5.2 Human Nervous System

Question 1

what is the function of the nervous system?

Answer 1

the nervous system allows the body to react to its surroundings and coordinate an appropriate response.

Question 2

how does a stimulus lead to a response being carried out by the body?

Answer 2

• stimulus is converted into an electrical impulse by the receptors.
• the electrical impulse passes along sensory neurones to the central nervous system (CNS).
• the CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response.

Question 3

what sequence of events describes how the nervous system works?

Answer 3

stimulus –> receptor –> coordinator –> effector –> response

Question 4

what is a reflex action?

Answer 4

a reflex action is an automatic and rapid response which does not involve any conscious input from the brain.

Question 5

why are reflec actions important?

Answer 5

reflex actions aid survival by preventing harm to the body.

Question 6

describe how a reflex action occurs via a reflex arc

Answer 6

• the stimulus is detected by a receptor.
• an electrical impulse passes along a sensory neurone to the spinal cord (part of the CNS).
• at a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap and stimulates a new impulse which passes along the relay neurone.
• the same process occurs at a synapse between a relay neurone and a motor neutone.
• at the effector, an appropriate response is carried out.

Question 7

what is the difference between a reflec pathway and a conscious pathway?

Answer 7

within a reflex pathway, the coordination centre is a relay neurone found in the spinal cord/unconscious parts of the brain. in a conscious pathway, the coordination centre is in the conscious part of the brain.

Question 8

what is the function of the cerebral cortex?

Answer 8

(front top of brain) - controls consciousness, intelligence, memory and language.

Question 9

what is the function of the cerebellum?

Answer 9

(back bottom behind the medulla) - controls muscular coordination

Question 10

what is the function of the medulla?

Answer 10

(above spinal cord infront of cerebellum) - controls unconscious activities e.g. breathing, heart rate

Question 11

why is the invvestigation and treatment of the brain difficult?

Answer 11

• the brain is a complec and delicate organ.
• the brain is easily damaged and destroyed.
• certain membrames prevent drugs from reaching the brain.
• the exact function of each part of the brain is not known.

Question 12

what methods are used by scientists to determine brain function?

Answer 12

• studying patients with brain damage
• electrical stimulation of the brain
• MRI scans

Question 13

what stimuli are the receptors of the eye sensitive to?

Answer 13

light intensity and colour

Question 14

what are the two main functions of structures found within the eye?

Answer 14

• focusing on near or distant objects - accommodation.
• adaptation to dim light.

Question 15

describe the structure and function of the retina

Answer 15

the retina is a light-sensitive layer found at the back of the eye.
light stimulates the retinal cels, resulting in impulses being sent to the brain.

Question 16

describe the structe and function of the optic nerve

Answer 16

the optic nerve connects the eye and the brain.
it carries impulses to the brain so that an image can be visualised.

Question 17

describe the structure and function of the sclera

Answer 17

the sclera is the tough outer layer of the eye which protects its intenal structures.

Question 18

describe the structure and function of the cornea

Answer 18

the cornea is the curved transparent layer at the front of the eye.
it lets light into the eye and allows light to be focused onto the retina.

Question 19

describe the structure and function of the iris

Answer 19

the iris is a muscle which controls the size of the pupil by contracting or relaxing. this allows the eye to adjust to bright and dim lighting

Question 20

describe the structure and function of the ciliary muscles and suspensory ligaments

Answer 20

the ciliary muscles and suspensory ligaments hold the lens in place and control its shape.

Question 21

describe how the iris alters the size of the pupil in both bright and dim light

Answer 21

• bright light: circular muscles contracy and radial muscles relax - makes pupil smaller to avoid retinal damage.
• dim light: circular muscles relax and radial muscles contract - makes pupil larger so more light can enter the eye.

Question 22

what is accommodation?

Answer 22

accommodation is the alteration of the lens’ shape in order to focus on near or distant objects.

Question 23

how does the eye focus on a nearby object?

Answer 23

• ciliary muscles contract.
• suspensory ligament loosen.
• lens becomes thicker and more curved - light rays are refracted strongly.

Question 24

how does the eye focus on a far away object?

Answer 24

• ciliary muscles relax.
• suspensory ligaments tighten.
• lens become thinner - light rays are refracted weakly.

Question 25

what is myopia?

Answer 25

myopia (short-sightedness) usually occurs when the lens of the eye is too curved. as a result, light is focused in front of the retina so images appear blurry.

Question 26

how can myopia be treated?

Answer 26

myopia can be treated using glasses with a concave lense, which spreads out light rays so they can be focused on the retina.

Question 27

what is hyperopia?

Answer 27

hyperopia (long-sightedness) usually occurs when the lends of the eye is too flat. as a result, light is focused behind the retina so images appear out of focus.

Question 28

how can hyperopia be treated?

Answer 28

hyperopia can be treated using glasses with a convex lense, which brings the light rays together so they can be focused on the retina.

Question 29

what are the two types of contact lenses?

Answer 29

contact lenses are lenses that are placed on the eye. there are two types:
- hard - rigid material, last a long time, must be kept sterile.
- soft - flexible material, last for a shorter time, more comfortable.

Question 30

what is laster eye surgery?

Answer 30

laser eye surgery is the use of lasers to fix visual defects in adults. to treat myopia, lasers reduce the thickenss of the cornea so light is refracted less strongly. to treat hyperopia, lasers alter the curvature of the cornea so that light is refracted correctly.

Question 31

how can replacement lenses be uised to treat visual defects?

Answer 31

a replacement lens can either implanted into the eye (along with the natural lens) or it may replace the natural lens altogether. risks of lens replacement include retinal damage, cataracts and infections.

Question 32

what are the risks of lens replacement?

Answer 32

risks of lens replacement include retinal damage, cataracts and infections

Question 33

where is body temperature controlled in the body?

Answer 33

body temperature is controlled by the thermoregulatory centre in the hypothalamus of the brain.

Question 34

how is temperature monitored by the body?

Answer 34

• thermoregulatory centre has receptors sensitive to blood temperature.
• skin has receptors sensitive to skin temperature - sends impulses to thermoregulatory centre.

Question 35

what physiological changes occur when the body temperature is too high?

Answer 35

• vasodilation - blood vessels near the surface of the skin dilate - more heat is radiated away.
• sweating - evaporation of water takes away heart energy form the surface of the skin.

Question 36

what physiological changes occur when the body temperature is too low?

Answer 36

• vasoconstriction - blood vessels near the surface of the skin contrict - less heat radiated away.
• shivering - respiration allows muscles to contract. it is an exothermic process, so heat energy is released.
• sweating stops.