Page 25 - How It Works - Book of Amazing Answers To Curious Questions, 12

Science*------------------Q�

What exactly 1. Quadriceps and 2. Sensory neuron 3. Interneuron
The interneuron provides a
hamstring muscles
The sensory, or afferent
neuron, receives an impulse
connection between the
The knee-jerk reflex means
that the quadriceps muscles from the femoral nerve. sensory and motor neurons.
is a l<nee-jerl< hamstring muscle relaxes.
contract at the same time the
reaction?

Why does your leg kick out when the
doctor taps just below your lmee?

octors often test the knee-jerk, or patellar reflex, to • Sensory neuron
look for potential neurological problems. Lightly • Motor neuron
• Interneuron
D tapping your patellar tendon just below the kneecap
stretches the femoral nerve located in your thigh, which in
turn causes your thigh muscle !quadriceps) to contract and 5. Spinal cord 4. Motor neuron
the lower leg to extend. When struck, impulses travel The spinal cord has both grey The motor, or efferent
along a pathway in the dorsal root ganglion, a bundle matter, which contains nerve cell neuron, carries the nerve
bodies, and white matter, which impulse to the muscles.
of nerves in the L4level of the spinal cord. Reflex actions contains the nerve fibres.
are performed independently of the brain. This allows them to
happen almost instantaneously- in about 50 milliseconds in
the case of the knee-jerk reflex. This reflex helps you to This reflex helps you to maintain
maintain balance and posture when you walk, without
having to think about every step you take. balance and posture when you walk
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Why do we get spots? bacteria that build up and cause
Inflammation
The trapped sebum attracts
a pustule, which can grow sore
and inflamed.
Find out what causes pimples to form on the surface of human skin Whitehead
Blockages can occur
beneath a layer of
implesare caused blocked by a few dead skin Epidermis Blackhead skin that prevents air
by sensitivity to the cells that haven't been shed Sebum helps slough away the cells When the blockage is nearer the from coming into
on the surface of the skin as they surface, the accumulation of sebum can
P testosterone properly, the sebum builds contact with the
die to make room for the fresh be exposed to the air, causing oxidation
hormone present in both up inside the hair follicle. cells generated in the dermis. which turns the substance black. sebum which results
in it staying white.
males and females, which This oily buildup is a
can trigger the breeding ground for
overproduction of an oily bacteria, which then
substance called sebum. accumulate and multiply
Sebum, which is produced around the area, making the
by sebaceous glands skin inflamed and infected.
attached to hair follicles in This results in the pimple.
the dermis, helps keep hair Whiteheads and
and skin waterproof. blackheads are types of
Your skin is constantly acne pimples known as
renewing itself, and while comedones. Blackheads are
new cells are produced in open comedones, which
the lower layers of skin, the means the blockage of
old dead cells are sloughed sebum is exposed to the air,
away from the surface. This, causing oxidation of the
©Science Photo Library
together with excessive sebum !similar to when Dermis
sebum production, can lead an apple browns). New skin cells are created in
the lower layers of skin.
to acne and pimples. Whiteheads, on the other Blockage
Sebum normally travels hand, are closed comedones If dead skin cells fail to be shed
through the hair follicle to and are not exposed to air Sebaceous gland Sebum properly, they can become blocked
Attached to the hair follicle, the The sebum travels up the hair inside pores. When this happens
the surface of the skin. as they're covered by a layer
sebaceous gland produces an oily, waxy follicle to waterproof the hair and sebum is plugged behind a barrier,
However, if a pore becomes of skin. substance called sebum. protect the surface of the skin. which can lead to a spot forming.
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