Spinal Cord Flashcards
Anatomy of Spinal Cord
- 1/2 inches wide. About 18 inches long.
- Four Regions: cervical, thoracic, lumbar, sacral.
- Gray Matter: neuron cell bodies -> nucleuses
- White Matter: myelinated axons -> tracts.
- Ends between L1 and L2
- 8 cervical spinal nerves
- 12 pairs of thoracic spinal nerves
- 5 pairs of lumbar spinal nerves
- 5 pairs of sacral spinal nerves
- 1 pair of coccygeal spinal nerves
Anatomy of Distal End of spinal cord
- conus medullaris: thin, conical spinal cord below lumbar enlargement.
- Filum terminale: Thin thread of fibrous tissue at end of conus medullaris that attaches to the coccygeal ligament
- Cauda Equina: Nerve Roots extending Below conus medullaris
Spinal Cord Structure
Posterior median sulcus: A shallow groove on the dorsal side of the spinal cord that marks the separation between the left and right dorsal columns.
Anterior median fissure: A deep groove on the ventral side of the spinal cord that divides it into right and left halves.
Ventral root: Contains motor neuron axons that transmit motor impulses from the spinal cord to the muscles.
Dorsal root: Contains sensory neuron axons that transmit sensory information from the periphery to the spinal cord
Dorsal root ganglia: Contain cell bodies of sensory neurons that carry signals to the spinal cord.
Spinal nerves: Mixed nerves that carry both sensory and motor information between the spinal cord and the body.
Anterior white commissure: A bundle of nerve fibers crossing from one side of the spinal cord to the other, located in front of the central canal.
Posterior gray commissure: A narrow band of gray matter that connects the two sides of the spinal cord’s gray matter, behind the central canal.
Anterior white column: Contains ascending and descending tracts of nerves that transmit motor and sensory information.
Lateral white column: Contains both ascending sensory and descending motor pathways.
Posterior white column: Contains ascending sensory tracts that transmit information about touch, pressure, and proprioception to the brain.
central canal: A fluid-filled channel in the center of the spinal cord that contains cerebrospinal fluid (CSF) and is involved in cushioning and protecting the spinal cord.
Denticulate Ligaments: Anchor the spinal cord within the vertebral column, providing stability.
Spinal Cord Horns
- Posterior Gray Horn: contains somatic and visceral sensory nuclei.
- Lateral Gray Horn: Contains Visceral Motor nuclei
- Anterior Gray Horn: Contains somatic Motor nuclei
Spinal Cord Meninges and spaces.
Meninges are the three protective membranes that surround the brain and spinal cord, consisting of the:1. 1.dura mater: outermost layer, dense collagen fibers.
2. arachnoid mater: middle layer, trabeculae of collagen and elastic fibers.
3. pia mater: innermost layer, delicate layer of elastic fibers and collagen that closer adheres to the spinal cord. Denticulate ligaments extend from the piamatter.
Meninges Spaces:
1. Epidural Space: Located between the dura mater and the vertebral wall, this space contains areolar tissue, blood vessels, and adipose tissue. Is the site for epidural anesthesia.
2. Subdural Space: A potential space between the dura mater and the arachnoid mater. It typically only exists under pathological conditions, or after death
3. Subarachnoid Space: Located between the arachnoid mater and pia mater, this space contains cerebrospinal fluid (CSF), which provides cushioning and nutrients to the spinal cord. Contains blood vessels
Define Dermatomes
Dermatomes are specific areas of skin that are innervated by the sensory fibers of a single spinal nerve root, allowing for the mapping of sensory regions corresponding to each spinal nerve. There are 31 spinal nerves therefore there are 31 dermatones.
Because spinal nerves exit the spine laterally, dermatomes associated with the torso and core are distributed horizontally. When viewed on a body map, they appear like stacked discs.
Peripheral Distribution of spinal Nerves:
Dorsal ramus: provides motor innervation to the deep / intrinsic back and sensory innervation to the skin of the posterior portion of the head, neck and back
Ventral ramus: A larger branch of the spinal nerve that carries both sensory and motor fibers to the limbs and the anterior and lateral parts of the trunk, contributing to the formation of major nerve plexuses like the cervical, brachial, lumbar, and sacral plexuses. innervates superficial and intermediate back muscles, trapezius, latissimus dorsi, rhomboids, and levator scapuli
Ramus communicans (plural: rami communicantes): Small branches that connect the spinal nerves to the sympathetic ganglia of the autonomic nervous system, involved in transmitting autonomic signals, specifically sympathetic impulses, between the spinal cord and the peripheral nervous system. Sensory: from visceral organs, motor: sympathetic fibers of ANS
This clean organization only exists for thoracic spinal nerves (T1-L2), all other spinal nerves form plexuses
Define Plexus
A network of intersecting spinal nerves formed by the ventral/anterior rami of adjacent spinal nerves (remember dorsal rami innervate back). These plexuses allow for the redistribution of nerve fibers from different spinal nerves, resulting in the formation of peripheral nerves that contain fibers from multiple spinal levels. Plexus nerves primarily innervate the limbs, anterior and lateral parts of the trunk, and other associated structures
- By mixing fibers from different spinal nerves, a plexus creates redundancy in nerve supply
- A plexus can integrate motor and sensory signals from different parts of the body, coordinating responses and enhancing the control of movements, particularly in complex regions like the limbs
- a single nerve emerging from a plexus can carry fibers from multiple spinal levels, providing a broader and more integrated innervation to specific body regions.
- Cervical Plexus: C1-C5, Innervates neck, diaphragm (phrenic nerve),
- Brachial Plexus: C5-T1, Innervates the chest, shoulder, arm, and hand, providing both motor and sensory functions.
- Lumbar Plexus: T12-L4, Innervates the lower abdomen, anterior and medial thigh, and part of the pelvis.
- Sacral Plexus: L4-S4, Innervates the posterior thigh, most of the lower leg, foot, and part of the pelvis.
Cervical Plexus and Nerves
- Anterior Rami of spinal nerves: C1-C5
- Innervates neck, thoracic cavity, diaphragmatic muscle
- Major nerve:
1. Phrenic nerve, controls diaphragm (c3, c4, c5 keep the diaphragm alive).
Brachial Plexus and Nerves
- Anterior rami of spinal nerves: C5-T1
- Innervates: pectoral girdle and upper limbs. All nerves from brachial plexus originate from larger nerve structures called trunks and cords.
- Major Nerves.
1. Musculocutaneous nerve: Innervates the muscles of the anterior arm, including the biceps brachii, brachialis, and coracobrachialis, and provides sensory innervation to the lateral forearm.
2. Median nerve: Innervates most of the anterior forearm muscles and some hand muscles, and provides sensory innervation to the lateral palm and fingers.
3. Ulnar nerve: Innervates the intrinsic muscles of the hand and some forearm muscles, and provides sensory innervation to the medial hand and fingers.
4. Axillary nerve: Innervates the deltoid and teres minor muscles, and provides sensory innervation to the skin over the deltoid region.
5. Radial nerve: Innervates the muscles of the posterior arm and forearm, including the triceps brachii and extensor muscles, and provides sensory innervation to the posterior arm, forearm, and hand.
Lumbar Plexus and Nerves
- Anterior Rami of Spinal Nerves: T12-L4
- Innervates the lower abdomen, anterior and medial thigh, and parts of the pelvis
- Major Nerves:
1. Femoral Nerve: Innervates the anterior thigh muscles, including the quadriceps and sartorius, and provides sensory innervation to the anterior thigh and medial lower leg via the saphenous nerve.
2. Obturator nerve: Innervates the medial thigh muscles, including the adductors, and provides sensory innervation to the skin of the medial thigh
Sacral Plexus and Nerves
- Anterior Rami of Spinal Nerves: L4-S4
- Innervates the pelvis, posterior thigh, most of the lower leg, the entire foot, and parts of the buttocks
- Major Nerves:
1. Pudendal nerve: Innervates the muscles of the perineum and provides sensory innervation to the 2. external genitalia and perineal region.
2. Sciatic nerve: Innervates the posterior thigh muscles and splits into the tibial and common fibular nerves to innervate the lower leg and foot.
3. Common fibular nerve: Innervates the muscles of the anterior and lateral compartments of the lower leg, and provides sensory innervation to the upper lateral leg and dorsum of the foot.
4. Tibial nerve: Innervates the muscles of the posterior compartment of the lower leg and the sole of the foot, and provides sensory innervation to the sole of the foot.
What are the five steps in a reflex
- Arrival of stimulus, activation of receptor.
- Activation of sensory neuron
- Information processing by postsynaptic cell
- Activation of motor neuron
- Response of peripheral effector
What are the classifications of reflexes?
The purpose of a reflex is to provide a rapid, automatic response to a stimulus, helping to protect the body from harm and maintain homeostasis by bypassing conscious brain processing.
Innate Reflex:
An innate reflex is an inborn, automatic response that is genetically programmed and not learned.
Example: The withdrawal reflex (typically involves at least two synapses), such as pulling your hand away from a hot object.
Acquired Reflex:
An acquired reflex is a learned response that develops through experience and repetition.
Example: The reflexive action of pressing the brake pedal when you see a red light while driving.
Autonomic Reflex:
An autonomic reflex is an involuntary reflex that controls the function of smooth muscles, cardiac muscles, and glands, typically involved in regulating internal body conditions.
Example: The regulation of heart rate in response to blood pressure changes (baroreceptor reflex).
Somatic Reflex:
A somatic reflex is a voluntary reflex that involves the contraction of skeletal muscles in response to a stimulus.
Example: The knee-jerk (patellar) reflex (monosynaptic), where tapping the patellar tendon causes the leg to extend.
Spinal Reflex:
A spinal reflex is a reflex that is mediated by the spinal cord, allowing for quick responses without involving the brain.
Example: The stretch reflex, like the knee-jerk reflex (monosynaptic), which is processed directly in the spinal cord.
Cranial Reflex:
A cranial reflex is a reflex that is mediated by the brain, specifically through cranial nerves.
Example: The blink reflex (polysnaptic), which involves blinking in response to a bright light or a sudden movement near the eyes.
Describe the Stretch Reflex
A stretch reflex is a monosynaptic reflex that occurs when a muscle is suddenly stretched, leading to an automatic contraction of the same muscle. This reflex helps maintain muscle tone and posture by resisting changes in muscle length. Sensory neuron -> Motor Neuron
Ankle Jerk
- Spinal Nerves Tested: The ankle jerk reflex primarily tests the S1 and S2 spinal nerves.
- What Happens: When the Achilles tendon is tapped, it causes a stretch in the calf muscles (specifically the gastrocnemius and soleus). This stretch activates the muscle spindles, sending a signal via the S1 and S2 sensory nerves to the spinal cord. The motor response is sent back through the same spinal nerves to cause the calf muscles to contract, resulting in plantar flexion (downward movement) of the foot.
Knee Jerk
- Spinal Nerves Tested: The knee jerk reflex primarily tests the L2, L3, and L4 spinal nerves, with the main contribution from L4.
- What Happens: When the patellar tendon is tapped, it causes a stretch in the quadriceps muscle. This stretch activates the muscle spindles in the quadriceps, sending a signal via the L2-L4 sensory nerves to the spinal cord. The motor response is sent back through the same spinal nerves to cause the quadriceps muscle to contract, resulting in the extension of the lower leg at the knee (knee jerk).
spinal reflex, innate reflex, somatic reflex, monosynaptic
Describe Cross Extensor reflex
The crossed extensor reflex is a reflex in which the contraction of flexor muscles on the ipsilateral side of the body is accompanied by the extension of muscles on the contralateral side. This reflex involves both ipsilateral and contralateral pathways, coordinating the simultaneous flexion and extension of opposite limbs to maintain balance and posture.
the withdrawl reflex is an ipsalateral reflex and is often accompanied by a crossed extensor reflex
