Chapter 12 Introduction to the Nervous System The Nervous Endocrine Systems control the body o 2 components of the Nervous System Central NS brain spinal cord Peripheral NS all nervous system tissue outside CNS Receptors transmit signals to the brain The brain is the origin of senses From Sensory Receptors to Brain AFFERENT PATHWAY From Brain to Motor Response EFFERENT PATHWAY Somatic Nervous System controls the Skeletal Muscle system Muscles attached to bones Neuron functional unit of nervous system see picture above the most important function of a neuron is its electrical excitability which allows it to produce electrical signals to transmit to other cells Neurons transmit signals via neurotransmitters Neurotransmitters are produced in the SOMA which is the receptive input region of the neuron They are packed in vesicles and then PROPOGATE or travel along the axon And then they are stored in the axon terminals Neurotransmitters are not produced unless the Soma is stimulated The soma receives its stimuli at the Dendrites of the Neuron The Dendrite receives the neurotransmitters from other neurons and thus is stimulates the produce and release other neurotransmitters to other neurons So information is relayed throughout the body from one neuron to another neuron It s like game Telephone the Dendrites are your ears They hear or receive the messages And the axon terminal is your mouth it passes the message on to the next person or neuron However instead of using words you are using tiny neurotransmitters to pass along the message The release of neurotransmitters by stimulation is action potential Myelin lipid covering the axon It increases the velocity of the electrical impulses form the soma to the axon terminal Speeds up the action potential the rate of impulse propagation aka travel is faster with larger axon diameter and myelin unmyelinated axons have slower impulse conduction than myelinated axons Neuromuscular junction is between the axon terminal and the muscle Spinal cord has grey and white matter Grey soma of neurons unmyelinated white matter axons primarily myelinated The cell of the Nervous System is the neuron Nerves have several connective tissue membrane layers o Endoneurium surrounds a single axon o Perineurium surrounds fascicles groups of axons o Epineurium surrounds the entire nerve wraps around many fascicles In the CNS a group of axons is called a tract In the Peripheral NS a group of axons is called a nerve Systems o Sensory systems respond to stimuli o Integrative systems evaluate information o Motor systems coordinate motor output There are 3 types of neurons 1st order 2nd order and 3rd order The impulse from neurons enters the posterior of the spine Makes a synapse Travels to the hypothalamus makes a synapse And then travels to the primary cortex which sends out signals for a motor response Corticospinal cortex to spine therefore it s a motor response efferent path b c it originates in the brain Medulla oblongata where axons cross the decussation of the pyramids only 80 of the axons cross Hypothalamus is responsible for the neuro endocrine system via the control of the pituitary gland aka hypophosis Hypothalamus controls cardiovascular function and body temp it also controls the endocrine system by controlling the pituitary gland Gyrus primary somatosensory area in brain post central gyrus sensory info pre central gyrus Medulla houses cardiovascular and respiratory control centers receptors in blood are a major motor info way signals are sent to medulla Types of Ion Channels Ligand Gate Channels for excited neurons it opens and closes in response to stimuli Voltage Gated Channels responds to direct change in the membrane potential channels channels are integral proteins are controlled by a change in electrical charge aka chemical stimulus Resting Membrane Potential At resting membrane potential the cell is NEGATIVE INSIDE and POSITIVE OUTSIDE The approximate charge of the cell or polarity at rest is about 70Mv The cell is negative due to negative charges from proteins Since the cell is negative it attracts the positive ion sodium into the cell Sodium easily diffuses into the cell because it has a high concentration outside of the cell So it naturally tends to want to go from a higher concentration outside of the cell to a lower concentration inside the cell REMEMBER THERE IS ALWAYS A HIGHER CONCENTRATION OF SODIUM Na OUTSIDE OF THE CELL The entrance of sodium stimulates the cell and produces an electrical charge called an action potential There are two types of action potentials DEPOLARIZATION AND REPOLARIZATION So as long as the cell is negative the Na will continue to diffuse into the cell through ion channels The more positive charge that the sodium brings in the less negative the cell becomes This process is called Depolarization the cell loses its original polarity 70mV and becomes more and more positive Depolarization stops when the cell becomes too positive this is at about 20 30mV give or take So the two main things that promote sodium diffusing into the cell are 1 The concentration gradient sodium always greater outside than inside and 2 The electrical gradient polarity of the cell is goes from negative to positive Once depolarization occurs the cell begins another action potential process of Repolarization which is the restoration of the negative charge Na channel is closed and the K channel is open The K concentration is higher inside the cell than outside making it too positive so K is leaving the cell start of repolarization and as it leaves the cell becomes less positive more negative The cell is not able to expel positive charges from sodium because that would require sodium to move against its concentration gradient Therefore positively charged potassium ions leave the cell via facilitated diffusion POTASSIUM LEAVING THE CELL MARKS THE START OF REPOLARIZATION As the positive charge of potassium is removed the cell restores its negative resting membrane potential Hyperpolarization may occur when the cell becomes more negative than its resting membrane potential 7 voltage This is why the cell needs the Sodium potassium pump that we learned about for the first test It helps to maintain homeostasis the proper balance of these ions in the cell The sodium potassium pump neutralizes the effects of depolarization and repolarization By taking excess sodium out and potassium in o IN DE REPOLARIZATION SODIUM ENTERS POTASSIUM LEAVES Depolarization
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