chapter 10- NS and eye

Question 1

stimulus

Answer 1

a change in the environment that causes a reaction (response) in a organism

Question 2

CNS

Answer 2

the central nervous system. consists of the brain and the spinal cord

Question 3

PNS

Answer 3

peripheral nervous system. consists of the cranial and spinal nerves, and the sense organs, and receptors (nerves)

Question 4

what happens when there is a stimulus?

Answer 4

when there is a stimulus, receptors in our sense organs are stimulated to produce nerve impulses, which are transmitted by nerves to the central nervous system, which transmits the nerve impulses (electrical signals) to the effectors (bring about a response) , which are either muscles or glands (also controls secretion of hormones).

Question 5

sensory neurones

Answer 5

transmits nerve impulses from the receptors to the CNS (circular cell body, one long nerve fibre between receptor and cell body, one short nerve fibre between cell body and CNS)

Question 6

relay neurones

Answer 6

transmits nerve impulses within the the CNS

Question 7

motor neurones

Answer 7

transmits nerve impulses from CNS to effector organs (irregular-shaped cell body, one long nerve fibre between cell body and effector

Question 8

synapse

Answer 8

junction between two neurones. the neurones releases chemicals that help transmit nerve impulses across the synapse

Question 9

reflex action

Answer 9

immediate response to a specific stimulus without conscious control.

there are two types of stimulus, both controlled by reflex centres : cranial reflexes (controlled by brain) and spinal reflexes (controlled by spinal cord)

Question 10

touching a hot object

Answer 10

he heat from the object will stimulate the thermoreceptors in the skin, producing nerve impulses, which are produced at the brain and transmitted along the sensory neurons to the spinal cord. at the spinal cord, the nerve impulses are transmitted across a synapse to the relay neurons, and then across another synapse to the motor neurons. the motor neurons transmit the nerve impulses from the spinal cord to the effector, the arm muscles. the biceps muscle contracts and causes your hand to withdraw suddenly. at the same time, a relay neurone transmits nerve impulses to the brain for pain sensation.

Question 11

motion of voluntary action

Answer 11

nerve impulses are initiated and generated at the brain. nerve impulses are transmitted via the relay neurons down to the spinal cord. nerve impulses are transmitted across a synapse from the relay neurons to the motor neurons, and finally to the effector muscles (arm muscles). arm muscles contract and hand is withdrawn

Question 12

which neurone is not involved in voluntary action?

Answer 12

sensory neurones

Question 13

reflex arc

Answer 13

the shortest pathway by which nerve impulses is transmitted from the receptor to effectors in a reflex action

Question 14

cornea

Answer 14

done shaped transparent layer that is able to refract light rays into the pupil of the eye

Question 15

conjunctiva

Answer 15

a mucus membrane that covers the sclera. it secretes mucus to keep the front of the eyeball moist

Question 16

pupil

Answer 16

hole in the centre of the iris, allowing light (the stimulus) to enter the eye

Question 17

iris

Answer 17

circular sheet of muscles, consisting of two sets of involuntary muscles (circular and radial muscles). it controls size of pupil and contains a pigment which gives the eye its colour (melanin)

Question 18

eyelid

Answer 18

protects the cornea from mechanical damage. squinting prevents excessive entry of light. blinking spreads tears over the eyes so that dust can be wiped off

Question 19

eyelash

Answer 19

shields eye from the dust particles

Question 20

tear glands

Answer 20

secretes tears to wash away dust particles, keep the cornea moist for atmospheric oxygen to dissolve and diffuse, and lubricates the conjunctiva, reducing friction when the eyelids move

Question 21

sclera

Answer 21

tough, white outer covering of the eyeball which is continuous with the cornea, protects the delicate inner structures, eye muscles (rectus muscles) attached to this layer facilitates the movement of the eyeball, and maintains the shape of the eyeball

Question 22

choroid

Answer 22

black pigmented middle layer which prevents the internal reflection of light. it contains blood vessels that transports oxygen and nutrients (glucose and AA molecules) to eyeball and removes metabolic waste products from the eyeball

Question 23

retina

Answer 23

innermost layer of the eye wall. it contains light-sensitive cells known as photoreceptors, consisting of rods and cones. they are connected to nerve fibres from the optic nerve, and retina is where images are formed and detected

Question 24

fovea

Answer 24

small yellow depression where images are focused. they contain the highest concentration of cones but have no rods. it enables a person to have detailed a colour vision in bright light

Question 25

blind spot

Answer 25

point where the optic nerve leaves the eye and does not contain photoreceptors, therefore it is not sensitive to light (image is formed on the blind spot, but it is not detected as the photoreceptors are not present)

Question 26

optic nerve

Answer 26

transmit nerve impulses from the eye to the brain when photoreceptors are stimulated

Question 27

lens

Answer 27

transparent, circular and biconvex structure. its shape or thickness can be changed in order to refract light onto the retina. it focuses light onto the retina (cataract : when lens become opaque as proteins denature)

Question 28

suspensory ligaments

Answer 28

attaches the edge of the lens to the ciliary, helps in focusing or accommodation

Question 29

ciliary body

Answer 29

contains ciliary muscles which control the curvature and thickness of lens

Question 30

aqueous chamber

Answer 30

space between the lens and the cornea. it is filled with aqueous humour, a transparent watery fluid. aqueous humour keeps the front of the eyeball firm and refracts light into the pupil

Question 31

vitreous chamber

Answer 31

space behind the lens. it is filled with vitreous humour, a transparent jelly-like substance, and keeps eyeball firm and refracts light onto the retina (floaters are bits of cellular debris which drift within the vitreous humour and may temporary show up in our field of view)

Question 32

describe the eye when we look in bright light

Answer 32

light ray enters the eye and photoreceptors in the retina are stimulated. nerve impulses are generated which will then be transmitted along the sensory neurone in the optic nerve to the brain. in the brain, nerve impulses are transmitted through across a synapse to the relay neurone and across another synapse to the motor neurone, then to the effector muscle, which are the circular and radial muscles in the iris. the circular muscles of the iris contract and the radial muscles of the iris relaxes, the pupil contricts, reducing the amount of light entering the eye, preventing damage of the photoreceptors.

Question 33

describe the eye when we look in dim light

Answer 33

light ray enters the eye and the photoreceptors in the retina are stimulated by the change in light intensity. nerve impulses are generated, and will be transmitted to along the sensory neurone to the brain via the optic nerve. in the brain, nerve impulses are transmitted to the relay neurone across a synapse and then across another synapse to the motor neurone. motor neurone transmits the nerve impulses to the effector muscles, the circular and radial muscles in the iris. the circular muscles relaxes and the radial muslces constracts, the pupil dilates to allow more light to enter the eye for a clearer vision.

Question 34

focusing

Answer 34

adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina

Question 35

focusing on a distant object

Answer 35

recuts muscles at the top of the eye contracts to pull eyeball upwards. ciliary muscles relax and the suspensory ligaments become taut. the lens becomes thinner and less convex. the light rays from the object are focused on the retina, decreasing the focal length. photoreceptors in the retina will be stimulated, and nerve impulses will be generated and transmitted along the sensory neurones in the brain via the optic nerve. the brain interprets the nerve impulses, and the person is able to see the image.

Question 36

focusing on a near object

Answer 36

recuts muscles at bottom of eye contracts to pull eyeballs downwards. the ciliary muscles contract, and the suspensory ligaments slackens, relaxing the pull on the lens. the lens becomes thicker and more convex. light rays from the near object will be focused on the retina. photoreceptors in the retina will be stimulated and nerve impulses will be generated whichare trasnmitted to the brain via the sensory neurone in the optic nerve. the brain interprets the nerve impulses, and the person is able to see the near object.

Question 37

question type : what is not a component of voluntary action?

Answer 37

sensory neurons (from receptors). since voluntary action does not use receptors, sensory neurones not involved.

Question 38

question type : what is blocked so that the patient has reflex action but cannot feel pain?

Answer 38

the path towards the brain

Question 39

question type : what is blocked so that patient has voluntary action but cannot feel pain?

Answer 39

at the receptors

Question 40

neurotransmitters

Answer 40

chemicals that transmits of nerve impulses between synapses and junctions (from sensory to relay, relay to motor, from motor to tissue)

Question 41

structure of eye needed for maintaining shape

Answer 41

aqueous and vitrous chamber, sclera

Question 42

structure of eye needed for accommodation

Answer 42

cornea, aqueous humor, ciliary muscles, suspensory ligaments, lens

Question 43

structure of eye needed for pupil reflex

Answer 43

circular and radial muscles of iris