C2.2 Neural signalling
The nervous system and neurons
Sensitivity: ability to detect changes in environment (external/internal) and respond appropriately.
Sensitivity
– Individual cells (prokaryotes, unicellular animals/plants)
– Entire organisms (prokaryotes , Animals, Plants)
Changes = stimulus
Receptor detects stimulus
Response done by effector
– Receptor and effector often not close need internal communication
⮚ All neurons have cell body: Nucleus + cytoplasm
⮚ From cell body, very fine and long cytoplasmic fibres = Axon
⮚ CF specialized for transmission of information = impulses
⮚Speed of impulses = 30-120 meters per second !!!
– Nervous coordination extremely FAST
– Response to stimuli almost instantaneous
Reflex arc
Neurons – structure and function
Dendrons and axons
⮚ Dendrons carry nerve impulse from dendrite to cell body
⮚ Axons carry nerve impulse from cell body to dendrite
Myelin sheath and Nodes of Ranvier
Myelin is a lipid that prevents ions to go in/out of axon
Speeds up conduction of nerve impulse along axon
Motor neurons
Reflex arcs and reflex action
Reflex arcs
The pathway
Connects sense cell/organ (receptor)
with muscle or gland (effector)
Via neurones
Reflex action
The response
Rapid, automatic, short-lived response to stimulus
Involuntary (reflex)
Does not involve brain
Generation of the resting potential
\(Na^{+}/K^{+}\) pump: Active transport Na+ and K+ across cell membrane
\(Na^{+}\) OUT \(3 Na^{+}\) out
\(K^{+}\) IN 2 \(K^{+}\) in
Overall: more negative inside cell
(more positive outside cell)
Hence the RMP.
“Resting potential”
Potential of the membrane when neuron not conducting impulse
