Nervous System and The Eye

Vocabulary flashcards covering key terms from the lecture on the nervous system, reflexes, the eye, and a comparison with the endocrine system.

Central Nervous System (CNS)

The brain and spinal cord; the main integration and control centers of the body.

Peripheral Nervous System (PNS)

All cranial nerves, spinal nerves, and sense organs that lie outside the CNS and relay information to and from it.

Cranial Nerves

Nerves that arise from the brain and connect to head and neck structures.

Spinal Nerves

Nerves that emerge from the spinal cord and connect to the rest of the body.

Neurone

A nerve cell specialized for transmitting electrical impulses.

Cell Body

Part of a neurone that contains the nucleus and most organelles.

Nerve Fibre

Any cytoplasmic extension of a neurone (axon or dendrite) that conducts impulses.

Synapse

Junction between two neurones, or a neurone and an effector, where neurotransmitters carry the impulse across a gap.

Sensory Neurone

Neurone that carries impulses from a receptor toward the CNS.

Relay Neurone (Interneurone)

Neurone located within the CNS that links sensory and motor neurones.

Motor Neurone

Neurone that transmits impulses from the CNS to an effector such as a muscle or gland.

Receptor

Structure that detects a stimulus and initiates a nerve impulse.

Effector

Muscle or gland that carries out a response to nerve impulses.

Nerve Impulse

An electrical signal that travels along a neurone.

Reflex Action

Immediate, involuntary response to a specific stimulus without conscious control.

Reflex Arc

The shortest pathway taken by nerve impulses from receptor to effector during a reflex action.

Reflex Centre

Part of the CNS (brain or spinal cord) where impulses are relayed in a reflex arc.

Spinal Reflex

Reflex that uses the spinal cord as its reflex centre, e.g., knee-jerk reflex.

Cranial Reflex

Reflex that uses the brain as its reflex centre, e.g., blinking or pupil reflex.

Voluntary Action

A deliberate movement under conscious control initiated in the brain.

Pain Receptor

Sensory receptor that detects tissue damage or noxious stimuli.

Thermoreceptor

Sensory receptor that detects changes in temperature.

Stretch Receptor

Receptor that responds to stretch in muscles or tendons.

Photoreceptor

Light-sensitive receptor found in the retina.

Osmoreceptor

Receptor that detects water potential changes in body fluids.

Accommodation (Focusing) Reflex

Automatic adjustment of the lens to focus light from objects at different distances on the retina.

Ciliary Muscles

Ring of smooth muscles in the ciliary body that contract or relax to change lens shape.

Suspensory Ligaments

Fibres that attach the lens to the ciliary body and transmit tension to alter lens curvature.

Lens

Transparent, flexible structure that further refracts light to focus it on the retina.

Sclera

Tough, outer white layer of the eyeball that protects against mechanical damage.

Choroid

Middle eye layer rich in blood vessels; black pigment absorbs stray light to prevent internal reflection.

Retina

Innermost layer containing photoreceptors that convert light into nerve impulses.

Yellow Spot (Fovea)

Region of the retina with the highest density of cones; produces the sharpest image.

Blind Spot

Point where the optic nerve exits the eye; contains no photoreceptors.

Cornea

Transparent, curved front layer that provides the greatest amount of light refraction.

Conjunctiva

Thin moist membrane covering the front of the eye; secretes mucus to lubricate the surface.

Aqueous Humour

Watery fluid in the anterior chamber that maintains eyeball shape, nourishes the cornea, and refracts light.

Vitreous Humour

Jelly-like fluid in the posterior chamber that maintains eyeball shape and refracts light onto the retina.

Iris

Coloured part of the eye containing circular and radial muscles that regulate pupil size.

Radial Muscles

Iris muscles that contract in dim light to dilate the pupil.

Circular Muscles

Iris muscles that contract in bright light to constrict the pupil.

Pupil Reflex

Automatic adjustment of pupil diameter in response to light intensity.

Rectus Muscles

External eye muscles that control eyeball movement.

Hormone

Chemical messenger produced by endocrine glands and transported in the blood.

Nerve Impulse vs Hormone

Impulses travel rapidly along neurones; hormones travel more slowly in the bloodstream but can affect many organs.

Endocrine System

Communication system that uses hormones carried by blood to regulate body functions.

Nervous System

Fast-acting communication network that uses electrical impulses along neurones.