2.85

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

Many reflexes protect you.
they happen very quickly so you dont harm yourself.
the pathway of the impulse along the neurons is called a reflex arc

Stimulus = hot flame
Receptor = heat sensor in the skin.

- The impulse travels to the spinal cord along the sensory neurone.
- In the spinal cord the impulse is passes on to the relay neurone.
- This passes the impulse on to the motor neurone.

Effector = Arm muscles. The motor neuron carries the impulse to the muscle in the arm

Response = Muscles contract to remove the hand from the hot object

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
Neurons:
Nerve cells are different from other cells, they do have a cell membrane, cytoplasm and nucleus, but they are different shape.
Part of the cell is stretched out to form the axon.
The axon can be over a metre long.

How the messages are carried:
The messages that nerves carry are called nerve impulses
They are electrical signals.
They pass very quickly along the axon of the neurone.

Each impulse is separate from the next, one after the other
some axons have a fatty sheath around them.
this insulated the axon and makes the impulse travel faster.

2.83

Brain and Spinal Cord = Central Nervous System

Brain is protected by the skull
Spinal Cord is protected by the back bone

The central nervous system is connected to difference parts of the body.
 Each nerve is made up of lots of nerve cells or neurons.

2.82

1. motor nerve
orange - in the spine
end- effector (muscel)
electrical/nerve impulse is inside the nerve from the cell body to the synaptic knob.
long structure = axon
in mamals it is surrounded by the schwann cell (contains fat) increases speed of nerve conduction
this links receptor to effector.
2. Endocrine system
endocrine gland contains hormone (protein or steroid)
eg: Adrenal glad
hormone secreated into blood (adrenaline)
then it will arrive at organ that it will have an effect on = target tissue.
they can have multiple targets and multiple effects
Nerves= fast Hormones= slow

2.77b

Controlled body temperature

Negative feedback loop – method of control – maintains constant conditions.

Humans= 37-38 degrees = co-ordinator

All internal conditions

We have receptors = hypothalamus in the brain

Responds to stimulus in the body – temp. eg: blood

Effector = skin

The response = increase / decrease in body temperature

Then this would FEEDBACK to hypothalamus

Eg:

Skin – sweat glands capillary network – blood to move closer or surface away from surface of the skin

In diagram = x = time y axis = regulation point

Body temp increase. = responses in the skin =cooling

On a hot day = blood vessels dilate

On cool day – body temp decrease – connects to hypothalamus

2.77a - Thermoregulation

Homeostasis ‘same’ ‘fixed/constant’

Homeothermic – ‘temperature’ same temp.

Eg: mamals = body temp (y) environment temp (x)

Homeothermic = thermo regulation

Eg: mammals = temp change then body temp. stays the same = Homeothermic Organism à Thermoregulation

OR some organisms have a body temperature that could vary in different environments.

Looking at 2.9:                  

Rate of reaction = optimum temp for that enzyme.

Optimum temp for the enzyme nearly the same temp of mammal body temp.

2.76

Changes = Light, Temperature, Pressure, Chemical
Organisms need RECEPTORS to indentify to these changes
and then they need EFFECTORS to respond to the changes (eg: muscel, glands)

The RESPONSE shows that the organisms can survive through changes in the environment.