Presentation on theme: "Neurons and Synapses Types of Neurons Sensory Motor Interneurons"— Presentation transcript:
1 Neurons and Synapses Types of Neurons Sensory Motor Interneurons Key words: Types of neurons; sensory neurons; motor neurons; interneurons; afferent nerves; efferent nerves
2 Sensory NeuronsINPUT From sensory organs to the brain and spinal cord.BrainDrawing shows a somatosensory neuronVision, hearing, taste and smell nerves are cranial, not spinalSensoryNeuronSpinalCordKey words: sensory neurons; afferent nerves; types of neurons
3 Motor NeuronsOUTPUT From the brain and spinal cord To the muscles and glands.SpinalCordBrainSensoryNeuronMotorKey words: Motor neurons; efferent nerves; types of neurons
4 InterneuronsInterneurons carry information between other neurons only found in the brain and spinal cord.SpinalCordBrainSensoryNeuronMotorKey words: interneurons; types of neurons
5 Structures of a neuronKey words: Neuron; sructures of neurons
6 The cell body Contains the cell’s Nucleus Round, centrally located structureContains DNAControls protein manufacturingDirects metabolismNo role in neural signalingKey words: Cell body; soma; cell nucleusInteresting facts:The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.)The relative inability to grow new neurons leads to two interesting questions:Q1: How do brain tumors (cancer) occur?A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons.Q2: If a person cannot grow new neurons, how does the brain change in order to accomodate new learning?A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.
7 Dendrites Information collectors Receive inputs from neighboring neuronsInputs may number in thousandsIf enough inputs the cell’s AXON may generate an outputKey words: dendriteInteresting facts:- The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons:1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree.2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.
8 Dendritic Growth Mature neurons generally can’t divide But new dendrites can growProvides room for more connections to other neuronsNew connections are basis for learningKey words: dendriteInteresting facts:- The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons:1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree.2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.
9 Axon The cell’s output structure One axon per cell, 2 distinct parts tubelike structure branches at end that connect to dendrites of other cellsKey words: axon; action potentialsInteresting facts:- The diameter of an axon may vary from approximately 1mm-20mm.- An axon may travel long distances to reach it's destination (longest axon is approximately 3 feet in humans and 10 feet in giraffes).
10 Myelin sheath White fatty casing on axon Acts as an electrical insulatorNot present on all cellsWhen present increases the speed of neural signals down the axon.Myelin SheathKey words: myelin sheath; action potentials; axonInteresting facts:- The myelin sheath is NOT a part of the axon. The myelin sheath is actually formed of glial cells (oligodendricytes and Schwann cells) that wrap around the axon.- You may have often heard the brain referred to as either white matter or gray matter. The myelin sheath appears white in nature. Hence, the term white matter refers to areas of the brain that are myelinated. Gray matter refers to areas of the brain that are unmyelinated.- When you accidentally cut yourself, you often visually notice that you've cut yourself before you actually feel any pain from the cut. The reason for this is that visual information uses myelinated axons; whereas, pain information uses unmyelinated axons.- The loss of myelin is a significant factor in the disease multiple sclerosis (MS). When myelin is lost, the high-speed transmission of information is slowed down or blocked completely, which could lead the person with the inability to walk, write or speak.
11 How neurons communicate Neurons communicate by means of an electrical signal called the Action PotentialAction Potentials are based on movements of ions between the outside and inside of the cellWhen an Action Potential occurs a molecular message is sent to neighboring neurons
12 Cell Membrane in resting state Ion concentrationsCell Membrane in resting stateK+Na+Cl-A-Outside of CellInside of CellKey words: ion concentrations; cell membrane; intracellular fluid; extracellular fluid; Na+; Cl-; K+Slide ten represents a schematic of the typical concentrations of the intracellular and extracellular fluids. There are large concentrations of sodium and chloride ions concentrations of on the outside of the cell (relative to inside the cell). There are large concentrations of potassium ions and protein molecules on the insde of the cell (relative to concentrations on the outside of the cell).
13 The Cell Membrane is Semi-Permeable Cell Membrane at restNa+Cl-K+A-Outside of CellInside of CellPotassium (K+) can pass through to equalize its concentrationSodium and Chlorine cannot pass throughResult - inside is negative relative to outside- 70 mvKey words: Cell membrane; semi-permeable; K+; Na+; Cl-The cell membrane is semi-permeable. That is, when the neuron is at rest, the cell membrane allows some ions (K+) to pass freely through the cell membrane, whereas other ions (such as Na+ and Cl-) cannot.Hit enter once and K+ ions will slowly pass through the cell membrane.After K+ animation is finished, hit enter again and animation showing that Na+ and l- ions cannot pass through the membrane will occur.
14 Resting Potential At rest the inside of the cell is at -70 microvolts With inputs to dendrites inside becomes more positiveif resting potential rises above threshold an action potential starts to travel from cell body down the axonFigure shows resting axon being approached by an AP
15 Depolarization ahead of AP AP opens cell membrane to allow sodium (NA+) ininside of cell rapidly becomes more positive than outsidethis depolarization travels down the axon as leading edge of the AP
16 Repolarization follows After depolarization potassium (K+) moves out restoring the inside to a negative voltageThis is called repolarizationThe rapid depolarization and repolarization produce a pattern called a spike discharge
17 Finally, Hyperpolarization Repolarization leads to a voltage below the resting potential, called hyperpolarizationNow neuron cannot produce a new action potentialThis is the refractory period
18 Neuron to NeuronAxons branch out and end near dendrites of neighboring cellsAxon terminals are the tips of the axon’s branchesA gap separates the axon terminals from dendritesGap is the SynapseCellBodyDendriteAxonKey words: axon terminal.
19 SynapseSendingNeuronSynapseAxonTerminalaxon terminals contain small storage sacs called synaptic vesicleskey words: axon terminal; synaptic vesicles; neurotransmittersvesicles contain neurotransmitter molecules
20 Neurotransmitter Release Action Potential causes vesicle to openNeurotransmitter released into synapseLocks onto receptor molecule in postsynaptic membrane
21 Locks and Keys Neurotransmitter molecules have specific shapes Receptor molecules have binding sitesWhen NT binds to receptor, ions enterpositive ions (NA+ ) depolarize the neuronnegative ions (CL-) hyperpolarize
22 Some Drugs work on receptors Some drugs are shaped like neurotransmittersAntagonists : fit the receptor but poorly and block the NTe.g. beta blockersAgonists : fit receptor well and act like the NTe.g. nicotine.
23 Summary 3 types of neurons The cell membrane Ion movements Action potentialsSynapseNeurotransmittersReceptors and ionsAgonists and antagonists