Neuronal Communication Flashcards
(103 cards)
1
Q
What is a neurone?
A
Cell that can transmit electrical impulses and communicates with other cells via synapses
2
Q
What are the three types of neurones?
A
- Sensory
- Relay
- Motor
3
Q
What is the function of neurones?
A
Rapidly transmit electrical impulses to allow coordination
4
Q
What are the components of neurones?
A
- Cell body
- Dendrons
- Axons
5
Q
What makes up the cell body?
A
Nucleus, mitochondria, and RER to allow protein synthesis of NEUROTRANSMITTERS
6
Q
What are dendrons?
A
Transmits electrical impulses towards TOWARDS the cell body, form a branching pattern with smaller dendrites
7
Q
What are axons?
A
- Transmit electrical impulses AWAY from the cell body
- Often very long, narrow cytoplasm covered by plasma membrane with microtubule support
8
Q
What do sensory neurones do?
A
Transmit electrical impulses from a receptor cell to a relay neurone, the brain, or a motor neurone.
9
Q
What is the structure of sensory neurones?
A
- Have one dendron that may branch into several dendrites
- Have one axon that may branch at its terminal
- Cell body in centre, between axon and dendron
10
Q
What do relay neurones do?
A
Transmit electrical impulses between neurones
11
Q
What is the structure of a relay neurone?
A
- Have a central cell body
- Have many short dendrons that branch into several dendrites
- Have many axons that branch out
12
Q
What do motor neurones do?
A
Transmit electrical impulses from a relay neurone or a sensory neurone to an effector
13
Q
What are effectors?
A
Muscles or glands
14
Q
What is the structure of a motor neurone?
A
- Have many dendrites that carry impulse towards the cell body
- Have a long axon that may have branches at its terminal
- NO DENDRONS
15
Q
What is myelin made from?
A
- Made by Schwann cells when the neurone is in the PNS
- Made by OLIGODENDROCYTES when the neurone is in the CNS
16
Q
What are Schwann cells?
A
Produce many layers of plasma membrane by growing around and around the axon of the neurone
17
Q
What is the advantage of myelinated neurones?
A
Rate of transmission is increased because saltatory conduction can occur. This means that electrical impulses can jump from one node of ranvier to the next, down the axon so increasing the speed of transmission of this impulse.
18
Q
What is Multiple Sclerosis (MS)?
A
A genetic disorder where the neurones become demyelinated because the Schwann cells are damaged. This damage disrupts the ability of parts of the nervous system to transmit signals (and slows them down), often resulting in physical and metal issue. Such as struggling to move.
19
Q
What do receptor cells do?
A
Act as TRANSDUCERS. They convert a stimulus (chemical, heat, kinetic energy) into an electrical impulse. They are also specific to a single type of stimulus
20
Q
What are the four types of mammalian receptor cells?
A
- Mechanoreceptors (pressure)
- Chemoreceptors (chemicals)
- Thermoreceptors (heat)
- Photoreceptors (light)
21
Q
What are chemoreceptor cells?
A
Transduce chemical energy into an electrical impulse
22
Q
What do chemoreceptor cells detect?
A
- External chemicals, e.g. odours by the olfactory system
- Internal chemicals, e.g. the carotid body detects blood pH
23
Q
What is the Pacinian Corpuscles?
A
Type of pressure receptor found in mammalian skin. They are sensitive to vibrations or surface texture
24
Q
Mechanism of Pacinian Corpuscles (Part 1) :
A
- Sensory neurone that ends inside Pacinian Corpuscles has a special plasma membrane
- Stretch-mediate sodium channel proteins in plasma membrane
- In normal state, sodium channel proteins have high impermeability to Na+ (channel too small)
- When pm is stretch or pressurised sodium channel increase permeability to Na+ (channels wider)
- When sensory neurone is not stimulated by PC, it has the resting potential with pm being polarised at +ve charge is outside cell
25
Mechanism of Pacinian Corpuscles (Part 2) :
6. When PC has pressure applied to it and the Na+ channel proteins open (pm deformed) Na+ floods into the sensory neurone by facilitated diffusion
7. Changes localised polarity where pressure is and that part of the membrane is depolarised
8. This results in a generator potential, which if greater than threshold voltage, will cause an action potential
9. Action potential will now pass a long the sensory neurone
26
What is the resting potential?
The potential difference across the whole plasma membrane of a neurone
27
What value is the resting potential of a neurone and where is the charge?
- Voltage is -70mV
| - LESS +VE charge on INSIDE
28
How is the resting potential created? Na+/K+ pump
- The Na+/K+ ATPase pump, pumps K+ from the tissue fluid into the neurone by active transport
- Na+ is pumped out of the nruones into the tissue fluid by the same mechanism
- This pump works ALL THE TIME
- This is done unequally so for every 3 Na+ pumped out of the cell, there are only 2K+ pumped into the cell
- Unequal pumping creates an electrochemical gradient, but not the -70mV
29
How is the resting potential created?
| Na+ channel protein
- Na+ channel protein is voltage gated
- Voltage created by the Na+/K+ pump causes the Na+ channel proteins to keep their pores closed
- Stops Na+ from diffusing down the concentration gradient and increases the concentration of +ve ions outside the neurone
- This still doesn't create the resting potential of -70mV
30
How is the resting potential created? K+ channel
- The voltage created by the Na+/K+ pump, keeps the voltage gated K+ channel pores open.
- This allows K+ ions to diffuse out of the cell, down the concentration gradient
- This increases the positive charge outside of the cell, and finally creates the resting potential of -70mV.
31
What is the role of the K+ channel that is NOT voltage-gated?
The pore is always open in order to make the plasma membrane permanently partially-permeable to K+
32
How is an action potential created? Part 1
1. Generator potential made by sensory receptor creates a localised voltage change in the plasma membrane
2. This voltage allows the Na+ voltage-gated channels to open, causing Na+ to diffuse into the cell
3. This reduces the positive charge outside the cell, partially depolarising the membrane and increasing the voltage to -60mV
4. Positive feedback occurs, the opening of the Na+ channels causes many more to open along the neurone and lots of Na+ channels to diffuse into the cell
5. The plasma membrane of the neurone is rapidly depolarising
33
How is an action potential created? Part 2
6. When -40mV is reached, the plasma membrane is now fully depolarised
7. The Na+ channel pores now close due to the voltage
8. The voltage-gated K+ channel proteins open their pores
9. As K+ ions are now diffusing out of cell, and there are no Na+ ions moving in, the membrane starts to repolarise as positive charge is building up outside of the cell
10. The plasma membrane is heading back towards -70mV
34
How is an action potential created? Part 3
11. The K+ ions continue to leave the neurone, causing the plasma membrane to become hyperpolarised
12. A voltage of about -84mV is reached
13. This causes the K+ voltage-gated channel proteins to close their pores
14. The Na+/K+ pump has never stopped working in the background and slowly re-established the resting potential of -70mV
35
What is an electrical impulse?
An action potential that starts at one end of the axon and spreads as a wave of depolarisation to the other end of a neurone
36
What is the refractory period?
-After an action potential has passed over a section of plasma membrane, there is a short period of a few milliseconds when an action potential cannot be initiated
37
What causes the refractory period?
- It is caused by the Na+ voltage gated channel proteins, and a property that they have
- They cannot reopen for a few milliseconds once they have closed at -40mV
38
Why is the refractory period important?
- It is vital because it makes it impossible for an action potential to travel backwards a long an axon
- It also means that action potentials cannot overlap each other
39
What are the two properties of action potentials?
1. Unidirectional
| 2. Discrete (cannot overlap)
40
In myelinated neurones, where are the transmembrane proteins?
- At the Nodes of Ranvier
| - Therefore, depolarisations of the axon plasma membrane can only occur here
41
How does saltatory conduction work?
- When an action potential is initiated at the start of a myelinated axon, sodium ions diffuse into the cytoplasm
- The sodium ions diffuse through the cytoplasm towards the next Node of Ranvier
- This is the localised current, a flow of ions
- When these sodium ions arrive at the next Node of Ranvier, they cause the voltage to change and acts as a localised generator potential
- This causes the voltage-gated Na+ channel proteins to open at this Node of Ranvier
- A NEW action potential is triggered at this node, giving the appearance that the current is jumping from one node to another
42
What factors affect the transmission of an action potential across an axon?
1. Myelinated or not myelinated
2. Axon diameter- lower resistance to ion flow in cytoplasm and a bigger surface allows for more transmembrane proteins
3. Temperature-Higher temperatures means Na+ ions have more kinetic energy and therefore diffuse into the neurone faster. But only up to temperatures where the transmembrane proteins are not denatured
43
What is the 'All or Nothing' principle?
- An action potential will not be triggered if a threshold value is not reached by the stimulus
- Threshold value has to be reached by the voltage generated by the localised generator potential
- If the threshold value is reached then an action potential will be triggered and will always be the same size
- Different sized stimuli will not generate different sized action potentials, only different frequencies
44
What is the synaptic cleft?
A gap that separates the axons of one neurone from the dendrite of the next neurone
45
What is the synaptic knob?
Swollen end of the pre synaptic neurone, with many mitochondria and extensive endoplasmic reticulum to synthesis neurotransmitters
46
What are synaptic vesicles?
Contain neurotransmitters that will fuse with the pre synaptic neurone and diffuse into the synaptic cleft
47
What are neurotransmitter receptors that are sodium ion channel proteins?
Specific protein molecules in post synaptic membrane, where the neurotransmitter will bind to
48
What are the two types of neurotransmitters?
1. Excitatory
| 2. Inhibitory
49
What are excitatory neurotransmitters?
- They cause localised depolarisation of the post-synaptic membrane
- If this reaches the threshold potential, then an action potential will be generated
- e.g Acetylcholine
- Common in the CNS and neuromuscular junctions
50
What are inhibitory neurotransmitters?
- Cause hyperpolarisation of the post synaptic membrane
- Prevent action potentials from being initiated
- e.g GABA (gamma-aninobutryic acid)
51
Transmission of an action potential across a synapse: Part 1
1. Arrival of action potential at end of pre-synaptic neurone causes voltage-gated calcium channels to open their pores
2. Calcium ions diffuse into the cell by facilitated diffusion
3. Influx of calcium ions causes synaptic vesicles to fuse with pre-synaptic neurone
4. Synaptic vesicles release acetylcholine into the synaptic cleft
52
Transmission of an action potential across a synapse: Part 2
5. Acetylcholine molecules fuse with receptor sites on the sodium ion channel in the membrane of the post-synaptic neurone
6. This causes the sodium ion channels to open, allowing Na+ ions to diffuse into the post-synaptic neurone
7. Influx of sodium ions generates a new action potential in the post-synaptic neurone
53
Transmission of an action potential across a synapse: Part 3
8. Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid, which diffuse back across the synaptic cleft into the pre-synaptic neurone
9. In addition to recycling the choline and acetyl, the breakdown of acetylcholine also prevents it from continuously generating a new action potential in the post-synaptic neurone
10.
54
What happens at electrical synapses?
-There is direct physical connection between the pre synaptic and post synaptic neurone
-Connection takes form of a channel called a gap junction which allows current, in the form of ions, to flow directly from one cell into another
-This allows very fast cell signalling, faster than chemical synapses
-
55
What are the roles of synapses?
- Ensure UNIDIRECTIONAL impulses as neurotransmitter receptors are only present in post synaptic membrane
- DIVERGENCE impulses from a single neurone can be passed to more than one neurone
- CONVERGENCE impulses from more than one neurone to be passed on to a single post synaptic neurone, so stimuli from different receptors produce a single result
- FILTER OUT background and low level stimuli, ensuring only stimulation that is strong enough will be passed on
56
What is summation?
If the neurotransmitter needs to be built up in the synaptic cleft in order for an action potential to be created
1. Temporal summation is from one stimulus
2. Spatial summation is from more than one stimuli
57
What are the two types of drugs?
1. Recreational
| 2. Medical
58
What are the two modes of action of drugs on synapses?
1. STIMULATE the nervous system by creating more action potentials in the post-synaptic neurone
2. INHIBIT the nervous system by creating fewer action potentials in the post-synaptic neurone
59
How is the mammalian nervous system STRUCTURALLY organised?
1. CENTRAL NERVOUS SYSTEM
- Consists of the brain and spinal cord
- Has nerve tracts instead of nerves
2. PERIPHERAL NERVOUS SYSTEM
- Consists of nerves and ganglia outside the brain and spinal cord
- Has sensory neurones that carry impulses from receptors to the CNS
- Have motor neurones that carry impulses from CNS to muscles and glands
60
What is a ganglion?
A group of neurone cell bodies in the PNS
61
How is the mammalian nervous system FUNCTIONALLY organised?
1. SOMATIC NERVOUS SYSTEM
- Associated with the voluntary control of body movements via skeletal muscles
2. AUTONOMIC NERVOUS SYSTEM
- Controls smooth muscle, cardiac muscles and glands
- It is involuntary
Both are part of the PNS
62
What are the two parts of the autonomic nervous system?
1. PARASYMPATHETIC
Rest and Digest
2. SYMPATHETIC
Fight or Flight
63
What are the differences in structure of neurones in sympathetic and parasympathetic nervous system?
```
SYMPATHETIC
-Short preganglionic neurone
-Long postganglionic neurone
-Uses noradrenaline
PARASYMPATHETIC
-Long preganglionic neurone
-Short postganglionic neurone
-Uses acetylcholine
```
64
What's the structural difference between neurones in the autonomic and somatic nervous system?
SOMATIC- heavily myelinated axon
| AUTONOMIC- lightly myelinated axon
65
What are the 5 areas in the human brain's gross anatomy?
1. Cerebrum
2. Cerebellum
3. Medulla Oblongata
4. Hypothalamus
5. Pituitary gland
66
What is the cerebrum?
-The largest part of the brain, which is highly convoluted (folded)
67
What is the structure of the cerebrum?
- Is divided into two cerebral hemispheres that control opposite sides of the body
- Outer layer of each cerebral hemisphere is the cerebral cortex, made from grey matter
- Grey matter is unmyelinated neurones, cell bodies and dendrites
68
What is the function of the cerebrum?
With the assistance from the cerebellum, the cerebrum controls all voluntary actions, and some involuntary actions, in the human body
69
What is the cerebellum?
- Plays an important role in motor control
- Does not initiate movement, but contributes to coordination, precision and accurate timing
- Receives impulses from sensory systems of the spinal cord and from other parts of the brain and integrates these impulses to fine-tune motor activity by sending impulses to the prefrontal lobe
70
Where is movement controlled in the cerebrum?
71
Where does reasoning and decision making occur in the cerebrum?
72
What is the medulla oblongata?
- Long stem like structure which makes up part of the brainstem
- Is responsible for autonomic or involuntary functions
- It contains:
1) The cardiac centre for heart rate and blood pressure
2) The respiratory centre for breathing rate
3) The vasomotor centre for blood pressure
4) The vomiting, sneezing, coughing and swallowing centres
73
What is the hypothalamus?
- The main controlling centre for the autonomic nervous system
- Links the nervous system to the endocrine system via the pituitary gland
- Functions include:
1) Monitoring composition of blood plasma
2) Controlling body temperature
3) Controlling hunger and thirst
4) Controlling fatigue, sleep and circadian rhythms
5) Stimulate or inhibits the pituitary gland by producing and releasing hormones
74
What is the pituitary gland?
- Is an endocrine gland
- Is divided into two sections
1) ANTERIOR gland, producing:
- ACTH (targets adrenal gland)
- TSH (targets thyroid gland)
- FSH and LH (targets ovaries)
- Growth hormone
2) POSTERIOR gland, producing:
- Oxytocin (target uterus and mammary glands)
- ADH (targets kidneys)
75
What are the features of reflexes?
1. Have a specific stimulus
2. Is an involuntary action
3. Nearly instantaneous response
4. Prevent damage to body
5. Involves a neural pathways that doesn't involve the cerebrum
76
What is the general reflex arc?
1) Stimulus
2) Receptor cells transduces energy to electrical energy
3) Action potential initiated in sensory neurone
4) Nervous impulses travels a long sensory neurone that enters the spinal cord via the dorsal root ganglion
5) Sensory neurone forms synapses with a relay neurone in the spinal cord
6) Relay neurone forms synapses with a motor neurone, which leaves the spinal cord via the ventral root
7) Motor neurone forms synapses with the effector
8) Effector produces response
77
What is the spinal cord?
- Is a long, thin, tubular structure made up of nervous tissue
- Extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column
78
What are the functions of the nervous systen?
1) Transmission of nervous impulses from the motor cortex to the effectors
2) Transmission of nervous impulses from sensory neurones to the sensory cortex
3) Coordinating reflexes
4) Controlling motor instructions for rhythmic movement, like walking
79
What is the knee-jerk reflex?
- Striking of patellar with a reflex hammer stretches the tendon of the quadriceps muscle
- Involves 2 motor neurones, 1 relay neurone and 1 sensory neurone
- The leg extends in slightly in a kick motion
- Check for nervous problems in spinal cord or cerebellum damage
80
What is the blinking reflex?
- Reflex blink is a cranial reflex involving pons in the lower brainstem
- Occur in response to an external stimulus such as contact with the cornea
- Response is consensual because both eyelids blink
- Involves 1 sensory, 1 relay and 1 motor neurone
- Check if lower brainstem is active, confirming if someone unconscious is brain dead or not
81
What are the three types of muscle?
1. Skeletal
2. Cardiac
3. Smooth
82
What are the features of skeletal muscle?
1. Striated appearance
2. Under conscious control of somatic nervous system
3. Muscle cells are called muscle fibres
4. Fibres arranged to contract in one direction
5. Rapid contraction but for a short length of time
83
What are the features of cardiac muscle?
1. Striated appearance but less pronounced
2. Under involuntary control of the autonomic nervous system
3. Muscle cells are called cardiomyocytes
4. Fibres arranged in a branching pattern and connected by intercalated discs
5. Intermediate contraction speed and length of time
84
What are the features of smooth muscle?
1. Non-striated appearance
2. Under involuntary control of the autonomic nervous system
3. Muscle cells are spindle shaped with a wide middle and tapering ends
4. Fibres arranged in a non-regular pattern
5. Slow contraction speed but can contract for a long length of time
85
What is the structure of skeletal muscle?
1. Muscle cells are extremely long and are made from many embryonic muscle cells fusing together to make a muscle fibre, making them stronger by reducing cell junctions laterally
2. Each muscle fibre is multinucleate
3. The cytoplasm in a muscle fibre is called the sarcoplasm
4. Bundles of muscle fibres are covered by an additional plasma membrane called the sarcolemma
5. Sarcolemma folds inwards to from T-Tubules to help spread electrical impulses to allow the muscle to contract as a whole
6. Many mitochondria to produce ATP for contraction
7. Endoplasmic reticulum is modified to form the sarcoplasmic reticulum, which contains many calcium ions for muscle to contract
8. Each muscle fibre contains myofibrils that are specialised organelles that allow the muscle fibre to contract longitudinally.
86
What is the structure of myofibrils?
1. Made from ACTIN and MYOSIN
2. Actin is thinner and made from two actin molecules twisted around each other
3. Myosin is thicker and made from many bulbous headed myosin molecules wrapped into a bundle
4. Myofibrils have a striped appearance with light and dark bands
5. The SARCOMERE is one repeat pattern of the dark and light bands. It is the functional unit of a myofibril
87
What is the structure of myosin?
- Has globular heads that are hinged, allowing them to move backwards and forwards
- One head is a binding site for each actin and ATP
- Tails of several hundred myosin molecules align to form the myosin filament
88
What is the structure of actin?
- Have a binding site for myosin, which is blocked by tropomyosin
- The tropomyosin is held in place by troponin
89
What is the structure of a sarcomere?
1. Sarcomere is defined as the segment between two adjacent Z-lines
2. The light band is where the actin and myosin do not overlap (AKA I-Band)
3. The dark band is where the actin and myosin filaments overlap. It contains the entire length of a myosin filaments (AKA A-band)
4. The H-zone is the lighter band in the middle of the dark band, where the actin filaments are absent
5. The Z line is the centre of each light band. It is made from several proteins and they create transverse stability for sarcomere
90
What are the features of slow-twitch muscles?
- Used for muscular endurance, they contract slowly but do not fatigue easily
- Use oxygen for aerobic respiration
- Have a large amount of mitochondria and many blood vessels
- Typically red in colour due to dense supply of capillaries and presence of myoglobin
- Prevalent in endurance athletes, such as marathon runners
- Prevalent in muscles that maintain body posture
91
What are the features of fast-twitch muscles?
- Used for muscular strength, they contract rapidly but fatigue easily
- Respire anaerobically and have less mitochondria, fewer blood vessels and fewer myoglobin
- Typically lighter in colour
- Prevalent in strength athletes and sprinters
- Contain more and thicker myosin fibres
- Contain creatine phosphate
92
What is the sliding filament theory?
-Skeletal muscles contract longitudinally and to achieve this, the actin filaments and myosin filaments in each myofibril slide past each other
93
What is the result of a sarcomere contracting?
1. Light band becomes narrower
2. Z lines move closer together
3. H zone becomes narrower
94
What happens when a muscle is relaxed?
The actin-myosin binding sites are blocked by tropomyosin.
| Tropomyosin is held in place by a globular protein called troponin
95
What are neuromuscular junctions?
- Synapses between a motor neurone and muscle fibres
- They are found at motor end plates
- There are many neuromuscular junctions along a muscle to ensure all muscle fibres contract simultaneously
96
What is a motor neurone?
A single motor neurone will connect all muscle fibres in a motor unit. When many motor neurones are stimulated then a strong muscle contraction is achieved
97
How does the depolarisation travel in the sarcolemma?
By travelling a long the T-Tubules
98
Action of muscle contraction: Part 1
1. Depolarisation of the T-Tubules causes the sarcoplasmic reticulum to release calcium ions
2. Calcium ions diffuse into the sarcoplasm down their concentration gradient
3. Calcium ions bind to troponin, causing a conformational change
4. This stops tropomyosin from blocking the myosin binding sites on the actin filaments
5. The myosin head now binds to the actin filaments at the myosin-actin binding site, forming an actin-myosin cross bridge
6. Myosin head now changes angle and pulls the actin filament along
7. The ADP is released from the myosin head
99
Action of muscle contraction: Part 2
8. ATP now binds to the ATP binding site on the myosin head
9. This causes myosin head to detach from the myosin-actin binding site
10. ATPase enzymes, which have been activated by the increased concentration of calcium ions in the sarcoplasm, hydrolyse the ATP on the myosin head to ADP
11. This causes the myosin head to change angle again, back to the original position
12. The cycle repeats itself many times
100
What are the three types of energy supply during muscular contraction?
1. Aerobic respiration
2. Anaerobic respiration
3. Creatine phosphate
101
Aerobic respiration as an energy supply:
- Most ATP in muscle contraction is produced this way
- Requires oxygen
- Happens in the mitochondria
- Used for low intensity and long term cycles of muscle contraction and relaxation
102
Anaerobic respiration as an energy supply:
- Fast way of producing ATP
- Used at the start of muscles that are doing rapid cycles of contraction and relaxation
- Does not required oxygen
- Produces lactic acid and is a short term solution
103
Creatine phosphate as an energy supply:
- Creatine phosphate is a store of phosphate groups that can be quickly used to produce ATP from ADP
- It is a very short term supply of phosphate
- Used for short bursts of very vigorous exercise
