Neuron:
A neuron is a specialized cell found in the brain, spinal cord, and nerves. A single neuron can be up to a metre long and is made up of three parts:
Neuron
1. Cell body (soma): The main part of the neuron containing the nucleus and organelles that control cell activities. It maintains the structure of the neuron and provides energy for its functions.
2. Axon: A long cylindrical fibre that carries nerve impulses away from the cell body to other neurons, muscles, or glands. It ends in synaptic terminals that release neurotransmitters.
3. Dendrites: Short, branched extensions of a neuron that receive signals from other neurons. They transmit these impulses toward the cell body.
2. Axon: A long cylindrical fibre that carries nerve impulses away from the cell body to other neurons, muscles, or glands. It ends in synaptic terminals that release neurotransmitters.
3. Dendrites: Short, branched extensions of a neuron that receive signals from other neurons. They transmit these impulses toward the cell body.
Types of neurons:
Neurons are classified as apolar, unipolar, bipolar, and multipolar based on their structure and number of processes. A nerve fibre consists of an axon along with its coverings. Nerve fibres may be myelinated or non-myelinated.
Classification of neurons
Based on function, neurons are of three types: sensory (afferent) neurons that carry impulses to the CNS, motor (efferent) neurons that transmit impulses to muscles and glands, and relay (interneurons) that connect sensory and motor neurons within the brain and spinal cord.
The action of sensory and motor neurons
A synapse is the junction where a nerve impulse passes from one neuron to another as an electrochemical signal through the synaptic cleft, from the presynaptic neuron (sender) to the postsynaptic neuron (receiver).
Transmission of an impulse:
Information received at the dendrites generates an electrical impulse that travels through the cell body and axon, triggering the release of neurotransmitters at the synapse, which then starts a similar impulse in the next neuron or effector cell. There are two types of synapses: electrical synapses, where impulses pass directly between neurons through gap junctions, and chemical synapses, where neurotransmitters cross the synaptic cleft to transmit the nerve impulse.
Transmission of nerve impulse
Neuromuscular junction:
The brain controls voluntary and involuntary actions by processing information and sending signals to muscles. A nerve impulse from the motor neuron reaches the neuromuscular junction, releasing chemicals that trigger muscle contraction. When the signal stops, muscle fibres return to their original length, causing muscle relaxation.
Neuromuscular Junction - Overall Mechanism
Reflex Action and Reflex Arc:
Reflex action is a quick, automatic, and involuntary response to a stimulus without conscious thinking, such as withdrawing the hand from a hot object. It occurs instantly to protect the body from harm and is controlled through a simple neural pathway.
A reflex arc is the neural pathway followed during a reflex action, involving a sensory neuron, relay neuron (interneuron), and motor neuron. It enables rapid protective responses in dangerous situations, even before the brain processes the signal.
Process of reflex action