M5, C13 Neuronal Communication Flashcards
Give an example of a stimulus in the internal environment and external environment
interenal - water potential, ion levels, temperature, blood glucose levels, cell pH
external - temperature, light intensity, humidity, new or sudden sound
Describe the nervous system
- 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
define:
a) sensory neurones
b) relay neurones
c) motor neurones
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
give two types of effector cells
muscle
gland
what is the basic steps impulses go through
receptor - sensory neurone - relay neurone - motor neurone - effector
what are the 4 main parts of a neurone and describe each part
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
define receptors
specialised cells that can detect changes in the body’s internal and external environment
define generator potential
start of the nerve impulse
receptors convert the energy of the stimulus into the generator potential
define transducers
give some examples
receptors which convert energy of the stimulus into a nerve impulse
- photoreceptors (light energy)
- thermoreceptors (thermal energy)
- mechanoreceptors (kinetic energy)
- chemoreceptors (chemical energy)
define pacinian corpuscle
specific sensory receptors that detect mechanical pressure
how does the pacinian corpuscle detect mechanical pressure? (5 steps)
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.
How is the resting potential established and maintained in neurones
- 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.
Why is a neurone active even though it is said to be resting
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
how is an action potential generated
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
define localised circuit
diffusion of sodium ions sidewards
how is the action potential transmitted along the cell
- 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
what is the refractory period during the action potential
- delay between one action potential and another
- prevents action potential travelling backwards
- caused by the time taken to restore resting potential
what is the structure of myelinated neurones
Have Schwann cells wrapped around their axons and dendrons.
The Schwann cells have a fatty substance called myelin in their membrane.
what are the gaps called between myelinated neurones
nodes of Ranvier
what is saltatory conduction
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
what increases the speed of conduction of action potentials
myelination
axon diameter (bigger diameter means less resistance)
temperature (diffusion increases with a higher temp until around 40 degrees where the proteins will denature)
what is the all-or-nothing principle
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
How are impulses transmitted across a synapse
- 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
define synapse
the junction between two neurones
what is the actual gap called between 2 neurones
synaptic cleft
define neurotransmitter
a chemical that diffuses from one neurone to the next
what are the 2 types of neurotransmitter
Excitatory - result in depolarisation of the postsynaptic membrane = action potential
Inhibitory - result in hyperpolarisation of the postsynaptic membrane - no action potential
give an example of a excitatory neurotransmitter and a inhibitory neurotransmitter
excitatory - acetylcholine
inhibitory - GABA
what is acetylcholinesterase
- 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
how could drugs affect synapses
- 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
what are the roles of synapses
- 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)
define summation
when the amount of neurotransmitter builds up sufficiently to reach the threshold which triggers an action potential
define spatial summation
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
define temporal summation
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
what are the 2 main branches of the nervous system
CNS - brain and spinal cord
PNS (peripheral nervous system) - neurones that carry impulses to and from the CNS
what 2 parts is the peripheral nervous system divided into
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
what 2 systems is the autonomic peripheral nervous system divided into
what are the neurotransmitters involved
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
what are the steps for the knee-jerk reflex
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
what happens during the blinking reflex
why do both eyes close as a result
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
in the brain, what does the cerebrum do? where is it located
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
in the brain what does the pituitary gland do? where is it located?
stores and releases hormones that regulate many body functions
it’s quite central
in the brain what does the hypothalamus do? where is it located?
regulatory centre for temperature and water potential
central
in the brain what does the medula oblongata do? where is it located?
used in automatic control eg. breathing and heart rate
top of spinal cord, bottom of brain
in the brain what does the cerebellum do? where is it located?
controls unconscious functions such as posture, balance and non-voluntary movement
back of brain
Define spinal cord
Column of nervous tissues running up the back
Surrounded by spine for protection
Why are reflex actions important for the survival of organisms
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
for involuntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope
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
for skeletal/voluntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope
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
for cardiac muscle, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope
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
name the features of a cell in skeletal muscle
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)
describe the structure and function of muscle fibres in skeletal muscles
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
what are myofibrils
what proteins are they made of
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
in myofibrils, describe the different bands that can be seen
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
what is the sliding filament model
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
In the sliding filament model, what happens to each of the bands of the myofibrils during contraction
The light bands become narrower
The Z lines move closer together, shortening the sarcomere
The H zone becomes narrower
Dark band remains same width
What is the structure of myosin (thick bands)
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
What is the structure of actin filaments (thin bands)
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
When a muscle is in resting state what has happened to the actin-myosin sites
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
describe what is happening when a muscle is stimulated to contract
(from the neuromuscular junction to muscle contraction)
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
What happens when a muscle stops being stimulated to contract
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
How is ATP used in muscle contraction
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.
what are the differences between a synapse and a neuromuscular junction (NJ)
-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
what are the similarities between a synapse and a neuromuscular junction (NJ)
- both involve neurotransmitters that have been released by exocytosis
- both have complementary receptors for that neurotransmitters
where does the ATP supply come from for the neuromuscular junction
- aerobic respiration
- anaerobic respiration
- creatine phosphate (the phosphate from this can be added to ADP to make an ATP molecule)
