Neuro

• Synapse is the communication or junction between two neurons, also known as an 'Interneuronal junction'
• More than 50 compounds have been identified as transmitter substances
• Each neuron divides to form over 2000 synaptic endings
• There are 10,000 synaptic knobs on a single spinal motor neuron, with 2000 on the cell body and 8000 on dendrites
• In the Cerebral Cortex, 98% of synapses are on dendrites (mostly excitatory) and 2% are on the soma
• Signals transmit in a forward direction, known as 'one-way conduction', from the pre-synaptic neuron to the post-synaptic neuron
• Types of synapse:

  • Functional:
  • Electrical
  • Chemical
  • Anatomical:
  • Axodendritic (e.g., cerebral & cerebellar cortex)
  • Axosomatic (e.g., cerebellum, autonomic ganglia)
  • Axoaxonal (e.g., cerebral cortex)
• Presynaptic terminals are located on dendrites, soma, or axon of another neuron
• Growth cones at the tip of growing axons migrate through tissues and are guided by attractants and repellants, as well as glial cells in the CNS to find the right target to make the right synapse
• Structures important to the function of the synapse:

  • Presynaptic vesicles contain neurotransmitter substances to excite or inhibit the postsynaptic neuron, with three types of vesicles
  • Mitochondria provide energy to synthesize neurotransmitter
• Arrival of action potential (AP) at the presynaptic terminal triggers the release of neurotransmitter into the synaptic cleft, leading to the binding of neurotransmitter to receptor proteins and the development of Excitatory Postsynaptic Potentials (EPSP) or Inhibitory Postsynaptic Potentials (IPSP)
• Synaptic transmission involves the opening of voltage-gated Ca++ channels in the presynaptic terminal, influx of Ca++, binding of Ca++ to protein molecules inside the presynaptic terminal, binding of transmitter vesicles to release sites, exocytosis of neurotransmitter into the synaptic cleft, and the binding of neurotransmitter to receptor proteins on the postsynaptic terminal
• Excitatory receptors lead to an increase in Na+ influx and a decrease in Cl- influx or K+ conductance, while inhibitory receptors increase Cl- conductance and K+ conductance, affecting the number of excitatory and inhibitory receptors
• Second messengers, such as "G-Proteins," prolong changes in neurons for seconds to months, are involved in memory processes, and activate various functions like opening channels, activating membrane enzymes, gene transcription, and intracellular enzymes
• The intrasomal membrane potential of neurons affects their excitability, with EPSP leading to the development of action potentials and IPSP inhibiting the transmission of nerve signals through the synapse
• EPSP develops through the release of excitatory transmitter, binding of transmitter, conformational change in excitatory receptors, rapid influx of Na+ ions, and a shift in membrane potential towards the positive side, leading to the generation of action potentials in postsynaptic neurons
• IPSP increases the negativity of the membrane potential beyond the resting membrane potential level, inhibiting the transmission of nerve signals through the synapse by opening Cl- or K+ channels in the postsynaptic membrane
• EPSP and IPSP play significant roles in synaptic inhibition in the CNS, regulating the transmission of nerve signals and ensuring appropriate neuronal responses
• The cerebral cortex is the outer layer of gray matter that covers most of the brain's hemispheres.
• The cerebellum, located at the back of the skull, controls balance and coordination.
• The medulla oblongata, located near the base of the brainstem, regulates vital functions such as breathing, heart rate, and blood pressure.
• Layers II-IV contain pyramidal cells, which have long dendrites extending into other layers.
• Layer V contains large pyramidal cells called Betz cells, which project axons downward toward the spinal cord.
• The medulla oblongata, situated at the base of the brainstem, regulates vital functions such as breathing, heart rate, blood pressure, and swallowing.
• The thalamus serves as a relay station between sensory pathways and the cerebral cortex.
• The pons connects the cerebrum to the spinal cord and plays a role in sleep patterns and motor control.