Chapter 13 The Spinal Cord and Spinal Nerves Flashcards
What are the protective structures of the spinal cord?
- Skull and vertebral column
- Meninges
- Cerebrospinal fluid (CSF) in the subarachnoid space
The meninges consist of three layers: dura mater, arachnoid mater, and pia mater.
What are the three layers of the meninges from superficial to deep?
- Dura mater
- Arachnoid mater
- Pia mater
The meninges encircle the spinal cord and brain, providing protection.
What is the function of the spinal cord in relation to homeostasis?
Provides quick, reflexive responses to stimuli
It acts as a pathway for sensory input to the brain and motor output from the brain.
What is a reflex arc?
The functional components of a reflex pathway
Reflex arcs contribute to homeostasis by enabling rapid responses.
Define a plexus.
A network of intersecting nerves
The main spinal nerve plexuses include cervical, brachial, lumbar, sacral, and coccygeal plexuses.
What are the major spinal nerve plexuses?
- Cervical Plexus (C1-C5)
- Brachial Plexus (C5-T1)
- Lumbar Plexus (L1-L4)
- Sacral Plexus (L4-S4)
- Coccygeal Plexus (Co1)
Each plexus innervates specific body regions.
What is the cervical enlargement?
An enlargement of the spinal cord that extends from C4 to T1
Nerves to and from the upper limbs arise from this region.
What are the functions of the major sensory and motor tracts in the spinal cord?
- Conduct sensory input to the brain
- Conduct motor output from the brain
These tracts function as pathways for nerve impulses.
Where does the spinal cord terminate in adults?
Between the first and second lumbar vertebrae (L1–L2)
In newborns, it extends to the third or fourth lumbar vertebra.
What is the cauda equina?
The bundle of spinal nerves that angle inferiorly in the vertebral canal
The term means ‘horse’s tail’ and consists of lumbar, sacral, and coccygeal nerves.
What is the central canal of the spinal cord?
A small space in the gray commissure filled with cerebrospinal fluid (CSF)
It extends the entire length of the spinal cord.
Fill in the blank: The anterior median fissure is a ______ on the anterior side of the spinal cord.
[wide groove]
What are the two types of roots connecting spinal nerves to the spinal cord?
- Posterior (dorsal) root
- Anterior (ventral) root
The posterior root contains sensory axons, while the anterior root contains motor axons.
True or False: The white matter of the spinal cord contains unmyelinated axons.
False
The white matter primarily consists of myelinated axons.
What are the regions of gray matter in the spinal cord called?
Horns
They are divided into anterior (ventral), posterior (dorsal), and lateral gray horns.
What is the function of the posterior gray horns?
Contain axons of incoming sensory neurons and interneurons
They are involved in processing sensory information.
What is the role of somatic motor neurons?
Provide nerve impulses for contraction of skeletal muscles
Somatic motor neurons are primarily located in the anterior gray horn.
What are the two main types of motor neurons involved in the spinal cord?
Somatic motor neurons and autonomic motor neurons
Somatic motor neurons control skeletal muscles, while autonomic motor neurons control cardiac muscle, smooth muscle, and glands.
What is the somatic motor neuron path that sends motor output to effectors?
Along their axons, through the anterior gray horn and anterior root to enter the spinal nerve
From the spinal nerve, somatic motor neuron axons extend to skeletal muscles.
What is the role of autonomic motor neurons in the spinal cord?
Motor output to cardiac muscle, smooth muscle, and glands
They are located in the lateral gray horn and send impulses to peripheral autonomic motor neurons.
Which spinal cord segments have the largest amount of gray matter?
Cervical and lumbar segments
These segments are responsible for sensory and motor innervation of the limbs.
What happens to the amount of white matter as you move from cervical to sacral segments of the spinal cord?
The amount of white matter decreases
More ascending axons are added in the cervical segments, while motor tracts decrease in thickness as you go down.
What are the distinguishing characteristics of the cervical spinal cord segment?
Larger diameter and more white matter; enlarged posterior and anterior gray horns in lower cervical segments
The upper cervical segments have a large posterior gray horn but a smaller anterior gray horn.
What is the function of spinal nerves?
Connect the CNS to sensory receptors, muscles, and glands
There are 31 pairs of spinal nerves named according to the vertebral column region from which they emerge.
What is the cauda equina?
The roots of lumbar, sacral, and coccygeal nerves that descend at an angle to reach their foramina
This occurs because the spinal cord ends near the superior border of L2.
What is a mixed nerve?
A spinal nerve containing both sensory and motor axons
The posterior root contains sensory axons, while the anterior root contains motor axons.
What are the three protective connective tissue coverings of spinal nerves?
Endoneurium, perineurium, epineurium
Endoneurium wraps individual axons, perineurium wraps nerve fascicles, and epineurium covers the entire nerve.
Which spinal nerves are known as intercostal nerves?
T2–T12
These nerves connect directly to the structures they supply in the intercostal spaces.
Define a dermatome.
An area of skin that provides sensory input to the CNS via one pair of spinal nerves
Adjacent dermatomes overlap, which can help locate damaged spinal cord regions.
What forms the cervical plexus?
Anterior rami of C1–C4 with contributions from C5
It supplies the skin and muscles of the head, neck, and upper part of the shoulders and chest.
What does the brachial plexus supply?
Nerve supply of the shoulders and upper limbs
It is formed by the anterior rami of C5–C8 and T1.
What is the main function of the spinal cord?
Nerve impulse propagation and integration of information
It serves as an integrating center for reflexes.
What are the two main sensory tracts in the spinal cord?
Spinothalamic tract and posterior funiculi
The spinothalamic tract senses pain and temperature, while the posterior funiculi convey touch and pressure.
What are the two types of descending motor pathways?
Direct (pyramidal) and indirect (extrapyramidal) pathways
Direct pathways originate from the cerebral cortex, while indirect pathways involve brainstem structures.
What is a reflex?
A fast, involuntary, unplanned sequence of actions that occurs in response to a stimulus
Reflexes can be inborn or learned.
What is the difference between a spinal reflex and a cranial reflex?
Spinal reflex integration occurs in the spinal cord; cranial reflex integration occurs in the brainstem
An example of a spinal reflex is the patellar reflex.
What is a reflex?
A reflex is a rapid, involuntary response to a specific stimulus.
What are inborn reflexes?
Inborn reflexes are reflexes that occur naturally, such as pulling your hand away from a hot surface.
What is a spinal reflex?
A spinal reflex is a reflex that occurs when integration takes place in the spinal cord gray matter.
What is a cranial reflex?
A cranial reflex is a reflex where integration occurs in the brainstem rather than the spinal cord.
What are somatic reflexes?
Somatic reflexes involve contraction of skeletal muscles.
What are autonomic (visceral) reflexes?
Autonomic reflexes involve responses of smooth muscle, cardiac muscle, and glands, and are generally not consciously perceived.
What is a reflex arc?
A reflex arc is the pathway followed by nerve impulses that produce a reflex.
What are the five functional components of a reflex arc?
- Sensory receptor
- Sensory neuron
- Integrating center
- Motor neuron
- Effector
What is the role of a sensory receptor in a reflex arc?
The sensory receptor responds to a specific stimulus by producing a graded potential.
What is a monosynaptic reflex arc?
A monosynaptic reflex arc involves a single synapse between a sensory neuron and a motor neuron.
What is a polysynaptic reflex arc?
A polysynaptic reflex arc involves more than two types of neurons and more than one CNS synapse.
What is reciprocal innervation?
Reciprocal innervation is when one muscle contracts while its antagonist relaxes, preventing conflict between opposing muscles.
What is the stretch reflex?
The stretch reflex causes contraction of a skeletal muscle in response to stretching of the muscle.
Fill in the blank: The _______ reflex operates as a feedback mechanism to control muscle tension.
[tendon]
What are tendon organs?
Tendon organs are sensory receptors that respond to changes in muscle tension.
What is the flexor (withdrawal) reflex?
The flexor reflex is a protective reflex that causes withdrawal of a limb from a painful stimulus.
What is the crossed extensor reflex?
The crossed extensor reflex helps maintain balance by causing extension of the opposite limb when one limb withdraws from a painful stimulus.
How many pairs of spinal nerves are there?
There are 31 pairs of spinal nerves.
What are the three connective tissue coverings associated with spinal nerves?
- Endoneurium
- Perineurium
- Epineurium
What is the function of the anterior rami of spinal nerves?
The anterior rami form networks called plexuses, except for T2–T12 which are intercostal nerves.
True or False: All spinal nerves contain both sensory and motor axons.
True
What is the spinal cord protected by?
- Vertebral column
- Meninges
- CSF
- Denticulate ligaments
What are the three meninges that cover the spinal cord?
- Dura mater
- Arachnoid mater
- Pia mater
What is the conus medullaris?
The conus medullaris is the tapered inferior portion of the spinal cord.
What are the branches of a spinal nerve?
The branches include the posterior ramus, anterior ramus, meningeal branch, and communicating rami.
What do the anterior rami of spinal nerves, except T2–T12, form?
Networks of nerves called plexuses.
What are intercostal nerves?
Anterior rami of nerves T2–T12 that do not form plexuses and are distributed directly to structures in intercostal spaces.
What are dermatomes?
Specific, constant segments of the skin served by sensory neurons within spinal nerves.
Why is knowledge of dermatomes important?
It helps determine which segment of the spinal cord or which spinal nerve is damaged.
What forms the cervical plexus?
The roots (anterior rami) of the first four cervical nerves C1–C4, with contributions from C5.
What do the nerves of the cervical plexus supply?
The skin and muscles of the head, neck, upper part of the shoulders, and innervate the diaphragm.
What forms the brachial plexus?
The roots (anterior rami) of spinal nerves C5–C8 and T1.
What do the nerves of the brachial plexus supply?
The upper limbs and several neck and shoulder muscles.
What forms the lumbar plexus?
The roots (anterior rami) of spinal nerves L1–L4.
What do the nerves of the lumbar plexus supply?
The anterolateral abdominal wall, external genitals, and part of the lower limbs.
What forms the sacral plexus?
The roots (anterior rami) of spinal nerves L1–L5 and S1–S4.
What do the nerves of the sacral plexus supply?
The buttocks, perineum, and part of the lower limbs.
What forms the coccygeal plexus?
The roots (anterior rami) of the spinal nerves S4–S5 and the coccygeal nerves.
What do the nerves of the coccygeal plexus supply?
The skin of the coccygeal region.
What are the two main functions of the spinal cord?
- Highway for nerve impulse propagation * Integrating center for spinal reflexes.
What are the main routes for sensory input in the white matter of the spinal cord?
- Posterior columns/funiculi * Spinothalamic tract.
What are the main routes for motor output in the white matter of the spinal cord?
- Direct pathways * Indirect pathways.
What is a reflex?
A fast, predictable sequence of involuntary actions in response to changes in the environment.
What are the components of a reflex arc?
- Sensory receptor * Sensory neuron * Integrating center * Motor neuron * Effector.
What types of reflexes are somatic spinal reflexes?
- Stretch reflex * Tendon reflex * Flexor reflex * Crossed extensor reflex.
What is a monosynaptic reflex arc?
A reflex arc that consists of one sensory neuron and one motor neuron.
What is an example of a stretch reflex?
The patellar reflex.
What is the nature of the stretch reflex?
Ipsilateral and important in maintaining muscle tone.
What does a polysynaptic reflex arc contain?
- Sensory neurons * Interneurons * Motor neurons.
What is the purpose of the tendon reflex?
To prevent damage to muscles and tendons when muscle force becomes too extreme.
What does the flexor reflex do?
Moves a limb away from the source of a painful stimulus.
What is the function of the crossed extensor reflex?
Extends the limb contralateral to a painfully stimulated limb.
What are some important somatic reflexes used to diagnose disorders?
- Patellar reflex * Achilles reflex * Babinski sign * Abdominal reflex.
