2.2 Central and Peripheral Nervous system Flashcards
Glial cell
Non-neuronal support cell in the CNS
Oligodendrocytes
Subtype of glial cell, produces myelin throughout the CNS,wrap multiple axons
Microglia
Rove body looking for things to engulf, digest
Astrocyte
Glue that holds everything together, provide metabolic and structural support… Protects neurons by regulating what passes between capillaries and neurons
Ependymal cells
Secrete cerebrospinal fluid that is in hollow spaces of brain
What makes up the blood brain barrier?
Astrocyte foot processes and endothelial cells that line blood vessels in brain
How do lipid soluble substances get across the BBB?
Still by diffusion
O2, CO2, nicotine, alcohol, steroids
How do small polar substances move through the BBB?
Transport proteins
amino acids, glucose, etc
What kind of metabolic rate does the brain have?
Extremely high!
What percent of cardiac output does the brain receive?
15-20% even though the brain only makes up 2% of body weight
Why is the brain so dependent upon constant supply of oxygen and glucose and removal of carbon dioxide?
Resting membrane potential!
How soon does fainting occur if blood flow or blood glucose drops?
Within seconds
How soon does irreversible brain damage occur if blood flow or blood glucose drops?
Within 4 minutes, takes so long because we have a reserve of oxygen in RBCs to draw from
Meninges
Connective tissue membranes surrounding the CNS
Dura mater
Outer tough layer
Arachnoid mater
Middle, spidery weblike tissue
Pia mater
Thin, bound tightly to brain surface
Subdural space
Between dura and arachnoid, contains interstitial serous fluid, helps cushion
Subarachnoid space
Between arachnoid and pia mater, contains CSF (most spacious)
Meningitis
Inflammation of connective tissue layers
Cerebrospinal fluid in comparison to blood plasma
Fewer ions and less protein
CSF
~150mL in brain / spine
Bathes brain and spinal cord (in subarachnoid space)
Functions of CSF
Buoyancy, protection, stabilizes nutrient delivery
Where is CSF secreted?
By ependymal cells in choroid plexuses located in ventricles (fluid filled cavities containing CSF)
Anatomical segments of spinal cord
Cervical, thoracic, lumbar, sacral
How many bilateral pairs of spinal nerves extending bilaterally to Peripheral nervous system are there?
31
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
What are the two “bulges” in diameter of the spinal cord?
-Cervical enlargement (supplies upper limbs)
-Lumbar enlargement
(supplies lower limbs)
Does an epidural enter the CSF?
NO, goes only into the epidural space (above dura mater), do not want to go through dura mater or else you could numb the entire body
White matter
Myelinated axons forming nerve tracts
What are tracts?
Bundles of related axons in the CNS (nerves in PNS)
Gray matter
Neuron cell bodies & dendrites (no myelin) forms a distinct H or butterfly shape
White matter components
Dorsal column
Vertebral column
Lateral column
Gray matter components
Posterior horn
Lateral horn
Anterior horn
Posterior horn and the dorsal root ganglion are composed of…
Cell bodies of SENSORY neurons, unmyelinated regions so are gray matter
Dorsal roots
Bundles of myelinated axons (white matter) leaving the sensory neuron cell bodies in PH or DRG
The afferent sensory axons synapse in…
Posterior horn
onto. ..
1. ) Interneurons (lead directly to motor tract)
2. )Ascending sensory tracts in spinal cord
Anterior horns
Contain cell bodies of somatic MOTOR neurons, descending tracts
Lateral horns
Contain cell bodies of autonomic neurons
Ventral roots
Convergence of axons carrying EFFERENT (outgoing) action potentials from both the motor and autonomic neurons-these APs originate in the brain and are carried on descending tracts
Dermatomes
A distinct area of skin innervated by the sensory nerves that form the pair of bilateral spinal nerves
Which viral disease is seen in specific dermatomes?
Shingles
Why are spinal cord injuries so permanent?
There is a disconnect between PNS and CNS and PNS nerves can’t grow back and reconnect to CNS tracts, wiring done only during embryonic stage
How stable are the neurons of the CNS?
They are on the edge of life, any disruption to blood supply can kill them
Reflex arcs
Simplest functional unit of nervous system
-Hard-wired, involuntary responses
SAME
Sensory afferent motor efferent
What do withdrawal reflexed typically involve?
Excitatory interneurons and inhibitory interneurons
Reciprocal innervation
Interneuron wiring pattern that causes necessary
-Extensor muscle relaxation (reciprocal inhibition)
-Flexor muscle contraction
(reciprocal activation)
Withdrawal reflex in leg
Leads to ipsilateral flexion, , you activate the effector that moves the affected limb away from the injury
Crossed extensor reflex
A withdrawal reflex in one lower limb causes extension of the opposite lower limb
Stretch receptors
Located in muscle spindles and tendon organs, cause the reflexes that we test
Intrafusal muscle fibers
Within a muscle spindle; info on muscle position and coordination(finesse)
Extrafusal muscle fibers
Outside spindle, mediate muscle contraction, muscle power
Golgi tendon organ
Afferent sensory innervation in tendons (muscle to bone) provide feedback on tension
Stretch myotactic reflex functions
Regulates muscle length, coordinates muscle recruitment when stretching occurs, protects from overstitching or pulling muscles
Golgi tendon reflex function
Regulates muscle tension, prevents tendon tears due to excessive muscle contraction
Golgi tendon relfex
Antagonistic muscles (hamstring) contracts in response to other muscle stress (quad) —> RECIPROCAL INHIBITION
