Podcast
Questions and Answers
What primarily fills the subarachnoid space surrounding the spinal cord?
What primarily fills the subarachnoid space surrounding the spinal cord?
Which layer of the meninges is the thickest and most durable?
Which layer of the meninges is the thickest and most durable?
What is the function of the cauda equina?
What is the function of the cauda equina?
Which structural component is primarily responsible for containing neuron cell bodies within the spinal cord?
Which structural component is primarily responsible for containing neuron cell bodies within the spinal cord?
Signup and view all the answers
How are the spinal nerves categorized based on their location?
How are the spinal nerves categorized based on their location?
Signup and view all the answers
What is the function of the ventral (anterior) root of the spinal cord?
What is the function of the ventral (anterior) root of the spinal cord?
Signup and view all the answers
Which major ascending tract decussates at the level of the medulla and conveys proprioception, fine touch, pressure, and vibration?
Which major ascending tract decussates at the level of the medulla and conveys proprioception, fine touch, pressure, and vibration?
Signup and view all the answers
Which of the following accurately describes the primary role of the lower motor neuron?
Which of the following accurately describes the primary role of the lower motor neuron?
Signup and view all the answers
What structures surround the nerve fibers, fasciculus, and entire nerve, respectively?
What structures surround the nerve fibers, fasciculus, and entire nerve, respectively?
Signup and view all the answers
Which extrapyramidal tract is primarily responsible for subconscious control of balance and muscle tone?
Which extrapyramidal tract is primarily responsible for subconscious control of balance and muscle tone?
Signup and view all the answers
Which of the following statements about the posterior spinocerebellar tract is correct?
Which of the following statements about the posterior spinocerebellar tract is correct?
Signup and view all the answers
What is the main function of sensory input provided by muscle stretch receptors in motor control?
What is the main function of sensory input provided by muscle stretch receptors in motor control?
Signup and view all the answers
Which statement correctly differentiates between Group Ia and Group II afferent fibers?
Which statement correctly differentiates between Group Ia and Group II afferent fibers?
Signup and view all the answers
Which division of the nervous system controls cardiac muscle activity?
Which division of the nervous system controls cardiac muscle activity?
Signup and view all the answers
What is the role of gamma (γ) motor neurons in muscle spindle physiology?
What is the role of gamma (γ) motor neurons in muscle spindle physiology?
Signup and view all the answers
Study Notes
Spinal Cord Anatomy
- Located within the vertebral canal of the vertebral column
- Surrounded by cerebrospinal fluid (CSF), meninges, and vertebral bone
- Protected by three layers of connective tissue membranes called meninges:
- Dura mater: Outermost layer, dense irregular connective tissue. Contains an epidural space filled with fat and connective tissue.
- Arachnoid mater: Middle layer, delicate elastic and collagen fibers. Contains a subdural space filled with interstitial fluid.
- Pia mater: Innermost layer, thin and transparent, adheres to the spinal cord. Contains a subarachnoid space filled with CSF.
- Extends from the medulla to the L2 vertebrae
- Contains two enlargements:
- Cervical enlargement: Supplies upper appendages.
- Lumbosacral enlargement: Supplies lower appendages.
- Conus medullaris: Tapered inferior end of the spinal cord.
- Cauda equina: Bundle of spinal nerves arising from the conus medullaris.
- Filum terminale: Pia mater extension that anchors the spinal cord to the coccyx.
-
Spinal nerves: 31 pairs of nerves that connect the spinal cord to the body. They are named after the vertebral segment they originate from.
- Divided into five regions: cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5), and coccygeal.
-
Internal spinal cord anatomy: Divided into gray and white matter.
-
Gray matter: Core of the spinal cord, shaped like a butterfly. Contains neuron cell bodies.
- Anterior horns: Contain motor neuron cell bodies controlling skeletal muscle.
- Posterior horns: Receive sensory information from the periphery.
- Gray commissure: Connects the left and right halves of the gray matter.
- Central canal: Extends the length of the spinal cord and contains CSF.
-
White matter: Outer region of the spinal cord, composed of myelinated axons of motor and sensory neurons arranged into columns.
- Anterior column: Contains tracts that carry motor information to the body.
- Posterior column: Contains tracts that carry sensory information to the brain.
- Lateral column: Contains tracts that carry both motor and sensory information.
-
Gray matter: Core of the spinal cord, shaped like a butterfly. Contains neuron cell bodies.
Spinal Cord Physiology
-
Conduction of nerve impulses: White matter tracts convey signals:
- Ascending tracts: Sensory information from receptors to the brain.
- Descending tracts: Motor commands from the brain to effectors.
- Decussation: Most nerve tracts cross over to the opposite side of the body.
- Center for spinal reflexes: Gray matter integrates and coordinates reflexive responses to stimuli.
-
Major Ascending Tracts: Carry sensory information to the brain.
- Fasciculus gracilis and fasciculus cuneatus: Posterior column; proprioception, fine touch, pressure, and vibration; decussates in the medulla; terminates in the sensory cortex.
- Anterior spinothalamic tract: Anterior column; crude touch and pressure; decussates immediately; terminates in the sensory cortex.
- Lateral spinothalamic tract: Lateral column; pain and temperature; decussates immediately; terminates in the sensory cortex.
- Anterior spinocerebellar tract: Lateral column; proprioception; decussates immediately and then again in the medulla; terminates in the cerebellum.
- Posterior spinocerebellar tract: Lateral column; proprioception; does not decussate; terminates in the cerebellum.
Major Descending Tracts
-
Somatic nervous system: Controls voluntary skeletal muscle activity.
- Upper motor neurons: Cell body in the primary motor cortex; axons descend to the spinal cord.
- Lower motor neurons: Cell body in the brainstem or spinal cord; axon extends to the neuromuscular junction.
- Lower motor neuron excitatory: Stimulates muscle contraction.
-
Autonomic nervous system: Controls involuntary smooth muscle, cardiac muscle, and gland function.
- Preganglionic neuron: Cell body in the brainstem or spinal cord; axon synapses with a postganglionic neuron.
- Postganglionic neuron: Cell body in a peripheral ganglion; axon innervates target organ.
- Pyramidal (corticospinal) tracts: Anterior and lateral columns; precise, voluntary motor control of skeletal muscle; upper motor neuron in motor cortex; lower motor neuron in anterior horn of spinal cord; decussates in the brainstem.
-
Extrapyramidal tracts: Subconscious motor activity; anterior and lateral columns; motor tone, posture, and coordination of movements.
- Rubrospinal tract: Red nucleus to anterior horn; subconscious control of upper limb tone and movement.
- Vestibulospinal tract: Vestibular nucleus to anterior horn; subconscious control of balance and muscle tone.
- Tectospinal tract: Superior and inferior colliculus to anterior horn; subconscious control of eye, head, and neck position.
- Reticulospinal tract: Reticular formation to anterior horn; subconscious control of reflex activity.
Spinal Organization of Motor Function
- α-motor neurons: Lower motor neurons that innervate skeletal muscles.
-
Control of muscle force:
- Motor unit recruitment: Increasing the number of motor units activated to increase force.
- Temporal summation: Increasing the frequency of action potentials to increase force.
-
Sensory input for motor control (proprioception):
-
Muscle spindles: Sensory receptors located within muscles that detect muscle stretch.
-
Intrafusal fibers: Modified muscle fibers within the muscle spindle.
- Nuclear bag fibers: Nuclei clustered at the midpoint.
- Nuclear chain fibers: Nuclei arranged in a single row.
-
Innervation:
- Group Ia afferent fibers: Respond to rate of stretch; have spiral endings on intrafusal fibers.
- Group II afferent fibers: Respond to muscle length; have spray endings on intrafusal fibers.
- γ-motor neurons: Innervate intrafusal fibers; adjust sensitivity of muscle spindles.
-
Intrafusal fibers: Modified muscle fibers within the muscle spindle.
-
Golgi tendon organs: Sensory receptors located within tendons that detect muscle tension.
- Structure: Spray of nerve endings in tendons and connective tissues; innervated by group Ib fibers.
- Function: Respond to high-threshold stretch; inhibit muscle activity to prevent tendon damage.
-
Muscle spindles: Sensory receptors located within muscles that detect muscle stretch.
Spinal Reflexes
- Fast, predictable, automatic responses to environmental changes.
-
Classification:
-
Type of sensory and effector:
- Viscerovisceral: Both sensory and effector are visceral.
- Viscerosomatic: Sensory is visceral, effector is somatic.
- Somatovisceral: Sensory is somatic, effector is visceral.
- Somatosomatic: Both sensory and effector are somatic.
-
Number of neurons:
- Monosynaptic: Two neurons involved.
- Polysynaptic: More than two neurons involved.
-
Type of sensory and effector:
-
Components of reflex arc:
- Receptor: Detects stimulus.
- Sensory neuron: Transmits information to the spinal cord.
- Integrating center: Spinal cord interneurons process information.
- Motor neuron: Carries signal to the effector.
- Effector: Muscle or gland that produces the response.
Types of Spinal Reflexes
-
Phasic stretch reflex:
- Monosynaptic; elicited by rapid muscle stretch.
- Example: Knee-jerk reflex.
- Receptor: Muscle spindles (Group Ia fibers).
-
Tonic stretch reflex:
- Monosynaptic and polysynaptic; elicited by slow muscle stretch.
- Receptor: Muscle spindles (Group Ia and II fibers).
-
Tendon reflex:
- Polysynaptic; elicited by high tension in the tendon.
- Receptor: Golgi tendon organ (Group Ib fibers).
- Function: Inhibits the ipsilateral muscle to protect the tendon.
-
Withdrawal reflex:
- Polysynaptic; elicited by painful stimuli.
- Receptor: Pain receptors.
- Function: Flexes the ipsilateral limb to withdraw it from the stimulus.
-
Crossed extensor reflex:
- Polysynaptic; coordinated with the withdrawal reflex.
- Function: Extends the contralateral limb to provide support and maintain balance.
Clinical Value of Reflex Evaluation
- Evaluate level of anesthesia: To assess the integrity of the spinal cord.
- Evaluate degree of intervertebral disk compression: To identify nerve root compression.
- Evaluate muscular weakness and disorders: To diagnose nerve and muscle pathology.
Spinal Cord Transection
-
Spinal shock: Transient period of areflexia, denervation supersensitivity, and hyperreflexia following spinal cord injury.
- Areflexia: Loss of all reflexes below the level of injury.
- Denervation supersensitivity: Hyperactive stretch and flexion reflexes.
- Hyperreflexia: Exaggerated reflexes with minimal stimulation.
- Babinski's sign: Extensor plantar reflex (toes curl upwards) due to damage to the corticospinal tract.
- Decerebrate rigidity: Exaggerated extensor activity due to brainstem transection.
Postural Reflexes
- Normal reflexes that help maintain posture.
-
Vestibuloocular reflex: Maintains focus on an object during head movements.
- Nystagmus: Involuntary eye movements that occur when head movement exceeds visual field.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on the anatomy of the spinal cord. This quiz covers key structures such as the meninges, spinal cord enlargements, and protective features. Understand the organization and function of the spinal cord within the vertebral column.
