Chapter 4 - Divisions Of The Nervous System

Question 1

Describe the main purpose of the Peripheral Nervous System

Answer 1

The PNS consists of nerve fibres that carry impulses to and from the central nervous system and groups of ganglia which lie outside the brain and spinal cord.

(Ganglia = groups of nerve cell bodies)

Question 2

Describe what Brain nerves are

Answer 2

There are 12 pairs of brain nerves, also known as cranial nerves.
Most cranial nerves are mixed nerves, meaning they contain sensory fibres as well as motor fibres. A few cranial nerves can only carry sensory impulses while others can only carry motor impulses.

Question 3

What are two examples of cranial nerves?

Answer 3

The optic nerve

The auditory nerve

Question 4

What is the difference between sensory and motor fibres?

Answer 4

Sensory fibres carry impulses into the brain.

Motor fibres carry impulses away from the brain.

Question 5

Describe what spinal nerves are

Answer 5

There are 31 pairs of spinal nerves. They are ALL mixed nerves and each is connected to the spinal cord by two roots.

Question 6

Explain the two roots that join spinal nerves to the spinal cord

Answer 6

The Ventral root
- contains axons of motor neurones that have their cell bodies in the grey matter of the spinal cord.

The Dorsal root
- contains the axons of sensory neurons that have their cell bodies in a small swelling on the dorsal root known as the dorsal root ganglion.

Question 7

What is a ganglion?

Answer 7

A ganglion (plural ganglia) is a group of nerve cell bodies outside the CNS.

Question 8

Explain the afferent division of the PNS

Answer 8

The afferent, or sensory, division of the PNS have sensory fibres. Some sensory nerves transport impulses from the skin, around the muscles and joints. These nerve cells are called Somatic Sensory neurons.
Other sensory nerves take impulses from internal organs, are are called Viseral Sensory neurons.

Question 9

Explain the Efferent Division of the PNS

Answer 9

The efferent, or motor, division has motor neurons. It is divided into the somatic division, which takes impulses from the CNS to the skeletal muscles.
The autonomic division carries impulses from the CNS to heart muscle, involuntary muscles and glands. The autonomic division is further divided into the sympathetic division and the parasympathetic division.

Question 10

Explain the main role of the autonomic nervous system

Answer 10

It is responsible for the control of the body’s internal environment and is involved in many of the mechanisms that maintain homeostasis.
It usually operates involuntarily and is regulated by nerve cells in the hypothalamus, medulla oblongata and cerebral cortex.

Question 11

What are some body functions regulated by the autonomic division? (9)

Answer 11

• Heart rate
• blood pressure
• body temperature
• digestion
• release of energy
• pupil diameter
• air flow
• defecation
• urination

Question 12

Describe the pathway of an impulse from the CNS to the an organ controlled by the autonomic division

Answer 12

The pathway consists of two neurons. One cell body is in the CNS and the other cell body is in a ganglion.
The pathway from the CNS to heart muscle p, involuntary muscle and glands is an important difference between the autonomic division and the somatic division.

Question 13

What are the some important differences between the autonomic and somatic divisions?

Answer 13

• the pathway of the impulse
• the ANS is further subdivided into sympathetic and parasympathetic divisions
• the main SNS neurotransmitter is acetycholine. The main ANS neurotransmitters are acetylcholine or noradrenaline.
• the effectors of SNS = skeletal (voluntary muscles)
  The effectors of ANS = heart muscle, glands and involuntary muscle.
• general function of SNS = response to the external environment
  General function of ANS = homeostasis
• effect on target organ SNS = always excitation
  ANS = excitation or inhibition

Question 14

Explain, in one sentence, what the sympathetic and parasympathetic divisions are for

Answer 14

The parasympathetic division generally produces responses that maintain the body during relatively quiet conditions.

The sympathetic division tends to produce responses that prepare the body for strenuous activity.

Question 15

Construct a table on the different effects that the sympathetic and parasympathetic divisions have on the body.

Answer 15

Refer to notes

Question 16

Explain what the fight or flight response is

Answer 16

In threatening situations the balance between the sympathetic and parasympathetic stimulations become unbalanced and the sympathetic becomes dominant. Situations that involve fear, anger, stress, danger or competition provoke the fight or flight response or alarm reaction and prepare the body for strenuous activity.

Question 17

What are some responses of the body caused by the activation of the sympathetic division? (7)

Answer 17

• increase of heart rate
• dilation of the blood vessels in skeletal muscles, heart and liver.
• constriction of the blood vessels in the kidneys, stomach, intestines and skin.
• Dilation of airways to the lungs.
• increased blood glucose levels
• increase of sweat
• release or Adrenalin and noradrenaline

Question 18

What are some differences between the nervous and hormonal systems? (6)

Answer 18

• nature of message
  NS = electrical impulses and neurotransmitters
  HS = hormones
• transport of the message
  NS = Along the membrane of neurones
  HS = by the blood stream
• cells affected
  NS = muscle and gland cells
  HS = all body cells
• type of response
  NS = usually local and specific
  HS = May be general and widespread
• time taken to respond
  NS = rapid
  HS = slower
• duration of response
  NS = brief, stops when stimulus stops
  HS = longer lasting, may continue after stimulation stops

Question 19

What are some similarities between the nervous and hormonal systems? (3)

Answer 19

• some substances function as both hormones and neurotransmitters (antidiuretic hormone, noradrenalin and dopamine)
• some hormones such as oxytocin and Adrenalin are secreted by neurons into the extracellular fluid.
• some hormones and neurotransmitters have the same effect on the same target cells. (Break down of glucose).

Question 20

What is the difference between a neuron and a nerve fibre?

Answer 20

A neuron is a singular nerve cell.

A nerve fibre is a bundle of nerve cells.