Download Skin, tongue and brain

Skin
The skin is the largest organ in the body. Scattered throughout the skin are millions of tiny
sense organs containing sensory nerve endings. Each sensory nerve cell is sensitive to
either:
1.
Touch
e.g. fingertips, tongue, lips (blind person uses fingertips – Braille)
2.
Pressure
e.g. fingertips, tongue
3.
Pain
e.g. tendons, muscles, ligaments: distributed evenly in the skin.
warning device to say if muscle is over-stretched
4.
Temperature e.g. front of fore arm, back of hand: hot and cold receptors distinguish
½ºC difference. The tongue is NOT temperature sensitive – this is
why it burns.
(cook tells if there are lumps in the food)
The distribution or density of each type of sensory receptor varies.
Hair movements
There are sensory receptor cells at the base of the hair in the skin. These are stimulated
when hairs move (by touch or wind). Cats and mice avoid obstacles in the dark using their
whiskers.
free nerve ending –
detects pain/cold
capillaries
near surface
of dermis
hair follicle
sweat duct /
pore
epidermis
dermis
sweat gland
layer of fat and
connective tissue
nerve ending
in hair
Tongue
The tongue is muscle. On its upper surface are taste cells grouped into taste buds. Taste is a
property of substances in solution.
There are four types of taste bud – each is specialised and sensitive to one particular taste:
1.
Sweet
property of sugars
at tip/front of tongue
2.
Sour
property of acids
at edge/sides of tongue
3.
Salt
property of strong acids
at tip/front of tongue
4.
Bitter
property of plant alkaloids
at back of tongue
bitter
sweet
and salt
sour
The 4 tastes are grouped into different parts of the tongue. The tongue is temperature
insensitive and that is why we burn it.
Flavour is a combination of taste and smell. This is shown by not being able to taste
properly when you have a cold.
Smell: there are small smell sensory receptors high up in the nasal cavity (i.e. the nose!) –
generally these are sensitive to harmful substances (e.g. decaying food).
Brain
The brain is a complex network of neurones and weighs approximately 1.5 kg. It contains
thousands of millions of neurones. Each neurone synapses with thousands of other
neurones. It needs protection because it is so important and the protection is given by the
skull bones.
cerebrum
medulla oblongata
responsible for
eyesight
hypothalamus
pituitary gland
cerebellum
spinal cord
Medulla oblongata positioned at the top of the spinal cord – where the spinal cord joins the
brain. It is the reflex centre for unconscious activities
(e.g. heart beat, blood pressure, blinking)
Cerebellum
this is the area concerned with muscular coordination. It receives nerve
impulses from all the sense organs concerned with muscular activity
Cerebrum
this is a dome shaped mass of neurones and is the largest part of the
brain. There are two cerebral hemispheres: the right and the left. In
the centre of the cerebrum is the grey matter. This is the part, which is
the most advanced in humans. It is responsible for all conscious
activity. The cerebrum receives nerve impulses from all the sense
organs and will be responsible for all the conscious activity. This
includes reasoning, decision-making, memory storage and emotions.
Hypothalamus
this lies on the underneath front part of the cerebrum. It is the part of
the brain that monitors and controls the body temperature, the
concentration of the salts in the blood and the concentration of CO2 and
acid in the blood. It is linked to the pituitary gland.
Pituitary gland
this controls the activity of all endocrine glands. Therefore, the
hypothalamus is the link between the nervous system and the endocrine
system in controlling and coordinating the body.