Communication By Neurones Flashcards
What is the central nervous system composed of?
-brain
-spinal cord
What are the 2 systems the peripheral nervous system makes up?
-somatic nervous system = voluntary e.g skeletal movements
-autonomic nervous system = involuntary e.g control of heart rate
What is an action potential?
Signals transmitted as changes in electrical potential along neurones
What stimuli are detected by your ears, tongue, nose, and retina?
-ears= sounds
-tongue= chemicals (taste)
-nose= chemicals (smell)
-retina= light changes
What does a sensory neurone do?
-transmit nerve impulses from receptors to the central nervous system (brain and spinal cord)
What is the structure of a sensory neurone?
-short dendrites
-one long dendron to carry nerve impulses from receptor cells to the cell body
-one short axon that carries impulses away from cell body to the CNS
What do motor neurones do?
-transmit nerve impulses from the CNS to effectors
What is the structure of a motor neurone?
-have many short dendrites that carry nerve impulses from CNS to the cell body
-one long axon that carries nerve impulses from the cell body to effector cells
What do relay neurones do?
-transmit nerve impulses between sensory neurones and motor neurones
What is the structure of a relay neurone?
-have many short dendrites that carry nerve impulses from sensory neurones to cell body
-one axon that carries nerve impulses from the cell body to motor neurones
What do all neurones have in their cell bodies and in their structure?
-a nucleus
-cytoplasm
-all other organelles that you’d usually find in a cell
-schwann cells
-nodes of ranvier
-myelin sheath (protects and provides insulation, remove cell debris by phagocytosis)
Explain the role of sensory receptors
-different stimuli have different forms of energy e.g light and chemical
-but your nervous system only sends information in the form of nerve impulses (electrical impulses)
-sensory receptors convert the energy of a stimulus into electrical energy, acting as transducers (something that converts one form of energy into another)
What are pacinian corpuscles and how do they work?
-they’re mechanoreceptors, detecting mechanical stimuli e.g pressure and vibrations, found in your skin
-they contain the end of a sensory neurone, called a sensory nerve ending, which is wrapped in lots of layers of connective tissue lamellae
-when a pacinian corpuscle is stimulated e.g by a tap on the arm, the lamellae are deformed and press on the sensory nerve ending. This causes deformation of stretch-mediated sodium channels in the sensory neurone’s cell membrane. The sodium ion channels open and sodium diffuses into the cell, creating a generator potential. If the generator potential reaches the threshold, it triggers an action potential
Describe the conditions of a neurones cell membrane when it is polarised at rest
-in its resting state the outside of the membrane is positively charged compared to the inside, because there are more positive ions outside the cell than inside
-this makes the membrane polarised, as there is a difference in charge
-the membranes resting potential is about -70mV
-the resting potential is created and maintained by sodium-potassium pumps and potassium ion channels in the membrane
Explain the role of the sodium-potassium pump
-moves 3 sodium ions out of the neurone, but membrane isn’t permeable to sodium ions so they can’t diffuse back in
-this creates a sodium ion electrochemical gradient because there are more positive sodium ions outside the cell than inside
-it also moves 2 potassium ions into the neurone, but the membrane is permeable to potassium ions so they diffuse back out through potassium channels
-this makes the outside positively charged compared to the inside
Explain the role of a stimulus in creating an action potential/ depolarisation of the membrane
-a stimulus excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down gradient, making the inside of the neurone less negative
-depolarisation occurs if the potential difference reaches the threshold, and the voltage gated sodium ion channels open, so more sodium ions diffuse into the neurone. This is positive feedback
Explain the stage of hyperploarisation
-at a potential difference of around +30mV the sodium ion channels close and voltage gated potassium ion channels open.
-the membrane is more permeable to potassium so potassium ions diffuse out of the neurone down gradient
-the potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone, causing potential difference to become more negative than the resting potential (-80mV)
Explain the stage of repolarisation
-most voltage gated potassium ion channels close
-sodium potassium pump removes 3 sodium ions and brings in 2 potassium ions
-this restores the resting potential of -70mV
Explain what the absolute refractory period is
-after an action potential, the neurone cell membrane can’t be excited again straight away, because the ion channels are recovering and they can’t be made to open
-sodium ion channels are closed during repolarisation
-potassium ion channels closed during hyperpolarisation
Explain how a wave of depolarisation is created through the neurone
-when an action potential happens, some of the sodium ions that enter the neurone diffuse sideways, causing sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part
-this causes a wave of depolarisation along the neurone
-the wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an action potential
Explain what the all or nothing response is
-once the threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus is. If the threshold isn’t reached, an action potential won’t fire.
What effect does a bigger stimulus have on an action potential?
-it causes action potentials to fire more frequently, as opposed to increasing in size
-so if the brain receives a high frequency of action potentials, it interprets this as a big stimulus and responds accordingly
Explain how myelin sheath affects the propagation of action potentials
Include what saltatory conduction is
-myelin sheath is an electrical insulator
-it is made up of schwann cells
-between the Schwann cells are small spaces called nodes of ranvier, and sodium ion channels are concentrated here
-in a myelinated neurone, depolarisation only happens at the nodes of ranvier
-neurones cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node, which is very fast= SALTATORY CONDUCTION
-in a non myelinated neurone the impulse travels as a wave along the whole length of the axon membrane, which is a bit slower
Explain which 2 other factors affect the propagation of action potentials
1) diameter of the axon = the greater the diameter, the faster the impulse speed, as reduces leakage of ions making it easier to maintain the potential
2) temperature = higher temperatures increase kinetic energy and rate of diffusion/ too high temperatures denatures the proteins in the cell membranes and affects fluidity of bilayer, stopping propagation
