ELECTRICAL COMMUNICATION IN ANIMALS The Nervous System

The nervous system  Composed of neurons  2 main systems:  Central nervous system(CNS) ________________________________  Peripheral nervous system (PNS) ________________________________

Neurons  Sensory neurons – ______________________  Motor neurons – _______________________  Connector neurons (interneurons) – _________________________________________ _________________________________________  Lots and lots of neurons in body and these can differ in shape and size.

Cell structure of Neurons  Cell Body _______– contains nucleus  Dendrites – ____________________________  Axon – ________________________________  Synapse – ________________________

Electrical Impulse  Electrical transmission down axon  Cell membrane of axon is _____________(diff charge between inside and outside of cell)  Axon not firing = _____________charged inside and _____________ on outside – called resting potential.  ___________________________ in membrane pumps Na ions (NA + ) out and K ions (K + )in.  If 2 K + ions are pumped in, 3 Na + ions get pumped out  build up of Na + outside and K + inside  more of a negative charge inside.

When a neuron fires  Na + diffuse in quickly in changing the resting potential.  Depolarises membrane  Inside of cell is now _____________ charged, called action potential.  Very quick  As soon as the Na + rush in the cell begins to pump out the K +. – Sodium-Potassium Pump  Na + then gets pumped out and K + in bringing the cell back to the resting potential.

Transferring a message  Depolarisation moves progressively down the axon.  Speed depends on: type of animal, size and length of axon, type of neuron.  Thicker the neuron – ______________________  Myelin sheath –  Covers axon. Made up of Schwann cells - insulates  speeds up message/electrical impulse  Animals that have no myelin sheath move slowly and/or have very thick axons.

Transmission animation One of the best animations you’ll ever see on this!!  potential.swf

Neurotransmitters  Travel across the synapse  Neurons don’t actually touch  Chemical messages travel through, called neurotransmitters.  Synaptic knobs at end of axon & contains lots of mitochondria and secretory vesicles that release neurotransmitters.  When impulse arrives, C + diffuse in from surrounding tissue  secretory vesicles moving towards presynaptic membrane  merge and release contents into synapse through exocytosis.  Neurotransmitters then diffuse across the synapse and bind with receptor proteins  protein channels opening up in the membrane of the dendrites  Na + diffuse into post synaptic neuron  partial depolarisation.  If lots of channels open then action potential initiated.  Important that it can be stopped – done by enzymes in synapse.

Neurotransmitters coordinating responses  Lots of synapses need to fire together to coordinate a response and initiate an action potential.  Some neurotransmitters hinder the transmission of impulses. Some cause inside on the postsynaptic membrane to become more negative than usual and harder for it to become depolarised  changes in responses by nervous system. E.g. stimulations and inhibiting.

Types of neurotransmitters  Acetylcholine  Found in synapses and nerve-muscle junctions in the voluntary NS  Decativated by enzyme _____________________  Muscle cells receive continuous signals  spasms.  Found in insecticides, nerve gas etc

Nerve Gas – How it works Symptoms  Initially – runny nose, tightness in the chest and constriction of the pupils  Soon after - have difficulty breathing, and will experience nausea and drooling The victim continues to lose control of his or her bodily functions, he or she will involuntarily salivate, urinate, defecate, and experience gastrointestinal pain.  This phase is followed by twitching and jerking, and ultimately the victim will become comatose and suffocate as a consequence of convulsive spasms Effects of Nerve Agents  Very long lasting and cumulative (increased successive exposures).  Survivors of nerve agent poisoning almost invariably suffer chronic neurological damage. Mechanism of Action  When a normally functioning motor nerve is stimulated it releases the neurotransmitter acetylcholine, which transmits the impulse to a muscle or organ. Once the impulse is sent, the enzyme acetylcholine esterase immediately breaks down the acetylcholine in order to allow the muscle or organ to relax.  Nerve agents disrupt the nervous system by inhibiting the enzyme acetylcholine esterase by forming a covalent bond with the site of the enzyme where acetylcholine normally undergoes hydrolysis (breaks down). The result is that acetylcholine builds up and continues to act so that any nerve impulses are continually transmitted, and muscle contractions do not stop.  This same action also occurs at the gland and organ levels, resulting in uncontrolled drooling, tearing of the eyes (lacrimation), and excess production of mucous from the nose (rhinorrhea).

Drugs and the nervous system  Recreational drugs affect signal transmission  Caffeine, amphetamines, ecstasy & cocain promote the release of noradrenaline (released in response to stress)  stimulants.  Opiates (heroin, morphine, codeine) block nerve transmission in the sensory pathways of the CNS that signal pain. They are used as pain killers.  Inhibit centers in brain that control coughing, breathing and digestion.  Psychedelic drugs (LSD & mescaline) block reabsorbtion of neurotransmitter dopamine  increased dopamine in brain  hallucinations.

Natural drugs and the nervous system  Endorphins  Relieve pain  Bring on feelings of euphoria  Lock onto same receptors in brain as do those of morphine.  Released when brain experiences pain as well as other things. E.g. acupuncture, chilli, chocolate etc.

Differences/Similarities between neurotransmitter and hormone? NeurotransmitterHormone Only affect cells in their areaParacrine hormones Noradrenaline very similar & respond to stress Adrenaline & responds to stress

When transmission fails  You can get sick and die!  E.g. Multiple sclerosis – _________________________________________ _____________________________  Poisons or venoms interfere with neurotransmitters. They block postsynaptic receptors between effector neurons and skeletal muscles which prevents the muscles contracting  ______________.  Parkinson’s disease – secretion of ____________ is disrupted.

Transferring signals between organisms  Visual signals  Light energy  photoreceptors (rods & cones)  converted into an action potential that travel along neurons to brain.  Olfactory signalling (smell)  Detected by specific olfactory receptor neurons lining the nose.  Olfactory signal relayed through the neurone using cyclic AMP as a second messenger  ion channels opening in cell membrane  increase in Na +  depolarisation of olfactory receptor neurons & initiates a nerve impulse that travels to the brain.  Can be used to detect pheromones.

Pheromones  Chemicals emitted by living organisms to send messages to individuals of the same species.  Social pheromones  When fear some animals will release pheromones that can be detected by others near by for assistance.  Sexual pheromones  Attractants  Mammals  E.g. dog’s marking territory with sniffing  Women and menstrual cycles.