Presentation on theme: "How Nerve Signals Maintain Homeostasis"— Presentation transcript:
1 How Nerve Signals Maintain Homeostasis 9.1 The Importance of the Nervous SystemPage1
2 9.1: The Importance of the Nervous System The nervous system is an elaborate communication system that has more than 100 billion nerve cells in the brain alone.Memory, learning and language are all a part of the nervous system.Has two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
3 CNS PNS Brain and spinal cord Protected by All the other neurons Meningesskull and vertebraePNSAll the other neuronsServes limbs and organsSensory and motor branchesExposed to toxins and more susceptible to injuries
5 CNS includes nerves of the brain and spinal cord and is the coordinating centre for incoming and outgoing information.The PNS includes the nerves that carry information between the organs of the body and the CNSPNS is divided further into the somatic and autonomic nerves.Somatic: controls the skeletal muscle, bones and skin.Autonomic: special motor nerves that control the internal organs of the body.Autonomic can be subdivided into the sympathetic and the parasympathetic.
13 Sympathetic nervous system Prepares the body for stress:increases heart rate,increases the release of glucose,dilates the pupils,increases blood flow to the skin,causes release of epinephrine
14 Parasympathetic nervous system Restores normal balance:decreases heart ratestores glucoseconstricts pupilsdecreases blood flow to the skin
15 Nerves are responsible for sensory (input), integrative, and motor output. Sensory Nervesmonitor external stimuli like temperature, light, and sound, etc.Use internal body receptors to detect variations in pressure, pH, CO2 concentration, levels of various electrolytes etc.
16 Integrative Nervessignals are brought together (integrated) to create sensations, to produce thoughts, or to add to memory.Decisions are made based on the sensory input.
17 Motor nerve output / response The nervous system responds to stimuli by sending signals to muscles, causing them to contract, or to glands, causing them to produce secretions.Muscles and glands are called effectorsThey cause an effect in response to directions from the nervous system.
19 Cells of NS Non-neural cells (neuroglial or simply glial) Neurons Provide oxygen and nutrients to neuronsProvide support, insulation and protection against pathogensRemove dead neuronsNeuronsreceive stimuliconduct action potentials
20 Non-neural Glial Cells Astrocytescover the surfaces of neurons and blood vessels.provide structural support and help form the blood brain barrier, thus playing a role in regulating what substances from the blood reach the neurons.Oligodendrocytesform the myelin sheaths of axons in CNSSchwann cellsform a myelin sheath called the neurilemma around each axon in PNS (sheath is 80% lipid + 20% protein)very important in saltatory nerve conduction
26 Types of Neurons Bipolar Unipolar Multipolar has only two nerve fibers (axon & dendrite)Unipolarsingle nerve fiberMultipolarmany nerve fibersOne is an axon, rest are dendrites
27 What are the 3 parts of all neurons? DendritesThe cell bodyThe axon
28 Neuron Structure Cell body: Contains nucleus Dendrites: Receive informationConduct nerve impulses toward the cell bodyAxon:Sends nerve impulses from the cell body to other neurons (effectors)Myelin Sheath:White coat of fatty protein that covers some axons
29 Schwann Cells:Individual cells that compose the myelin sheathInsulates the nerve cellNodes of Ranvier:Areas between the sections of myelin sheath
30 Neurons Dendrites (“receivers”) Cell Body Axon terminals (“Transmitters “)
32 Functional Differences b/w Neurons Sensory (afferent) Neuronscarry nerve impulses from peripheral body parts into the brain or spinal cordPNS to CNSHave specialized dendrite endsInterneurons (association)within the brain or spinal cordLink with other neuronsMotor (efferent) Neuronscarry nerve impulses out of the brain or spinal cord to effectorsCNS to PNSMotor impulses stimulate muscles to contract and glands to release secretions
34 Sensory Neurons Afferent neurons Sense and relay stimuli (information) from the environment to the CNSLocated in clusters outside of the spinal cordTypes of sensory receptors: thermoreceptors (temp.), photo (vision), pain, pressure, mechano (hearing), chemo (taste and smell)
35 Interneurons/Association Neurons Neurons that link together neurons in the bodyMainly in the spinal cord and brainhuman brain contains ~100 billion interneurons averaging 1000 synapses on each or some 1014 connections
36 Motor Neurons Efferent Neurons Relay information to the effectors Muscles, organs and glandsThe axons connecting your spinal cord to your foot can be as much as 1 m long (although only a few micrometers in diameter).
40 Reflex Arcs Sensory neurons are stimulated by pricking rose thorns Signal travels to spinal cord along sensory neuronsSynapse with interneurons within CNSInterneurons stimulate motor neuronsStimulus travels along motor axons to muscleMuscle contracts to withdraw hand
46 The Speed of Nerve Impulses Myelinated nerve fibres speed up nerve impulsesNerve impulses jump from one node to another… speeding up nerve action (known as saltatory conduction)
47 Neuron Repair Neurilemma: Thin membrane that surrounds the axon Promotes regeneration of damaged neuronsNot in all nerve cellsWhite Matter:Nerve cells in the brain that contain myelinated fibres and a neurilemmaGrey Matter:Nerve cells in the brain and spinal cord that lack a myelin sheath and neurilemmaWhy are spinal and brain injuries often permanent?
48 How to Fix “Irreparable” Damage to the CNS Reattach two torn nerves- limited success2. Grafts from the PNS- more successful…CNS cells that are left alone however, had no regeneration
49 Stem Cells Cells that have not specialized into tissue cells Experiments are being done on replacing damaged cells using stem cellsE.g. pp. 415…rats with reconnected spinal cordsPage 417 # 1-6