Chapter 10: The Nervous System and The Eye Flashcards
What is sensitivity?
The ability of an organism to detect and respond to changes in the environment
What is the role of the nervous system in humans?
- Allows organisms to detect changes in their surroundings and respond to it
- Enables the coordination of the different parts of the body
What does the Central Nervous System consist of?
Brain
Spinal cord
What does the Peripheral Nervous System consist of?
Cranial nerves
Spinal nerves
Sense organs (receptors)
What are the 5 sense organs and the stimuli to which they respond?
1. Eye
- Light, stimulates photoreceptors on retina
2. Ear
- Sound waves, detected by eardrum in the form of vibrations
3. Tongue
- Four tastes, stimulate receptors on taste buds
4. Nose
- Odours, stimulate olfactory receptors lining the nasal cavity
5. Skin
- Sensations of pain, pressure, heat and cold, stimulate nerve endings in skin
What are the differences between a sensory and a motor neurone?
Sensory neurone: Short axon
Motor neurone: Long axon
Sensory neurone: Long dendron
Motor neurone: Short dendron
Sensory neurone: Circular cell body
Motor neurone: Irregularly-shaped cell body
Sensory neurone: Transmits nerve impulses from the receptors to the central nervous system
Motor neurone: Transmits nerve impulses from the central nervous system to the effectors
What is a reflex action?
- An immediate response to a specific stimulus without conscious control
- Involuntary, not under the control of a person’s will
What are the processes which occur within the body after touching a hot object?
- Heat stimulates the receptors in the skin
- Nerve impulses are produced
-transmitted along the sensory neurone
-across a synapse to the relay neurone in the spinal cord
-to the motor neurone across a synapse - At the same time, nerve impulses are transmitted to the brain
- The motor neurone transmits the nerve impulses to the effector
- The effector muscle contracts, resulting in the withdrawal of the hand from the hot object
Which part of the nervous system perceives pain?
The brain
What is the reflex arc?
A reflex arc is the shortest pathway which nerve impulses travel from the receptor to the effector in a reflex action
What is a synapse?
A junction between two neurones/
A junction between a neurone and an effector
Where do relay neurones lie?
Within the grey matter of the spinal cord and brain
How does the nervous system process a sensation?
- Receptors in skin are stimulated
- Nerve impulses are produced and transmitted by a sensory neurone
- to a relay neurone in the CNS
- The brain receives the nerve impulses
- The brain interprets the impulses
- The sensation is felt
How does the nervous system process a voluntary action?
- Nerve impulses are produced in the brain
- Nerve impulses are transmitted to a relay neurone in the CNS
- and transmitted to a motor neurone
- Effector muscles receive nerve impulses from the motor neurone
- Muscle contracts
- The action is carried out
How does the nervous system process a reflex action?
- Receptors are stimulated
- Nerve impulses are produced and transmitted by a sensory neurone
- to a relay neurone in the CNS
- and to a motor neurone
- Effector muscles receive the nerve impulses from the motor neurone
- Muscle contracts
- The action is carried out
Comparison between a voluntary action, an involuntary action and a reflex action?
Voluntary: Controlled by our will
Involuntary: Not controlled by our will
Reflex: A sudden action in response to something
Voluntary: Does not require a stimulus
Involuntary: Does not require a stimulus
Reflex: Requires a stimulus
Voluntary: Regulated by brain
Involuntary: Regulated by brain
Reflex: Regulated by brain or spinal cord
Voluntary: Produced by choice
Involuntary: Occurs throughout our lifetime
Reflex: Produced during an emergency
Voluntary: Choice-dependent speed
Involuntary: May be slow or quick
Reflex: Always quick
What are the three layers of the wall of the eyeball?
- Sclera
- Choroid
- Retina
What is the function of the sclera?
- Continuous with the cornea
- Attached to eye muscles
- Facilitate movement of eyeball
What is the function of the choroid?
- Prevents internal refraction of light
- Contains blood vessels
-carry oxygen and nutrients to the eyeball
-remove metabolic waste products from
What is the function of the retina?
- Contains photoreceptors (rods and cones)
-Rods-> more sensitive to light, enable us to see in dim light (but only in black and white)
-Cones-> enable us to see colours in bright light
-Photoreceptors: detect light changes, convert light waves into nerve impulses - Connected to nerve fibres in optic nerve
What is the function of the fovea?
- Where images are focused
- Contains cones but not rods
- Enables a person to have detailed colour vision in bright light
What is the blind spot?
- Region where optic nerve leaves the eye
- Does not contain photoreceptors
What is the function of the optic nerve?
- Transmits nerve impulses to the brain when photoreceptors are stimulated
What is the function of the lens?
- Transparent, circular, biconvex structure
- Shape or thickness changed in order to refract light onto the retina
What is the function of the cornea?
- Refracts light rays into the eye
What is the function of the eyelid?
- Protects the cornea from mechanical damage
- Squinting prevents excessive entry of light which may damage the retina
- Blinking spreads tears over the eyes so that dust can be wiped off
What is the function of the tear gland?
- Secretes tears to:
-wash away dust particles
-moisten cornea for absorption of dissolved oxygen
-lubricate the conjunctiva, reducing friction when the eyelids move
What is the function of the conjunctiva?
- Secretes mucus to keep the front of the eyeball moist
What is the function of the iris?
- Circular sheet of 2 sets of involuntary antagonistic muscles (circular and radial muscles)
- Contains pigment which gives the eye its colour
What is the function of the eyelash?
- Shields eye from dust particles
What processes occur within the eye in bright light?
- More light enters the eye
- Photoreceptors on the retina are stimulated
- Nerve impulses are transmitted to the brain through sensory neurone in the optic nerve
- The relay neurone in the brain transmits nerve impulses via the motor neurone to the iris of the eye
-Circular muscles of the iris contract
-Radial muscles of the iris relax - Size of pupil decreases and pupil constricts
- Less light enters the eye
What processes occur within the eye in dim light?
- Less light enters the eye
- Photoreceptors on the retina are stimulated
- Nerve impulses are transmitted to the brain through sensory neurone in the optic nerve
- The relay neurone in the brain transmits nerve impulses via the motor neurone to the iris of the eye
-Circular muscles of the iris relax
-Radial muscles of the iris contract - Size of pupil increases and pupil dilates
- More light enters the eye
What are the properties of the image formed on the retina?
- Vertically inverted
- Laterally inverted
- Smaller in size than actual object
What is the pathway for the formation of an upright image at the brain?
- Inverted image formed on the retina
- Photoreceptors are stimulated
- Nerve impulses generated are transmitted through the optic nerve
- Nerve impulses reach the optic centre of the brain
- The brain interprets the information and forms an upright image
What is focusing?
- The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina
What happens within the eye when looking at nearby objects?
- Light rays from a near object are divergent
- A greater angle of refraction is needed to focus on the object
- Ciliary muscles contract
- Suspensory ligaments slacken
- Lens becomes thicker and more convex
- Focal length decreases
- Light rays are focused sharply on the retina
- Photoreceptors on the retina are stimulated
- Nerve impulses are transmitted to the brain via the optic nerve
- The brain interprets the impulses
- Person sees the near object
What happens within the eye when looking at distant objects?
- Light rays from a distant object are parallel
- A smaller angle of refraction is needed to focus on the object
- Ciliary muscles relax
- Suspensory ligaments become taut
- Lens is pulled thinner and less convex
- Focal length increases
- Light rays are focused sharply on the retina
- Photoreceptors on the retina are stimulated
- Nerve impulses are transmitted to the brain via the optic nerve
- The brain interprets the impulses
- Person sees the distant object
Why does the shape of the eyeball being too long cause myopia?
When the eyeball is too long, light rays converge in front of the fovea and cause an unclear image to be formed on the retina.
What are some causes of myopia?
(8 pts.)
- Eyeball too long
- Lens too strong
- Lens too convex
- Lens not elastic enough
- Lens not flexible enough
- Ciliary muscles are unable to relax
- Cornea is too curved
- Cornea is too convex
