CNS 2: Spinal Cord PDF

CNS 2: Spinal Cord Devin Mott PT, DPT Objectives Differentiate between white and grey matter Describe the location of ascending and descending tracts (afferent vs efferent) Describe the role of interneurons in reflexes Spinal Cord and Spinal Nerves (1 of 2) Spinal cord ○ Hollow tube run...

CNS 2: Spinal Cord Devin Mott PT, DPT Objectives Differentiate between white and grey matter Describe the location of ascending and descending tracts (afferent vs efferent) Describe the role of interneurons in reflexes Spinal Cord and Spinal Nerves (1 of 2) Spinal cord ○ Hollow tube running inside the vertebral column, from foramen magnum to second lumbar vertebrae ○ Like a sophisticated neural information superhighway Spinal Cord and Spinal Nerves (2 of 2) External anatomy ○ Contains 31 segments, each with a pair of spinal nerves ○ Ends at L2 in conus medullaris where cauda equina hangs ○ Spinal nerves dangle loosely, floating in cerebral spinal fluid (CSF) ○ Cervical and lumbar enlargements are two widened areas Regions Extends from the brain to L1 ○ Consists of: Cervical region Thoracic region Lumbar region Sacral region Coccygeal region Meninges (1 of 3) The meninges are a protective covering of both the brain and spinal cord. They help to set up layers that act as cushioning and shock absorbers. ○ Dura mater Outer layer is thick fibrous tissue Meninges (2 of 3) They help to set up layers that act as cushioning and shock absorbers. ○ Arachnoid mater Middle layer is a wispy, delicate layer, resembling a spider web, composed of collagen and elastic fibers acting as a shock absorber and transporting dissolved gases and nutrients as well as chemical messengers and waste products. Meninges (3 of 3) They help to set up layers that act as cushioning and shock absorbers. ○ Pia mater Innermost layer, fused to the neural tissue, containing blood vessels that serve the brain and spinal cord Meningeal Spaces (1 of 3) A series of spaces are associated with the meninges. ○ Between the dura mater and the vertebral column is a space filled with fat and blood vessels called the epidural space. ○ Between the dura mater and the arachnoid mater is the subdural space filled with a tiny bit of fluid. Meningeal Spaces (2 of 3) Spaces ○ Between the arachnoid mater and the pia mater is the large subarachnoid space filled with CSF that acts as a fluid cushion. Meningeal Spaces (3 of 3) These three membranes and their fluid-filled spaces, together with the bones of the skull and vertebral column, form a strong protective system against CNS injury. Figure 9–8 A Sliced View Transverse view White matter Gray matter Central canal Dorsal root and ventral root: merge to form a spinal nerve ○ Dorsal root is sensory: axons extend from the soma within the dorsal root ganglion ○ Ventral root is motor Gray Vs White Matter Gray matter ○ Central canal ○ Consists of somas (cell bodies) surrounding the central canal White matter ○ Consists of axons ○ Nerves are organized into tracts or columns ○ Located outside the gray matter area Ventral and Dorsal Roots Ventral Root: ○ Cell bodies of motor neurons Dorsal Root: ○ Sensory axons (cell body - DRG - outside of spinal cord) Internal Structure White Matter: ○ Axons (tracts) Grey: ○ Dorsal Horn Sensory ○ Lateral Horn Sympathetic ○ Ventral Horn Motor Internal Anatomy of the Spinal Cord (1 of 8) The spinal cord is divided in half by an anterior median fissure (deep groove) and a posterior median sulcus (shallow groove). The interior of the spinal cord is then divided into a series of sections of white matter columns and gray matter horns. Internal Anatomy of the Spinal Cord (2 of 8) Three types of horns ○ Dorsal horn involved in sensory functions ○ Ventral horn involved in motor function ○ Lateral horn dealing with autonomic functions The horns are the regions where the neuron’s cell bodies reside. Internal Anatomy of the Spinal Cord (3 of 8) White matter of spinal cord contained in dorsal, lateral, and ventral columns ○ Columns act as nerve tracts, pathways, or axons ○ Run up and down the spinal cord to and from the brain Internal Anatomy of the Spinal Cord (4 of 8) Information from ascending pathways ○ Dorsal column tract carries fine-touch and vibration information to the cerebral cortex ○ Spinothalamic tract carries temperature, pain, and crude touch information to the cerebral cortex ○ Spinocerebellar tract carries information about posture and position to the cerebellum Internal Anatomy of the Spinal Cord (5 of 8) Information from descending pathways ○ Corticospinal tract: orders from cerebral cortex to motor neurons in ventral horn of spinal cord ○ Corticobulbar tract: orders from cerebral cortex to motor neurons in brain stem Internal Anatomy of the Spinal Cord (6 of 8) Descending pathways ○ Reticulospinal and rubrospinal tracts: information from the various regions of brain to brain stem and ventral horn, which helps to coordinate movements Internal Anatomy of the Spinal Cord (7 of 8) The commissures, gray and white, connect left and right halves of the cord so the two sides of the CNS can communicate. The central canal is a cavity in the center of the spinal cord filled with CSF. The spinal roots project from both sides of the spinal cord in pairs, and fuse to form spinal nerves. Internal Anatomy of the Spinal Cord (8 of 8) The dorsal root, with the embedded dorsal root ganglion, a collection of sensory neurons, carries sensory information while the ventral root is motor. Figure 9–9 Tracts: Motor Medial Corticospinal Tract ○ Neck, Shoulder, Trunk Muscles Reticulospinal Tract ○ Postural and gross limb muscles Lateral Vestibulospinal Tract ○ Postural Responds to gravity info Medial Vestibulospinal Tract ○ Neck Responds to input regarding head motion Tracts: Motor (most important) Lateral Corticospinal Tract ○ Controlling all VOLUNTARY movement ○ Pathway: Starts in primary motor cortex > brain stem (area called pyramids where 88% of fibers cross to contralateral side) > lateral spinal cord > synapse with motor neuron > spinal nerve Tracts: Sensory Spinothalamic ○ Fast nociception, temperature, crude touch Body: First order: DRG > 2nd Order: Dorsal Horn > 3rd Order: Thalamus Face: 1st order: Trigeminal Nerve > 2nd Order: Spinal Nucleus of CNV > Thalamus Dorsal Column/Medial Lemniscus ○ Light touch and proprioception 1st order: DRG > 2nd order: NC or NG > Third Order: Thalamus Spinocerebellar ○ Movement related information Ipsilateral Cerebellum Spinal Nerves (1 of 3) Nerves are the connection between the CNS and the world outside the CNS. ○ Part of the PNS All nerves consist of bundles of axon, blood vessels, and connective tissue. Nerves run between the CNS and organs or tissues, carrying information into and out of the CNS. Spinal Nerves (2 of 3) The nerves connected to the spinal cord are called spinal nerves, each named for the spinal cord segment to which they are attached. All spinal nerves are mixed nerves which means they carry both sensory and motor information. Spinal Nerves (3 of 3) Spinal nerves from the thoracic spinal cord project directly to the thoracic body wall without branching. All other spinal nerves branch extensively, recombining with nerves from other spinal cord segments before projecting to peripheral structures (plexuses). Figure 9–10 Interneurons Work to modulate sensory information Coordination of movement patterns Autonomic regulation Reflexes Monosynaptic (what they test at the Dr.’s Office): ○ Simple arc reflex: single synapse between afferent and efferent Polysynaptic: (complex response: 2-100s of reflexes) ○ Involves reciprocal inhibition ○ Example: Withdrawal Reflex Primitive Reflex Babinski ○ Pyramidal tract lesion Grasp Reflex ○ Frontal Lobe Lesion and Lewy Body Dementia Glabellar Tap Reflex ○ PD Spinal Cord Injuries Anterior Cord Syndrome Central Brown Sequard Cauda Equina Brown Sequard Spaces Epidural Space ○ Between ligamentum flavum and dura mater Contains adipose, connective tissue, ervesm venous plexus, lymphatics Subdural Space ○ Potential space Subarachnoid Space ○ Between arachnoid and pia mater Filled with CSF Site of lumbar puncture for dx of meningitis (typically tested L3/L4)