Nervous System Basics

• The nervous system is responsible for coordinating and controlling all the actions in an organism.
• Includes the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS comprises of the brain and the spinal cord; whereas, the PNS includes all the nerves running from CNS to the rest of the body.

Neuron Structure

• A neuron or nerve cell, is the basic unit of the nervous system.
• Each neuron consists of a cell body, dendrites, and an axon.
• The cell body contains the nucleus and other cell organelles.
• Dendrites convey signals towards the cell body, and axons convey signals away from the cell body.

Synapses

• A synapse is the junction or gap where signals are passed from one neuron to another.
• The signal is transferred from the axon of the first neuron to the dendrites of the next using neurotransmitters.

Reflex Actions

• Reflex actions are rapid and involuntary responses to specific stimuli, controlling by the spinal cord.
• They work on a pathway called a reflex arc which includes receptors, sensory neurons, interneurons in the spinal cord, motor neurons, and effectors (muscles or glands).

Nerve Impulses

• Nerve impulses or action potentials are electrical signals that travel along the length of neurons.
• They are started by a stimulus, are self-propagating, and occur in an all-or-nothing fashion.
• At resting potential, the neuron is negatively charged inside. A stimulus causes depolarisation where the inside of the neuron becomes positive and impulse is propagated. Repolarisation restores the resting potential.

Roles of Medulla Oblongata and Cerebellum

• The medulla oblongata controls involuntary functions like heartbeat and breathing.
• The cerebellum manages coordination of movement and balance.

The Eye as a Sensory Organ

• The eye is a complex sensory organ that detects light and converts it into electro-chemical impulses in neurons.
• When light enters the eye, it hits the retina. The retina contains photoreceptor cells called rods and cones which convert light energy into electrical signals.
• These signals then travel to the brain through the optic nerve.
• The iris controls the amount of light reaching the retina by controlling the size of the pupil.
• The lens focuses light onto the retina, adjusting its shape for near and far objects, a process called accommodation.

Role of Skin and Muscles

• Skin responds to touch, pressure, pain, and temperature stimuli, and sends signals to the brain via sensory neurons.
• Muscles receive signals from motor neurons to contract or relax, allowing the body to move.