Lecture 1 - Neurons and Glia PDF

-The nervous system is the most complex of the systems in the body. Not only true for humans, true for all animals. -We have learned a lot about the nervous system int he last 100 years with new technologies developing Basic functions of the nervous system have been known since 400 B.C. We...

-The nervous system is the most complex of the systems in the body. Not only true for humans, true for all animals. -We have learned a lot about the nervous system int he last 100 years with new technologies developing Basic functions of the nervous system have been known since 400 B.C. We know this because there are ancient texts that have been found in Egypt and Greece that go into the basic functioning of the nervous system The Basic Functions of the Nervous System: -1. The nervous system gathers information on both the external (outside of the body) and internal (inside of the body) environments ◦Gathers information on the temperature of the room, how much light is in the room, people around you, etc. (external environment) ◦Body temperature, composition of body fluids, blood pressure (internal environment)- -2. To process information that it has gathered ◦it takes the information that is gathered and integrates it (puts it together) ◦one piece of information is not significant ◦puts it together with other information it has gathered Determines the appropriate response to the gathered information ◦Nervous system considers all the possible responses that could be made to the information that is processed ◦does not just consider one response, considers all responses that could be used, and uses the most appropriate one ◦If you are touching a stove, your nervous system considers the information and determines a response for touching a hot surface (jerking the hand away) -3. Produce a coordinating response to the integrated information ◦the response that is produced will depend on the information gat is gathered in process ◦EX: simple motor act (jerking hand away) or it could be more complex (turning off stove) ◦response depends on the information gathered and processed with maybe simple motor act  or more complex set -Nervous system is also responsible for producing physiological responses to information production/release of hormones you may not be aware of the response (release of a hormone in response of information) it is not only responsible for actions that we can see, but actions that we cannot see (hormones) Structures of the Nervous System -the nervous system is generally divided into 2 broad divisions -One of the divisions of the nervous system is the Central Nervous System (CNS) CNS includes the brain and spinal cord CNS is contained within the skull and vertebral canal that runs down the center of the vertebrae -Peripheral nervous system (PNS) includes ganglia (clusters of neurons located outside of the CNS), nerves that innervate structures in the periphery (muscles, sensory receptors), sensory receptors and structures of the nervous system (taste buds, photoreceptors, auditory receptors in ears) enteric nervous system part of the PNS that is located in the walls of the digestive tract ◦the enteric nervous system is thought to have as many neurons in it as the brain does ◦sometimes considered the 3rd division of the nervous system, but most consider it part of the PNS Functional Divisions of the Nervous System -the nervous system can be divided into 3 divisions -Sensory division the part of the nervous system that gathers and carries out the initial processing of sensory information also sometimes referred to as the Afferent Division ◦Afferent : to conduct information inward -Integrative division receives sensory information from multiple sensory inputs (visual, auditory) integrates that information  applies meaning to the information determines a response to the information ◦EX: holding up a pencil, you know what that object is. you can say "that is a pencil", you know what it is used for. your nervous system is seeing this object, identifying it (color, length), applying meaning to it (that is a pencil), and what you do with that object (write with it). integrative division applies meaning to the information -Motor division part of the nervous system that innervates and controls the muscles and glands of the body this division is also known as the Efferent Division ◦Efferent : to convey information outward Information in this division is being conveyed to the periphery motor division can be subdivided to the: ◦Somatic motor subdivision ‣ controls the skeletal muscles of the body (muscles under voluntary control) ‣ have voluntary control of these muscles ◦Visceral motor subdivision ‣ also known as the autonomic nervous system ‣ further divided to the Sympathetic subdivision and Parasympathetic subdivision ‣ Visceral motor is responsible for regulating the activity of the involuntary muscles and glands of the body You do not have voluntary control of this part of the nervous system, it works by itself Regulates the activity of the smooth muscle in: ◦the digestive tract as well as secretions of glands and glandular cell secretions in the digestive tract (enzymes and acids for digestion) ◦blood vessels ◦lung airways ◦urinary bladder  ◦reproductive tract ◦heart muscle (not smooth muscle) secretion of glands (endocrine glands that secrete hormones) Cells of the Nervous System -Two types of cells Neurons ◦basic functional units of the nervous system ◦neurons are the cells that carry out the functions above; carrying out, determining, and producing a response for information Glial cells ◦serve a support function for the neurons ◦provide structural support / structural framework of the nervous system that the neurons are attached to or supported by ◦trophic factors that keep the neurons alive ◦not involved int he gathering or processing of information; serve a support function to the neurons ◦there are many moire glial cells than there are neurons ‣ for every neuron there are 50 glial cells ‣ glial cells make up most of the valuable neural tissue ◦glial cells play a critical role in maintaining the normal functioning in neurons ◦dysfunctioning of glial cells lead to dysfunctioning in normal neuron functions ‣ Alzheimer's disease is a dysfunctioning of glial cells, which disrupts normal functioning of neurons ‣ glial cells play a critical role in maintaining the normal role of the nervous system Neurons -cells that are specialized for transferring information from one part of the nervous system to another -this transfer of information from neuron to neuron is achieved by the translation of a chemical signal into an electrical signal, and then the translation of the electrical signal back into a chemical signal  Chemical -> electrical -> chemical -neurons translate chemical signals to electrical signals, and those signals back to chemical signals in terms of a language, electrical language and chemical language ; neurons translate this language Basic Structural Components of a Neuron -cell body: in a neuron it is also known as the soma (Latin for body) -in the cell body you find most of the organelles of the neuron nucleus, golgi complex, endoplasmic reticulum -neurites: cell processes extending from the soma -2 types of neurites: dendrites ◦dendrites serve to increase the surface area for contacts from other neurons ◦dendrites receive chemical signals from other neurons and convert this chemical signal into an electrical signal ◦a typical neuron will have hundreds of dendrites extending from its soma axon (other type of neurite) ◦a neuron will only have one axon extending from the soma ◦the axon of a neuron conveys electrical signal away from the soma to the ends of the axon ◦even though there is only one axon that extends from the soma, the axon can branch to form axonal collaterals ‣ they can contact multiple target cells with one axon ‣ multiple target cells can be contacted by axon collateral ◦ends of the axon collaterals form axon terminals (axon bouton) ‣ axon terminal is what makes the contact on the target cell ‣ these target cells can be other neurons, muscle fibers, gland cells, etc.  ‣ when the electrical signal reaches the axon terminal, the electrical signal initiates a series of events that translate the electrical signal into a chemical signal, that is released from the axon terminal. ‣ axon terminal receives electrical signal from the axon and translates it into a chemical signal -the dendrites receive signals from other neurons, translate the chemical signals into an electrical signal (post-synaptic potential or PSP). that electrical signal is conveyed by the dendrite to the soma, the soma conveyed the electrical signal (PSP) to the axon. the first part of the axon (axon hillock) transcribes the electrical signal it receives from the soma into a different type of electrical signal (action potential). The action potential is conducted down the axon to the axon terminals. when the action potential reaches the axon terminal, the axon terminal initiates a series of events that leads to the release of chemical signal from the axon terminal to the target cell. the signal that is conveyed by the dendrites is referred to as a post-synaptic potential (PSP) -the contacts that are made between axon terminal and target cells are called synapses -there are 2 types of synapses -electrical synapses very rare in humans (vertebrates) find these in the nervous system of invertebrates (shrimp, squid, clams) what you see at an electrical synapse is: Axon-> Synaptic cleft EE axon terminal-> target cell membrane gap junctions are between the target cell and axon terminal  when action potential goes down the axon and through the protein pores, it cal pass straight through the when it passes through the target cell, it initiates a response in the target cell at this type of a synapse, rather than the electrical being translated into a chemical, it goes through through the axon to the target cell -Chemical synapse most common type of synapse axon terminal opposite to the target cell is called the presynaptic membrane membrane bound vesicles int eh axon terminal (called synaptic vesicles) contain a chemical signal called a neurotransmitter on the postsynaptic membrane. you would see receptors that are able to bind to the neurotransmitter that are in the vesicles in the axon terminal when an action potential goes down an axon and enters the axon terminal, it initiates a chain of events that lead to synaptic vesicles fusing with the membrane when the synaptic vesicle fuses with the presynaptic membrane, the neurotransmitter thats inside is released to the synaptic cleft the neurotransmitter diffuses across the synaptic cleft and binds to the receptor on the postsynaptic membrane of the target cell the binding of the neurotransmitter to the receptor in the postsynaptic membrane initiates a post- synaptic potential (PSP) in the target cell -dendrites and axons of neurons can be very long axons for the feet have cell bodies in the spinal cord, send dendrites from spine to muscles in the feet most of the organelle of the neuron are int he soma (cell body) the process that is responsible for the movement of materials from the soma, along the axon and dendrites -axoplasmic transport initially referred to as axonal transport, largely occurs in axons but we know now it also occurs in  other cells (dendrites) Cytoplasm of Axon and Dendrites -axons and dendrites are filled with cytoskeletal elements -neurofilaments : skeleton of neurite provide mechanical support for the neurite and support for the neurite membrane -microfilaments: like the muscles of the neurite involved in changing the shape and position of the neurite -microtubules extend longitudinally along the axons and dendrites play an important role in axonal transport * act like the roads in axonal transport ◦the roads that things are transported along 2 Types of Axonal Transport -Slow axonal transport used to move cytoskeletal elements (neurofilaments) and enzymes along neurites occurs at a rate of 1-10 mm (millimeters) per day occurs as a result of a combination of cytoplasmic flow (flow of the cytoplasm through the cell) and transport along microtubules through slow motor proteins. ◦slow motor proteins walk along the microtubules, down the dendrite, transporting their cytoskeletal element or enzyme -Fast axonal transport occurs at a rate of 400-1,000 mm per day utilizes two different families of motor proteins ◦dyenins: responsible for retrograde axonal transport (transport along the neurite toward the soma - back toward the cell body) ◦kinesins: responsible for anterograde axonal transport (transport along the neurite from the soma toward the end of the neurite - away from the cell body) these motor proteins walk along the microtubules  as they are walking along the microtubules, they are carrying the material along the microtubules materials moved by fast axonal transport: ◦synaptic vesicles ◦old membrane components (membrane of neurites is constantly being replaces, as it is removed it is broken down and moved) ◦mitochondria -green structures: microtubules -kinesin is transporting a synaptic vesicle along the axon; it is walking along the microtubules. this process involved the hydrolysis of ATP (energy) -the foot section of the motor protein (kinesin) binds to the microtubule. to release it, it requires that it bind ATP. binding would trigger the release of the foot from the microtubule. after this it would hydrolyze the ATP and release the energy required to move the motor protein to the next binding site along the microtubule.