1
Q
what are the functions of the spinal cord?
A
- Integrates info and relays signal btwn PNS and brain
- Connects brain to PNS
- processes spinal cord reflexes
2
Q
what are the SC’s layers of protection?
A
- vertebral column
- meninges
- CSF
3
Q
what are the CT coverings that wrap the SC?
A
- dura mater
- arachnoid mater
- pia mater
4
Q
what is the dura mater?
A
- most superficial of the meninges
- layer of dense irregular CT that is continuous w/ brain’s dura mater and epineurium
5
Q
what is the epidural space?
A
space between vertebral canal walls and the dura mater
- contains fat + CT
6
Q
what is the arachnoid mater?
A
- thin avascular CT covering made of loosely woven collagen and elastin fibres that resembles spider’s web
- continuous w/ arachnoid mater of brain
7
Q
what is the subdural space?
A
space btwn dura mater and arachnoid mater
- filled w/ IF
8
Q
what is the pia mater?
A
thin layer of squamous/cuboidal cells interlaced w/ collagen and elastin fibres
- adhered to surface of SC and brain
- denticulate ligaments suspend SC in place
9
Q
what are denticulate ligaments?
A
suspends SC in place, on pia mater
10
Q
what is the subarachnoid space?
A
space btwn arachnoid mater and pia mater
- contains CSF
11
Q
what is the function of cerebrospinal fluid?
A
- shock-absorber
- makes SC float weightlessly in subarachnoid space
- nourishes CNS
12
Q
where can CSF be found?
A
- ventricles of brain
- subarachnoid space in SC
13
Q
what is a spinal tap/lumbar puncture?
A
removal of CSF from subarachnoid space
- btwn L3-L4 or L4-L5
- used to diagnose pathologies or administer drugs
14
Q
what are the two enlargements of the spinal cord?
A
- cervical enlargement
- lumbosacral enlargement
15
Q
how long is the SC?
A
SC extends from medulla oblongata to ~L2
16
Q
what is the conus medullaris?
A
the inferior portion of SC that tapers into a cone, around L1 or L2
17
Q
what is the filum terminale?
A
the inferior portion of the pia mater
- anchors SC to the coccyx
- fused to other meningeal layers
18
Q
can spinal taps damage spinal cord?
A
NO, spinal taps done btwn L3-L4 or L4-L5, and SC terminates ~L1-L2
19
Q
what is special about the direction the lumbar, sacral, and coccygeal nerves go?
A
they extend downward from spinal cord because spinal cord stops only at L2
- these nerves extend downward, adjacent to filum terminale to supply the inferior portion of the body
20
Q
what is the cauda equina?
A
the tail-like collection of the lumbar, sacral, and coccygeal nerves that extends downward from the inferior portion of the SC
- resembles a horse’s tail
21
Q
how many pairs of spinal nerves are there?
A
31 pairs that extend bilaterally from SC
22
Q
what are spinal roots?
A
large bundles of axons in SC
23
Q
what are spinal rootlets?
A
smaller bundles of axons in SC
24
Q
what is the posterior root and rootlets?
A
bundles of sensory axons that receive sensory input from skin muscles and internal organs and send to the brain
25
what are the spinal ganglia?
cluster of cell bodies in SC
26
what is the anterior root and rootlets?
bundles of motor neuron axons that receive motor input from brain and send to the effectors
27
what is white matter?
bundles of myelinated axons (tracts) that carry **sensory** info to/from brain
28
what is grey matter?
dendrites, clusters of cell bodies (nuclei), unmyelinated axons, and neuroglia that **integrate (summate)** nerve impulses
29
describe what the grey matter of the SC looks like
- shaped like an "H" or butterfly
- paired posterior and anterior grey horns
- lateral grey horns on anterior grey horns (mainly found closer to inferior portion of SC)
30
what is the grey commissure?
grey matter of SC that crosses midline
31
what is the central canal?
space inside SC filled with CSF and runs entire length of spinal cord
32
what are the posterior (dorsal) grey horns?
axons of **sensory** neurons, cell bodies, and axons of **interneurons**
- all axons unmyelinated
33
what are anterior (ventral) grey horns?
**somatic (voluntary)** motor nuclei to skeletal muscles only
34
what are lateral grey horns?
**autonomic (involuntary)** motor nuclei
- found in thoracic, upper lumbar, mid-sacral segments)
- autonomic only, regulates activity of smooth and cardiac muscle, glands
35
describe what the white matter of the SC looks like
- white matter surrounds grey matter
- **grooves** divide the WM into 2 hemispheres
- divided into **funiculi** by grey horns
- anterior, posterior, and lateral white funiculi
36
what are funiculi?
portions of SC's WM that contain tracts (axon bundles in CNS)
37
what are tracts?
contains axons w/ common origin or destination, carrying similar info
38
what are ascending tracts?
tracts that carry **sensory** information **up** to the brain
- found in posterior portion of SC
39
what are descending tracts?
tracts that carry **motor** information **down** from the brain
- found in posterior portion of SC
40
how are tracts named?
for where neurons are located, begin, and end
spinothalamic tract begins in spinal cord (spino) and ends in thalamus (thalamic)
41
what are direct (pyramidal) motor tracts?
relays info from sensory to motor
42
what are indirect (extrapyramidal) motor tracts?
relays info from sensory, to inter, to motor
43
how many cervical nerve pairs are there?
8 cervical nerve pairs
44
how many thoracic nerve pairs are there?
12 thoracic nerve pairs
45
how many lumbar nerve pairs are there?
5 nerve pairs
46
how many sacral nerve pairs are there?
5 sacral nerve pairs
47
how many coccygeal nerve pairs are there?
1 coccygeal nerve pair
48
why is there a large amt. of grey matter in cervical and lumbar segments of the SC?
- more sensory and motor neurons found in the posterior and anterior grey horns are needed to service the lower limbs
- SC doesn't extend to lower limbs
49
why does amt of white matter in SC decrease from superior to inferior?
- lots of white matter in superior portion b/c lots of sensory info needed to be taken to brain in cervical portion
- increasing # of motor tracts in inferior portion b/c lower limbs
50
what are the 2 non-reflex fxns. of the SC?
1. grey matter receives and **Integrates** incoming/outgoing info.
2. white matter tracts **conduct** nerve impulses rapidly to/from the brain
51
how does the anatomy of the SC affect how information is processed?
internal anatomy of SC permits info processing to proceed in an organized fashion
52
describe how sensory info is processed by SC
1. Sensory receptors detect a sensory stimulus
2. Sensory neurons convey sensory input in the form of nerve impulses along their axons, which extend from sensory receptors → spinal nerve → posterior root.
From the posterior root, axons of sensory neurons may proceed along 3 paths:
2.1. **posterior gray horn** → white matter → ascending sensory tract → brain
2.2. **posterior gray horn** → interneurons → white matter → ascending sensory tract → brain
2.3. **posterior gray horn** → interneurons → somatic motor neurons → reflex!!
53
describe how somatic motor info is processed by SC
1. SC sends nerve impulses from brain to somatic motor neurons of the anterior gray horn
- signal travels along motor tracts from brain, synapsing either:
1.1 **directly** w/ somatic motor neurons
1.2 **indirectly** w/ interneurons
2. nerve impulse travels from somatic neurons of anterior grey horn → anterior root → spinal nerves → skeletal muscles
54
describe how autonomic motor info is processed by SC
1. SC sends nerve impulses to autonomic motor neurons of the lateral gray horn
2. nerve impulse travels from lateral grey horn → anterior grey horn → anterior root → spinal nerves
3. from spinal nerve, autonomic motor neuron axons synapse w/ another autonomic motor neuron in PNS → smooth/cardiac muscle, glands (autonomic motor neurons usually in series w/ autonomic effector)
55
what are spinal nerves?
parallel bundles of hundreds-thousands of axons, blood vessels, and associated neuroglia wrapped in CT
- branch from SC into roots & rootlets and connect CNS to sensory receptors, muscles, and glands
56
what is the endoneurium?
CT covering that wraps around a single neuronal axon fibre
57
what is the perineurium?
CT covering that wraps around many fibres bundled into a fascicle
58
what is the epineurium?
CT covering that wraps fascicle bundles tgt into a nerve and fills in spaces around the fascicles
59
why are the endoneurium, perineurium, and epineurium all highly vascularized?
to supply the nerve w/ blood
60
at what bone surface marking do spinal nerves exit the vertebral column?
intervertebral foramen of vertebrae
61
what are the two roots that connects the spinal nerves to the SC?
posterior and anterior roots
62
what are mixed spinal nerves?
spinal nerves that contain both sensory and motor axons due to both posterior root (w/ sensory axons) and anterior root (w/ motor axons) coming together
- all spinal nerves are mixed
63
what is the dorsal root/ spinal ganglion?
clusters of sensory neuron's cell bodies
64
what are rami?
branches of the spinal nerves
65
what are posterior rami?
spinal nerve branches that suppy deep muscles and skin of posterior trunk (the back)
66
what are anterior rami?
spinal nerve branches that supply anterior/lateral trunk and limbs
67
what are meningeal branches
spinal nerve branches that supply meninges, vertebrae, and blood vessels of spinal cord
68
what are communicating rami?
spinal nerve branches that supply **autonomic nervous system**
69
what is a plexus?
weblike network of rami from multiple nerves
70
which spinal nerves do not form plexuses?
anterior rami of T2-T12 (they are intercostal nerves)
- connects directly to structures in intercostal spaces (intercostal muscles, CT, blood vessels)
71
which rami do not branch directly into tissue they service?
anterior rami
- forms plexuses w/ rami from other nerves
- connect axons of adjacent nerves
72
what is the cervical plexus?
weblike network of rami that supplies skin and muscles of the head, neck, and upper part of the shoulders and chest
- connects with some cranial nerves
- **phrenic nerve** supplies diaphragm
73
what is the brachial plexus?
weblike network of rami that supplies upper limbs and some neck and shoulder muscles
74
what is the lumbar plexus?
weblike network of rami that supplies anterolateral abdominal wall, external genitals, and part of lower limbs
75
what is the sacral plexus?
weblike network of rami that supplies the buttocks, perineum, and lower limbs
- **sciatic nerve** is the largest nerve in the body
76
what is the largest nerve in the body?
sciatic nerve
77
what are dermatomes?
areas of skin that provide specific sensory input and serviced by a specific somatic sensory nerve
78
what is the only cranial nerve that specifically senses signals for most of the face and scalp?
the trigeminal (V) nerve
79
how can you predict which nerves are damaged using dermatomes?
if you stimulate the skin in a particular dermatome but the sensation is not perceived, you can predict which nerves are damaged and can tract to specific signal segment
80
what is the only spinal nerve that does not service a dermatome?
C1
81
what is a reflex?
a rapid, **involuntary** response to a stimulus
- can be inborn or acquired
82
what integrates the spinal reflexes?
the grey matter of the spinal cord
83
which kind of reflexes are the ones we are conscious of?
somatic reflexes
(doesn't mean they are voluntary, only that we are aware of it)
84
what is a reflex arc?
the path of nerve impulses that result in a reflex
85
what are the components of a reflex arc?
1. sensory receptor
2. sensory neuron
3. integration center (SC in spinal reflexes)
4. motor neuron
5. effector
86
what are the somatic spinal reflexes?
1. stretch reflex
2. tendon reflex
3. flexor (withdrawal) reflex
4. crossed extensor reflex
87
what is a monosynaptic reflex arc?
reflex arc involving only one synapse
(sensory → motor neuron)
- no interneurons involved
88
what is a polysynaptic reflex arc?
reflex arc involving many synapses
(sensory → multiple interneurons → motor neuron)
89
what is a stretch reflex?
a monosynaptic, ipsilateral reflex arc (with a polysynaptic reflex arc to antagonistic muscles) that controls muscle length and prevents overstretching of muscles by causing involuntary muscle contraction
- involves reciprocal innervation
90
how does the stretch reflex work?
1. muscle stretch sensed by muscle spindles
2. muscle spindle sends nerve impulse along somatic sensory neurons → posterior root of spinal nerves → spinal cord
3. at integrating centre, somatic sensory neuron forms **excitatory** synapse and activates motor neuron in anterior grey horn
4. if depol. of motor neurons reaches threshold, nerve impulse sent from anterior root of spinal nerves → PNS neurons that release **ACh** into NMJ
5. muscles bind and respond to ACh, resulting in contraction
91
what are muscle spindles?
sensory receptors that sense change in muscle length, plays role in stretch reflexes
92
what is reciprocal innervation?
- the components of a neural circuit simultaneously cause contraction of agonist and relaxation of its antagonist
- nerve services both agonist and antagonist muscles
- nerve has opposite effect on agonist and antagonist muscles, but effects work at the same time
93
why is reciprocal innervation important?
Reciprocal innervation prevents conflict between opposing muscles and is vital in coordinating body movements
94
what is the tendon reflex?
polysynaptic, ipsilateral reflex arc that mediates stretch reflex and decreases muscle tension to prevent tearing of the tendons when muscles are contracted by causing muscle relaxation before muscle force results in torn tendons
95
how does the tendon reflex work?
1. tendon organs sense changes in muscle tension btwn muscle belly and tendon
2. tendon organs send nerve impulses along sensory neuron → integrating centre in SC
3. sensory neuron forms **inhibitory** synapse w/ interneuron
4. Interneuron sends nerve impulse that **hyperpolarizes** a motor neuron
5. Motor neuron sends **fewer** nerve impulses to NMJ, less ACh in synapses
6. Muscle relaxes
96
what are tendon organs?
sensory receptors that sense changes in muscle tension at jxn. btwn muscle belly and tendon
97
what is the flexor (withdrawal) reflex?
polysynaptic, ipsilateral reflex arc that permits flexion away from a stimulus, even before the pain is processed and perceived
98
how does the flexor (withdrawal) reflex work?
1. dendrites of a pain-sensitive neuron are stimulated
2. sensory neurons send nerve impulses to spinal cord
3. integrating centre sends several nerve impulses to interneurons that branch to multiple spinal segments
4. interneurons form **excitatory** synapses with motor neurons, sending nerve impulses along these motor neurons
5. ACh at NMJ causes muscle contraction away from painful stimulus
99
what is an intersegmental reflex arc?
- nerve impulses from one sensory neuron ascend and descend in the spinal cord and activate interneurons in several segments of the spinal cord
- a single sensory neuron can activate several motor neurons, thereby stimulating more than one effector
100
what is the crossed extensor reflex?
contralateral, polysynaptic reflex arc that is activated by painful stimuli alongside the flexor (withdrawal) reflex
- permits balance to be maintained as limb is jerked away from pain stimulus
101
how does the crossed extensor reflex work?
1. pain-sensitive neuron is stimulated
2. sensory neuron sends nerve impulses to spinal cord
3. integrating centre activates interneuron that branch to multiple spinal segments and synapse w/ motor neurons on **opposite side** of body from the stimulus
4. interneurons excite motor neurons that activate extensor muscles → propagate nerve impulses to NMJ
5. ACh released into NMJ of **unstimulated** limb, weight can now be transferred to activated opposite limb during flexor reflex
102
why is the crossed extensor reflex contralateral?
so that weight can be transferred to opposite limbs during flexor reflex, permitting balance maintenance as we jerk away from stimulus
103
what is decussation?
crossing over
104
what is transection?
injury that severs spinal cord, leading to loss of sensation and motor control below level of injury
105
what happens in C1-C3 transection?
no function maintained from neck down, need ventilator for breathing
106
what happens in C4-C5 transection?
diaphragm function maintained, can breathe
107
what happens in C6-C7 transection?
some arm and chest muscles maintained, can feed and dress oneself
108
what happens in T1-T3 transection?
intact arm function
109
what happens in T4-T9 transection?
control of trunk above umbilicus
110
what happens in T10-L1 transection?
most thigh muscles maintained, can walk w/ long braces
111
what happens in L1-L2 transection?
most leg muscles maintained, can walk w/ short leg braces
112
Evalina’s severe headaches and other symptoms were suggestive of meningitis, so her physician ordered a spinal tap. List the structures that the needle will pierce from the most superficial to the deepest. Why would the physician order a test in the spinal region to check a problem in Evalina’s head?
The needles will pierce the epidermis, dermis, and subcutaneous tissue and then go between the vertebrae through the epidural space, the dura mater, the subdural space, the arachnoid mater, and into the CSF in the subarachnoid space. CSF is produced in the brain, and the spinal meninges are continuous with the cranial meninges.
113
Sunil has developed an infection that is destroying cells in the anterior gray horns in the lower cervical region of the spinal cord. What kinds of symptoms would you expect to occur?
The anterior gray horns contain cell bodies of somatic motor neurons and motor nuclei that are responsible for the nerve impulses for skeletal muscle contraction. Because the lower cervical region is affected (brachial plexus, C5–C8), you would expect that Sunil may have trouble with movement in his shoulder, arm, and hand on the affected side.
114
Allyson is in a car accident and suffers spinal cord compression in the lower spinal cord. Although she is in pain, she cannot distinguish when the doctor is touching her calf or her toes and she is having trouble telling how her lower limbs are positioned. What part of the spinal cord has been affected by the accident?
Allyson has damaged her posterior funiculi in the lower (lumbar) region of the spinal cord. The posterior funiculi are responsible for transmitting nerve impulses responsible for awareness of muscle position (proprioception) and touch—which are affected in Allyson—as well as other functions such as light pressure sensations and vibration sensations. Relating Allyson’s symptoms to the distribution of dermatomes, it is likely that regions L4, L5, and S1 of her spinal cord were compressed.
115
Why is the crossed extensor reflex classified as a contralateral reflex arc?
the motor impulses leave the spinal cord on the side opposite the entry of sensory impulses
116
Why is the flexor reflex classified as an intersegmental reflex arc?
impulses go out over motor neurons located in several spinal nerves, each arising from a different segment of the spinal cord.
117
What initiates a nerve impulse in a sensory neuron? Which branch of the nervous system includes all integrating centers for reflexes?
A sensory receptor produces a generator potential, which triggers a nerve impulse if the generator potential reaches threshold. Reflex integrating centers are in the CNS.
118
Based on its name, list the origin and destination of the spinothalamic tract. Is this a sensory or a motor tract?
The spinothalamic tract originates in the spinal cord and ends in the thalamus (a region of the brain). Because “spinal” comes first in the name, you know it contains ascending axons and thus is a sensory tract.
119
What is the origin of the sacral plexus?
The origin of the sacral plexus is the anterior rami of spinal nerves L4–L5 and S1–S4.
120
Why does complete severing of the spinal cord at level C2 cause respiratory arrest?
Severing the spinal cord at level C2 causes respiratory arrest because it prevents descending nerve impulses from reaching the phrenic nerve, which stimulates contraction of the diaphragm, the main muscle needed for breathing.
121
Which is the only spinal nerve that does not have a corresponding dermatome?
C1
122
Why are all spinal nerves classified as mixed nerves?
All spinal nerves are classified as mixed because their posterior roots contain sensory axons and their anterior roots contain motor axons.
123
Lateral gray horns are found in which segments of the spinal cord?
Lateral gray horns are found in the thoracic and upper lumbar segments of the spinal cord.
124
What is the difference between a horn and a column in the spinal cord?
A horn is an area of gray matter, and funiculus is a region of white matter in the spinal cord.
125
What portion of the spinal cord connects with nerves of the upper limbs?
The cervical enlargement connects with sensory and motor nerves of the upper limbs.
126
What are the superior and inferior boundaries of the spinal dura mater?
The superior boundary of the spinal dura mater is the foramen magnum of the occipital bone. The inferior boundary is the second sacral vertebra.
