Nervous Coordination

• Hormones can be amines, proteins and steroids, they are secreted by glands making up the endocrine system
• Hormones such as adrenaline can bind to receptors due to their specific polypeptide tertiary structure for a second messenger model
• Hormones can be steroids which can bind with a receptor to help the compound to diffuse through the plasma membrane
• The hormone can also alter the cell membrane permeability by depolarising it, allowing molecules such as glucose inside
• The nervous system is faster, lasts for a shorter amount of time and is a temporary change, nerves will travel to specific areas of the body
• Sensory neurones can be identified with their cell body extending from the axon between axon terminal and dendron, they have one dendron only
• Motor neurones can be identified by their cell body adjacent to the dendrites with an axon travelling to the axon terminal, they have multiple dendrons
• The interneurone is identified by its central cell body between dendron and axon
• Dendrites are branched fibres from dendrons, extensions of the cell body receiving action potentials from other nerve cells
• The nervous system is adapted because it enacts rapid and reversible change which is necessary in a constantly changing environment of an organism
• The axon carries the action potential away from the cell body toward other neurones at the axon terminal
• Schwann cells surround the axon, providing electrical insulation and can also perform phagocytosis to remove cell debris
• The myelin sheath can acts as an electrical insulator: by surrounding the schwann cell, there are only intermediate conductive areas of the axon in the nodes of ranvier where the membrane can be depolarised, increasing speed by decreasing surface area of conductive tissue
• The axon terminals are where the synapses are, transmitting the action potentials to other neurones
• Cathode Ray Oscilloscopes can be used to to measure the speed and magnitude of action potentials
• Speed of action potential travel can be increased by increasing axon diameter and myelination, by increasing diameter, less ions will leak from the axon due to a longer diffusion distance
• There are permanently open channels in the membrane of the axon allowing for sodium and potassium ion diffusion
• Saltatory conduction is where action potentials jump between nodes of ranvier
• The size and shape of voltage sensitive gates will change depending on ion size and can be opened and closed depending on the voltage
• The resting potential is around -65mV
• To establish a resting potential, 3 sodium ions are pumped out of the axon and 2 potassium ions are pumped into the axon, some sodium ions diffuse back into the axon through open sodium ion channels, some potassium ions diffuse back out of the axon through open potassium ion channels, however, more potassium ion channels are open and more sodium ion channels close, polarising the membrane due to the outside being more positive than the inside of the axon
• An action potential forms, voltage gated sodium ion channels begin to open due to stimulus and voltage gated potassium ion channels close, sodium ions then diffuse into the membrane, depolarising the membrane
• If a stimulus is sufficient, the threshold value of - 55mv will be reached, this causes all sodium ion channels to open in the all or nothing theory, increasing the membrane potential to 40mV
• The first action potential generates a positive charge on the internal membrane due to movement of sodium ions into the axon, these positive ions diffuse right toward the adjacent local negative charge, this stimulates voltage gated sodium ion channels to open causing the action potential to move along the axon
• Action potentials dont move backwards due to the refractory period after a membrane becomes hyperpolarised, the charge of the previous section of membrane is further from the threshold potential than the adjacent membrane at resting potential so the action potential travels right
• Speed of action potential transmission can be increased by temperature as ions have a higher kinetic energy, increasing rates of diffusion across the axon membrane
• In an action potential, sodium ions experience a sudden influx, then potassium ions diffuse out down an electrochemical gradient
• The refractory period is where the sodium ion channels are closed so another action potential cannot be generated
• The refractory period ensures unidirectional movement, that impulses are separate and limits the number of action potentials, limiting the strength of a stimulus
• An action potential is +40mV
• The all or nothing law means that any generator potential below the threshold will not generate an action potential, but every action potential will be the same voltage
• A stronger stimulus increases the frequency of action potentials
• Organisms detect the number of action potentials received to judge the strength of the stimulus, the type of neurone also distinguishes the stimulus
• The synaptic knob will be next to the post synaptic membrane where the action potential is transferred
• Acetylcholine is an excitatory neurotransmitter
• When the action potential arrives at the synaptic knob, voltage gated Ca2+ channels open, causing calcium ions to diffuse into the neurone
• Calcium ions cause vesicles at the synaptic knob to fuse with the synaptic knob membrane, allowing neurotransmitter to diffuse across the synaptic cleft
• Neurotransmitter molecules such as acetylcholine bind to ligand gated receptors on sodium ion channels, causing them to open, allowing sodium ions to diffuse into the post synaptic membrane, depolarising the membrane
• The neurotransmitter is hydrolysed by enzymes and the products are reabsorbed by the synaptic knob to be reassembled for another action potential, this prevents the neurotransmitter from keeping sodium ion channels open, preventing constant depolarising
• The synapse is unidirectional as vesicles of neurotransmitters are only on the synaptic knob and complimentary receptors are only present on the post synaptic membrane