5.1.3 Neuronal Communication COMPLETE Flashcards
DEFINITION- Neurone
Specialised cells that transmit action potentials from one pat of the body to another
DEFINITION- Cell Body
Contains the cells nucleus and other organelles
DEFINTION- Dendrites
Small extensions of cell body, create large SA and carry impulse towards cell body as receive them
DEFINITION- Axon
Single long fibre that carries nerve impulses away from the cell body
DEFINITION- Axon Terminal
Release the neurotransmitters into the synapse
DEFINITION- Motor Neurone
Carries action potential from the CNS to the effector, ie. muscle or gland
Short Dendtrites, Long axon
DEFINTION- Sensory Neurone
Carries an action potential from sensory receptor to the CNS
Long dendrites, Short Axon
DEFINITION- Relay Neurone
Connects the sensory and motor neurone
Short axon and dendtrites
DEFINITION- Polarised
Produce positive and negative charges at opposite ends
Depolarisation
A reduction in the difference of electrical potential across the plasma membrane. Cell becomes more positively charged as more NA ions flood in, positive feedback. Voltage gated NA channels have opened
Resting Potential
-70V, the potential difference across a membrane when its at rest, maintained by Na and K pumps. Some K channels still open
DEFINITION- Threshold Potential
Critical level to which a membrane potential must depolarise to, to initiate action potentials
DEFINITION- Action Potential
Change in electrical potential associated with the passage of an impulse along a membrane
DEFINITION- Hyperpolarisation
K ion gates are slow to shut so too many pass through reducing membrane potential, Na/K pump restores the resting potential.
DEFINITION- Refractory Period
Short period of time where no action potentials are generated
DEFINITION- Voltage Gated Channels
Voltage across a membrane will open/ close the gates
DEFINITION- Local Currents
Movements of ions along a neurone close to the cell surface membrane
DEFINITION- Saltatory Conduction
When an action potential only jumps through the Nodes of Ranvier in myelinated neurones
DEFINITION- Nodes of Ranvier
The gaps between the Schwann Cells
DEFINITION- Myelin Sheath
Fatty, insulative layers of Schwann cells wrapped around the axon
DEFINITION- Neurotransmitter
A chemical substance which is released at the end of a nerve fibre when a nerve impulse has arrived
DEFINITION- Cholinergic Synapse
Synapses that use Acetylcholine as their neurotransmitter
DEFINITION- Synaptic Knob
Where an action potential is converted into a chemical message, interacts with the recipricant neurone
DEFINITION- Acetylcholine
A neurotransmitter used at the neuromuscular junction
DEFINITION- Acetylcholinesterase
The enzymes that catalyses the breakdown of acetylcholine
DEFINITION- Exocytosis
The release of cell contents via a vesicle through diffusion out the exterior membrane
DEFINITION- All or nothing
Unless the threshold potential (-50V) is reached, no action potential will form
DEFINITION- Summation
Low level stimuli can be amplified and push multiple neurones into one
DEFINITION- Myelinated Neurone
Transmits action potentials faster as only travel through the Nodes of Ranvier (100m/s). Has long local currents along with saltatory conduction. Voltage gated NA channels only at the gaps.
DEFINITION- Demyelination
Damage to the myelin sheath which slows/ stops impulses. Can cause neurological problems
DEFINITION- Multiple Sclerosis
Progressive disease, causes damage to myelin sheath and affects the CNS
DEFINITION- Acclimatisation
When the synapse runs out of vesicles due to a prolonged strong stimulus, avoids overstimulation
Adaptions of Neurones
LONG- transmit over long distance NA/K PUMPS- actively transports 3Na out and 2K in using ATP GATED ION CHANNELS- control the entry and exit of ions ORGANELLES IN CELL BODY- produce the neurotransmitters MYELIN SHEATH- insulates so becomes faster
How resting potential is maintained
Phospholipid bilayer is impermeable to ions
channel protein pumps 3Na out and 2K in using ATP
second K ion channel so moves faster rate down electrochemical gradient
inside axon is more negative
Effect of a stimulus on resting potential
triggers the opening of Na channel proteins, casuing a tempory reversal and Na diffuses in
down the electrochemical gradient
K Channels opening
At 40mV Na channels close but K channels open, both voltage gated
Repolarisation
K ions diffuse out of the cell down the electrochemical gradient. Inside of the cell becomes negative again so even more K channels open
Non Myelinated Neurones
Uses local currents and has a refractory period. Action potential moves across as Na gates open as the Na ions moves along the axon away from high conc.
Factors Affecting Transmission of action potential
MYELIN SHEATH- increases transmission speed due to saltatory conduction, voltage gated Na channels only at nodes of ranvier.
DIAMETER OF AXON- increased diameter means increased speed due to lessened leakage and resistance.
TEMP- increases diffusion rate
REFRACTORY PERIOD- allows recovery, prevents overlap and keeps it to one direction
Sensory Receptors
- Specialised cell that detects change in our surroundings
- Specific to single types of stimuli
- Energy Transducers convert one form of energy into elecctrical
The Pacinian Corpuscle
- Mechanoreceptor in the skin that detects mechanical stimuli
- The end of the senory neurone is found in the centre of the corpuscle and is surrounded by layers of connective tissue called lamella. seperated by gel
How Pacininian corpuscles work
- When pressure is exerted they change shape
- Membrane stretches and Na ion channels open
- This depolarises the membrane and forms a generator potential
- If large enough it’ll initiate and action potential
- This is then transmitted along the CNS
Cholinergic Synapses
- Use Acetylcholine as a neurotransmitter
- Action potentials can’t cross the synpse so they release neurotrasnmitters
Transmission across the Synpase
- Action potential arrives at the synaptic knob
- voltage gated Ca ion channels open and they diffuse into the synpatic knob
- Causes Synaptic vesicles to move and fuse with presynaptic membrane
- Acetylcholine released by exocytosis and they diffuse across the cleft binding to Na+ receptors on post synaptic membrane
- Na channels open and Na+ diffuse across postsynaptic membrane into the postsynaptic neurone
- A generator potential is created, if there is a sufficent number and it reaches the threshold potential a new action potential is created
Acetylcholinesterase
Is the enzyme in the synaptic cleft that breaks down the acetylcholine on the postsynaptic membrane.
Breaks down into ethanoic acid and choline
Roles of the Synpapse
- Transmit Information
- Unidirectional
- Act as junctions
- Summation
- Acclimatisation
- Learning
Transmit information
Convey impulse from one neurone to the next
Unidirectional
Postsynpatic membrane has receptors, presynaptic membrane has vesicles. So only moves in one direction
Act as junctions
DIVERGENCE- allows single stimulus to create many responses
CONVERGENCE- Allows a number of impulses to be combined into a single one e.g. retina
Summation
TEMPORAL- Low level signals can be amplified, if persistant itll cause the release of many vesicles
SPATIAL- Also casued if several presynaptic neurones ech release acetylcholine into one synapse.
Acclimatisation
If a stimulus is powerful and prolonged a synapse may run out of vesicles containing neurotransmitter. Said to be fatigued so no longer responds, prevents overstimulation
Learning
It is believed that synapses have a role in the brain and allow the recall of events.
