Chapter 10 - The Nervous System and the Eye Flashcards
The nervous system and the endocrine system work together to….
Maintain the internal environment in the human body (aka homeostasis)
What does the nervous system use to coordinate activities in the body?
Nerve impulses
What does the endocrine system depend on for effective coordination of activities?
Hormones
Homeostasis is carried out by the nervous system, which involves what stages?
Stimulus –> Receptor –> Reflex/Control centre –> Effector –> Response
What does the nervous system in humans do?
Regulates bodily functions and activities and how we react to the surroundings
What is the stimulus?
- Homeostatic control is always triggered by a stimulus
- It is a change in the environment that causes an organism to react
What is the receptor?
The receptor in sense organ detects the stimulus and sends nerve impulses down the sensory neurone and relay neurone to reach the control centre
What is the reflex centre?
- The brain and the spinal cord which act as a coordination centre
- After processing info, the brain or the spinal cord sends nerve impulses down the relay neurone and motor neurone to the effector (to ‘instruct’ us on how to react to the stimulus)
What is the effector?
- The effector brings about a response
- The effector is a muscle (In endocrine system, effector is an endocrine gland)
What is a response?
- A response is the organism’s reaction to a stimulus
- The muscles contract (n endocrine system, a gland secreted hormones)
What is the ability to respond to a stimulus known as?
Sensitivity or irritability (e.g. touching a hot object [stimulus], and moving hand away [response to stimulus])
What is the nervous system made up of?
1) Central nervous system
- Brain
- Spinal cord
2) Peripheral nervous system
- Cranial nerves
- Spinal nerves
- Sense organs
What are neurones?
Nervous tissue have nerve cells aka neurones. Bundles of neruones are called nerves
Describe the sensory neurone
Structure: Has a circular cell body, with a nucleus, cytoplasm, cell membrane, organelles, a long nerve fibre towards the receptor and a short one towards relay neurones
Function: Transmits nerve impulses from receptors to CNS
What is a nerve fibre?
A strand of cytoplasm extending from the cell body
Describe the relay neurone
Structure: Intermediate neurone within the CNS
Function: Transmits nerve impulses from the sensory neurone to the motor neurone
Describe the motor neurone
Structure: Irregular shape of cell body containing nucleus, cytoplasm, cell membrane, organelles
Function: Transmits nerve impulses from CNS to effector to produce a response
What is a reflex arc?
The shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action
Describe the pathway of a reflex arc
Stimulus → Receptors → Sensory Neurone → CNS (Relay Neurone) → Motor Neurone → Effector → Response
What is a synapse?
The junction between 2 neurones where nerve impulses are not able to cross from one neurone to the next directly (due to the tiny spaces between)
What happens when a nerve impulse reaches one end of a neuron?
It stimulates the release of chemicals into the synapse that diffuse across the tiny space where they trigger the formation of a new nerve impulse in the next neurone
What do nerve impulses not carry?
They do not carry sensations (e.g. pain, cold). Nerve impulses are just electrical impulses that travel down the neurones within a fraction of a second
What are sensations?
When holding ice, the temperature receptors n skin are stimulated and nerve impulses produced are transmitted to the brain. The brain interprets the nerve impulses and that is the sensation of coldness
(Receptor –> Sensory neurone –> Relay neurone in SC –> Brain)
What are voluntary actions?
When raising a hand in class, nerve impulses are produced in the brain, transmitted by a relay neurone from the brain, down the spinal cord. In spinal cord, nerve impulses are transmitted to the motor neurone, to the effector muscles in the arm. The muscles contract and arm is raised
(Brain –> Relay neurone in SC –> Motor neurone –> Effector)
What is a reflex action?
An immediate response to a specific stimulus without conscious control
Describe reflex actions
- Involuntary actions
- Rapid + automatic
- Simplest form of response
- Impossible to prevent consciously
What happens when a person touches an extremely hot object?
- Receptors in skin (nerve endings) are stimulated
- Nerve impulses are produced
- Nerve impulses are transmitted to the spinal cord by the sensory neurone
- In spinal cord, nerve impulses are transmitted to the relay neurone across a synapse to the motor neuone
- The motor neurone transmits the nerve impulses from the spinal cord to the biceps muscle (effector) causing it to contract causing hand to withdraw
- In spinal cord, nerve impulses from sensory neurone can be sent to the brain to feel pain
(Receptor –> Sensory neurone –> Relay neurone –> Motor neurone –> Biceps muscle)
What are the differences between endocrine (hormonal) and nervous control?
1) Endocrine –> involves hormones as signals
Nervous –> involves nerve impulses as signals
2) Endocrine –> hormones are transported by blood
Nervous –> Nerve impulses transmitted by neruone
3) Endocrine –> Slow responses generally
Nervous –> Fast responses generally
4) Endocrine –> Responses may be short lived
Nervous –> Responses are short lived
5) Endocrine –> Always involuntary
Nervous –> Can be voluntary or involuntary
6) Endocrine –> May affect more than one target organ
Nervous –> Usually localised (a particular part of the body)
What is the eye responsible for?
The eyes are the sensory organs responsible for sight
What are the eyes sensitive to?
Light
Each eyeball lies in a hollow in the skull called the ____
Orbit
What are eyes attached to the skull with?
Rectus muscles which control eye movement
What are the external structures of the eye?
1) Eyelashes
2) Eye lid
3) Sclera
4) Pupil
5) Iris
6) Conjunctiva
7) Tear gland
What is the function of the eyelashes?
Shield eye from dust particles to prevent them from entering the eye
What is the function of the eye lid?
- Protects cornea from mechanical damage/injury
- Blinking action to spread tears which wipe the dust particles off the cornea
- Prevents excessive light from entering eyes by being partly closed aka squinting and prevents retina becoming damaged
- Covers eyes to prevent evaporation when sleeping
What is the function of the sclera?
White part surrounding the iris which provides structure, strength and protection to the eye from mechanical damage
What is the function of the pupil?
A hole in the center of the eye where light passes through
What is the function of the conjunctiva?
A thin transparent, mucous membrane covering the sclera in front. Secretes mucus to maintain the front of the eyeball moist
What is the purpose of the tear gland?
Secretes tears to
- wash away dust particles - keep cornea moist for oxygen to dissolve so that it can diffuse into the cornea
- lubricate the conjunctiva to reduce friction when eyelids move
What is the retina?
_ Innermost layer of eye
- Light sensitive layer where images are formed
- Has photo receptors (cells) that are connected to the nerve endings from the optic nerve.
- Photoreceptors detect and process light that enters the eye
What is the lens?
- Transparent, circular and biconvex structure
- Elastic and changes shape/thickness to focus light onto the retina
What is the blind spot?
- Small region of the retina where the optic nerve leaves the eye
- No rods/cones, not sensitive to light
- Can’t see the object if it falls on the blind spot
What is the optic nerve?
- Transmits nerve impulses to the brain when photoreceptors in the retina are stimulated
What is the fovea?
- Small yellow depression in the central part of the retina
- Images are focused, greatest concentration of cones, but no rods
- Enables person to see detailed colour in bright light
What is the vitreous chamber?
- Space behind the lens filled with vitreous humour
- Keeps eyeball firm and helps refract light onto the retina
What is the choroid?
- Middle layer of eyeball
- Pigmented black to prevent internal reflection of light
- Contains blood vessels that bring oxygen and nutrients to eyeball and remove metabolic waste products
What is the cilary body?
- Thickened region at he front end of the choroid
- Has ciliary muscles that control the curvature or thickness of lens
What is the suspensory ligament?
Connective tissue that attaches the edge of the lens to the ciliary body and holds lens in place
What it the cornea?
- Dome shaped transparent layer continuous with the sclera
- Refracts light rays into eye
- Causes greatest amount of refraction of light into eye
What is the aqueous chamber?
- Space between the lens and cornea
- Has aqeuous humour, transparent watery fluid
- Keeps front of the eyeball firm and refracts light into the pupil
What is the iris?
- Circular sheet of muscles
- Controls size of pupil, how much light entering eye by responding to different light intensities by the involuntary muscles - circular and radial
- Contains pigment that gives the eye colour
What is the pupil reflex?
Reflex action controlled by the brain without conscious effort (type of cranial reflex). Pupil changes in size in response to changes in light intensity
What happens if light is too intense?
Retina may be damaged
What happens if light is too little?
Not able to see clearly
When light intensity changes which muscle causes what to change?
The iris muscles cause pupil size to change
What are the advantages of the pupil reflex?
1) No conscious effort, automatic, no learning required
2) Prevents excess light entering the eye that can damage retina
3) Immediate response
4) Allows enough light to enter that enable us to see
What are the iris muscles made up of?
1) Circular muscles
2) Radial muscles
They are antagonistic muscles
Which muscles relax and contract under bright light?
- Radial muscles relax
- Circular muscles contract
- Pupil size decreases/ pupil constricts
Which muscles relax and contract under dim light?
- Radial muscles contract
- Circular muscles relax
- Pupil size increase/dilates
What is the reflex arc of the pupil? (summarised)
Stimulus (light intensity) –> receptor (retina) –> sensory neurone (in optic nerve) –> relay neurone in brain –> motor neurone –> effector (iris muscles)
What is the proper explanation for the reflex arc of the pupil?
1) Light intensity entering the eye changes
2) Receptors in retina stimulated and trigger nerve impulses in the sensory neurone in the optic nerve
3) The nerve impulses are transmitted first across a synapse to the relay neurone in the brian and then across another synapse to the motor neurone
4) Motor neurone transmits nerve impulses to the effector (iris muscles)
5) Iris muscles contract
When light falls on an object, rays of light are reflected from object, some fall onto the eye. How are light rays refracted?
1) Light rays are refracted through the cornea and aqueous humour onto the lens
2) Lens causes further refraction and rays are brought to a focus on the retina
3) The image on the retina stimulates the rods/cones depending on light intensity, image formed is
- upside down (inverted)
- laterally inverted
- diminished (smaller in size)
What happens when nerve impulses are produced when light falls on the rods and cones?
Nerve impulses are transmitted via optic neve to the brain and brain interprets these impulses so that we see the object the right way up, front to back and the correct size
What is focusing?
The adjustment of the lens of the eye so that the clear images of objects at different distances are formed on the retina
When focusing the ____ or ____ of the lens are adjusted to allow light rays to be focused on the ____
When focusing the thickness or curvature of the lens are adjusted to allow light rays to be focused on the retina
Describe the light rays when looking at a distant object
- Light rays from a distant object are almost parallel to each other
- Light rays are refracted through the cornea and the aqueous humour into the pupil
- Since rays are almost parallel, lens need to be thinner as only little refraction is needed
What are the changes in the eye when focusing on a distant object?
1) Ciliary muscles relax, pulling on the suspensory ligaments
2) Suspensory ligaments become taut, pulling on the edge of the lens
3) Lens become thinner and less convex
4) Light rays from the distant object are sharply focused on the retina
5) Photoreceptors are stimulated
6) Nerve impulses produced are transmitted by the optic nerve to the brain. Brain interprets nerve impulses and person sees object
Describe the light rays when looking at a near object
- Diverging light rays reflecting off the near object are refracted through the cornea and the aqueous humour into the pupil
- Since rays reaching the eye are diverging, lens need to be thicker to bend the light rays more
What are the changes in the eye when focusing on a near object?
1) Ciliary muscles contract, relaxing their pull on the suspensory ligaments
20 Suspensory ligaments slacken, relaxing their pull on the lens
3) The lens, being elastic, becomes thicker and more convex
4) Light rays from near objects are sharply focused on the retina
5) Photoreceptors are stimulated
6) Nerve impulses produced are transmitted by the optic nerve to the brain. The brain interprets the nerve impulses and the person sees the object
