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Biol 221 Worksheet Nervous System I Organization, Cells, & Physiology I. Nervous System Functions List the three basic functions carried out within the nervous system 1. _____________________________________ 2. _____________________________________ 3. _____________________________________ Which of these functions controls muscles & glands? _________________________________________ Which monitors the environment? _________________________________________ Which makes decisions regarding appropriate responses to sensory information? _________________________________________ II. Nervous System Structural Subdivisions (based on location & structure) The brain and the spinal cord belong to the ________________(CNS/PNS). Nerves belong to the _________________(CNS/PNS). Sensory and motor functions are carried out by the _______________(CNS/PNS). Integration of sensory and motor functions occurs in the ______________(CNS/PNS). III. Peripheral Nervous System (PNS) A. Two Functional Divisions of the PNS The PNS can be subdivided into two functional divisions; _______________________ (Sensory/Motor) that carries information towards the CNS, and ________________________(Sensory/Motor) that carries commands away from the CNS. Sensory information is carried toward the CNS by ____________________(afferent/efferent) fibers (i.e. axons). Motor commands are carried away from the CNS by ____________________(afferent/efferent) fibers. 1 B. Sensory/Afferent Division of the PNS The sensory division of the PNS is further subdivided into Somatic Sensory and Visceral Sensory. Both of these sensory divisions of the PNS are ________________ (afferent/efferent). The Somatic Sensory division carries information to the CNS from ________________________________________________________________________. The Visceral Sensory division of the PNS carries information to the CNS from ____________________________________________________________. C. Motor/Efferent Division of the PNS The motor division of the PNS is further subdivided into the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS). Both of these motor divisions of the PNS are __________________(afferent/efferent). The Somatic Nervous System ________________________ (voluntarily/involuntarily) controls ____________________ muscles. The Autonomic Nervous System ________________________ (voluntarily/involuntarily) controls _________________ muscle, ________________ muscle, and _________________. D. Autonomic Nervous System Branches Both branches of the ANS are motor/efferent in function and involuntarily control the same organs but with opposite effects; therefore, they are ___________________________ to one another. Also known as the housekeeping branch, the _______________________ (Sympathetic/Parasympathetic) branch maximizes growth, healing, and digestion. This branch of the ANS originates from _____________________________ regions of the CNS, and is relative energy _______________________________(costly/conservative). Commonly referred to as the fight or flight branch, the _______________________ (Sympathetic/Parasympathetic) branch readies the body to respond to an immediate and serious threat. This branch of the ANS originates from _____________________________ regions of the spinal cord, and is relative energy ____________________________ (costly/conservative). 2 IV. Neurons Neurons are the basic functional cell of the nervous system, and are highly specialized to conduct nerve impulses. A. Neuron Anatomy There are three basic parts to a neuron. The ___________________ is where the nucleus and many other organelles are found. ___________________ (dendrites/axons) are numerous, shorter and highly branched _____________________ (afferent/efferent) processes that arise from the cell body. ________________(dendrites/axons) are singular, long __________________(afferent/efferent) processes that originate at the axon hillock of the cell body. Axons may have branches called _________________________, but all axons have numerous branches at their ends called ______________ _____________________________. Changes in organelles reflect the special needs of these cells, for example ___________________ help reinforce from within, and _____________ bodies are specialized forms of rough endoplasmic reticula. B. Structural Classification of Neurons The structural approach to classifying (naming) neurons is based on simply counting the total number of processes that arise directly from the cell body (sum of dendrites and axon). A neuron with just one attached process is called ______________________________; a neuron with two attached processes is called __________________________, and a neuron with more than two total processes is called __________________________________________________. C. Functional Classification of Neurons The functional approach to classifying neurons is based on the direction in which the cell transmits relative to the CNS. Neurons that carry information from receptors toward the CNS are __________________________ sensory/motor neurons, and are also known as _____________________________ (afferent/efferent) neurons. Neurons that carry information away from the CNS to effectors are __________________________ sensory/motor neurons, and are also known as _____________________________ (afferent/efferent) neurons. 3 V. Neuroglia Neuroglia are diverse cells of the nervous system that retain the ability to mitotically divide. Match the glial cell to its location and function(s). Each organelle will have more than one correct answer, and locations may apply to more than one type of glial cell. _____________Astrocyte _____________Ependymal cell _____________Microglial cell _____________Oligodendrocyte _____________Satellite cell _____________Schwann cell a. PNS b. CNS c. Myelinates part of one axon d. Myelinates multiple axons e. phagocyte f. helps form the blood-brain barrier g. lines ventricles h. protects & cushions ganglia i. links blood vessels & neurons j. derived from white blood cells k. derived from epithelial cells l. produces & helps circulate CSF VI. Neuron Physiology A. Myelination A ________________ sheath forms when a Schwann cell or part of an oligodendrocyte repeatedly wraps an ____________ (axon/dendrite). Myelinated axons conduct _________________________ (faster/slower) than non-myelinated axons. Most axons are ___________________________(myelinated/non-myelinated). 4 Oligodendrocytes myelinate axons in the ______________ (PNS/CNS), and Schwann cells myelinate axons in the ______________ (PNS/CNS). Nodes of Ranvier (also called neurofibril nodes) are locations along a myelinated axon where there is no ______________________. Because the entire cell wraps the axon when Schwann cells are involved, a ___________________________ forms external to the myelin sheath. B. Resting Membrane Potential Prior to carrying a nerve impulse, a neuron’s cell membrane must first be ______________________(polarized/depolarized). This is caused by the sodium potassium pump forcing high numbers of sodium ions _________________ (outside/inside) the neuron and large numbers of potassium ions _______________________(outside/inside) the neuron. The resultant measureable difference in charge across the resting neuron’s cell membrane is called its’ _____________________ __________________________ ___________________________. C. Conduction of a Nerve Impulse along a Neuron First, an appropriate _________________________ stimulus opens ________ (Na+/K+) channels in the neuron’s cell membrane. The cell membrane ______________________________ (depolarizes/repolarizes) as ___________ (Na+/K+) flows __________________ (into/out of) the neuron, along its entire length from __________________________ (dendrite/axon) to ___________________(dendrite/axon). Shortly after they open, ______________(Na+/K+) channels close and ________________(Na+/K+) channels ______________(open/close). The cell membrane then ________________________________________ (depolarizes/repolarizes) as ___________ (Na+/K+) flows __________________ (into/out of) the neuron, along its entire length from _______________________ (dendrite/axon) to __________________ (dendrite/axon). Neurons must repolarize before they can be successfully restimulated to conduct. The time required to repolarize a neuron 5 before it can generate another action potential is called the __________________________________ period. Neurons will either respond to a stimulus by first depolarizing then repolarizing (this is a nerve impulse, also called an action potential), or by not responding with an action potential. There is no partial action potential. This is called the __________ or _________ Principle. D. Types of Conduction When successfully stimulated, unmyelinated neurons are capable of ___________________________(continuous/saltatory) conduction. In this type of conduction all of the ions channels for first Na+ then K+ must open then close in sequence along the entire length of the cell membrane. This results in a relative ________________ (slower/faster) rate of conduction. In contract, myelinated neurons are capable of ___________________________(continuous/saltatory) conduction. In this type of conduction only ions channels for first Na+ then K+ must open then close at nodes of Ranvier. In this type of conduction, the action potential seems to leap from node-to-node; this is a much ________________ (slower/faster) rate of conduction. E. Synaptic Transmission Once an action potential arrives at the end of a presynaptic axon, the axon terminals (or synaptic knobs if present) _______________________ (depolarize/repolarize). This change triggers opening of ion channels that allow ______________(Ca2+/Na+/K+) to _____________ (enter/exit) the presynaptic neuron. The influx of this ion causes ______________________________ (endocytosis/exocytosis) of synaptic vesicles, releasing neurotransmitter molecules. The Neurotransmitters diffuse across the ___________________ ______________ and bind to _______________________________ on the postsynaptic cell membrane, opening _____________ (Na+/K+) channels. If enough ____________ (Na+/K+) flows ________________ 6 (into/out of) the neuron, then it will __________________________________ (depolarize/repolarize), and an action potential will occur. F. Neurotransmitters Neurotransmitters that raise the threshold of a neuron, making it more difficult to stimulate a neuron to generate an action potential, are called _________________ (excitatory/inhibitory) neurotransmitters. For example, if a neurotransmitter opens a K+ channel, then K+ will flow out of the cell, making it even more _____________(positive/negative) outside, thereby raising the resting membrane potential. This is called hyperpolarization. Likewise, if a neurotransmitter opens a Cl- channel then Cl- will flow into the cell, making it more _____________(positive/negative) inside, thereby hyperpolarizing the membrane. In contrast, neurotransmitters that open Na+ channels in the membrane, may cause the membrane to depolarize. Neurotransmitters that do this are called _________________________ (excitatory/inhibitory). List the three ways that neurotransmitters are removed from the synapse: 1. __________________________________________ 2. __________________________________________ 3. __________________________________________ G. Sensory Receptors Receptors are always located in the ______(CNS/PNS), always perform a __________________(sensory/motor) function, and respond only to specific stimuli. List the three basic types of receptors (based on structural complexity) and either give examples of the various stimuli to which they respond, or give an example of their name. 1. ________________________________________________________________________ 2. ________________________________________________________________________ 3. ________________________________________________________________________ 7 H. Where are neuron cell bodies located in the nervous system? A group of neuron cell bodies in the __________(CNS/PNS) is called a ganglion. A cluster of neuron cell bodies in the ___________ (CNS/PNS) is called a nucleus. The cell bodies of sensory/afferent neurons are always located in the (CNS/PNS) and are found in ___________________ (ganglia/nuclei), or in special sense organs. The cell bodies of interneurons are always located in the _________ (CNS/PNS) in either gray matter or in nuclei. The cell bodies of some motor neurons are located in gray matter in the ________ (CNS/PNS), while the cell bodies of other motor neurons may be found in ganglia in the (CNS/PNS). 8