2.85 Reflex arc

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

Source: http://content.answcdn.com/main/content/img/oxford/Oxford_Sports/0199210896.reflex-arc.1.jpg

Source: http://moodle.schoolnet.lk/file.php/21/assets/images/ks4/reflex.gif

1. Reflexes are involuntary
- cannot be suppressed
- the reflex arc is the pathway of the impulse along the neurones

2. Stimulus: pain
Receptor: pain receptor in finger
- Impulse travels to the spinal cord along the sensory neurone
- [spinal cord] Impulse is passed on to the relay neurone (connecting the sensory/motor without going to the brain // quicker time) and to the motor neurone
- Effector: Muscle
Response: Withdrawal of hand

3. Number of synapses
- one between each neurone; three

2.84 Sensory repsonses

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

http://www.usmanscience.com/12bio/classnotes/nervous_system_notes_files/image002.gif

1. Sensory nerves: Receptors
- Sends messages along the sensory neurones to the central nervous system

2. Motor neurones: Effectors
- Receive messages from the CNS

3. Impulses
- Passed from receptor to coordinator via axon in sensory nerves
- Brain generates information
- Generates another impulse down the motor nerves to the effector

Voluntary actions - Involvement of brain
Involuntary actions - Passed through the spinal cord (less distance)

4. Structure of neurone
- Meeting of nerves - do not actually touch
- Synapses: a gap in which the electric current jumps through
- Some axons have a fatty sheath around them
- Insulates axon, makes the impulse travel faster

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

1. Central nervous system controls and coordinates actions

- voluntary and involuntary actions

2. Consisted of brain and spinal cord

- brain is protected inside the skull

- spinal cord is protected inside the backbone

3. CNS connected to different parts of the body by nerves

- nerves made out of nerve cells and neurones

4. Receptors: sense organs

- response sent along sensory neurones

Source: http://www.empowher.com/files/ebsco/images/si2012.jpg

2.82 Communication

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

1. Nerves (Motor nerves)

Electrical impulse = nerve impulse

Carried down inside the nerve from the cell body [spine] to the synaptic knob [muscle/effector] through the axon

Axons are surrounded by Schwann cells

Schwann cells contain fat and form a myelin sheet (increases the speed of nerve conduction)

Source: http://www.wikimedia.org

==

2. Endocrine system

Endocrine gland (produces hormones; proteins or steroids)

e.g. Adrenal gland

Hormone is secreted into blood

e.g. Adrenaline into the blood

Sent to target tissue

e.g. Adrenaline sent to heart

Hormones can have multiple targets and multiple effects

==

3. Communication using nerves vs hormones

Nerves

- Fast

- Electrical impulses

- Travel through nerves

- Impulses only last a short time

Hormones

- Relatively slow

- Chemical messengers

- Travel through bloodstream

- Effects last longer

2.77b Thermoregulation 2

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 - A method of control / maintaining constant conditions

Body temperature
Receptor: Hypothalamus
Hypothalamus responds to stimulus (body temperature / temperature of blood)
Co-ordinator - Compares the body temp. to the constant (37/38˚c)
Effector - Skin
Response - an increase or decrease of the body temperature
Response feeds back to the receptor

Source: www.click4biology.info

Source: www.click4biology.info

1. Features of the skin for temperature control
- Sweat glands
- Capillary network
Allows blood to move closer or further away from the surface of the skin

Source: www.wikimedia.org

2. Temperature regulation point / Time graph
- Body temp. increases => Cooling (sweating)
- Increased blood flow
- Vasodilation (blood vessels widen)
- More blood flow to the surface
- Increases exchange of heat to the outside of the body (sweat / radiation)
- Hairs flat
- Body temp. decreases => Heating
- Shivering
- Vasoconstriction (blood vessels constrict)
- Decreases heat exchange to the outside
- Raised hairs
- Efficiency of regulation varies with the amount of deviation from the x-axis

Source: www.click4biology.info

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

Homeo - Same

Stasis - Fixed point/conditions / maintenance

1. Homeostasis - Body conditions are kept constant

2. Homeothermic - Maintaining the same temperature

Mammals:

- Homeothermic organisms

- Body temperature remains constant with varying environmental temperatures (made possible by thermoregulation)

3. Mammals maintain a constant body temperature

Rate of reaction (enzyme catalysed reaction) / Temperature graph

Source: bbc.co.uk

Maximum rate of reaction is achieved at the optimum temperature

Optimum temperature is approx. the same as the temperatures mammals maintain their bodies at

2.76 Sensitivity

understand that organisms are able to respond to changes in their environment

MRS GREN
S - Sensitivity

1. Sensitivity - an organism's response to changes in the enviroment

2. Possible stimuli:
- Light
- Temperature
- Pressure
- Chemicals

3. Receptors - Detection of changes

4. Effectors - Generates a response (muscles / glands)
The response ensures that the organism is able to survive changes in the environment