5.1.3 Neuronal Communication Flashcards
What are the three types of neurone?
- relay neurone
- sensory neurone
- motor neurone
Name 8 parts of a neurone
- dendrite
- cell body
- myelin sheath
- schwann cells
- node of ranvier
- axon
- dendron
- terminal end branches
What is a dendrite?
Small extensions that conduct nerve impulses towards the cell body
What is the cell body?
Contains a nucleus, cytoplasm, rough ER, mitchondria and produces neurotransmitters and ATP
What is a myelin sheath?
Lipid covering that insulates the axon - speeding up the nerve impulse conduction by allowing saltatory conduction
What is a shwann cell?
A cell that wraps itself around the axon and produces myelin sheath
What is a node of ranvier?
A gap between schwan cells with no myelin sheath
What is an axon?
Conducts nerve impulses away from the cell body, thin long cytoplasm with plasma membrane
What is a dendron?
Present in a sensory + relay neurone - conducts nerve impulses to the cell body
What are terminal end branches?
Connect neurone to muscle (motor end plate)
What is the function of sensory neurones?
Conducts nerve impulses from sensory receptor cells to relay neurones (in brain or spinal cord)
What is the function of relay neurones?
Conduct nerve impulses between neurones like sensory to motor
What is the function of motor neurones?
Conducts nerve impulsesa from relay neurones (brain or spinal cord) to muscle or glands (effectors)
Give key details about relay neurones
- cell body normally in CNS
- cell body central to neurone
- dendrites connect directly to cell body
- many short axons
- many short dendrons
- in between sensory and motor neurones
Give key details about motor neurones
- cell body in CNS
- cell body at end
- dendrites connect directly to cell body
- long axon
- no dendrons
- ends at motor end plate
Give key details about sensory neurones
- cell body not in CNS
- cell body in middle of neurone
- dendrites not part of cell body
- shorter axon
- dendron present
- comes from receptor
What is saltatory conduction?
When action potential jumps from one node of ranvier to the next
- conserves ATP as sodium-potassium pump only has to operate at nodes
- speds up conduction of nerve impulses
What is an electrochemical gradient?
A concentration gradient of ions
How is the resting potential maintained?
- sodium-potassium ion pump uses ATP to actively transport 3NA+ out of the axon and 2K+ into the axon
- many K+ ion channels are open, so K+ ions diffuse back out of axon
- voltage gated Na+ ion channels closed
- fewer Na+ ion channels are open, so fewer Na+ ions can diffuse back in
What is the charge of resting potential?
Polarised -70mw
Give properties of sensory receptors
- specific to a single type of stimulus
- tranducers - convert one form of energy into a different form of energy
Give 4 types of sensory receptors
- mechanoreceptor
- chemoreceptor
- thermoreceptor
- photoreceptor
Give key details about photoreceptors
Stimulus: light
Receptors: cone + rod cells
Organ: eye
Give key details about chemoreceptors
Stimulus: chemicals
Receptors: olfactory receptor
Organ: nose
Give key details about thermoreceptors
Stimulus: heat
Receptors: end bulbs of krause
Organ: eye
Give key details about mechanoreceptors
Stimulus: pressure/movement
Receptors: pacinian corpsucle
Organ: skin
What is a transducer?
Converts mechanical energy to electrical energy
Outline the structure of the pacinian corpsucle
- axon of sensory neurone
- myelin sheath
- single neurone ending, surrounded by capsule of connective tissue
- lamellae separated by gel
How does pressure on the pacinian corpsucle casue an action potential?
- Shape of corpsucle changed
- Stretch-mediated Na+ channels in neurone membrane open
- Na+ ions diffuse in
- Memrbane is depolarised
- Generator potential created
- Greater pressure = more Na+ ion channels open = greater generator potential
- If threshold reached an action potential is developed
- Conducted along sensory neurone
How does different levels of pressure affect the action potentials released?
Greater pressure = greater frequency of nerve impulses
Maxinum frequency limited by refractory period
Amplitude of ther action potential NEVER changes
What is the all or nothing law?
- if stimulus isn’t strong enough = generator potential doesn’t reach threshold
- depolarisation of the membrane is insufficient
- no action potential created
What is depolarisation?
The charge between the outside and inside of the axon reaching +40mw, resulting in an action potential
Explain the state of the axon membrane at resting potential
- voltage gated K+ ion channels closed
- K+ ion channels open
- voltage gated Na+ ion channels closed
- most Na+ ion channels closed
Explain the state of the axon membrane at depolarisation
- Na+ ions from sensory receptor generator potential diffuse down the axon + change the voltage
- voltage gated Na+ ion channels open
- Na+ ions diffuse into the axon from outside neuron
- if above -50mw threshold, all Na+ ion channels open - positive feedback
- 40mw action potential
Explain the state of the axon membrane at repolarisation
- when +40mw reached
- voltage gated Na+ ion channels close
- voltage gated K+ ion channels open
- K+ ions diffuse down electrochemical gradient changing the charge
Explain the state of the axon membrane at hyperpolarisation
- large amounts of K+ ions diffuse cause voltage below resting potential
- voltage gated K+ ion channels close
Why are unmyelinated neurones slower?
- have voltage gated Na+ ion channels along whole lenght of axon
- all channels have to open to pass an impulse
- localised circuit shorter + more of them
Why are myelinated neurones quicker?
- schwann cells insulates
- saltatory conduction - action potential jumps from node to next
- only have voltage gated Na+ ion channels at nodes of ranvier
- localised circuit longer + less of them
- diffusion quicker than opening all ion channels
What is multiple sclerosis (MS)?
- autoimmune disease
- own immune system treats antigens on myelin sheath as non-self
- schwann cells damaged so less insulation
- prevents saltatory conduction
- slows conduction of action potentials
How does temperature affect the speed of nerve impulse conduction?
- higher temp = molecules have more kinetic energy
- faster Na+ ion diffusion accross + into axon membrane
- faster movement of vesicles
- fastrer diffusion of neurotransmitter at synpatic cleft
- faster depolarisation of action potential + faster repolarisation
- above 40 degrees = ion channels + pumps denature
- fluidity of phosophloipd bilayer disrupted
- synaptic enzymes denature
How does axon diameter affect the speed of nerve impulse conduction?
Wider axon diamter = faster rate of conduction - less resistance to flow of ions in cytoplasm
What is the all or nothing law?
- if the stimulus is not strong enough
- depolarisation will not be enough
- to reach threshold potential (-50mw)
- action potential can only be generated if stimuls reaches threshold potential
- once threshold is reached, action potential (+40mw) will always occur
- action potentials are never generated unlesss threshold potential is reached
What is the refractory period?
A period of time during wehich a second stimulus will be unabvle to cause an impulse
Explain the concept of the refractory period
- following an action potential
- Na+ + K+ ions are redistributed
- restores resting potential
- voltage gated Na+ ion channels are closed and cannot open
- duringh which another action potential cannot be generated
- determines maximum frequency of nerve impulse transmission
- nerve impulses condicted in 1 direction along axon
- prevents action potentials overlapping
How do pufferfish toxins work?
- tetradotoxin
- blocks voltrage gated sodium ion channels in human nerve cells
- prevents action potentials
- piuffer fish have different shaped sodium channels so not affected
What is the synapse?
Where two neurones meet
- gap between neurones is called synaptic cleft
- neurotransmitters chemicals cross the gap
Name parts of the synapse
- presynaptic neurone
- voltage gated Ca2+ ion channel
- vesicles with acetlycholine neurotransmitter
- mitochondria
- Na+ ion chennels with acetlycholine receptor
- postsynaptic neurone
Explain how an action potential moves accross a synapse
- Na+ moves along axon into presynaptic knob, causing depolariusation
- Voltage gated Ca2+ ion channels open
- Ca2+ ions diffuse into the neurone
- Vesicles containg acetylcholine move towards presynaptic membrane + fuse
- Acetylcholine released by exocytosis into synaptic cleft
- Acetylcholine diffuses accross cleft + attaches to receptors on postsynaptic membrane
- Receptors are on Na+ ion channels - causes channels to open and Na+ to diffuse into postsynaptic neurone
- Depolarisation occurs in post synaptioc neurone
- If threshold reached, action potential fired
- Acetylcholine broken down in cleft by enzyme acetylcholinesterase
- Choline + ethanoic acid formed - diffuse back into presynaptic cell
- Choline + ethanoic acid recombine with ATP to form acetylcholine, stored in vesicles in presynaptic cell
How do synapses only allow conduction of nerve impulses in one direction?
- only the presynatpic neuronce produces + releases acetylcholine
- only presynaptic membrane has Ca2+ ion channels
- only postsynaptic membrane has specific receptors for acetylcholine
- acetylcholine is broken down at postsynaptic membrane
Why is ATP important for synapses and nerve impulse conduction?
- sodium/potassium pump uses ATP to restore + maintain resting potential
- ATP needed for acetycholine formatrion
- ATP needed for vesicle formation
- movement of vesicles uses ATP
- exocytosis uses ATP when vesicles fuse with cell surface membrane of presynaptic neurone
- active transport uses ATP - acetylcholine transported into vesicle + Ca2+ transported out of pre-synaptic neurone
What are excitatory neurotransmitters?
Cause depolarisation of the post synaptic membrane, causing an action potential above the threshold
e.g. synapses that use acetylcholine as a neurotransmitter that causes Na+ ion channels to open and Na+ ions move into the neuron
What are inhibitory neurotransmitters?
Cause hyperpolarisation so bigger stimulus is required to reach the threshold
e.g. inhibitory synapses that use GABA that cause cl- ion channels to open rather than Na+ ion channels
What are vesicle snares?
Proteins that are complementary to membrane receptors (snares) to allow exocytosis
- can be digested by toxin’s enzymes so no exocytosis occurs
What is divergence?
One pre synaptic neurone connects to many post synaptic neurones
- allows nerve impulses to be conduced to many parts of the nervous system
- single stimulus = number of responses
What is convergence?
Nerve impulses from different parts of the nervous system giving one response
- stimuli from different receptors interacting to produce a single response
Define summation
The amount of neurotransmitter builds up to sufficient level to reach the threshold
Define spatial summation
When a number of presynaptic neurones connect to one postsynaptic neurone
Define temporal summation
When a single presynaptic neurone releases neurotransmitter as a result of an action potential several times overa short periods
Why are synapses important?
- ensure one direction action potential
- allows integration
- allows summation
- filters out low level stimuli
- prevents over-stimulation of neurones
How does nicotine affect synapses?
- nicotine binds to acetylcholine receptors
- opens Na+ ion channels
- causes depolarisation
- remains in receptor for longer + remains in refractory stage for longer
Give key features of reflex arcs
- rapid
- short lived
- automatic
- not learned
- response the same each time
- for safety
Explain the path of a reflex arc
- Stimulus
- Receptor
- Sensory neurone
- Relay neurone (In spinal cord)
- Motor neurone
- Effector
- Response
Explain the knee jerk response
- Stimulus hits patellar tendon
- Sensory neurones conduct nerve impulse to the spinal cord
- Nerve impulse conducted down the motor neurone to extensor muscles, contracting
- Response is knee jerk - maintains posture + balance
Explain the blinking reflex
- Stimulus from cornea being touched
- Nerve impulse conduced down sensory neurones
- Nerve impulses conducted down really neurone in lower brain stem
- Down motor neurone which branches to both eyes and to eyelid muscles
