1 Neurons & Nerv Neurons & Nerv ous Systems ous Systems Human Nervous System Human Nervous System Nervous system has three specific Nervous system has three specific functions functions Receiving sensory input Receiving sensory input Performing integration Performing integration Generating motor output Generating motor output Regulating autonomous functions Regulating autonomous functions
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Neurons & Nervous Systems 1 Human Nervous System Nervous system has three specific functions Receiving sensory input Performing integration Generating.
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1Neurons & NerNeurons & Nervous Systemsvous Systems
Human Nervous SystemHuman Nervous System
Nervous system has three specific Nervous system has three specific functionsfunctions
Any long axon is also called a nerve fiberAny long axon is also called a nerve fiber
4Neurons & NerNeurons & Nervous Systemsvous Systems
Types of NeuronsTypes of Neurons
Motor NeuronsMotor NeuronsAccept nerve impulses from the CNSAccept nerve impulses from the CNSTransmit them to muscles or glandsTransmit them to muscles or glands
Sensory Neurons Sensory Neurons Accept impulses from sensory Accept impulses from sensory receptorsreceptors
Transmit them to the CNSTransmit them to the CNS
InterneuronsInterneuronsConvey nerve impulses between Convey nerve impulses between various parts of the CNSvarious parts of the CNS
The membrane potential (voltage) The membrane potential (voltage) when the axon is not conducting an when the axon is not conducting an impulseimpulse
The inside of a neuron is more negative The inside of a neuron is more negative than the outside -65 mVthan the outside -65 mV
Due in part to the action of the sodium-Due in part to the action of the sodium-potassium pumppotassium pump
6Neurons & NerNeurons & Nervous Systemsvous Systems
Action PotentialAction Potential
An action potential is generated only An action potential is generated only after a stimulus larger than the after a stimulus larger than the thresholdthreshold
Gated channel proteinsGated channel proteins
Suddenly allows sodium to pass Suddenly allows sodium to pass through the membranethrough the membrane
Another allows potassium to pass Another allows potassium to pass through other directionthrough other direction
7Neurons & NerNeurons & Nervous Systemsvous Systems
Propagation of Action PotentialsPropagation of Action Potentials
In myelinated fibers, an action In myelinated fibers, an action potential at one node causes an potential at one node causes an action potential at the next nodeaction potential at the next node
Conduction of a nerve impulse is an Conduction of a nerve impulse is an all-or-nothing eventall-or-nothing event
Intensity of signal is determined by Intensity of signal is determined by how many impulses are generated how many impulses are generated within a given time spanwithin a given time span
8Neurons & NerNeurons & Nervous Systemsvous Systems
Transmission Across a SynapseTransmission Across a SynapseA synapse is a region where neurons A synapse is a region where neurons nearly touchnearly touch
Small gap between neurons is the Small gap between neurons is the synaptic cleftsynaptic cleft
Transmission across a synapse is carried Transmission across a synapse is carried out by neurotransmittersout by neurotransmitters
Sudden rise in calcium at end of one Sudden rise in calcium at end of one neuronneuron
Stimulates synaptic vesicles to merge with Stimulates synaptic vesicles to merge with the presynaptic membranethe presynaptic membrane
Neurotransmitter molecules are released Neurotransmitter molecules are released into the synaptic cleftinto the synaptic cleft
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Synaptic IntegrationSynaptic Integration
A single neuron is on the receiving A single neuron is on the receiving end ofend of
Many excitatory signals, andMany excitatory signals, and
Many inhibitory signalsMany inhibitory signals
IntegrationIntegration
The summing of signals fromThe summing of signals from
Excitatory signals, andExcitatory signals, and
Inhibitory signals Inhibitory signals
10Neurons & NerNeurons & Nervous Systemsvous Systems
CNS: Brain and Spinal CordCNS: Brain and Spinal Cord
Spinal cord and brain are wrapped in Spinal cord and brain are wrapped in three protective membranes, three protective membranes, meningesmeninges
Spaces between meninges are filled Spaces between meninges are filled with cerebrospinal fluid (CSF)with cerebrospinal fluid (CSF)
Fluid is continuous with that of central Fluid is continuous with that of central canal of spinal cord and the ventricles canal of spinal cord and the ventricles of the brainof the brain
Blood Brain Barrier (BBB): Functional Blood Brain Barrier (BBB): Functional barrier between blood and CSFbarrier between blood and CSF
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Spinal CordSpinal CordThe spinal cord has two main functionsThe spinal cord has two main functions
Center for many reflex actionsCenter for many reflex actions
Means of communication between the Means of communication between the brain and spinal nervesbrain and spinal nerves
The spinal cord is composed of gray The spinal cord is composed of gray matter and white mattermatter and white matter
Cell bodies and short unmyelinated Cell bodies and short unmyelinated fibers give the gray matter its colorfibers give the gray matter its color
Myelinated long fibers of interneurons Myelinated long fibers of interneurons running in tracts give white matter its running in tracts give white matter its colorcolor
12Neurons & NerNeurons & Nervous Systemsvous Systems
The BrainThe Brain
Cerebrum is the largest portion of the Cerebrum is the largest portion of the brain in humansbrain in humans
Communicates with, and coordinates Communicates with, and coordinates the activities of, the other parts of the the activities of, the other parts of the brainbrain
Longitudinal fissure divides into left Longitudinal fissure divides into left and right cerebral hemispheresand right cerebral hemispheres
13Neurons & NerNeurons & Nervous Systemsvous Systems
Cerebral CortexCerebral Cortex
A thin but highly convoluted outer A thin but highly convoluted outer layer of gray matterlayer of gray matter
Covers the cerebral hemispheresCovers the cerebral hemispheres
Contains motor areas and sensory Contains motor areas and sensory areas as well as association areasareas as well as association areas
Primary motor area is in the frontal Primary motor area is in the frontal lobe just ventral to central sulcuslobe just ventral to central sulcus
Primary somatosensory area is just Primary somatosensory area is just dorsal to central sulcusdorsal to central sulcus
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CerebrumCerebrumRest of cerebrum is composed of white Rest of cerebrum is composed of white mattermatter
Descending tracts communicate with Descending tracts communicate with lower brain centerslower brain centers
Ascending tracts send sensory Ascending tracts send sensory information to primary somatosensory information to primary somatosensory areaarea
Basal nucleiBasal nuclei
Integrate motor commandsIntegrate motor commands
Ensure that the proper muscle groups are Ensure that the proper muscle groups are either activated or inhibitedeither activated or inhibited
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DiencephalonDiencephalonA region encircling the third ventricleA region encircling the third ventricle
Consists of hypothalamus and thalamus Consists of hypothalamus and thalamus
Hypothalamus forms floor of the third Hypothalamus forms floor of the third ventricleventricle
Thalamus consists of two masses of gray Thalamus consists of two masses of gray matter located in the sides and roof of matter located in the sides and roof of the third ventriclethe third ventricle
Pineal glandPineal gland
Also located in the diencephalonAlso located in the diencephalon
Secretes melatoninSecretes melatonin
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CerebellumCerebellum
Separated from the brain stem by the Separated from the brain stem by the fourth ventriclefourth ventricle
Receives sensory input from the eyes, Receives sensory input from the eyes, ears, joints, and musclesears, joints, and muscles
Sends motor impulses out the brain Sends motor impulses out the brain stem to the skeletal musclesstem to the skeletal muscles
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Brain StemBrain Stem
Contains the midbrain, the pons, and the medulla Contains the midbrain, the pons, and the medulla oblangataoblangata MidbrainMidbrain Acts as a relay station for tracts passing Acts as a relay station for tracts passing betweenbetween The cerebrum, andThe cerebrum, and The spinal cord or cerebellumThe spinal cord or cerebellum
PonsPons Helps regulate breathing and head movementsHelps regulate breathing and head movements
Medulla oblongataMedulla oblongata Contains reflex centers for vomiting, coughing, Contains reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowingsneezing, hiccuping, and swallowing
18Neurons & NerNeurons & Nervous Systemsvous Systems
Limbic SystemLimbic System
Complex network of tracts and Complex network of tracts and “nuclei”“nuclei”