2.85 Reflex Arc

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

Stimulus --> Receptor --> coordinator --> effector --> response
(Hot surface) --> (heat sensor) --> CNS --> (Muscle) --> (remove finger)

2.84 Electrical 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

• The receptors detect a stimuli
• The receptors then send a message along the sensory neuron to the spinal cord
• electrical impulses (signals) are sent through the nerves to the central nervous system
• These impulses pass really quickly through the axons
• The quicker the electricity goes to the CNS the quicker you react therefore the axon is surrounded by fat to insulate the axon so that the electricity flows quicker
• The brain then detects that there is something going on
• electrical signals are sent down the motor neurons to the effectof

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

Receptor --> coordinator --> effector

• The central nervous system is made up of your brain and spinal cord which are made of delicate nervous tissue. The brain is protected by the skull and the spine by the backbone
• The central nervous system controls your actions and it is connected to different parts of the body by nerves.
• These nerves that connect the CNS to the body are made up of nerve cells or neurons
• Sense organs are our receptors and they send messages to the CNS telling it what has happened. These messages are sent along the sensory neurons
• Muscles and glands are our effectors and the CNS sends them a message that tells the muscles what to do. The messages are sent along the motor neurons

2.82 - Communications

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

Ways of connecting the coordinator to the effector:

1)

• -The yellow part on the left is the cell body and it is embedded inside the spine and it would connect to the effector (muscle)
• -The electrical impulse (nerve impulse) is carried along the nerve (orange structure) from the cell body to the synaptic knob where it connects to the muscle. (it can be up to a meter long)
• - In mammals the axon is surrounded but the "schwann cell", these contain a lot of fat and creates the "mylin sheath". This increases the speed of nerve conduction.

2)

• Endocrine system involves the endocrine gland which produces a chemical called a hormone (protein, steroids). eg: Adrenal gland
• The hormone is secreted into the blood (Adrenaline) 
• It travels through the blood stream to the organ it affects called the target tissue.
• Hormones can have multiple targets (multiple effects)

Differences:

Nerves are fast and use electrical impulses.

Hormones are slow and use chemicals

2.77a - Thermoregulation

Homeostasis: Conditions are kept the same
Homeothermic: Temperature is kept the same

Mammals (Homeothermic): when the environmental temperature changes their body temperate stays the same. They keep their body at the optimum temperature

2.76 - Sensitivity

Organism respond to changes in their environment eg:
-Light
-Temp
-Pressure
-Chemical
For these changes organisms require Receptors and Effectors (Muscles, Glands) to respond to the changes.
The response ensures that the organism is able to survive changes in the environment