Lecture 3: Peripheral nervous system Flashcards
what is a nervous system
A biological systems that can =
Receive and process info = stimul from environment = ext anf internal
Coordinate and carry out an apprioate action to respond to those stimuli
What is vertebrate nervous system divided into
Cns and pns
What is apart of structural division of nervous system
Cns =brain and spinal cord
And pns = cranial, spinal and peripheral nerves
What is apart of functional division of nervous system
Brain and spinal cord functions
Motor eff and sensory aff
What does cns divide into
Brain = recipes and processes sensory info, initiates motor responses
Spinal cord = carries signals to anf from brain, controls reflexive responses
What does pns divide into
Motor eff= carries and executes signals from cns to muscles and glands
sensory aff = Carries signals (somatic and visceral) from tissues and organs to cns
What is motor efferent divided into
Somatic = innervates skeletal muscles, voluntary
Autonomic = innervates smooth and cardiac muscle, glands, involuntary
What is focus of ANAT 314 nervous system
Pns
Spinal cord
Sensory aff
Somatic
Describe pathway of functional division fo vertebrate nervous system
Pns inbound stimuli —> cns processing corridnation —> pns outbound action
Describe sensory/aff
Visceral sensory (hr, nauseam hungry) gva = usually internal, tells us about internal homeostasis of body,also joint position in space
Somatic sensory (poke, pressure,hot/cold, pain, skin, bursae, light stimuli)
Describe motor/eff
Visceral motor = Gland secretion, vasodilation
Somatic motor = muscle contraction, possibly motion
Describe neurons
Cell of nervous system
Basic cellular units, messengers
Communicate through chain like connections
Info travels unidrectionally as electrical impulses along neurons
Describe generic multipolar neuron = all parts of it
Dendrite = receives info generally short
Cell = processes info
Axon = relays info in form of electricity can be v long, myelin sheath = insulation, increases speed of electrical impulses
Synapses = pass info onto other nerves or effector organ chemically, axons branch, connects with other neuron dendrites
What is multipolar neuron
Motor/eff
Target organ = effector like muscle
What is unipolar neuron
Pseudo uni polar = sensory aff
Sensory receptors in skin/snyovium or muscle = receives info like dendrites
Cell body between axon - branched axon, no dendrites
And then relays info to cns via axon
Describe which type of neuron where and why
In bound stimuli = pseudounipolary sensory neuron
Synapse on neurons in spinal cord = inter neurons, brain, etc
Then outbound action = motor neuron multipolar
Many of these make up spinal nerves
What is spinal nerve
Bundle of sensory and motor neurons
Their axons ONLY = emerge from spinal cord at regular intervals to modulate sensory and motor info from/to body’s periphery
Describe hierarchy neurons
Mixed neuron. Bundles = aff and eff
—> nerve fibers (bundled together, like myofibrils) —> wrap anf bundle = by ct sheaths = make typical named nerve
What else is in neuron
Blood vessels = vascular supply
And fat = insulation
What is spinal nerve - info it carries
Mixed = sensory and motor neurons
But flow of info = unidirectional= from sensory to cns to Motor or cns to motor (if not response to sensory info)
Carried by same nerve fiber, both ways
What is spinal nerve - direction/pathway
Skin receptor —> aff Neuron —> snyapse on interneuron in cns —> synapse on eff neuron —> muscle
Multipolar
Always going in both directions along nerve fiber but carried by individual nerves = in a particular direction
What are spinal and named nerves
Bundles of axons motor and sensory axons
Cell bodies = in specific places
Describe posterior dorsal root ganglion
Outside spinal cord
Group of cell bodies for the sensory neurons = aff cell bodies, right by vertebral column
Contains sensory neuron cell bodies for that spinal nerve
Pseudounipolar
Describe anterior ventral horn
Inside spinal cord
Group fo cell bodies for motor neurons
Eff = generic multipolar
Motor neuron cell bodies for that spinal nerve
Name parts of spinal nerve
Rootlets
Roots
Rami
Define rootlets
Axon bundles from sensory neurons - post and Motor neurons-ant
Emergence of fibers
Converge into roots
Define roots
Convergence of rootlets
Posterior root ganglion = cell bodies of sensory nerurons
Define spinal nerve
Convergence of roots
Emerges from vertebral Collumn = now mixed nerve
Define rami
First split of spinal nerve into 2 rami
Name and describe the 2 rami
Posterior ramus= angles straight back,sensory and motor to intrinsic back muscles and associated skin
Anterior ramus= sensory and motor to everything else, BIGGER
What is spinal cord
PART OF cns from which spinal nerves emerg at regular intervals from superior (closest to brain) to inferior (closest to coccyx)
How are spinal nerve pairs named - all
Relation to vertebrae, bilateral symmetric
Thoracic = 12, lumbar = 5, sacral =5, coccygeal = 1 = ALL NAMED AFTER SUPERIOR VERTEBRA
Cervical nerves = 8, named after inferior vertebra, exception = c8, spinal nerve but no vertebra
Describe spinal cord enlargements
Cervical and lumbar = correspond with plexuses involved in providing innervation to the limbs = more neurons required
Where is cervical enlargement
Brachial plexus = c5-t1
Where is lumbar enlargement
Lumbosacral plexus = l1-s4
What is conus medullaris
Spinal cord ends at l2 = tapers to point
End of cord
What is Cauda equina
Horse tail, axons of inferior spinal nerves
Continuation of spinal nerves = axons
Why does cauda equina develop
Unequal growth of spinal cord (shorter) and vertebral column (longer)
= axons dragged ifneriorly during their growth to exit below their respective vertebrae
Why does cauda equina develop = follow through years
3 months = vert column and spinal cord grow at same rate
As newborn = drags axons down, difference, vert column outpaces spinal cord growth
Biggest length cauda equina = as adult
What are meninges of spinal cord
3 membranes envelop and support anf protect brain and spinal cord
Name 3 meninges
Dura mater
Arachnoid mater
Pia mater
Describe dura mater
Tough mother
Outer fibrous layer
Most protective
Describe arachnoid mater
Spidery mother
Middle layer
Cushioning
Underside dura mater, adhered
Describe pia mater
Tender mother
Adhered to cord/brain, suspend them to dura/arachnoid via denicualte ligaments
What are denticulate ligaments
Suspends pia to other layers
What else can we see on spinal cord
More rootlets = cervical enlargement of brachial plexus, thicker, more fibers travel to periphery
Name the 3 spaces between meninges
Extradural/epidural space
Subdural space
Subarachnoid space
Describe extradural space
With fat
Injections can be made here for pain control
Upon dura mater
Between bones of vert column and dura mater
Venous plexus
Describe subarachnoid space
Under arachnoid mater
Cerebrospinal fluid circulates in space
Describe sampling csf
Filum terminals = continuation of pia mater
conus medullaris = anywhere past here = more subarachnoid space = lumbar puncture = spinal tap possible here
Describe epidural injections
Injections into epidural spavce = block sensation and/or reduce inflammation of nerves during labour, surgeries or to treat chronic pain
Steroids/anesthetics injected
Between vert column and lig and dura mater= numbs dorsal root ganglions nearby
How many pairs of spinal nerves
31 pairs
Describe how spinal nerves become named nerves
Spinal nerves emerge from cord, coalesce, cross over and branch again to form named peripheral nerves =
Innervates multiple structures, especially in limbs
Multiple spinal levels = multiple structures
Ex= sciatic = comes from l4-s3, spinal nerve roots in spinal cord, 5 spinal nerves all contribute
What does each spinal nerve have
Each will have discrete area of sensory innervation, also contribute to innervation of specific set of muscles
Bc of segmental organization fo spinal nerves
What are dermatomes
Discrete area of skin innervates by a single spinal nerve
What are myotomes
Group fo muscles innervates by a single spinal nerve
Ex = lower limb myotomes = l3 primarily knee extensors and hip flexors, l5 = primarily hip extensors and knee flexors
Clinically useful= test for dysfunction in specific areas, lose sensation and weakness of certain motions
