4. Divisions of the nervous system

Question 1

What is the peripheral nervous system formed by?

Answer 1

nerve fibres, arranged into nerves that arise from the brain and spinal cord
12 pairs arise from the brain (cranial nerves)
most are mixed, carrying impulses both to and from the brain

Question 2

What are sensory fibres?

Answer 2

nerves fibres that carry impulses into the CNS

Question 3

What are motor fibres?

Answer 3

nerves fires that carry impulses away from the CNS

Question 4

What is the ventral root?

Answer 4

spinal nerve containing the axons of motor neurons that have cell bodies in the grey matter of the spinal cord

Question 5

What is the dorsal root?

Answer 5

spinal nerve which contains the axons of sensory neurons that have cell bodies in a small swelling on the dorsal root ganglion

Question 6

What does the afferent division of the PNS do?

Answer 6

Carries impulses into the CNS through sensory nerve cells from recpetors in the skin, joints and muscles, known as somatic sensory neurons
Also has sensory nerve cells that take impulses from the internal organs into the CNS known as visceral sensory neurons

Question 7

What does the efferent division do?

Answer 7

It has fibres that carry impulses away from the CNS

Question 8

What are the two divisions of the efferent division?

Answer 8

The autonomic division and the somatic sensory division

Question 9

What does the autonomic division of the PNS do?

Answer 9

carries impulses from the CNS to heart muscle, involuntary muscle and glands
Is further dvidied

Question 10

What does the somatic division of the PNS do?

Answer 10

takes impulses from the CNS to skeletal muscles
controls the internal environment
Operates often without conscious control
Regulated by nerve cells in the medulla oblongata, hypothalamus and cerebral cortex

Question 11

What are the divisions of the autonomic division of the PNS?

Answer 11

sympathetic: fight or flight response

parasympathetic response: rest and digest

Question 12

What body functions are regulated by the ANS?

Answer 12

heart rate, blood pressure, body temperature, digestion, energy release, pupil diameter, airflow to lungs, defecation, urination

Question 13

What are some key differences between the ANS and SNS?

Answer 13

the ANS pathway involves 2 motor neurons while SNS only has 1
Most organs under ANS receive both sympathetic and parasympathetic nerve fibres, so ANS is divided into sympathetic and parasympathetic divisions
ANS, the main neurotransmitters are acetylcholine or noradrenaline, while the key SNS neurotransmitter acetylcholine

Question 14

What are the differences in the effects of parasympathetic and sympathetic on the body?

Answer 14

Parasympathetic generally produces responses that maintain the body during quiet stable conditions
Sympathetic prepares the body for strenuous physical activity

Question 15

What do the different divisions of the ANS release?

Answer 15

the parasympathetic releases acetylcholine while sympathetic releases noradrenaline

Question 16

What is the parasympathetics response on the heartbeat?

Answer 16

A normal heartbeat has an inbuilt rate of contraction at 100bpm but the parasympathetic nervous system keeps it down to 70-80bpm

Question 17

If the sympathetic division becomes dominant, what will occur?

Answer 17

• rate and force of heartbeat increases,
• blood vessels involved in high activity dilate
• blood vessels of organs not involved in activity constrict
• airways in the lungs dilate, rate and depth of breathing increases
• blood glucose levels rise as liver converts glycogen into glucose
• adrenal medulla releases adrenaline and noradrenaline to intensify and prolong the above responses

Question 18

What are points of comparison in hormonal and nervous coordination?

Answer 18

• nervous responses are more rapid due to the fact that hormones are transported by the bloodstream
• nervous responses are immediate and last for short time, hormones are slow but last long time
• nervous messages are an electrochemical change along the membrane of a neuron but endocrine messages are chemicals transported by blood
• nervous impulses travel to specific parts of the body, influencing one effector, hormones travel to all over the body and often affect a number of different organs

Question 19

What are some similarities between the nervous and endocrine system?

Answer 19

• some substances function as hormones and neurotransmitters (noradrenaline, antiduretic hormone, dopamine)
• some hormones (oxytocin, adrenaline) are secreted by neurons into the extracellular fluid
• Some hormones and neurotransmitters have the same effect on the same target cells (eg. noradrenaline and glucagon both act on liver cells to cause glycogen to be broken into glucose)