Neuronal communication Flashcards
1
Q
neurone structure
A
- cell body - contains nucleus, endoplasmic reticulum and mitochonria (produce neurotransmitters)
- dendron - extensions from cell body, divide into dendrites - transmit electrical impulses towards cell body
- axon - elongated nerve fibres transmitting impulses away from cell body
2
Q
cell signalling
A
one cell releasing a chemical that has an effect on a target cell
- locally - eg. between neurones at a synapse
- across large distances - uses hormones eg. pituitary gland secretes ADH, which acts on the kidney
3
Q
motor neurone structure and function
A
- cell body in spinal cord or brain
- axons can be very long
- cell body and dendrites on one end of the axon, axon terminals on the opposite end
- transmit impulses from relay neurone or sensory neurone to effector
4
Q
sensory neurone structure and function
A
- cell body in dorsal root ganglia just outside spinal cord
- dendrites and dendron on one end, cell body in middle on a stalk, axon and axon terminals on other end
- transmit impulses from sensory receptor to relay neurone, motor neurone or brain
5
Q
relay/intermediate neurone structure and function
A
- cell body in brain or spinal cord and connects with sensory and motor neurones
- cell body in the middle surrounded by dendrites with axon shown as more defined part
- transmit impulses between neurones
6
Q
schwann cells
A
- wrap their cell membranes around the axon and produce layers of plasma membrane - myelin sheath
- insulates axon - impulse travels much faster
7
Q
nodes of ranvier
A
- gaps in myelin - every 1-3mm
- electrical impulse ‘jumps’ from node to node in myelinated neurones
8
Q
nerve
A
- bundle of neurones surrounded by perineurium
9
Q
sensory receptors
A
- convert stimuli into a nerve impulse - generator potential (they’re transducers)
- specific to one type of stimulus
10
Q
what is the pathway of an impulse?
A
- receptor, sensory neurones, relay neurones, spinal cord/brain, motor neurone, effector
11
Q
mechanoreceptor
A
- pressure/movement
- eg. parcinian corpuscle in skin
12
Q
chemoreceptor
A
- detects chemicals
- eg. in nose
13
Q
thermopreceptor
A
- detects heat
- eg. on tongue
14
Q
photoreceptor
A
- detects light
- eg. cones in eye
15
Q
transducer
A
a device that converts one form of energy to another
16
Q
how does the parcinian corpuscle produce an electrical signal?
A
- they are mechanoreceptors that detect pressure and movement
1. resting potential - stretch mediated sodium ion channels closed
2. when pressure is applied, the layers of tissue and therefore the membrane will stretch
3. stretch mediated sodium ion channels open in the axon membrane
4. sodium ions diffuse through the channel, if enough sodium ions make it through the channel, voltage gated Na+ channels open, it reaches the threshold, becomes depolarised and creates an action potential
17
Q
- action potential - resting potential
A
- sodium-potassium pump - 3 Na+ ions actively transported out the axon for every 2 K+ ions pumped in
- inside of axon polarised - negatively charged at -70mV
- Na+ ion channels closed
- K+ ion channels open - can diffuse out
- voltage gated channels closed
18
Q
- action potential - depolarisation
A
- some Na+ ion channels open and there is rapid influx of sodium ions down electro-chemical gradient
- inside of axon becomes more positive
- the change in charge causes voltage gated Na+ ion channels to open and more sodium ions diffuse in - positive feedback
19
Q
- action potential - repolarisation
A
- when the potential difference reaches around +40mV, voltage gated sodium ion channels close and voltage gated potassium channels open
- potassium ions move out of the cell restoring the negative charge but the position of the ions is reversed
- so many K+ ions leave the axon that the potential difference becomes even more negative than the resting potential briefly - hyperpolarisation
20
Q
- action potential - refractory period
A
- sodium and potassium ion channels close
- sodium potassium ion pump was always working but the action can be seen
- resting potential restored as Na+ ions return to outside and K+ ions to the inside of the neurone
- this area of the membrane is now able to generate another action potential
21
Q
propagation of action potential along a neurone
A
- A stimulus causes depolarisation of the axon membrane - becomes more positive and is attracted to the negative charge along the axon
- localised electrical circuits are established by the influx of Na+ and cause voltage gated Na+ channels to open further along the axon
- Na+ influx along the axon membrane, meanwhile, behind the depolarisation K+ channels open and begin to leave down their electrochemical gradient and voltage gated Na+ channels close
- the axon membrane behind the depolarisation has returned to its resting state - repolarised
- due to the refractory period, the action potential flows one way - voltage gated Na+ channels closed, preventing movement into the axon
22
Q
saltatory conduction
A
- movement of an action potential across a myelinated neurone
- Na+ ions move into membrane at nodes of ranvier
- a long localised electrical circuit is created between the nodes of Ranvier
- action potential ‘jumps’ from node to node
- this transmits a nerve impulse much faster
23
Q
how is saltatory conduction more energy efficient?
A
- repolarisation uses ATP in the sodium potassium pump
- less repolarisation needed as it only occurs at nodes of ranvier
24
Q
factors that affect speed of action potential
A
- mylination
- axon diameter - bigger diameter, faster impulse as less resistance to flow of ions in cytoplasm
- temperature - higher, faster as ions diffuse faster at higher temps (up to 40 degrees)
25
excitatory neurotrasnmitter
- result in depolarisation of postsynaptic neurone and if threshold reached, action potential triggered eg. acetylcholine
26
inhibitory neurotransmitter
- result in hyperpolarisation of postsynaptic membrane preventing action potential eg. GABA
27
synapse
- when neurones meet but do not join
- made up of synaptic cleft. presynaptic neurone, postsynaptic neurone, synaptic knob, synaptic vesicles, neurotransmitter receptors
28
how does an impulse travel across a synapse?
- action potential arrives
- depolarisation of presyanptic membrane causes Ca+ channels open and they diffuse in to activate cytoskeleton to move vesicles
- vesicles containing neurotransmitter fuse with presynaptic membrane and release neurotransmitter into synaptic cleft by exocytosis
- neurotransmitter diffuses across synaptic cleft to post-synaptic membrane and binds with receptors
- Na+ channels open and diffuse into posysynaptic neurone - membrane is depolarised an action potential produced
29
transmission across cholinergic synapse
- common at neuromuscular junctions
1. acetycholine released from vesicles in presynaptic knob and diffuses across synaptic cleft
2. binds to specific receptors on postsynaptic membrane
3. triggers action potential in posysynaptic neurone
4. acetylcholine hydrolysed by acetylcholinesterase on postsynaptic membrane
5. breakdown products taken back to presynaptic knob to be reformed into acetylcholine
30
role of synapses
- ensure impulses are unidirectional - receptors only present on postsynaptic membrane
- allow on impulse form one neurone to be transmitted to multiple synapses so a single stimulus creates multiple responses
- many neurones may feed into the same synapse so many stimuli from different receptors produce a single response
- filters out low level stimuli
- cell signalling
31
brain function
- processes all info from sensory neurones from internal and external environment
- produces coordinated response via motor neurones and release of hormones
32
cerebrum function and adaptations
- controls voluntary actions eg. learning, memory, personality, thought
- highly convoluted - increases SA and therefore capacity for complex activity
- split into 2 hemispheres controlling opposite sides of body
33
cerebellum
- controls unconscious functions eg. coordinating balance, posture and non-voluntary movement
34
medulla oblongata
autonomic control eg. breathing, heart rate, swallowing
35
hypothalamus
- regulates temperature and water balance
- produces hormones
- has one centre for parasympathetic NS and one for sympathetic NS
36
pituitary gland
- stores and releases hormones that regulate body functions
- anterior and posterior section
37
part of brain that helps 2 hemispheres communicate
corpus callosum
38
cerebral cortex
thick layer of grey substance that covers the 2 hemispheres
39
how is nervous system split up
CNS and PNS
CNS - spinal cord and brain
PNS - somatic NS and autonomic NS
autonomic NS - sympathetic NS and parasympathetic NS
40
central NS
brain and spinal cord
41
peripheral NS
all neurones connecting CNS to the rest of your body
42
somatic NS
- under conscious control
- used to voluntarily choose to do something
- carries impulses to muscles
- myelinated neurones
- acetylcholine released at effector - stimulatory
- effector - skeletal muscle
43
autonomic NS
- operates unconsciously
- eg. heart beat
- made up of sympathetic and parasympathetic NS
44
parasympatheic NS
- active during relaxation
- generally decreases an activity eg. heart rate
- neurone lightly myelinated before ganglion and unmyelinated after
- releases acetylcholine at effector - smooth muscle
45
sympathetic NS
- active when stressed
- ganglion just outside spinal cord
- lightly myelinated before ganglion, unmyelinated after OR lightly myelinated before adrenal medulla, blood vessel after
- releases noradrenaline at effector - smooth muscle
46
reflex arc for withdrawal reflex
1. stimulus heat from candle
2. thermoreceptor in skin detects heat
3. sensory neurone passes nerve impulse to spinal cord
4. relay neurone passes impulse across spinal cord
5. motor neurone passes impulse to muscle - it contracts and hand moves away
47
spinal cord structure
- it is a column of nervous tissues running up the back
- surrounded by spine for protection
- different neurones emerge from the spinal cord at intervals
- relay neurones run through spinal cord to connect sensory to motor
48
knee-jerk reflex
- used by doctors to detect nervous problems
- neural circuit only goes up to spinal cord, not brain
- helps you be able to stand without conscious thought
1. leg is tapped just below knee cap, stretches patellar tendon and acts as stimulus
2. this causes extensor muscle on top of thigh to contract
3. at the same time, a relay neurone relaxes the flexor muscle on the underneath of the knee
- causes leg to kick
49
smooth muscle
- found in walls of intestine, blood vessels, uterus etc.
- involuntary movement
- non-striated
- no regular arrangement
- slow, long contraction
- fibres are uninucleated
50
cardiac muscle
- stripy - fainter than skeletal muscle
- fibres are branched for simultaneous contraction and uninucleated
- involuntary
- short and fast contraction and length
eg. atrial and ventricular muscle
51
skeletal muscle
- striated
- rapid and short contraction
- voluntary
- muscle cells form long fibres containing several nuclei
- each fibre surrounded by sarcolemma (membrane) with many infoldings - T-tubules
- contain sarcoplasm, many mitochondria (for ATP) and sarcoplasmic reticulum
- contain many myofibril organelles
52
myofibrils
- found in skeletal muscle fibres
- long organelles specialised for contraction
- line up in parallel for maximum force
- contain 2 types of protein filaments - thin actin, thick myosin
- alternating dark and light bands - where actin and myosin do and don't overlap
53
sarcomere structure
- made up of thick myosin filaments and thin actin filaments
- space between two Z lines is one sarcomere
- M line - down middle of myosin
- Z line - middle of actin
54
actin filaments
- made up of actin
- tropomyosin coiled around actin
- troponin contains 3 polypeptide chains connected to actin, tropomyosin and calcium ions
55
myosin filaments
- made up of bundles of myosin
- each myosin molecule consists of a tail and 2 heads which stick out
56
how does the appearance of the sarcomere change when contracting?
- light band becomes narrower
- Z lines move closer together
- H zone becomes narrower
- dark band stays the same width
57
power stroke / sliding filament model after sarcoplasm
1. tropomyosin prevents myosin head attaching to binding site on actin
2. Ca2+ from action potential released from sarcoplasmic reticulum bind to troponin and cause tropomyosin to pull away from binding sites on actin
3. myosin head attaches to binding site on actin
4. myosin head changes shape, moving actin filament along - ADP is released
5. Atp molecule fixes to myosin head causing it to detach from the actin filament
6. hydrolysis of ATP to ADP by myosin provide energy to change myosin head back to normal position
7. myosin head reattaches to binding site further along actin filament and cycle repeated
58
what is ATP used for in muscle contraction?
- movement of myosin heads back to original position
- sarcoplasmic reticulum reabsorbing Ca2+ from sarcoplasm
59
how does signal get across a neuromuscular junction?
1. action potential arrives at neuromuscular junction (there are many along a muscle - all contract at same time so more powerful)
2. Ca2+ channels open and Ca2+ diffuse to synaptic knob causing vesicles to fuse with presynaptic membrane
3. acetylcholine released into synaptic cleft by exocytosis and diffuses across synapse to receptors on postsynaptic membrane (sarcolemma)
4. Na+ channels open and depolarisation occurs
5. acetylcholine broken down by acetylcholinesterase into choline and ethanoic acid to prevent muscle being overstimulated
6. choline and ethanoic acid recombined in neurone using ATP from mitochondria
60
how does signal go from sarcoplasm to muscle fibre?
1. depolarisation of sarcolemma spreads through muscle fibre through T-tubules - in contact with sarcoplasmic reticulum
2. SR - Ca2+ actively absorbed from sarcoplasm, Ca2+ channels open and it diffuses into sarcoplasm, flooding it
3. Ca2+ bind to troponin causing it to change shape
61
spatial summation
multiple presynaptic neurones release neurotransmitters to one postsynaptic neurone building up enough to cause an action potential
62
temporal summation
one presynaptic neurone releases a high frequency of neurotransmitters as a result of lots of action potentials building up enough to trigger an action potential in the postsynaptic neurone
