17/10/25
Neuron Structure and Intracellular Signal Transmission
The Brain and Behaviour
Main Points:
● Specialisation of cells, different environments of different types of cells and cells indirect communication with
the outside world makes a nervous system important
● The two main systems which coordinate activity include the endocrine system and nervous system
● The nervous system involves the generation and transmission of electrical impulses to reach specific target
cells and modify the activity of certain cells
● Endocrine system secretes hormones into the bloodstream which deliver a slow overall reaction to reaction
activities
● The nervous system is specialised to deliver electrical impulses between two cells and thus deliver a faster
and more coordinated reaction
● They have a unique shape and structure to the typical cell
● Cells cannot store energy and thus must have glucose and oxygen supplied constantly otherwise they stop
working and die within the span of a few minutes.
● Neurons do not divide, instead they emerge from neuron stem cells
Supporting cells:
● Glial cells create a protective environment for neurons and also develop from neural stem cells including the
astrocytes, microglia and oligodendrocytes
● Astrocytes form part of the Blood brain barrier and carry nutrients from the blood to the neuron, remove
waste products away from the neuron and hold the neurons in place
● Microglia are smaller and release chemicals that aid the repair of damaged neurons and performs
phagocytosis
● Oligodendrocytes wrap themselves around axons and produce the myelin sheath in the CNS
Resting potential:
● Ions concentrations differ from the inside and the outside of the cell, if the membrane were non permeable
then no electrical activity would happen but protein channels in the membrane open up to let ions in and out
Sodium/potassium pump:
● channels work against equilibrium with potassium being let in and kicking out sodium ions, this requires
ENERGY
Features of an action potential:
● Ion specific channels in the membrane can open up either by chance or stimulation to facilitate the
movement of ions
● Action potential caused by processes of depolarisation starting from the axon pillock and travelling down the
axon. The reason why it doesn’t go backwards is because after the AP has occurred, it is relatively harder to
depolarise again unlike the next membrane which is still at resting potential.
● Properties of the action potential include not being able to decay, so it stays strong enough to propagate
down the axon, it’s fast, it’s an all or nothing thing
● Saltatory conduction -> at each node of Ranvier after each myelin sheath portion, a new AP is generated so
the transmission down the axon jumps (the myelin sheath ensures smooth and sufficient conduction)
● So many Na+ ions enter the membrane that the cell reaches complete depolarisation, this will trigger every
Na+ channel to close up and K+ channels to open to let potassium out until the membrane repolarises. Since
there are fewer K+ ions inside the cell than outside, this causes some hyperpolarisation
● If the membrane potential at the axon hillock remains below -50 mV the resting potential returns but if it gets
above this threshold then it’ll trigger more Na+ channels in the axon hillock to open, creating an action
potential
● If positive ions enter or negative ones leave, the cell becomes depolarised and if negative ions enter or
positive ones leave this leads to hyperpolarisation
Neuron Structure and Intracellular Signal Transmission
The Brain and Behaviour
Main Points:
● Specialisation of cells, different environments of different types of cells and cells indirect communication with
the outside world makes a nervous system important
● The two main systems which coordinate activity include the endocrine system and nervous system
● The nervous system involves the generation and transmission of electrical impulses to reach specific target
cells and modify the activity of certain cells
● Endocrine system secretes hormones into the bloodstream which deliver a slow overall reaction to reaction
activities
● The nervous system is specialised to deliver electrical impulses between two cells and thus deliver a faster
and more coordinated reaction
● They have a unique shape and structure to the typical cell
● Cells cannot store energy and thus must have glucose and oxygen supplied constantly otherwise they stop
working and die within the span of a few minutes.
● Neurons do not divide, instead they emerge from neuron stem cells
Supporting cells:
● Glial cells create a protective environment for neurons and also develop from neural stem cells including the
astrocytes, microglia and oligodendrocytes
● Astrocytes form part of the Blood brain barrier and carry nutrients from the blood to the neuron, remove
waste products away from the neuron and hold the neurons in place
● Microglia are smaller and release chemicals that aid the repair of damaged neurons and performs
phagocytosis
● Oligodendrocytes wrap themselves around axons and produce the myelin sheath in the CNS
Resting potential:
● Ions concentrations differ from the inside and the outside of the cell, if the membrane were non permeable
then no electrical activity would happen but protein channels in the membrane open up to let ions in and out
Sodium/potassium pump:
● channels work against equilibrium with potassium being let in and kicking out sodium ions, this requires
ENERGY
Features of an action potential:
● Ion specific channels in the membrane can open up either by chance or stimulation to facilitate the
movement of ions
● Action potential caused by processes of depolarisation starting from the axon pillock and travelling down the
axon. The reason why it doesn’t go backwards is because after the AP has occurred, it is relatively harder to
depolarise again unlike the next membrane which is still at resting potential.
● Properties of the action potential include not being able to decay, so it stays strong enough to propagate
down the axon, it’s fast, it’s an all or nothing thing
● Saltatory conduction -> at each node of Ranvier after each myelin sheath portion, a new AP is generated so
the transmission down the axon jumps (the myelin sheath ensures smooth and sufficient conduction)
● So many Na+ ions enter the membrane that the cell reaches complete depolarisation, this will trigger every
Na+ channel to close up and K+ channels to open to let potassium out until the membrane repolarises. Since
there are fewer K+ ions inside the cell than outside, this causes some hyperpolarisation
● If the membrane potential at the axon hillock remains below -50 mV the resting potential returns but if it gets
above this threshold then it’ll trigger more Na+ channels in the axon hillock to open, creating an action
potential
● If positive ions enter or negative ones leave, the cell becomes depolarised and if negative ions enter or
positive ones leave this leads to hyperpolarisation
