Nervous SystemCells of the Nervous SystemPeripheral Nervous SystemImpulse ConductionNerve CircuitCh48 p1023-1026, 1040-1041
Role of nervous system To transmit information rapidly The brain receives information about theenvironment and responds accordingly
How the nervous system works1. Detection of stimulus2. Processing in brain3. Response in other part of bodyFig. 48.1Afferent neuronsEfferent neurons
How the nervous system worksFunction Description ComponentsSensoryInputDetection ofstimulusSensory receptorAfferent / sensory neuronsIntegration Processingin the brainCentral Nervous system(brain & spinal cord)MotorOutputResponse inother bodypartEffector cells (muscle cellsor glands)Efferent / motor neurons
Overview of the nervoussysteminterneuronsBrainandSpinalCordCentral Nervous System Peripheral Nervous SystemExternal sensesInternal sensesneurons2. Integration: processingby the CNSParasympatheticSympatheticneurons3. Motor output:response by effectorcells1. Sensory input: detectionby sensory receptors
Central versus PeripheralNervous SystemCentral Nervous System(CNS)Peripheral NervousSystem (PNS)Brain and spinal cord Afferent neurons(Sensory) and efferentneurons (motor) thatconnect to the CNS
Peripheral nervous system Everything outside the CNS paired spinal nerves + paired cranial nerves See Fig. 48.16 on page 1040.
Motor output The conduction of signals from integrationcenters to effector cells. Effector cells: carry out the body’s responseto a stimulus.
Organization of the PNS Somatic nervous system: responds toexternal and internal stimuli by sendingsignals to skeletal muscles (voluntary) Autonomic nervous system: respond tostimuli by sending signals to smooth muscle,cardiac muscle and organs of the body(involuntary)
Sympathetic andParasympathetic Sympathetic nervous system prepares body for stress affected by epinephrine / norepinephrine Parasympathetic nervous system restores body to normal balance affected by acetylcholine
Sympathetic andParasympathetic Often have antagonistic effects (but notalways)Sympathetic Parasympatheticarousal and energygenerationcalmingincreased heart rate andrate of gas exchange inlungsdecreased heart rateand rate of gasexchange in lungs
Neuron Nerve: a group of neurons bundled together Nerve cell = neuron Neuron: the structural and functional unit of thenervous system Excitable cell: cell capable of producing large, rapid electrical signals(changes in membrane potential) Neurons & muscle cells Mature neurons lose ability to undergo cell division
Components of a neuronComponents Description FunctionCell body(soma)Main part of cellContain nucleus &organellesCarries out basic cellfunctions (i.e. proteinsynthesis, metabolism)Dendrites Short, branchedextensionsReceives input fromother neuronsAxon (nervefiber)one per neuron, longextension, can branchSends informationAxon hillock Site where axonoriginatesWhere action potentialinitiatesSynapticterminalEnds of axons Contains & releasesneurotransmitters (NT)
Direction of impulse conductionDendritesCell bodyAxon hillockAxonSynapticterminalFig. 48.2a
Types of neurons Sensory neurons Interneurons (CNS) Motor neurons
Sensory Neuron also known as afferent neurons carries signals from sensoryreceptors to the CNS for processing found in clusters of neurons: ganglia
Interneuron also known as association neurons receives incoming signals from sensoryneurons delivers outgoing signals to neuronsresponsible for responses Can be excitatory or inhibitory
Motor Neuron also known as efferent neurons connected to tissues that respond accordingwhat was detected muscle contraction gland secretion of hormones
Supporting cells (glial cells) Consists of 90% of the cells in the nervoussystem Provide structural and metabolic support toneurons Types: Astrocytes (CNS) Oligodendrocytes (CNS) Schwann cells (PNS)
Astrocytes Star-shapedcell Provide structuraland metabolicsupport for neuron Communicatewith neurons No electrical conductionhttp://www.sfn.org/content/Publications/BrainBriefings/astrocytes.html
Blood-Brain Barrier Blood vessels in the brain are completelysealed off with the help of astrocytes This contributes to the barrier between bloodand brain.
Oligodendrocytes (CNS) andSchwann cells (PNS) Cells that wrap themselves around the axon of aneuron to provide insulation for electrical impulsespassing through axon Cell form a layer called the myelin sheath cell membrane have a lot of lipid molecules. lipid molecules are poor electrical conductors provides electrical insulation Neurilemma: myelin sheaths wrapped around eachother Analogy: insulation around wires
Direction of impulse conductionTransmitting cellPresynaptic(axon of neuron)SynapseTarget cellPostsynaptic(dendrite of neuronor effector cell)
Divergent nerve circuitNerve impulse in ONEpresynaptic neuronNerve impulses in SEVERALpostsynaptic neurons Example: visual information sensed by photoreceptorssent to several parts of the brain
Convergent nerve circuitNerve impulse in SEVERAL presynaptic neuronsNerve impulse in ONE postsynaptic neuron Example: information from several sources like vision,touch and hearing is used to identify an object in theenvironment
NeuronNeuron NeuronNeuron Example: Processing and storing of memoriesCircular nerve circuit
Simplest type of nerve circuit Reflex arc: a type of nerve circuit thatregulates the reflex Reflex: rapid, involuntary responses to stimuli Intergration occurs in the spinal cord ratherthan in the brain
Knee-jerk reflexStep reflex Description* Stimulus Tapping of tendon12SensoryneuronStimulus detected by stretch receptors in sensoryneuron. Conducts nerve impulse to spinal cord.A3 ExcitatoryinterneuronSensory neurons synapse with motor neurons inspinal cord.A4 Motor neuron Conducts nerve impulse to quadricep muscle.A5 Effector Quadricep muscle contracts.B3 InhibitoryinterneuronSensory neurons synapse with interneurons.Interneurons synapse with motor neurons.B4 Motor neuron Conducts nerve impulse to hamstring muscle.B5 Effector Inhibits contraction of hamstrings (relaxation).