Peripheral nervous system- PNS

Question 1

Main components of the PNS

Answer 1

Somatic division:
Responsible for voluntary actions.
Includes: skeletal muscles, touch, pain.

Autonomic:
Responsible for involuntary actions..
Includes: organs and vessels.

Both contain motor and sensory neurones.

Question 2

Somatic motor neurones

Answer 2

Contains cell body in the spinal cord or the brainstem and sends information to the skeletal muscles.

Cell body—-Efferent fibres—-> Skeletal muscles.

Question 3

Somatosensory neurones

Answer 3

Axons of the primary sensory neurones.

Exteroceptive- carries information from the external environment.

Proprioceptive- Carries information from within the body

Skin/ muscle/ joint –Afferent fibres—> Cell body in dorsal root ganglia or cranial nerve ganglia—-> Afferent fibre—> CNS

Question 4

Spinal nerves

Answer 4

Branching from the spinal cord via NERVE ROOTS and provides motor and sensory supply to everywhere BUT the head and neck.

Formed when the ventral and dorsal spinal roots merge in the intervertebral foramen.

Provides sympathetic supply to the whole body.

31 pair of spinal nerves:
8 pairs of Cervical
12 pairs of Thoracic
5 pairs of Lumbar
5 Pairs of Sacral
1 pair of coccygeal

Question 5

Peripheral nerves

Answer 5

Nerves that arise from cranial or spinal nerves.

Gives supply from the CNS to the rest of the body.

Question 6

Nerves roots

Answer 6

Connects spinal nerves to the spinal cord and sits in the vertebral canal.

Composed of 2 roots on each side of the spinal column:
Ventral (anterior): brings out efferent fibres

Dorsal (posterior): takes in afferent fibres-
Contains dorsal root ganglia (bulge)- location of cell bodies of the sensory neurones.

Question 7

Primary rami

Answer 7

Primary rami is the branch off the spinal nerve, from/to the body.

Composed of the dorsal (posterior) and ventral (anterior) ramus.

Involved in motor, sensory and sympathetic functions.

Dorsal rami: supplies a section on the back
Ventral rami: supplies most places in the body.

Question 8

Dorsal (posterior) rami

Answer 8

Branch of the spinal nerve, smaller of the two ramus:

Supplies:

• Skin of the paravertebral gutter: middle section of the back.
• Erector spinae muscles of the back: group of back muscles around the vertebral column.
• Facet joints of the vertebral column- zygapophyseal joint.

Question 9

Facet joint between vertebrae is called…

Answer 9

Zygapophyseal joint

Question 10

Ventral (posterior) rami

Answer 10

Branch of the spinal nerve, larger of the two ramus:

Supplies hypaxial muscles: most of the skeletal muscles

Forms the intercostal nerves and the four nerve plexuses:
Cervical
Brachial
Lumbar
Sacral
(note, no thoracic, since intercostal nerves are present)

Question 11

Nerve plexus

Answer 11

Formed from the merging of multiple ventral ramus.

Allows multiple innervation of a muscle.

Plexuses:
Cervical- merging of C1-C4
Brachial- merging of C4-C8
Lumbar- merging of L1-L4, T12
Sacral- L4-S4

Question 12

Dermatome

Answer 12

Area of the skin innervated by one spinal nerve.

Arises from the somite in the mesoderm.

T10 is the umbilicus strip, located of the belly button.

Loss of sensation on a dermatome could indictae spinal or nerve root damage.

I.e loss of sensation at T10, could indicate T10 spinal nerve damage

Question 13

Embryonic development of myotomes and dermatomes

Answer 13

Dermatomes and myotomes arise from the mesoderm at week 3

They originate from somites: paired blocks that horizontally segment the body.

One pair of spinal nerves supplies a pair of somites.

Question 14

Myotomes

Answer 14

Muscle group innervated by one spinal nerve.

This is very conserved in the thorax, seen by intercostak muscles being supplied by intercostal nerves.
I.e T5 supplies 5th intercostal muscles.

However, more than one spinal nerve innervate other muscle groups.

Question 15

Referred pain

Answer 15

Involved in dermatomes.

Cutaneous pain in specific dermatomes can indicate damage to visceral organs.

Examples:
Pain in C3-C5 (shoulder region) indicates diaphragm irritation.

Question 16

Autonomic nervous system

Answer 16

Nerve supply that controls involuntary actions, characterised by the sympathetic and parasympathetic system.

Regulates activity of the internal organs and maintains the internal environment

Sympathetic:
Stems from the thoracic and lumbar spinal cord.
Maximises metabolic resources

Parasympathetic:
Stems from the cervical and sacral region of the spinal cord.
Conserves metabolic reserves.

Composed of a disynaptic pathway (except adrenal medulla)

Question 17

General nerve pathway of the autonomic nervous system

Answer 17

Disynaptic pathway:

CNS—-preganglionic nerve—< Autonomic ganglia——-postganglionic nerve——–< effector organ

BUT adrenal medulla is monosynaptic:

CNS——-preganglionic neurone—–< Adrenal medulla.

Question 18

Sympathetic trunk

Answer 18

Composed of interconnected paravertebral ganglia.

All preganglionic sympathetic axons enter through the sympathetic trunk in the nerve pathway.

Question 19

The sympathetic pathway to the musculoskeletal system, the heart, lungs and the head

Answer 19

Spinal cord——–T1-L2—–< Sympathetic trunk—— primary rami——–< effector organs

At the synapse to the sympathetic trunk, acetylcholine is used.

At the synapse to effector organs, noradrenaline is used.

Question 20

The sympathetic pathway to the abdomen

Answer 20

Spinal cord ——-T1- L2——-sympathetic trunk (does not synapse, just passes through)——splanchnic nerves—–< Prevertebral ganglia—–< abdomen

Acetylcholine is released at the synapse to the prevertebral ganglia
Noradrenaline is released at the synapse to abdominal cells.

Question 21

Sympathetic nervous pathway to the adrenal medullar

Answer 21

Spinal column————-< Adrenal medulla—- release of adrenaline and noradrenaline into the blood.

Acetylcholine is released at the synapse to the medulla.

Question 22

The parasympathetic pathway to the head, heart, lungs and abdomen.

Answer 22

Brainstem——–cranial nerves—–< Ganglia close to effector organ——-< effector organ

Acetylcholine is released at both synapses.

Question 23

The parasympathetic pathway to the pelvic organs

Answer 23

Sacral spinal cord——- Pelvic splanchnic nerves——< ——–< Pelvic organs

Acetylcholine is released at both synapses.

Question 24

Parasympathetic system

Answer 24

Section of the autonomic system that conserves and increases metabolic preserves.

Contains two nerve pathways-

1. To the head, heart, lungs and abdomen.
2. To the pelvic organs

Uses acetylcholine as a neurotransmitter.

Nerves arise from the cervical and sacral spinal cord regions.

There is no parasympathetic supply to the skin: including sweat glands, hair follicles and blood vessels.

Question 25

Parasympathetic cranial nerves

Answer 25

Cell bodies of the preganglionic neurones are located in the brain stem.

Ganglia is located close to effector organs.
Example of effect organs:
Pupil
Lacrimal glands
Parotid and submandibular glands.

Question 26

Effect of the parasympathetic system on the follow organs:

Cardiac muscle
Bronchi
Sweat glands
Hair follicles
Blood vessels in the skin
Pupil
Lacrimal glands
Parotid and submandibular glands.

Answer 26

Cardiac muscle- decreases cardiac output

Bronchi- bronchoconstriction.

Sweat glands- no effect

Hair follicles- no effect

Blood vessels in the skin- no effect

Pupil- constricts

Lacrimal gland- increased tear production

Parotid and submandibular gland- increased saliva production.

Question 27

Vagus nerve

Answer 27

Parasympathetic nerve that innervates:

• Heart: decreases cardiac output
• Lungs: bronchoconstriction
• Abdominal organs: peristalsis.

Its preganglionic axons synapse with postganglionic axons close/ on the viscera.

Question 28

Parasympathetic sacral nerves

Answer 28

Parasympathetic nerves originating from the sacral spinal cord.

Preganglionic axons exit through splanchnic nerves.

Preganglionic nerves synapse with postganglionic axons of the pelvic region.

Question 29

Effect of the sacral parasympathetic nerves on:

Bladder
Rectum
Sexual function

Answer 29

Bladder- Urination

Rectum- Defecation

Sexual function- stimulates sexual arousal.