general organisation of the nervous system II

Question 1

What is the peripheral nervous system?

Answer 1

Axons leave the CNS to supply motor fibres to muscles and collect sensory information . Axons in the PNS are collected together into bundles called nerves

Somatic Nerves
Nerves of Special Sensation
Autonomic Nerves

All sensory axons weather somatic/autonomic have there cell bodies outside the CNS in ganglia- NO SYNAPSES
All motor ganglia

Question 2

Describe the Somatic Nerves

Answer 2

Supply the body wall , skeletal muscle and skin- contain motor and sensory fibres

Question 3

Describe nerves of special sensation

Answer 3

Sight smell taste hearing and balance

Question 4

What is special about somatic nerves?

Answer 4

Somatic nerves- special case- somatic nerves are those of special case- spinal nerves originate from spinal cord if they arise from the brain

Spinal nerves leave the spinal chord from anterior and posterior

Question 5

Describe Spinal Nerves

Answer 5

Like the reflex action

Motor neurones comme out together from the final common pathway- giving a reaction
At the same time, fibres can travel to medulla and thalamus

Question 6

Myotome

Answer 6

The area of muscle supplied by the spinal nerve

Question 7

Dermatome

Answer 7

The area of skin supplied by the sensory nerve

Question 8

Describe the nerve plexuses

Answer 8

The anterior rami of all spinal nerves except T2- T12 branch and rejoin at plexuses

Fibres from different ventral origins criss cross each other and redistribute so that each end branch of a plexus contains fibres from several spinal nerves AND fibres from several spinal nerves from each ventral ramus travels to periphery from different roots.

Therefore each limb muscle receives nerve supply from more than 1 spinal nerve- why one nerve doesn’t result in paralysis

Question 9

Describe the Autonomic nerves-

Answer 9

Involved in regulating the internal environment of the the body

Sensory and Motor fibres travel in company

Sensory fibres of spinal nerves, sensory ganglia of cranial nerves, sensory fibres of ANS have cells in the cell body

Question 10

What can the motor nerves innervate

Answer 10

Motor fibres innervate smooth muscle and glands (eg salivary gland)
AND
on the most part the gastric intestinal system- this is because it has its own nerve supply therefore can continue without needing the the ANS. So the motor nerves have no direct control
THIS IS SIMILAR TO CARDIAC MUSCLE

Question 11

Describe the Autonomic motor pathway

Answer 11

Consists of two neurones in series

cell body in the CNS with the axon extending to the autonomic ganglion where it synapses.
Axon arising from the cell body travels to the effector organ eg smooth muscle.

Question 12

Contrast the autonomic and somatic nervous pathways

Answer 12

ANS —> Preganglionic neurone = myelinated
Postganglionic neurone=unmyelinated
SNS —> Somatic motor neuron is myelinated

ANS—> 2 neurones linked by ganglia
SNS—-> 1 neurones straight to skeletal muscle

ANS—-> visceral
SNS ——> somatic

Question 13

Name the 2 types of motor neurone in the ANS

Answer 13

Sympathetic
Parasympathetic

In the trunk and head they act antagonistically

Question 14

Describe the sympathetic nervous system

Answer 14

Arise from T1-L2
Distribution- all points of the body wall and viscera
Function- moderate visceral function eg Heart Rate, peristalsis, sweating- it will increase heart rate and increase rate of sweating

Question 15

Name the type of second order post-ganglionic neurons

Answer 15

Sympathetic chain ganglia (paired)
Collateral ganglia (unpaired)
Adrenal Medulla

Question 16

Describe the sympathetic chain ganglia

Answer 16

innervate visceral effectors in thoracic cavity, head and body wall..
Post ganglionic fibres will supply the SMOOTH MUSCLE in the walls of the blood vessels. They contract to vasoconstrict the Blood vessels- eg when they hot.
However, the smooth muscles elsewhere will have to relax to prevent the BP increasing too much.
These fibres will rejoin the spinal nerves because they are distributed around the body- go along the walls of the blood vessels.
SWEAT GLAND
ERRECTOR PILLI MUSCLE
INFLUENCE THE VISCERA IN THORAX- the HR and breathing

plexuses formed from the post ganglionic neurones. which rest on the oesophagus and abdominal nerve

Question 17

Describe the Collateral ganglia

Answer 17

Innervate visceral effectors in abdominopelvic cavity. These originate from splanchnic nerves- which sit on the aorta (hence why unpaired) These supply the bladder, kidney, small intestine, penis and scrotum

Question 18

Describe the Adrenal Medulla

Answer 18

there is no motor ganglion hence no synapse which means that it will release the NTs allowing the kidney to produce hormone

Question 19

What is meant by strong sympathetic activity

Answer 19

Staring eyes, cold, clammy skin, dry mouth, hair standing on end and sinking feeling in the pit of the stomach.

Usually this more gentle and controlled- it is balanced against the parasympathetic. (ABOVE IS EXTREME)

Lead to smooth controlled visceral function

Question 20

Describe the roles for sensory fibres

Answer 20

Concerned with the regulation of visceral activity- rarely reaches consciousness.
eg. fullness of urinary bladder

eg Sensory fibres from the autonomic nervous system. Linked heart pain and referred through the somatic NS but the T1-L2

Question 21

Describe the parasympathetic nervous system

Answer 21

Arises in the craniosacrial region 
Originates from Cranial Nerves III, VII IX  AND X (vagus)
and Sacrial Nerves S2-S4 
Distribution is Head and Trunk only 
Key:  Antagonistic to sympathetic

Question 22

Describe the Vagus Nerve

Answer 22

NB with all of the parasympathetic nerves- the post ganglionic fibres are found on the walls of the organs that are being innervated.

This influences the HR, breathing rate and the abdominal region

Question 23

Describe what reaches out from the S2-S4

Answer 23

A plexus is formed (hypogastric plexus) in the lower part of the abdominal region.

Visceral function of the organs in the lower abdminopelvic region