The nervous system and reflexes (Chapter 15)

Question 1

What do communication systems within animals coordinate?

Answer 1

The activities of receptors and effectors

Question 2

What do receptors detect and why?

Answer 2

There are receptors that detect stimuli 1) in the surrounding environment 2) in the body bc the information they receive comes from the internal and external environment

Question 3

What are the two types of information transfer used in animals to coordinate the body’s activities?

Answer 3

1) nerves that transmit information in the form of electrical impulses
2) hormones that travel in the blood

Question 4

What does the endocrine system consist of?

Answer 4

Glands that secrete hormones

Question 5

What is the mammalian nervous system made up of?

Answer 5

1) CNS - brain and spinal cord

2) PNS - cranial nerves (attached to the brain) and spinal nerves (attached to the spinal cord)

Question 6

Where do neurones carry information to?

Answer 6

Directly to their target cells

Question 7

What are the three types of neurone?

Answer 7

1) sensory
2) motor
3) relay/intermediate/connector

Question 8

What do sensory neurones do?

Answer 8

Transmit impulses from receptors to CNS

Question 9

What do relay neurones do?

Answer 9

Transmit impulses from sensory neurones to motor neurones

Question 10

What do motor neurones do?

Answer 10

Transmit impulses from the CNS to effectors

Question 11

Describe the structure of neurones

Answer 11

• Nucleus in the cell body
• Thin cytoplasmic processes (dendrites and axons) extend from the cell body
• Organelles in the cytoplasm of the axon e.g. mitochondria and small regions of rough ER

Question 12

What is the difference between the axon and dendrites?

Answer 12

1) dendrites - very short and often have many branches

2) axon - much longer and conducts impulses over long distances

Question 13

What do the ends of the branches of the axon contain?

Answer 13

Large numbers of mitochondria and many vesicles containing transmitter substances

Question 14

Describe the structure of a motor neurone

Answer 14

• Cell body lies within the spinal cord or brain
• There are many highly branched dendrites to give a large surface area for the endings of other neurones
• All have a motor end plate (a connection with a muscle)

Question 15

Describe the structure of a sensory neurone

Answer 15

• One long axon with a cell body that may be near the source of stimuli or in a swelling of a spinal nerve (ganglion)
• Dendrites receive inputs from the sensory receptor

Question 16

Where are all relay neurones found?

Answer 16

In the CNS

Question 17

How are the axons of some neurones protected?

Answer 17

They are surrounded by myelin and protected within nerves

Question 18

What are nerves not protected by myelin called and what proportion of nerves are like this?

Answer 18

• Unmyelinated neurones (about 2/3 of all neurones)

Question 19

What is myelin made by?

Answer 19

Schwann cells (specialised cells)

Question 20

How is myelin made?

Answer 20

1) myelin is made when Schwann cells wrap themselves around the axon all along its length
2) the Schwann cells spiral around, enclosing the axon in many layers of its CSM, forming an enclosing sheath (myelin sheath)

Question 21

Describe the myelin sheath

Answer 21

• Made largely form lipid, together with some proteins
• It affects the speed of conduction of nerve impulses
• It provides electrical insulation

Question 22

What are the nodes of Ranvier?

Answer 22

The small, uncovered areas of axon between nodes of Ranvier

Question 23

Describe the nodes of Ranvier

Answer 23

• They occur roughly every 1-3 mm in human neurones

- They are very small (2-3 μm)

Question 24

What is a reflex arc?

Answer 24

The pathway along which impulses are transmitted from a receptor to an effector without involving the conscious region of the brain

Question 25

What is a reflex action?

Answer 25

A fast, automatic response to a stimulus, that is a very useful way of responding to danger signals - the response to each specific stimulus is always the same

Question 26

What is an example of a reflex arc in the brain?

Answer 26

Those controlling focusing and how much light enters the eye

Question 27

How does a reflex arc which doesn’t involve a relay neurone work?

Answer 27

The impulse passes directly from the sensory to the motor neurone

Question 28

Describe how a reflex action happens

Answer 28

1) within the spinal cord, the impulse will also be passed onto other neurones which take the impulse up the cord to the brain
2) this happens at the same time as impulses are travelling along the motor neurone to the effector
3) ∴ the effector responds the the stimulus before there is any voluntary response involving the conscious region of the brain

Question 29

What is a stimulus?

Answer 29

An external condition that is detected by the body and triggers a response

Question 30

What is a nerve?

Answer 30

A bundle of neurones

Question 31

What is the difference between the nervous and endocrine system?

Answer 31

Nervous - faster transmission
- short term effects
- very local target 
- messages as 'impulses' in nerve cells
- neurones
Endocrine - slower transmission
- longer term effects
- more widespread targets
- messages as chemicals, travelling in the blood stream 
- glands/secretions
- plays an important role in development