2.85

describe the structure and functioning of a simple reflex arc illustrated by the withdraw of a finger from a hot object.

the different parts of the nervous system may be involved when your body responds to a stimulus- simplest response is reflexes.

reflexes are rapid, automatic responses to a specific stimulus that often acts to protect you in someway. eg. blinking if something gets in your eye or sneezing if you breathe in dust.

the pathway that signals travel along during a reflex is called a reflex arc:

stimulus -> receptor -> sensory neurone -> relay neurone in CNS -> motor neurone -> effector -> response.

simple reflexes are usually spinal reflexes- means that the signals are processed by the spinal cord not the brain. the spinal cord sends a signal back to the effector.

effectors are parts of the body that respond eg. muscles or glands.

example of spinal reflexes include touching a hot object:

2.83

recall that the central nervous system consists of the brain and spinal cord and is linked to the sense organs by nerves. 

(diagram of areas of the brain and the nervous system)

The sense organs are connected to the rest of the rest of the nervous system, which is made up of the brain, spinal cord and peripheral nerves.

in the brain and spinal cord, information is processed and decisions made. the brain and spinal cord together are called the central nervous system.

the brain coordinates the actions in the body. 

different areas of the brain are responsible for different actions.

signals are sent through the nervous system in the form of electro-chemical pulses.

2.82 communication

describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems.


1st way.
-in first diagram there is a motor nerve, orange part will be connected to the spine and the other end will be connected to the effector- most likely a muscle.
-the electrical impuse or the nerve impulse is carried along inside the nerve along the orange structure from the cell body to the synaptic knob where it connects to the muscles- can be a meter long. (single cell shown in orange)
-long structure is the axon.
-in mammals the axon is surrounded by a second kind of cell called a schwann cell- contains lots of fat and they form a myelin sheath- increase speed of nerve conduction.
-one way of linking coordinator or receptor to an effector.

2nd way.

-endocrine system .

- involves the endocrine gland produces chemical called hormones. (hormones can be proteins or steroids- different kinds)

-produced in the endocrine gland example would be Adrenal gland.

-the hormone is secreted into the blood- hormone travels into the blood.

-we would be secreting adrenaline from the adrenal gland into the blood. this will travel into the blood stream and arrive at the organ that will have an effect on called the target tissue or target organ which it will have an effect on.

-contrast with the nerve system it is possible that hormones can have multiple targets and effects.

comparison between communication based on nerves and communication based on hormones.

- nerve impulses are fast and hormones are relatively slow.

2.77b Thermoregulation

undertand that homoeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis. 


-negative feedback loop- method of control and maintaining constant conditions.
-in the case of humans our fixed body point is our body temperature (around 37/38 degrees)
- in order for it to work we have receptors- hypothalamus (region of the brain)
-responds to the stimulus- temperature of body and blood.
-body temp feeds into the brain and is compared- if the body temp needs to be increased or decreased then it is brought about bye the effectors eg. skin.
-response is either decrease or decrease in body temp. feedback to the hypothalamus, and based on the input, a new output would be produced.

-diagram of skin- sweat glands, capilary network- allow blood to move closer or further away from surface of skin.

-x axis- time
-level on y- regulation points 37/ 38 degrees
-if the body temp increase- input to hypothalamus, stimulates response in the skin for cooling- sweating
and increased of blood flow to surface of skin.
-blood vessels dilate (widen) so more blood can flow to the surface.
-increases exchange of heat to outside of body by evaporation of sweat and radiation.
-this brings about the cooling of blood which returns body temp to fix level

-if body temp falls, this feeds to the hypothalamus and switches on regulation to increase the body temp- causes shivering, raised hairs.
-forces blood to travel deeper through tissue and reduces heat exchange with external environment.
-temp varies (of blood) up and down around the fixed point (37/38) making efficiency of the system is determined by how far they deviate from fixed point.

2.77a Thermoregulation

understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis
- homeo- the same    stasis- fixed point or set of conditions.
-homeostasis- conditions are kept the same or constant.
-homeothermic- (thermic= temperature) maintaining the same temperature.
-mammals- when environmental temp increase or decrease the body temperature remains constant.
-they carry out a process called thermoregulation.
-other organisms body temperature vary with environmental temp

-maximum rate of reaction is achieved by an optimum temperature for that enzyme.

-both graphs (ideas) are related because the optimum temp for that enzyme reaction is approximately the same as the the temp at which the mammals maintain their body conditions.

2.76 Sensitivity

understand that organisms are able to respond to to changes in their environment.


-MRS GREN   (s- sensitivity)
-type of changes in the environment include changes in light levels, temperature, pressure levels and chemicals.
-in order to detect the changes, organism requires receptors and in order to respond the organisms have effectors such as muscles or glands- shows that organisms are able to survive the changes of the environment.