5.3 neuronal communication Flashcards
what is the Pacinian corpuscle
a pressure sensor found in the skin
Define sensory receptor
cells/sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and create an action potential
what is a tranducer
a cell that converts one form of energy into another most sensory receptors are tranducers
give examples of different receptors and the energy changes that they detect
Pacinian corpuscle in skin senses changes in pressure and changes mechanical energy to electrical
light sensitive cells in the retina detect changes in light intensity and change light energy to electrical
describe the action of the Pacinian corpuscle to generate a generator potential
The sensory receptor is an oval shaped structure that consists of rings of connective tissue wrapped around the end of the nerve cell.
When pressure on the skin changes this deforms the rings of connective tissue causing them to push against the nerve ending. This causes sodium ion channels to open and sodium ions to flood in which is called a generator potential
What is a failed initiation
the pressure change wasn’t sufficient enough to open many sodium ion channels. So, not enough sodium ions entered to reach the threshold potential, so sodium ion voltage gated channels do not open, and an action potential doesn’t occur
give the neural communication pathway
sensory receptor –> sensory neurone –> relay neurone (CNS)–> motor neurone –> effector
describe the sensory neurone
this neurone carries an action potential from the sensory receptor to the CNS
They contain a long dendron carrying the action potential to the cell body with a nucleus and then to the shorter axon and axon terminal
describe the relay neurone
they connect sensory and motor neurones
They contain many short dendrites and a short axon (no dendron )
describe the motor neurone
they carry an action potential from the CNS to the effector (muscle or gland)
The motor neurone has its cell body with a nucleus in the CNS and a long axon that carries an action potential to the effector
What are myelinated neurones associated with
Schwann cells
Describe the structure of a myelinated neurone
It has many Schwann cells wrapped around the axon/dendron so the sheath consists of many layers of membrane and thin cytoplasm
Describe the structure of non-myelinated neurones
they are also associated with Schwann cells, but several neurones may be in one loosely wrapped Schwann cell and action potential moves in a wave here
What are the advantages of myelinated neurones
Myelinated neurones can transmit an action potential quicker. This is because sodium ions are unable to diffuse through the fatty sheath, so they do so at the nodes of Ranvier. This elongates the local current causing the action potential to jump between the nodes of Ranvier
Define resting potential
The potential difference across the membrane while the neurone is at rest -60mV
describe how a resting potential is achieved
Sodium-potassium ion pumps use ATP to pump 3 sodium ions out for every 2 potassium ions in
The sodium ion channels are kept closed, however, some of the potassium ion channels are left open so the plasma membrane is more permeable to potassium ions
Potassium ions tend to diffuse out of the cell
The cell cytoplasm contains organic anions
The interior of the cell is maintained at a negative potential
Define action potential
Brief reversal of the potential difference across the plasma membrane causing a peak of +40mV
Outline how an action potential is achieved
The neurone is at rest
the sodium ion channels in the plasma membrane open and sodium ions diffuse into the membrane
THRESHOLD POTENTIAL of -50mV is reached
DEPOLARISATION - positive feedback then causes sodium ion voltage gated channels to open and more sodium ion to diffuse in
A value of +40mV is reached which is an action potential. Sodium ion voltage gated channels close and potassium ion voltage gated channels open
REPOLARISATION - potassium ions diffuse out
HYPERPOLARISATION - where potential difference overshoots slightly
Potassium ion voltage gated channels close and the sodium-potassium ion pumps restore the resting potential
Describe how action potential is transferred along the neurone
when an action potential occurs the sodium ion channels open allowing sodium ions to diffuse along the neurone from the region of higher concentration to the region ahead at resting potential. This is called a local current.
The sodium ion channels which were closed now open due to the slight depolarisation which allows a rapid influx of sodium ions
At the point where sodium ions are moving to the region ahead what is happening at the previous region
The sodium ion channels close and potassium ion voltage gated channels open allowing an exit of potassium ions. This causes repolarisation and hyperpolarisation and then the restoration of the resting potential
What is a refractory period
Following an action potential in one region of the neurone it is impossible to have another action potential immediately after because the concentration of ions must be restored by the pumps and to allow the cell to recover
how could you describe the movement of an action potential across a myelinated neurone
saltatory conduction
Describe saltatory conduction
Sodium and potassium ions are unable to diffuse through the fatty insulating myelin sheath. So, the ionic movements needed to generate an action potential occur at the nodes of Ranvier and not much of the length.
This creates an elongated local current so the action potential jumps between the nodes speeding it up.
How can you detect the intensity of a stimuli
Higher frequency = more intense stimulus
When the stimulus is more intense it causes more sodium ion channels top open in the sensory receptor producing more generator potentials
What is a synapse?
the junction between 2 or more neurones
Name the 11 components at a synapse junction
vesicles with acetylcholine
mitochondria
SER
presynaptic membrane
calcium ion voltage gated channels
presynaptic neurone
synaptic cleft
post synaptic neurone
post synaptic membrane
receptors
sodium ion channels
describe the sodium ion channels in the post synaptic membrane
specialised sodium ion channels that can respond to the neurotransmitter
These channels consist of 5 polypeptide units, 2 of which have a receptor that is complementary to the neurotransmitter
when acetyl choline binds to the receptor it causes the sodium ion channel to open
Describe transmission across synapses
1- Action potential arrives at the pre-synaptic bulb
2-The calcium ion voltage gated channels open and calcium ions diffuse into the bulb
3-Calcium ions cause the synaptic vesicles to move and fuse with the pre-synaptic membrane
4-Aetylcholine is released by exocytosis and diffuses across the cleft and binds to receptor sites on the sodium ion channels on the post-synaptic membrane
5-sodium ion channels open and sodium ions diffuse across the cleft into the post-synaptic bulb
6-Agenerator potential or EXCITATORY POST-SYNAPTIC POTENTIAL is created and if enough of them combine to reach the threshold potential an action potential is created
What are the 2 types of nerve junctions
divergence - one goes to many
convergence - many go to one
What is an EPSP
excitatory post-synaptic potential
define summation
when the effects of several EPSPs are added together until threshold potential is reached
describe temporal summation
When several action potentials in the same pre-synaptic neurone
describe spatial summation
action potentials arriving from many pre-synaptic neurones
Why is spatial summation useful
When we are being warned of danger from many different stimuli
Why is divergence useful
allows one action potential to be transmitted to several parts of the neurone system which is useful in a reflex arc
Define habituation
nervous system no longer responds to a stimulus due to the synapse becoming fatigues
What are some things synapses are able to do
filter out low level signals
adaptable
ensure action potentials are carried in the right direction
