5.3 Neuronal communication Flashcards
What is a synapse
Junction between two neurones
What chemical transmit impulses across synapse
Neurotransmitters
What is the function of synapses
Electrical impulses that cannot cross junction
Neurotransmitters send impulses between neurones/from neurones to effectors for excitatory or inhibitory response
Summation of sub threshold impulses
Describe the structure of a synapse
Presynaptic neurone ends in synaptic knob- lots of mitochondria, ER and vesicles of neurotransmitters
Synaptic cleft- gap which separates the axon of one neurone from the dendrite of the next neurone
What happens in the presynaptic neurone when an action potential is transmitted between neurones
Wave of depolarisation travels down presynaptic neurone, causing voltage gated calcium channels to open
Vesicles move towards and fuse with presynaptic membrane
Exocytosis of neurotransmitter into synaptic cleft
How do neurotransmitters cross the synaptic cleft
Simple diffusion
What happens in the postsynaptic neurone when an action potential is transmitted between neurones
Neurotransmitter binds to specific receptor on postsynaptic membrane
Sodium ion channels open
If influx of sodium ions raises membrane to threshold potential,action potential is generated.
What features are common to all sensory receptors
Act as energy transducers which establish a generator potential
Respond to specific stimuli
Describe the features of all neurones
Cell body - contains organelles and high proportion of RERR
Dendrons- branch into dendrites which caddy impulses towards the cell body
Axon - long,unbranched fibre carries nerve impulses away from cell body
Describe the structure and function of a sensory neurone
Usually unipolar
Transmits impulses from receptors to CNS
Describe the structure and function of a relay neurone
Usually bipolar
Transmits impulses between neurones
Describe the structure and function of a motor neurone
Multipolar
Transmits impulses from the relay neurones in the CNS to effectors
Describe the additional features of a myelinated neurone
Schwann cells- Wrap around axons
Myelin sheath- made from myelin rich membranes
Nodes of Ranvier- very short gaps between neighbouring Schwann cells where there is no myelin sheath
What 3 process Schwann cells are involved in
Electrical insulation
Phagocytosis
Nerve regeneration
What is resting potential
Potential difference(voltage) across neurone membrane when not stimulated Usually about -70mV in humans
How is resting potential established
Membrane is more permeable to K+ than Na+
Sodium potassium pump actively transports 3Na+ out of cell and 2k+ into cell
Requires ATP energy from respiration
Name the stages in generating an action potential
Depolarisation
Repolarisation
Hyper polarisation
Return to resting potential
What happens during de polarisation
Stimulus -> causes facilitated diffusion of sodium ions into cell down electrochemical gradient
p.d across membrane becomes more positive
If membrane reaches threshold potential of -50mv voltage gates Na+ channel opens
What happens during REpolarisation
Voltage-gated sodium ion channels close and voltage-gates K+ channel open
Facilitated diffusion of K+ ions out of cell down their electromechanical gradient
p.d across membrane becomes more negative
What happens during hyperpolarisation
- ‘Overshoot’ when K+ ions diffuse out =
What is resting potential
Resting axon on where the inside of axon always have a negative electrical potential compared to the outside of axon
What is the potential difference of resting potential
-70mV
Lower than the outside of the axon
What two factors are considered for the establishment of resting potential
Active transport of sodium and potassium ions
Differential membrane permeability
Explain the process of the AT of sodium and potassium ions
Uses carrier protein called sodium and potassium pump, present in membranes of neurone
Uses ATP , 3 sodium ions out for every 2 potassium ion in
More positive ions outside the axon
Creates electrochemical gradient
Explain the differential membrane permeability have on resting potential
Allow sodium and potassium ion to move via facilitated diffusion
Protein channels less permeable to sodium ions then potassium ions
Potassium faster rate > sodium
What is action potential
Occurs via a brief change in the distribution of electrical charge caused by rapid movement of sodium and potassium ion across axon membrane
Action potentials travel as a wave of depolarisation across the length of the neurone.
What happens into transmission along an axon
An action potential triggered in the neurone causes depolarisation of that section of the axon
Opening of sodium ion channels, influx generating an action potential
Previous section of the axon is in the repolarisation stage
Makes action potential discrete, impulse can only travel one direction
Define the channel proteins that allow sodium or potassium ions or diffuse through the cell membrane
Voltage gated channel proteins
Depending on electrical potential
Closed when axon membrane is in resting potential
What happens after the action potential has been initiated in the neurone
Depolarisation moves in one direction along the entire length of an axon like a wave
What goes on in the transmission of electrical impulses along an axon
The action potential(AP) causes depolarisation of the section of the axon
Current causes sodium ion channels causes an influx of sodium, generating an AP
Previous section of axon in repolarisation (closing of sodium ion channel,opening of potassium ion)
Travels in one direction,discrete
What is the all or nothing principle
Impulse is only transmitted if the initial stimulus is sufficient to increase the membrane potential above a threshold potential
What happens if the stimulus is weak
The receptor cells won’t be sufficiently depolarised as a result the sensory neurone will not be depolarised
What faceless affect the speed of conduction across a neurone
Myelination
Diameter of an axon
Temperature
How does diameter affect the speed of conduction
Impulses will be conducted at a higher speed along with a thicker axon as they will have an axon membrane, greater SA, greater rate of diffusion via protein channels
How does temperature affect the speed of conduction
Cooler temperature means there is less kinetic energy available for facilitated diffusion of potassium and sodium ions
What is a summation
Sometimes impulses is insufficient to generate an action potential in the post synaptic neurone, therefore the effect of multiple impulses can be added to gen an action potential
What are the benefits of summation
Effect of a stimulus can be magnified
Combination of different stimuli can trigger a response
Avoids the NS to being overwhelmed
What are the 2 types of summation
Temporal and spatial
Temporal
Multiple impulses arrive within quick succession
Spatial
Multiple impulses arriving simultaneously at different synaptic knobs
What does excitory neurotransmitters have an effect on the post synaptic neurone
Stimulate the generation of an action potential by opening the sodium ion channels in the post synaptic membrane, causing depolarisation
What affect does inhibitory neurotransmitter
Prevent the generation of an action potential
Opening of potassium ion channels in the post synaptic membrane resulting in hyper-polarisation
What is the cell membrane of muscle fibres and the muscle cells cytoplasm
Sarcolemma
Sarcoplasm
How are transverse tubles made
Bits of sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm. These folds are called T tubles and spread electrical impulses throughout the sarcoplasm to reach parts of muscle fibre
What do muscle fibres contain
Sarcolemma
Sarcoplasm
Sarcoplasmic reticulum
Myofibrils
What do myofibrils contain
Thick myosin filaments - A bands
Thin actin filaments - I bands
Many short units called sarcomere
What are the features of a MYOSIN filaments
Globular heads that are hinged
Binding site for actin and for ATP
What are the features of an actin filament
Binding site for myosin
2 other proteins called tropomyosin and troponin are found between actin filaments. Proteins attach to each other and help myofilaments move past each other
What occurs in the myofibrils when at rest
Muscle actin myosin binding site is blocked by tropomyosin
Held in place by troponin
List the 5 structures of the brain
Hypothalamus - controls body temperature
Cerebrum - allows you to see,hear, learn and think
Pituitary gland - controls hormone release by body glands
Medulla Oblongata - controls BR and HE
Cerebellum - co ordinates muscle,balance and posture
Which part of the nervous systems controls unconscious activities
Autonomic nervous system e.g digestion
Explain the process of muscle contraction
Action potential from motor neurone,stimulates a muscle cell,depolarises sarcolemma
Spread down t tubles to the sarcoplasm reticulum
SR releases stored calcium ions into the sarcoplasm
Calcium ion binds onto troponin,change shape
Pulls out tropomyosin out
Exposes binding site
Calcium ions activate ATPase which breaks down ATP for muscle contraction
Provides energy to break actin myosin cross bridge
State one internal factor which causes a response in: plant and animal
water potential in plant cells Blood pH
Describe how cells are able to communicate with one another
Cells releases a chemical which has an effect on a target cell
how and why is co ordination is required in multicellular organisms
Organism needs to respond to internal/external changes for survival
Occurs by electrical impulses/nervous system in animals
Different organs work together to ensure homeostasis e.g brain and skin in temperature control
Cells communicate through cell signalling
State the difference between the function of a motor and a sensory neurone
sensory neurone transmit impulses to the CNS/from receptor whereas motor neurones transmit impulses from the CNS to an effector
Describe the difference between a myelinated and non myelinated neurone
Axon of a myelinated neurone is covered in myelin, Electrical insulator, sheath is formed formed by Schwann cells, gaps in the myelin sheath known as nodes of Ranvier, saltatory conduction, impulse transmits much faster
Describe the role of a sensory receptor in the body
Detect stimuli, convert energy into a nervous impulse
State the transformation that takes place in a cone cell
Light energy is converted into a nervous impulse/action poetical
Explain how your body detects that your finger has touched a pin
Touch pin -> exerts mechanical pressure on your skin, pacnian corpuscle found within skin detects pressure -> changes shape of Pacinian corpuscle -< stretch mediates sodium channel in neuronal membrane stretches -> channel widens -> sodium ion diffuse into a membrane -> membrane is depolarised/ generator potential created
State how the body detects the difference between a small and a large stimulus
The larger the stimulus the more frequent the nerve impulse/action potential
State the difference between depolarisation,repolarisation and hyper polarisation
Depolarisation – voltage/potential difference becomes more positive; repolarisation – voltage/potential difference becomes more negative hyperpolarisation – when potential difference is lower than resting potential
Describe what would happen if a refractory period did not exist
The axon could be immediately depolarised after an action potential (1); therefore the action potential could travel backwards / in both directions / not reach target cell (1)
Describe how the movement of ions establishes an action potential
Resting potential: sodium potassium pump actively transports sodium and potassium ions, 3 NA+ move out 2 KA+ move in, ka + can diffuse through potassium ion channels, sodium ions can not
More positive ions outside than inside the axon
