nervous coordination of muscles

-the nervous system and the hormonal system

the nervous system uses nerve cells to pass electrical impulses along their length

They stimulate their target cells by secreting chemicals, known as NEUROTRANSMITTERS directly onto them This results in rapid communication between specific parts of an organism

• they are short-lived • restricted to a localised area • the effect is temporary and reversible • transmission is by neurones and is rapid

a reflex action such as the withdrawal of the hand from an unpleasant stimulus

it produces chemicals (hormones) that are transported in the blood plasma to their target cells

the target cells have specific receptors on their cell surface membranes and the change in the concentration of hormones stimulates them This results in a slower, less specific form of communication between parts of an organism

The responses are long-lasting and widespread an example of hormonal coordination is the control of blood glucose concentration, which produces a slower response but has a more long term and more widespread effect

• communication is by chemicals called hormones • transmission is by the blood system • hormones travel to all parts of the body, but only target cells respond • response is widespread • response is slow • response is often long-lasting

• communication is by nerve impulses • transmission is by neurones • transmission is very rapid • nerve impulses travel to specific parts of the body • response is localised • response is short-lived • effect is usually temporary and reversible

neurones (nerve cells) are specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another

a cell body dendrons an axon Schwann cells a myelin sheath nodes of Ranvier

it contains all the usual cell organelles, including a nucleus and large amounts of rough endoplasmic recticulum. This is associayed with the production of proteins and neurotransmitters

they are extensions of the cell body which subdivides into smaller branched fibres, called dendrite that carry nerve impulses towards the cell body

it is a single long fibre that carries nerve impulses away from the cell body

shwann cells which surround the axons protecting it and providing electrical insulation They also carry out phagocytosis (the removal of cell debris) and play a part in nerve regeneration Schwann cells wrap themselves around the axon many times, so that layers of their membranes build around it

a mylein sheth, which forms a covering to the axon and is made up of the membranes of the Schwann cells These membranes are rich in a lipid known as mylein Neurones with a mylekun sheath are called myelinated neurones

these are constrictions between adjacent Schwann cells where there is no myelin sheath The constrictions are 2-3 micrometres long and occur every 1-3 mm in humans

sensory neurones motor neurones intermediate/relay neurones

it is the difference in electrical charge between the outside and inside of the neuron when an impulse isn’t being conducted this means there is no stimulus to send impulses

about -70mV because there are more Na+ and K+ ions outside the neuron and so the inside of the neuron is negative

1) by sodium-potassium pump, which involves active transport and therefore ATP (active transport of the sodium and potassium ions) 2) 2 K+ions are pumped into the neuron via the sodium - potassium pump and 3 Na_ ions are transported out of the neuron 3)because the K_ ions are transported into the neuron, this creates a concentration of K+ ions inside the neurone and also a concentration gradient of Na+ ions outside the neuron. Therefore, the K+ ions can diffuse out of the neuron again creating a negative resting potential • the sodium potassium pump becomes less permeable to sodium ions and so they can’t be transported back into the neuron. This meant that the resting potential is maintained at -70mV

1) when an impulse is received from receptors, sodium ion channels open, so Na+ ions enters the neuron, this causes them to become depolarised. Therefore, the charge becomes more positive. 2) if depolarisation reaches the threshold potential (-50mV) voltage - gated sodium ions are activated, leading to an eve higher influx, causing an action potential (+40mV) 3) Voltage - gated Na+ channels close whilst voltage gated K+ channels open, so reporalisation occurs as K+ ions leaves the neuron 4) When most of the L+ ions have left the neuron, this occurs hyperpolarisation so the voltage - gated K+ ion channels close 5) the sodium potassium pump therefore returns a neuron back to its resting potential

when the potential of a neuron is returning back to its negative state as the k+ ion are leaving