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BIOL 235 Human Anatomy and Physiology > Chapter 13: The Spinal Cord and Spinal Nerves > Flashcards

Chapter 13: The Spinal Cord and Spinal Nerves Flashcards

1
Q

What is the role of the spinal cord in homeostasis?

A

The spinal cord contributes to homeostasis by providing quick, reflexive responses to stimuli, serving as the pathway for sensory input to the brain and motor output from the brain.

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2
Q

What are the protective structures of the spinal cord?

A

The spinal cord is protected by the vertebral column, meninges (dura mater, arachnoid mater, pia mater), and cerebrospinal fluid (CSF) in the subarachnoid space.

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3
Q

What is the function of the meninges?

A

The meninges (dura mater, arachnoid mater, pia mater) protect the spinal cord and brain, providing cushioning and a shock-absorbing environment, and enclosing CSF.

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4
Q

Describe the anatomy of the vertebral column in relation to the spinal cord.

A

The vertebral column surrounds the spinal cord in the vertebral canal, formed by stacked vertebrae. It provides protection for the spinal cord against injury.

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5
Q

What is the significance of CSF in protecting the spinal cord?

A

CSF provides a buoyant environment that suspends the spinal cord, acting as a shock absorber to protect it from mechanical damage.

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6
Q

What is the function of the dura mater?

A

The dura mater is the thick, outermost meningeal layer that provides mechanical protection for the spinal cord. It forms a sac that extends from the foramen magnum to the second sacral vertebra.

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7
Q

What is the role of the arachnoid mater?

A

The arachnoid mater is the middle layer of the meninges, consisting of a delicate web of fibers, and it lies between the dura mater and pia mater. It has a subdural space filled with interstitial fluid.

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8
Q

What is the function of the pia mater?

A

Directly adheres to the spinal cord and brain. It contains blood vessels that supply oxygen and nutrients to the spinal cord.

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9
Q

What is the anatomical structure of the spinal cord?

A

The spinal cord extends from the medulla oblongata to the second lumbar vertebra in adults. It has enlargements at the cervical and lumbar regions where nerves to the limbs arise.

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10
Q

What are the cervical, brachial, lumbar, sacral, and coccygeal plexuses?

A

These are networks of nerves that emerge from specific spinal cord regions: cervical (C1–C5), brachial (C5–T1), lumbar (L1–L4), sacral (L4–S4), and coccygeal (Co1).

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11
Q

What is the function of the cervical enlargement?

A

The cervical enlargement, located from C4 to T1, gives rise to nerves that control the upper limbs.

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12
Q

What is the function of the lumbosacral enlargement?

A

T9-T12, gives rise to nerves controlling the lower limbs.

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13
Q

What is the conus medullaris?

A

The conus medullaris is the tapered end of the spinal cord, which ends at the L1-L2 level in adults.

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14
Q

What is the filum terminale?

A

The filum terminale is an extension of the pia mater that anchors the spinal cord to the coccyx.

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15
Q

How are spinal nerves connected to the spinal cord?

A

Spinal nerves connect to the spinal cord through roots (dorsal and ventral), which contain sensory and motor axons, respectively.

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16
Q

What is the cauda equina?

A

The cauda equina is a bundle of nerve roots from the lumbar, sacral, and coccygeal regions that extend inferiorly from the conus medullaris within the vertebral canal.

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17
Q

How do spinal nerves exit the vertebral column?

A

Spinal nerves exit the vertebral column through the intervertebral foramina between adjacent vertebrae, with the nerve roots angling inferiorly in lower spinal regions.

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18
Q

What are the major components of the spinal cord’s white matter?

A

The white matter of the spinal cord consists primarily of myelinated axons that form sensory and motor tracts connecting the spinal cord to the brain.

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19
Q

What is the role of gray matter in the spinal cord?

A

The gray matter in the spinal cord contains the cell bodies of neurons and interneurons. It is involved in processing and integrating sensory and motor information.

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20
Q

What is a reflex arc?

A

A reflex arc is the neural pathway involved in a reflex action, consisting of sensory neurons, interneurons (if present), motor neurons, and an effector organ.

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21
Q

How do reflexes contribute to homeostasis?

A

Reflexes provide rapid, automatic responses to stimuli, helping to maintain homeostasis by protecting the body from harm (e.g., withdrawal from a painful stimulus).

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22
Q

What are some examples of reflexes involving the spinal cord?

A

Examples include the withdrawal reflex (e.g., pulling away from a hot object) and the patellar reflex (knee-jerk response).

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23
Q

What is the first step in how the spinal cord processes sensory input and motor output?

A

Sensory receptors detect sensory stimuli.

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24
Q

What happens after sensory neurons transmit input as nerve impulses from sensory receptors?

A

Sensory neurons transmit input along their axons from sensory receptors into the spinal nerve and posterior root. From there, they can follow one of three paths: (1) ascend to the brain, (2) synapse with interneurons, or (3) connect to motor neurons.

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25
Q

What is the second path that sensory neuron axons may follow after entering the posterior gray horn?

A

Sensory neuron axons may synapse with interneurons in the posterior gray horn, whose axons then ascend to the brain via the white matter of the spinal cord as part of a sensory tract.

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26
Q

What is the third path that sensory neuron axons may follow after entering the posterior gray horn?

A

Sensory neuron axons may synapse with interneurons in the posterior gray horn, which connect to somatic motor neurons for spinal reflexes (reflex arc).

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27
Q

What does motor output to skeletal muscles involve?

A

Motor output to skeletal muscles involves somatic motor neurons of the anterior gray horn, which are regulated by the brain through motor tracts that descend into the spinal cord.

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28
Q

How do somatic motor neurons send motor output to skeletal muscles?

A

When activated, somatic motor neurons send motor output nerve impulses along their axons, through the anterior gray horn and anterior root to enter the spinal nerve, extending to skeletal muscles.

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29
Q

What is involved in motor output to cardiac muscle, smooth muscle, and glands?

A

Motor output to cardiac muscle, smooth muscle, and glands involves autonomic motor neurons in the lateral gray horn, which send motor output nerve impulses through the anterior gray horn and root to enter the spinal nerve.

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30
Q

How do autonomic motor neurons in the spinal cord interact with peripheral autonomic motor neurons?

A

Autonomic motor neuron axons from the spinal cord synapse with a second group of autonomic motor neurons located in the PNS. These axons then synapse with cardiac muscle, smooth muscle, and glands.

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31
Q

How does the amount of gray matter vary across different spinal cord segments?

A

Gray matter is larger in the cervical and lumbar segments, which are responsible for sensory and motor innervation of the limbs.

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32
Q

Why does the amount of white matter decrease from cervical to sacral segments of the spinal cord?

A

As the spinal cord ascends, more ascending axons are added, increasing white matter. As it descends, the motor tracts decrease in thickness because more descending axons leave to synapse with neurons in the gray matter.

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33
Q

What are the distinguishing characteristics of the cervical spinal segment?

A

Has a relatively large diameter, large amounts of white matter, and an oval shape. C1–C4 have a large posterior gray horn and small anterior gray horn, while C5+ have enlarged posterior gray horns and well-developed anterior gray horns.

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34
Q

What are the distinguishing characteristics of the thoracic spinal segment?

A

The thoracic segment has a small diameter due to relatively small amounts of gray matter. Except for the first thoracic segment, the gray horns are small, with a small lateral gray horn present.

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35
Q

What are the distinguishing characteristics of the lumbar spinal segment?

A

Is nearly circular, with very large anterior and posterior gray horns. There is a small lateral gray horn in the upper segments, and it has relatively less white matter.

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36
Q

What are the distinguishing characteristics of the sacral spinal segment?

A

Is relatively small but has large amounts of gray matter, relatively small amounts of white matter, and the anterior and posterior gray horns are large and thick.

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37
Q

What are the distinguishing characteristics of the coccygeal spinal segment?

A

Resembles the lower sacral spinal segments but is much smaller.

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38
Q

What are spinal nerves, and what is their function?

A

Spinal nerves are associated with the spinal cord and are bundles of axons and neuroglial cells wrapped in connective tissue. They connect the CNS to the PNS.

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39
Q

How are spinal nerves named and numbered?

A

Based on the region and level of the vertebral column from which they emerge. There are 31 pairs.

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40
Q

Where does the spinal cord end, and what is the arrangement of the lumbar, sacral, and coccygeal nerves?

A

Near the superior border of L2. The roots of the lumbar, sacral, and coccygeal nerves descend at an angle to reach their respective foramina before emerging, forming the cauda equina.

41
Q

Where does the first cervical pair of spinal nerves emerge from?

A

Between the occipital bone and C1

42
Q

How do spinal nerves exit the vertebral canal?

A

C1–C7 exit above their vertebrae. C8 exits between C7 and T1. T1–L5 exit below their vertebrae. Sacral and coccygeal nerves exit the sacral canal.

43
Q

What is the structure of a typical spinal nerve at the spinal cord?

A

Has posterior root (sensory axons) and anterior root (motor axons). The posterior root contains a spinal ganglion with sensory neuron cell bodies. These roots unite at the intervertebral foramen to form a mixed spinal nerve.

44
Q

What are the connective tissue coverings of spinal nerves?

A

Endoneurium (around individual axons), perineurium (around nerve fascicles), and epineurium (around the entire nerve). The dura mater of the spinal meninges fuses with the epineurium as the nerve passes through the intervertebral foramen.

45
Q

What is the function of the different branches/rami of a spinal nerve?

A

The posterior ramus serves the deep muscles and skin of the posterior trunk. The anterior ramus serves the muscles and skin of the limbs and the anterior trunk. The meningeal branch supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges. The communicating rami are components of the autonomic nervous system.

46
Q

What is a plexus, and what are the major plexuses in the body?

A

A network of axons formed by the anterior rami of spinal nerves, except T2-T12. Cervical, brachial, lumbar, sacral, and coccygeal plexuses. They give rise to nerves that supply specific regions.

47
Q

What are intercostal nerves, and what do they supply?

A

Intercostal nerves are the anterior rami of spinal nerves T2-T12, which do not form plexuses. They directly connect to the structures in the intercostal spaces, including the intercostal muscles, abdominal muscles, and skin over the chest and abdomen.

48
Q

What are dermatomes, and how are they useful?

A

Dermatomes are regions of skin supplied by sensory neurons from a single spinal nerve. They are useful for locating damaged spinal cord regions. If sensation in a specific dermatome is lost, the corresponding nerves are likely damaged. Dermatomes overlap, so damage to one nerve may not result in significant loss of sensation.

49
Q

How can knowledge of dermatomes be applied therapeutically?

A

Knowledge of dermatomes can be used to block pain by cutting posterior roots or using local anesthetics. Complete anesthesia of a region may require cutting or blocking multiple adjacent spinal nerves due to overlapping dermatomes.

50
Q

What forms the cervical plexus?

A

The cervical plexus is formed by the roots (anterior rami) of the first four cervical nerves (C1–C4), with contributions from C5.

51
Q

Where is the cervical plexus located?

A

The cervical plexus is located on each side of the neck alongside the first four cervical vertebrae.

52
Q

What does the cervical plexus supply?

A

The cervical plexus supplies the skin and muscles of the head, neck, and superior part of the shoulders and chest.

53
Q

What forms the brachial plexus?

A

The brachial plexus is formed by the roots (anterior rami) of spinal nerves C5–C8 and T1.

54
Q

Where is the brachial plexus located?

A

The brachial plexus extends inferiorly and laterally on either side of the last four cervical and first thoracic vertebrae, passes above the first rib posterior to the clavicle, and enters the axilla.

55
Q

What does the brachial plexus supply?

A

The brachial plexus provides almost the entire nerve supply of the shoulders and upper limbs.

56
Q

What forms the lumbar plexus?

A

The lumbar plexus is formed by the roots (anterior rami) of spinal nerves L1–L4.

57
Q

What is the primary function of the lumbar plexus?

A

The lumbar plexus supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs.

58
Q

What forms the sacral plexus?

A

The sacral plexus is formed by the roots (anterior rami) of spinal nerves L4–L5 and S1–S4.

59
Q

Where is the sacral plexus located?

A

The sacral plexus is situated largely anterior to the sacrum.

60
Q

What does the sacral plexus supply?

A

The sacral plexus supplies the buttocks, perineum, and lower limbs.

61
Q

What is the largest nerve that arises from the sacral plexus?

A

The sciatic nerve, which is the largest nerve, arises from the sacral plexus

62
Q

What are the two principal functions of the spinal cord in maintaining homeostasis?

A

The two principal functions of the spinal cord in maintaining homeostasis are nerve impulse propagation and integration of information.

63
Q

How does the white matter of the spinal cord function?

A

The white matter contains sensory and motor tracts, which act as highways for nerve impulse propagation—sensory input travels toward the brain, and motor output travels from the brain toward effector tissues.

64
Q

What does the gray matter of the spinal cord do?

A

The gray matter receives and integrates incoming and outgoing information.

65
Q

What are the two main sensory pathways in the spinal cord?

A

The two main sensory pathways in the spinal cord are the spinothalamic tract and the posterior funiculi.

66
Q

What types of sensory information does the spinothalamic tract carry?

A

The spinothalamic tract carries nerve impulses for sensing pain, temperature, itch, and tickle.

67
Q

What types of sensory information are conveyed by the posterior funiculi?

A

The posterior funiculi convey nerve impulses for touch, pressure, vibration, and conscious proprioception (awareness of the positions and movements of muscles, tendons, and joints).

68
Q

What is the difference between direct and indirect motor pathways in the spinal cord?

A

Direct motor pathways (pyramidal pathways) convey voluntary movement signals from the cerebral cortex to skeletal muscles, while indirect motor pathways (extrapyramidal pathways) help coordinate body movements with visual stimuli and regulate muscle tone and equilibrium.

69
Q

What types of muscles are involved in autonomic reflexes?

A

Autonomic reflexes involve smooth muscle, cardiac muscle, and glands.

70
Q

What are the five functional components of a reflex arc?

A

The five components of a reflex arc are: 1) Sensory receptor, 2) Sensory neuron, 3) Integrating center, 4) Motor neuron, 5) Effector.

71
Q

What happens in the sensory receptor component of a reflex arc?

A

The sensory receptor responds to a specific stimulus by producing a graded potential called a generator potential, which can trigger nerve impulses in the sensory neuron if it reaches the threshold depolarization.

72
Q

What occurs in the integrating center of a reflex arc?

A

The integrating center processes the nerve impulses, which may involve one or more synapses between sensory neurons, motor neurons, and sometimes interneurons.

73
Q

What is a monosynaptic reflex arc?

A

A monosynaptic reflex arc involves only one synapse between a sensory neuron and a motor neuron, such as in the patellar reflex.

74
Q

What is a polysynaptic reflex arc?

A

A polysynaptic reflex arc involves more than two types of neurons and more than one CNS synapse.

75
Q

What is the effector in a reflex arc?

A

The effector is the part of the body that responds to the motor nerve impulse, like a muscle or gland.

76
Q

What is the difference between somatic and autonomic reflexes?

A

Somatic reflexes involve skeletal muscle contractions, while autonomic reflexes involve smooth muscle, cardiac muscle, or gland responses.

77
Q

What is the stretch reflex, and how does it function?

A

The stretch reflex is a monosynaptic reflex that causes muscle contraction in response to stretching, helping to prevent overstretching. It involves sensory neurons, motor neurons, and an integrating center in the spinal cord.

78
Q

What role do muscle spindles play in the stretch reflex?

A

Muscle spindles monitor changes in muscle length and generate nerve impulses in response to stretching.

79
Q

What happens when a muscle spindle is stretched?

A

When a muscle spindle is stretched, it generates nerve impulses that travel through the sensory neuron to the spinal cord, where they activate motor neurons causing the muscle to contract.

80
Q

What is reciprocal innervation?

A

Reciprocal innervation is when a neural circuit causes contraction of one muscle and relaxation of its antagonistic muscle at the same time, preventing conflict between opposing muscles.

81
Q

How does the brain regulate muscle spindle sensitivity?

A

The brain regulates muscle spindle sensitivity through smaller motor neurons that innervate muscle spindles, ensuring proper signaling over a wide range of muscle lengths during voluntary and reflex contractions.

82
Q

How does the stretch reflex help maintain posture?

A

The stretch reflex helps maintain posture by activating muscles, like calf muscles, to contract when they are stretched, helping the body respond to changes in position.

83
Q

What is an example of a reflex that involves the brainstem rather than the spinal cord?

A

An example of a reflex involving the brainstem is the tracking movement of the eyes when reading a sentence.

84
Q

What is the function of the tendon reflex?

A

The tendon reflex controls muscle tension by causing muscle relaxation to prevent tendon damage from excessive force.

85
Q

How does the tendon reflex compare to the stretch reflex?

A

The tendon reflex is less sensitive than the stretch reflex and can override it when tension is great, such as when dropping a heavy weight.

86
Q

Where are the sensory receptors for the tendon reflex located?

A

The sensory receptors are called tendon (Golgi tendon) organs and are located within a tendon near its junction with a muscle.

87
Q

What do tendon organs detect?

A

Tendon organs detect changes in muscle tension caused by passive stretch or muscular contraction.

88
Q

How does the tendon reflex operate?

A

The tendon reflex is polysynaptic. When tension increases on a tendon, sensory neurons activate an inhibitory interneuron that relaxes the muscle by inhibiting motor neurons.

89
Q

What role does the excitatory interneuron play in the tendon reflex?

A

The excitatory interneuron activates motor neurons controlling antagonistic muscles, causing them to contract while the muscle attached to the tendon organ relaxes.

90
Q

What is reciprocal innervation in the tendon reflex?

A

Reciprocal innervation refers to the simultaneous contraction of antagonistic muscles and relaxation of the muscle attached to the tendon organ.

91
Q

How does the tendon reflex protect muscles and tendons?

A

It prevents damage by inhibiting motor neurons when tension increases, causing muscle relaxation and relieving excess tension.

92
Q

What is the flexor reflex?

A

The flexor reflex (withdrawal reflex) causes a body part to withdraw in response to a painful stimulus, such as stepping on a tack.

93
Q

How does the flexor reflex operate?

A

The sensory neuron from the painful stimulus activates interneurons that stimulate motor neurons to contract flexor muscles, withdrawing the limb.

94
Q

What is an intersegmental reflex arc?

A

An intersegmental reflex arc involves a sensory neuron activating motor neurons in multiple spinal cord segments, controlling several muscles at once.

95
Q

What happens when you step on a tack regarding balance?

A

The pain also initiates the crossed extensor reflex to help maintain balance by causing extension of the opposite limb.

96
Q

How does the crossed extensor reflex operate?

A

The sensory neuron from the painful stimulus activates interneurons that excite motor neurons to extend the opposite limb for balance.

97
Q

What is the difference between the flexor and crossed extensor reflexes?

A

The flexor reflex is ipsilateral (same side of the body), while the crossed extensor reflex is contralateral (opposite side of the body).

98
Q

What is reciprocal innervation in the flexor and crossed extensor reflexes?

A

In both reflexes, when one set of muscles contracts (e.g., flexors in the stimulated limb), the antagonistic muscles (e.g., extensors) relax to prevent conflict between them.

BIOL 235 Human Anatomy and Physiology (5 decks)

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