Peripheral Nervous System

Question 1

Where is the peripheral nervous system?
Afferent information -
Efferent information -

Answer 1

Branches off the CNS and consists of all the nerves outside the CNS
Afferent - sensory info gathered by peripheral and will send it to brain
Efferent - motor signals via peripheral nervous system

Question 2

What are the functions of peripheral system ?

Answer 2

Communication system of the body
Key role in sending information from different body areas to the brain (Afferent) and carrying commands from the brain to various body parts (efferent)
Coordinates involuntary and voluntary responses of many organs eg skin, digestive system etc

Question 3

What makes up the cranial nerves?

Answer 3

Cranial nerves are 12 pairs of nerves that connect directly to your brain - 11 of them are part of peripheral nervous (2nd cranial nerve controls vision and is part of the CNS)

These 11 nerves - part of senses - smell, sound, taste and touch
The vagus nerve which is one of the 11 extends down and attaches to all vital organs from the neck to colon.

Question 4

Describe what makes up the spinal nerves -

Answer 4

31 pairs of nerves attach to spine at about each segment bone level (vertebra) in spine
All exit spine via intervertebral foramen
Consists of - C1-C8
T1-T12
L1-L5
S1-S5 and C0
Can combine into plexus, branch and travel together

Question 5

Dermatomes -

Answer 5

Defined strip of skin that is innovated by a single spinal nerve

Question 6

Myotomes -

Answer 6

Group of muscles innovated by a single spinal nerve

Question 7

Peripheral is broken down into two sub-groups:
Somatic -
Autonomic -

Answer 7

Somatic - voluntary actions and conscious control. Sensory and motor signals

Autonomic - regulates internal environment of the body. Involuntary control of automatic processes eg digestion and heart rate
Divided into two further systems:
Parasympathetic - rest and digest (cranio-sacral nerves). Calms body, restores resting hr
Sympathetic - fight and flight (thoraco-lumbar nerves)

Question 8

Gives examples of how a nerve can be damaged:

Answer 8

Nerve is cut eg in surgery
Compressed eg tumor
Nerve is stretched eg fracture or dislocation
Nerve is crushed eg drop something on your hand
Penetrating injury which takes out nerve and tissue eg gunshot

Question 9

Stages and nerve injury types:
Neuropraxia -
recovery?

Answer 9

Most mild
Endoneurium (layer outside myelin) is in tact. Axon in tact
Mild compression/de myelination at this level
De myelination can cause mild conduction block and therefore mid weakness in muscles
Recovery is complete (spontaneous) eg crutch palsy

Question 10

Stages and nerve injury types:
Axonotmesis -
Recovery?

Answer 10

Endoneurium still intact. Axon is damaged - not in act and mild de myelination (more moderate than neuropraxia) therefore motor and sensory loss is greater. Moderate conduction block
Can recover without surgery and complete recovery (spontaneous)
Eg fracture (closed)
Dislocation

Question 11

Stage and types of nerve injury:
Neurotmesis-
Recovery?

Answer 11

Endoneurium and axon are NOT in tact. Significant demyelination
Recovery is poor and bad prognosis - surgery is likely
Severe conduction block
Eg open fractures o gunshot wounds

Question 12

Stages of nerve recovery (proximal segment change)
1) chromatolysis -

Answer 12

Nerve injury causes a proximal segment change (site before injury)
Cell body picks up signals of injury and the nucleus wil migrate to periphery of cel body (edge)
Nissil granules (RER) disperse near nucleus and cel body will swell
mRNA formed in nucleus and goes to RER o proteins can be made
Golgi apparatus package proteins to vesicles which are then transported down neurone to repair.

Question 13

Stages of nerve recovery (proximal segment change)
2) after chromatoysis..

Answer 13

Degenerate myelin at adjacent node destroy the adjacent node of ranvier and myelin and swchann cell
This leaves a gap along the axon.

Question 14

Stages of nerve recovery
After stage 2 - distal segment change occurs:

Answer 14

Cell membrane of axon and myelin is broken down - leaving just fragments
Endoneurium releases serotonin and histamines which stimulates macrophages. These macrophages will eat axon and myelin fragments, leaving just Schwann cells
*this is why an intact Endoneurium is essential for recovery

Question 15

What is proximal and distal segment change together in nerve recovery ?

Answer 15

Called wallerian degeneration

Question 16

Nerve recovery - after distal segment change
Regeneration process -

Answer 16

Within 24hours axonal sprouts begin to form - guided by Schwann so they connect to distal stump.
Endoneurium helps keep this all enclosed
Schwann cells begin myelination
And stumps eventually fuse. Everything regenerates
Nucleus returns to centre of cell body

Question 17

Spinal cord injury
Primary injury -
Secondary injury -

Answer 17

Primary - initial mechanical trauma. Disrupts axons, blood vessels and cell membranes

Secondary - minutes/months/years after initial spinal cord injury
Vascular damage, ion imbalances, excitoxicity, calcium influx, cell death and scar formation

Question 18

Spinal cord injury - why doesn’t the CNS regenerate?

Answer 18

Initial - branches of major blood vessels supplying spinal cord are damaged. Fluid will leak out therefore increasing the pressure
Decreased oxygen to cells and nutrients therefore cannot make energy - lead to cell death due to calcium influx.
Overall BP will decrease as pressure increases in spine
Cell death therefore cell contents will begin to leak out
Autophagy occurs, encapsulating dead cells, digest and recycles them
Inflammation occurs- non-specific, clean and repair promotes autophagy ad cell death due- everything is cleared away
This begins scar formation - glial scar - never full recovery as neurones and other contents have been whipped out.

Question 19

Spinal cord injury
What is autophagy ?

Answer 19

Bodies protective mechanism - encapsulates dead cells, digests and recycles them
This is the reason no one can have a full recovery from a spinal cord injury, as the body naturally will want to remove all the contents.
Therefore there are no neurones left to re-build in the damaged area