Anatomy of the Peripheral Nervous System (PNS)

Question 1

What is the Peripheral nervous system (PNS)

Answer 1

-Everything outside of CNS
-Two types of nerves:
Cranial nerves (12 pairs)
Spinal nerves (31 pairs)
-Ganglia
-Enteric plexuses (GIT)
-Other nerve plexuses
-Sensory receptors

Question 2

Ganglia

Answer 2

Small masses of nerve tissue

Question 3

Plexus

Answer 3

Branching network of nerves

Question 4

Why does the PNS matter?

Answer 4

-Sends information between your body and brain
-Carries out brain’s commands to your body

Question 5

Sciatica

Answer 5

-Severe back pain radiating to legs
-Caused by compression or inflammation of the sciatic nerve
-Common in pregnant women due to muscle tension and joint changes

Question 6

In/Output from the PNS

Answer 6

Afferent (sensory) - input
Efferent (motor) - output

Question 7

Afferent (sensory)

Answer 7

-Carry information from sensory receptors to the CNS
Somatic: From skin, muscles, joints (reflex actions)
Visceral: From internal organs

Question 8

Efferent (motor)

Answer 8

-Carry info from CNS to organs
Somatic: Innervate skeletal muscles
Autonomic: Innervate smooth muscle, cardiac muscle, glands (parasympathetic & sympathetic)

Question 9

Autonomic nervous system

Answer 9

Autonomic: sympathetic & parasympathetic divisions

-Sympathetic - ‘fight or flight’ –> respiratory rate increases
-Parasympathetic - ‘rest and digest’

Question 10

Key anatomical differences between ANS divisions

Answer 10

1. site of origin
2. lengths of fibres
3. location of their ganglia

Question 11

Types of nerves

Answer 11

Sensory neurons: activated by external physical or chemical stimuli

Motor neurons: found in the spinal cord connect spinal cord to organs, muscles, glands

Interneurons: connect motor neurons to sensory neurons, allowing signalling

Question 12

Nerve fasicles

Answer 12

Bundles of axons

Question 13

In the PNS, where do axons lie?

Answer 13

Within peripheral nerves

Question 14

Connective tissue, three layers:

Answer 14

Endoneurium: Around individual axons in a fascicle
Perineurium: Wraps each fascicle
Epineurium: Covers all fascicles to form the entire nerve

Question 15

Blood vessels

Answer 15

Provide oxygenated blood, and take away deoxygenated blood, and other wastes

Question 16

Nerve fibre types

Answer 16

Myelinated axons: rapidly transmit impulses over long distances

unmyelinated axons: slower or shorter distance transmissions

Question 17

Dorsal root

Answer 17

sensory - afferent

Question 18

Ventral root

Answer 18

motor - efferent

Question 19

Spinal nerves branch to form?

Answer 19

Dorsal and ventral rami

Question 20

Dorsal rami

Answer 20

Innervation to the skin and back muscles (smaller)

Question 21

Ventral rami

Answer 21

Innervation to the rest of trunk and limbs (larger)

Question 22

Ramus (pleural), Rami (singular)

Answer 22

Small branches or extensions from a main structure

Question 23

nerve plexuses are formed by ventral rami

Answer 23

-Contains fibers from different spinal nerves (ventral rami)
-Fibers from each rami take multiple paths to the periphery
-Overlapping territories: Each area gets input from multiple spinal nerves

Question 24

4 main plexuses

Answer 24

Cervical
Brachial
Lumbar
Sacral

Question 25

Cervical

Answer 25

Under sternocleidomastoid, skin innervation

Question 26

Brachial

Answer 26

located in neck and shoulder, innervates the upper limb

Question 27

Lumbar

Answer 27

located within psoas muscle, innervates abdominal wall, anterior and medial thigh

Question 28

Sacral

Answer 28

located posterior to lumbar plexus, innervates buttocks, lower limb, pelvis

Question 29

Sciatic nerve

Answer 29

Largest branch, serves most of thigh, leg and foot muscles, ‘sciatica’.

Question 30

Brachial plexus injuries

Answer 30

-Brachial plexus injuries common, can weaken or paralyze arm
-Ulnar nerve vulnerable (‘funny bone’)
Example: Carpal tunnel syndrome, median nerve compressed

Question 31

Cranial nerves

Answer 31

12 pairs
-Sensory, motor or both
-Arranged along the longitudinal axis of brain
-CN1 attaches to the cerebrum
-CN2 attaches to the diencephalon
-CN3-CN12 attach to the brainstem