2.84-2.85 Nerve Impulses and Responses

Electrical Impulses: is a method of transporting information of environmental change from the receptor to the coordinator in order to receive a response.

1. Impulses are sent to the coordinator from the receptor. 
2. While making a decision, receptors are affected by an environmental change, electrical impulse is then sent to the Central Nervous system through the sensory nerves. The brain then coordinates a response. 

An uncoordinated response: A reflex, Example- withdrawing your hand after touching something really hot

1. Pain receptor detects the hot temperature (stimuli)
2. Sensory nerve sends electrical impulse to the brain. 
3. The motor nerve sends signals to the effector which is the muscle in this case. The muscle then contracts and hand is withdrawn. 

2.83 Central Nervous System

1. The central nervous system is made up of the spinal cord and the brain. All the nerves branch out from the spinal cord. 
2. The Central Nervous System allows the body to respond to any changes in the environment.

How the CNS works: 

1. Nerve impulses from the receptors travel through sensory nerves till they reach the spinal cord and brain. 
2. The response is coordinated by the brain 

2.82 Communication

Nerve system 

1. motor nerve-The orange/yellow part in the nerve would be embedded in the spine 

1. The end is connected to an effector, most likely a muscle 
2. The electrical impulse or nerve impulse is carried down the orange structure from the cell body to the synaptic knob, where it connects to the muscle. 
3. The long structure is known as the axon. 
4. In mammals, the axon is surrounded by schwann cells, which contain a lot of fat. They form a myelin sheath. 
5. The effect of this is to increase the speed of nerve conduction. 

Endocrine System 

1. The endocrine system involves an endocrine gland. 
2. This produces hormones, could be protein or steroids. They are produced and manufactured in endocrine glands an e.g. of this would be adrenal gland. 
3. The hormone is secreted into the blood.This will travel through the blood stream in order to get to its target organ or target tissue on which it will have an effect. 
4. Hormones can have multiple targets and can bring about multiple effects.
5. Communication based on nerves- Nerve impulse is fast
6. Communication based on hormones- Nerve impulse is slow. 

2.77b Thermoregulaation

1. here we are developing the idea of the control of body temperature. 
2. Negative feedback loop- method of control and maintaining constant conditions. Keeps the human body at about 37 to 38 degrees.
3. In order for this to work we have a receptor- hypothalamus- region of the brain, responds to stimulus-temperature of blood. 
4. Body temp feeds into the brain and is compared to the theoretical level of control. 
5. If the body temp needs to be increased or decreased, bought about through the action of the effector such as the skin.
6. The response to this would either be an increase or decrease in body temperature. 
7. This would intern feedback to the hypothalamus. 
8. One of the major components of skin are sweat glands and the capillary networks (allows blood to move closer or further away from the skin)
9. x axis represents time and y axis represents temperature. 

1. If the body temp increases the input into the hypathalamus stimulates responses in the skin which bring about cooling, done through sweating or the flow of blood to the surface of the skin through the blood vessels which dilate (widen) in order to get more blood flow to the surface. 

1. This further increases the exchange of heat to the outside of the heat through radiation and evaporational sweat.
2.  this brings about cooling of the blood which returns the body temp to fixed level. 
3. Body temperatures can fall in a cold environment. 
4. When the body temperature decreases, this feeds into the hypothalamus which then swicthes on and brings about regulation to increase the body temperature such as shivering, vasoconstriction or raised hair

2.77a thermoregulation

1. homeostatis-the conditions are kept same or constant. 
2. Homeothermic- the idea of maintaining the same temperature. 
3. In mammals for instance, when the environmental temperature increases or decreases, their body temp remains constant, They are called homeothermic organisms and carry out the process of thermoregulation. 
4. the reason why mammals wish to maintain their body temperature: 

1. 
   
2. As you can see on the x axis we have the temperature and on the y axis we have the rate of reaction (enzyme ctalysed reaction). 
3. The max rate of reaction is achieved at the optimum temperature.
4. The optimum temp for the enzyme reaction is approximately the same temperature at which the mammals maintain their body conditions 

2.76 Sensitivity

1. Organisms are able to respond to changes in the environment
2. The types of changes in the environment include changes in light levels, temperature, pressure levels and chemicals. 
3. In order to detect these changes in the environment organisms have receptors.
4. In order to respond to the changes in the environment organisms have effectors such as muscles and glands. 
5. It is the response that ensures that the organism is able to survive the changes in the environment.