HNS02 Peripheral Nervous System Flashcards
***Division of nervous system
CNS:
- Brain
- Spinal cord
PNS:
- Sensory division
—> Visceral sensory division (very complicated, different versions, referred pain)
—> Somatic sensory division
- Motor division
—> Visceral motor division: Sympathetic + Parasympathetic
—> Somatic motor division
PNS
Consists of nerve fibres and nerve ganglia outside the brain and spinal cord, and special nerve ending
Only Cranial nerve within CNS: Optic nerve
Nerve ganglia
Collection of cell bodies
Classification of PNS
Based on anatomical structures
- Cranial nerves + Cranial nerve ganglia (comes out from brain)
- Spinal nerves + Spinal nerve ganglia (comes out from spinal cord)
- Autonomic nerves + ganglia
Based on function
- Somatic nervous system (SoNS)
- Autonomic nervous system (ANS)
Based on direction
- Sensory (Afferent)
- Motor (Efferent)
Cranial nerves
- 12 pairs
- arise mainly from within the brain
- ALL belongs to PNS, except Optic nerve (CN2)
1: Olfactory
2: Optic
3: Oculomotor
4: Trochlear
5: Trigeminal
6: Abducent
7: Facial
8: Vestibulocochlear
9: Glossopharyngeal
10: Vagus
11: Accessory
12: Hypoglossal
Spinal nerves
- 31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal)
- Axons from neurons in spinal cord (Ventral root) + Dorsal root ganglia
—> Spinal nerves
—> Somatic Sensory + Somatic Motor + Autonomic Sensory + Autonomic Motor (4 types of signal) - 4 plexuses (branching network of intersecting nerves):
1. Cervical plexus (C1-C4)
2. Brachial plexus (C5-T1)
3. Lumbar plexus (T12/L1-L4)
4. Sacral plexus (L4-S4)
Cranial nerve sensory ganglia vs Spinal nerve sensory ganglia
Cranial nerve sensory ganglia:
- Trigeminal ganglion (CN5; for sensation of oral cavity + nasal cavity)
- Geniculate ganglion (CN7; sensation of face, taste)
- Spiral ganglion (CN8)
- Vestibular ganglion (CN8)
- Superior (jugular) ganglion of Glossopharyngeal (CN9)
- Inferior (petrosal) ganglion of Glossopharyngeal (CN9)
- Superior (rostral) ganglion of Vagus nerve (CN10)
- Inferior (nodose) ganglion of Vagus nerve (CN10)
Spinal nerve sensory ganglia:
1. Dorsal root ganglion (group of cell bodies of primary sensory neurons)
Somatic NS: Motor system vs Sensory system
Motor system:
- Cell bodies located in CNS (Brainstem / ***Ventral horn of spinal cord)
- One step system: Only 1 neuron
- Axons organised into nerve bundle + located in PNS
- Terminals / Nerve endings located in skeletal muscle to form NMJ
Sensory system:
- Cell bodies located in PNS (sensory ganglia)
- Axons (***pseudo-unipolar) divided into:
—> Central axons: projects into CNS and terminates within CNS
—> Peripheral axons: connects with peripheral organ and forms sensory endings (specialised dendrites)
Autonomic NS
- Sympathetic + Parasympathetic
- 2 neuron system: Presynaptic (Preganglionic) + Postsynaptic (Postganglionic) neuron
- Centre (presynaptic neurons) of SNS: located in Lateral horn of T1-L2/3 spinal cord (intermediolateral cell column)
- Centre of PNS: located in Brainstem + S2-S4 spinal cord
- Higher centre of ANS: located in Hypothalamus
- Special division: Enteric nervous system
Major functions of ANS
SNS: Eye: Pupillary dilation Sweat gland: Sweat secretion Heart: ↑ HR Bronchi: Dilation GI tract: Inhibition of movement Bladder: Relaxation Genitalia: Orgasm
PNS: Eye: Pupillary constriction Sweat gland: None Heart: ↓ HR Bronchi: Constriction GI tract: Enhance of movement Bladder: Contraction Genitalia: Sexual arousal
Arrangement of postganglionic neuron in Sympathetic NS
- Paravertebral ganglia
- contain postganglionic neuron
- located very close to vertebral column
- form chains on either side of vertebral column —> ***Sympathetic chain / trunk
—> 3 cervical ganglia
—> 12 thoracic ganglia
—> 4 lumbar ganglia
—> 4-5 sacral ganglia
—> 1 Ganglion impar - Prevertebral ganglia (Prevertebral plexuses)
- also contain postganglionic neuron
- anterior, further away to vertebral column
- in ***abdominal region
- major ones:
—> Celiac ganglia
—> Aorticorenal ganglion
—> Superior mesenteric ganglia
—> Inferior mesenteric ganglia
- minor ones: superior / inferior hypogastric plexuses
Paravertebral ganglia
- Interconnected with spinal nerves via communicating rami
- White communicating ramus (ONLY in T1-L2):
—> carries small **myelinated **presynaptic fibres from lateral horn
—> sympathetic trunk / chain - Gray communicating ramus (at every pairs of spinal nerves):
—> carries **unmyelinated **postsynaptic fibres from ganglion
—> back to spinal nerve (入sympathetic chain兜個圈出返黎)
—> supply body
- Whole flow: Presynaptic neuron (in lateral horn) —> spinal nerve —> synapse with Postsynaptic neuron in sympathetic trunk —> spinal nerve —> supply body
- Presynaptic neuron can go up above T1/L2, but can only do so within sympathetic chain
—> must enter respective level (T1-L2) first via White ramus
—> then travel up / down in sympathetic chain to synapse with other postsynaptic neuron
(∴ white rami只有 T1-L2有, gray ramus可以度度有, 甚至多過一, 一個sympathetic ganglia裡面有好多postsynaptic fibres出 e.g. cervical ganglia得3個, 但控制好多部位)
Presynaptic fibres route (within Paravertebral ganglia)
- Synapse with postsynaptic fibres at the same level (T1-L2)
- Travel up and down to synapse with upper / lower postsynaptic fibres at different levels of paravertebral ganglia
- Pass through paravertebral ganglia without synapsing —> via splanchnic nerves —> reach prevertebral ganglion
- i.e. Splanchnic nerve route
- arise from T5 and below
- T5 or above: cardiac, pulmonary, carotid plexuses: ***Postsynaptic fibres
Postsynaptic fibres route (within Paravertebral ganglia)
- Spinal nerve route (i.e. Gray ramus)
- Sympathetic nerve route (i.e. Splanchnic nerves in cardiac and pulmonary plexuses / carotid plexuses: NOT presynaptic fibres ∵一早已經係sympathetic chain synapsed左 —> 變左做postsynaptic fibres)
Splanchnic nerves (Presynaptic fibres)
- Greater splanchnic nerves
- sympathetic
- T5-T9
- to Celiac plexus - Lesser splanchnic nerves
- sympathetic
- T10-T11
- to Abdominal aortic plexus / renal plexus (include superior mesenteric ganglion) - Least splanchnic nerves
- sympathetic
- T11-T12
- to Abdominal aortic plexus / renal plexus - Lumbar splanchnic nerves
- sympathetic
- L1-L2
- to Abdominal aortic plexus / hypogastric plexus - Sacral splanchnic nerves
- sympathetic
- mostly presynaptic (sacral part of sympathetic trunk to inferior hypogastric plexus) - Pelvic splanchnic nerves
- ***parasympathetic
- S2-S4
- to Terminal ganglia (very close to organs)
Note:
- ALL splanchnic nerves are presynaptic except for cardiopulmonary nerves (from Stellate ganglia) and minor parts of sacral splanchnic nerves (一早係sympathetic chain裡面synapse左)
Adrenal medulla
Chromaffin cells act as postsynaptic neurones
—> receive presynaptic sympathetic fibres from Celiac / Renal plexus
—> very long presynaptic fibres, very short postsynaptic fibres
Arrangement of Parasympathetic NS: Parasympathetic ganglia
- Parasympathetic ganglia of head and neck
- Ciliary ganglion
- Pterygopalatine ganglion
- Submandibular ganglion
- Otic ganglion - Terminal ganglia
Arrangement of Parasympathetic NS: Nerves carry parasympathetic fibres
Nerves carry parasympathetic fibres (presynaptic fibres):
- CN 3 (Oculomotor)
- CN 7 (Facial)
- CN 9 (Glossopharyngeal)
- CN 10 (Vagus)
- Pelvic splanchnic nerves
Rmb: Cranial nerve只係講緊anatomical location, 唔係function
Enteric nervous system
Digestive tract’s own nervous system
2 plexuses:
- Myenteric (Auerbach’s) plexus
- Submucosal (Meissner’s) plexus
- embedded in lining of GI tract
- does not arise from brainstem / spinal cord
- regulates **motility + **secretion of GI tract
- coordinates local reflexes
- self-contained (even without spinal cord can still self-regulate)
- communicates with sympathetic / parasympathetic
- capable of operating independently of brain and spinal cord
- contains own efferent, afferenyt neurones and interneurons
- can form local reflex arc independently of CNS (does not need to pass through spinal cord)
Structure of nerve fibres
Axon and myelin sheath (surrounded by endoneurium)
—> Nerve fascicle (surrounded by perineurium)
—> Nerve trunk (surrounded by epineurium)
Unmyelinated neurons:
- groups of axons fit into a groove/grooves of Schwann cells (axons嵌入Schwann cell)
- no nodes of Ranvier
- series of Schwann cells cover entire length of axons
Glial cells in PNS
- Perineuronal satellite cells:
- do not form myelin sheath
- within ganglia surrounding cell body controlling microenvironment
- electrical insulation
- pathway for metabolic exchanges - Schwann cells: myelin sheath in PNS
Nerve endings
- NMJ
- Spinal motor neuron axon endings on muscle fibres
- Axon terminals contain vesicles of ACh
- Synaptic cleft located between axon terminal and muscle cell membrane - Sensory nerve endings
- in skin, muscles, tendons, internal organs etc.
- responsible for afferent sensory inputs related to touch, pain, temperature, pressure, special senses etc.
Disorder and injury of PNS
- Peripheral nerves capable of regeneration under certain circumstances (e.g. Schwann cell wrapped around weakened/narrowed axon)
- Peripheral Neuropathy: functional disturbances and pathological changes in PNS, damage to neurons and their myelin sheath
- Neuritis: inflammation of PNS
- Injury: injury to axons / cell bodies of axons
e. g. IM injection: deltoid avoid radial nerve, buttock avoid sciatic nerve
Seddon’s Classification of Peripheral nerve injuries
- Neurapraxia: injury without any anatomical discontinuity but resulting in functional disruption (nerve concussion)
- Axonotmesis: microscopic division of nerve fibres (axons) without obvious discontinuity of the nerve sheath (epineurium / 出面still intact)
- Neurotmesis: complete anatomic division of the nerve fibres with obvious discontinuity of the nerve sheath
