Unit 19: etc. Flashcards
(14 cards)
*See notes for Central Nervous System: Brain (pg.s 9 + 10)
What is the structural overview for the central nervous system: Spinal Cord?
- Foramen magnum to L1/L2 (conus medullaris) - NOTE: spinal cord DOES NOT go to end of lumbar spine (L5)
- Nerves continue down from spinal cord through vertebral foramina as cauda equina (horse’s tail)
- Exit at intervertebral foramina
- Filum terminale = CT extension of pia mater that anchors the conus medullaris of spinal cord to the coccyx. Also = location where CSF samples are taken
Info about the cross-sectional structure of the Spinal Cord
a) anterior median fissure (separation) and posterior median sulcus (bigger separation)
- separate cord into R and L halves
b) central canal - contains CSF
c) gray matter = cell bodies and dendrites of lower motor neurons and interneurons. They = ‘H’ shaped
- cross bar of ‘H’ = gray commissures
- horns = dorsal (sensory), lateral (motor - little bump on
side of ‘H’), and ventral (motor)
d) white matter = myelinated axons containing ascending (sensory) and descending (motor) tracts. Forms columns:
i. dorsal column
ii. lateral column
iii. ventral column
Info about functions of Spinal Cord
Basically = highway for communication btw. brain and body:
- transmission of motor impulses (somatic and autonomic) from brain to the body
- transmission of sensory impulses from body to brain
- coordinates reflexes for rapid responses to stimuli
- fast, predictable, automatic responses to changes in
environment (ex. = withdrawal reflex)
- contains neural circuits for repetitive movements like walking/running (central pattern generators)
More info about PNS: sensory (afferent) division
- stimulus to receptor to CNS
- PNS consists of receptors and first order neurons
Info about PNS receptors
Detect changes in environment - classified by location, type of stimulus received, and structure of receptor
Info about location of receptors in PNS
i. exteroceptors - detect stimuli in external environment, so receptors are at body surface (e.g. touch, special senses)
ii. interoceptors - detect stimuli in internal environment (in viscera and blood vessels)
iii. proprioceptors (perception of where muscles are - ex. w/ morphine) - located in joint, skeletal muscles, etc..
- monitor body position (stretch receptors, muscle
spindles) - balance and movement
Info about type of stimulus received by PNS receptors
i. mechanoreceptors = detect mechanical stimuli (pressure, touch, hearing, etc.)
ii. thermoreceptors = monitor temperature
iii. chemoreceptors = chemical
iv. photoreceptors = light
v. nociceptors = pain
Info about structure of receptor (general senses only) for PNS receptors
i. free nerve endings = terminal dendrites of unipolar sensory neurons (e.g. pain, root hair plexus)
ii. encapsulated nerve endings = terminal dendrites enclosed in CT (e.g. tactile [Meissner’s] and lamellated [Pacinian] corpuscles)
Info about PNS first order neurons
- = unipolar neuron attached to or associated w/ a receptor (may be encapsulated)
- axon travels in cranial/spinal nerves to CNS
- cell bodies in: sensory ganglia of cranial nerves, and dorsal root ganglia of spinal cord
- axon terminals in: brain, and dorsal horn of spinal cord
Info about PNS: motor (efferent) division
CNS to effector (are in PNS as soon as leave spinal cord). 2 subdivisions:
1) Somatic
- effector = skeletal muscle
- consists of lower motor neurons = SINGLE multipolar
neuron
a) cell bodies in ventral horn of spinal cord to effector
b) cell bodies in motor nuclei of brainstem to effector (e.g.
facial motor nucleus for CN VII)
2) Autonomic
- effector = smooth muscle, cardia muscle, glands
- 2 successive multipolar neurons from CNS to effector:
a) preganglionic neuron (MYELINATED - cell body in brain stem or lateral horn of spinal cord)
b) postganglionic neuron (UNMYELINATED - cell body in autonomic ganglion [so outside CNS])
*See pg. 16 of notes for charts (look all the way to the 2 subdivisions [SNS and PSNS] for autonomic)
Nervous system pathways overview
2 pathways = ascending pathway (sensory), and descending pathway (motor)
Info about NS ascending pathway (sensory)
Conducts impulses from general sense receptors into brain. 3 successive neurons from receptor to cortex:
a) First Order Neuron = receptor to spinal cord (PNS)
b) Second Order Neuron = interneuron, multipolar (CNS) - cell body in dorsal horn of spinal cord or medulla (CNS) - decussates (crosses over) in medulla
c) Third Order Neuron - interneuron, multipolar - cell body in thalamus - impulses to postcentral gyrus (sensory cortex) (CNS)
Axons of 1st and 2nd order neurons for ASCENDING SPINAL TRACTS:
a) Dorsal (Posterior) Column Pathway/Tract
- sensations can be precisely located (touch)
- receptors = free nerve endings, Meissner’s etc.
b) Spinothalamic Pathway/Tracts
- non-specific, difficult to localize
- receptors = temperature, pain
c) Spinocerebellar Pathway/Tracts
- ascending tracts from spinal cord to cerebellum
- receptors = proprioceptors
- 2nd order neuron directly to cerebellum (NO 3rd order),
so no conscious perception or decussation
Info about NS descending pathway (motor)
Conduct impulses from brain to effector. 2 neuron pathways:
a) Upper Motor Neuron (CNS) = multipolar interneurons; cell bodies in cortex or brainstem nuclei
b) Lower Motor Neuron (cell bodies in CNS and axons in PNS)
Axons of upper motor neurons form DESCENDING SPINAL TRACTS:
a) Corticospinal Tracts = cell bodies in cerebral cortex; tracts mainly decussate in medulla
b) Indirect Tracts = cell bodies in brainstem nuclei; receive impulses from motor cortex, basal nuclei, and cerebellum
