NERVOUS SYSTEM - SPINAL CORD - SEPT 2024 PDF

RNB 10603 BASIC ANATOMY & PHYSIOLOGY 1 TOPIC 5 NERVOUS SYSTEM PART 3: Spinal Cord 1  LEARNING OUTCOME At the end of the session, the students should be able to: 1. describe how the spinal cord is protected; 2. describe the gross structure and internal structu...

RNB 10603 BASIC ANATOMY & PHYSIOLOGY 1 TOPIC 5 NERVOUS SYSTEM PART 3: Spinal Cord 1  LEARNING OUTCOME At the end of the session, the students should be able to: 1. describe how the spinal cord is protected; 2. describe the gross structure and internal structure of the spinal cord; 3. explain the functions of the spinal cord; 4. state the functions of the nerve tracts in the spinal cord: sensory (afferent) and motor (efferent); 5. explain the reflex activity. 2  SPINAL CORD ◼ The spinal cord is the elongated, almost cylindrical part of the CNS. ◼ Located within the vertebral canal. ◼ Extend from the foramen magnum at the base of the skull to the 2nd lumbar vertebra. ◼ surrounded by the meninges and cerebral spinal fluids (CSF). ◼ The spinal cord communicates between the brain and the PNS. ◼ Spinal nerves allow movement and sensation. If damaged, paralysis can occur. 3  SPINAL CORD STRUCTURE: Protection and Coverings ◼ Vertebrae ◼ Spinal meninges ✓ Three layers of connective tissue ◼ Dura mater ◼ Arachnoid mater ◼ Pia mater ✓ Continuous with cranial meninges ◼ Cerebrospinal fluid (CSF) ✓ acts as a cushion to protect the nerve tissues 4 5  SPINAL CORD STRUCTURE: Spinal Meninges and Spaces ◼ Epidural space: between vertebrae and dura mater ◼ Dura mater: tough ,dense connective tissue ✓ Extends to vertebra S2 (well beyond spinal cord) ◼ Arachnoid mater: resembles spider’s web ✓ Extends into subarachnoid space ◼ Subarachnoid space ✓ CSF circulates in this space ◼ Pia mater: thin, delicate layer ✓ Adheres to surface spinal cord (and brain) ✓ Contains blood vessels 6 Spinal Meninges and Spaces 7 GROSS ANATOMY OF SPINAL CORD ◼ ≈ 42-45cm long in adult, about the thickness of the little finger ◼ Spinal cord is shorter than the vertebral column, nerves that arise from the lumbar, sacral & coccygeal regions of the spinal cord do not leave the column at the same level = cauda equine ◼ Cauda equina (meaning horse’s tail) ✓ Extends inferior to end of spinal cord ✓ Consists of roots of lumbar, sacral and coccygeal spinal nerves 8 9 GROSS ANATOMY OF SPINAL CORD ◼ The spinal cord has 2 enlargements: ✓ cervical enlargement: contains nerves that supply the upper limbs ✓ lumbar enlargement: contains nerves that supply the lower limbs ◼ In the spinal cord, white matter surrounds a centrally located H-shaped mass of gray matter ◼ Spinal nerves= the paths of communication between the spinal cord & specific regions of body 10 GROSS ANATOMY OF SPINAL CORD ◼ 2 roots (bundle of axons) connect each spinal nerve to a segment of the cord: i. Posterior (dorsal root) ✓ Contains only sensory axon (conduct nerve impulses from sensory receptors in the skin, muscles & internal organs into CNS) ✓ Each posterior root has a swelling - posterior (dorsal) root ganglion, contains the cell bodies of sensory neuron ii. Anterior (ventral root) ✓ Contains axons of motor neurons (conduct impulses from the CNS to effectors (muscles and glands) 11 12  INTERNAL STRUCTURE OF SPINAL CORD ◼ Gray matter forms “H” (like a “butterfly”) ✓ Three horns on each side; sites of cell bodies ◼ Posterior (dorsal) gray horns: contain sensory neurons ◼ Anterior (ventral) gray horns: contain somatic motor neurons (provide nerve impulses for contraction of skeletal muscles) ◼ Lateral gray horn: contain autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle and glands ✓ Small central canal in middle filled with CSF 13  INTERNAL STRUCTURE OF SPINAL CORD ◼ White matter (surrounds gray matter “H”) ✓ Consists primarily of myelinated axons ✓ Organized into regions called white columns ◼ Posterior, anterior and lateral white columns ◼ Contain tracts (bundles of axons) i. Sensory (ascending) tracts: impulses ascending towards the brain ii. Motor (descending) tracts: carry nerve impulses from the brain down the spinal cord ✓ Sensory and motor tracts of the spinal cord are continuous with sensory and motor tracts in the brain 14 Internal Structure of Spinal Cord 15 Internal Structures of The Spinal Cord 16 Internal Structures of The Spinal Cord 17 18 Spinal cord nerve tracts 19  FUNCTIONS OF SPINAL CORD ◼ Pathways for nerve impulses within tracts ✓ Ascending (sensory), example: spinothalamic ✓ Descending (motor), example: corticospinal ◼ Reflexes - fast, involuntary sequences of actions in response to stimuli ✓ Can be simple (withdrawal) or complex (learned sequence such as driving car) ✓ At different levels ◼ Spinal (reflex arc): simple ◼ Cranial: more complex 20  FUNCTIONS OF THE NERVE TRACTS Somatic Sensory Pathways ◼ Neurons that transmit impulses towards the brain are called sensory (afferent, ascending) neuron ◼ 2 main sources of sensation: ❑ Skin = cutaneous receptors ❑ Tendons, muscles & joints = proprioceptors ◼ Relay sensory information from somatic sensory receptors (periphery) to the primary somatosensory area (cerebral cortex) ◼ Most sensory input to right side of body reaches left side of brain (and vice versa) 21  FUNCTIONS OF THE NERVE TRACTS Somatic Sensory Pathways ◼ Crossing to the other side (decussation) occurs either at the level of entry into the spinal cord or in the medulla oblongata ◼ Posterior column - medial lemniscus pathway senses ❑ Fine touch: body location, texture, size ❑ Proprioception: position and motion of body parts ❑ Vibrations: fluctuating touch stimuli ◼ Spinothalamic pathways ❑ Anterior and lateral spinothalamic tracts ❑ Relay impulses for pain, tickle, itch, hot, and cold sensations 22 Somatic Sensory Pathways 23 Sensory nerve tracts 24 FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways ◼ Neurons that transmit nerve impulses away from the brain = motor (efferent / descending) neurons ◼ Signals come from ✓ Upper motor neurons: via corticospinal tracts ✓ Basal ganglia: help with muscle tone ✓ Cerebellum: coordination ✓ Sensory neurons or interneurons via reflexes 25 FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways ◼ Impulses activate lower motor neurons ✓ Cell bodies in anterior gray of spinal cord ✓ Axons → ventral root → spinal nerve → muscle → voluntary movements ◼ Motor neuron stimulation results in: ✓ Contraction of skeletal (voluntary) muscle ✓ Contraction of smooth (involuntary) muscle, cardiac muscle and the secretion by glands controlled by nerves of the autonomic nervous system 26 FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways ◼ Voluntary muscle movement ✓ Under conscious (voluntary) control, originate in the cerebrum ✓ Skeletal muscle activity is regulated by output from the midbrain, brain stem & cerebellum ✓ Associated with coordination of muscle activity, e.g. fine movement & maintenance of posture and balance 27 FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways ◼ Efferent nerve impulses are transmitted from the brain to other body parts via bundle of nerve fibres (tracts) in the spinal cord ◼ The motor pathways from the brain to the muscles are made of two neuron ◼ The pathways, or tracts are: ✓ Pyramidal (corticospinal) - Motor fibers within the internal capsule ✓ Extrapyramidal - Motor fibers DO NOT pass through the internal capsule 28  FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways ◼ The pyramidal (corticospinal) tracts cross over (decussate) at the medulla oblongata ◼ The extrapyramidal tracts are connected with many parts of the brain, such as the basal ganglia, thalamus and cerebellum 29 Somatic Motor Pathways 30 Tracing a Pain Impulse... Source → peripheral nerve towards spinal cord → enters dorsal horn of spinal cord → crosses to opposite side of spinal cord → ascends up spinal cord (lateral spinal thalamic tract)→ thalmus → sensory cortex 31 FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways Upper motor neuron: ◼ Its cell body is in the primary motor area of cerebrum ◼ The axons pass through the internal capsule, pons and medulla oblongata ◼ The axons of the upper motor neuron make up the pyramidal tracts and decussate in the medulla oblongata 32 FUNCTIONS OF THE NERVE TRACTS Somatic Motor Pathways Lower motor neuron: ◼ Its cell body is in the anterior horn of grey matter in the spinal cord ◼ Near its termination in skeletal muscle the axon branches into many tiny fibers = motor end plate ◼ The lower motor neuron is the final common pathway for the transmission of nerve impulses to skeletal muscles 33 Voluntary muscle movement 34  REFLEXES ACTIVITY ◼ Reflex is the mechanism by which the sensory impulse is automatically converted into a motor effect ◼ Reflex activity / action is an involuntary and immediate motor response to a sensory stimulus ◼ It is the basic defense mechanism of the nervous system ✓ happens very fast ✓ Most reflexes never reach the brain but regulated by the spinal cord 35  REFLEXES ACTIVITY Reflex Arc ◼ A reflex arc is referred to the pathway by which a reflex action travels, from the stimulus to the reflex muscle movement ◼ 5 components of reflex arc: 1. Sensory receptor 2. Sensory neuron 3. Integrating center 4. Motor neuron 5. Effector 36  REFLEXES ACTIVITY Reflex Arc ◼ 5 components of reflex arc: 1. Sensory receptor 2. Sensory neuron 3. Integrating center 4. Motor neuron 5. Effector 37  REFLEXES ACTIVITY Reflex Arc 1. Sensory receptor: responds to stimulus 2. Sensory neuron: through dorsal root ganglion and root → posterior horn 3. Integrating center: single synapse between sensory and motor neurons 4. Motor neuron: from anterior horn → ventral root → spinal nerve 5. Effector: muscle responds 38 39  REFLEXES ACTIVITY Types of Reflexes ◼ Deep tendon reflexes ✓ Elicited on stroking the tendon ✓ Basically stretch reflexes ✓ Example: knee jerk / patellar reflex, ankle jerk ◼ Visceral reflexes ✓ At least one part of the reflex arc is the autonomic nerve ✓ Also called autonomic reflexes ✓ Example: pupillary light reflex – the pupil constrict in response to light 40 Example of Reflex Arc: Patellar Reflex 41 Patellar Reflex 42  REFLEXES ACTIVITY Types of Reflexes ◼ Spinal reflex ✓ Integrate reflex activity between the afferent input and the efferent input without involving the brain ◼ Pathological reflexes ✓ Not present in normal condition ✓ Presence indicates pathological condition within the body ✓ Example: Babinski’s sign 43  REFLEXES ACTIVITY Types of Reflexes ◼ Spinal reflex 44 Spinal reflex 45  REFLEXES ACTIVITY Types of Reflexes ◼ Pathological reflexes Babinkski’s reflex 46  Clinical significance of reflexes ◼ Test for simple muscle reflexes, such as the patellar reflex, are basic to any physical exam when motor nerve or spinal damage is suspected. ◼ These test can help to locate the damage 47 SUMMARY - SPINAL CORD 48 Ascending and Descending Tract of the Spinal Cord 49 50 THANK YOU 51