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Nervous System . Chapter 7, Part 1. General Functions of the Nervous System. Monitors changes Processes and Interprets Effects a Response. What is the Central Nervous System. The brain and the spinal cord make up the central nervous system or CNS.
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Nervous System Chapter 7, Part 1
General Functions of the Nervous System Monitors changes Processes and Interprets Effects a Response
What is the Central Nervous System The brain and the spinal cord make up the central nervous system or CNS. It acts as the integrating and command centers of the nervous system.
What is the Peripheral Nervous System The part of the nervous system outside of the CNS. The nerves outside of the brain and spinal cord. They serve as communication lines between the body and the brain and spinal cord.
Sensory (Afferent) Division Bring information to the spinal cord and brain. Fibers bringing information to the brain from skin, muscles, and joints are called somatic sensory fibers. Fibers bringing information to the brain from visceral organs are called visceral sensory fibers.
Motor (Efferent) Division • Carries impulses from the CNS to effector organs (muscles and glands). • There are two subdivisions: • Somatic Nervous System • Allows conscious or voluntarily control of our skeletal muscles (voluntary nervous system). • Autonomic Nervous System • Takes care of activities that are automatic or involuntary such as smooth and cardiac muscles, and glands (involuntary nervous system).
Two Principal Cell Types • Supporting cells, also known as neuroglia. • Astrocytes, microglia, Ependymal cells, Oligodendrocytes, Schwann cells, and Satellite cells. • Neurons.
Astrocytes Star-shaped cells. Nearly half of the neural tissue Form barrier between capillaries and neurons to protect them from harmful substances in the blood. Braces neurons and anchors them to their nutrient supply lines.
Microglia Spiderlike phagocytes that dispose of debris, including dead brain cells and bacteria.
Ependymal Cells Line the cavities of the brain and the spinal cord. Cilia help to circulate the cerebrospinal fluid (CSF).
Oligodendrocytes Wrap their extensions around nerve fibers producing a fatty insulating covering called myelin sheaths.
Schwann Cells Form the myelin sheaths around nerve fibers found in the peripheral nervous system (PNS).
Satellite Cells They are the protective cushioning cells for the neurons.
Function of Neurons Highly specialized cells that transmit messages from one part of the body to another. Neurons cannot divide or reproduce. They have three parts; dendrites, cell body, and an axon
Cell Body Metabolic center of the neuron Contains the usual cellular organelles except for centrioles (which is why they do not divide).
Nissl Substance and Neurofibrils This is the rough endoplasmic reticulum (ER) and their filaments. They are important for maintaining the cell shape.
Dendrites These are processes that bring information toward the cell body. They vary in number and length.
Axons These are processes that move the nerve impulse away from the cell body. There is typically only one axon per neuron, but occasionally there can be a collateral branch.
Neurotransmitters Chemicals released by the axonal terminals. There are over a hundred different neurotransmitters that we know of. Dopamine, serotonin, acetylcholine, norepinephrine are a few.
Synaptic cleft This is the gap found between an axonal terminal and the next neuron.
Synapse This is the functional junction of the axonal terminal, the synaptic cleft, and the next neuron.
Myelin It is a whitish, fatty material that has a waxy appearance. It protects and insulates the fibers and increases the transmission rate of a nerve impulse.
Myelin Sheath and Neurilemma • Myelin Sheath • Encloses the axon. • Neurilemma • Is found external to the myelin sheath. • Together they enclose the axon and insulate it.
Nodes of Ranvier This the gap, or indentation, found between Schwann cells.
What are nuclei? They are clusters of neuron cell bodies found in the CNS
What are ganglia? These are small collections of cell bodies found in a few sites OUTSIDE the CNS in the PNS.
Difference between gray matter and white matter. White matter is made of dense collections of MYELINATED fibers (tracts) Gray matter contains mostly UNMYELINATED fibers and cell bodies.
Five types of sensory receptors Naked nerve endings – Pain and temperature receptors. Meissner’s corpuscle – light touch receptor. Pacinian corpuscle – deep pressure receptor. Golgi tendon organ (proprioceptor) – registers tension or force. Muscle spindle (proprioceptor) – registers stretching.
What are association neurons? A third category of neurons. Also called interneurons. They connect the motor and sensory neurons. They allow communication between neurons.
Three types of neurons • Multipolar neuron • Containing several processes. • All motor and association neurons are multipolar • The most common structural type. • Bipolar neuron • Rare in adults. • Found only in some special sense organs (eye, ear). • Unipolar neuron • Have a single process leaving the cell body. • Moves nerve impulses both toward and away from the cell body.
Polarized When the plasma membrane is resting or inactive. There are fewer positive ions sitting on the inner face of the neuron’s plasma membrane than there are on its outer face. The major positive ions inside the cell are potassium (K+) The major positive ions outside the cell are sodium (Na+)
Depolarization The inward rush of sodium ions changes the polarity of the neuron’s membrane. The inside becomes more positive than the outside.
Action Potential Commonly referred to as the nerve impulse. It is an all-or-none response. Results when the stimulus is strong enough and the sodium in-rush is great enough and depolarization occurs.
Repolarization The outflow of positive ions from the cell which restores the electrical conditions at the membrane. A neuron cannot conduct another impulse until the neuron is repolarized.
Saltatory conduction Fibers that have myelin sheaths conduct impulses much faster when they are insulted (myelinated). When myelinated the impulse jumps or leaps from node to node along the length of the fiber (saltatory conduction).
Reflex Arcs • A reflex is a rapid, predictable, and involuntary response to stimuli. • They occur over a neural pathways and move in one direction. • There are a minimum of 5 elements • Sensory receptor, a sensory neuron, the integration center, the motor neuron, and finally the effector.
