B10 - The Human Nervous System Flashcards
Define Homeostasis
the balancing act of regulating the internal conditions of a cell or organism to maintain optimal conditions for functioning in response to internal and external changes.
Why is Homeostasis important?
Enzymes work the best in certain conditions, such as in a specific pH or temperature, and so to control functions of a cell it is important to maintain optimum conditions. If not optimal, then enzymes can denature, reducing their ability to catalyse metabolic reactions
Controlled internal conditions
include – temperature, water content and blood glucose
Stimuli
changes in the internal or external environment detected by receptors
Receptors
cells that detect stimuli
Example of sense organ
skin, eye, nose
Coordination Centers
areas which receive and process the information from the receptors and then send out signals and coordinate the responses of the body. Include: the brain, the spinal cord and some organs (the pancreas)
Effector
muscles or glands that respond to stimuli, the muscles contract and the glands secrete chemical substances and hormones
Nerves
bundles of neurons (cells that pass along the electrical impulses
CNS
(central nervous system) made up of the brain and spinal cord
Sensory Neurons
The cells that carry the impulses to your CNS from your sense organs
Motor neuron
carry information from the CNS to the rest of your body where the effectors respond.
Reflex arc
A receptor detects a stimulus. The electrical impulse travels at through the sensory neurone to a CNS where the sensory neurone passes the impulse to the relay neurone via a synapse. The impulse is passed along to a muscle or gland, the effector.
Reflex actions are automatic, rapid and do not involve the conscious parts of the brain
Synapses
junctions between neurones which form physical gaps. When an impulse reaches a synapse, a chemical is released which then diffuses across the synapse and then starts a new electrical impulse.
Cerebral cortex
concerned with consciousness, intelligence, memory and language
Cerebellum
concerned mainly with coordination muscular activity and balance
Medulla
concerned with unconscious activities such as controlling your heartbeat, the movements of the gut and breathing
Hypothalamus
controls body temperature
Pituitary gland
produces hormones
Electrically simulating different parts of the brain
this is when scientists expose the brain by removing the top of the scull and stimulate different areas to see the effects. This tends to be done on conscious patients as there are no sensory nerve endings in the brain.
MRI scans
magnetic resonance imaging, is used to see which area of the brains affected after a
tumour or stroke
Sclera
white outer layer, tough and strong to protect the eyeball.
Cornea
transparent area at the front of the eye to let in light, curves surface refracts lights to focus on the retina
Iris
controls size of the pupil by contracting or relaxing muscles
Pupil
hole through which lights enters the eye
Lens
a clear disk held in place by suspensory ligaments and cilary muscles. Fine tunes the light rays to produce a clear image on the retina.
If light is focused either in front or behind the reitna, the image is blurred.
What do pupils do depending on the light intensity?
In dim light, the pupil is dilated to let more light in and in bright light the pupil becomes constricted to prevent damage to the light- sensitive cells in the retina
Define Accomodation
the process of changing the lens shape to focus on near or distant objects.
To focus on distant objects: the ciliary muscles relax, suspensory ligaments tight and the lens flattens/thins
To focus on a near object: the ciliary muscles contract, suspensory ligaments loose and the lens gets thicker/ more curved
Myopia
Short sightedness - result of curved lens or long eyeball, Treated with a concave leans. Image formed in front the retina
Hyperopia
long sightedness - result of a flat and thin lens or short eyeball. Treated with a convex lens. Image formed behind the retina.
Ways to treat eye problems
contact lenses, laser eye surgery (changes shape or thickness of the lens), replacement lenses.
The body’s negative feedback loop
When our internal conditions are optimal, the body does not need to respond. If an internal condition changes and is no longer optimal, this stimulus is detected and the body works to counteract (reverse) the change and return conditions to the optimum. This process is called negative feedback and needs all of the components of the nervous system to work together.
Positive Feedback
It makes a small change even bigger. An example of positive feedback in the body is the release of oxytocin (hormone), which increases the number of contractions during childbirth.
Neurotransmitters
chemicals that diffuse across synapses and bind to receptors on the next neurone
What happens at a synapse?
- The electrical impulse reaches the end of the neurone before the synapse. This triggers the release of chemicals called neurotransmitters
- The neurotransmitters diffuse across the synapse.
- The neurotransmitters bind to receptors on the next neurone.
- The presence of the neurotransmitter causes the production of an electrical impulse in the next neurone.