Co-ordination and response in humans Flashcards
What is homeostasis?
the maintenance of a constant internal environment
What are the different examples of homeostasis in the body?
Temperature
Water
Glucose
Describe Temperature homeostasis
Thermoregulation
If too hot - Skin acts to increase heat loss
Hair erector muscles relax, makes hairs lie flat
Less air trapped near the skin surface
More heat lost by radiation
Sweat glands make sweat
Blood vessels near skin surface dilate, more blood gets near surface (vasodilation)
Increases heat loss
If too cold - Skin acts to reduce heat loss
Hair erector muscles contract, makes hairs stand upright
Traps warm air near skin surface
Less heat lost by radiation
Sweat glands stop making sweat
Blood vessels near the skin surface get narrower (vasoconstriction)
Less blood gets near surface
Reduces heat loss
Describe Water homeostasis
Osmoregulation
The kidneys control the water content of the blood
Too much - large volume of dilute urine
Too little - small volume of concentrated urine
The part of the brain Hypothalamus detects changes to internal conditions
Sends signals to other parts of brain
Creates the feeling of thirst
What is vasoconstriction?
Muscle in the walls of arteries contracts, so arteries get narrower
This means less blood flows into the capillaries in the skin
Therefore less heat is lost from the skin by radiation
Skin appears pale
What is vasodilation?
Muscle in walls of arteries relax, so arteries get wider
This means more blood flows into the capillaries in the skin
Therefore more heat is lost by radiation
Skin appears red
What does a co-ordinated response require?
A stimulus, a receptor and an effector
Whats a stimulus?
Change in the internal or external environment
Whats a receptor?
Detects stimulus eg. sense organ
Whats an effector?
Carries out response - muscle or gland
Whats a co-ordinator?
Carries out response e.g. brain
Whats a response?
Bodys reaction to the stimulus
How does the nervous system control responses?
Made of neurones
Messages transmitted in the form of electrical impulses
Messages transmitted along nerve fibres
Messages travel very quickly
Effects of message usually only last a very short while
The system is made of:
The CNS - which consists of the brain and spinal cord
Nerves - which branch out from the CNS to all parts of the body
What are the three types of nerve cells?
Sensory Neurones - Transmit more impulses from receptors to the CNS
Motor Neurones - Transmit nerve impulses from the CNS to effectors
Relay neurones - transfer impulses from the sensory to motor neurones
How does the hormonal system control responses?
Made of secretory cells
Messages transmitted in the form of chemicals called hormones
Messages transmitted through the blood system
Effects of messages usually last longer
What are reflex actions?
These ara automatic, rapid responses without conscious thought
They protect the body from harm
They involve three neurones only
What are nerve impulses?
Electrical impulses are transmitted alone the axons of neurones
Between neurones there are tiny gaps called synapses
When a nerve impulse reaches a synapse chemicals are released that diffuse across the gap
There are called neurotransmitters
Describe the structure and function of the eye as a receptor
The eye is a sense organ
Sense organs contain receptors that detect changes in the environment
Electrical impulses travel from the sense organs to the CNS along sensory neurones
The eye contains photoreceptors - these detect light
The retina at the back of the eye is made of two types of photoreceptor
-Cones - detect colour and detail. Need bright light to be stimulated
-Rods - these can detect low levels of light but not colour
Describe the function of the eye in focussing on near and distant objects
To focus light in the retina the cornea refracts light so it enters the pupil
The lens then focusses light onto the retina
The shape of the lens has to be changed to focus on objects from different distances
Describe the function of the eye in responding to changes in light intensity
The pupil is the opening that allows light into the eye
The iris controls the size of the pupil
In the iris there are two sets of muscles
-radial muscles
-circular muscles
Describe the function of the eye in responding to bright light
Small pupils: - Radial muscles in iris are relaxed Circular muscles in iris contract Constricts the pupil Protects the retina from damage
Describe the function of the eye in responding to low light
Large pupils:- Radial muscles in iris are constricted Circular muscles in iris are relaxed Dilates the pupil Allows more light into the eye for better vision
Describe the function of the eye in focussing on close objects
Shape of lens: round
Ciliary muscle: contracts
Suspensory ligaments: loosen
Describe the function of the eye in focussing on distant objects
Shape of lens: Thinner and flatter
Ciliary muscle: Relaxes
Suspensory ligaments: Tighten
