U1T3 - Keywords (2) Flashcards
Animals
Nervous System
Consists of CNS + many peripheral nerves.
CNS
Brain + spinal cord. Integrates incoming info from peripheral nerves + coordinates effective response.
Centrons
Contains nucleus, mitochondria + other organelles + Nissi’s granules.
Dendrons
Fine threads of cytoplasmic threads which deliver impulses towards cell body in neurone.
Axons
Fine cytoplasmic threads which carry impulses away from cell body in neurone. Terminate in synaptic bulbs.
Sensory neurones
Have dendrons + axons with similar long length so cell body quite central. Carry impulses from receptors to CNS.
Motor neurones
Long axons with dendrites. Carry impulses from CNS to effectors.
Dendrites
Short dendrons
Relay neurones
Shorter overall, shorter dendrons + axons. Connect neurones within CNS.
Myelinated Neurone
Neurone wrapped in Schwann cells, created electrically insulating myelin sheath rich in lipid myelin. Between each SC, nodes of Ranvier exposed. Speed of impulse transmission greatly increased as local current only exists as nodes of Ranvier.
Nodes of Ranvier
Small patch of neurone membrane exposed in myelinated neurone.
Potential Difference
Difference in charge between 2 regions (e.g. inside + outside cell).
Polarised Cells
Cells with potential difference across membrane.
Neurones
Have excess of positively charged ions surrounding them, resulting in potential diff of -70mV. More + charged cells outside cell + cell contains many proteins which are - charged. Have cell body + extended nerve fibre.
Resting Potential
PD across CSM. (Neurones polarsed as electrochemical gradient across CSM) When neruones have excess of + charged ions around them, resulting in pot diff of -70mV. More + charged cells outside cell + cell contains many proteins which are - charged. Maintained as CSM mostly impermeable to flow of sodium ions when not conducting impulse.
Threshold Potential
-55mV in mammals. Is met when enough transmembrane proteins + positively charged ions open.
Action Potential
When PD across membrane reaches peak of around +40mV after stimulus applied and threshold potential reached and neurone becomes depolarised.
Sub Threshold Stimulus
A stimulus which doesn’t cause threshold potential to be reached and action potential isn’t fired. Display all or nothing principle in this case.
All or Nothing Principle
Action potential always peaks at same value regardless of stimulus intensity. More intense stimuli result in more frequency firing of action potentials.
Repolarisation
After depolarisation, neurone actively re-establishes it’s resting potential using this. Positively charged ions both diffuse and are actively pumped out of neurone into surrounding fluid.
Refractory Period
Period of time taken for repolarisation. Neurone can’t be stimulated during this time. Limits speed at which action potential fires + so allows coordinator (CNS) to detect each action potential as discrete event. Also ensures impulses travel in 1 direction.
Impulse
Propogation of action potentials along axon by flow of current in a series of localised currents.
Voltage Gated Ion Channels.
Transmembrane proteins. Able to sense localised changes in charge + respond by changing shape so positively charged ions flow into cell, resulting in depolarisation, making action potential more likely.
Saltatory Conduction
Due to fast transmission speed of myelinated neurone, localised currents jump from one node to the next, myelin sheath prevents depolarisation in myelinated zones, hence why it must jump to nodes of Ranvier so fast.
Synapse
Junction between axon of 1 neurone + dendrite of adjacent as they aren’t in physical contact. Electrical signals can jump across this gap. Includes synaptic bulb, synaptic cleft + post-synaptic neurone. Filter out low level background stimuli to prevent overload + overstimulation.
Tropism
Growth response
Acetylcholine
Primary neurotransmitter in CNS. Acts to make depolarisation more likely, found in excitatory synapses as its actions results in EPSP. Broken down into choline + ethanoic acid by ecetylcholinesterase.
EPSPs
Excitatory Post Synaptic Potential.
GABA
Neurotransmitter. Associated with IPSPs. Released at inhibitory synapses. Hyperpolarises neurone membrane resulting in lower PD across membrane which reduces likelihood of action potential so more + ions must move in to reach threshold potential. Reduces anxiety.
IPSPs
Inhibitory Post Synaptic Potentials. Central in reducing anxiety through reducing num of impulses which reach brain + reducing possibility of reflex actions being prevented.
Ciliary Muscles
Ring of muscle surrounding lens. Contains muscular ring of ciliary muscle around eye. Suspensory ligaments extend from ciliary body + hold lens in place. Adjusts lens shape to focus light rays.
Lens
Flexible fluid filled sac. Transparent biconcave structure with refractive properties which refracts light + focuses light rays on retina.
Refracted
Bent.
Retina
Inner layer of eyeball containing light sensitive receptor cells (rods + cones), bipolar cells + ganglion cells.
Visual Transduction
The process of converting light energy into an energy potential occurring.
Bleaching
When light strikes rhodopsin, causing it to break down into retinal + opsin.
Retinal Convergence
Many rods can synapse onto 1 bipolar sense resulting in high rod sensitivity so summation can occur.
Summation
Small amount of neurotransmitter released from few rod cells can be added together to open enough ion channels in bipolar cell to form action potential. Explains why rods provide decreased visual acuity as image formed is due to patch of cells being stimulated rather than single cell. Provides complexity + flexibility of synapses.
Light Adapted Eye
When rhodopsin almost entirely broken down as cones used for vision in bright light.
Dark Adapted Eye
After 30 mins in dark room so rhodopsin has reformed to allow rods to be sensitive.
Binocular Vision
Use of 2 eyes to form image, allows better distance perception + stereoscopic vision so brain can form 3D image. Distance between eyes + placement of head on animal determine visual field. Prey animals have eyes on side of head to have wide vision for predators.
Sarcolemma
Outer membrane of muscle fibre. Here, synapses of motor neurones make contact in motor end plates. Also forms T-tubules.