2.8 Reflex

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

Reflex is the simplex type of response. It is very quick and is involuntary (automatically happen without you being able to consciously controlling it). Reflex reactions are often for self-protection, such as blinking, sneezing, or pulling your hand away from a hot object. 

stimulus --> receptor --> sensory neurone --> relay neurone in CNS --> motor neurone --> effector --> response

Impulse are usually passed from sensory nerves and remains in the spinal cord without going into the brain. The response is then processed in the spinal cord itself and then pass directly through the motor nerves to the effector (muslce) to bring about a response. It made the response much faster. 

Input produces the same output. This means it is a ‘fixed decision’ to bring about reflex. 

The small nerve called relay nerve in the spinal cord directly connects sensory nerve to the motor nerve so the response can take place. 

They know which relay nerve to target because it is encoded within our DNA.

For example, you touch something hot you will immediately pull your hand away from it --> this is reflex

The “OUCH” came AFTER the reflex and it decided by the brain (as part of the information goes into the brain as well) 

This happens after because reflex response is always faster. 

The reflex arc for touching hot object:

Stimulus (pain sensor responding to heat) --> sensory neuron --> spinal cord --> relay neuron --> motor neuron --> effector (muscles) --> response (pulling your hand away from the heat source)

2.84 How information is carried

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

Sense organs are the receptors and send message along the sensory neurones to the CNS. 

Muscles and glands are effecters and receive messages the motor neurones from the CNS.

Relay neurons connect other neurones together. 

Neurones can be very long to pass information from one part of the body to another. 

Impulse, which are electric signals,  are passed from the receptor to the coordinator by sensory nerves to the spine and into the brain.

The brain will then generates information and brings about a response by sending information down the spine through motor nerves. It can be either voluntary or involuntary. 

Voluntary response always involve the brain. 

Involuntary response is called reflex, controlled by the spinal cord. 

The impulses are passed very quickly along the axon of the neurone. 

When nerves meet, they do not actually touch but form a gap called synapses. Impulses "jump" from one synapse to another. More specifically, chemicals are releases which pass across this gap by diffusion. They travel along one nerve after another.

Some axon has fatty sheath and protein around it which insulates the axon and therefore information can be carried along faster. 

2.83 Nervous system

2.83 Central Nervous System

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

Nervous system controls our action and coordinates different parts of our body for movement and response, both voluntarily and involuntarily. 

The central nervous system includes brain and spinal cord, both made up of delicate tissues. Information and decision is processes and made in the CNS.

The peripheral nerves connects organs to the central nervous system. Each nerves is made up or nerve cels or neurones.

Signals are sent through the form of electro-chemical impulses.

2.82 Communication

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

1. Nervous system

The cell body of the nerve would be connected to the spine

The other end, synaptic knob, of the nerve would be connected to the effector, which is most likely a muscle

The electrical impulse, or nerve impulse, is carried along inside the nerve down the axon from the cell body to the synaptic knob, which can be a meter long (and it is a single cell).

In mammals, the axon can be surrounded by another kind of cell known as the schwann cell. It contains a great deal of fats and formed a myelin sheath, which helps increase the speed of nerve conduction (for information to be passed).

2. Hormone - Endocrine system

Hormones can be proteins or steroids.

Made in the endocrine glands

Travel in blood

Effect the target tissue

Endocrine gland produces chemical known as hormone. 

Eg) adrenal gland which produces adrenaline

The hormone is secreted into the blood and travels through the stream and arrive at target tissue/ organ that will have an effect on.

Hormones can have multiple target and brings about multiple effects.

Nerves transfer impulses much faster than hormone does.

The picture only shows a motor nerve. 

2.77b) Thermoregulation

Controlling body temperature

Components of skin which controls body temperature

Sweat gland

Capillary network - allows blood to move closer of further away from the surface of the skin 

If the body temperature increases, the input to the hypothalamus stimulate responses in the skin which bring about cooling, such as sweating or the flow of blood to the surface of the skin increases. Blood vessel dilates and increase the exchange of heat to the outside of the body by processes such as sweat and vasodilation. This results in cooling of the blood.

- Sweating

- Vasodilation

- Hairs flat

--> decrease body temperature

In the cold environment, out body temperature will fall and hypothalamus brings about regulations in increase of body temperature

- Shivering

- Vasoconstriction

- Hairs raised

--> increase body temperature

Efficiency of the system responding to stimuli--> how far it deviates from the fixed point

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

Homeostasis - Conditions are kept at the same or constant throughout

Homeothermic - Temperature are kept the same or constant

Organisms such as mammal keeps their body temperature constant despite changes in the temperature of the environment. These organisms are called homeothermic organisms. 

Mammals always keep their body temperature constant because enzymes have a point of temperature which is called optimum temperature (maximum) . They would try to keep their body temperature as close to the optimum temperature as possible. 

2.76) Sensitivity

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

Sensitivity - the characteristic in which organism respond to changes in their environment

Types of stimuli

- Light

- Temperature

- Pressure

- Chemical 

Receptor is needed to detect such changes in the environment

The response is produced by effectors which are muscles or glands. 

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