Presentation on theme: "How Nerve Signals Maintain Homeostasis"— Presentation transcript:
1 How Nerve Signals Maintain Homeostasis Chapter 9
2 The Nervous System Intro Every single stimulus (light, touch, feeling of muscles moving, pressure, blinking, etc.) involves your nervous system.Coordinated motions (which do not seems to be coordinated) are controlled mostly by the nervous system.nervous system + endocrine system control the actions of the body.
3 The Nervous System Elaborate communication system Contains 100 billion nerve cells in the brain alone.Humans: memory, learning, language, etc.
4 Vertebrate Nervous System 2 main divisions:Central nervous system (CNS)Brain + spinal cord coordinating centreIncoming and outgoing info.Peripheral nervous system (PNS)Info between organs of body and CNS.Two peripheral divisions:SomaticSkeletal muscles, bones, and skinSensory somatic PNS: relay info about environment to CNS.Motor somatic PNS: initiate appropriate responds.AutonomicMotor nerves which control internal organs of body.SympatheticParasympathetic
6 Nerve Cells Glial cells Neurons Nonconducting cells structural support and metabolism of nerve cells.NeuronsFunctional units of nervous system (conduct electricity)Sensory neurons“afferent neurons”Sense and relay info (stimuli) from environment to CNS(ex// photoreceptors, chemoreceptors, thermoreceptors, etc.)Ganglia: clusters of sensory receptors.InterneuronsIntegrate and interpret sensory and motor neurons (found mostly in the CNS)Motor neurons“efferent neurons”Relay info to effectors: muscles, organs, and glands (can produce a response)
7 Anatomy of a Nerve Cell (Neuron) All neurons contain:DendritesReceive info from other nerve cellsConduct info towards the neuron’s cell bodySoma: neuronal cell body (containing nucleus)AxonExtension of cytoplasmCarries nerve impulse towards other neurons or effectors.Creates an “attachment” to other neurons.Super super thin (100 could fit inside single human hair!)
8 Myelin Sheath Insulation Myelin sheaths are formed by special glial cells called Schwann cellsMyelin sheaths prevents the loss of ions from axon.(important when you understand how these cells work!)Made of ‘fatty protein’
9 Nodes of Ranvier Between sections of myelin sheath Nerve impulses jump from one node to another speed up movement of nerve impulses.Nerve impulses move much faster along myelinated nerve fibres than nonmyelinated ones.(Nerve impulses move much faster along smaller diameter axons)
10 NeurilemmasThin membrane which surrounds the axon in peripheral nervous systemPromotes regeneration of damaged axonsSevered neurons can be rejoined.(feeling gradually returns to your finger following a paper cut)
11 White and Grey Matter White matter Grey matter Nerve cells within the brain that contain myelinated fibres and neurilemmaMyelinated axons white in appearanceGrey matterNerve cells within the brain and spinal cord referred to as grey matter: lack myelin sheath and neurilemma do not regenerate after injuryDamage to grey matter is usually permanent.
14 Categories of NeuronsSensory Neurons: AFFERENT neurons: relay info from environment CNSLocated in clusters called gangliaPhotoreceptors (eyes)Chemoreceptors (tongue and nose)Thermoreceptors (skin and hypothalamus)InterneuronsInterpret sensory info and send info to outgoing motor neurons (mostly in CNS)Motor neurons: EFFERENT neurons: relay info from interneurons effectors (produce a response)Musclesorgans,glands
16 Organization of Nerves Most nerves are part of many neurons/axons held together in a ‘bundle.’
17 Neural Circuits Reflex Example: touching a hot stove Involuntary and often unconsciousExample: touching a hot stoveHow long does it take you to remove your hand?Nerve impulse is carried to the spinal chord motor neuron (skipping brain) sensation felt after removing hand.
18 Reflex arc Simplest nerve pathway. Occurs without brain coordination Five essential components:ReceptorSensory neuronInterneuron (spinal chord)Motor neuronEffector