Organism Level Systems Booklet (Part 1)

Nervous System

The system that enables humans to react to their surroundings and coordinate behavior.

Neuron

A nerve cell that transmits electrical impulses between different parts of the body.

Reflex Arc

The fixed neural pathway that controls a reflex response.

Synapse

The junction between two neurons where neurotransmitters transmit impulses.

Myelin Sheath

A fatty coating on a neuron that insulates it and increases the speed of electrical impulses.

Effector

A muscle or gland that carries out a response to a stimulus.

Central Nervous System (CNS)

Consists of the brain and spinal cord, responsible for coordinating responses.

Peripheral Nervous System (PNS)

Made up of all nerves that extend from the CNS, including sensory receptors.

Neurotransmitter

A chemical messenger that transmits signals across a synapse.

Voluntary Response

A response that requires conscious thought and originates from the brain.

Involuntary Response

A response that occurs automatically without conscious control.

Relay Neuron

An intermediate neuron that connects sensory and motor neurons in the CNS.

Cerebrum

The part of the brain responsible for higher-order functions such as intelligence and memory.

Cerebellum

The part of the brain responsible for balance, muscle coordination, and movement.

Medulla

The part of the brain controlling unconscious activities like heart rate and breathing.

Sensory Neuron

Carries impulses from sense organs to the CNS.

Motor Neuron

Carries impulses from the CNS to effectors.

Cornea

The transparent front part of the eye that refracts light.

Pupil

The opening in the eye that controls how much light enters.

Lens

The transparent structure in the eye that focuses light onto the retina.

Retina

The inner surface of the eye that contains light-sensitive cells.

Accommodation

The process by which the eye adjusts its focus on near or distant objects.

Short-sightedness (Myopia)

A condition where distant objects appear blurry due to light focusing in front of the retina.

Long-sightedness (Hyperopia)

A condition where close objects appear blurry due to light focusing behind the retina.

Color Blindness

A condition where a person cannot distinguish certain colors.

Ciliary Muscles

Muscles that control the shape of the lens to focus light.

Suspensory Ligaments

Tissues that hold the lens in place and allow it to change shape.

Reflex Response

An involuntary, fast neural response to a stimulus.

Stimulus

Any change in the environment that can elicit a response.