Chapter 04: Divisions Of The Nervous System

Question 1

• Whats the function of the N.S?
• What are the 2 main parts of the N.S?
• How many pairs of nerves arise from the brain and spinal cord?
• What are dorsal roots?
• What are the ventral roots?
• The PNS is subdivided into what 2 divisions? Describe each.
• What is the efferent division subdivided into? Describe each.
• What is the autonomic division further subdivided into?

Answer 1

• Detects changes in our external and internal environment and responds appropriately to these changes to maintain homeostasis.
  1. CNS: The control centre, consists of the brain and spinal cord.
  2. PNS: connects the CNS with the receptors, muscles and glands.
• 12 pairs of cranial nerves from the brain and 31 pairs of spinal nerves.
• A root linking spinal nerves to spinal cord containing axons of sensory neurones that have their cell bodies in the dorsal root ganglion.
• A root linking spinal nerves to spinal cord containing axons of motor neurones having their cell bodies in the grey matter of the spinal cord.
  1. Afferent division: carries info to the CNS.
  2. Efferent division: carries info away from the CNS.
  1. Somatic: carries messages to skeletal muscles.
  2. Autonomic: carries messages to involuntary muscles.
  1. Sympathetic division: Produce responses that prepare the body for fight or flight responses, raising action of body.
  2. Parasympathetic division: Relaxes the body back to normal state.

Question 2

• What is the function of the autonomic N.S?
• Nerve cells that regulates the ANS are located in what 3 locations?
• What are some body functions that is regulated by the ANS?
• What is a ganglion and purpose?
• Describe 6 differences between the somatic and autonomic divisions of the PNS.

Answer 2

• Controls the body’s the mechanisms that keep the internal environment constant.
• Medulla oblongata, hypothalamus and cerebral cortex.
• HR, BP, body temp, digestion, release of energy, pupil diameter, air flow to the lungs, defecation and urination.
• Nerve cell bodies groups found outside the CNS eg dorsal root ganglion. It links 2 neurones - one from the CNS and the other ending in an effector.
  1. A.D nerves carry impulses to involuntary internal organs where as somatic nerves carries impulses to skeletal muscles.
  2. Impulse pathway of the CNS to effector via A.D consists of 2 neurones with a synapse in a ganglion, whereas only 1 neurone in S.D.
  3. A.D effectors have 2 sets of nerve fibres- sympathetic fibres and parasympathetic fibres, whereas S.D effectors have only 1 set.
  4. Acetylcholine is the only neurotransmitter in the S.D. Whereas in the S.D, it is either acetylcholine or noradrenaline.
  5. Control of the A.D is involuntary whereas is voluntary in the S.D.
  6. S.D fibres just excites the effector. Whereas in the A.D, sympathetic fibres excite effector but also parasympathetic fibres inhibit effectors.

Question 3

• Parasympathetic and sympathetic nerve endings release different chemicals to the effectors, what are they?
• If the ventral root of a spinal nerve were damaged, would it affect the sensory functions or the motor functions of that nerve? Explain.
• Compare the effects of the sympathetic and parasympathetic stimulation to the following body structures:
  1. Heart. 2.Lungs. 3.Stomach and intestines. 4.Liver
  5. Iris of the eye. 6.Sweat glands. 7.Salivary glands
  8. Blood vessels of skin. 9.Blood vessels of skeletal muscle
  10. Blood vessels of internal organs. 11.Urinary bladder
  12. Adrenal medulla

Answer 3

• Parasympathetic nerve endings release acetylcholine and sympathetic nerve endings release noradrenaline.
• Motor functions as the axons of the motor neurones are in the ventral root of a spinal nerve.
  1. S.S would increases rate and strength of contraction, whereas P.S would decrease rate and strength of contraction.
  2. S.S Dilates bronchioles, whereas P.S constricts bronchioles
  3. S.S decreases movement whereas P.S Increases movement
  4. S.S Increases breakdown of glycogen releasing glucose, whereas P.S increases uptake of glucose and synthesis of glycogen.
  5. S.S Dilates pupil, whereas P.S constricts pupil.
  6. S.S increases sweat secretion, whereas P.S has no effect.
  7. S.S decreases saliva secretion, and P.S increases saliva secretion
  8. S.S constricts vessels, whereas P.S has little effect
  9. S.S dilates vessels, whereas P.S has no effect
  10. S.S Constricts vessels (except in heart and lungs). Whereas P.S has little effect.
  11. S.S relaxes muscles of wall whereas P.S constricts muscles of wall
  12. S.S stimulates hormone secretion, whereas P.S has no effect.

Question 4

-In threatening situations what happens to the balance between the sympathetic and parasympathetic stimulation?
-List 7 responses that would prepare the body for fight or flight.
Compare the nervous system and endocrine system in terms of:
1. Nature of message
2. Transport of message
3. Cells affected
4. Type of response
5. Time taken to respond
6. Duration of response
-Explain 3 similarities of the nervous and endocrine systems.

Answer 4

• The sympathetic stimulations become dominant.
  1. H.R, force of contraction and B.P increases.
  2. Blood vessels in organs involved in strenuous activity dilate.
  3. Blood vessels in organs not involved in strenuous activity constrict.
  4. Airways in lungs dilate and B.R increases.
  5. Blood glucose level rises- liver converts more glycogen to glucose.
  6. Secretion of sweat increases.
  7. Adrenal medulla release adrenalin and noradrenaline intensifying the above responses.
  1. NS: Electrical impulses and neurotransmitters ES: Hormones
  2. NS: Along the membrane of neurones ES: Bloodstream
  3. NS: Muscles, glands and other neurones ES: All body cells
  4. NS: Usually local and specific ES: Widespread
  5. NS: millisecondsES: seconds - days
  6. NS: stops as stimulus stops ES: Can continue after stimulus has stopped.
  1. Some substances function as both hormone and neurotransmitters. Eg noradrenaline and antidiuretic hormone.
  2. Neurones secrete hormones such as oxytocin and adrenaline.
  3. Some hormones and neurotransmitters have the same effect on the same target cells. Eg noradrenaline and the hormone glucagon both act on liver cells to cause glycogen to be broken down into glucose.

Question 5

• Urinary retention (inability to empty the bladder) and incontinence (involuntary leaking of urine) are both possible symptoms of disease of the autonomic N.S. Which part of the autonomic division would be affected in each case?
• If the dorsal root of a spinal nerve were damaged, would there be any effect to the autonomic functions controlled by that nerve?
• If a drug stimulated acetylcholine receptors, would it affect the autonomic division, the somatic division or both? Explain ur answer.
• The drug atropine occupies acetylcholine receptors at the synapse. Ophthalmologist once used atropine when they needed to dilate a patient’s pupils. Explain why atropine would have this effect.
• Describe the nervous and hormonal changes that would take place in someone who is in extreme fear.

Answer 5

• Overstimulation of the sympathetic division may cause urinary retention as the bladder muscles would not constrict enough to push out urine. Overstimulation of the parasympathetic division could mean that the bladder muscles contract pushing urine out.
• No, the A.N.S controls activity through motor nerves that exit from the ventral root of the spinal cord.
• Both as both divisions use acetylcholine as the neurotransmitter that allows impulses to travel from axons to effectors.
• Atropine blocks the effects of acetylcholine, so that when placed in the eye, muscles in the eye cannot be stimulated to contract so the pupils dilates.
• Nervous changes: sympathetic stimulation would become dominant preparing the body for fight or flight. Whereas Hormonal changes: sympathetic stimulation would cause the adrenal medulla to release the adrenaline and noradrenaline intensifying the fight or flight responses.

Question 6

• How is the autonomic nervous system linked to the central nervous system?
• Describe how a muscle fibre is stimulated.

Answer 6

• Through cranial nerves from the cerebrum and spinal nerves from the spinal cord.
• When a nerve impulse travels down a motor neurone, acetylcholine is released from the axon terminals. This diffuses across the synapse and combines with special receptor sites on the motor end plate. Depolarisation occurs and a muscle action potential is generated in the sarcolemma covering the muscle fibre, resulting in the muscle shortening. The acetylcholine is destroyed by an enzyme, acetylcholinesterase and the fibre relaxes.

Question 7

-Explain the division of the nervous system.

Answer 7

-NS splits into PNS and CNS; CNS consist of brain and spinal cord; PNS splits into Afferent and Efferent division; Efferent division splits into somatic and autonomic division; autonomic division splits into sympathetic and parasympathetic division.