IB Biology : neural signalling C2.2

done, but did not do saltatory conduction

Stimuli

a change in the environment

sensory imput

stimuli which are perceived by our senses, like smell, sight, touch, taste and hearing

nervous system

organised network of neurons in the body which transmits nerve impulses between parts of the body.

parts of nervous system

• central nervous system

• peripheral nervous system → somatic nervous system (voluntary control) and automic NS

• autonomic NS: sympathetic (fight, flight or freeze), parasympathetic (rest and digest)

structure of a neuron

• contains nucleus, but no centrioles as it doesn’t reproduce

• dentrites are small, branched extentions of axon head

• synaptic knobs

• cell body = soma

• the thing connection the neuron body and the long thing (axon) is the axon hillock

action potential

a rapid, temporary change in the electrical membrane potential of a neuron or other excitable cell

schwann cell

type of glial cell that separates and insulates nerve cells. in the peripheral nervous system, schwann cells secrete myelin

myelin sheath

a protective, insulating layer around the axon, made up of 75% lipids and 25% proteins

Oligodentrites

secrete myelin in the central nervous system

name of spaces without myelin in schwann cells

nodes of Ranvier

types of neurons

• sensory neurons

• intermediary/relay neurons

• motor neurons

Resting potential ration of Na, Cl, organic anions and K ions

Sodium and chloride ions greater concentration outside

Potassium, and organic anions greater concentration inside

causes potential difference between inside and outside

inside negative, outside positive

resting potential

potential of the cell when not stimulated, -70mV, disturbed when neuron conducts signals

nerve impulse

temporary reversal of electrical potential in membrane → the signal transmitted along a nerve fibre, which is transmitted to another neuron or effector cell

sodium potassium pump

takes 3 sodium ions out of cell, and 2 potassium ions inside of cell using ATP

causes a negative charge to build up inside of cells. neuron is polarised

resting potential

potential difference across neuron cell membrane when cell isn’t stimulated

Action potential

sudden depolarisation and polarisation of the electrical potential across a plasma membrane, as a nerve impulse passes through a neuron.

factors which generate an action potential

1. sodium potassium pump

2. leakage of ions back across the membrane by simple diffusion

3. negatively charged proteins inside the nerve fibre

process of depolarisation

• stimuli/ neurotransmitter binds to receptor

• sodium channels opens

• sodium ions diffuse inside of cell

• reverses polarity of axon fiber and depolarises it ( positively charged ions charge in )

• this travels as a wave throughout the entirety of the axon

factors for nerve conduction velocity

• amount of myelination: more myelin, faster the action potential moves

• diameter of axon: larger diameter, faster propagation. this is because less SA for leakage of ions

• temperature: the warmer, the faster the transmittion

proper term for speed at which a nerve impulse travels down

nerve conduction velocity

squid axon

no myelin sheath, but because half a mm thick still have reasonably fast nerve impulse

what are synapses ?

 they are junctions between neurons and effector cells. neurotransmitters can only go in one direction

synaptic knob

end part of axon terminal

synaptic cleft

space between two neurons

neuromuscular junction

specialised synapse betwen a motor neuron and muscle fiber

the motor neuron releases acetylcholine, which binds on receptors of sarcolema, and causes depolarisation of sarcolema → release of calcium from sarcoplasmic reticulum

speed variation of nerve impulse with and without myelin sheath

myelin sheath, faster

types of neurons and their characteristics

• motor neuron : many fine dentrites, and a single fine long axon. Carry impulses from CNS to a muscle (effector)

• sensory neuron: cell body is partway thought the axon

• relay neuron: numerous short fibres and no myelin sheath. Occur in the CNS, connect sensory and motor neurons

leakage

the membrane of the axon is much more permeable for potassium that for sodium

so potassium can more easily leak out

neuroglandar junctions

junctions between neurons and glandural cells (glands)

two types of neurotransmitters

• small molecules ( synthesised in axon terminal and stored in membrane bound molecules )

• large peptide molecules ( synthesised by ribosomes and transported by the vesicles)

How to measure changes in membrane potentials

Using an oscilloscopes, with miliseconds and millivolts

action potentials during nerve impulses, the steps

1. resting potential, -70mV

2. Threshold is reached

3. depolarisation, sodium flows in, peaks at 40mV

4. repolarisation, decreases again, as potassium goes in

5. hyperpolarisation (temporarily goes under -70mV)

6. goes back to resting potential

release of neurotransmitters

• action potential travels down presynaptic neuron,

• the action potential causes the voltage gated calcium ion channels to open

• calcium ions flow into the presynaptic neuron

• the ions induce exocytosis in the vesicles, go in synaptic cleft

• vesicules fuse with the membrane and release the neurotransmitters into synaptic cleft

• neurotransmittors bind to receptors on postsynaptic neuron or effector cell

• (easy, always say it) a postsynaptic response is initiated

what happens after neurotransmitter binds

• neurotransmitter ( acetylcholine ) diffuse through synaptic cleft, bind to receptors. Acteylcholinesterase breaks it down

• sodium ion channels open and sodium goes into neuron, causing depolarisation

• potential goes from -70mV (resting potential), to -50mV (threshold potential)

• the sodium ions flood the axons, making local current, causing voltage gated sodium channels to open and enter the axon, causes action potential

• diffusion both inside and outside axon can cause action potential to be reached

• the potential goes up to +40mV, in a positive feedback loop

• sodium channel closes, voltage gated potassium channels to open, making potassium ions diffuse out, briefly causing hyperpolarisation

• this causes depolarisation of the membrane, eventually closing potassium channel

• sodium potassium pump restarts , leading to resting potential of -70mV

refractory period neuron

period after repolarisation where cell is unable to generate action potential, allowing action potential to move in an unidirectional manner along the axon

quick overview of sodium potassium channel

• requires atp

• 3 sodium ions out

• 2 potassium ions out

• causes negative charge inside the cell

how does myelination increase speed of conduction of action potential

• myelinated: action potential jumps from one node of ranvier to the next

• unmyelinated: continusly propagates only length of axon

oscilloscope

• graph displaying device which can be used to measure the membrane potential across an action membrane

• can be used to record and display voltage changes

• electrodes are placed on both sides of the membrane

• horizontal is time in ms and vertical is membrane potential in mV

saltatory conduction

• sodium-potassium pumps and channels are clustered at nodes of Ravier

• myelin sheath covering provides electrical resistance to leakage of ions, and prevents depolarisation of the membrane

exogenous chemicals

• act as agonists for receptors

• mimic the effect of the actual (endogenous) neurotransmitters

• neural communication pathways are altered

• originate from outside the body

neonicotinoids effects on bees

• class of chemicals similar to nicotine

• completely block synaptic transmition by irreversibly binding to the acetylcholine receptors

• acetylcholine cannot bind to receptors and transmition is prevented

• causing paralysis and death

• bad as oftentimes used in pesticides

cocaine effects

• binds to the synapse of the dopamine receptor re-uptake pumps, which causes it remain the in synaptic cleft

• binds to dopamine transporter protein

• prevents dopamine from binding to dtp, causing it to build up in the synapses

• amplifies the signal

• it will bind to the dopamine receptor constantly

inhibitory neurotransmitters

• certain neurotransmitters bind to the membrane, and cause a more negative membrane potential, making action potential reaching threshold unlikely

• example: GABA → binds to receptors on cell membrane, activate negative ion channels which flow in

• membrane is even more negative, more difficult to depolarise

hyperpolarisation

• when the membrane potential of a neuron is more negative than it’s resting potential

• can occur when potasium ion channels open, causing many potassium ions to diffuse out

• or when chloride ion channel open, leading to influx of negative ions

• this makes action potential more difficult to achieve

summation

• combined effect of the excitatatory and inhibitory stimuli such as K^+ ions going out and Na^+ ions going in

• inhibitory synapse activates at the same time as excitatory synapse

• effects cancel out so action threshold is not reached and no action potential is generated

• prevent random impulses from being sent out

all-or-nothing principle

when a stimulus is generated, either it is transmitted in the form of action potential or nothing is transmitted at all

perception of pain

• nociceptors: nerve endings responsible for detecting pain

• free nerve endings: spread throughout the skin and detect many things, such as pain, temperature and itching

• nerve endings have positive ion channels, which can be triggered by factors such as high temperature, acid or capsaicin.

• when they open, the positive ions cause threshold potential for nerve impulses to be reached, which are communicated to the brain

differences between neuron with or without myelin

• presence of myelin

• conduction speed 10x faster with myelin

• more energy efficient, less energy required due to insultaed jumping signal

• nodes of ranvier in myelin, none in myenliness

• rapid signal transmittion over long distances, vs slower signal transmission for short distances

• myelin is while, non myelin is grey

• myelin = less vulnerability to damage

• both use action potential, both have dentritesd

receptor for capsaicin

Transmembrane receptor protein V1 (TRPV1) → respond to temperatures over 43C°

consciousness

a state of being aware and responsive to ones surroundings

how does consciousness emerge

from the interactions of individual neurons in the brain → doesn’t emerge from one neuron exactly, isn’t controlled by ani ndividual component alone

comes from “cerebrum” part of the brain

example of the consequences of interactions