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Biology 30 Reading Notes Section 11.1 Pages 374 - 382 Name:______________________ Structures and Processes of the Nervous System ______________________ is the maintenance of a constant internal environment. Slight fluctuations ______________ and _____________ these “normal” levels are common, so our internal systems are often said to be in a state of dynamic _________________. ___________________ are the basic structural and functional units of the nervous system. They are specialized to respond to _______________ and __________________ stimuli, to conduct electrochemical signals, and to release ____________________ that regulate various body processes. _____________ cells support neurons. These cells _______________ the neurons, remove their ________________, and defend against __________________. Glial cells also provide a supporting framework for all of the nervous-system tissue. Cells of the Nervous System The three types of neuron are the sensory neuron, interneuron, and motor neuron. ■ _____________________ neurons gather information from sensory receptors and transmit these impulses to the __________________ nervous system. ■ ____________________ are found entirely within the central nervous system. They act as a ___________ between the sensory and ______________________ neurons. They __________________ and _____________________ incoming sensory information, and relay outgoing _____________________ information. ■ Motor neurons transmit information from the central nervous system to _______________, glands, or other _______________ (effectors). The basic neural pathway used is a _______________, which is a withdrawal reflex. For example: ____________ organ (eye) detects the ball → sensory ____________ →spinal cord (_______________) → motor neuron → causes muscle to act to withdraw (move the head) out of the way of the ball The axons of some neurons are enclosed in a fatty, insulating layer called the ______________________, which gives the axons a glistening white appearance. These axons are said to be _________________. The myelin sheath protects myelinated neurons and _________________ the rate of nerve impulse transmission. ___________________ cells, a type of glial cell, produce myelin in certain parts of the CNS and PNS. The Structure of a Neuron ____________________ have specialized cell structures that enable them to transmit nerve impulses. Different types of neurons are different _______________ and _____________________. There are four common features of a neuron, including: ________________, a cell body (soma), an __________________ and branching ends. ___________________ are short, branching terminals that receive nerve impulse from other neurons or ____________________ receptors, and relay the impulse to the ___________________. The dendrites are numerous and highly ____________________, thus increasing the ___________________ available to receive information. The _______________ contains the nucleus and is the site of the cell’s ____________________. It will also process the input from the ___________________. A neuron typically has one _____________. Which can range from 1mm to 1 m, depending on the neurons' location in the body. The _________________ end of the axon branches into many fibres. To communicate with adjacent neurons, glands, or muscles, the axon terminal releases _________________signals into the space between it and the receptors or dendrites of neighbouring cells. The axons of some neurons are enclosed in a fatty, insulating layer called the _____________________, which gives the axons a glistening white appearance. These axons are said to be ____________________. The myelin sheath protects myelinated neurons and ___________________ the rate of nerve impulse transmission. ___________________, a type of glial cell, produce myelin in certain parts of the CNS and PNS. Action Potential $ A nerve impulse consists of a series of _______________ _______________ . $ In _______________ neurons, action potentials occur only at ___________ ____ _______________ because the myelin sheath _______________ the axonal membrane that it encircles. $ A neuronal membrane is said to be _______________ if the _______________ potential is reduced to less than the resting potential of ___________. $ If the membrane at a node of Ranvier becomes _______________ to _______, a dramatic change occurs in the membrane called an ________ _______________. $ It is called an “ _______________ ” event because a depolarization between -70mV and -55 mV has _______ __________. $ Any depolarization between -55 mV up to 0 will produce _______________ action potentials. $ The potential difference of -55 mV is called the _____________ _____________ . $ When the _______________ _______________ reaches threshold, special structures in the membrane called ________-_______ sodium channels open and make them very _______________ to sodium ions. $ The ions are driven by their _______________ _______________ , and the potential difference across the membrane in that tiny region of the axon is ______. $ As a result of the change in membrane potential, the sodium channels close and voltage-gated _______________ channels open. The potassium ions now move down their _______________ _______________ . $ As a result the membrane is _______________ , and the membrane potential _______________ to nearly __________. $ For the next few milliseconds after an action potential, the membrane cannot be _______________ to undergo another action potential. This is called the _______________ _______________ . Nerve Impulse $ A nerve impulse consists of a series of _______________ _______________ . $ When an action potential occurs at a node of Ranvier, sodium ions flow into the _______________ , creating a relatively high _______________ of sodium inside the _______________ at that _______________ . $ The sodium ions inside the axon cannot _______________ out. Instead, they diffuse in _________ directions along the _________. $ When the sodium ions reach _______________ nodes of Ranvier, the positive charges _______________ the _____ __________ charge inside the axonal membrane, causing the membrane at the nodes of Ranvier to become _______________ to threshold. $ At one node the membrane is _______________ , which means that it cannot be _______________ to undergo another action potential yet. $ The other membrane of the node is ______ _________ so the depolarization initiates an action potential at this node. $ The ___________process occurs at each node until it reaches the end of the _______________ . $ Because action potentials are forced to “__________” from one node of Ranvier to the next due to the _______ ________ , the conduction of an impulse along a myelinated neuron is called a _______________ _______________ . $ The transmission of an impulse along an unmyelinated axon is much _______________ than the saltatory conduction along a myelinated axon. $ _______________ _______________ is caused by the breakdown of the myelin sheath surrounding the axons in the _______________ . $ MS is thought to be an _______________ disease, in which the body’s own immune system breaks down the _______________ . Signal Transmission across a Synapse $ The simplest neural pathways have at least _________ neurons and one connection between the neurons. (Others can involve thousands of _______________ and their _______________ .) $ The connection between two neurons, or a neuron and an effector, is called a _______________ . $ A _______________ _______________ is a synapse between a motor neuron and a muscle cell. $ An impulse travels the length of the axon until it reaches the far end, called the _______________ _______________ . $ Most neurons are not directly _______________ , but have a gap between them called the _______________ ___________. $ Chemical messengers called ___________________________ carry the neural signal from one neuron to another or signal from one neuron to another, or from a neuron to an _______________ . $ When an action potential arrives at the end of a presynaptic neuron, the impulse causes sacs that contain _______________ to fuse with the membrane of the _______________ . These sacs, called _______________ ___________, release their contents into the synaptic cleft by _______________ . The neurotransmitters then diffuse across the synapse to reach the _______________ of the postsynaptic _______________ , or cell membrane of the _______________ . $ Upon reaching the postsynaptic membrane, the neurotransmitters bind to specific receptor _______________ in this membrane. $ Neurotransmitters have either _______________ or _______________ effects on the postsynaptic membrane. $ If the effect is _______________ , the receptor proteins will trigger ion channels that open to allow positive ions, such as _______________ , to flow into the postsynaptic neuron. As a result, the membrane becomes slightly _______________ . $ If the neurotransmitter is _______________, the receptor will trigger _______________ channels to open, allowing potassium ions to flow out. This results in a more negative transmembrane potential, resulting in _______________ . $ A single cell body may be receiving signals from many _______________ neurons at the same time. $ One of the functions of the cell body is to _______________ all of the incoming signals. $ If the _______________ stimuli are strong enough, the _______________ will reach the point at which the _______________ is connected to the cell body and an impulse will be generated. $ The _______________ neuron will then return to ____________ ___________ . $ After the _______________ has had its effect, _______________ break it down and _______________ it so that its components can be reabsorbed by the _______________ _________. Neurotransmitters in Action $ _______________ is a _______________ that crosses a neuromuscular junction. It _______________ the muscle cell membrane, causing _______________ and _______________ of muscle fibre. $ Cholinesterase is released into a synapse, where it breaks down _______________ . It is one of the _______________ acting enzymes. It allows the ion channels to close and the membrane to _______________ in a fraction of a second. ( A nerve gas called __________ destroys this function by blocking the release of cholinesterase into the _______________ junction.) $ Several neurological disorders have been linked to _______________ _______________ or _______________ production. $ Certain drugs can alter the proper action of _______________ .