neural communication 5.1.3 Flashcards
general structure of a neurone
dendrites= send impulses to the cell body
axon= sends impulses away from the cell body
cell body= releases neurotransmitters contains the nucleus
myelin sheath= insulation. Made by Schwan cells
node of Ranvier=gape between the myelin sheath
transducers
-a cell that converts one form of energy into another. e.g. sensory receptors to an electrical impulses
4 types of sensory receptors
- mechanoreceptors= pressure +movement e.g. Pacinian corpuscles
-chemoreceptors= chemicals e.g. smell and taste
-thermoreceptor=heat
-photoreceptors=light can be found in the retina
Pacinian corpuscles
-when pressure is appllied the membrane surrounding the neurone streches causing gaps between phospholipids,
-this opens sodium channels
-sod ium rushes in along electrochmical gradient generating an action potential
resting potential
- sodium-potassium pump moves 3 sodium ions out and 2 potassium ions in by active transport
-sodium ion channels closed and potassium ion channels are open allowing facilitated diffusion
-therfore membrane is more permeable to potassium ions - therefore the membrane is polarised.( more positive outside than inside)
-resting potential= -70
depolarisation
- stimulus causes sodium ion channels to open so sodium ions diffuse into the cell. (membrane is more permeable to sodium)
-when the potential difference reaches -55v, positive feedback occurs so more sodium ion channels open and more sodium ions diffuse into the cell.
-depolarisation occurs (inside more positive than outside). reaches+40v
repolarisation
- sodium ion channels close and potassium channels open. potassium diffuses out of the cell bringing the potential difference back to more positive than inside.
-there is a potential difference overshoot. making the cell hyperpolarised
-original potential difference is returns and resting potential is maintained by the sodium-potassium pump - reactionary period= recovery period. after action potential neurones cant be excited straight away
cholinergic synapse in neurotransmission
- action potential in pre-synaptic neurone causes depolarisation of the membrane therefore opening voltage-gated calcium ion channels to open
-calcium ions move down the electrochemical gradient causing acetylcholine vesicles to fuse with the membrane releasing ACTH by diffusion
-ACTH binds to complementary receptors on the post-synaptic neurone causing sodium channels to open - sodium ions diffuse into the post synaptic neurone, down the electrochemical gradient causing depolarisation triggering a new action potential
-ACTH left in the cleft is hydrolysed by acetylcholinesterase into aecetic acid + choline. sodium ion channels close
-mitochondria in the pre-synaptic neurone undergo respiration producing ATP which binds to acetate and choline reforming ATCH
synaptic divergences and convergence
- divergence=one neurone connects to many information can be dispersed to different parts of the body
-convergence= many neurones connect to one neurone. information can be amplified
types of summation
- spatial summation=many different neurones collective trigger a new action potential by combining neurotransmitters being released to generate a new action potential
- allows convergence =one post-synaptic cell receives impulses from a number of different presynaptic cells
-divergence= impulse from on presynaptic cell is spread over multiple postsynaptic cells - alos filkters out bavkground of low level stimuli
-temporal=one neurone releases neurotransmitters repeatedly over a short period of time to add up enough to exceed a threshold
-filters out background of low level stimuli
why can impulses only be transmitted one way
- receptors for neurotransmitters are only on the postsynaptic neurone
myelinated neurone vs unmyelinated neurone
- in myelinated neurones action potential jumps from one node to the next (saltatory conduction) .it is fast and travel long distances
-in non myelinated neurones. Action potential need to be generated along the whole axon
importance of frequency of stimuli
-If there is a stronger stimuli, the magnitude of the action potential does not get larger
-however= there will be a higher frequency of nerve impulses
all-or-nothing principle
-action potential is only generated if the stimulus reaches the threshold value of -55mv.
-action potential is the same magnitude regardless of the strength of the stimulus
inhibitory and excitatory synapses.
inhibitory=less likely to initiate a action potential
exicitory=more likely too
Sensory neurone
- Dendron present and links to the cell body;
-Cell body in the middle of the neurone; and not in the CNS; -dendrites don’t connect to the cell body;
-axon is shorter than the motor neurone;
-Neurone connects to the sensory receptor;
Motor neurone
-No dendrons;
-Cell body is at the end of the neurone; and in the CNS; dendrites are directly connected to the cell body;
- axon is longer than the sensory neurone;
Relay neurone
-short axon
-dendrites present
-found in the CNS
Saltatory conduction
-Membrane is only depolorised at the nodes of ranvier;
-creates a longer localised circuit; -increases the rate of impulse transmission;
Why does the synapse allow transmission in one direction
• Vesicles containing neurotransmitter are only found in the presynaptic knob;
• Receptors on the sodium voltage gated channels can only be found on the postsynaptic membrane;
• Calcium channel can only be found on the presynaptic membrane;
Outline the role of the synapse
-Allows neurones to communicate/cell signaling;
- Ensure transmission in one direction;
- Allows convergence/impulses from more than one neurone to be passed to a single neurone;
- Allows divergence/impulses from a single neurone to be passed to more than one neurone;
-Filters out ‘background’ of low level stimuli;
- Prevent fatigue/overstimulation;
-Allows many low level stimuli to be amplified;
