Sensory input, Receptors, and Reflex Arc

Question 1

What is homeostasis? What is the main way that it is achieved?

Answer 1

The maintenence of a constant internal environment, despite and in response to changes in the external environment.
Achieved via alternation between the sympathetic and parasympathetic nervous systems.

Question 2

What is a receptor? What is the term used for a group of receptors?

Answer 2

Any structure capable of receiving information, both internal and external.
The term used for a group of receptors is a sensory organ.

Question 3

What is a spinal reflex arc?

Answer 3

A rapid, involuntary and stereotyped response to an external stimulus. Occurs to protect the body from harm. Involuntary, as in order to save time the response is not processed in the brain. The response is not processed in the brain until after the response is complete.

Question 4

What are the stages of a spinal reflex arc?

Answer 4

1) Sensory receptor receives stimulus
2) Impulse travels past the dorsal root ganglion, towards the spinal cord
3) Dorsal root travels from the dorsal root ganglion into the grey matter of the spinal cord
4) Interneuron connects sensory neuron to motor neuron body
5) Impulse travels through efferent pathway towards effector
6) Effector (skeletal muscle) contracts

Question 5

What are the 4 characteristics of a spinal reflex arc?

Answer 5

Requires a stimulus, involuntary, rapid, stereotyped

Question 6

Describe the difference between, protective, learned and acquired reflexes.

Answer 6

Protective reflexes are present from birth (e.g. blinking when someone claps in your face)
Learned reflexes are conscious and deliberate, and develop in early childhood (e.g. chewing, swallowing, sucking)
Acquired reflexes are subconscious, and develop through repetition. It is believed that around 10,000 hours of repetition are required to establish this reflex (e.g. emergency braking in a car, riding a bike)

Question 7

List and describe structure and function of the different types of receptors.

Answer 7

1) Pain receptors (AKA nocireceptor)
Found on most organs, excepting the brain. Alert the brain that damage to tissue is occurring. They do not adapt, meaning that pain will continue until the stimulus is removed.

2) Thermal receptors
Located centrally (hypothalamus, measures core temp. through blood) and peripherally (skin, measures environmental temperature). The receptors for cold and hot are separate.

3) Osmoreceptors
Located in the hypothalamus. Measures water balance. Water balance is changed by Anti Diureitic hormone, if need be.

4) Touch receptors
Located on both skin surface and deeper in the skin. Sensitive to pressure. They adapt, meaning that the neuron will stop firing, despite the stimulus still being present. Greater concentration on fingertips and sex organs.

5) Chemoreceptors
Located in the nose, mouth and internally, and stimulated by particular chemicals. Receptors in blood vessels may be sensitive to the pH of the blood.