Zusammenfassung der Ressource
2.2 Neurons and Synaptic Transmission
- The structure and function of neurons
- Types of Neuron
- Sensory Neuron
- Carry messages from the peripheral nervous
system to the central nervous system.
- Relay Neuron
- Found between the sensory
input and motor
output/response.
- Mainly in the brain and spinal
cord and allow sensory and
motor neurons to
communicate.
- Motor Neuron
- Found in the CNS
- Connects the CNS to effectors such
as muscles and glands in order to
control muscle movement.
- When stimulated they release
neurotransmitters that bind to the
receptors on muscles to trigger a
response which lead to movement.
- Structure of a Neuron
- Cell Body
- Includes the nucleus
which contains the
genetic material.
- Axon
- Carries impulses in the form of an
electrical signal known as an action
potential, AWAY from the cell body.
- Myelin Sheath
- Insulates the axon to
protect it and speed up
electrical transmission.
- Dendrites
- Branch like structures that
receive nerve impulses from
neighbouring neurons or
sensory receptors
- Node of Ranvier
- Gaps between the myelin
sheath that speed up
transmission of impulses.
- Terminal buttons
- At the end of an
axon, communicate
with the next
neuron.
- Electrical transmission
- When a neuron is at resting state the inside
of a cell is negatively charged, compared to
the outside.
- When a neuron is activated by stimulus,
inside becomes positively charged causing
an action potential.
- This creates an electrical
impulse which travels
down the axon.
- Synaptic Transmission
- Excitation and Inhibition
- Neurotransmitters can have
one of two effects on
neighbouring neurons.
- Excitation
- Causes it to become
positively charged and
more likely to fire. DEPOLARISATION
- E.G Adrenaline
causes exhitation
- Inhibtion
- Causes an increased negative
charge and less likely to fire. HYPERPOLARISATION
- E.G Serotonin causes
inhibition in the
receiving neuron
- Summation
- Majority rules. The action potential will only be
triggered if the sum of the excitatory and inhibitory
signals when it reaches threshold.
- Synaptic vesicles containing
neurotransmitter are ONLY PRESENT on
presynaptic membrane.
- Receptors for the neurotransmitter ONLY
present on the postsynaptic membrane.
- Diffusion of the neurotransmitters mean they
can only go from high to low concentration.
- So can only move in ONE DIRECTION.
- Electrical impulse or action potentials
reach the presynaptic terminal.
- Impulse triggers release of neurotransmitters
- Neurotransmitters
released from vesicles
and cross the synapse
- - Diffuse across synapse
-Bind to receptor sites on
post synaptic neuron
- Stimulation of postsynaptic
receptors by neurotransmitters
result in either excitation or
inhibition
- Chemical message is converted
back into an electrical impulse.
- Neurotransmitters are broken down and
reabsorbed into the presynaptic neuron.