Chapter 13: Spinal Cord and Nerves Flashcards
(95 cards)
1
Q
Epineurium.
A
Outermost layer of entire nerve. Covers spinal and cranial nerves. Made of fibroblasts and collagen fibres.
2
Q
Dura mater.
A
Superficial layer, thick and strong, made of dense irregular connective tissue, forms sac from foramen magnum, continuous with dura mater of brain and with epineurium.
3
Q
Arachnoid mater.
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Middle layer, thin and avascular, arranged in spiderweb, made of thin loosely arranged collagen and elastic fibres, continuous with arachnoid mater of brain.
4
Q
Subdural space.
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Space between dura mater and arachnoid mater that contains interstitial fluid.
5
Q
Pia mater.
A
Inner layer. Made of thin transparent connective tissue, squamous cells, cuboidal cells, collagen fibres, elastic fibres, and blood vessels. Connects to the surface of the brain and spinal cord, and supplies oxygen and nutrients. Extends entire length of spinal cord to protect it against sudden displacement.
6
Q
Subarachnoid space.
A
Between arachnoid mater and pia mater that contains CSF to absorb shock.
7
Q
Do spinal meninges cover the spinal nerves?
A
Yes, until they exit the spinal column through the intervertebral foramina.
8
Q
Hey.
A
You’re doing great :)
9
Q
Epidural space.
A
Between dura mater and wall of vertebral canal.
10
Q
Where does the spinal cord extend to in adults?
A
From medulla oblongata to superior border of L2.
11
Q
Where does the spinal cord extend to in infants?
A
From medullar oblongata to L3-L4.
12
Q
Cervical enlargement.
A
Superior. C4-T1. Nerves to and from the upper limbs arise here.
13
Q
Lumbar enlargement.
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Inferior. T9-T12. Nerves to and from the lower limbs arise here.
14
Q
Conus medullaris.
A
Spinal cord terminates as a tapering conical structure and ends at intervertebral discs between L1-L2.
15
Q
Filum terminale.
A
Extension of pia mater that arises from conus medullaris and fuses with arachnoid mater and dura mater to anchor spinal cord to coccyx.
16
Q
How many pairs of spinal cervical, thoracic, lumbar, sacral and coccygeal nerves are there?
A
Cervical: 8. Thoracic: 12. Lumbar: 5. Sacral: 5. Coccygeal: 1.
17
Q
Roots.
A
Bundles of axons.
18
Q
Rootlets.
A
Smaller bundles of axons.
19
Q
How do roots and rootlets connect spinal nerves to the spinal cord?
A
Two roots connect each spinal nerve to a spinal segment by rootlets.
20
Q
Posterior/dorsal root and rootlets.
A
Contain sensory axons. Conduct nerve impulses from sensory receptors in skin, muscles, and internal organs.
21
Q
Posterior/dorsal root ganglion.
A
Contains cell bodies of sensory neurons.
22
Q
Anterior/ventral root and rootlets.
A
Contain motor axons. Conduct nerve impulses to effectors.
23
Q
Cauda equina.
A
Roots of lower spinal nerves that run along the filum terminale like wisps of hair.
24
Q
Anterior median fissure.
A
Groove that penetrates the white matter of the spinal cord to divide it into right and left sides, located on the anterior/ventral side.
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Posterior median fissure.
Narrow furrow that penetrates the white matter of the spinal cord to divide it into right and left sides, located on the posterior/dorsal side.
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Anterior/ventral white commissure.
Anterior to gray commissure. Connects white matter of right and left sides of the spinal cord.
27
The anterior and gray horns divide the white matter on each side into 3 columns:
Anterior/ventral white columns, posterior/dorsal white columns, lateral white columns. Each column contains bundles of axons that have a common origin or destination, and carry similar information. They are tracts that are continuous with the tracts in the brain.
28
Gray matter on each side of the spinal cord is divided into horns:
Posterior/dorsal gray horns, anterior/ventral gray horns, lateral gray horns.
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Posterior/dorsal gray horns.
Contain axons of incoming sensory neurons, and cell bodies and axons of interneurons.
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Anterior/ventral gray horns.
Contain somatic motor nuclei which provide nerve impulses for contraction of skeletal muscles.
31
Lateral gray horns.
Between posterior and anterior horns. Present only in thoracic and upper lumbar segments. Contain autonomic motor nuclei which regulate the activity of cardiac muscle, smooth muscle and glands.
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Gray commissure.
Forms the crossbar of the H-shaped gray matter.
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Central canal.
In the centre of the gray commissure. Extends entire length of spinal cord. Filled with CSF. Continuous with the medullar oblongata.
34
Describe the sensory input and motor output of the spinal cord.
Sensory receptors detect sensory stimulus --> posterior root --> axons of sensory neurons may proceed along 3 possible paths: (a) axons of sensory neurons extend into white matter of spinal cord and ascend to brain, (b) axons of sensory neurons enter posterior gray horn and synapse with interneurons whose axons extend into the white matter of the spinal cord and then ascend to the brain, (c) axons of sensory neurons enter posterior gray horn and synapse with interneurons that synapse with somatic motor neurons involved in spinal reflex --> axons from higher brain centres form motor tracts that descend from brain into white matter of spinal cord --> synapse with interneurons --> synapse with somatic motor neurons --> impulse travels through anterior gray horn and anterior root to spinal nerve --> axons of somatic motor neurons extend to skeletal muscles --> impulses from autonomic motor neurons in lateral gray horn travel to anterior gray horn --> anterior root --> spinal nerve --> axons of autonomic motor neurons from spinal cord synapse with another group of autonomic motor neurons in PNS --> axons synapse with cardiac muscle, smooth muscle, glands.
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Spinal nerves.
Parallel bundles of axons and their associated neuroglia cells wrapped in several layers of connective tissue that connect the CNS to sensory receptors, muscles and glands.
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How are spinal nerves named and numbered?
Based on the region and level of the vertebral column that they emerge from.
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Where does the first cervical pair of spinal nerves emerge from?
Spinal cord between occipital bone and atlas (C1).
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Spinal nerves C1-C7 exit the vertebral canal:
Above their corresponding vertebrae.
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Spinal nerve C8 exits the vertebral canal between:
C7 and T1.
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Spinal nerves T1-L5 exit the vertebral canal:
Below their corresponding vertebrae.
41
How do the sacral and coccygeal spinal nerves exit the spinal cord?
The roots enter the sacral canal. S1-S4 nerves exit the sacral canal via the 4 pairs of anterior and posterior sacral foramina. S5 and Co1 nerves exit the sacral canal via the sacral hiatus.
42
Where do the anterior and posterior roots of each spinal nerve unite?
Intervertebral foramen.
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What do the anterior and posterior roots contain?
Anterior: motor axons. Posterior: sensory axons.
44
Is a spinal nerve a sensory nerve, motor nerve or mixed nerved?
Mixed nerve.
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Endoneurium.
Innermost layer that wraps around individual axons within a nerve. Made of collage fibres, fibroblasts, macrophages and connective tissue.
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Perineurium.
Middle layer around fascicles. Made of thick connective tissue, 15 layers of fibroblasts, and collagen fibres.
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What fills the spaces between fascicles.
Extensions of epineurium.
48
Rami.
Spinal nerves divide into several branches after passing through intervertebral foramen.
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Posterior/dorsal ramus.
Serves the deep muscles and skin of the posterior surface of the trunk.
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Anterior/ventral ramus.
Serves the muscles and structures of the upper and lower limbs, and the skin of the lateral and anterior surfaces of the trunk.
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Meningeal branch.
Re-enters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of spinal cord and meninges.
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Rami communicantes.
Components of autonomic nervous system.
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Plexuses.
Axons from anterior rami of spinal nerves (except T2-T12) do not go directly to the body structures they supply. They form networks on both sides of the body by joining with various numbers of axons from anterior rami of adjacent nerves.
54
Cervical plexus.
Formed by anterior rami of C1-C4 nerves with contributions from C5. There is one on each side of the neck alongside C1-C4. Supplies skin and muscles of head, neck, superior shoulders and chest. Anterior rami of C3-C5 are involved in breathing (diaphragm).
55
Brachial plexus.
Formed by anterior rami of C5-T1 nerves. Extends inferiorly and laterally on either side of these vertebrae, passing above the first rib and entering the axilla. Provides almost the entire nerve supply of the shoulders and upper limbs.
56
Lumbar plexus.
Formed by anterior rami of L1-L4 nerves. Supplies the anterolateral abdominal wall, external genitals, and lower limbs.
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Sacral plexus.
Formed by anterior rami of L4-L5 and S1-S4 nerves. Supplies buttocks, perineum, and lower limbs.
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What is the largest nerve in the body, and where does it arise?
Sciatic nerve. Arises from sacral plexus.
59
Intercostal nerves.
The anterior rami of spinal nerves T2-T12 do not enter into the plexuses, and are known as intercostal nerves or thoracic nerves. They directly connect to the structures that they supply.
60
Dermatome.
An area of the skin that provides sensory input to the CNS via a pair of spinal nerves. Allows for the determination of damaged regions of spinal cord.
61
What are the functions of the spinal cord?
Propagate nerve impulses and integrate information.
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What is the function of the white matter in the spinal cord?
Propagate sensory and motor information.
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What is the function of gray matter in the spinal cord?
Receive and integrate incoming and outgoing information.
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What are the main routes that allow sensory impulses to travel to the brain?
Spinothalamic tract and posterior column.
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Spinothalamic tract.
Conveys nerve impulses for pain, temperature, itch, tickle.
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Posterior column.
Consists of the gracile fasciculus and the cuneate fasciculus. Convey nerve impulses for touch, pressure, vibration, conscious proprioception.
67
What are the main pathways that allow motor impulses to travel down the spinal cord?
Direct motor pathways (pyramidal) and indirect motor pathways (extrapyramidal).
68
Direct motor pathways.
Consist of the lateral corticospinal tract, the anterior corticospinal tract, and the corticobulbar tract. Convey nerve impulses that originate in the cerebral cortex. Destined to cause voluntary movements of skeletal muscles.
69
Indirect motor pathways.
Consist of the rubrospinal tract, the tectospinal tract, the vestibulospinal tract, the lateral reticulospinal tract, and the medial reticulospinal tract. Convey nerve impulses from the brainstem to cause automatic movements, coordinate body movements with visual stimuli, maintain skeletal muscle tone, sustain contraction of postural muscles, and regulate muscle tone in response to head movements.
70
Reflex.
Involuntary unplanned sequence of actions that occurs in response to a particular stimulus.
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Spinal reflex.
When integration takes place in spinal cord gray matter. Example: knee jerk.
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Cranial reflex.
When integration takes place in the brainstem. Example: tracking movements of eyes when reading.
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Somatic reflex.
Involve contraction of skeletal muscles.
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Autonomic/visceral reflex.
Not consciously perceived. Involve smooth muscle, cardiac muscle, gland responses, heart rate, digestion and urination.
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Monosynaptic reflex arc.
A reflex pathway with one synapse in the CNS. Ipsilateral.
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Polysynaptic reflex arc.
A reflex pathway with more than one synapse in the CNS.
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Stretch reflex.
Somatic spinal reflex. Causes contraction of a skeletal muscle in response to stretching of the muscle. Helps maintain posture.
78
What type of reflex arc is involved in a stretch reflex?
Monosynaptic reflex arc.
79
How can you elicit a stretch reflex?
By tapping on tendons attached to muscles at the elbow, wrist, knee and ankle joints.
80
Why would a muscle contract after it is stretched?
To relieve the stretching.
81
How is the stretch reflex protective?
It prevents injury by preventing overstretching of muscles.
82
Describe the steps that occur in a stretch reflex.
Stretching of a muscle stimulates muscle spindles --> generate nerve impulses that propagate along a somatic sensory neuron --> through posterior root of spinal nerve --> into spinal cord --> synapse with motor neuron in anterior gray horn --> nerve impulses propagate along motor neuron axon into anterior root --> through peripheral nerve --> to stimulated muscle --> forms NMJs with skeletal muscle fibres of stretched muscle --> ACh released at NMJss triggers muscle APs in the stretched muscle --> contraction.
83
What also happens during a stretch reflex?
A polysynaptic reflex arc to the antagonist muscles. Involves 3 neurons and 2 synapses. An axon collateral from the sensory neuron synapses with inhibitory interneuron in integrating centre --> synapses with and inhibits motor neuron that normally excites antagonist muscles --> antagonist muscles relax while stretched muscle contracts.
84
Reciprocal innervation.
When the components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonists.
85
Tendon reflex.
Ipsilateral. Operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn.
86
How does the tendon reflex relate to the stretch reflex?
The tendon reflex is less sensitive than the stretch reflex, but it can override the stretch reflex when tension is great (which can make you drop a very heavy weight).
87
What are sensory receptors for the tendon reflex?
Tendon organs. Detect and respond to changes in muscle tension that are caused by passive stretching or muscular contraction.
88
Why does the frequency of inhibitory impulses increase as tension on the tendon organ increases?
Inhibition of the motor neurons to the muscle developing excess tension causes relaxation of the muscle.
89
Describe the steps that occur in the tendon reflex.
Tension on tendon organ increases --> tendon organ is stimulated --> nerve impulses propagate to spinal cord along sensory neuron --> stimulates an inhibitory interneuron that synapses with a motor neuron --> inhibits/hyperpolarizes motor neuron --> muscle relaxes and relieves excess tension.
90
Flexor and cross extensor reflexes.
Are polysynaptic reflexes.
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Flexor reflex.
Ipsilateral. Moves a limb away from the source of a possibly damaging stimulus. Involves contraction of more than one muscle group.
92
What reflex arc is involved in the flexor reflex?
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, allowing a single sensory neuron to activate several motor neurons and effectors.
93
Describe the steps that occur in the flexor reflex.
Step on a tack --> dendrites of pain-sensitive neuron are stimulated --> nerve impulses propagate to spinal cord --> sensory neuron activates interneurons --> extend to several spinal cord segments --> activate motor neurons --> generate nerve impulses which propagate to axon terminals --> ACh is released by motor neurons --> flexor muscles in thigh contract and withdraw the leg.
94
Cross extensor reflex.
Contralateral. Maintain balance.
95
Describe the steps that occur in the cross extensor reflex.
Step on a tack with right foot --> sensory receptor of pain-sensitive neuron is stimulated --> nerve impulses propagate to spinal cord --> sensory neuron activates interneurons --> synapse with motor neurons on left side of spinal cord --> motor neurons generate APs which propagate to axon terminals --> ACh released by motor neurons causes extensor muscles of thigh of unstimulated left limb to contract --> left leg extension --> support body while right foot is contracting from the tack.
