Topic 8 pt1 grey matter

Mollys

what is the benefit of detecting stimuli?

by detecting external and internal changes that occur in the environment, the chances of their survival increases

what is a stimulus?

A change in the environment

What do receptors do?

Detect the stimulus or change in environment.

what do effectors do?

they bring about a response to the stimulus. including glands and muscle cells

what are hormones?

chemical messengers

what produces hormones?

glands

why do glands secrete hormones?

in response to a stimulus

how do hormones travel around the body?

by the blood

what is the cell that has receptors for a hormone called?

target cells

what happens when a hormone bind with a target cell?

triggers a response (they act as effectors)

what rate is nervous communication like?

fast

what are nervous communications?

electrical impulses

where do nerve impulses affect?

localised areas, neurones are cells and they carry electrical impulses to other cells

how long do nervous communications last?

short duration

what are hormonal communications?

using chemicals

what is the rate of hormonal communication?

slower

where do hormones affect?

widespread area as they travel in the blood to target cells around the body

how long do hormonal communications last?

longer duration

what is the central nervous system?

consisting of the brain and the spinal cord, relay neurones are found here

What is the peripheral nervous system?

consisting of nerves (bundles of sensory neurones) entering the CNS and nerves (bundles of motor neurones leaving the CNS

What is the somatic nervous system?

nerves that control voluntary actions. they stimulate the skeletal muscles

What is the autonomic nervous system?

nerves that control involuntary actions. they stimulate smooth muscles, cardiac muscle and glands

What is the sympathetic nervous system?

nerves that stimulate fight or flight

What is the parasympathetic nervous system?

nerves that stimulate rest and digest

what is a neurone?

a single cell

what is a nerve?

a bundle of neurones and blood vessels surrounded by a protective coating

what is the function of a neurone?

to conduct electrical impulses

why are there branched dendrites on a neurone?

so that the neurone can form synapses (and receive impulses from) lots of different neurones
they then conduct the nerve impulses towards the cell body

what is the function of the axon?

It carries impulses away from the cell body

why does the axon branch off into axon terminals?

so that the neurone can form synapses with many other neurones to pass on nerve impulses

why are axons myelinated?

it increases the rate of conduction

what does a sensory neurone do?

carries electrical impulses from receptors to relay neurones in the central nervous system

how can you identify a sensory neurone?

as it has the cell body at the centre of the axon but not in line with the axon

what does a relay neurone do?

found in the central nervous system, they integrate electrical impulses they receive from sensory neurones and pass them onto motor neurones

how can you identify a relay neurone?

the cell body is in the centre of the axon and it is in line with the axon

what does a motor neurone do?

carries electrical impulses out of the central nervous system to effects (muscles or glands)

what is a reflex arc?

the simplest nerve pathways in response to stimuli, they produce rapid involuntary responses

Why are reflex arcs important?

as they prevent damage to the body and increase survival

how does a reflex come from touching a hot plate?

1) the heat stimulus detected by the skin receptors
2) an electrical impulse passes along a sensory neurone to the spinal cord in the central nervous system
3) a neurotransmitter is released at the end of the sensory neurone
4) this starts an electrical impulse in the relay neurone, this releases neurotransmitter in the end of the relay neurone
5) this starts an electrical impulse in the motor neurone, this impulse travels down the arm muscle (effector) and when it contracts it moves the hand away from the hot plate

what is the pupil?

the hole that enables light to enter the eye

what is the iris?

the pigmented ring of muscle around the pupil

what muscles are in the iris?

an antagonistic pair
- circular muscles
- radial muscles

what happens to the pupil in bright light?

constricts

why does the pupil constrict in bright light?

1) photoreceptors in the retina detect lots of light
2) many nerve impulses pass along the sensory neurones in the optic nerve
3) nerve impulses pass along relay neurones in the midbrain
4) nerve impulses pass along parasympathetic motor neurones to the circular muscles in the iris
5) circular muscles in the eye contact (whilst the radial muscles will relax)
6) this makes the pupil constrict
7) less light enters the eye preventing damage to the eye

what happens to the pupil in dim light?

it dilates

why does the pupil dilate in dim light?

1) photoreceptors in the retina detect less light
2) fewer nerve impulses pass along the sensory neurones in the optic nerve
3) nerve impulses pass along relay neurones in the midbrain
4) nerve impulses pass along parasympathetic motor neurones to the circular muscles in the iris
5) radial muscles in the eye contact (whilst the circular muscles will relax)
6) this makes the pupil dilate
7) more light enters the eye allowing an image to be seen

what is the resting potential?

the voltage (potential difference) across the cell surface membrane of a neurone at rest. it is -70mV (the neurone is polarised as it is more negative on the inside)

what cause the resting potential?

the result of uneven ion distribution on either side of the cell surface membrane. the ions diffuse across without proteins as the fatty acid tails in the centre prevent diffusion of ions across the membrane

what proteins are in the cell surface membrane of a neurone?

1) sodium- potassium pumps
2) potassium ion channels
3) voltage gated sodium ion channels
4) voltage gated potassium ion channels

what do sodium-potassium pumps do?

Sodium-potassium pumps are carrier proteins that carry 3Na+ ions out of the cell and 2K+ into the cell. These pumps act against the concentration gradients of these two ions, so are driven by energy supplied by hydrolysis of ATP.

what do potassium ion channels do?

they make the membrane slightly permeable to potassium ions (K+)

what do voltage gated sodium ion channels do?

Voltage-gated sodium channels are not open at the resting potential but open when the potential difference (voltage) across the membrane depolarises (becomes more positive). they make the membrane more permeable to sodium ions

what do voltage gated potassium channels do?

Voltage-gated sodium channels are not open at the resting potential but open when the potential difference (voltage) across the membrane reaches +40mV. they make the membrane more permeable to potassium ions

how is the resting potential established?

1) sodium- potassium pumps actively transport 3 sodium ions out of the neurone for every 2 potassium ions into the neurone
2) this sets up concentration gradients, a higher concentration of sodium outside of the neurone and a higher concentration of potassium inside of the neurone
3) as there are a few open potassium ion channels, a few potassium ions diffuse out of the neurone down the concentration gradient. this removal of positive ions makes the inside of the neurone more negative than the outside
4) at -70mV diffusion stops even though there is a high concentration of potassium inside the neurone. this si as the concentration gradient is matched by an opposing electrical gradient (the positive potassium ions are attracted into the neurone as it is negative)

what are action potential?

a series of changes in the voltage across a neurones cell surface membrane

what is a neurone stimulated by to trigger an action potential?

either a stimulus if it is the beginning of a nerve pathway or a neurotransmitter if it is from another neurone

what happens during depolarisation of a neurone?

- a stimulus or neurotransmitter will open some sodium ion channels in the cell surface membrane of the neurone. this allows sodium ions to diffuse into the neurone down the electrochemical gradient. the movement of ions into the neurone makes the inside more positive (depolarises it)
- if enough sodium ion channels open then enough sodium diffuses into the neurone then it will pass the threshold potential and the action potential is triggered. as it becomes more positive, more sodium ion channels open and more sodium ions diffuse into the neurone making it more positive until +40mV is reached

what are the voltage values during depolarisation?

-70mV to +40mV

what ion channels are involved in depolarisation?

voltage gated sodium ion channels

what ions are moving during depolarisation and where and why?

sodium ions into the neurone down the electrochemical gradient as there is a higher concentration outside of the neurone and it is negative inside the neurone and more positive on the outside so they move down the chemical and the electrical gradient

what happens during repolarisation?

- at +40mV the voltage gated sodium ion channels suddenly close and the voltage gates potassium ions open. potassium ions diffuse out of the neurone down the electrochemical gradient. the removal of these positive ions makes the voltage inside the neurone more negative (repolarising)

what are the voltages during repolarisation?

+40mV to -70mV

what ion channels are involved in repolarisation?

voltage gated potassium channels

what ions are moving in repolarisation where and why?

potassium ions moving out of the neurone down the electrochemical gradient as there is a higher concentration inside of the neurone and it is more negative outside the neurone and more positive on the inside so they move down the chemical and the electrical gradient

what happens during hyperpolarisation?

even once the voltage reaches -70mV, the potassium ions will continue to diffuse out of the membrane as it is more permeable to potassium ions than at rest. the inside becomes more negative as potassium ions leave out of the neurone

what are the voltage values during hyperpolarisation?

-70mV to -90mV

what ions are moving in hyperpolarisation and why?

potassium ions out of the neurone as the membrane is more permeable to potassium ions than it is at rest

what happens during the refractory period?

- the voltage gated potassium ion channels suddenly shut. the membrane is then less permeable to potassium ions. at -90mV the electrical gradient is stronger than the concentration gradient and so a few potassium ions diffuse back into the neurone due to the electrical gradient

what are the voltage values for the refractory period?

-90mV to -70mV

what ion channels are involved in hyperpolarisation?

potassium ion channels

what ion channels are involved in the refractory period?

potassium ion channels

what ions are moving in the refractory period where and why?

potassium ions into the neurone as the electrical gradient is stronger than the concentration gradient out of the neurone as the inside of the neurone is so negative.

why cant an action potential be triggered in the refractory period?

as the voltage gated ion channels cannot reopen.

what direction does the sodium ion concentration gradient act for the duration of an action potential?

into the neurone

what direction does the potassium ion concentration gradient act for the duration of an action potential?

out of the neurone

what happens if many action potentials occur?

sodium-potassium pumps will actively pump sodium out of the neurone and potassium ions into the neurone to restore the steep concentration gradients

what is an electrochemical gradient?

when both the chemical and the electrical gradient are acting in the same direction causing the ions to more in the same direction

how can the type of stimulus be deduced from a nerve impulse?

depending on the neurone it travels along

how can the intensity of a stimulus be indicated by nerve impulses?

from the frequency of the nerve impulses

how do action potentials travel along a neurone?

as a sequence, the sodium ions diffusing into the first part of the neurone do not just depolarise and start an action potential there. the positively charged sodium ions will flow as a current to the adjacent part of the neurone. they will depolarise the next section and trigger an action potential there too by the opening of voltage gated sodium channels.

when is conduction fastest for neurones?

when they are myelinated

why are myelinated neurones faster at conduction?

as they have the myelin sheath (schwann cells) acting as an insulator. it prevents the flow of ions across the cell surface membrane of the neurone as the only voltage gated channels (sodium and potassium) are at the nodes of Ranvier. so depolarisation and therefore action potentials can only occur at the nodes of Ranvier.

What is saltatory conduction?

as action potentials can only occur at the nodes of Ranvier, sodium ions can diffuse into here as there are voltage gated channels and then flow further along the neurone because of the insulation and enough sodium ions reach the next node of Ranvier as they go down the electrochemical gradient to depolarise the next node, this opens enough voltage gated sodium ions to cause the depolarisation here and beginning an action potential

what are synapses?

gaps between neurones

how can neurones form connections with other neurones?

via synapses
divergence- from one neurone into many
integration- from many neurones into a few

how is information passed from neurone to neurone?

with synapses that pass nerve impulses (electrical) into chemicals (neurotransmitters)

what is the presynaptic neurone?

the neurone before the synapse

which neurone releases the neurotransmitter at a synapse?

the presynaptic neurone

what is a neurotransmitter?

a chemical that travels from one neurone to another across a synapse.

what is the synaptic cleft?

the space between the presynaptic and the postsynaptic neurone

what is the neurone after the synapse called?

postsynaptic neurone

what happens at a synapse?

1) a nerve impulse travels along the presynaptic neurone
2) voltage-gated calcium ion channels then open in the presynaptic membrane
3) calcium ions (Ca2+) diffuse into the presynaptic neurone
4) this triggers the vesicles (containing neurotransmitter) to move towards and fuse with the presynaptic membrane
5) the neurotransmitter is released by exocytosis and diffuses across the synaptic cleft
6) the neurotransmitter then binds to the receptors on the postsynaptic membrane
7) sodium ion channels open and sodium ions diffuses into the postsynaptic neurone causing depolarisation
8) if the depolarisation passes the threshold level then an action potential is initiated in the postsynaptic neurone
9) neurotransmitter is then removed from the synaptic cleft to stop it triggering multiple action potentials in the postsynaptic neurone. this may be by breaking it down with an enzyme or reuptaken into the presynaptic neurone

What is acetylcholine?

neurotransmitter

what is the enzyme that breaks down acetylcholine?

acetylcholinesterase

what are reuptake proteins?

protein that reuptakes neurotransmitter to be used again when another action potential is needed and so it doesnt trigger another in the postsynaptic neurone

what determines whether an action potential occurs in the postsynaptic neurone?

on the number of nerve impulses arriving along presynaptic neurones and the type of synapse

why does a nerve impulse travelling along a presynaptic neurone to an excitatory synapse make it more likely for an action potential to occur in the postsynaptic neurone?

it makes the membrane of the postsynaptic neurone more permeable to sodium ions.

what has to happen to trigger an action potential in the postsynaptic neurone?

lots of nerve impulses in the presynaptic neurone to lead to release of enough neurotransmitter to depolarise the postsynaptic neurone past the threshold level to trigger an action potential

how do many nerve impulses reach the presynaptic neurone to release enough neurotransmitter to cause an action potential?

- there can be lots of different excitatory neurones (spatial summation)
- one excitatory neurone one after another with many nerve impulses (temporal summation)

What is spatial summation?

postsynaptic neuron is stimulated by a large number of terminals at the same time