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Topic 6: Human health and physiology

Topic 6: Human health and physiology. 6.5 – PART I Nerves. The Nervous System. Central NS. Peripheral NS. Made up of sensory and motor neurons Neuron is the individual cell that carries the electrical impulse throughout the body

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Topic 6: Human health and physiology

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  1. Topic 6: Human health and physiology 6.5 – PART I Nerves

  2. The Nervous System Central NS Peripheral NS Made up of sensory and motor neurons Neuron is the individual cell that carries the electrical impulse throughout the body Nerve – Many individual neurons grouped into a single structure Analogy Nerve is a telephone cable Each wire in the cable is a neuron • Brain/Spinal cord initiates a response when needed (motor response) • Neurons carry this information • Sensory neurons bring info to CNS; motor neurons carry response to muscles

  3. Tracing the nervous system pathway • Electrical impulse called an action potential • Imagine that you have just touched the arm of the person sitting next to you • This was an accident and you immediately removed your hand Nervous System Pathway

  4. Stimulation and Interpretation • Touched arm triggers pressure receptor which starts an • action potential or nerve impulse • Receptors are designed to transform particular kinds of • stimuli into action potential • Interpretation of touch occurs in the brain • - chain of neurons take impulse to CNS • Sensory info reaches spinal cord by spinal nerves • Sensory neurons run from receptors to spinal cord • Action potential reaches the spinal cord and is routed • through CNS for interpretation • In the spinal cord and brain the action potential is carried by • relay neurons • You became aware of the touch by interpretation by your brain

  5. Your brain moved your hand • Action pathway began in the brain’s relay neurons, passed • down the spinal cord, and out a spinal nerve • Action potential travels across motor neurons to muscle • Motor neuron sends a chemical signal to the muscle which • results in the contraction and thus movement

  6. What is a nerve impulse? • Begins with neurons within a nerve that carry the action potential • Conductor of impulse is the axon • Axons of organisms with highly developed nervous system (e.g. humans) surrounded by membrane structure called myelin sheath • Myelin sheath increase rate at which action potential is passed down the axon

  7. Resting Potential - The state of an area of neuron ready to send action potential - Area is said to be polarized - Characterized by active transport of Na+ and K+ in different directions - Na+ actively transported out - K+ actively transported in - Collection of negatively charged organic ions in axon; creates relatively positive charge outside and negatively charged internal environment

  8. The reversal and restoration of the electrical potential across a plasma membrane as a nerve impulse passes along a neuron Action Potential - Self propagating wave of ion movement in and out of the neuron membrane - Channels open and Na diffuses in - Shortly after, K diffuses out - This diffusion (Na in and K out) is the impulse or action potential - Nearly instantaneous event that occurs in one area of the axon: DEPOLARIZATION - This axon area initiates the next area to open up the Na channels, then K, and the action potential continues down the axon - Self-propagating: impulse begins in the dendrite end and will self-propagate to far axon- end

  9. Websites Overview: The Nerve Impulse - http://bcs.whfreeman.com/thelifewire/content/chp44/4402s.swf MyelinatedvsUnmyelinated axon - http://www.blackwellpublishing.com/matthews/actionp.html

  10. Return to resting potential - Neurons send dozens of action potential signals in a short period of time - Na/K ions must be returned to positions characteristic of resting potential - Active transport must be used (i.e. repolarization) - Time it takes to send action potential and then repolarize is called refractory period

  11. Synaptic Transmission What happens when one nerve meets another nerve? • Sensory pathway flows in one direction; terminal end of axon adjoins the dendrite of another cell • Presynaptic/postsynaptic neurons • Chemical communication between cells (i.e. synapse)

  12. Principles of Synaptic Transmission • Far end of axon is terminal button • Within terminal button are vesicles filled with chemicals called neurotransmitters (NTs) • NTs are any chemical used for synaptic transmission (there are many such chemicals)

  13. Websites Presynaptic and Postsynaptic Neurons - http://outreach.mcb.harvard.edu/animations/synaptic.swf

  14. Sequence of events when action potential reaches terminal buttons • Ca ions diffuse into terminal buttons (signals vesicles to move) • NT vesicles fuse with plasma membrane; NT release • NT diffusion from presynaptic to postsynaptic neuron across synaptic gap • NT binds with receptor protein on postsynaptic neuron membrane • Binding opens ion channel and Na ions diffuse through to create action potential • Postsynaptic depolarization • NT broken into two or more fragments by enzymes and released from receptor • Ion channel closes • NT fragments diffuse back across gap and are reassembled at presynaptic neuron

  15. Any questions?

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