the human nervous system Flashcards
what is the function of the nervous system?
the nervous system allows the body to react to their surroundings and coordinate an appropriate response.
how does a stimulus lead to a response being carried out by the body?
-stimulus —> receptor —> coordinator—> effector —> response
1. stimulus is detected by a receptor and converted into an electrical impulse
2. the electrical impulse passes along sensory neurones to the central nervous system (CNS)
3. the CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response
what is a reflex action?
an automatic and rapid response which does not involve any conscious input from the brain
why are reflex actions important?
- aid survival by preventing harm to the body
- reduce chance of injury
describe how a reflex action occurs via a reflex arc
- the stimulus is detected by a receptor
- an electrical impulse travels along a sensory neurone to the spinal chord (apart of the CNS)
- at a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap which stimulates a new impulse which passes along the relay neurone
- the same process occurs at a synapse between a relay neurone and a motor neurone.
- at the effector, an appropriate response is carried out
describe a method for measuring reaction time (required practical)
- Sit down on the chair and place your forearm of your non-dominant hand on the table with your hand hanging over the end of the table.
- Have your partner hold the ruler in line so that the 0 mark is level with the top of your
thumb. - Your partner will drop the ruler without telling you beforehand, and you will catch the ruler as quickly as you can.
4.Note and record the number level with the top of your thumb after you have caught the ruler - Repeat the test at least 5 times.
- Swap places with your partner and repeat steps 1-5
- Find reaction times by using a conversion table to convert the ruler measurements.
what are the control variables for reaction time?
- always measure the ruler at the top of the thumb
- keep conditions of room same (lighting, level of bg noise)
what is the difference between a reflex pathway and a conscious pathway?
Within a reflex pathway, the coordination centre is a relay neurone found in the spinal chord/unconscious parts of the brain.
In a conscious pathway, the coordination centre is in the conscious parts of the brain
what is the function of the cerebral cortex?
controls consciousness, intelligence, memory and language
what is the function of the cerebellum?
controls muscular coordination (movement)
what is the function of the medulla?
controls unconscious activities e.g. breathing, heart rate
why is the investigation of the brain difficult?
- the brain is a complex, delicate organ
- the brain is easily damaged and destroyed
- certain membranes prevent drugs from reaching the brain
- the exact function of each part of the brain is not known
what methods are used by scientists to determine brain function?
- studying patients with brain damage
- electrical stimulation of the brain
- rMRI scans
what stimuli are the receptors of the eye sensitive to?
light intensity and colour
what are the 2 main functions of structures found in the eye?
- focusing on near or distant objects - accommodation
- adaptation to dim light
describe the function of the retina
- the retina is a light sensitive layer found at the back of the eye
- light stimulates the retinal cells, resulting in impulses being sent to the brain
describe the structure and function of the optic nerve
- the optic nerve connects the eye and the brain
- it carries impulses to the brain so that an image can be visualised
describe the structure and function of the sclera
the sclera is a tough outer layer of the eye which protects its internal stuctures
describe the structure and function of the cornea
- the cornea is a curved transparent layer at the front of the eye
- it lets light into the eye and allows light to be focused onto the retina
describe the structure and function of the iris
- a muscle which controls the size of the pupil by contracting or relaxing
- this allows the eye to adjust to bright and dim lighting
describe the structure and function of the ciliary muscles and the suspensory ligaments
the ciliary muscles and the suspensory ligaments hold the lens in place and control its shape
describe how the iris alters it’s size of the pupil in both bright and dim light
- bright light —> circular muscles contract and radial muscles relax, makes pupil smaller to avoid retinal damage
- dim light —> circular muscles relax and radial muscles contract, makes pupils larger so more light can enter the eye
what is accommodation?
accommodation is the alteration of the lens’ shape in order to focus on near or distant objects
how does the eye focus on a nearby object?
- ciliary muscles contract so they have a smaller diameter
- suspensory ligaments loosen
- lens becomes thicker and more curved- light rays are refracted strongly
