6.2.1 nerve impulses

structure of cellulose

chain of beta glucose - unbranched - 1,4 glycosidic bonds to make unbranched

every other glucose is inverted to make sure hydroxyl groups are in right position for reaction

describe the function of the capsule in biology

protection also can help bacterial cells stick together (fro further protection)

state what is happening during prophase in mitosis

chromosomes condense

chromosomes become visible - this differentiates from interphase and mitosis

nuclear envelope disappears

centriole moves to opposite ends of the cell

brain structure

cerebrum / cerebral cortex

Controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory. 

The outer layer is called the cerebral cortex, which is split into two hemispheres and is highly folded. 

cerebellum

Controls balance, coordination of movement and muscular activity.

medulla oblongata

Controls unconscious activities such as heart rate and breathing rate,

hypothalamus

Regulating centre for temperature and water balance within the body.

neurones

specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another.

neurone = single nerve cell

nerve = bundle of neurones (nerve cells) surrounded by tough connective tissue

cell body of a neurone cell

cell body contains all the usual cell organelles including

• nucleus

• large amounts of RER

the large RER is associated with the production of proteins and neurotransmitters

Dendrons

• are extension of cell body which subdivide into smaller branched fibres called dendrites

• dendrites carry nerve impulses towards the cell body

myelin sheath - fatty ;layer around axon

axon and Schwann cells

an axon í a single long fibre that carries nerve impulses away from the cell body

the axon is surrounded by Schwann cells which protect it and provide electrical insulation

salutary conduction takes place - iron channels open and impulse can jump from uninsulated area to uninsulated area - increasing the speed the impulse moves down

Schwann cells and myelin sheath

• Schwann cells carry out phagocytosis to remove cell debris and play a part in nerve regeneration

• the Swann cells wrap around the axon many times - layers of their membranes build up around it

• Schwann cell membranes are rich in a lipid called myelin

• a Schwann cell envelops and rotates around the axon forming myelin sheath

• neurones with a myelin sheath are called myelinated

node of Ranvier

between adjacent Schwann cells there are constrictions where there is no myelin sheath, these are called nodes of Ravier

the constrictions are 2-3um long and occur every 1-3mm in humans

diagram of mammalian motor neurone

active transport defined

the movement of molecules and ions through a cell membrane against their concentration gradient form a region of low concentration to a region of high concentration using ATP

describe the difference between a channel protein and a carrier protein

channel proteins are water filled pores that go straight through the membrane, structured shape allowing charged substances (ions) to diffuse through cell membrane, - facilitated diffusion for specific ions

carrier proteins can switch between 2 shapes, allowing the binding site of the carrier to be open on different sides of the membrane.

neurones are cells with long projections called axons. describe the structure of an axon membrane

normal cell membrane - cell membranes are a phospholipid bilayer and are important as they establish the boundary of each cell

L2 - maintaining the resting potential

nerve impulse

a self-propagating (self sustaining) wave of electrical activity that travels along the axon membrane

it is a temporary reversal of the electrical potential difference across the axon membrane

the reversal is between two states

• the resting potential - axon not transmitting an impulse

• the action potential - axon is transmitting an impulse

what is electrical potential difference due to?

across cells membrane is due to unequal ion concentrations

resting potential

• resting potential occurs in resting axons - neurons that are not transmitting impulse

• the inside of the axon always has a negative electrical potential compared to the outside of the axon

• there’s always something happening inside it - it isn’t actually resting.

• at resting potential (-70mV) the axon is said to be polarised

• it is more negative inside the axon than outside

the -70mV resting potential is achieved through the movement of ions (specifically Na+ and K+) across the axon membrane

movement of ions across axon membrane

the phospholipid bilayer of the axon prevents sodium Na+ and potassium K+ ions diffusing across it and can cross the membrane in one of two ways

• facilitated diffusion via channel proteins - both Na and K moving down their respective concentration gradients

• active transport via a carrier protein with K+ are actively transported into the axon and Na+ out of the axon via a special carrier called a sodium potassium pump

establishing and maintaining the resting potential

two factors contribute to establishing and maintaining the resting potential

• differential membrane permeability

• the active transport of sodium ions and potassium ions (via the Na+/ K+) pump

what does differential membrane permeability mean?

the axon membrane is not equally permeable to all ions

it allows some ions to pass through more easily than others due to distribution of (open) ion channel proteins in the membrane so it differs

at resting - more permeable to potassium ions and sodium ions - effecting the amount of ions that are entering and leaving the axon