Coordination - The Eye and Ear Flashcards
What is a stimulus?
A change in the environment of an organism that produces a response
The sequence of events in the coordination system:
Stimulus ➡ receptor ➡ CNS ➡ effector ➡ response
The function of receptors:
To detect a stimulus by changing the energy they receive into electrical energy in nerve impulses
A nerve cell is called _______
Neurone
How are impulses that travel along the nerve cell caused?
Due to the movement of ions in and out of the neurone
What makes up the CNS?
Brain and spinal cord
Where is the cell body of the sensory neurone located?
Outside the CNS
Where is the cell body of the muscle neurone located?
Inside the CNS
What is a myelin sheath?
Covering made up of lipids (fatty material called myelin) by membranes of specialised cells that surround an axon as it develops
What is its function?
It insulates the axon and prevents short circuits with other axons
Speeds up the conduction of the impulses
Pathway in synapses (integrating info. in CNS):
Pre-synaptic neurone ➡ electrical impulses ➡ neurotransmitters (vesicles) ➡ diffuse ➡ receptors (membranes) ➡ post-synaptic neurone ➡ generate impulses ➡ broken down by enzymes
What are reflex actions?
A reflex action is a rapid and involuntary (not started by impulses from the brain) response to a stimulus
What is a reflex arc?
Nerve pathway of a reflex action
Pathway for a reflex action:
Receptors ➡ sensory neurones ➡ dorsal root ➡ synapse ➡ relay neurone ➡ motor neurone ➡ ventral root ➡ effector
Where are the cell bodies of sensory neurones located in a reflex pathway?
Swelling in the spinal nerve called the dorsal root ganglion
Location of grey matter:
The tissue in the middle of the spinal cord and outer part of the brain
Consists of mainly nerve cell bodies
Location of white matter:
The tissue in the middle of the brain and outer part of the spinal cord
Consists of mainly nerve cell axons
Receptors and effectors for the knee-jerk reflex (acts in situations where the knee joint is unexpectedly flexed eg. helping you to stop from tripping or falling over):
Receptors: stretch receptors in the tendons below the knee
Effectors: thigh muscles (contract)
The largest part of the brain?
Evaluate it
Cerebrum: 2 cerebral hemispheres
: cerebral cortex
Functions of the cerebrum:
- Contains sensory areas
- Motor areas
- Higher activities: memory, emotions, personality
Other parts of the brain (not cerebrum):
Cerebellum
Medulla (cardiac and respiratory center)
Hypothalamus
Pituitary gland
Meninges
The functions of the cerebellum:
- Coordinating the contraction of sets of muscles
- Maintaining balance
Oval window
Membrane covered opening leading from the middle ear to the cochlea in the inner ear
Eustachian tube
Connecting the ear to the throat so that air pressure on both sides of the eardrum is equalised
Organ of Corti
Located in a membrane between the middle and outer canals
Receptor cells have sensory hair cells embedded in the second membrane
How is the frequency of sound determined?
By seeing which hair cells have been stimulated: Those near the oval window are sensitive to higher frequencies
How is the loudness of sound determined?
By the amplitude of vibrations of the hair cells: Loud sounds produce high amplitude vibrations which result in more nerve impulses per second in the sensory neurones
Parts of the ear involved in its functioning as an organ of balance:
Detecting movement
Semicircular canals
Ampulla
Cupula (embedded hair cells)
Position of the head
Utriculus
Sacculus
Otolith (CaCO₃ crystals)
Damage to the ear:
NIHL (damage to hair cells)
Eardrum rupture/ Ossicles damages
Tinnitus
Choroid
Contains blood vessels and pigment cells that prevent light from being reflected inside the eye
Rods and cones
Rods: dim light and cannot differentiate between colors
(3) Cones: bright light and can detect different colors of light
Place in the centre of the retina that has the highest concentration of cones
Fovea
Where is light refracted?
At the cornea and the lens
Where is the image produced?
An inverted image on the retina
Purpose of iris-pupil reflex:
To ensure that light is falling on the retina at the right intensity
Detail the response of the iris-pupil reflex
Bright: Circular Contract
: Radial Relax
What is the blind spot?
An area on the retina where the optic nerve leaves the eye. It contains no rods/cones so no image is formed
Why is the blind spot not a problem?
Our brain pieces together the image from both the eyes so the blind spots are canceled.
The optic nerve leaves the eye at the edge of the retina where the vision is not sharp anyway
Advantages of having two eyes:
- Cancelling of the blind spot
- A wider field of view
- Stereoscopic vision
Advantages of stereoscopic vision:
Judge distance
depth
speed
Define accommodation:
Changes taking place in the eye which allow it to focus on objects at different distances
What is the lens made up of?
Cells containing an elastic crystalline protein
Relate the size of the lens to its refractive index
A fatter lens will refract light more
What holds the lens in place?
Suspensory ligament (fibres)
Ciliary muscles (rings of muscles)
Changes in the lens to focus on distant object:
Lens has to be flat (less convex): Ciliary muscles relax
: Pressure pushes outwards on the lens
: Stretching ligaments
Where does light fall due to long-sightedness?
Behind the retina
Where does light fall due to near-sightedness?
In front of the retina
Cause of long sight:
Lens not convex enough or eyeball too short
corrected by convex lens to converge light b4 it enters the eye
Detail regular astigmatism
The surface of the cornea or lens is rounder in one direction
Vision will be focused in one direction and no the other
Detail irregular astigmatism
The curvature of the surface of the cornea /lens is uneven in more than one direction
Cataracts
The lens becomes cloudy and opaque
