Overview of Control and Co-ordination

The small intercellular space of about 20–30 nm present between presynaptic and postsynaptic neurons is called synaptic cleft.

The process by which a nerve impulse is conducted from the presynaptic neuron to the postsynaptic neuron by neurotransmitters is called synaptic transmission.

The type of synapse in which transmission of impulse occurs directly through a narrow gap by electrical current is called electrical synapse.

The type of synapse in which transmission of impulse occurs through chemical neurotransmitters across a wider synaptic gap is called chemical synapse.

1. Nerve Impulse
   A nerve impulse is a wave of bioelectrical (electrochemical) disturbance that travels along the neuron membrane.
2. Resting (Polarized) State
   In a resting neuron, the membrane is polarized with excess Na⁺ outside and K⁺ inside, creating a resting potential of about –70 mV.
3. Sodium–Potassium Pump
   Active transport of Na⁺ out and K⁺ into the neuron against their gradients using ATP energy is called the Na⁺/K⁺ exchange pump.
4. Role of Ion Channels
   Voltage-gated Na⁺ and K⁺ channels regulate membrane permeability and enable change from resting potential to active potential during impulse conduction.