Peripheral nervous system- PNS Flashcards
Main components of the PNS
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.
Somatic motor neurones
Contains cell body in the spinal cord or the brainstem and sends information to the skeletal muscles.
Cell body—-Efferent fibres—-> Skeletal muscles.
Somatosensory neurones
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
Spinal nerves
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
Peripheral nerves
Nerves that arise from cranial or spinal nerves.
Gives supply from the CNS to the rest of the body.
Nerves roots
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.
Primary rami
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.
Dorsal (posterior) rami
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.
Facet joint between vertebrae is called…
Zygapophyseal joint
Ventral (posterior) rami
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)
Nerve plexus
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
Dermatome
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
Embryonic development of myotomes and dermatomes
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.
Myotomes
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.
Referred pain
Involved in dermatomes.
Cutaneous pain in specific dermatomes can indicate damage to visceral organs.
Examples:
Pain in C3-C5 (shoulder region) indicates diaphragm irritation.
Autonomic nervous system
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)
General nerve pathway of the autonomic nervous system
Disynaptic pathway:
CNS—-preganglionic nerve—< Autonomic ganglia——-postganglionic nerve——–< effector organ
BUT adrenal medulla is monosynaptic:
CNS——-preganglionic neurone—–< Adrenal medulla.
Sympathetic trunk
Composed of interconnected paravertebral ganglia.
All preganglionic sympathetic axons enter through the sympathetic trunk in the nerve pathway.
The sympathetic pathway to the musculoskeletal system, the heart, lungs and the head
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.
The sympathetic pathway to the abdomen
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.
Sympathetic nervous pathway to the adrenal medullar
Spinal column————-< Adrenal medulla—- release of adrenaline and noradrenaline into the blood.
Acetylcholine is released at the synapse to the medulla.
The parasympathetic pathway to the head, heart, lungs and abdomen.
Brainstem——–cranial nerves—–< Ganglia close to effector organ——-< effector organ
Acetylcholine is released at both synapses.
The parasympathetic pathway to the pelvic organs
Sacral spinal cord——- Pelvic splanchnic nerves——< ——–< Pelvic organs
Acetylcholine is released at both synapses.
Parasympathetic system
Section of the autonomic system that conserves and increases metabolic preserves.
Contains two nerve pathways-
- To the head, heart, lungs and abdomen.
- 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.
Parasympathetic cranial nerves
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.
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.
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.
Vagus nerve
Parasympathetic nerve that innervates:
- Heart: decreases cardiac output
- Lungs: bronchoconstriction
- Abdominal organs: peristalsis.
Its preganglionic axons synapse with postganglionic axons close/ on the viscera.
Parasympathetic sacral nerves
Parasympathetic nerves originating from the sacral spinal cord.
Preganglionic axons exit through splanchnic nerves.
Preganglionic nerves synapse with postganglionic axons of the pelvic region.
Effect of the sacral parasympathetic nerves on:
Bladder
Rectum
Sexual function
Bladder- Urination
Rectum- Defecation
Sexual function- stimulates sexual arousal.
