2.85- Reflex arc

Describe the structure and functioning of a simple reflex arc illustrated by the withdrawalof a finger from a hot object

• The hot object is the stimuli
• The receptor is the sensor in our finger and this detects the hot object
• The electrical impulse travels along the sensory nerve to the CNS
• It is then passed on to the relay nerve which in turn passes it onto the motor nerve
• The impulse is then carried to the finger to which the response is to move the finger away
• The brain also receives some of the impulse but not all of it
• This makes the process faster and prevents more damage

2.84- Impulses

Understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses

• Receptors:
• These detect the stimuli like temperature
• They are connected to the CNS by the sensory nerve
• The electrical impulse travels to the CNS using the sensory nerve
• It is then transferred to the motor nerve by the relay nerve
• The motor nerve carry the impules from the CNS to the effectors
• The genes store the information about which relay nerve connects where
• Some impulses also go to the brain 

2.83- Central Nervous system

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

• The nervous system coordinates the activities of all the parts of your body
• The nervous system consists of the brain and the spine
• The brain is protected by the skull and the spine is protected by the vertebrae
• The central nervous system contains millions of neurons
• The spinal cord:
• Conducts sensory information from the peripheral nervous system to the brain
• Conducts motor information from the brain to the various effectors
• The brain:
• Receives sensory input from the spinal cord as well as its own nerves
• Initiates appropriate and coordinated motor outputs

2.82- Communication

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

1. First way to connect the coordinator to the effector:

• The left side of the nerve would be embedded in the spine
• The right side will be connected to the effector (muscle)
• The electrical impulse is carried inside the nerve from the cell body to the synaptic knob
• This is where it connects to the muscle
• The long structure in the middle is known as the axon
• This is surrounded by the schwann cells which is a layer of fat
• These form Myelin sheath which increases the speed which increases the speed of nerve conduction

    2. Second way of connecting the coordinator to the effector:

• This is known as the endocrine system
• The endocrine gland produces a chemical (hormones) 
• The hormone is secreted into the blood
• The hormones travels through the blood stream and goes to the target tissue
• The hormones can effect multiple target tissues and can bring about multiple effects

1. Nerve Impulses:
• Fast
• Nervous coordination is Instantaneous
• Sent through neurons
• Enables body to react to external environment
2. Hormone Impulses:
• Really slow
• Prolonged effect on body
• Enables body to react to internal environment 

2.77b- 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

• Negative feedback loop is a method of control and maintaining constant conditions
• Receptors- Hypothalamus responds to the temperature of the blood
• The ideal temperature in a human is 37-38 degrees
• The temperature is fed back to the brain so that the required changes in the temperature can be made
• Effectors- Skin can be used to change the temperature of the blood 
• Skin:
• Sweat Glands- used to control body temperature
• Capillary networks- allow blood to move closer or further away from the surface of the skin
• If body temperature increases, the hypothalamus will make the body cool down by:
• Sweating
• Increase blood flow, the blood vessels dilate which increases the exchange of heat to the outside of the body by the processes of radiation and evaporation of sweat
• If body temperature decreases, the hypothalamus will make the body heat up by:
• Shivering 
• Vasoconstriction
• Raised hairs

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


Homestasis- Where the conditions are kept the same or constant
Homeothermic- The temperature is kept the same

In mammals, when the temperature of the environment changes, their body temperature remains constant as they carry out thermoregulation which is an example of Homeostasis. These are Homeothermic organisms.

By looking at the rate of reaction to temperature graph, we see that there is an optimum temperature. Which is why mammals try to keep their body temperature at the optimum temperature as much as possible.

2.76- Sensitivity

Understand that organisms are able to respond to changes in the environment


Stimuli- Changes in the environment (light, temperature,pressure, chemical)
Receptors- Detect changes in the environment
Effectors- Respond to changes in the environment (muscles and glands)

The response ensures that the organism is able to survive the changes in the environment.