Nervous Coordination in Organism

Nervous coordination

The nervous system in humans coordinates and regulates body functions through specialized cells known as neurons. The nervous system enables organisms to respond to stimuli, control movements, and regulate physiological processes.

Properties of neurons

1. Excitability: Neurons are capable of responding to stimuli. This means that they can detect changes in the environment (internal or external) and react to them.
2. Conductivity: Neurons have the ability to conduct nerve impulses. These impulses carry information from one part of the body to another, allowing for communication within the nervous system.
3. Cell Structure: Neurons have a specialized structure with a long cytoplasm that forms fine, thread-like extensions. This allows them to carry signals over long distances.

Structure of neurons

Neurons are composed of several key parts:

1. Cell Body (Soma): This is the main part of the neuron, which contains the nucleus and other organelles essential for cell function.
2. Dendrites: These are short, branched extensions of the neuron that receive signals from other neurons or sensory cells and conduct these impulses toward the cell body.
3. Axon: This is a long, slender projection that carries nerve impulses away from the cell body to other neurons or effector cells. The axon is typically covered by a layer of cells called Schwann cells that form the myelin sheath.
4. Myelin Sheath: This fatty insulating layer covers the axon and speeds up the transmission of nerve impulses. It also helps to prevent interference between the signals traveling along different axons.
5. Nodes of Ranvier: These are small gaps in the myelin sheath between adjacent Schwann cells. The presence of these nodes allows for the faster transmission of electrical impulses along the axon through a process called saltatory conduction, where impulses jump from node to node.
6. Axon Terminals: These are the ends of the axon, where the neuron makes synaptic connections with other neurons or effector cells (like muscles or glands).

Classification of neurons

Neurons are classified into three main types based on their function: sensory neurons, motor neurons, and relay (intermediate) neurons.

Sensory neurons (afferent neurons)

Function: Sensory neurons carry nerve impulses from the sense organs (e.g., skin, eyes, ears, nose, tongue) to the central nervous system (CNS), which includes the brain and spinal cord.

Structure:

1. Sensory neurons have a long dendron (a branch-like projection) that originates from a sense organ, where it is stimulated by environmental changes such as light, sound, or touch.
2. The dendron conducts the nerve impulse towards the cell body, and the axon transmits the impulse to the CNS (brain or spinal cord).
3. Axon: The long, thread-like part of the neuron that transmits impulses away from the cell body.
4. The cell body of sensory neurons is located outside the CNS, in a structure called the dorsal root ganglion.

Example: When you touch something hot, sensory neurons transmit the impulse from your skin to your spinal cord and brain.

Key Points:

1. Sensory neurons are essential for sensing external and internal changes.
2. Sensory input is vital for the brain to interpret the environment, but no sensation occurs until the brain interprets the impulses received from sensory neurons.

Motor neurons (efferent neurons)

Function: Motor neurons carry nerve impulses away from the CNS to muscles or glands, which result in movement or secretions.

Structure:

1. Motor neurons have short dendrites and a long axon that transmits signals to effector organs (muscles or glands).
2. The cell body of motor neurons is located inside the CNS, in the brain or spinal cord.

Example: When the brain sends a signal to move your hand away from a hot object, motor neurons transmit the signal to the muscles in your arm, causing it to contract and pull the hand away.

Relay neurons (intermediate neurons)

Function: Relay neurons serve as connectors or intermediaries between sensory and motor neurons. They transmit impulses between neurons within the CNS.

Structure:

Relay neurons are typically located in the brain and spinal cord. They have short dendrites and axon but are more complex in their branching structure compared to motor and sensory neurons.

Example: In a reflex action, a relay neuron transmits the impulse from a sensory neuron to a motor neuron, allowing for a quick, automatic response.

Adaptations of a neurone to its function

1. Myelin Sheath covers some axons, providing insulation and protection, and allowing for faster transmission of nerve impulses.
2. Schwann Cells secrete the myelin sheath, aiding in insulation.
3. Numerous Dendrites increase the surface area for receiving and transmitting nerve impulses.
4. Wide Distribution of neurones throughout the body ensures efficient communication between different parts.
5. Elongated Axons in some neurones allow long-distance transmission of information.
6. Branched Dendrites at the neurone ends help receive impulses from other neurones.

Nerve impulse

A nerve impulse is an electrical signal that travels along the axon of a neurone when the cell is activated. Because neurones are not physically connected, there is a small gap—called the synaptic gap or synaptic cleft—between the axon terminals of one neurone and the dendrite, cell body of another neurone, or an effector organ. This connection point is known as a synapse, and it allows the transmission of impulses across neurones or to target organs.