Neurones and Synapses
Neurones:
-Motor Neurones: carry impulses from the CNS( brain or spinal cord) to effectors (muscles and
glands)
-Sensory Neurones: carry impulses from receptors to the CNS
-Connector: (relay, association or intermediate) neurones – connect neurones within the CNS
Function: To conduct nerve impulses
-Nerves are bundles of neurones
Axon: Transmits impulses away from the cell body (in motor neurones entire nerve fibre is an axon)
Dendron: Carries impulses to the cell body
Dendrites: very small extensions that can conduct impulses into a dendron or into the cell body
directly
Synaptic bulbs: Axons terminate in synaptic bulbs
Myelinated: Dendrons and axons are covered with a myelin sheath, (myelin sheath is both protective
and serves to speed up nervous conduction.)
Schwann Cells: forms myelin sheath
Nodes of Ranvier: Small gaps between Schwann Cells in the myelin sheath
The Resting Potential
-The potential difference across the cell surface membranes of neurones, neurones are polarised.
-Excess of positively charged ions (Na+) outside the membrane compared to the inside. At rest,
outside is positive relative to inside, around 70mV potential difference.
-This differential is maintained as the cell surface membrane is largely impermeable to the flow of
sodium ions when not conducting an impulse.
Action Potential
-When a neurone is stimulated the cell surface membrane becomes permeable to ions
Resting potential with inside of axon -70mV relative to outside.
Membrane becomes permeable and positive ions diffuse into the axon- starting to become
polarised
At -55mV gated channels open and positive ions flood in at a rapid rate. Rapid depolarisation
o the membrane takes place. Inside becomes +40mV relative to outside= action potential.
Positive ions diffuse out and are also pumped out of the axon. Refractory period as the
membrane cannot become polarised again until resting potential is restored. Slight
overshoot at the end, axon membrane becomes slightly more negative than the normal
resting period (hyperpolarisation)
Resting potential is restored and axon can conduct another nerve impulse if needed.
Neurones:
-Motor Neurones: carry impulses from the CNS( brain or spinal cord) to effectors (muscles and
glands)
-Sensory Neurones: carry impulses from receptors to the CNS
-Connector: (relay, association or intermediate) neurones – connect neurones within the CNS
Function: To conduct nerve impulses
-Nerves are bundles of neurones
Axon: Transmits impulses away from the cell body (in motor neurones entire nerve fibre is an axon)
Dendron: Carries impulses to the cell body
Dendrites: very small extensions that can conduct impulses into a dendron or into the cell body
directly
Synaptic bulbs: Axons terminate in synaptic bulbs
Myelinated: Dendrons and axons are covered with a myelin sheath, (myelin sheath is both protective
and serves to speed up nervous conduction.)
Schwann Cells: forms myelin sheath
Nodes of Ranvier: Small gaps between Schwann Cells in the myelin sheath
The Resting Potential
-The potential difference across the cell surface membranes of neurones, neurones are polarised.
-Excess of positively charged ions (Na+) outside the membrane compared to the inside. At rest,
outside is positive relative to inside, around 70mV potential difference.
-This differential is maintained as the cell surface membrane is largely impermeable to the flow of
sodium ions when not conducting an impulse.
Action Potential
-When a neurone is stimulated the cell surface membrane becomes permeable to ions
Resting potential with inside of axon -70mV relative to outside.
Membrane becomes permeable and positive ions diffuse into the axon- starting to become
polarised
At -55mV gated channels open and positive ions flood in at a rapid rate. Rapid depolarisation
o the membrane takes place. Inside becomes +40mV relative to outside= action potential.
Positive ions diffuse out and are also pumped out of the axon. Refractory period as the
membrane cannot become polarised again until resting potential is restored. Slight
overshoot at the end, axon membrane becomes slightly more negative than the normal
resting period (hyperpolarisation)
Resting potential is restored and axon can conduct another nerve impulse if needed.
