Science form 3 chapter 1

Function of Human Nervous System

detect stimuli, send information in the form of impulse, interpret impulses, produce appropriate responses

Human Nervous System

Consists of the central nervous system and the peripheral nervous system

central nervous system

consists of the brain and spinal cord

peripheral nervous system

Consists of 12 pairs of cranial nerves connecting the brain to the sensory and internal organs and 31 pairs of spinal nerves connecting the spinal cord to the skeletal muscle

voluntary action

Conscious action, conducted under one's will, control by the brain

Involuntary action

Actions that occur immediately without conscious control or prior thoughts

medulla oblongata

Breathing, heartbeat, peristalsis, secretion of saliva

spinal cord (reflex action)

Withdrawing hand when accidentally touching hot object

Ciliary muscle

Controls the thickness of the eye lens through contraction and relaxation

eye lens

Transparent and elastic convex lens which focuses light onto the retina

Sclera

Strong layer which maintains the shape of the eyeball and protects it

Choroid

Black layer that prevents the reflection of the light in the eye and supplies oxygen and nutrients to the eye

Retina

Layer containing photoreceptors which detects light and produces nerve impulses

Yellow spot

most sensitive part of the retina as it has many photoreceptors

Blind spot

Part of the retina which is not sensitive to the light as there are no photoreceptors and an exit point for all the optic nerve fibres

Optic nerve

nerve fibres that carries nerve impulses impulses from the retina to the brain to be interpreted

Vitreous humour

A transparent jelly-like substance which helps to maintain the shape of the eyeball and focuses light onto the retina

Conjuctiva

transparent membrane which protects the front part of the sclera

aqueous humour

Transparent fluid which maintains the shape of the eyeball and focuses light into the eye

Pupil

opening in the center of the iris which contols the quantity of light entering the eye

Iris

Colored part of the eye which controls the size of pupil

Cornea

Transparent layer which refracts the light and focuses light onto the retina

suspensory ligaments

Strong muscle which hold the eye lens in its position

Rod cells

Sensitive to different light intensities including faint light but not sensitive to the colour of light

Cone cells

Sensitive to the colour of light under bright condition. 3 types of cone cells which are sensitive to blue, green, red light

Mechanism of sight (1)

Light rays from the object enter the eye through cornea, aqueous humour and eye lens before reaching the retina. These parts of eye focus the light rays from the object onto the retina. The object will appear smaller and inverted

Mechanism of sight (2)

The light rays stimulate photoreceptors to produce nerve impulses that are sent to the brain

Mechanism of sight (3)

The brain interprets nerve impulses. The smaller inverted image on the retina will then appear upright

Ear lobe (outer ear)

Collects and directs sound waves to the ear canal

Ear Canal (Outer Ear)

Directs sound waves to the ear drum

Ear drum (middle ear)

Vibrates according to the sound waves received and transfer the vibrations to the ossicles

Ossicles (middle ear)

Amplify sound vibrations and transfer them to the oval window

Oval window (middle ear)

Collects and transfers sound vibrations from the ossicles to the cochlea

Eustachian tube (middle ear)

Balance the air pressure on both sides of the ear drum

Cochlea (inner ear)

Detects and converts sound vibrations into nerve impulses

semicircular canals (inner ear)

Detect the position of the head and help to balance the body

Auditory nerve (inner ear)

Send nerve impulses from the cochlea to the brain to be interpreted

Sensory cells for smell

About 10 million cells, located at the roof of nasal cavity, tiny and covered with a layer of mucus

Function of sensory cells for smell

Chemical substances will dissolve in this layer of mucus and stimulate cell to produce nerve impulses. The nerve impulses are then sent to the brain to be interpreted to determine the type of smell

function of nose and nasal cavity

The nasal cavity is also lined with mucus. Mucus warms and moistens air current before it enters the lung. Hair in the nostrils trap dust and dirt so that only clean air enters the lungs

Why is a person suffering from the flu unable to detect smells?

Too much mucus is being produced. Mucus prevents chemicals from stimulating the smell receptors

Structure of tongue

Tiny nodules known as papillae on the surface of the tongue. The papillae is covered with hundreds of taste buds. Each taste buds contain 10 to 50 taste receptors

Taste receptors

Detect the tastes of sweet, sour, salty, bitter, umami

Function of taste buds

When food is chewed, part or all the chemical substances will dissolve in the saliva. These dissolve chemical substances will diffuse into the taste buds through the pores and stimulate taste receptors to produce nerve impulses. The nerve impulses are then sent to the brain to be interpreted to determine the type of tastes

5 types of skin receptors

Pain receptor, cold receptor, heat receptor, pressure receptor, touch receptor

Parts of the skin that are very sensitive

Fingertips, lips, back of the neck

Parts of the skin that are less sensitive

Knee, elbow

number of receptors

The higher the number of the receptors present, the more sensitive the skin. The nearer the receptors, the more sensitive the skin is towards stimuli

thickness of epidermis

The thinner the epidermis, the more sensitive the part of the skin

optical illusion

Occurs when the object that is seen differs from the actual object because the brain is unable to interpret the object seen due to distractions around the object

blind spot (limitation of sight)

The eye cannot see the image that falls on the blind spot because blind spot does not have photoreceptors.

short-sightedness

inability to see distant objects clearly, image is focus in front of the retina, cause by eye lens too thick or eyeball too long

How short sightedness is corrected?

Concave lens

long-sightedness

Inability to see near object clearly, image is focused behind the retina, cause by eye lens too thin or eyeball too short

How long sightedness is corrected?

Convex lens

Astigmatism

Seeing part of the object clearer than the rest of the object, image is focused on different points on retina

How Astigmatism is corrected

Cylindrical lens

presbyopia

Inability to see distant or near object clearly because of eye lens too hard and less elastic due to ageing

Response of plant

Tropism and nastic movement

Tropism

Directional response of a plant toward stimulus such as light, water, gravity and touch. Occurs slowly and less significantly

positive tropism

Parts of plant grow toward stimulus

negative tropism

Parts of plant grow away from stimulus

Plants need to be responsive towards stimuli

So that they can respond appropriately and ensure their sustainability and survival

Phototropism

Response of plants towards light. Shoots grow towards light so that they can obtain sunlight for photosynthesis(positive). Roots show grow away from sunlight to grip and stabilise the plant(negative)

Hydrotropism

Response of plants towards water. Roots grow towards water to absorb dissolve mineral salt (positive). Shoots grow away from water to obtain sunlight.

Geotropism

Response of plants towards gravity. Roots grow towards the gravity to grip and stabilise the plant (positive). Shoots grow away from tha gravity to obtain sunlight (negative)

Thigmotropism

Response of plants towards touch. Twinning stems or tendrils cling onto whatever object or plant they come contact with to grow upwards to obtain sunlight and grip objects to stabilise (positive). Roots avoid any objects that obstruct their search for water (negative).

Nastic movement

Response of plant towards stimuli but does not depend on direction. Occurs rapidly than tropism.

Examples of nastic movement

Mimosa s.p. close the leaves inward when touched. Venus flytrap will close when insects touched it. Serves as a defence against enemy or strong wind

stereoscopic vision

Both eyes are used to look at an object, both eyes at the front of the head, forms 3D object, able to estimate the location and the position of an object accurately, smaller field of vision, predators have stereoscopic vision, field of vision overlap, enable to determine the position and location of their prey accurately

monocular vision

An eye is used to look an object, an eye at each side of the object, does not form 3D image, unable to determine the position and location of an object accurately, wider field of vision, field of vision do not overlap, preys have monocular vision, enables prey to detect their predators at any angle

stereophonic hearing

Refers to hearing using both ears. Helps to determine the direction and location of sound accurately, helps prey to escape from their predators.

Human frequency range

20 Hz to 20,000 Hz

electric field

Helps fish to determine its direction and detect agitation from an object or other nearby organisms.

Pheromones

Help beetles find its mates

lateral line

Detect the changes in air pressure, detect preys and assist in movement

Why we should not look directly at the sun during eclipse and use the x ray film

The film reduces the light which enters the eyes. The less light reaches the retina, less likely to damage the retina