Nervous System, Sense Organs, Hormones, and Tropic Responses

Vocabulary practice flashcards covering Chapter 14: Nervous System, Sense Organ - Eye, Hormones in Humans, and Tropic Responses.

Stimulus

A change in an organism's internal or external environment which may result in a response.

Irritability

The ability of an organism to respond to a stimulus; also known as sensitivity.

Central Nervous System

The coordinator component of the nervous system consisting of the brain and the spinal cord.

Peripheral Nervous System

The system consisting of cranial nerves from the brain, spinal nerves from the spinal cord, and sense organs.

Grey Matter

The region of the CNS composed mainly of neuronal cell bodies, forming the outer layers of the brain and the inner 'H'-shaped portion of the spinal cord.

White Matter

The region of the CNS composed mainly of nerve fibres, forming the central parts of the brain and the outer layers of the spinal cord.

Ganglion

A swell or bulge located on the dorsal root of a spinal nerve that contains the cell bodies of sensory neurones.

Cerebrum

Part of the forebrain consisting of two cerebral hemispheres, concerned with intelligence, memory, learning, and overall control of voluntary actions.

Hypothalamus

Part of the forebrain responsible for regulating body temperature, appetite, sleep, and emotions.

Pituitary Gland

Known as the master gland, located in the forebrain; controls the secretions of many other endocrine glands in the body.

Cerebellum

Part of the hindbrain that controls muscular coordination, especially in maintaining balance.

Medulla Oblongata

Part of the hindbrain that controls involuntary actions such as heartbeat, peristalsis, and contraction and dilation of blood vessels.

Sensory Neurone

A neurone that transmits nerve impulses from receptors to the central nervous system.

Motor Neurone

A neurone that transmits nerve impulses from the central nervous system to effectors.

Relay Neurone

A neurone in the grey matter of the spinal cord that conducts nerve impulses between sensory neurones and motor neurones across synapses.

Myelin Sheath

A layer of mostly lipid substance wrapped around an axon that insulates the neurone for faster nerve impulse transmission.

Node of Ranvier

A gap along the nerve fibre where the myelin sheath is absent, allowing nerve impulses to jump from node to node to increase transmission speed.

Synapse

A minute gap and junction between two neurones or between a neurone and an effector across which impulses pass via neurotransmitters.

Reflex Action

An immediate, automatic response to a specific stimulus that is not under conscious control.

Reflex Arc

The shortest pathway along which nerve impulses travel from the receptor to the effector during a reflex action.

Sclera

The white-coloured, strong, and rigid outermost coat of the eye that maintains its shape and offers protection.

Cornea

The transparent layer of the sclera at the front of the eye that allows light to enter, refracts light rays, and focuses them onto the retina.

Choroid

A dark middle layer of the eye rich in blood capillaries that supplies oxygen and nutrients, absorbs light, and prevents internal light reflection.

Ciliary Muscles

Muscles extending from the choroid that change the thickness and curvature of the lens to adjust focus for near or far objects.

Yellow Spot

The point of the retina located directly in line with the pupil, densely packed with photoreceptors, where light sensitivity and detail perception are highest.

Blind Spot

The region on the retina where optic nerves exit the eye, lacking light-sensitive cells so images focused here cannot be detected.

Rods

Light-sensitive cells in the retina that provide black and white vision in dim light, detect movement, and contain the pigment rhodopsin.

Cones

Photoreceptor cells in the retina responsible for high-detail and colour vision (red, green, and blue types) that function best in bright light.

Rhodopsin

A light-sensitive pigment in rod cells derived from vitamin A that bleaches in bright light and regenerates in the dark.

Accommodation

The process of adjusting the focal length and thickness of the eye lens to form clear images of objects at varying distances on the retina.

Hormone

A chemical substance produced and secreted in small quantities by an endocrine gland, transported in blood to alter the activity of target organs.

Exocrine Glands

Glands that release their chemical secretions through ducts, such as sweat glands and salivary glands.

Endocrine Glands

Ductless glands that secrete hormones directly into the bloodstream for transport throughout the body.

Insulin

A hormone secreted by beta cells of the islets of Langerhans that lowers blood glucose concentration by increasing cell uptake, glycogen synthesis, and tissue respiration.

Glucagon

A hormone secreted by alpha cells of the islets of Langerhans that increases blood glucose levels by converting glycogen, fats, and amino acids into glucose.

Type 1 Diabetes

Juvenile-onset diabetes where the islets of Langerhans produce insufficient insulin, requiring regular insulin injections for treatment.

Type 2 Diabetes

Late-onset diabetes usually affecting people above age 40, characterized by body cells failing to properly respond to available insulin.

Adrenaline

A hormone produced by the adrenal medulla that prepares the body for 'fight or flight' by increasing heart rate, breathing rate, and blood sugar levels.

Tropism

A plant growth movement determined by the direction of an external stimulus.

Phototropism

A tropic plant growth response in which the direction of growth is determined by the directional source of light.

Gravitropism

A tropic plant growth response in which the plant grows in response to the force of gravity.

Auxin

A plant growth substance (indoleacetic acid) synthesized in active shoot and root tips that regulates cell elongation and directional growth responses.

2,4-D

A synthetic plant growth substance similar to auxin used as a selective weedkiller by overstimulating weed growth and exhausting their food reserves.