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116 terms

PCOM: Anatomy 3 - week 5, White Matter (pg. 56) through the cranial nerves (pg. 70)

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composition of white matter
mostly myelinated axons
two general type of myelinated axons
ascending/sensory
descending/motor
where ascending axons lead
higher brain centers
where descending axons lead
ventral horns of the spinal cord
divisions of white matter in the spinal cord
posterior/dorsal column
lateral column
ventral/anterior column
another term for white matter columns
funiculi
subdivisions of columns in the spinal cord
tracts
characteristics of axons within each tract
have the same function and destination
important characteristic of the pathway of tracts (in both directions)
the decussate (cross contra-laterally) at some point in their pathway
general structure of ascending pathways
they are a chain of 3 neurons
types of neurons in ascending pathway chains
1st order
2nd order
3rd order
location of 1st order neurons
unipolar cell body in the dorsal root ganglia
function of 1st order neurons
carry impulses from sensory receptors (located in the skin, muscles & joint proprioceptors) into the spinal cord & synapse with 2nd order neurons
location of 2nd order neurons
cell bodies in the dorsal horn of the spinal cord or in the nuclei of the MO
function of 2nd order neurons
transmit impulses to thalamus or cerebellum where they synapse
location of 3rd order neurons
cell bodies found in the thalamus
function of 3rd order neurons
relay sensory input to the somato-sensory cerebral cortex
the three main ascending pathways of the spinal cord
dorsal column medial lemniscal pathways
anterolateral pathways
spinocerebellar pathways
location of the three main ascending pathways of the spinal column
paired sets of three on each side of the spinal cord
function of the dorsal column medial lemniscal pathway
transmits sensations that can be localized on the body
examples of localized sensations
discriminative touch & vibration, 2 point discrimination, stereognosis, from joint and muscle proprioceptors
2 point differentiation
the ability to recognize that there are two pints of contact
stereognosis
the ability to differentiate what an object is using at least two points of contact
discriminative touch
the ability to identify exactly where the sensation of touch or vibration is occurring on the body
structures of the dorsal column medial lemniscal pathway
the fasciculus cuneatus and the fasciculus gracilis - paired tracts in the the dorsal matter - and the medial lemniscal tract (or lemnisucus)
pathway of the medial lemniscal tract
arises in the MO and terminates in the thalamus
1st order axons of the dorsal column medial lemniscal pathway
enter the spinal cord and travel up toward the MO and form paired tracts - either the fasciculus gracilis or the fasciculus cuneatus which synapse with 2nd order neurons in the MO
from where the fasciculus cuneatus arises
1st order axons of the neck, upper extremities and upper trunk (above the diaphragm)
from where the fasciculus gracilis arises
1st order axons of the lower extremities and lower trunk
2nd order neurons of the dorsal column medial lemniscal pathway
the nucleus cuneatus or the nucleus gracilus - located in the MO
pathway of the 2nd order axons of the dorsal column medial lemniscal pathway
2nd order axons of the DCMLP form the medial lemniscus and travel to the thalamus where they synapse with 3rd order neurons of the DCMLP
where the medial lemniscus decussates
in the MO
3rd order neurons of the DCMLP
located in the thalamus
where 3rd order axons of the DCMLP terminate
in the somatosensory cortex (in the cerebral hemispheres)
structures of the anterolateral pathways
ventral/anterior spinothalamic tract
lateral spinothalamic tract
where the tracts of the anterolateral pathways decussate
in the spinal cord
function of the lateral spinothalamic tract
pain and temperature
function of the anterior/ventral spinothalamic tract
crude touch - not localized sensation
pressure
structures of the spinocerebellar pathways
anterior spinocerebellar tract
posterior spinocerebellar tract
functions of the spinocerebellar tracts
transmit proprioceptive information from the trunk and lower limbs to the cerebellum to coordinate skeletal muscle activity
two types of descending pathways of the spinal cord
direct/pyramidal tracts
indirect/extrapyramidal tracts
two types of neurons of the motor tracts
upper motor neurons
lower motor neurons
what the upper motor neurons form
the pyramidal interneurons of the motor cortex
the subcortical motor neurons that give rise to the indirect (extrapyramidal) tracts
what the lower motor neurons form
arises with the ventral horn motor neurons and innervates the skeletal muscles
gross pathway of the pyramidal pathway
begins in the motor cortex (precentral gyri) and runs to the ventral horns of the white matter of the spinal cord
pathways of the axons of the pyramidal tracts
run from the cell bodies in the precentral gyri through the white matter of the brain and descend as either the lateral or ventral corticospinal tract
where the axons of the lateral corticospinal tract decussate
in the MO - the pyramidal decussation
where the axons of the anterior corticospinal tract decussate
in the spinal cord at the level in which they synapse in the ventral horn motor neurons
function of the corticospinal tracts
upper motor neurons carry impulses from the cerebral cortex to the lower motor neurons of the ventral horns which activate skeletal muscles
where collateral impulses from the corticospinal tracts go
to the basal nuclei (deep in the cerebral white matter) and the cerebellum
pyramidal tract that synapses with the cranial nerve motor nuclei
the corticobulbar tract - located above the head and neck
function of the cranial nerve motor nuclei
govern head and neck motor activity (i.e. chewing, swallowing, etc)
the four extrapyramidal tracts
tectospinal tract
vestibulospinal tract
rubrospinal tract
reticulospinal tract
characteristic of the tracts of the extrapyramidal pathway
anatomically complex and multi-synaptic
function of the tectospinal tract
mediate head movement for visual tracking - originates in the superior colliculi of the midbrain (corpora quadrigemina)
function of the vestibulospinal tract
transmits motor impulses to mediate balance and equilibrium while standing and moving - originate in the vestibular nuclei of the MO
function of the rubrospinal tract
transmits motor impulses to assist with limb flexion - originates in the red nuclei of the midbrain
function of the reticulospinal tract
transmits nerve impulses that influence muscle tone for maintaining posture and balance - originate in the reticular formation located deep in the central column of the brain stem
what forms the PNS
all neural structures outside of the CNS -
sensory receptors
peripheral nerves
ganglia
efferent motor endings
what forms sensory receptors
specialized dendritic endings
how sensory receptors are classified
2 ways -
stimulus detected
body location
mechanoreceptors
respond to mechanical force
thermoreceptors
respond to temperature changes
photoreceptors
only in the retina - respond to light energy
chemoreceptors
respond to chemicals (smell, taste)
nociceptors
respond to pain signals (stimulus created by trauma to cells causing electro-chemical response)
substance that mediates pain response
substance P
proprioceptors
arise from specific locations for position sense
two types of simple receptors of general senses
unencapsulated
encapsulated
muscle spindles
encapsulated nerves endings in the perimysium of skeletal muscle that detect stretch and enact a protective contraction reflex
structure of muscle spindle nerves
modified skeletal muscle fibers called intrafusal fibers enclosed in a CT capsule
golgi tendon organs
proprioceptors located in tendons near the tendenomuscular junction which monitor muscle tension and enact a protective inhibition of contraction of muscle
general structure of a nerve
consistes of many peripheral axons bound into fascicles
CT sheath of peripheral axons
endoneurium
CT sheath of each fascicle
perineurium
CT sheath that encloses groups of fascicles that form the nerve
epineurium
other structures contained within the nerve
blood and lymph vessels
term for nerves containing both motor and sensory fibers
mixed nerves
classifications of motor nerve fibers
somatic
autonomic
function of somatic motor nerves
motor nerves of skeletal muscle
function of autonomic motor nerves
motor nerves of glands, smooth muscle, and cardiac muscle
classifications of mixed nerve fibers
somatic afferent - from the body
somatic efferent - to the skeletal muscle
autonomic afferent - from the effector organs
autonomic efferent - to the effector organs
classifications of peripheral nerves
spinal - arise from spinal cord
cranial - arise from brain stem
term for a group of neuronal cell bodies of the nerves of the PNS
ganglia (ganglion, singular)
ganglia of the afferent somatic nerves
dorsal root ganglion
ganglia of the autonomic efferent nerves
autonomic ganglia
when PNS nerve axons may be able to regenerate
if the cell body remains intact and damage is not too extensive
first stage of axon regeneration after trauma (within hours)
Wallerian degeneration - axon distal to the injury site degenerates due to lack of nutrients from the cell body
2nd stage of axon regeneration (within 1 week)
macrophages degrade the degenerated distal axon; the neurilemma remains intact
3rd stage of axon regeneration
Schwann cells undergo mitosis and migrate to the injury site and release chemicals that stimulate the growth of the proximal axon and form a regeneration tube that guide the regenerating axon "sprouts" across the injury site
axon regeneration rate
about 1.5 mm/day
why CNS axons do not regenerate
oligodendrocytes contain growth inhibiting proteins and astrocytes form scar tissue, blocking axonal growth
number of cranial nerves
12 pair
cranial nerves that do not originate from the brainstem
I & II
areas innervated by the Cranial nerves, and the one exception
Except for CN X (Vagus) cranial nerves only innervate head and neck structures
mnemonic for names of the cranial nerves
Oh, Oh, Oh, Tubby Teens And Fresh Virgins Give Very Awful Head
mnemonic for the type of functions of cranial nerves - motor, sensory, or both
Some Say Money Matters, But My Brother Says Big Boobs Matter More
Function and origin of the CN I, the Olfactory Nerve
sensory - axons arise from olfactory receptor cells; function in sense of smell
function and origin of CN II, the Optic nerve
sensory - axons arise from ganglia in the retina; function in vision
Cranial nerves that move the eyeball
CN III, IV, VI
functions of CN III, the Oculomotor nerve
Somatic and Autonomic Motor:
- 4 of 6 extrinsic eye muscles - inferior oblique, superior, inferior and medial rectus
- parasympathetic motor to muscles of the iris: sphincter pupillae (constrict pupils) and ciliary muscle (shape of lens for focus)
- levator palpebrae superioris: raises the upper eyelid
functions of CN IV, the Trochlear nerve
somatic motor:
superior oblique muscle of the eye
three division of CN V, the Trigeminal nerve
opthalmic
maxillary
mandibular
function of the opthalmic division of the Trigeminal nerve
Sensory:
anterior scalp
upper eyelid, nose, nasal cavity mucosa
cornea
lacrimal gland
function of the maxillary division of the Trigeminal nerve
Sensory:
nasal cavity mucosa
palate
upper teeth
skin of cheek
upper lip
lower eyelid
function of the mandibular division of the Trigeminal nerve
BOTH
Sensory:
anterior tongue (except taste buds)
lower teeth
skin of chin
temporal scalp
Somatic Motor:
muscles of mastication
function of CN VI, the Abducens nerve
Somatic Motor:
lateral rectus muscle of the eye
Five branches of CN VII, the Facial nerve
temporal
zygomatic
buccal
mandibular
cervical
functions of CN VII, the Facial nerve
BOTH:
Somatic motor:
muscles of facial expression
Parasympathetic Motor:
lacrimal glands
nasal & palatine glands
submandibular and sublingual glands
Sensory:
taste buds on anterior 2/3 of tongue
functions and branches of CN VIII, the Vestibulocochlear nerve
Sensory:
vestibular branch for equilibrium
cochlear branch for sense of hearing
functions of CN IX, the Glossopharyngeal nerve
BOTH
Motor:
somatic motor - stylopharyngeus muscle (elevates pharynx during swallowing)
parasympathetic motor - parotid glands
Sensory:
taste, touch, pressure from posterior 1/3 of tongue and pharynx
from carotid bodies monitoring O2 and CO2 levels
baroreceptors (next to carotid bodies) monitoring Blood Pressure
distinctive characteristic of CN X, the Vagus nerve
fibers emerge from the skull and descend through the neck to the thorax and abdomen
functions of CN X, the Vagus nerve
BOTH
Motor:
somatic motor - laryngeal and phayngeal muscles of swallowing
parasympathetic motor - to heart, lung, abdominal organs for heart rate, force of contraction, and digestive organ activity
Sensory:
visceral sensory from the thoracic and abdominal viscera
baroreceptors in the aortic arch (blood pressure)
chemo receptors from the carotid and aortic bodies (O2 & CO2 levels)
distinctive characteristic of CN XI, the accessory nerve
it arises from ventral rootlets of C1 to C5 cord levels, enters the foramen magnum and exits the jugular foramen
function of CN XI, the Accessory nerve
Somatic Motor:
trapezius & SCM muscles
function of CN XII, the Hypoglossal nerve
Somatic motor:
- intrinsic and extrinsic tongue muscle for mixing food and chewing
- tongue movement for swallowing and speech