The Nervous System

Introduction FTwo organ systems, the nervous and endocrine systems, coordinate organ system activity. FThe nervous system provides swift but brief responses to stimuli FThe endocrine system adjusts metabolic operations and directs long-term changes FTwo organ systems, the nervous and endocrine systems, coordinate organ system activity. FThe nervous system provides swift but brief responses to stimuli FThe endocrine system adjusts metabolic operations and directs long-term changes

The Nervous System FThe nervous system includes al the neural tissue in the body. FIts anatomical divisions include the central nervous system (CNS) (the brain and spinal cord FAnd the peripheral nervous system (PNS) (all neural tissue outside the CNS) FThe nervous system includes al the neural tissue in the body. FIts anatomical divisions include the central nervous system (CNS) (the brain and spinal cord FAnd the peripheral nervous system (PNS) (all neural tissue outside the CNS)

FFunctionally it can be divided into an afferent division which brings sensory information to the CNS FAnd an efferent division which carries motor commands to muscles and glands FFunctionally it can be divided into an afferent division which brings sensory information to the CNS FAnd an efferent division which carries motor commands to muscles and glands

FThe efferent division includes the somatic nervous system (voluntary control over skeletal muscle contractions FAnd the autonomic nervous system (involuntary regulation of smooth muscle, cardiac muscle, and glandular activity. FThe efferent division includes the somatic nervous system (voluntary control over skeletal muscle contractions FAnd the autonomic nervous system (involuntary regulation of smooth muscle, cardiac muscle, and glandular activity.

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Cellular Organization in Neural Tissue FThere are two types of cells in neural tissue FNeurons, which are responsible for information transfer and processing FNeuroglia, which provide a supporting framework and act as phagocytes. FThere are two types of cells in neural tissue FNeurons, which are responsible for information transfer and processing FNeuroglia, which provide a supporting framework and act as phagocytes.

Neurons FSensory neurons: form the afferent division of the PNS and deliver information to the CNS FMotor neurons: stimulate or modify the activity of a peripheral tissue, organ or organ system FSensory neurons: form the afferent division of the PNS and deliver information to the CNS FMotor neurons: stimulate or modify the activity of a peripheral tissue, organ or organ system

FInterneurons: may be located between sensory and motor neurons; they analyze sensory inputs and coordinate motor outputs.

FA typical neuron has a cell body, an axon, and several branching dendrites and synaptic terminals

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FNeurons may be described as unipolar, bipolar, or multipolar F8-3

Neuroglia FFour types FAstrocytes: largest and most numerous FOligodendrocytes: myelinate CNS neurons FMicroglia: phagocytic white glod cells FEpendymal: produce and help circulate cerebral spinal fluid FFour types FAstrocytes: largest and most numerous FOligodendrocytes: myelinate CNS neurons FMicroglia: phagocytic white glod cells FEpendymal: produce and help circulate cerebral spinal fluid

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FNerve cell bodies in the PNS are clustered into ganglia. FTheir axons are covered by myelin wrappings of Schwann cells. FNerve cell bodies in the PNS are clustered into ganglia. FTheir axons are covered by myelin wrappings of Schwann cells.

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Anatomical organization FIn the CNS, a collection of neuron cell bodies that share a particular function is called a center FA center with a a discrete anatomical boundary is called a nucleus. FPortions of the brain surface are covered by a thick layer of gray matter called the neural cortex FIn the CNS, a collection of neuron cell bodies that share a particular function is called a center FA center with a a discrete anatomical boundary is called a nucleus. FPortions of the brain surface are covered by a thick layer of gray matter called the neural cortex

FThe white matter of the CNS contains bundles of axons, or tracts that share common origins, destinations and functions. FTract in the spinal cord form larger groups called columns FThe white matter of the CNS contains bundles of axons, or tracts that share common origins, destinations and functions. FTract in the spinal cord form larger groups called columns

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Neuron Function: Membrane Potential FThe resting potential, or membrane potential of an undisturbed nerve cell, is due to a balance between the rate of sodium ion entry and potassium ion loss and to the sodium-potassium exchange pump

FAny stimulus that affects this balance will alter the resting potential of the cell F8-7

FAn action potential appears when the membrane depolarizes to a level known as the threshold. FSteps include; opening of sodium channels and opening of potassium channels, return to normal permeability FAn action potential appears when the membrane depolarizes to a level known as the threshold. FSteps include; opening of sodium channels and opening of potassium channels, return to normal permeability

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Propagation of an Action Potential FIn continuous propagation, an action potential spread across the entire excitable membrane surface in a series of small steps. FDuring saltatory propagation, the action potential appears to leap from node to node. FIn continuous propagation, an action potential spread across the entire excitable membrane surface in a series of small steps. FDuring saltatory propagation, the action potential appears to leap from node to node.

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FAction potentialAction potential FAction potentialAction potential

Neural Communication FA synapse is a site where intercellular communication occurs through the release of chemicals called neurotransmitters. FA synapse where neurons communicate with other cell types is a neuroeffector junction. FA synapse is a site where intercellular communication occurs through the release of chemicals called neurotransmitters. FA synapse where neurons communicate with other cell types is a neuroeffector junction.

Structure of a Synapse FNeural communication moves from the presynaptic neuron to the postsynaptic neuron over the synaptic cleft F8-10

Synaptic function and Neurotransmitters FCholinergic synapses release the neurotransmitter acetylcholine (Ach) FAch is broken down in the synaptic cleft by the enzyme acetylcholinesterase (AChE) FCholinergic synapses release the neurotransmitter acetylcholine (Ach) FAch is broken down in the synaptic cleft by the enzyme acetylcholinesterase (AChE)

Other neurotransmitters FNorepinephrine-excites FDopamine-inhibits FGABA -inhibits FSerotonin-inhibits FNorepinephrine-excites FDopamine-inhibits FGABA -inhibits FSerotonin-inhibits

F8-11, table 8-1

Fneurotransmittersneurotransmitters Fneurotransmittersneurotransmitters