-
Gray Matter
- primarily cell bodies
- - sensory & motor
- control of body
Ganglia (PNS)
Nuclei (CNS
-
White Matter
- primarily myelinated axons
- - transmission of information
Nerves (PNS)
Tracts (CNS)
Columns (CNS)
-
Organization of the
Nervous System
- CNS: Brain and Spinal Cord (SC)
- PNS: neural tissue outside of the CNS
- -delivers sensory info to the CNS
- -delivers motor commands to periphery
-
What connect CNS to
PNS
- 12 pairs of cranial nerves= extend off the brain
- 31 pairs of spinal nerves = extend off the sc
-
Spinal Cord: Vertebrae
- •Cervical Region
- –7 vertebrae; 8 spinal nerves
- •Thoracic Region (Most job to do)
- –12 vertebrae; 12 spinal nerves
- •Lumbar Region
- –5 vertebrae; 5 spinal nerves
- •Sacral Region
- –5 fused vertebrae; 5 spinal nerves
- •Coccyx Region
- –4 fused vertebrae; 1 spinal nerve
-
The spinal cord is protected
by:
- 1.Adipose Tissue & blood
- vessels: in epidural space
- 2.Cerebral spinal fluid: contained in
- subarachnoid space, ventricles of brain and central canal of SC
- 3.Vertebrae
- 4.Meninges
-
Vertebrae:
- “enclose” SC
- •Spinal nerves ‘exit’ via intervertebral foramen
-
Vertebrae (cont.)
- •Spinal column (bone) outgrows spinal cord (CNS tissue) at ~4 yrs. Old Why?
- •Children up to 4 y. o. neurons still grow
- •Adult SC ends ~ L1 (conus medullaris)
- •Cauda equina begins
- Dorsal & ventral roots of L2–S5 spinal nerves extend inferiorly in spinal column
- & look like horse’s tail
-
Meninges
- 4.Collagen & elastin coverings of SC (and brain):
- -protects from canal -provides stability and shock absorption
- 3. Membranes (layers) of Meninges:
- A: Dura Mater
- B: Arachnoid Mater
- C: Pia Mater
-
Dura Mater
- A.“tough mother”; outermost.
- Attached to periosteum of cranium and
- spinal column
- Tethers spinal cord at the top &
- bottom of spinal canal:
- Top: dura “blends with” foramen magnum periosteum & becomes
- continuous with cranial dura
- Bottom: dura “blends with” coccygeal ligament, which eventually blends with periosteum of coccyx
- ie) Filum terminale externus: “terminal
- thread”; extensions of dura (and pia) at the base of SC
- (L1) that extend into sacrum & eventually form the coccygeal ligament (which
- blends with coccyx periosteum
-
Arachnoid Mater
- “spidery mother”;middle
- -trabeculae extend to underlying
- pia
-
Pia Mater
- C.“delicate mother”; innermost
- -communicates with above arachnoid mater
- -firmly interwoven with underlying neural
- tissue
- -vascularize
- -laterally extend from SC to provide lateral
- stability
- -denticulate ligaments
- -vertically extends to coccyx to provide
- vertical stability
- -filum terminale internus
-
epidural space
- between vertebrae & underlying dura
- -contains blood vessels and adipose tissue (good for anesthesia)
-
subdural ‘space’:
between dura & underlying arachnoid
-
subarachnoid space
- between arachnoid and pia mater
- -contains blood vessels & CSF
-
Lumbar Puncture
- Lumbar puncture/spinal
- tap: CSF removed from subarachnoid space
- detect infections, inflammation, cancer
-
Spinal Meningitis
- •Inflammation of meninges due to bacterial or viral infection
- •Bacterial: usually more severe and contagious
- –H. influenzae type B, N. meningitidis, Strep. pneumoniae
- •Viral: more frequent,
- usually milder, usually not fatal
- •Infants, children, those in close
- contact
- •Sx:
- –Fever (105), nuchal rigidity (stiff
- neck), photophobia, headache, vomiting
- –Can lead to deafness, convulsions,
- retardation, death
- •Tx:
- –Confirm with LP. Head CT to determine
- if cranial meninges involved
- –Antibiotics such as Rifampin, steroids, i.v. fluids
- –Preventative Vaccines: HiB for children, Meningococcal for college, Pneumococcal for
- elderly
-
Spinal Anesthetic:
- ‘local’ blockage of sensory & motor nerves
- -injection into subarachnoid space/CSF @ L3-L4
- \more diffuse anesthesia
- -analgesic effects are immediate
-
Epidural Anesthetic
- local blockage of sensory (+~motor) nerves
- -indwelling catheter
- into epidural space (usually lower lumbar but can be higher)
-
Gray Matter: nuclei/cell bodies, unmyelinated axons
Spinal Horns: “Tips” of each line
in “H” shaped gray matter in SC
- A: Dorsal (posterior) horns: process sensory
- information
- B: Ventral (anterior) horns: process motor
- information
- C: Lateral (side) horns: process motor
- information
-
Dorsal horn:
- Visceral: sensory input from organs
- -Somatic: sensory input from
- skin, skel. muscles, joints
-
Ventral horn:
Somatic: motor output to skeletal muscles
-
Lateral horn:
- -Visceral: motor output to organs (glands, smooth
- muscle)
- -only located in thoracic & lumbar regions of spinal cord
-
Dorsal
Horn
- ‘posterior’ gray matter of SC (spinal cord)
- -Somatic (skeletal muscle) and visceral (organs) nuclei here receive sensory information from peripheral receptors (in skeletal muscles,
- organs).
- -Afferent fibers carry
- such sensory information from periphery to CNS
- -Axons from dorsal
- roots synapse here
-
Ventral horn
- ‘anterior’ gray matter of SC
- -Somatic motor nuclei
- here send motor information to peripheral receptors (in skeletal muscles)
- -Efferent fibers
- carry such motor information from CNS to periphery
- -Motor
- nuclei are located here
-
Dorsal Root
- Axons from dorsal
- root ganglia (nuclei in PNS)
- -transmits sensory information (a.k.a. afferent
- fibers) from periphery to dorsal horn nuclei in SC
-
Dorsal Root Ganglia:
- cell bodies of sensory neurons
- -receptor is in periphery
- -axon is the ‘dorsal root’
- -synapse on nuclei in dorsal horn of SC
-
Ventral Root:
- Axons from ventral (& lateral) horn nuclei in SC
- -axons of somatic & visceral motor neurons
- -relay motor information to periphery (a.k.a. efferent
- fibers)
- -muscle movement, glandular secretions, etc.
-
Ventral Root Ganglia
non existent, nuclei of motor fibers are in ventral horn of SC
-
Gray Matter Study Tid Bits
- SAME:
- Sensory-Afferent, Motor-Efferent
- DAVE:
- Dorsal-Afferent, Ventral-Efferent
- Cell body of sensory
- neurons is located in dorsal root ganglia
- Cell body of motor
- neurons is located in ventral horn
- • Location nuclei
- within gray matter determine which body part it controls
- Neurons in ventral
- horn of lumbar region control legs & ‘below”
- -Neurons in dorsal
- horn of cervical region are sensory for neck and arms
-
Spinal Nerves:
- joining of ventral & dorsal roots
- - sensory + motor axons bundled
- together
- -classified
- as mixed nerves since they transmit
- sensory AND motor info.
- 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
-
Muscle innervations= myotomes
Spinal Nerve
Mapping: Dermatomes
- •Specific bilateral region of the skin monitored by a single pair of spinal nerves
- –Overlapping
- –Sensory + motor
- •Clinical diagnostic tool
- –Determine damage to spinal nerve
- –Location of regional anesthetic
-
Herpes Zoster (Shingles)
- •Acute, localized infection of Varicella-zoster virus
- –Same virus that causes chickenpox
- –Painful, blistering rash on skin
- –Contagious? Yes chickenpox, not shingles
- Etiology:
- Chickenpox virus from
- childhood lies latent for years in DRG
- Reactivated??? virus
- travels from ganglia to skin of corresponding dermatome resulting an eruption
- of vesicles
- Tx:: Usually disappears on its own
- Anti-viral drugs (Acyclovir)
- NSAIDs for pain
- Preventative Varicella vaccine
-
White Matter
- outer section of SC; myelinated axons
- 3 columns on each side of SC
- -a column is a groups of tracts
- -combination of sensory and motor tracts
- -anterior
- -lateral
- -posterior
-
Tract
bundle of similar myelinated axons
-sensory or motor
-
Ascending tracts
carry sensory info. to brain
-
Descending tracts:
carry motor commands to SC
-
Nerve Plexuses
- Plexus:
- Network of nerves that innervate specific areas
- Details: during development, smaller muscles ‘blend’
- together ® larger, complex
- muscles. The nerves (sensory and motor)
- of these muscles ‘blend’ too ® series of compound
- nerve trunks
- •Cervical plexus: Neck, diaphragm
- •Brachial plexus: Chest, arms
- •Lumbar plexus: Lower torso, legs
- •Celiac (solar) plexus:Stomach/diaphragm
-
Neuronal
Organization: Overview
- •Sensory Neurons: info. to CNS
- –~10 million
- –Skin and viscera
- –Conscious / unconscious
- •Interneurons: relays
- –~20 billion
- –Coordinate incoming and outgoing
- signals
- •Motor Neurons: info. from CNS
- –~0.5 million
- –Effectors such as muscle (and glands)
- •Somatic: skeletal
- •Autonomic: cardiac & smooth
- Voluntary
- and involuntary
-
Interneurons (a.k.a. Association
Neurons)
- •Neuronal Pools
- –Interneurons organized into pools
- •Functional groups of interconnected
- neurons
- •Excitatory & inhibitory
- •Local or diffuse CNS locations
- –Arranged as “neural circuits”
- •Interneurons interactions
-
•Types of Neural Circuits
- 1.Serial Processing (pain)
- 2.Reverberation (+feedback,
- breathing, maintaining consciousness)
- 3.Convergence( breathing,)
- 4.Divergence
- 5.Parallel Processing
-
Serial Processing
- 1)Stepwise progression to next neuron ie: Pain sensation;
- pain en route to consciousness
-
Reverberation
- Collateral axon branches feed back to starting point
- -Positive feedback and \ self perpetuating
- -Continues until
- inhibitory stimuli or fatigue ie: Breathing &
- maintaining consciousness
-
Convergence:
- Several neurons synapse on one postsynaptic neuron.
- -Neurons may be from different neuronal pools and have different functions
- -inhibitory & stimulatory; conscious &
- subconscious ie: Breathing (diaphragm is subconscious but can be conscious)
-
Divergence:
- From one neuron to several or from one neuron pool to several pools.
- Permits broad distribution ie: Visual stimuli distributed to
- consciousness and brain regions that control posture and balance
-
Parallel Processing:
- Multiple neurons or neuronal pools processing same information simultaneously
- -Divergence occurs first
- Complex behavior or reflexes ie: Withdrawal reflex
- Withdraw limb, shift weight, feel pain,
- curse
-
Reflexes
- Rapid, automatic
- motor responses to specific stimuli.
- -involuntary
- -little variability
- -can be modified over time & under certain
- circumstances
- -may have more than one synapse
- -simple neural processing that demonstrates relationship between sensory and motor fibers
- -serves as foundation for more complicated
- responses
-
Cranial reflexes:
- via cranial nerves. Most processing occurs in brain
- stem & may include transmitting impulse to higher centers in brain.
-
Spinal reflexes:
- via spinal nerves. Most processing occurs in the spinal cord but may include transmitting impulse to
- higher centers in the brain.
-
Reflex Arc Overview
- Neuronal circuit that directs a specific motor response.
- -usually reaction opposes
- initial stimuli; arc is negative feedback
-
Monosynaptic Reflex
Receptors= muscle spindles
- Only one synapse
- ie) patellar/stretch reflex
- -Automatic, fast
- regulation of muscle length
- -no input from brain
- -sensory afferent directly synapses with motor neuron in
- SC
- -no interneuron involved
- -motor neuron does processing
- -monosynaptic; fast
-
Polysynaptic Reflex:
Overview
- -Sensory neuron
- synapses on interneuron(s) in SC before motor neuron is stimulated.
- -sensory ®interneuron(s) ®motor neuron
- More complicated response:
-
Polysynaptic
Reflex: Withdrawal Reflex
- Quickly move away from stimulus
- (especially pain)
- -Pain receptor
- stimulated
- - stronger stimuli ® more dramatic reaction
- - Sensory neuron
- synapses on interneuron in SC
- Interneuron:
- 1) stimulates flexor muscle (biceps) 2) inhibits extensor
- muscle (triceps) 3) relays message up SC & to brain
- Reciprocal Inhibition: If biceps AND triceps were both stimulated,
- no movement would occur (flexors & extensors are opposing). Interneurons coordinate the stimulation of biceps AND relaxation of
- triceps. (Reciprocal meaning vice versa)
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