B5: Homeostasis and response Flashcards
what is homeostasis?
- the maintenance of a constant internal environment in order to maintain optimum conditions for enzyme and cellular function.
Give 3 examples of conditions maintained by homeostasis in the body
• Blood glucose concentration
• Body temperature
• Water levels
What two types of responses are used in body control systems?
Nervous and chemical
What three components do all control systems have?
• Receptors
• Coordination centres
• Effectors
What is the function of a receptor?
Receptors detect changes in the environment (stimuli).
What is the function of an effector?
Effectors (muscles or glands) bring about responses to stimuli.
What is the function of a coordination centre?
- obtain and process information from receptors.
- Eg brain and spinal cord
What is the function of the nervous system
- allows the body to react to its surroundings and coordinate an appropriate response.
How does a stimulus lead to a response being carried out by the body?
• Stimulus is converted into an electrical impulse by the receptors.
• The electrical impulse passes along sensory neurones to the central nervous system (CNS).
• The CNS coordinates an appropriate response and an electrical impulse is sent along motor neurones to the effector, which carries out the response.
Describe the sequence of events on the way the nervous system works
Stimulus— receptor— coordinator— effector—response
Define a ‘reflex action’
- an automatic and rapid response
- which does not involve any conscious input from the brain
Why are reflex actions important ?
- Reflex actions aid survival by preventing harm to the body
Describe how a reflex action occurs via a reflex arc (4 marks)
- the stimulus is detected by a receptor
- an electrical impulse passes along a sensory neurone to the spinal cord (part of the CNS)
- At a synapse between a sensory neurone and a relay neurone, a chemical diffuses across the gap
- this 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 the knee jerk reflex (4)
- receptor detects pain and sends electrical impulses along the sensory neurone
- electrical impulses then move to the relay neurone in the spinal cord
- the electrical impulses are then transmitted from relay neurone to the motor neurone
- motor neurone sends impulses to the effector ( the muscle )
- muscle contracts
- so knee jerks away from pain
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 cord/ unconscious parts of the brain.
- In a conscious pathway, the coordination centre is in the conscious part of the brain.
What is the function of the cerebral cortex. And where is it found
- the outer layer of the brain which is divided into two hemispheres.
- Is responsible for higher-order processes such as intelligence, memory, consciousness and personality
What is the function of the cerebellum and where is it found
- this is underneath the cerebral cortex
- is responsible for balance, muscle coordination and movement
What is the function of the medulla and where is it found ?
This region controls unconscious activities such as heart rate and breathing
Give 4 reasons why the investigation and treating of the brain difficult
- the brain is a complex and delicate organ
- the brain is easily damaged
- certain membranes prevent drugs from reaching the brain
- the exact function of each part of the brai is not known
What methods are used by scientists to determine brain function?
- studying patients with brain damage
- electrical stimulation of the brain
- MRI scans
delte
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How can we study patients with brain damage?
- observing the changes in an individual following damage on a certai area of the brain
- this can provide information on the role this area has
How can we use electrical stimulation to map out the regions of the brain?
- Tiny electrodes can be pushed into different parts of the brain
- tiny jolts of electricity stimulate these regions and the mental or physical changes in the individual effects can be observed.
How can we use MRI scanning techniques?
- to create an image of the brain.
- it can be used to show which part of the brain is affected by a tumour, or which part is active during a specific task.
- the scanners can detect changes in blood flow
evaluate the benefits and 2 risks of procedures carried out on the brain and nervous system
Risk:
- high level of risk due to the complexity of the brain
- If surgery is undergone more permanent damage or side-effects may be created, which could affect the patients’ quality of life.
Benefits
- improves quality of life and patient health
- treats disorders of some kind
What stimuli are the receptors of the eye sensitive to?
Light intensity and colour
What are the 2 main functions of structures found within the eye?
- accommodation ( focusing on near or distant objects)
- adaptation to dim light
Describe the structure and 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 the 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 scelta is the tough white outer layer of the eye which protects its internal structures
Describe the structure and function of the cornea
- the cornea is the curved transparent layer at the front of the eye
- it lets light into the eye and refracts it
Describe the structure and function of the iris
- The iris is 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 suspensory ligaments
The ciliary muscles and suspensory ligaments hold the lens in place and control its shape
Describe how the iris alters the 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 pupil larger so more light can enter the eye
How does the eye focus on a nearby object
- ciliary muscles contract
- suspensory ligaments loosen
- lens becomes thicker and more curved- light rays are refracted strongly
How does the eye focus on distant objects?
Ciliary muscles relax
Suspensory ligaments tighten
Lens becomes thinner - light rays are refracted weakly
How can myopia be treated?
Myopia can be treated using glasses with a concave lens, which spreads out light rays so they can be focused on the retina
What is hyperopia?
- long-sightedness
- occurs when the lens of the eye is too flat or short. As a result , light is focused behind the retina so images appear out of focus.
How can hyperopia be treated?
- treated using glasses with a convex lens , which brings the light rays together so they can be focused on the retina.
What are two types of contact lenses?
- hard- rigid material, last a long time , must be kept sterile
- soft- flexible material, last for a shorter time, more comfortable
What is laser eye surgery and how does it treat myopia and hyperopia
- the use of lasers to fix visual defects in adults
- to treat myopia, lasers reduce the thickness of the cornea so light is refracted less strongly.
- to treat hyperopia, lasers alter the curvature of the cornea so light is refracted correctly
How can replacement lenses be used to treat visual defects?
A replacement lens can either be implanted into the eye along with the natural lens
Give three risks of lens replacement
- retinal damage
- cataracts
- infections
Where is body temperature controlled in the body?
- the thermoregulatory centre in the hypothalamus of the brain
How is temperature monitored by the body?
- thermoregulatory centre has receptors sensitive to blood temperature
- skin has receptors sensitive to skin temperature - sends impulses to thermoregulatory centre
What physiological changes occur when the body temperature is too high.
Vasodilation- blood vessels near the surface of the skin dilate - more heat is radiated away as more blood flows closer to the surface of the skin
Sweating- sweat evaporates from skin surface resulting in increased heat energy transfer away from the body
What physiological changes occur when the body temperature is too low?
Vasoconstriction- blood vessels near the surface of the skin constrict so less heat is radiated away
Shivering- respiration allows muscles to contract as it is an exothermic reaction so heat energy is released
Sweating stops
Give the name of the body’s coordination system which involves hormones
The endocrine system
What is a hormone ?
- A hormone is a chemical messenger secreted by a gland.
- It travels in the blood to a target organ , where it causes a response