurons: There are two types of these types of neurons. One has multiple dendrites and a branched axon. Another one has branched mesh like dendrites. 3.) Invertebrate Motor Neuron: In these neurons the body cell connects only to the dendrites. Dissecting a Neuron: : Dissecting a Neuron: The Cell Body:: The Cell Body: The cell body contains the nucleus and the other organelles of the cells. It also has two different kinds of fiber like processes or extensions. Dendrites Axons Cell Body Function:: Cell Body Function: The cell body is also known as the “soma”. It can be thought of as the “powerhouse” or “factory” of a nerve cell. It produces all of the proteins for dendrites, axons, and synaptic terminals. It contains specialized organelles such as: The mitochondria The Golgi Apparatus Ribosomes Endoplasmic Reticulum Secretary Glands Polysomes to provide energy and make the parts There is also a production line to assemble the parts into the completed products. Diagram of Cell Body: : Diagram of Cell Body: Cell Body Parts: Dendrites : Dendrites The word dendrite comes from the Greek word Dendron for “tree.” Dendrites are short, highly branched processes that receive incoming messages from other cells and carry these messages and information as an electrical signal toward the cell body. A cell typically has many dendrites. Dendrites are usually not longer than a millimeter long and many times are much shorter. These special receivers on the cell generally are the main apparatus for receiving messages from other cells. They function mainly as “antennae” of the neuron and are covered by thousands of synapses. Surface of Dendrites: Surface of Dendrites Nerve cells can have dendrites that branch many times. Their Surface: Is many times irregular and covered in dendritic spines. In these dendritic spines is where the synaptic input connections are made. Their surface sometimes is smooth and tapered examples of these include dendrites in the spinal cord. At the ends of the dendrites there are enlargements, protrusions, along with other different structural specializations . Axons:: Axons: The Axon is located at the end of the soma and it controls the firing of the neuron. It is capable of sending electrical signals across very long distances. Many are split into several branches and from this are able to send information to different targets. Axons of many neurons are wrapped in a myelin sheet. This sheet is composed of interstitial cells and is wrapped around the axons to form several concentric layers. Axon Hillock:: Axon Hillock: This is a very specific part of a nerve cell: This is where the axon is joined to the nerve cell. It is from there that the electrical firing known as action potential actually occurs. Synapse: Synapse Synapses are the junctions formed with other nerve cells where the presynaptic terminal of one cell comes into contact with the photosynaptic membrane of another. The brain is said to have approximately 100-500 trillion synapses. At these junctions, the neurons become excited, inhibited, or modulated. There are two types of synapse: Electrical Chemical Connection Between Synapses and Electrical Synapses : Connection Between Synapses and Electrical Synapses http://bcs.whfreeman.com/thelifewire/content/chp44/4402003.html Electrical Synapses: Electrical Synapses Membranes of two communicating neurons become very close to each other and close at the synapse. At this point they are actually linked together by an intercellular specialization called gap junction. This gap junction is between pre and postsynaptic neurons. In organisms with electrical synapse based systems, chemical synapses often coexist. Electrical synapses conduct nerve impulses much faster than chemical synapses. Chemical Synapses:: Chemical Synapses: These are specialized junctions in which neurons signal to each other as well as non-neuronal cells such as those in muscles or glands. These synapses allow neurons to form circuits within the central nervous system. They are very important when it comes to the biological computations that underlie perception and thought. They are also what allows the nervous system to connect to and control the rest of the body. Up Close Chemical Synapse:: Up Close Chemical Synapse: Synaptic Terminal: : Synaptic Terminal: A Synaptic terminal is a bulb at the end of an axon in which neuron transmitter molecules are stored and released. There major function is to store and release neurotransmitter molecules. An example of a neurotransmitter molecule is acetylcholine. This neurotransmitter is found in the entire human body. Neurotransmitters: : Neurotransmitters: These are the chemicals involved which allow the transmission of signals from one neuron to the next across synapses. They are found at the axon endings of motor neurons where they are able to stimulate the muscle fibers. There are many notable examples. Examples of Neurotransmitters:: Examples of Neurotransmitters: 1 st Example: Serotonin This transmitter has a lot to do with mood and emotion. It is an inhibitor neurotransmitter and it has been found that too little serotonin is linked to depression, problems with anger, control, obsessive compulsive disorder, and worst suicide. Serotonin was found in blood in 1948 by Irvine Page who was the one who gave it the name serotonin. It was finally John Welsh in 1954 who discovered it was actually a neurotransmitter in mollusks. Betty Twarg found this neurotransmitter in vertebrates in 1952. Recent Drugs have been found to “vacuum” up excess serotonin in a persons system as well. Neurotransmitter Examples:: Neurotransmitter Examples: 2 nd Example: Dopamine It was discovered in 1950 by a Swedish scientist named Arvid Carlsson. It is another inhibitory neurotransmitter, this means that when this neurotransmitter finds its way to receptor sites, it blocks the tendency of a neuron to fire. Dopamine has a lot to do with reward mechanisms in the brain. Drugs such as cocaine, heroin, and opium have been shown to increase levels of dopamine. The disease schizophrenia has been shown to have involve excessive amounts of dopamine. PreSynaptic and Postsynaptic Cell:: PreSynaptic and Postsynaptic Cell: A presynaptic cell is the cell that releases the neurotransmitter that will signal a postsynaptic cell, during a chemical synapse. This is also known as the transmitting cell. A postsynaptic cell is known as the target cell. A post synaptic cell is the cell during a chemical synapse that receives a signal from the presynaptic cell. Then the cell responds with depolarization.