Somatic and autonomic nervous system

Question 1

Where are the cell bodies of somatic motor fibres located?

Answer 1

In the ventral horn of the spinal cord

Question 2

How are afferent and efferent nerve fibres geographically located?

Answer 2

They are located within the same mixed spinal nerve

Question 3

Where do efferent somatic motor fibres terminate?

Answer 3

At motor end plates, which form neuromuscular junctions

Question 4

What symptoms occur if motor fibres are lost or damaged?

Answer 4

Weakness or paralysis of the effector they innervate

Question 5

What sensory information can somatic sensory fibres carry, in what different parts of the body?

Answer 5

Skin: touch, pain, temperature
Joints: proprioception, pain
Tendons/muscles: reflex control

Question 6

Where are the cell bodies of somatic sensory fibres located?

Answer 6

Dorsal root ganglion in the dorsal horn of the CNS

Question 7

What do afferent and efferent mean?

Answer 7

Afferent is towards the CNS, and efferent is away from the CNS

Question 8

What is the difference between spinal roots/horns and rami?

Answer 8

The dorsal and ventral horns/roots are within the spinal cord, and make up the posterior and anterior divisions of the grey matter. The dorsal horn contains the ends of afferent sensory nerve fibres and the ventral horn the cell bodies of efferent motor fibres.

These two horns are connected by relay neurons in the grey matter of the spinal cord, and both afferent and efferent nerves travel within the same mixed spinal nerve from/to the organ they are sensing/effecting.

Once within the same mixed spinal nerve, they split into anterior/ventral and posterior/dorsal rami, the former supplying muscles and skin of the trunk and limbs and the latter supplying muscles and skin of the back

https://en.wikipedia.org/wiki/Ventral_ramus_of_spinal_nerve#/media/File:Spinal_nerve.svg

Question 9

What is the main target of a local anaesthetic?

Answer 9

Sensory somatic nerve fibres

Question 10

Give an example of a local anaesthetic and its mechanism of action

Answer 10

Lidocaine, a local anaesthetic of the amide type
They act by reversibly binding voltage gated sodium channels located in the nerve membrane from the inside. It keeps them locked in an open state that prevents them from inactivating and reactivating to cause another depolarisation, breaking the action potential cycle. This aborts the generation of pain signals by sensory fibres

Question 11

What are visceral afferent fibres, where do their cell bodies lie and what is their relation (in course) to other nerves?

Answer 11

Responsible for pain upon pathologies in the thoracic and abdominal organs.
Cell bodies lie in dorsal root ganglion of dorsal horn
They are typically not present in mixed spinal nerves, and instead follow the paths of autonomic nerves

Question 12

Describe generally the fibres of the somatic nervous system, and provide their conduction velocity. Why are these characteristics important?

Answer 12

Type A or B: fast velocity of conduction, myelinated axons, up to 120ms
Often involved in reflex responses and corrective movements that must be carried out instantaneously in order to protect the body, thus the time from signal to effect is correspondingly quick

Question 13

Regarding the structure of somatic nerve fibres, what type is anomalous?

Answer 13

Pain fibres, which are often type C unmyelinated

Question 14

Fill out table on nerve fibre types

Answer 14

Notability–>revision–>anatomy–>nerve fibres

Question 15

What is the function of the ANS?

Answer 15

Efferent fibres involved in the involuntary control of systems throughout the body

Question 16

What are the two “major” divisions of the ANS, and what are their respective general functions?

Answer 16

Sympathetic (fight or flight) and parasympathetic (rest and digest)

Question 17

Where are the cell bodies of preganglionic ANS efferents located, and where do their axons synapse?
What type of fibre do these tend to be?

Answer 17

From in the CNS, to ganglia in the PNS

Type B; myelinated and slow-medium velocity

Question 18

What is the preganglionic neurotransmitter in both major divisions of the ANS?

Answer 18

ACh

Question 19

Where do parasympathetic nerves originate from? Give examples of the most important nerves and their innervations.

Answer 19

Extremities of spinal cord: cranial nerves (CNI-CNXII) and sacral nerves (S1-S5)
Vagus nerve (CNX) innervates thoracic viscera and most abdominal viscera
Sacral nerves innervate hindgut and urogenital tract

Question 20

Where do sympathetic nerves originate from?

Answer 20

T1-L2, innervating all viscera

Question 21

Where are parasympathetic ganglia located?

Which neurotransmitter do post-ganglionic neurons use?

Answer 21

Usually within end-organ

ACh

Question 22

1. Where are sympathetic generally ganglia located?
2. Which neurotransmitter do post-ganglionic neurons use?
3. What exceptions are there to your answer to question 1?

Answer 22

1. In discrete ganglia quite close to the spinal cord, found within a paravertebral chain of ganglia
   The ganglia are distinguished as cervical, thoracic, lumbar and sacral, and correspond in number quite closely with the vertebrae
2. NAd
3. Midline/prevertebral ganglia found between paravertebral chain and target organs, which are made up of the coeliac, superior mesenteric and inferior mesenteric ganglia, supplying the fore-, mid- and hindgut

Question 23

How does the position of their respective ganglia explain the difference in parasympathetic and sympathetic function?

Answer 23

The parasympathetic ganglia are not interconnected, and thus postganglionic fibres work/are stimulated independently, thus providing more targeted supply to the organs, whereas sympathetic stimulation causes a more global response regardless of which preganglionic nerve is stimulated, as signalling will be shared along the paravertebral chain

Question 24

Where is adrenaline secreted and how does this relate to the ANS?

Answer 24

Adrenaline is secreted by the renal medullary cells into the bloodstream, and therefore they act as modified sympathetic ganglia, boosting the sympathetic response through hormone action (as they can bind adrenergic receptors)

Question 25

What do visceral afferent fibres have receptors for?

Answer 25

Stretch (mechanoreceptors)

Chemicals (chemoreceptors)

Question 26

What two kinds of responses do visceral afferent fibres promote?

Answer 26

Involuntary autonomic reflex, such as baroreflex (maintenance of blood pressure)

Sensation and mixed autonomic/somatic motor effects for a response that can be partially controlled by higher thought, such as urination

Question 27

What is the minor division of the ANS called?
What is its function?
Where are ganglia located?
What neurons make it up?

Answer 27

Enteric nervous system
Coordinate activities of the gut
Myenteric and submucosal plexi
Sensory (detecting stretching of gut wall), motor (controlling smooth muscles contractions of gut wall) and secretomotor (controlling secretions of gut wall)

Question 28

How is activity of the ENT modulated?

Does it require this innervation to function?

Answer 28

By sympathetic splanchnic (coeliac and superior + inferior mesenteric) nerve post-ganglionic fibres, and parasympathetic vagus nerve pre-ganglionic fibres

No, can function in isolation