Anatomy Lecture 1 (NS, Spinal Cord) 2024-2025 PDF

Lecture N1 Overview of the nervous system – the functional organization; basic divisions; spinal cord; meninges Function of the Nervous System  Sensory  Motor  Behavior  Higher cognitive Function of the Nervous System  Sensory input -...

Lecture N1 Overview of the nervous system – the functional organization; basic divisions; spinal cord; meninges Function of the Nervous System  Sensory  Motor  Behavior  Higher cognitive Function of the Nervous System  Sensory input - monitoring of changes (stimuli) occurring both inside and outside the body.  Integration - processes and interprets the sensory input and decides what should be done at each moment.  Motor output – causes the effect, by activating muscles or glands  Functional Classification of Neurons  Sensory (afferent) neurons – conduct nerve impulses from sensory receptors  Somatic sensory (afferent) fibers – deliver impulses from the skin, skeletal muscles, and joints (soma = body)  Visceral sensory (afferent) fibers – transmit impulses from the visceral organs.  Motor (efferent) neurons - conduct nerve impulses from CNS  The somatic (voluntary) nervous system - consciously or voluntarily controls our skeletal muscles.  The autonomic (involuntary) nervous system (ANS) - activity of smooth muscle, cardiac muscle, glands. Sympathetic nervous system Parasympathetic nervous system  Interneurons – links between sensory and motor neurons  Terminology Peripheral nervous system (PNS) – cranial and peripheral nerves Afferent – arriving information to the CNS Efferent – exiting information out of CNS Nerve – a bundle of axons located outside of brain and spinal cord Tract - a bundle of axons located inside of brain and spinal cord Nucleus – a group of neurons within the CNS with a similar function, connectivity and neurotransmitters Ganglia – a group of neurons outside of the CNS with a similar function, connectivity and neurotransmitters Somatic nervous system–afferent and efferent systems that regulated motor innervation of skeletal muscles and sensory information from the external environment. Autonomic nervous system – afferent and efferent systems that regulate  Gross Anatomy of the Nervous System  Brain  Cerebrum (Cerebral Hemispheres)  Diencephalon  Thalamus  Hypothalamus  Brain stem  Midbrain  Pons  Medulla  Cerebellum  Spinal cord  Structure of Spinal Cord The spinal cord finishes growing at the age of 4. The vertebral column finishes growing at the age 14-18. In adults the spinal cord occupies only the upper 2/3 of the vertebral column. Spinal cord is usually longer in males (approximately 45 cm.) than in females (approximately 42 cm.)  Structure of Spinal Cord  Margins of the spinal cord: Foramen magnum at the base of the scull L1/L2 vertebra - conus medullaris  Cauda equina (“horse’s tail”): collection of nerve roots at inferior end of vertebral canal  Filum terminale - from the tip of the conus medullaris till the 1st coccygeal vertebra (Co1) and anchors the spinal cord in place  Two enlargements: Cervical level (C5 – T1 spinal segments) – upper limbs Lumbosacral level (L1 – S3 spinal segments) – lower limbs  Spinal Meninges Dura mater – extends to the posterior surface of the vertebral body of S2 Subdural space  Arachnoid mater Subarachnoid space Pia mater  Meninges 3 meninges:  dura mater (outer)  arachnoid mater (middle)  pia mater (inner)  Intima pia – adherent to the surface of the spinal cord  Epipia – carries blood vessels that supply and drain spinal cord 3 potential spaces  epidural: outside dura  subdural: between dura and arachnoid  subarachnoid: deep to arachnoid Spinal Cord Pia Mater The spinal cord is attached to the dura by lateral denticulate ligaments (20-21 pairs) emanating from the pial folds The denticulate ligament is a flat continuous sheet between the anterior and posterior roots. Sleeve like projections from the denticulate ligaments at the posterior and anterior rootlets extend out through the arachnoid mater to attach onto the dura mater. Structure of Spinal Cord Spinal cord comprises 31 segments: Cervical – 8 (C1 – C8) Thoracic - 12 (T1 – T12) Lumbar – 5 (L1 – L5) Sacral – 5 (S1 – S5) Coccygeal – 1 (Co1) Spinal vertebrae: Cervical – 7 (C1 – C7) Thoracic -12 (T1 – T12) Lumbar – 5 (L1 – L5) Sacral – 5 (S1 – S5) Coccyx – 4 (3-5) (fused)  Spinal cord and spinal nerves Anterior median fissure Anterolateral sulci Posterior median sulcus Posterolateral sulci Ventral root Dorsal root Dorsal root swellings – ganglion (somas of sensory neurons) Spinal nerve proper (leaving the dural sheath) – intervertebral foramen Spinal cord gray matter  The grey matter - butterfly-shaped central part of the spinal cord and is comprised of neuronal cell bodies.  Grey matter tructures:  The dorsal/posterior horn - neurons receive somatosensory information from the body, transmitted to the brain via the ascending pathways.  The ventral/anterior horn - motor neurons that innervate skeletal muscle.  The lateral horn - contain sympathetic neurons  White matter - axons surrounds the gray matter; contains pathways that connect the brain with the rest of the body. Internal Features Ventral/anterior horns – motor neurons Dorsal/posterior horns – sensory information Intermediolateral cell column T1 to L2 region – preganglionic cell bodies of the sympathetic nervous system Gray commissure Central canal - CSF Spinal cord and spinal nerves External Features The anterior median fissure The posterior median sulcus Rootlets coalesce and form anterior and posterior roots that converge and form 31 pairs of spinal nerves. Cervical enlargement – C5 to T1 (upper extremities) Lumber enlargement – L1/2 to S3 (lower extremities) Sympathetic ganglia – T1 – L2  Spinal Nerve Branches Anterior ramus - innervates the skin and muscles of the anterior aspect of the trunk. Posterior ramus - innervates the post-vertebral muscles and the skin of the back. Meningeal branch - reenters the vertebral canal, provides sensory and vasomotor innervation to the spinal meninges Communicating branches - connect with a string of sympathetic chain ganglia alongside the vertebral column  Meningeal Branches Each spinal nerve gives rise to 2-4 small recurrent meningeal nerves near the point of division into anterior and posterior rami These nerves reenter the intervertebral foramen to supply dura, ligaments, intervertebral discs, and blood vessels.  Anterior Rami Anterior rami Intercostal nerves - skin and intercostal muscles (the internal oblique, external oblique, and transverse abdominal muscles).  Grey Matter - Spinal Cord Nuclei Spinal neurons are organized into nuclei (8) and lamina/Rexed’s lamina (10 zones) Neuronal cells are grouped according to their structure and function Each lamina is composed of neurons which led Rexed to propose a new classification based on 10 layers (laminae) Spinal cord white matter White matter is made of axons - pathways that connect the brain with the rest of the body. Anterior/ventral funiculus - limited medially by the ventral median fissure, laterally - by the ventrolateral sulcus. Lateral funiculus – limited ventrally and dorsally by the ventrolateral and dorsolateral sulci. Posterior/dorsal funiculus – limited laterally by the dorsolateral sulcus, and medially - the dorsal median sulcus.  White matter of the spinal cord Ascending fibers: sensory information from sensory neurons of body up to brain Descending fibers: motor instructions from brain to spinal cord Stimulates contraction of body’s muscles Stimulates secretion from body’s glands Peripheral Nervous System Gray and White Matter of Nervous System Grey matter increases until the age of 8 - 10. After year eight, the grey matter begins to decrease in areas of the brain, but the density of the grey matter increases. In an autopsy study of normal brains from age 20 to 90:  White matter loss (by volume) was 28 percent  Neocortical (gray matter) loss, was 12 percent. Spinal Blood  Anterior spinal artery – supplies anterior 2/3 of Supply the spinal cord  Two posterior spinal arteries – supply posterior 1/3 of the spinal cord  Anterior and posterior radicular arteries (from ascending cervical, deep cervical, intercostal, lumbar and sacral arteries) - 31 pairs alongside the dorsal and ventral roots of spinal nerves.  Supply:  Spinal cord  Spinal nerve roots  Anterior and posterior spinal arteries  Arterial vasocorona – anastomose between the spinal arteries – supplies pia mater Spinal Blood Supply Anterior spinal artery (from vertebral aa.) – anterior median fissure Posterior spinal arteries (from the vertebral artery or the posterior-inferior cerebellar artery) – run along the posterolateral sulcus Arteria radicularis magna/artery of Adamkiewicz (from T10 – T12)  Blood Supply Three anterior spinal veins Three posterior spinal veins Anterior and posterior spinal veins drain into radicular veins.  Vertebral Venous Plexuses The radicular veins empty into the (internal and external) vertebral venous plexuses. The network empties into the vertebral (neck) and segmental (trunk) veins.  Functions of the Spinal Cord Conduction – input and output (up and down along the spinal cord) Neural integration – receive input from multiple sources, integrate the information, execute the appropriate output Locomotion – walking with repetitive, coordinated contractions of several muscle groups in the limbs (pattern generation) Reflexes – spinal reflexes play vital role in posture, motor coordination, and protective responses to pain or injury  Reflexes Reflexes - quick, involuntary, stereotyped reactions of glands or muscles to stimulation.  Stimulation – sensory input  Quick - five steps in a simple neural reflex.  Involuntary - occur without intent, often without our awareness, and they are difficult to suppress  Stereotyped—they occur in essentially the same way every time  Reflex Arc Arrival of a stimulus and activation of a receptor Activation of a sensory neuron Information processing in the CNS Activation of a motor neuron Response by a peripheral effector  Reflex Arc 1. Somatic receptors in the skin, muscles, and tendons 2. Afferent nerve fibers, which carry information from these receptors to the posterior horn of the spinal cord or to the brainstem 3. An integrating center, a point of synaptic contact between neurons in the gray matter of the cord or brainstem 4. Efferent nerve fibers, which carry motor impulses to the muscles 5. Effectors, the muscles that carry out the response Patellar Tendon  Biceps tendon Biceps tendon Triceps tendon Spina Bifida Nerve root impingement Spinal nerve impingement Disc protrusion Thank You