Nervous coordination and muscles Flashcards
what are nerve impulses?
electrical signals that pass along nerve cells knows as neurones
what are the two main types of coordination in animals?
nervous system
hormonal system
how does the nervous system work?
uses nerve cells to pass electrical impulses along their length
they stimulate their target cells by secreting chemicals know as neurotransmitters
results in rapid communication between specific parts of an organism
the responses produced are often short lived and restricted to a localised region of the body
an example of nervous coordination is reflex action
how does the hormonal system work?
the hormonal system 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 often long lasting and widespread
what is a bundle of neurones known as?
nerves
what do neurones coordinate?
neurones coordinate the activities of sensory receptors
decision making centres in the central nervous system
and the effectors such as muscles and glands
what did the long fibre that neurones have called?
an axon
what is the axon of some neurones insulated by?
a fatty sheath with small uninsulated sections along its length
-nodes if ranvier
the sheath is made of myelin, a substance made by specialised cells known as Schwann cells
myelin is made when schwann cells wrap themselves around the axon along its length
what is a mammalian motor neurone made up of?
a cell body
dendrons
an axon
schwann cells
a myelin sheath
nodes of ranvier
what is a cell body made up of?
nucleus
large amounts of rough endoplasmic reticulum
associated with the production of proteins and neurotransmitters
what are dendrons?
extensions of the cell body which subdivide into smaller branched fibres, called dendrites that carry nerve impulses towards the cell body
what is an axon?
a single long fibre that carries nerve impulses away from the cell body
what are schwann cells?
surround the axon
protecting it and providing electrical insulation
carry out phagocytosis (the removal of cell debris)
play a part in nerve regeneration
schwann cells wrap themselves around the axon many times, so that layers of their membranes build up around it
what is a myelin sheath?
forms a covering to the axon and is made up of the membranes of the schwann cells
these membrane are rich in a lipid known as myelin
neurones with a myelin sheath are called myelinated neurones
what are nodes of ranvier?
constrictions between adjacent schwann cells where there is no myelin sheath
the constrictions are 2-3 micromètres long and occur every 1-3 mm in humans
what does the presence of schwann cells mean?
the electrical impulse does not travel down the whole axon
jumps from one node to the next
the ‘jumping’ of the electrical impulse between nodes of ranvier is called saltatory conduction
this speeds up the conduction of the impulse and it’s transfer from one cell to another
what is a nerve impulse?
a self propagating wave of electrical activity that travels along the axon membrane
it is a temporary reversal of the electrical potential difference across the axon membrane
this reversal is between two states:
resting potential
action potential
what is the resting potential?
in a resting axon
(one that is not transmitting impulses)
the inside of the axon always had a negative electrical potential compared to outside the axon
in this condition the axon is polarised
what is the potential difference when there are no impulses?
-70mV
65
what two factors contribute to establishing and maintaining the resting potential?
the active transport of sodium ions and potassium ions
differential membrane permeability
how is the movement of ions such as sodium, potassium ions across the axon membrane controlled?
-the phospholipid bilayer of the axon plasma membrane prevents sodium and potassium ions diffusing across it
how does the phospholipid bilayer of the axon plasma membrane prevent sodium and potassium ions from diffusing across it?
proteins known as channel proteins
span this phospholipid bilayer
these proteins have channels called ion channels which pass through them
some of these channels have gates which can be opened or closed so that sodium or potassium ions can move through them by facilitated diffusion at any one time but not on any other occasion
some channels however remain open all the time so the sodium and potassium ions move unhindered through them by facilitated diffusion
some carrier proteins actively transport potassium ions into the axon and sodium ions out of the axon
this mechanism can be called a sodium potassium pump
how does the active transport of sodium and potassium ions establish and maintain resting potential?
carrier proteins called sodium potassium pumps are present in the membranes of neurones
these pumps use ATP to actively transport 3 sodium ions out of the axon for every 2 potassium ions that they actively transported in
this means that there is a larger concentration of positive ions outside of the axon than there are inside the axon
the movement of ions via the sodium potassium pumps establishes an electrochemical gradient
how does a differential membrane permeability establish and maintain the resting potential?
the cell surface membrane of neurones has selective protein channels that allow sodium and potassium ions to move across the membrane by facilitated diffusion
the protein channels are less permeable to sodium ions than potassium ions
this means that potassium ions can diffuse back down their concentration gradient,out of the axon, at a faster rate than sodium ions
what are action potentials?
the impulses which neurones transmit, which travel extremely quickly along the neurone cell surface membrane from one end of the neurone to the other
how do action potentials happen?
they occur via very brief changes in the distribution of electrical charge across the cell surface membrane
caused by the rapid movement of sodium ions and potassium ions across the membrane of the axon
what is a nerve impulse in an axon?
a moving area of charge
what is the resting potential?
when a neurone maintains a less positive charge in the inside of the axon
this is maintained by the sodium potassium pump
