The Nervous System and the Eye Flashcards
What is a neurone?
Specialised cells which transmit information through nerve responses
What is a nerve?
A bundle of several neurones
Nerve cell = a single neurone
What is a nerve impulse?
Electrical signal (current) that travels along a neurone
Two examples of reflexes
Knee jerk reflex
Pupil reflex
What is the cell body?
The part of a neurone which contains the nucleus
What is the dendrite?
Extensions at which nerve impulses are received from other cells at synapses and transmitted to the cell body
What is the axon?
Extension which carries nerve impulses to other neurone or effector organ (muscle or gland)
What is the myelin sheath?
Fatty sheath which insulates the axon (preventing short-circuits of electrical impulses) and speeds up the conduction of nerve impulses, made of Schwann cells
What are the steps of the reflex arc?
- Stimulus (could be pain)
- Receptor
- Sensory neurone (anywhere where you feel sense)
- Relay neurone (in the central nervous system)
- Motor neurone
- Effector (muscle, gland)
- Response
Way to remember the reflex arc?
Steve Receives Stamps Regularly Meanwhile Emily Runs
What is a reflex?
Involuntary and almost immediate response to a stimulus
What does the central nervous system consist of and how is it linked to the sense organs?
The brain and the spinal cord are the two parts of the central nervous system. They are linked to the sense organs by nerves
What are the three parts of the spine?
Intervertebral disc
Spinal cord
Vertebral column (encloses and protect the spinal cord)
What is a synapse?
A tiny gap between 2 neurones across which impulses pass by diffusion of a neurotransmitter
What is are neurotransmitters?
Chemicals that transmit signals from one neurone to another across a synapse
Two examples of diseases linked to defective neurotransmitter function
Schizophrenia
Depression
Steps of transmitting of a nerve impulse across a synapse
- Nerve impulse travels along the axon to the synapse in the form of an electrical signal
- The vesicles containing the neurotransmitters move to the membrane of the axon terminal
- Neurotransmitter is emptied into the synapse
- Neurotransmitter diffuses across the synapse
- Neurotransmitter binds to the receptor on the surface of the dendrite
- Binding of the neurotransmitter triggers a new nerve impulse
- The nerve impulse travels along the dendrite to the axon
What is the function of the conjunctiva in the eye? And what is it?
It is a layer covering the cornea and sclera
Helps lubricate the eye
What is the function of the cornea in the eye? And what is it?
It is a clear covering over the eye
Helps refract and focus light
What is the function of the lens in the eye? And what is it?
It a transparent structure behind the pupil
Refracts and focuses light
What is the function of the pupil in the eye? And what is it?
It is a hole in the centre of the iris
Controls the amount of light entering the eye
What is the function of the iris in the eye? And what is it?
It is a pigmented tissue
Controls the amount of light entering the eye
What is the function of the suspensory ligaments in the eye? And what are they?
They are ligaments connecting the ciliary muscle and the lens
Involved in controlling accommodation
What is the function of the ciliary muscle in the eye? And what is it?
It is a ring of muscle connected to the lens via suspensory ligaments
Controls accommodation
What is the function of the retina in the eye? And what is it?
It is the inner layer of the eye containing photoreceptors (rods + cones)
Responds to light stimulus
What is the function of the optic nerve in the eye? And what is it?
It is a sensory nerve (part of the CNS)
Carries nerve impulses from retina to brain
What process happens to the pupil in dim light which allows it to dilate?
- The stimulus of a dim light is picked up by the retina which sends a nerve signal to the optic nerve.
- The optic nerve acts as a sensory neurone and sends the signal to the CNS
- The nerve signal goes through a relay neurone and into a motor neurone
- The signal is sent to the muscles in the iris which respond
What are the muscles in the iris?
Radial muscles
Circular muscles
What happens in the iris when in dim light?
- Radial muscles contract
- Circular muscles relax
- Pupil dilates (gets bigger)
What happens in the iris when in bright light?
- Radial muscles relax
- Circular muscles contract
- Pupil gets smaller
What do rods do in the retina?
Help with vision in dim light
What do cones do in the retina?
Provide colour vision
What is accommodation in the eye?
The reflex that makes the eye focus on an object by changing the shape of its lens
What happens to light that is reflected from an object?
The light is refracted (bent) by the cornea and the lens forming an upside down image on the retina
What causes short sightedness and how can it be cured?
The eye is too long so the point of focus is before the retina
Corrective concave lenses are used
What causes far sightedness and how can we cure it?
The eye is too short so the point of focus is behind the retina
Corrective convex lenses are used
