Nervous system- module 5 Flashcards
What dos the sensory neurone do
Transmit nerve impulses from receptors to CNS
what does the Relay neurone do
Transmits nerve impulses between sensory and motor neurones
role of motor neurone
Transmit nerve impulses from CNS to receptors
flow diagram of stimulus to response in nervous system
Stimulus -> receptor - sensory neurone - relay - motor - effector - response
what are Pacinian corpuscles
Mechanoreceptors. they detect mechanical stimuli, such as pressure and movement.
Found deep in the skin are abundant in fingers and soles of the feet
How do Pacinian corpuscles convert pressure into a nervous impulse? process
1) pressure applied to Pacinian corpuscle
2)Lamellae become deformed and press on sensory nerve ending
3)Stretch mediated sodium channels change shape (widen) in the sensory neurone cell
4)sodium ion channels open
5) sodium ions diffuse into cell
6)creates generator potential (if threshold met)
7) Leads to action potential (nerve impulse) down sensory neurone
structure of sensory neurone
Short dendrites & long dendron to carry impulses from receptor cells to cell body.
One short axon that carries impulses from cell body to CNS
structure of motor neurone
Short dendrites that carry nerve impulses from CNS to cell body (located in CNS).
One long axon that carries impulses from cell body to effectors.
structure of cell body of neurone
Cell body- contains nucleus and other organelles. Has large amounts of ER & mitochondria to make neurotransmitters.
where do dendrites and axons carry electrical impulses
Dendrites and dendrons carry electrical impulses towards cell body.
Axons- carry nerve impulses away from cell body.
How is resting potential maintained
1)when a neurone is transmitting an impulse, the potential difference across its membrane is called a resting potential
2)the potential difference across the membrane at rest is around -70mV
3)This resting potential is due to sodium-potassium pumps and potassium ion channels
4)The pumps use active transport to pump 3 sodium ions(Na^+) out of the neurone for every 2 potassium ions(K^+). This requires ATP
5) The membrane isn’t permeable to sodium ions, so they can’t move back into the neurone. This creates a sodium ion electrochemical gradient
6) Potassium ion channels are open when the neurone is at rest, so the membrane is permeable to potassium ions
7)Some potassium ions move by facillitated diffusion back outr of tge neurone down the concentration gradient
8)In total, more positive ion move out of the neurone rather than in, making the outside of the neurone more positively charged than the inside. The membrane is said to be polarised
What happens after a stimulus to a neurone
energy of stimulus triggers some sodium ion channels to open, making the membrane more permeable to Na+
Na+ ions diffuse into axon down electrochemical gradient. Makes inside of neurone less negative
what happens during depolarisation
potential difference reaches the threshold (around -55mV) which opens voltage-gated sodium ion channels -> more Na+ diffuse into neurone - this is positive feedback
what happens at a potential difference of +40mV
voltage-gated sodium ion channels close and voltage-gated potassium ion channels open.
Sodium ions can no longer enter the axon
Potassium ions diffuse out of the axon, causing the inside of the axon to become more negative than the outside
what happens during hyperpolarisation
as the voltage-gated potassium ion pumps are slow to close, too many potassium ions diffuse out of the neurone.
This causes the potential difference to become more negative than the the resting potential (less than -70mV)
What happens during repolarisation
the sodium potassium pumps returns the membrane to resting potential by pumping sodium ions out and potassium ions in
refractory period
what is it
what does it ensure
After an action potential, the neurone can’t be excited straight away
the ion channels need to recover and can’t be made to open.
This acts as a time delay and ensures that action potentials don’t overlap and pass as separate impulses.
It also ensures impulses are unidirectional -only travel in one direction
Wave of depolarisation
-when an action potential happens, some sodium ions diffuse sideways, opening channels in the next part of the neurone.
-they always move away from areas in the refractory period as the channels can’t open there- these are called localised currents
-This triggers the action potential in the next segment
this means a wave of depolarisation moves along the neurone - the electrical impulse is said to ‘propagate’ down the axon
Wave of depolarisation
-when an action potential happens, some sodium ions diffuse sideways, opening channels in the next part of the neurone.
-they always move away from areas in the refractory period as the channels can’t open there- these are called localised currents
-This triggers the action potential in the next segment
this means a wave of depolarisation moves along the neurone - the electrical impulse is said to ‘propagate’ down the axon
what effects the speed of conduction of action potentials
Myelination
Axon diameter
Temperature
how does axon diameter affect the speed of conduction of action potentials
The bigger the axon diameter, the faster the impulse is transmitted.
There is less resistance to the flow of ions in the cytoplasm, compared with that in a smaller axon
how does temperature affect the speed of conduction of action potentials
the higher the temperature, the faster the nerve impulse. Because ions diffuse faster at higher temperatures. Generally only occours up to 40oC because denature
Myelination
-myelin sheath = electrical insulator
it is made of schwann cell wrapped around the axon or dendron
-The bare parts between schwann cells are called the nodes of Ranvier
-Sodium ion channels are concentrrated at these nodes
-Myelinated axons transfer electrical impulses much faster than non-myelimnated axons (due to saltatory conduction)
Saltatory Conduction
-depolarisation can only occour at nodes of Ranvier where no myelin is present -> sodium ions can only pass through channels here
-Longer localized circuits arise between the adjacent nodes -> action potential ‘jumps’ from one node to another
-Quicker as less channels to open, so less ions to move
-energy efficient -> less ATP needed for repolarisation in Na+K+ pump
-Myelin not permeable to sodium or potassium ions
-sodium ions diffuse into axon during depolarisation, diffuse along axon, sets up local current - causes sodium to diffuse to next node
-Sodium moves towards more negative region
