M5, C13 Neuronal Communication

Question 1

Give an example of a stimulus in the internal environment and external environment

Answer 1

interenal - water potential, ion levels, temperature, blood glucose levels, cell pH

external - temperature, light intensity, humidity, new or sudden sound

Question 2

Describe the nervous system

Answer 2

• transmission is very rapid
• response is localised
• effect is temporary and reversible
• response is short-lived
• transmission is by neurones
• response is rapid
• nerve impulses travel to specific parts of the body
• communication is by nerve impulses

Question 3

define:

a) sensory neurones
b) relay neurones
c) motor neurones

Answer 3

sensory neurones - transmit impulses from receptor cells to the central nervous system

relay neurones - transmit impulses between neurones

motor neurones - transmit impulses from the CNS to an effector cell

Question 4

give two types of effector cells

Answer 4

muscle

gland

Question 5

what is the basic steps impulses go through

Answer 5

receptor - sensory neurone - relay neurone - motor neurone - effector

Question 6

what are the 4 main parts of a neurone and describe each part

Answer 6

cell body - contains nucleus, mitochondria and ER, produces neurotransmitters

dendron - carries impulses towards cell body

dendrite - smaller branches of the dendrons

axon - carries impulses away from cell body

Question 7

define receptors

Answer 7

specialised cells that can detect changes in the body’s internal and external environment

Question 8

define generator potential

Answer 8

start of the nerve impulse

receptors convert the energy of the stimulus into the generator potential

Question 9

define transducers

give some examples

Answer 9

receptors which convert energy of the stimulus into a nerve impulse

• photoreceptors (light energy)
• thermoreceptors (thermal energy)
• mechanoreceptors (kinetic energy)
• chemoreceptors (chemical energy)

Question 10

define pacinian corpuscle

Answer 10

specific sensory receptors that detect mechanical pressure

Question 11

how does the pacinian corpuscle detect mechanical pressure? (5 steps)

Answer 11

1) There are sodium ion channels in the plasma membrane of the sensory neurones, which in its normal state are too narrow to allow sodium ions through. The pacinian corpuscle has a resting potential.
2) When pressure is applied to the Pacinian corpuscle, the shape changes - the membrane stetches.
3) The sodium ion channels widen so sodium ions can now diffuse into the sensory neurone.
4) The potential of the membrane changes - becomes depolarised. Results in generator potential.
5) A nerve impulse is created which passes along the sensory neurone.

Question 12

How is the resting potential established and maintained in neurones

Answer 12

• sodium-potassium pump where 3 sodium ions are pumped out for every 2 potassium ions that are pumped in
• there are sodium ion channels and potassium ion channels. more sodium ion channels are closed, whereas many potassium ion channels are open, allowing more potassium ions to diffuse out than sodium ions diffusing in

This results in a more negative inside of the cell as ore positively charged ions are outside the cell. This creates the resting potential of -65mV. Said to be polarised.

Question 13

Why is a neurone active even though it is said to be resting

Answer 13

the sodium-potassium pump involves active transport so requires ATP
3 sodium ions are actively pumped out and 2 potassium ions are actively pumped in

Question 14

how is an action potential generated

Answer 14

1) neuron has a resting potential - most Na ion gated channels are closed / some potassium ion channels are open
2) the energy of the stimulus triggers some sodium voltage-gated channels to open. Diffusion of Na ions into neuron increases. the inside is less negative
3) Once the threshold potential is met, more sodium ion channels open due to the increase of positive charge.
4) the inside now becomes more positive to +40mV so the voltage-gated sodium ion channels close and voltage-gated potassium ion channels open. this means the membrane is more permeable to potassium ions
5) Potassium ions diffuse out resulting in the inside becoming more negative than the outside
6) the neuron eventually becomes more negative than the resting potential (hyperpolarisation). the voltage-gated potassium ion channels now close. the sodium-potassium pump now has a large effect when pumping sodium ions out and K ions in. the neuron returns to resting potential

Question 15

define localised circuit

Answer 15

diffusion of sodium ions sidewards

Question 16

how is the action potential transmitted along the cell

Answer 16

• The stimulus causes the first section of the cell to carry out an action potential
• When the threshold potential is met, there is an influx of sodium ions into that section of the cell
• There is a higher concentration of sodium ions in that section of the cell compared to the rest so localised circuits form
• This creates a threshold potential in that section of the cell so an action potential follows - starting with the opening of voltage-gated sodium ion channels causing depolarisation
• The section of the cell before has to return to resting potential before another impulse is sent

Question 17

what is the refractory period during the action potential

Answer 17

• delay between one action potential and another
• prevents action potential travelling backwards
• caused by the time taken to restore resting potential

Question 18

what is the structure of myelinated neurones

Answer 18

Have Schwann cells wrapped around their axons and dendrons.

The Schwann cells have a fatty substance called myelin in their membrane.

Question 19

what are the gaps called between myelinated neurones

Answer 19

nodes of Ranvier

Question 20

what is saltatory conduction

Answer 20

the neurone’s cytoplasm conducts enough electrical charge to depolarise to the next node, so the impulse ‘jumps’ from node to node
happens in myelinated neurones at the nodes of Ranvier

Question 21

what increases the speed of conduction of action potentials

Answer 21

myelination
axon diameter (bigger diameter means less resistance)
temperature (diffusion increases with a higher temp until around 40 degrees where the proteins will denature)

Question 22

what is the all-or-nothing principle

Answer 22

the action potential is created when the threshold potential is met
no matter how large the stimulus the size of the action potential will be the same
when the stimulus is large it just creates more frequent action potentials, increasing the number of impulses sent

Question 23

How are impulses transmitted across a synapse

Answer 23

• An action potential arrives at the end of the presynaptic neurone. This causes calcium ion channels to open and calcium ions enter the synaptic knob
• The influx of calcium ions cause synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft
• Acetylcholine diffuses across the cleft and binds with receptors on the postsynaptic membrane. This causes sodium ion channels to open and sodium ions diffuse into the neurone
• This cause a new action potential to occur in the postsynaptic neurone

Question 24

define synapse

Answer 24

the junction between two neurones

Question 25

what is the actual gap called between 2 neurones

Answer 25

synaptic cleft

Question 26

define neurotransmitter

Answer 26

a chemical that diffuses from one neurone to the next

Question 27

what are the 2 types of neurotransmitter

Answer 27

Excitatory - result in depolarisation of the postsynaptic membrane = action potential

Inhibitory - result in hyperpolarisation of the postsynaptic membrane - no action potential

Question 28

give an example of a excitatory neurotransmitter and a inhibitory neurotransmitter

Answer 28

excitatory - acetylcholine

inhibitory - GABA

Question 29

what is acetylcholinesterase

Answer 29

• an enzyme located on the postsynaptic membrane
• it hydrolyses acetylcholine into choline and ethanoic acid
• these diffuse back across the cleft and enter the presynaptic neurone
• ATP is used to recombine the 2 chemicals into acetylcholine and repackaged into vesilces

Question 30

how could drugs affect synapses

Answer 30

• could be similar to the shape of the neurotransmitter so the channels would open when they aren’t meant to
• could block receptors on postsynaptic membrane
• could inhibit acetylcholinesterase
• could block calcium ion channels

Question 31

what are the roles of synapses

Answer 31

• ensure impulses travel in one direction (receptors are only present on postsynaptic membrane
• can allow an impulse from one neurone to be transmitted to a number of neurones (a single stimulus creates a number of simultaneous responses)
• a number of neurones may feed into the same synapse (many stimuli produce a single result)

Question 32

define summation

Answer 32

when the amount of neurotransmitter builds up sufficiently to reach the threshold which triggers an action potential

Question 33

define spatial summation

Answer 33

when a number of presynaptic neurones connect to one postsynaptic neurone
each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone

Question 34

define temporal summation

Answer 34

when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period
this builds up in the synapse until the quantity is sufficient to trigger an action potential

Question 35

what are the 2 main branches of the nervous system

Answer 35

CNS - brain and spinal cord

PNS (peripheral nervous system) - neurones that carry impulses to and from the CNS

Question 36

what 2 parts is the peripheral nervous system divided into

Answer 36

Somatic - motor neurones carry impulses from CNS to skeletal muscles under CONSCIOUS control

Autonomic - motor neurones carry impulses from CNS to cardiac muscle, smooth gut muscle and glands under UNCONSCIOUS control

Question 37

what 2 systems is the autonomic peripheral nervous system divided into
what are the neurotransmitters involved

Answer 37

Sympathetic - gets body ready for action “fight or flight”. the neurones secreted is noradrenalin

Parasympathetic - calms body down “rest and digest”. neurones secreted are acetylcholine

Question 38

what are the steps for the knee-jerk reflex

Answer 38

1) leg tapped below kneecap
2) stretches patellar tendon (stimulus)
3) initiates reflex arc that causes extensor muscle on top of thigh to contract
4) at the same time, relay neurone inhibits motor neurone of flexor muscle causing it to relax
5) so the extensor muscle is contracting and flexor hamstring muscle relaxing causing the leg to kick

Question 39

what happens during the blinking reflex

why do both eyes close as a result

Answer 39

1) cornea of eye irritated by foreign body
2) triggers impulse along a sensory neurone
3) impulse passes through a relay neurone in the lower brain stem
4) impulses sent along branches of the motor neurone to initiate a motor response to close eyelids
5) both eyes are closed because this is a consensual response

Question 40

in the brain, what does the cerebrum do? where is it located

Answer 40

the biggest part all over the top of the brain. split into 2 hemispheres

it controls voluntary actions like learning, memory, personality and conscious thought

Question 41

in the brain what does the pituitary gland do? where is it located?

Answer 41

stores and releases hormones that regulate many body functions

it’s quite central

Question 42

in the brain what does the hypothalamus do? where is it located?

Answer 42

regulatory centre for temperature and water potential

central

Question 43

in the brain what does the medula oblongata do? where is it located?

Answer 43

used in automatic control eg. breathing and heart rate

top of spinal cord, bottom of brain

Question 44

in the brain what does the cerebellum do? where is it located?

Answer 44

controls unconscious functions such as posture, balance and non-voluntary movement

back of brain

Question 45

Define spinal cord

Answer 45

Column of nervous tissues running up the back

Surrounded by spine for protection

Question 46

Why are reflex actions important for the survival of organisms

Answer 46

Avoid body being harmed and reduce severity of damage
The brain can deal with complex responses involuntary which reduces time
Reflexes are present at birth so provide immediate protection
The reflex arc is short so means it’s extremely fast

Question 47

for involuntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

Answer 47

structure: non-striated, smooth, spindle cell shaped, one nucleus per cell
slow speed of contraction and slow to fatigue
autonomic nervous system
examples: organ walls, blood vessels, iris, uterus
appearance: unstriped, uninucleated

Question 48

for skeletal/voluntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

Answer 48

structure: lots of nuclei, long, striated
speed of contraction: rapid and quick to fatigue
nervous system: somatic
examples: bulk of body muscle tissue
appearance: stripy, multinucleated

Question 49

for cardiac muscle, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

Answer 49

structure: branched, uninucleated, discs between cells, some striations
speed of contraction and fatigue: intermediate speed and never fatigues
nervous system: autonomic
examples: found only in the heart
appearance: some striations, uninucleated

Question 50

name the features of a cell in skeletal muscle

Answer 50

sarcolemma (cell-surface membrane)
sarcoplasm (cytoplasm)
mitochondria
myofibrils (cause contraction)
nucleus (many nuclei per cell)
sarcoplasmic reticulum (endoplasmic reticulum)
T tubules (a fold of the sarcolemma)

Question 51

describe the structure and function of muscle fibres in skeletal muscles

Answer 51

Muscle fibres are enclosed in a plasma membrane called sarcolemma
They contain a number of nuclei and are much longer than normal cells
They make the muscle stronger
Have lots of mitochondria to provide ATP for muscle contraction
Has a modified version of ER called sarcoplasmic reticulum which extends the muscle fibre and contains calcium ions

Question 52

what are myofibrils

what proteins are they made of

Answer 52

myofibrils are long, cylindrical organelles made of protein and specialised for contraction. they are lined up in parallel in the skeletal muscle

actin - thinner filament, 2 strands twisted around each other

myosin - thicker filament, consists of long, rod-shaped fibres

Question 53

in myofibrils, describe the different bands that can be seen

Answer 53

Because of the way the myofilaments are arranged, the myofibril appears to have dark and light bands, giving the muscles a striated appearance.
The dark bands consist of thick filaments (myosin) and some thin filaments (actin).
At the centre of the dark band is the H-zone, where only thick filaments are present.
The light bands, are the regions containing thin filaments only (actin), and are found between the dark bands.
There is a Z-line found at the centre of each light band where the sarcomere distance between each adjacent Z-line

Question 54

what is the sliding filament model

Answer 54

where myosin and actin filaments slide over one another to make the sarcomeres contract
the myofilaments themselves don’t contract

the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract

Question 55

In the sliding filament model, what happens to each of the bands of the myofibrils during contraction

Answer 55

The light bands become narrower
The Z lines move closer together, shortening the sarcomere
The H zone becomes narrower
Dark band remains same width

Question 56

What is the structure of myosin (thick bands)

Answer 56

They have globular heads that are hinged which allows them to move back and forwards

On the head is a binding site for each of actin and ATP

The tails are aligned together to form the myosin filament

Question 57

What is the structure of actin filaments (thin bands)

Answer 57

2 strands of actin wrapped around each other
a long strand of tropomyosin wrapped around the actin
attached to the tropomyosin are heads called troponin

Question 58

When a muscle is in resting state what has happened to the actin-myosin sites

Answer 58

They are blocked by tropomyosin
This means the myosin heads can’t bind to the actin
So the filaments can’t slide past each other
The muscle can’t contract

Question 59

describe what is happening when a muscle is stimulated to contract
(from the neuromuscular junction to muscle contraction)

Answer 59

1) An action potential arrives at a motor neurone
2) A neurotransmitter diffuses across the cleft and binds to the receptors on the sarcolemma
3) A wave of depolarisation spreads around the sarcolemma down the T-tubules to the sarcoplasmic reticulum
4) Causes sarcoplasmic reticulum to released stored calcium ions into the sarcoplasm
5) The influx of calcium ions triggers muslce contraction. They diffuse into the myofibril
6) Calcium ions bind to the troponin causing it to change shape
7) This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
8) This allows the myosin to bind to the binding site
9) An actin-myosin cross-bridge is formed
10) With the addition of ATP, the myosin head which is attached to the actin moves to the side in a rowing action

Question 60

What happens when a muscle stops being stimulated to contract

Answer 60

1) Calcium ions leave their binding sites on the troponin
2) the ions are moved by active transport back into the sarcoplasmic reticulum
3) Troponin molecules return to its original shape so the tropomyosin block the actin-myosin binding site again
4) Actin filaments slide back to their relaxed position which lengthens the sarcomere

Question 61

How is ATP used in muscle contraction

Answer 61

ATP is broken down by ATPase into ADP which releases energy.
This energy is used to move the myosin head which is moved along the actin filament to cause muscle contraction.
The energy is also used to remove the myosin head and position it in another place on the actin.

Question 62

what are the differences between a synapse and a neuromuscular junction (NJ)

Answer 62

-synapse is from a neurone to a neurone
NJ is from motor neurone to muscle

-synapse creates new action potential
NJ makes muscle contraction

-the neurone before the junction on the synapse is round and is called the synaptic knob
the neurone before the junction on the NJ is flat called the motor-end plate

Question 63

what are the similarities between a synapse and a neuromuscular junction (NJ)

Answer 63

• both involve neurotransmitters that have been released by exocytosis
• both have complementary receptors for that neurotransmitters

Question 64

where does the ATP supply come from for the neuromuscular junction

Answer 64

• aerobic respiration
• anaerobic respiration
• creatine phosphate (the phosphate from this can be added to ADP to make an ATP molecule)