2.85

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


Key Points:
1. A synapse is the gap between different neurones - this allows the electrical impulse to jump across at faster speed and results in a faster impulse. They also function as a resistor and a junction box. Synapses are easily affected by drugs and this can either slow down or heighten peoples' reactions.
2. Reflex arcs are stimulation's caused by the body to protect one from harm or damage. An example would be something very hot.
3. STIMULUS (HEAT) -> RECEPTOR (PAIN SENSOR IN SKIN) -> COORDINATOR (CENTRAL NERVOUS SYSTEM) -> EFFECTOR (ARM MUSCLE) -> RESPONSE (REFLEX ARC)
4. In specifics, the heat causes the pain sensor in the skin to send a message along the sensory neurone to the central nervous system, in which it gets passed on to the relay neurone which then passes to the motor neurone and carries the impulse to the muscle (in this case the arm muscle), and causes a reflex.
5. Some other examples of reflexes are: Blinking with dust in your eye, Coughing when liquid or food goes down the trachea, blinking when someone claps in your face etc.

2.84

2.84: 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


Key Points:
1. Messages are carried by nerve impulses and these happen very quickly. These are electrical signals.
2. An impulse travels across the axon rapidly because it can jump from one fat globule to the next (however this only occurs in mammals). This insulates the axon as well.
3. In multiple sclerosis the fatty globules break down and impulses also slow down or even stop. This disease causes people to lose control of their muscles.
4. The axon can be over 1 meter long.
5. Nerve cells have a different structure to other cells, but retain the basic things like cytoplasm, cell membrane and a nucleus. Their shape is stretched out to form the axon.

2.83

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


Key Points:
1. The main parts of the nervous system are the brain and the spinal cord.
2. They are made up of nervous tissue , and the brain is protected by the skull and the spinal cord is protected by the back bone.
3. Nerves are what connect the central nervous system to the rest of the body, and these are made of neurones
4. Sense organs are receptors - they send messages to central nervous system.  These are sent via the sensory neurones.
5. Muscles and glands are effectors - the central nervous system send them impulses along motor neurones

2.82 Communication

Key Points:
1. Responses can be controlled by nervous or hormonal communication. In the example, the motor nerve is shown and one side is embedded in the spine and the other end is in the effector, probably the muscle.
2. The electrical impulse is carried down inside the nerve from the cell body to the structure called the synaptic knob -> connects to muscle. These cells can be up to a meter long.
3. The long structure is known as an axon. In mammals the axon is surrounded by a lot of fat in globules - this is to increase the speed on impulses.
4. The second way is known as endocrine system. This involves an endocrine gland and this produces a hormone. Manufactured in the glands, the adrenal glands. The hormone is secreted into the blood, the hormone being adreneline. This will arrive at the target tissue/organ.
5. Contrasting with the nerve system, some hormones can have multiple targets and bring about multiple effects.

Nerves = Fast, electrical impulse, single effect, reflex, carried down the axon.
Hormones = Relatively slow, can have multiple effects, secreted into blood.

2.77b Thermoregulation

1. In humans we must maintain a constant temperature - 38-37 C. In order for this to work our receptors, the Hypothalamis, responds to the stimulus, the temperature of blood, and if there is need for change then the skin will change the temperature.
2. The response will be either an increase or decrease in body temperature. Feedback to hypothalamis and based on new input, new output produced.
3. Major component of skin - Sweat glands and capillary network. Allows blood to move closer or further away to the skin.
4. Stimulates cooling which involves sweating and the bloodflow to the surface of the skin increases. Dilated blood vessels. Increases exchange of heat like radiation and evaporation.
5. Stimulates heating, which involves shivering, raised hairs. reduces heat exchange with the external environment. Vary UP and DOWN around the fixed point

2.77a Thermoregulation

Key Points:
1. Homeostasis is the process in which the internal environment of an organism is kept constant and relative to the outside environment. It also affects water content and body temperature.
2. Homeo - Something being the same Stasis - Fixed Conditions. The idea is that the conditions are kept constant. Homeothermic refers to temperature, and maintaining the same temperature.
3. Some organisms keep their body temperature constant when the temperature changes, and some adapt to it. The name of the first process is called thermoregulation.
4. Homeostatis also keeps the optimal temperature for enzymes.
5. The optimum temperature for the enzyme reaction is roughly the same as which mammals maintain their body conditions.

2.76 Sensitivity

Key Points:
1. Organisms are able to respond to changes in the environment.
2. S from MRSGREN stands for sensitivity. This characteristic enables organisms to respond to changes in the environment.
3. Types of change = Light levels, Temperature, Pressure and Chemical changes.
4. To detect and respond to these stimuli, the organism must possess receptors and effectors.
5. An example of an effector is a muscle or a gland.