Biological 2
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- Created by: carolinemather
- Created on: 04-05-18 19:16
Glial Cells
- Non-neuronal - do not carry messages
- Supportive role in holding neurons in place, supplying nutrients and oxygen, providing insulation
- Destroy pathogens
- Remove dead neurons
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The Neuron
- Neuron - the basic unit of structure and function in the Nervous System, in both CNS and PNS
- 100-150 billion neurons, each with different functional capabilities
- Each enuron can be connected to 1000 or more other neurons - estimated 100 trillion connections
- Sensory neurons - respons to external stimuli and transmit sensory info to CNS
- Motor neurons - carry messages from CNS to muscles and glands
- Interneurons - Transmit messages to other neurons (located in the CNS)
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How do Neurons Communicate?
- Primary function - transmit info
- Generating a signal within the neuron, called electrical transmittion
- Passing the message from one neuron to another, called chemical transmission
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Electrical Transmission
- Mebrane defines the intracellular and extracellular compartments
- If we place an electrode inside and outside of the membrane, we would see a difference in electrical charge
- At rest, the inside of the neuron would be more negative than the outside
- Due to the positively and negatively charged particles (ions) contained in the intracellular and extracellular fluids
- Resting membrane potential is -70mv and the neuron is polarised
- Movement of ions is limited by membrane and special channels
- Membrane has selective permeability - some can pass and some cant
- Concentration gradient- ion movement from high to low concentration
- Electrostatic forces - act on the ions ie. opposites attract and like signs repel
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Sodium-Potassium Pump
- Voltage dependent and fully operational at RMP
- If the membrane potential becomes less negative the SPP braks down - neuron is stimulated
- Na+ rush into the cell and reverse the normal polarity
- Inside of the cell becomes positive
- Active neuron is depolarised
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Action Potential
- All or nothing event - either axon fires or it doesnt
- After an action potential occurs, there is a brief refractory period when the neuron cannot be stimulated again
- Then axon returns to a resting state
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Electrical to Chemical Transmission
- Once the electrical signal has reached the axon terminals, neurons communicate with eachother by means of chemical signalling
- Chemical transmission is vital for our understanding of how drugs work and influence behaviour
- Communication occurs at the synapse, where a neuron comes into close contact with the surface of the cell body (Axo-somatic)
- Can also be dendrties (axo-dendritic) or the terminals of another cell (Axo-axonic)
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Neurotransmitters
- Neurotransmitter molecules bind to receptors on the membrane of the postsynaptic cell and change the electrical characteristics of that cell, known as postsynaptic potentials
- Changes can be excitatory or inhibitory
- Excitatory NTs make it more likely that the postsynaptic neuron will fire - causes postsynaptic neurons sodium channels to open, triggering action potential (depolarisation)
- Inhibitory NTs make is less likely that the postsynaptic neuron will fire - causes positive potassium ions to flow from the neuron, making it more negative (hyperpolarisation)
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Synapse - Ending Chemical Transmission
- Autoreceptors - on presynaptic membrane prevent further release of neurotransmitter
- Degradation - neurotransmitter is broken down and deactivated by enzymes
- Re-Uptake - neurotransmitter is taken back up by the pre-synaptic terminal and the effect of the neurotransmitter is diminished
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What are Neurotransmitters?
- Formed within a neuron
- Released when action potential occurs
- Can alter activity of postsynaptic cell
- Deactivated by reuptake or broken down by enzymes
- Neuromodulators - diffuse away from the synapse to target further away cells
- Neurohormones - can travel further throughout the body
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Criteria to be a Neurotransmitter
- Substance must be present in nerve terminals
- Precursors and enzymes must be present
- Nerve stimulation must cause its release
- Exogenous application should mimic effect of nerve stimmulation
- Specific receptors for the substance must be present
- Blocking release of the substance should prevent the presynaptic neuron from altering the activity of the postsynaptic cell
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Key Neurotransmitters
- Norepinephrine - increase heart rate, cause contraction of smooth muscles of blood vessels
- Acetylcholine - Excitatory effects, control of muscle
- Serotonin - appetite, mood and sleep
- Dopamine - movement, reward, addiction
- Glutamate - Most abundant
- GABA- Inhibitory, stops neurons firing uncontrollably
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Endorphins
- Neuropeptides (Endogenous Opiates)
- Released from terminal buttons, cell body and axons
- Diffuse widely
- Inhibit pain sensitivity
- Associated with wellbeing and relaxation
- Released in primates during grooming
- Released during sex, laughter, massage and exercise
- Laughter associated with comedy increased pain tolerance for actors and audience
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Drugs and Brain
- Influence the action of neurotransmitters at the synapse
- Drugs have an affinity for a receptor
- Some drugs facilitate transmission - agonists
- Inhibit transmission - antagonists
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Serotonin
- Monoamine - indoleamine - neurons containing it are serotonergic
- Synthesised from tryptophan, obtained from grains, meat and dairy
- Implicated in mood, appetite and sleep
- Low in depression
- Agonist drugs mimic serotonin
- Increase in tryptophan increases serotonin
- Reserpine interferes with serotonin storage
- MDMA increases serotonin
- SSRIs (prozac) inhibit reuptake of serotonin
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MDMA
- Stimulant
- Increases release of dopamine and serotonin
- Associated with euphoria, relaxation and closeness
- Heavy users show loss of neurons containing serotonin
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Depression
- Emotional: sadness, numbing
- Cognitive: Negative self view, guilt, blame, hopelessness
- Motivational: trouble getting started, physical inertia, difficulty making decisions
- Somatic: loss of appetite, sleep disturbance, fatigue, loss of libido, hypochondriasis
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Biochemical Theories of Depression
- Monoamine - depression is the result of a deficit in NTs Noradrenaline and Serotonin
- Based on observed side effects of antihypertensive drug reserpine
- Caused depression in normal patients
- Later found drug interfered with storage of NA and 5-HT in synaptic vesicles
- Artificial depletion of 5-HT and NA also induces depressive symptomatology
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Antidepressants
- Tricyclics
- Block transporter proteins that reabsorb serotonin, dopamine and neuropinepherine into presynaptic neuron
- Prolong presence of the NTs
- Selective Serotonin Reuptake Inhibitors
- Prozac
- Prevent reuptake of serotonin
- Monoamine Oxidase Inhibitors
- Block enzyme monoamine oxidase- processes serotonin
- More serotonin available
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