Vet Prep Structural and Functional Biology Meninges PDF Spring 2025

Vet Prep Structural and Functional Biology Meninges Dr. Melissa Kehl Courtesy of Dr. Melania Crisan  Learning Objectives Describe where the spinal cord ends in dog. Describe membranes around CNS (central nervous system),...

Vet Prep Structural and Functional Biology Meninges Dr. Melissa Kehl Courtesy of Dr. Melania Crisan  Learning Objectives Describe where the spinal cord ends in dog. Describe membranes around CNS (central nervous system), spaces they create and the contents of these spaces. Describe production of CSF, its function and its circulation. Describe access points to the epidural and subarachnoid spaces, why these places are preferred, and structures to avoid.  OVERVIEW central nervous system (1) brain (2) spinal cord peripheral nervous system (3) peripheral nerves The peripheral nervous system is divided into (4) sensory or afferent system (5) motor or efferent system The brain and spinal cord are contained within a continuous space provided by the cranial cavity of the skull and the vertebral canal.  1. spinal cord 2. dorsal root 4. ventral root 5. spinal nerve 6. dorsal branch of spinal n. 7. ventral branch of spinal n. 8. body of vertebra 10. epaxial muscles Transection of the vertebral column TVA 5TH Ed. Dyce, Sack and Wensing  Spinal cord and cauda equina Dog Spinal cord ends around lumbosacral junction. The spinal nerves after L7 travel caudally within the vertebral canal. They exit when they reach their corresponding vertebrae. This cluster of spinal nerves is known as cauda equina because it looks like a horse tail. FYI Cauda equina syndrome (CES) is caused by compression of the nerve roots passing from the lower back toward the tail at the level of the lumbosacral junction. Lumbosacral stenosis is most commonly caused by degenerative changes to the intervertebral disc, arthritis of the joints, and abnormal proliferation of the ligaments. Dogs with abnormal shape to their last lumbar or sacral vertebrae and German Shepherd dogs are predisposed to developing lumbosacral stenosis. Neoplasia (cancer) and infection at the level of the lumbosacral disc (discospondylitis) may also cause signs of CES. What are the symptoms of cauda equina syndrome? The most common neurologic sign associated with cauda equina syndrome is pain in the lower back. Signs of pain may include decreased willingness to jump up and climb up stairs, low tail carriage or reduced tail wagging, difficulty posturing to defecate, and whimpering/crying if the lower back is touched. In some cases, dogs will have a weakness or lameness in one or both hind limbs—this occurs secondary to compression of the nerve root that supplies the sciatic nerve as it exits at the lumbosacral joint. Severe compression of the nerve roots can lead to fecal and urinary incontinence, which is irreversible in most cases. How is it diagnosed? The first step in diagnosing cauda equina syndrome is through a neurologic examination. The doctor will observe the dog’s gait for any lameness and/or stiffness. A physical examination will include palpation over the spine to determine the site where the dog is most painful. Manipulation of the hips and tail will elicit pain response in most dogs suffering this syndrome. The doctor will also test reflexes, proprioception (foot placement), and anal tone. Radiographs are taken for abnormal shape of the lumbosacral joint, spinal arthritis at the lumbosacral joint, infection of the disc space, or tumors. How is it treated? Dogs that are exhibiting mild pain and have never had an episode of back pain before are usually treated with strict rest and pain medications. In cases where the dog is not responding to conservative medical therapy or exhibiting neurologic symptoms, surgical intervention is necessary. The procedure is called a dorsal laminectomy and involves removing the “roof” of the spinal canal to release the entrapped nerve roots and remove the associated ruptured intervertebral disc, if present. What is the post-operative prognosis? Prognosis is very good in dogs with mild neurologic signs (i.e. pain only, mild weakness). Dogs with severe nerve root compression and subsequent urinary or fecal incontinence have a very poor prognosis, and the majority of dogs never become continent again—even with surgery. Many dogs with lumbosacral disease have other back problems (i.e. chronic intervertebral disc disease) and hip or other orthopedic disease, which can affect their recovery after surgery. Recovery is also slower in overweight dogs, and obese patients must be put on a strict diet to reduce their weight.  Meninges The brain and spinal cord are surrounded by 3 continuous membranes of connective tissue called meninges. 1. DURA MATER Dura mater – is the outer and thickest layer. In the vertebral canal, the dura is separated from the periosteum of the bony canal. Inside the cranial cavity, the dura and the periosteum are fused. 2. ARACHNOID trabeculae The arachnoid is attached to the dura and sends delicate trabeculae to the pia. These trabeculae have blood vessels that course on the surface of the pia. 3. PIA MATER Innermost meningeal layer. Intimately follows the brain’s gyri and sulci (bumps and grooves). Pia is the region of some CSF production. Note: A 4th membrane which is not a meninx is the periosteum lining the vertebral canal and skull.  Meninges SPINAL CORD SKULL Epidural space https://www.marvistavet.com/meningioma.pml  Vertebral Canal Dorsal view of the opened vertebral canal. The dura mater has been dissected and is reflected. Spinal Cord Dura Dorsal Root of a Spinal Nerve (covered by Mater pia mater) TVA 5TH Ed. Dyce, Sack and Wensing.  Membrane spaces in Vertebral Canal Epidural space Only present Spinous around spinal cord Red line = periosteum Process Blue line = dura mater Yellowline Yellow line= =arachnoid arachnoid Subdural space Green line = pia mater (potential space only) arch Not normally present Subarachnoid Space Contains CNS Vertebral Body  Membrane spaces in Cranium In skull, dura mater is fused to periosteum - hence no epidural space in skull Red line = periosteum Blue line = dura mater Yellow Yellow line line = arachnoid = arachnoid Green line = pia mater Olfactory nerve (surrounded by meninges) Clinical: Possible route for meningitis! Nose to brain II connection. I  CSF (Cerebral Spinal Fluid) Function Shock absorption: the CSF encasing the brain absorbs the shock so that it does not smack against the skull. Nutrition: CSF supplies the central nervous system with essential nutrients, such as glucose, proteins, lipids, and electrolytes. Intracranial pressure: A steady flow of CSF keeps the pressure around the brain stable. Too much CSF, possibly due to a traumatic brain injury or brain tumor, raises intracranial pressure. Waste removal: CSF washes through the subarachnoid space, cleaning up toxins and waste products Temperature: CSF circulation keeps the temperature of your brain and spine stable. Immune Function: CSF contains numerous immune cells that monitor the central nervous system for foreign agents that could damage vital organs.  CerebroSpinal Fluid Clear colorless CSF is formed from the blood plasma by ultrafiltration through the “blood– cerebrospinal fluid barrier” at the choroid plexuses. Gross visual examination: Normal CSF is clear, colorless, and odorless. It has the consistency of water. Cloudy indicates infection and/or inflammation. https://slideplayer.com/slide/12078519/  Red line = periosteum CSF Sampling Sites Blue line = dura mater Yellow line = arachnoid arachnoid Cerebellum Green line = pia mater Sacrum skull Cerebellomedullary cistern Sacral cistern (also called lumbar cistern) CSF Sampling Sites https://vcahospitals.com/know-your-pet/cerebrospinal-fluid-collection-and-examination  CSF Sampling Sites - Equine CSF collection from the atlantooccipital space requires general anesthesia. The atlantooccipital space is located just caudal to the poll, on the dorsal midline, at the level of the wings of the atlas. The lumbosacral space is usually accessed in the awake, standing patient; this avoids the risk of recovery from general anesthesia. However, the lumbosacral space is technically more difficult to enter, and patients may display violent reactions to pain from the procedure. Sedation is needed. https://veteriankey.com/equine-clinical-procedures/  Epidural Anesthesia Used in obstetrics to numb the pudendal nerve to prevent excessive straining. Be especially careful not to pierce the cauda equina (way too many nerves). Avoid hitting the venous sinus (blood vessels within vertebral canal). Should not inject into CSF (brain connection). Avoid femoral, obturator and sciatic nerves.  Epidural Anesthesia http://www.tsvs.net/ www.vcahospitals.com 1. In the dog, the spinal cord ends around what region of the vertebral canal? A)Cervical B)Thoracic C)Lumbar D)Caudal/coccygeal E)Occipital  2. Which of the meninges is labelled by a star? (4 choices) A)Pia mater B)Dura mater C)Arachnoid D)Periosteum brain 3. Which of the following is NOT a function of the Cerebrospinal Fluid (CSF)? A) Temperature B) Nutrition C) Waste removal D) Immune function E) Blood flow Practice Question Answers: 1.C 2.A 3.E