Peripheral nervous system
Nervous system
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Central Nervous System
• brain
• spinal cord
Peripheral Nervous System
• peripheral nerves
• cranial nerves
• spinal nerves
Division of PNS
Sensory Division
• picks up sensory information and delivers it to the
CNS
Motor Division
• carries information to muscles and glands
Divisions of the Motor Division
• Somatic – carries information to skeletal muscle
and skin
• Autonomic – carries information to smooth muscle,
cardiac muscle, and glands
Spinal Cord
• Surface structure
– A. Meanings:
• 1. Pia mater
• 2. Arachnoid
• 3. Dura mater
– B. Spaces:
• 1. Subarachnoid space - CSF fluid-filled, between
arachnoid & pia mater
– below end of spinal cord = lumbar cistern
• 2. Epidural space - outside dura, between it and
bone of spinal canal
– - contains adipose tissue surrounding a venous plexus
Grooves
Posterior Median Sulcus & Anterior Median
Fissure
– Dorsal & Ventral median sulci
– midline grooves on their respective surfaces.
– a. anterior median fissure = largest of external grooves
(a good orientation landmark)
• contains anterior spinal artery, within pia mater tissue
– b. Posterior / Dorsal median sulcus - more shallow
• Dorsal Septum = tissue extends from floor of sulcus deeper
into cord
• 2. Posterolateral Septum & Anterolateral
Fissure (dorsolateral & ventrolateral sulci)
– where the dorsal and ventral roots respectively
enter and exit the spinal cord.
• 3. Posterior Intermediate Septum - only
found in the cervical and thoracic cords
– marks the separation of fibers carrying sensory
information from the lower extremity more
medial bundle = fasciculus gracilis
– and fibers carrying sensory information from
the upper extremity more lateral bundle =
fasciculus cuneatus
Spinal Cord & Vertebral Segments
• Spinal Cord has 31 pairs of spinal nerves
exiting it:
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8 cervical
12 thoracic
5 lumbar 5 sacral
1 coccygeal
Spinal column
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Vertebral column has 26 bones:
7 cervical (1=atlas; 2=axis)
12 thoracic
5 lumbar
1 sacral (fused)
1 coccyx (fused)
Spinal column & cord
• Due to embryological growth pattern from ~
3rd month on, spinal cord ends up shorter
than the spinal canal,
– a. cord segments don't match number of
vertebral bodies at same level
– b. cervical spinal nerves exit above the
corresponding vertebral body (C8 above T1)
– c. caudal to C8, spinal nerves exit below the
corresponding vertebral body
Cord landmarks
• 1. Conus Medullaris
– By adulthood, as spinal column grows faster than cord
– Spinal cord ends at level of lower border of L1 or at disk
between L1 & L2 vertebral bodies
• 2. Cauda Equina
– (horse’s tail) - caudal to the conus medullaris
• a. contains lumbosacral nerve roots - to the lower extremities
• b. lumbar puncture or myelogram is given below level of L1 vertebra
to avoid damage to the spinal cord.
• 3. Filum Terminale
– pia mater & neuroglia; - represents vestige of embryonic tail
• a. tapered thin filament - from end of conus medullaris, runs through
cauda equina
• b. attached to dorsal surface of coccyx by coccygeal ligament
(surrounding dural layer)
Cord landmarks
• 4. Cervical & Lumbosacral Enlargements
– accommodate the innervation of the upper and lower
extremities
– a. C4-T1: includes spinal nerves that make up brachial
plexuses
– b. L2-S3: lumbar & sacral plexuses
• 5. Lumbar cistern
– The subarachnoid space caudal to the end of the spinal
cord, common site for lumbar puncture (lumbar tap)
Ventral & Dorsal Roots
• 1. Dorsal roots break up into rootlets to enter cord
all along dorsal surface at each level
• 2. Ventral roots form by convergence of rootlets
exiting from the ventral surface
• 3. Dorsal Root Ganglion - found on the dorsal root
just before it joins the ventral root
– sensory nerve cell bodies (unipolar / pseudounipolar)
Spinal Nerve
• formed by junction of dorsal & ventral roots, both
sensory & motor
• 1. Dorsal ramus: supplies innervation to skin,
fascia, ligaments & deep muscles of back
• 2. Ventral ramus: supplies ventral & lateral trunk
as well as the limbs
– also forms the plexuses to the extremities
• 3. Rami Communicans: ventral branches of
spinal nerve join to form sympathetic trunk
– next to the vertebral body.
Dermatome
• an area of skin that the sensory nerve fibers of a
particular spinal nerve innervate
Sensory receptors
• three groups
– exteroceptive senses – senses associated with
body surface; touch, pressure, temperature,
pain
– proprioceptive senses – senses associated
with changes in muscles and tendons
– visceroceptive senses – senses associated
with changes in viscera
Autonomic Nervous System
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functions without conscious effort
controls visceral activities
regulates smooth muscle, cardiac muscle, and glands
efferent fibers typically lead to ganglia outside CNS
Two Divisions
• sympathetic – prepares body for fight or flight
situations
• parasympathetic – prepares body for resting and
digesting activities
Sympathetic Division
• Origin from the intermediolateral cell
column of thoracic and lumbar (L1 - L2 or
L1 - L3) segments.
• Some preganglionic fibers terminate in
paravertebral ganglia.
Parasympathetic Division
• Parasympathetic components derived from
the brain and sacral segments of spinal cord.
• Cranial source
– Cranial nerve III (oculomotor nerve). Edinger-Westphal
nucleus and ciliary ganglion
– Facial nerve (VII): superior salivatory nucleus and
submandibular ganglion
– VII: Lacrimal nucleus and pterygopalatine ganglion
– Glossopharyngeal nerve (IX): inferior salivatory
nucleus and otic ganglion
– Vagus nerve: Dorsal nucleus and ganglia in pulmonary
plexus, plexuses in gastrointestinal tract
• Sacral segment (S2 – S4)
– Sacral autonomic nucleus
Neurotransmitters
Cholinergic Fibers
• release acetylcholine
• preganglionic sympathetic fibers
• preganglionic parasympathetic fibers
• postganglionic parasympathetic fibers
Adrenergic Fibers
• release norepinephrine
• postganglionic sympathetic fibers
• Exceptions:
• Sympathetic innervation of sweat gland is cholinergic
Receptors
• Alpha
– blood vessels of skin and internal organs, smooth muscle on pupil
and internal sphincters
– Constriction while alpha is stimulated
• Beta
– cardiac muscles, bronchus, blood vessels of skeletal muscles
– Dilation while beta is stimulated
• Muscarinic
– end of all postganglionic parasympathetic nerve fibers
– Slow, excitatory action
• Nicotinic
– between preganglionic and postganglionic neurons
– Rapid, excitatory action
Blood Supply of the spinal cord
• 1. two Posterior Arteries - together supply
the dorsal horns and dorsal columns
• 2. one Anterior Spinal Artery - supplies all
other areas of the spinal cord
– Both anterior and posterior spinal arteries
branch off vertebral artery
• 3. segmental spinal arteries (small) –
branches from cervical vertebral artery,
thoracic intercostals, and abdominal aorta