1
Q
Why must the functions of organs be coordinated?
A
To maintain a constant internal environment (homeostasis)
2
Q
How can cells communicate?
A
- transfer signals locally
transfer signals across large distances
3
Q
What is the role of neurones?
A
Transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment
4
Q
Describe the structure and function of dendrons
A
- short extensions which come from the cell body
- divide into dendrites
- sends impulses towards cell body
5
Q
Describe the structure and function of axons
A
- singular elongated nerve fibres that transmit impulses away from the cell body
- can be very long
- narrow cytoplasm
6
Q
Describe the functions of the 3 different neurones
A
Sensory= transmit impulses from a sensory receptor to a relay neurone, motor neurone or the brain
Relay= transmit impulses between neurones
Motor= transmit impulses from a relay neurone or sensory neurone to an effector
7
Q
Describe the structure of the 3 types of neurones
A
Sensory= One dendron, one axon, cell body located in PNS
Relay= Short dendrons, short axons
Motor= Short dendrites, Long axon, cell body located in CNS
8
Q
What is a myelin sheath and how is it formed?
A
- Schwann cells form layers of membrane by growing around the axon many times
- acts as an insulating layer and allows myelinated neurones to conduct the electrical impulse at a faster speed
9
Q
Compare transmission speed between myelinated and non myelinated neurones
A
myelinated= 100m/s
non= 1m/s
Myelinated is much faster due to saltatory conduction
10
Q
How do myelinated neurones transmit impulses faster compared to non myelinated?
A
- electrical impulse jumps from one node of ranvier to the next
- saltatory conduction
- in non myelinated the impulse does not jump, it transmits continuously along the nerve fibre
11
Q
What is the main role of sensory neurones?
A
- They are specific to a single type of stimulus
- they act as a transducer (convert a stimulus into a nerve impulse)
12
Q
What is a transducer?
A
- Converting a stimulus into a nerve impulse
13
Q
What is the pacinian corpuscle and where is it located?
A
- sensory receptors that detect mechanical pressure
- converts mechanopressure into a nerve impulse
- located deep within skin and are most abundant in the fingers and feet
14
Q
Describe the structure of the pacinian corpuscle.
A
- end of sensory neurone is within the centre
- surrounded by layers of connective tissue
- each layer of tissue is separated by a layer of gel
- within the membrane there are stretch mediated sodium channels
15
Q
How does the pacinian corpsucle convert mechanical pressure into a nervous impulse?
A
- At resting state the SM Na+ channels are too narrow to allot sodium to diffuse through
- Pressure changes shape, causes membrane of neurone to stretch which widens the SM Na+ channels
- Na+ diffuses in and causes interior to become positive
- Membrane depolarises resulting in a generator potential which creates an action potential which passes down the sensory neurone to the CNS
16
Q
Briefly describe propagaton in a myelinated neurone
A
- Schwann cells are tightly wrapped around a neurone. They have a high PL content with very few ion channels and Na/ K+ channels are not present along myelinated outside
- Stimulus triggers depolarisation, voltage gated Na+ channels open at a NODE
- Na+ diffuses in and depolarises the axon at the node making it positive relative to the outside
- positive Na+ ions attracted sideways to -ve charge at the next node, creating a LEC
- voltage gated Na+ channels open, Na+ diffuses in and depolarises the node
- LEC’s form between nodes, triggers next node to depolarise, only these regions need to repolarise.
- This is why it is said that the AP ‘jumps’, called saltatory conduction
17
Q
What is saltatory conduction?
A
The process where an action potential jumps between the nodes of ranvier along a myelinated axon
18
Q
Why is conduction slower in non myelinated neurones?
A
- fewer ion channels
- the opening of channels and flow of ions takes time
- reducing the no. of places that this can happen speeds up AP transmission
- also have longer local circuits
19
Q
Why is saltatory conduction more energy efficient in myelinated neurones?
A
- repolarisation requires ATP for the action of the SPP
- due to saltatory conduction and only having certain regions (nodes) requiring repolarisation, less ATP is required
- makes impulse conduction more efficient
20
Q
What are 3 factors that increase the transmission speed of AP’s?
A
Myelination (saltatory conduction)
Axon diameter= bigger diameter means faster transmission, less flow resistance of ions in the cytoplasm
Temperature= higher is faster up to 40C before proteins denature, diffusion of ions is faster
21
Q
Define generator potential
A
The change in potential difference due to a stimulus is called a generator potential
22
Q
Describe what happens when the stimulus detected is small
A
- only a few gated sodium channels open
- few sodiums ions diffuse in
- change in PD is not enough to reach threshold level so sodium ion voltage gated channels do not open, resulting in no generator potential
- AP is not generated
23
Q
What is the all or nothing principle?
A
- a certain level of stimulus always triggers a response no matter the size of the stimulus.
- the action potential is the same size
- size of stimulus can be transmitted by the freq that the APs are generated
24
Q
Describe propagation in a non myelinated neurone
A
- Stimulus causes membrane to depolarise
- Voltage gated Na+ channels open, sodium diffuses into axon down ECG
- Sodium ions move sideways, attracted to the negative charge. This creates a localised electric circuit
- Causes voltage gated sodium channels to open, more sodium diffusion which depolarises the membrane
- LEC forms between the next region of the membrane and continues to carry the AP along
- In previous regions of the membrane voltage gated Na+ channels close, K+ open and diffuse out of the axon repolarising the membrane
- The SPP actively transports Na+ out and polarises the axon back to its resting potential
25
What is the refractory period?
- short period of time where transmitting another action potential cannot happen
- where Na+ and K+ channels are closed and cannot open for a short period of time
26
What are the advantages of refractory periods?
- ensures AP's go in one direction
- Keeps APs separate so they don't combine
- limits the number of action potentials transmitted during a period of time
27
How is a **resting potential** *maintained* and *created*?
- Maintained by the action of the SPP which involves active transport which requires ATP
- the pump moves 2 potassiu ions in and 3 sodium out
- this creates an electrochemical gradient
- potassium diffuses out, sodium diffuses in
- the membrane is more permeable to potassium (more channels) so more potassium is moved out which results in the -70mv resting potential
( resting potential arises due to different ion concentrations inside and out )
28
Briefly describe the stages of **synaptic transmission**.
1. An AP arrives at the synaptic knob
2. depolarisation leads to opening of calcium channels, calcium diffuses into knob
3. vesicles move towards/ fuse with pres membrane (exocytosis)
4. NT is release into synaptic cleft and diffuses down CG to post synaptic membrane
5. NT binds to complementary receptor on membrane
6. sodium channels on post-s membrane widen, sodium diffuses in to reach the threshold potential to generate an action potential/ nerve impulse (if there is enough sodium)
7. NT is degraded by enzymes and released from receptor to travel back to pres memb
8. sodium channels close, post-s memb can re establish resting potential
29
Why do neurotransmitters in **synaptic transmission** need to be broken down?
if they are permanently bound to sodium channels they will constantly trigger an action potential even in the absence of a stimulus
30
In a cholinergic synapse, which neurotransmitter is broken down and what is the products?
Acetylcholine (NT) is broken down by Acetylcholine esterase (enzyme) which produces choline and acetate (products)
| Substitute into synaptic transmission steps
31
What is summation?
The rapid build up of NT in a synapse to generate an action potential
32
What is spatial summation?
Multiple neurones collectively trigger a new AP by combining the NT they release to exceed the threshold value
33
What is temporal summation?
One neurone releases NT repeatedly over a short period of time to exceed the threshold value
34
Why do action potentials only travel in one direction?
- Vesicles containing NT are only in the presynaptic knob
- The presynaptic knob does not have complementary receptors for NT's, only postsynaptic does
35
Explain excitatory synapses
- They depolarise the postsynaptic membrane
- If the threshold is reached action potential is initiated
36
Explain inhibitory synapses
- causes hyperpolarisation of post synaptic membrane
- this means that the threshold potential is less likely to be reached, prevents an action potential from initiating
37
What makes up the PNS?
- All of the other neurones that connect the CNS to the body
- E.g sensory neurones (receptros --> CNS) and motor neurones (CNS --> effectors)
38
What makes up the CNS?
- brain
- spinal cord
39
What is the somatic nervous system?
- Conscious control, used when we voluntarily decide to do something
40
What is the autonomic nervous system?
- Subconscious control and is used when the body does something automatically
- Carries nerve impulses to glands, smooth muscle and cardiac muscle
- E.g heart rate, digesting food
41
Compare the actions of sympathetic and parasympathetic nervous systems
Salivary glands
- S reduces production, P increases
Lung
- S relaxes bronchial muscle, P contracts
Kidney
- S decreases urine secretion, P increases
Stomach
- S peristalsis reduced, P gastric juice secreted
Small intestine
- S peristalsis reduced, P increases digestion
42
Name differences between types of neurone
- Motor neurones have their cell body in the CNS, long axon that carries the AP to an effector
- Sensory neurones have a long dendron, cell body outside CNS, short axon carrying AP to CNS
- Relay connect the others, many short dendrites, short axon
42
Name some features of the pre synaptic bulb
- Many mitochondria for ATP
- large amount of SER which packages the NT into vesicles
- large numbers of vesicles containing acetylcholine
- voltage gated calcium ion channels
43
How is communication between nerve junctions and neurones controlled?
- low level action potentials can be amplified by summation
- synapses can filter out unwanted low level signals
- the post synaptic membrane can be made more sensitive to acetylcholine by the addition of more receptors, more likely to fire an AP
Biology
flashcards
Decks in class (24)
# Cards
-
Biological membranes33
-
Communicable diseases65
-
Biological molecules54
-
Nucleic acids33
-
Enzymes32
-
Exchange surfaces32
-
Cell structure30
-
Cell organelles22
-
Cell division40
-
Transport in animals57
-
Transport in plants49
-
Classification and evolution51
-
Biodiversity57
-
Homeostasis69
-
Ecosystems31
-
Plant hormones27
-
Hormones67
-
Photosynthesis33
-
Nerves44
-
Nerves- the brain regions6
-
Respiration34
-
Inheritance38
-
Manipulating genomes23
-
Cellular control33
