Vet Prep Structural and Functional Biology Spring 2024 PDF

Meninges Vet Prep Structural and Functional Biology 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,...

Meninges Vet Prep Structural and Functional Biology 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 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. Dog 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 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. trabeculae 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. Membrane spaces in Vertebral Canal Epidural space Only present around spinal cord Spinous Process Subdural space arch (potential space only) Not normally present Subarachnoid Space Contains CNS Vertebral Body Red line = periosteum Blue line = dura mater Yellow line = arachnoid Green line = pia mater 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 line = arachnoid Yellow line = arachnoid Green line = pia mater Olfactory nerve (surrounded by meninges) Clinical: Possible route for meningitis! Nose to brain connection. II I CSF 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/ 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. 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 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