5.5.5: The mammalian nervous system

Question 1

What is the most obvious division of the nervous system?

Answer 1

• The central nervous system (CNS)

- The peripheral nervous system (PNS)

Question 2

What is the peripheral nervous system divided into?

Answer 2

• The sensory system

- The motor system

Question 3

What is the motor system divided into?

Answer 3

• The somatic nervous system

- The autonomic nervous system

Question 4

What does the central nervous system consist of?

Answer 4

• Brain

- Spinal cord

Question 5

Describe the neurones in the brain?

Answer 5

• Much of the brain is composed of relay neurones, which have multiple connections enabling complex neuronal pathways.
• Most of these cells are non-myelinated cells and the tissue looks grey in colour.
• It is known as grey matter.

Question 6

Describe the neurones in the spinal cord?

Answer 6

• Many non-myelinated neurones making up the central grey matter.
• Also, contains a large number of myelinated neurones making up an outer region of white matter.

Question 7

What is the function of the myelinated neurones in the spinal cord?

Answer 7

-These myelinated neurones carry action potentials up and down the spinal cord for rapid communication over longer distances.

Question 8

What is the spinal cord protected by?

Answer 8

-The spinal cord is protected by the vertebral column.

Question 9

What is between each of the vertebrae in the spinal cord?

Answer 9

-Between each of the vertebrae, peripheral nerves enter and leave the spinal cord carrying action potentials to and from the rest of the body.

Question 10

What is the role of the peripheral nervous system (PNS)?

Answer 10

-To ensure rapid communication between the sensory receptors, the CNS and the effectors.

Question 11

What is the PNS composed of?

Answer 11

• Sensory and motor neurones.

- These are usually bundled together in a connective tissue sheath to form nerves.

Question 12

Describe the sensory nervous system and the arrangement of the neurones in it.

Answer 12

• The sensory fibres entering the CNS are dendrons of the sensory neurones.
• These neurones conduct action potentials from the sensory receptors into the CNS.
• These neurones have their cell body in the dorsal root leading into the spinal cord and a short axon connecting to other neurones in the CNS.

Question 13

What does the motor nervous system do?

Answer 13

-The motor nervous system conducts action potentials from the CNS to the effectors.

Question 14

What does the somatic nervous system consist of?

Answer 14

-Motor neurones that conduct action potentials from the CNS to the effectors that are under voluntary (conscious) control, such as skeletal muscles.

Question 15

What does the autonomic nervous system consist of?

Answer 15

• Motor neurones that conduct action potentials from the CNS to the effectors that are not that are not under voluntary control.
• This includes the glands, the cardiac muscle and smooth muscle in the walls of the blood vessels, the airways and the wall of the digestive system.

Question 16

Describe the myelination of the nerves in the somatic nervous system.

Answer 16

-These neurones are mostly myelinated so that responses can be rapid.

Question 17

Describe the myelination of the nerves in the autonomic nervous system.

Answer 17

-The control of many of these effectors (not under voluntary control) does not require rapid responses, and the neurones are mostly non-myelinated.

Question 18

How many neurones connect the CNS and the effector in the somatic nervous system?

Answer 18

-There is always one single motor neurone connecting the CNS to the effector.

Question 19

How many neurones connect the CNS and the effector in the autonomic nervous system?

Answer 19

-There are at least two neurones involved in the connection between the CNS and the effector. These neurones are connected at a small swelling called ganglia.

Question 20

What does autonomic mean and how does this explain the function and role of the autonomic nervous system?

Answer 20

• Self-governing.
• The autonomic nervous system operates to a large extent independently of conscious control.
• It is responsible for controlling the majority of the homeostatic mechanisms nd also plays a vital role in regulating the internal environment of the body.

Question 21

How can the autonomic nervous system be further divided?

Answer 21

• The sympathetic system which prepares the body for activity.
• The parasympathetic system which conserves energy.

Question 22

How are are the parasympathetic and autonomic nervous systems antagonistic?

Answer 22

-The action of one system opposes the action of the other.

Question 23

What does the sympathetic system consist of?

Answer 23

-Many nerves leading out of the CNS each leading to separate effectors.

Question 24

What does the parasympathetic system consist of?

Answer 24

-A few nerves leading out of the CNS, which divide up and lead to different effectors.

Question 25

Where is the ganglia in the sympathetic and parasympathetic nervous systems?

Answer 25

Sympathetic system: ganglia just outside the CNS.

Parasympathetic system: ganglia in the effector tissue.

Question 26

Compare neurone lengths in the sympathetic and parasympathetic nervous systems.

Answer 26

Sympathetic system: Short pre-ganglionic neurones.

Parasympathetic system:Long pre-ganglionic neurones (variable in length, dependent upon the position of the effector).

Question 27

Compare the neurotransmitters in the sympathetic and parasympathetic nervous systems

Answer 27

Sympathetic system: Uses noradrenaline as the neurotransmitter.

Parasympathetic Uses acetylcholine as the neurotransmitter.

Question 28

What are the effects of the sympathetic system?

Answer 28

Increases activity (prepares the body for activity):

• Increases heart rate.
• Dilates pupils.
• Increases ventilation rate.
• Reduces digestive activity.
• Orgasm.

Question 29

What are the effects of the parasympathetic system?

Answer 29

Decreases activity (conserves energy):

• Decreases heart rate.
• Constricts pupils.
• Reduces ventilation rate.
• Increases digestive activity.
• Sexual arousal.

Question 30

When is the sympathetic nervous system most active?

Answer 30

-During times of stress

Question 31

When is the parasympathetic nervous system most active?

Answer 31

-During sleep or relaxation