5.3 Flashcards
What are sensory receptors
Specialised cells that can detect changes in our surroundings, most are energy transducers that convert 1 form of energy to another, each type of transducer adapted to detect changes in a certain energy form, may be change in light level or chemicals present
What is a stimulus
Change in environment, change in every level or new chemical present
How do sensory receptors respond to stimulus
Create signal in form of electrical energy called nerve impulse
What sensory receptor and energy change involved with stimulus change in light intensity
Light sensitive cells in retina (rods and cones), light to electrical
What sensory receptor and energy change involved with stimulus change in temp
Temp receptors in skin and hypothalamus, heat to electrical
What sensory receptor and energy change involved with stimulus change in pressure on skin
Pacinian corpuscles in skin, movement to electrical
What sensory receptor and energy change involved with stimulus change in sound
Vibration receptors in ear, movement to electrical
What sensory receptor and energy change involved with stimulus change in movement
Hair cells in inner ear and movement to electrical
What sensory receptor and energy change involved with stimulus change in muscle length
Muscle spindles in skeletal muscles, movement to electrical
What sensory receptor and energy change involved with stimulus change in chemicals in air
Olfactory cells in nose epithelial lining, chemical to electrical
What sensory receptor and energy change involved with stimulus change in chemicals in food
Chemical receptors on tongue taste buds, chemical to electrical
What is the pacinian corpuscle
Pressure sensor that detects changes in pressure on skin
What is the pacinian corpuscle structure
Corpuscle is an oval shape structure consisting of series of concentric rings of connective tissue wrapped round end of nerve cell
How does pacinian corpuscle work
When pressure on skin changes it deforms rings of connective tissue pushing against nerve endings, corpuscle only sensitive to changes in pressure that deform rings of connective tissues so when pressure constant they stop responding
What is embedded in a plasma membrane
Cell surface membranes contain proteins, some are channels that allow movement of ions across membrane by facilitated diffusion, others transport proteins actively move ions across membrane against concentration gradient, requires use of energy in form of ATP
What happens if Channel proteins always open
If channel proteins always open then ions can diffuse across membrane until in equilibrium, if channels can be closed action of active pumps create concentration gradient across membrane
What specialised channel proteins do cells associated with nervous system have
Sodium ion channels and potassium ion channels and gates to open and close these channels
What are sodium ion channels sensitive to and what does this mean
Small movements of membrane, so when membrane deformed by changing pressure sodium channels open allowing sodium ions to diffuse into cell producing generator potentials
What do membranes contain in nerve associated cells and what does this mean
Contain sodium potassium pump that actively pump 3 sodium ions out of cell and 2 potassium ions into cells, when channel proteins closed pump makes concentration gradient
What does the sodium potassium pump in a nerve cell cause
Concentration of sodium ions outside cell increase while concentration of potassium ions inside cell increase, so membrane has more permeability to potassium ions, some leak out of cell and membrane less permeable to sodium ions so don’t leak into the cell
What is the result of the ionic movements of a sodium potassium pump in nerve related cell membranes
Result of ionic movements is potential gradient across cell membrane, cell negatively charged inside compared with outside, negative potential enhanced by presence of negatively charged anion inside cell
When is cell membrane polarised
When cell inactive, negatively charged inside to outside
How is nerve impulse created
By altering permeability of nerve cell membrane to sodium ions, achieved by opening sodium ion channels as channels open, membrane permeability increased and sodium ions move across membrane down concentration gradient into cell and this movement of ions creates charge across membrane
What is depolarisation
Inside cell becomes less negative that usual
What is generator potential
Change in potential across receptor membrane
What happens if small stimulus detected
Only few sodium ion channels open
What happens the larger the stimulus detected
More gated channels will open, if enough gates opened and enough sodium ions enter cell, potential difference across cell membrane changes significantly and initiates impulse/action potential
What happens when stimulus detected
Energy converted to depolarisation of receptor cell membrane, and impulse transmitted to other parts of the body
How are impulses transmitted
Along neurones as action potentials
How are action potentials carried
As a rapid depolarisation of membrane caused by influx of sodium ions
What are the 3 different types of neurones and function
Motor neurone carries action potential from central nervous system to an effector like muscle or gland, sensory neurones carry action potentials from sensory receptor to CNS, relay neurone connects sensory and motor neurone
Do neurones have similar or different basic structure
Similar all enabling transmission of action potentials
What are neurone cells specialised features
They’re very long to transmit action potentials over long distance, plasma membrane has gated ion channels, sodium potassium pump use ATP to actively transport sodium ions out and potassium ions in, neurones maintain potential difference across plasma membrane
What are neurone cells further specialised features
Cell body contains nucleus, mitochondria and ribosomes, dendrites connect to other neurones and carry impulse to cell body, axon carries impulse away from from body, neurones surrounded by fatty layer that insulates cell from electrical activity in other nerve cells, fatty layer composed of Schwann cells closely associated with neurone
How are motor neurones different from other neurones
Have cell body in CNS and have long axon that carries action potential out of effector
How are sensory neurones different from other neurones
Long dendrons carrying action potential from sensory receptor to cell body which is positioned outside CNS, have short axon carrying action potential to CNS
How are relay neurones different from other neurones
Connect sensory and motor neurone, have short dendrites and axon, number of divisions of axon is variable, conduct impulse in coordinated pathways
What is a myelinated neurone
Insulated by myelin sheath
What are associated with Schwann cells
Sensory and motor neurones associated with Schwann cells make up fatty myelin sheath
What is structure of a myelin sheath
Schwann cells wrapped tightly round neurone so sheath consists of layers of membrane and thin cytoplasm from Schwann cells
What are in gaps of myelin sheath
Nodes of ranvier (very short)
What does it mean that myelin sheath is tightly wrapped around neurone
Prevents movement of ions across membrane so movement of ions across membrane only occurs at nodes of ranvier (so action potential jumps from one node to next making more rapid conduction)
What are non-myelinated neurones
Associated with Schwann cells but several neurones may be hid in 1 loosely wrapped cell meaning action potential moves along neurone in wave instead of jumping node to node
What is main advantage of myelinated neurones
Transmit action potential quicker than non-myelinated neurone
What do myelinated neurones carry
Action potentials from sensory receptor to CNS and from CNS to effectors, carrying over long distances but increased spread of myelinated neurone means rapid response to stimulus
Why and when are non myelinated neurones used
Shorter and carry action potentials shorter distances so used in coordinating body functions like breathing and action of digestive system, so increased speed of transmission less important
When is a neurone at rest
When not transmitting action potential
At rest what is a neurone doing
Pumping ions across plasma membrane, as with sensory receptors sodium/potassium pumps use ATP to pump 3Na+ out of cell of 2K+ pumped in
What are gated sodium and gated potassium ion channels doing at rest
Na ion channels kept closed but some K+ left open so plasma membrane more permeable to K+ than Na+, k+ ions tend to diffuse out of cell
What does neurone cell cytoplasm contain and what does this mean
Contains large organic anions, so interior of cell maintained at negative potential compared with outside (cell membrane polarised)
When does ion exchange occur on myelinated neurones
Nodes of ranvier
At rest what do neurones maintain and what causes depolarisation
Concentration of Na+ across plasma membrane, if some Na+ channels open, Na+ diffuses down concentration gradient into cell from tissue fluid causing depolarisation
What occurs at generator region of neurone
Gated channels are opened by action of synapse, when a few gated channels open it allows a few Na+ into cell producing small depolarisation (generator potential), this may go no further but if more channels open generator potentials sum produces larger depolarisation, if threshold net action potential occurs
What are most Na+ channels in neurones opened by
Potential difference across membrane
What happens when enough generator potentials to reach threshold potential
Voltage gated channels open
How is opening of voltage gated channel positive feedback
Small depolarisation of membrane causes change to increase depolarisation further
What does opening of voltage gated Na+ channels allow
Large influx of Na+ and depolarisation reaches +40mV on inside of cell, once value reached action potentials transmitted by neurone
Why is action potential all or nothing response
It’s self perpetuating (once it starts at 1 point of neurone continues to end of neurone)
What are the first 3 stages of an action potential
1.membrane starts in resting state, polarised and inside cell (-70mV), higher concentration of Na+ outside than inside cell and higher K+ inside cell 2.Na+ channels open and some Na+ diffuses into cell, 3.membrane depolarises meeting threshold (-50mV)
What are the middle 3 stages of an action potential
4.positive feedback causes near sodium ion gated channels to open and Na+ floods in, as more Na+ enters cell becomes more positively charged than outside 5.potential difference across membrane reaches +40mV, inside cell positive v outside 6.Na+ channels close and K+ channels open
What are the last 3 stages of an action potential
7.K+ diffuses out of cell brining potential difference back to negative inside v outside (repolarisation) 8.potential difference overshoots slightly making cell hyperpolarised 9.original potential difference restored so cell returns to resting state
What happens after action potential
Na+ and K+ in wrong place, concentration of ions inside v outside must be restored by action of sodium/potassium pumps, for short time after each action potential impossible to stimulate cell membrane to reach another action potential (called refractory period)
What does refractory period allow
Cells to recover after action potential and ensures action potentials only transmitted in 1 direction
What is a synapse
Junction between 2 or more neurones where 1 neurone can communicate with another neurone (synaptic cleft in between both)
How do action potentials travel and what can’t they travel through
Travel along neurones as series of ionic movements across neurones membrane, but can’t bridge gap between 2 neurones, so action potential in pre-synaptic terminal releases neurotransmitters that diffuse across synaptic cleft and generates new action potential in post-synaptic terminal
What are synapses that use acetylcholine called
Cholinergic synapses
What is the pre-synaptic bulb
Swelling at the end of pre synaptic neurone containing specialised features
What specialised features do pre-synaptic bulb contain
Many mitochondria as active processes need ATP, large amount of smooth endoplasmic reticulum to packages neurotransmitters into vesicles, many vesicles with acetylcholine to diffuses across synaptic cleft, many voltage gated calcium ion channels on cell surface membrane
What does the post synaptic membrane contain
Specialised sodium ion channels that can respond to neurotransmitters, these channels have 5 polypeptide molecules, 2 of which have acetylcholine receptors
What occurs in post synaptic membrane when acetylcholine present
Receptor sites complementary to acetylcholine, when acetylcholine present in synaptic cleft it binds to receptor site and causes sodium ion channels to open
What are the first 4 steps for transmission across synapse
1.action potential arrives at synaptic bulb 2.voltage gated calcium ion channels open 3.calcium ions diffuse into synaptic bulb 4.calcium ions cause synaptic vesicles to move and fuse with pre-synaptic membrane
What are the middle 4 steps for transmission across synapse
5.acetylcholine released by exocytosis 6.acetylcholine diffuses across synaptic cleft 7.acetylcholine molecules bind to receptor site on sodium ion channels in post synaptic membrane 8.sodium ion channel opens
What are the last 4 steps for transmission across synapse
9.sodium ions diffuse across post synaptic membrane into post synaptic neurone 10.excitatory post synaptic potential created 11.if sufficient generator potential then threshold reached 12.new action potential created in post synaptic neurone
What happens if acetylcholine left in synaptic clef
Continues to open sodium ion channels in post synaptic membrane and continues to cause action potential
What does acetylcholinerase enzyme in post synaptic cleft do
Hydrolyses acetylcholine to acetic acid and choline to stop signal transmission so synapse doesn’t continue to produce action potentials in post synaptic neurone
What happens to acetic acid and choline once acetylcholinerase hydrolyses acetylcholine
It’s recycled and they re enter synaptic bulb by diffusion and recombine to acetylcholine using ATP from respiration in mitochondria, recycled acetylcholine stored in synaptic vesicles for further use
How is action potential all or nothing response
Once action potential starts it’s conducted along whole length of neurone and doesn’t vary in size or intensity
What is an example of cell signalling in transmission across neurones
Pre synaptic membrane releases neurotransmitter into synaptic clef and post synaptic neurone responds
How does cell signalling across synapse work in cholinergic synapses
Signal sent to next neurone consists of acetylcholine molecules, more intense stimulus transmitted as more frequent action potentials
What is main role of synapse
To connect 2 neurones so signal can pass
How can nerve junctions be more complex than than simple connection between 2 neurones
Nerve junctions often involve a few neurones (either from different places converging on 1 neurone or 1 neurones sensing signals to several neurones that diverge to different effectors)
What happens when 1 action potential passes down axon to synapse
It causes a few vesicles to move to and fuse with pre synaptic membrane, relatively small number of acetylcholine molecules diffusing across synaptic cleft produces small depolarisation which is an EPSP and on its own won’t cause an action potential (may take several EPSP to reach threshold and cause action potential)
What is summation
Effect of several EPSPs combine together to increase membrane depolarisation until threshold reached
What is temporal summation
Results from several action potentials in same pre synaptic neurone
What is spatial summation
From action potentials arriving from several different pre-synaptic neurones
What is Inhibitory post synaptic potentials
Can be produced at some pre synaptic neurones, these reduce effect of summation and prevent action potential in post synaptic neurone
What does nerve junctions having serval neurones enable
Synapses to control communication passed along nervous system
What does several pre synaptic neurones converging on 1 post synaptic neurone allow
Allows action potentials from different parts of nervous system to contribute to generating action potential in 1 post synaptic neurone creating a certain response (spatial summation) useful when stimulus warning us of danger
What could the combination of several EPSPs be prevented by
Prevented by production of action potential by 1 IPSP
What does 1 pre synaptic neurone diverging into several post synaptic neurones allow
1 action potential to be transmitted to several parts of nervous system, useful in reflex arc, 1 post synaptic neurone elicits response and another informs brain
What do synapses ensue
Action potentials transmitted in right direction (only pre synaptic bulb has acetylcholine vesicles) so if action potential started half way along neurone and ends at post synaptic membrane, won’t cause response in next cell
What can synapses filter out
Unwanted low level signals, if low level stimulus creates action potential in pre synaptic neurone it’s unlikely to pass across synapse to next neurone as several acetylcholine vesicles must be released to create action potential in post synaptic neurone
How can low level action potentials be amplified
By summation, if low level stimulus persists it will generate several successive action potentials in pre synaptic neurone, release of acetylcholine vesicles over short period enables post synaptic EPSPs to combine together and produce action potential
What may happen to synapse after repeated stimulation
A synapse may run out of vesicles with neurotransmitter, synapse is fatigued to nervous system doesn’t respond to stimulus, explains why we get used to smells and background noises and avoid over stimulation of effector which could cause damage
What is creation and strengthening of specific pathways in nervous system is thought to be
Basis of conscious thought and memory, synaptic membranes adaptable especially post synaptic membrane can be made more sensitive to acetylcholine by addition of more receptors meaning post synaptic neurone more likely to fire an action potential creating specific pathway in response to stimulus
