UNIT 5 BIOLOGY: COORDINATION

BECAUSE SPECIES HAVE EVOLVED AND BECOME ADAPTED TO PERFORM SPECIALIST FUNCTIONS - LOST ABILITY TO PERFORM OTHER FUNCTIONS, DIFFERENT GROUPS OF CELLS EACH CARRY OUT OWN FUNCTON (DEPENDENT ON OTHERS) THESE DIFFERENT FUNCTION SYSTEMS MUST BE COORDINATED 

2 MAIN FORMS OF COORDINATION IN MAMMALS: 

• NERVOUS SYSTEM -  when electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto cells so the nervous RESPONSE IS LOCALISED, neurotransmitters are quickly removed once theyve done their job so the RESPONSE IS SHORT LIVED and electrical impulses are really fast, so the RESPONSE IS RAPID  - allowing animal to respond quickly. 
• HORMONAL SYSTEM 

MADE UP OF GLANDS AND HORMONES - (gland is a group of cells specialised to secrete hormones) (hormones are chemical messengers - protein/peptides e.g. insulin)

HORMONES ARE SECRETED WHEN A GLAND IS STIMULATED - a change in concentration of a specific substance can stimulate gland, also electrical impulses can stimulate them 

HORMONES DIFFUSE DIRECTLY INTO BLOOD AND ARE TAKEN AROUND CIRCULATORY SYSTEM 

THEY DIFFUSE OUT OF THE BLOOD ALL OVER THE BODY BUT EACH HORMONE WILL ONLY BIND TO SPECIFIC RECEPTORS FOR THAT HORMONE

HORMONES TRIGGER A RESPONSE IN EFFECTORS 

not released directly onto effectors - have to travel through blood, SLOWER COMMUNICATION, arnet broken down as quickly as neurotrasnmitters so effects of hormones last much LONGER, hormones are transported all over the body, so the response is WIDESPREAD 

CHEMCIALS THAT ARE RELEASED FROM CERTAIN CELLS AND HAVE AN EFFECT ON CELLS IN IMMEDIATE VICCINITY 

TYPICALLY RELEASED BY INJURED OR INFECTED CELLS AND CAUSE SMALL ARTERIES AND ARTERIOLES TO DIALATE 

THIS LEADS TO A RISE IN TEMPERATURE AND SWELLING OF INFECTED AREA - INFLAMMATORY RESPONSE 

HISTAMINE - stored in white blood cells,

released when injury occurs or in response to an allergen.

causes dialation of small arteries and increased permeability of cappilaries - leading to SWELLING, REDNESS AND ITCHING 

PROSTAGLANDIS - found in cell membranes -

cause dialation of small arteries,

their release is following an injury increases the permeablity of capillaries,

they also affect blood pressure and neurotransmitters - affect pain sensation 

HISTAMINE - stored in white blood cells,

released when injury occurs or in response to an allergen.

causes dialation of small arteries and increased permeability of cappilaries - leading to SWELLING, REDNESS AND ITCHING 

PROSTAGLANDIS - found in cell membranes -

cause dialation of small arteries,

their release is following an injury increases the permeablity of capillaries,

they also affect blood pressure and neurotransmitters - affect pain sensation 

LIGHT - stems grow towards light for photosyntheiss 

GRAVITY - plants need to be anchored firmly and minerals from soil and so roots grow down 

WATER - all roots plants grow towards water for photosynthsis 

PLANTS RESPOND TO EXTERNAL STIMULI BY PLANT GROWTH FACTORS (this name is used because)

• exert influence by affecting growth 
• unlike animal hormones, made by cells located throughout the plant rather than in particular organs 
• unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on a distant target organ.

EXAMPLE - INDOLEACTIC ACID (IAA) - CAUSES PLANT CELLS TO ELONGATE 

TROPISM - growth movement in response to a directional stimulus

tip of a shoot will grow towards the light 

this is beacsue : 

• cells in the tip of the shoot produce IAA, which is then transported down the shoot
• IAA is initially transported to all sides as it begins to move down shoot 
• light causes the movement of IAA from the light side to the shaded side of shoot 
• a greater concentration of IAA builds up on shaded side 
• IAA causes elongation, so shaded side grows more and faster causing the shoot to bend towards the light 

NEURONES - specialised cells adapted to rapidly carrying electrical impulses from one part of the body to another

made up of:

• CELL BODY - contains a nucleus, large amounts of rough endoplasmic reticulum for production of proteins and neurotransmitters 
• DENDRONS - small extensions off cell body, subdivide into smaller branches called dendrites which carry nerve impulses to cell body 
• AXON - a single long fibre that carries nerve impulses away from cell body 
• SHWANN CELLS - surround axon, protect and provide electrical insulation, carry out phagocytosis and play a part in nerveregeneration.
• MYELIN SHEATH - forms a covering to the axon and is made up of the membranes of the swhaan cells, rich in lipids called myelin, myelinated neurones trasnmit nerve impulses faster than unmylenated ones 
• NODES OF RANVIER - gaps between adjacent shwaan cells where there is no myelin sheath 

SENSORY NEURONES -  trasnmit nerve impulses from receptor to CNS, they have one dendron (carries towards cell body) and one axon (carries away)

MOTOR NEURONES - trasnmit nerve impulses from cns to effectors, they have a long axon and many short dendrites 

INTERMEDIATE NEURONES - transmit nerve impulses between neurones, numerous short processes 

MOVEMENT OF IONS, SUCH AS SODIUM IONS AND POTTASIUM IONS IS CONTROLLED:

PHOSPHOLIPID BILAYER OF AXON PLASMA MEMBRANE PREVENTS SODIUM AND POTTASIUM IONS DIFFUSING ACROSS IT 

INTRINSIC PROTEINS SPAN THE PHOSPHOLIPID BILAYER, THESE PROTEINS CONTAIN ION CHANNELS WHICH PASS THROUGH THEM SOME OF THESE CHANNELS HAVE GATES, WHICH CAN BE OPENED OR CLOSED TO ALLOW SOIDUM OR POTTASIUM IONS TO PASS THROUGH 

SOME INTRINSIC PROTEINS ACTIVLEY TRASNPORT POTASSIUM IONS INTO AXON AND SODIUM ION OUT OF THE AXON - SODIUM POTTASIUM PUMP 

AS A RESULT OF THESE CONTROLS - INSIDE OF AXON IS NEGATIVLEY CHARGED COMPARED TO OUTSIDE - CALLED RESTING POTENTIAL - AXONS IS POLARISED 

• sodium ions activley transported out of axon by sodium pottasium pumps
• pottassoim ions activley transported into axon by sodium pottasium pumps 
• active transport of sodium is greater than potassium, 3 sodiumsn for every 2 pottasium - more sodium in tissue fluid surrounding axon - more pottasium in cytoplasm of axon 
• as both try to diffuse naturally in and out of axon, the pottasium channels are open, whilst most of the gates that allow sodium channles through are closed 
• this futher increases potenitial difference of a negative inside and positive outside

• sodium ions activley transported out of axon by sodium pottasium pumps
• pottassoim ions activley transported into axon by sodium pottasium pumps 
• active transport of sodium is greater than potassium, 3 sodiumsn for every 2 pottasium - more sodium in tissue fluid surrounding axon - more pottasium in cytoplasm of axon 
• as both try to diffuse naturally in and out of axon, the pottasium channels are open, whilst most of the gates that allow sodium channles through are closed 
• this futher increases potenitial difference of a negative inside and positive outside

WHEN A STIMULUS IS RECIEVED BY A RECEPTOR OR NERVE ENDING, ITS ENERGY CAUSES A TEMPORARY REVERSAL OF CHARGES ON THE AXON MEMBRANE - AS A RESULT NEGATIVE CHARGE INSIDE THE MEMBRANE OF AROUND -65MV TURNS TO +40MV - THIS IS KNOWN AS AN ACTION POTENTIAL 

AND MEMBRANE IS SAID TO BE DEPOLARISED 

THE DEPOLARISATION OCCURS BECAUSE THE CHANNELS IN THE AXON MEMRANE CHANGE SHAPE - OPEN OR CLOSE - VOLTAGE GATED CHANNELS 

• at resting potential some pottasium voltage gates are open, but the sodium voltage gates channels are closed 
• energy of stimulus causes some sodium voltage gates in the axon membrane to open and sodium ions diffuse into axon through these channels along electrochemical gradient - being positivley charged they trigger a reversal in potential diffference across the membrane (less negative inside)
• once action potential of around +40mv has been reached sodium ion channels close and voltage gates on potassium ion channels open and pottasium diffuses out of axon - repolarisation 
• the outward diffsuion of pottasium ions cause an over shoot - hyper polarisation - more negative on the inside then usual

AS ONE REGION OF AXON PRODUCES AN ACTION POTENTIAL AND BECOMES DEPOLARISED, IT ACTS AS A STIMULUS FOR THE DEPOLARISATION OF NEXT REGION OF AXON 

IN MEANTIME THE PREVIOUS REGION RETURNS TO RESTING POTENTIAL - REPOLARISATION 

LIKE A MEXICAN WAVE IN A STADIUM 

FATTY SHEATH OF MYELIN AROUND AXON ACTS AS AN INSULATOR 

PREVENTS ACTION POTENTIALS FROM FORMING 

BETWEEN EACH MYELIN SHEATH THERE ARE NODES OF RANVIER WHERE ACTION POTENTIAL CAN OCCUR 

ACTION POTENTIALS JUMP FROM NODE TO NODE - SALTATORY CONDUCTION 

THIS MEANS IT PASSES MUCH FASTER THAN AN UNMYLENINATED AXON 

FACTORS AFFECTING:

• MYELIN SHEATH - saltatory conduction 
• DIAMETER OF AXON - greateer the diameter, faster the speed of conductance - less leakage of ions from a large axon 
• TEMPERATURE - affects rate of difusion of ions, the higher the temp the faster the nerve impulse, energy for active transport comes from respiration, respiration needs enzymes, enzymes are affected by temp - denature when too hot 

ONCE ACTION POTENITAL HAS BEEN CREATED, THERE IS A PERIOD AFTERWARDS WHEN THE INWARD MOVEMENT OF SODIUM IONS IS PREVENTED BECAUSE THE SODIUM VOLTAGE GATES ARE CLOSED 

DURING THIS TIME IT IS POSSIBLE FOR A FURTHER ACTION POTENTIALS TO BE GENERATED

KNOWN AS REFRACTORY PERIOD 

• ENSURES THAT AN ACTION POTENTIAL IS PROPGATED IN ONE DIRECTION 
• PRODUCES DISCRETE IMPULSES - due to refractory period, a new action potential cannot be formed immediatley behind the first one, ensusures sepeartion between action potentials
• LIMITS NUMBER OF ACTION POTENTIALS - 

CERTAIN LEVEL OF STIMULUS CALLED THRESHOLD VALUE - TRIGGERS AN ACTION POTENTIAL 

BELOW THE ACTION POTENTIAL NO ACTION POTENTIAL IS GENERATED 

HOW DOES A ORGANISM PERCEIVE THE SIZE OF A STIMULUS//

• BY THE NUMBER OF IMPULSES PASSING IN A GIVEN TME - LARGER THE STIMULUS THE MORE IMPULSES ARE GENERATED IN A GIVEN TIME 
• BY HAVING DIFFERENT NEURONES WITH DIFFERENT THRESHOLD VALUES - THE BRAIN INTERPRETS THE NUMBER AND TYPE OF NEURONES THAT PASS IMPULSES AS A RESULT OF A GIVEN STIMULUS AND THEREBY DETERMINES ITS SIZE.

THE POINT WHERE THE AXON OF ONE NEURONE CONNECTS WITH THE DENDRITE OF ANOTHER OR WITH AN EFFECTOR 

IMPORTANT IN LINKING NEURONES TOGETHER 

SYNAPSES TRANSMIT IMPULSES FROM ONE NEURONE TO ANOTHER BY MEANS OF CHEMICALS CALLED NEUROTRANSMITTERS 

NEURONES SEPERATED BY GAP CALLED SYNAPTIC CLEFT

NEURONE THAT RELEASES NEUROTRANSMITTER IS CALLED PRESYNAPTIC NEURONE 

AXON OF THIS NEURONE ENDS IN A SWOLLEN PORTION KNOWN AS SYNAPTIC KNOB 

THIS POSSES MANY MITOCHONDRIA AND ENDOPLASMIC RETICULUM - REQUIRED FOR MANAFACTURE OF NEUROTRANSMITTERS

ONCE MADE, NEUROTRANSMITTERS STORED IN SYNAPTIC VESICLES -once released it diffuses across to postsynaptic neurone - which has receptors on membrane to reciev it 

• A SINGLE IMPULSE ALONG ONE NEURONE CAN BE TRASNMITED TO A NUMBERR OF DIFFERENT NEURONES AT A SYNAPSE (JUNCTION)

• A NUMBER OF IMPULSES CAN BE COMBINED AT A SYNAPSE, THIS ALLOWS STIMULI FROM DIFFERENT RECEPTORS TO INTERACT AND PRODUCE A SINGLE RESPONSE 

IMPORTANT TO KNOW :

• neurotransmitters made only in presynaptic neurone and not in post synaptic
• neurotransmitter is stored in synaptic vesicles and released into synapse only when action potential reaxhes the synaptic knob 
• neurotransmittwe diffuses across to bind to receptor molecules on post synaptic neurone and sets up a new action potential in post synaptic neurone 

A CHOLENERGIC SYNAPSE IS ONE WHICH THE NEUROTRANSMITTER IS ACETYL CHOLINE 

COMMON IN VERTEBRATES, WHERE THEY OCCUR IN THE CENTRAL NERVOUS SYTEM AND AT NEUROMUSCULAR JUNCTIONS 

• arrival of action potential at end of presynaptic neurone causes calcium ion channels to open and calcium ions enter synaptic knob 
• influx causes synaptic vesicles to fuse with presynaptic membrane, releasing acetlyl choline into cleft 
• acetyl choline fuses with receptors sites on the sodium ion channel on the post synaptic membrane - causing sodium ion channels to open, allowing sodium ions to diffuse in 
• influx of sodium ions generates new action potential in post syanaptic 
• acetylcholinesterase hydrolyses acetyl choline in to acetyl and choline, which diffuse back across synaptic cleft
• atp is released by mitochondria to recombine the acetyl choline so it can be recycled 
• soidum ion channels close in the absecnce of acetly choline in receptor sites