Unit 1 – Nervous System

Structure of a Neuron

The neuron is the basic functional unit of the nervous system, specialized for the transmission of electrical and chemical signals.

• Cell Body (Soma): Contains the nucleus and organelles; responsible for metabolic activities.

• Dendrites: Branch-like extensions that receive signals from other neurons.

• Axon: Long, slender projection that transmits electrical impulses away from the cell body.

• Axon Terminal: The endpoint of an axon where neurotransmitters are released.

• Neurilemma: The outermost layer of the nerve fiber, important for regeneration.

• Synapse: The junction between two neurons where information is transmitted chemically.

Conduction of Nerve Impulses

Nerve impulses are electrical signals that travel along neurons, allowing communication throughout the nervous system.

• Ion Exchange: Movement of ions (Na+, K+) across the neuronal membrane is essential for impulse conduction.

• Depolarization: A rapid influx of Na+ ions causes the inside of the neuron to become more positive.

• Repolarization: K+ ions exit the neuron, restoring the negative internal environment.

• Action Potential: The rapid change in membrane potential that travels along the axon.

Equation:

(Ohm's Law, relating voltage, current, and resistance in nerve conduction)

Myelination

Myelination refers to the presence of a myelin sheath around axons, which increases the speed of nerve impulse conduction.

• Gray Matter: Contains neuron cell bodies and is involved in processing information.

• White Matter: Consists of myelinated axons, responsible for transmitting signals over long distances.

• Function: Myelin allows for saltatory conduction, where impulses jump between nodes of Ranvier.

Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across synapses.

• Synapses: Sites of neurotransmitter release and reception.

• Receptors: Proteins on the postsynaptic membrane that bind neurotransmitters.

• Enzymes: Break down neurotransmitters to terminate the signal (e.g., acetylcholinesterase).

• Examples: Acetylcholine, dopamine, serotonin, GABA.

Central Nervous System vs. Peripheral Nervous System

The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

• Central Nervous System (CNS): Includes the brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Consists of nerves outside the CNS; transmits signals between the CNS and the rest of the body.

Brain Structure and Function

The brain is composed of several regions, each with specialized functions.

• Cerebrum: Responsible for higher brain functions such as thought and action.

• Brain Stem: Includes the thalamus, hypothalamus, midbrain, pons, and medulla oblongata; controls vital functions.

• Cerebellum: Coordinates movement and balance.

• Lobes of the Cerebrum: Frontal, parietal, temporal, occipital; each lobe has distinct functions (e.g., frontal for reasoning, occipital for vision).

Somatic Nervous System

The somatic nervous system controls voluntary movements and transmits sensory information.

• Reflex Arc: The pathway involved in a reflex action, including receptors, sensory neurons, interneurons, motor neurons, and effectors.

• Example: Knee-jerk reflex.

Autonomic Nervous System

The autonomic nervous system regulates involuntary bodily functions and is divided into sympathetic and parasympathetic divisions.

• Sympathetic Nervous System: Prepares the body for 'fight or flight' responses (increases heart rate, dilates pupils).

• Parasympathetic Nervous System: Promotes 'rest and digest' activities (slows heart rate, stimulates digestion).

The Eye

The eye is the organ of vision, composed of several parts that work together to process visual information.

• Parts of the Eye: Outer (cornea, sclera), middle (iris, lens), inner (retina).

• Vision Defects: Myopia (nearsightedness), Hyperopia (farsightedness), Glaucoma (increased intraocular pressure).

The Ear

The ear is responsible for hearing and balance, consisting of three main regions.

• Outer Ear: Pinna and auditory canal; collects sound waves.

• Middle Ear: Tympanic membrane and ossicles; transmits vibrations.

• Inner Ear: Cochlea and vestibular system; processes sound and maintains balance.

Additional info: Some content was inferred and expanded for clarity and completeness, such as the functions of brain regions and the structure of the eye and ear.