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Unit 1 – Nervous System

Structure of a Neuron

The neuron is the fundamental unit of the nervous system, responsible for transmitting electrical and chemical signals throughout the body.

• Key Components: Cell body (soma), dendrites, membrane, neurilemma, axon, axon terminal, synapse.

• Function: Dendrites receive signals, the cell body processes them, and the axon transmits the signal to other neurons or effectors.

• Synapse: The junction between two neurons where neurotransmitters are released to propagate the signal.

Conduction of Nerve Impulses

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

• Ion Exchange: Movement of ions across the neuron membrane is essential for impulse conduction.

• Phases:

  • Depolarization: Sodium ions () rush into the neuron, making the inside more positive.

  • Repolarization: Potassium ions () exit the neuron, restoring the negative internal environment.

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

Equation:

Myelination

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

• Gray Matter: Contains mostly neuron cell bodies and unmyelinated fibers.

• White Matter: Composed primarily of myelinated axons, facilitating rapid signal transmission.

• Function: Myelin insulates axons and enables saltatory conduction, where impulses jump between nodes of Ranvier.

Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another.

• Examples: Acetylcholine, dopamine, serotonin, norepinephrine.

• Synapses: Sites where neurotransmitters are released and bind to receptors on the postsynaptic neuron.

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

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).

Brain Structure and Function

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

• Cerebrum: Responsible for higher brain functions such as thought, memory, and voluntary movement.

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

• Cerebellum: Coordinates movement and balance.

• Lobes of the Cerebrum: Frontal, parietal, temporal, occipital – each lobe has specialized functions.

Somatic Nervous System

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

• Reflex Arc: Pathway involving receptors, sensory neurons, interneurons, motor neurons, and effectors.

• Function: Enables quick, involuntary responses to stimuli (e.g., knee-jerk reflex).

Autonomic Nervous System

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

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

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

• Comparison Table:

The Eye

The eye is a complex organ responsible for vision, composed of several parts with specialized functions.

• Parts of the Eye: Outer (cornea, sclera), middle (choroid, iris), 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 ear 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: These notes are based on a summary of key concepts for a biology or neuroscience unit, not general chemistry. No chemistry-specific content is present.