Nerves and Muscles Part 1

HideShow resource information
  • Created by: G
  • Created on: 23-05-14 15:09
View mindmap
  • Nerves and Muscles
    • Nerves and Homones
      • Nervous communications consists of neurones passing electrical impulses along their length.
        • Neurones pass directly to target cells.
      • Hormonal communication  consists of the endocrine system secreting hormones directly into the bloodstream.
        • Hormones pass to all parts of the body but stimulate target cells in a lock and key fashion- the hormone receptors have specific hormone receptor proteins on their surface.
          • Hormones= chemical signalling messengers that are released directly into the bloodstream.
    • Chemical Mediators
      • Histamine
        • Largely responsible for inflammation.
        • Made by White cells called mast cells in response to cell damage or bacterial infection.
        • Affects cells locally-makes blood capillaries more permeable so white blood cells and fluid accumulates in the affected area.
      • Prostaglandins
        • Group of substances with a variety of localised effects including inflammation.
        • First found in prostate gland but secrete to most organs in the body.
        • Effects= stimulating contraction of smooth muscle (uterus) and controlling platelets during blood clotting,
    • Motor Neurones
      • A motor neurone is a cell that carries nerve impulses away from the CNS to an effector such as a gland or muscle.
      • Myelinated means that the axon is protected by a fatty myelin sheath made from several layers of cell membrane.
        • Myelin sheath= non-conducting fatty layer around the axon.
          • Role of myelin sheath= Insulate the axon, protect the axon and spped up the transmission of the nerve impulses.
        • Sections are made by individual schwann cells that wrap around the axon many times.
          • In between the section of myelin there are nodes of Ranvier where the axon membrane is exposed.
            • Role of myelin sheath= Insulate the axon, protect the axon and spped up the transmission of the nerve impulses.
      • Key Features
        • A cell body that contains the nucleus and other organelles.
        • An elongated axon that carries impulses away from the cell body.
        • One or more dendrites that take impulses towards the cell body.
    • Resting Potential
      • Resting potential is the potential difference across the axon membrane of a nerve cell when the cell is at rest.
      • Once resting potential is established, the neurone is ready to transmit an impulse.
        • Resting potential is as a result of two processes occurring together.
          • Active Transport-sodium-potassium pump is a protein responsible for the active transport of positive ions.
          • Unequal facilitated diffusion- there are sodium channels and potassium channels.
            • Both are gated so that by changing their shape they can open up and allow the ions to diffuse freely.
              • Difference between the two is that the potassium channels are more 'leaky' and so potassium diffuses out faster than sodium diffuses in.
                • High conc of positive ions outside axon so the area has an overall positive charge compared to inside.
                  • There are negative ions inside and outside the axon membrane mostly cl- and negatively charged proteins.
                    • It's the movement of positive ions that establishes a resting potential and brings about an action potential.
    • Generation of an action potential
      • Action potential is a nerve impulse that rapidly reverses a resting potential and spreads rapidly along an axon.
      • For about a millisecond, the resting potential is reversed in one area of the axon so that the inside becomes positively charged. Reversal spreads along the axon while the original area recovers and establishes a resting potential again.
        • Depolatisation- Gated Na+ channels open, allowing Na+ to diffuse in and reverse the resting potential.
        • Repolarisation- gates Na+ channels close preventing further diffusion inwards. Gated K+ chanels open allowing + charged potassium ions to diffuse out rapidly.
        • Hyperpolarisation- an 'undershoot' results from the gated K+ channels still being open when the active transport mechanism begins to re-establish a resting potential by pumping sodium channels out.
        • The gate K+ channels return to their normal permeability and a resting potential is re-established.
      • Self-propogating- means that depolarisation in one area of the axon will automatically cause depolarisation of the next region.
        • Both sodium and potassium channels are voltage gated which means that their shape and therefore permeabilty depends on the voltage (charge) across the membrane.

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Nerves and Muscles resources »