NERVOUS SYSTEM
Human nervous system
Organisation of the nervous system
Autonomic nervous system
Structure of a typical neuron
Structure of neurons
* sensory neuron: transmit external stimuli (light, touch, smell) or internal conditions (blood pressure, muscle tension).
* interneuron: in the brain or ganglia for integration of sensory input.
* motor neuron: transmit signals to muscle cells causing them to contract.
MEMBRANE POTENTIAL
Membrane potential is the difference in voltage or electric potential between the inside and outside of a cell.
Resting potential and action potential
SYNAPSE
SYNAPSE
Synapse is a junction where each branched end of an axon transmits information to another cell.
Structure of a synapse
Consists of:
(i) Presynaptic neuron. Consists of synaptic knob which contain vesicles. Vesicles contain neurotransmitter. Examples of neurotransmitter are acetylcoline and noradrenalin. Also embedded on the presynaptic membrane are the voltage-gated calcium channels.
(ii) Synaptic cleft. The gap of less than 50 nm separates the presynaptic neuron from the postsynaptic neuron.
(iii) Postsynaptic neuron. There are natrium channels embedded on the postsynaptic membrane. Receptors are found on the ligand gated ion channels.
Transmission of impulse across synapse
The synaptic knob contains vesicles with neurotransmitter/ noradrenalin/ acetylcholine.
When the impulse reaches the synaptic knob, the voltage-gated calcium channels at the
presynaptic membrane are induced to open.
Calcium ions from
extracellular fluid diffuses into the synaptic knob. The increase in the concentration of calcium ions, trigger the fusion of vesicles to the presynaptic
membrane. The vesicles rupture and release the neurotransmitter/noradrenalin/ acetylcholine to the synaptic
cleft via exocytosis.
Neurotransmitter/ Noradrenalin/ Acetylcholine moves to
the postsynaptic membrane. When the neurotransmitter/ noradrenalin/ acetylcholine attaches to the receptors on
the postsynaptic membrane, the ligand-gated ion channels open. Sodium ions diffuse into
and potassium ions diffuse out of the postsynaptic neurons. The postsynaptic membrane depolarizes and generates
excitatory postsynaptic potential (EPSP). When the depolarization is above the
threshold level, action potential is produced at the postsynaptic membrane.
NOTES:
(I) Acetylcholine: secreted by parasympathetic nerves.
(II) Noradreline: secreted by sympathetic nerves.
Endocrine system of human
Thyroid glands
Adrenal gland
Gonads
Pancrease
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.