Nerves

Chapter 13: The Nervous System

Introduction

  • Lecture presented by Steven Bassett, Southeast Community College

  • Focus on Nervous Tissue

  • © 2018 Pearson Education, Inc.

Page 2: Overview of the Nervous System

Structure of the Nervous System

  • Central Nervous System (CNS):
      - Comprises the brain and spinal cord.

  • Peripheral Nervous System (PNS):
      - All nervous tissue outside the CNS.

Page 3: Organisation of the Nervous System

Key Pathways

  • Information Flow:
      - Sensory information travels from spinal cord to brain (ascending pathways shown in red).
      - Motor commands travel from brain to PNS (descending pathways shown in green).

  • Nervous System Divisions:
      - CNS components: spinal cord and brain.
      - PNS components: spinal (31 pairs) and cranial (12 pairs) nerves.

Page 4: CNS & PNS Overview

CNS

  • Function: Processes sensory information and directs motor commands.

  • Afferent Division (sensory): Carries sensory information to CNS.

  • Efferent Division (motor): Carries motor commands away from CNS.

PNS Subdivisions

  1. Somatic Nervous System:
       - Controls voluntary movements of skeletal muscles.

  2. Autonomic Nervous System:
       - Manages involuntary body functions.
       - Divisions:
         - Parasympathetic: Rest-and-digest response.
         - Sympathetic: Fight-or-flight response.

Types of Receptors

  • Special Sensory Receptors:
      - Provide sensations of smell, taste, vision, balance, and hearing.

  • Somatic Sensory Receptors:
      - Monitor skeletal muscles, joints, skin surface; provide position sense, touch, pressure, pain, and temperature sensations.

  • Visceral Sensory Receptors:
      - Monitor internal organs.

Effectors

  • Target tissues include:
      - Skeletal muscles.
      - Smooth muscles.
      - Cardiac muscles.
      - Glands.

Page 5: Neural Tissue Organization

PNS Components

  • Gray Matter:
      - Comprises ganglia, which are collections of neuron cell bodies.

  • White Matter:
      - Comprises nerves, which are bundles of axons.

CNS Gray Matter Organization

  • Neural Cortex: Gray matter on the surface of the brain.

  • Nuclei: Collections of neuron cell bodies in the interior of the CNS.

  • Centers: Specialized processing functions in the CNS.

  • Higher Centers: Most complex processing centers found in the brain.

CNS White Matter Organization

  • Tracts: Bundles of CNS axons sharing a common origin, destination, and function.

  • Columns: Several tracts forming an anatomically distinct mass.

Pathways

  • Connect brain with other organs and systems in the body:
      - Sensory Pathway: Ascending pathways carrying sensory information.
      - Motor Pathway: Descending paths carrying motor commands.

Page 6: Major Brain Regions

Cerebrum

  • Functions:
      - Conscious thought processes.
      - Memory storage and processing.
      - Regulation of skeletal muscle contractions.

  • Anatomical Features:
      - Gyri: Ridges.
      - Sulci: Grooves.
      - Fissures: Deep grooves.

Diencephalon Components

  1. Thalamus: Relay center for sensory information.

  2. Hypothalamus: Controls emotions, autonomic functions, and hormone production.

  3. Mesencephalon (Midbrain):
       - Generates reflexive somatic motor responses.
       - Maintains consciousness.

Cerebellum

  • Coordinates complex motor patterns.

  • Adjusts output of somatic motor centers in the brain and spinal cord.

Brainstem Components

  • Pons: Relays sensory information to cerebellum and thalamus.

  • Medulla Oblongata: Controls autonomic functions related to cardiovascular, respiratory, and digestive systems.

Page 7: Brain Anatomy

Features

  • Structures of the brain include:
      - Corpus callosum
      - Thalamus
      - Hypothalamus
      - Cingulate gyrus
      - Pineal gland
      - Mesencephalon
      - Cerebellum
      - Cerebral cortex (gray matter)
      - Sulcus
      - Fissure (deep sulcus)

Page 8: Cerebellum and Components

  • Key structures of the cerebellum include:
      - Anterior lobe
      - Posterior lobe
      - Arbor vitae (tree-like structure of white matter)
      - Cerebellar cortex

  • Cerebellar Peduncles: Connect cerebellum to brainstem.

Page 9: Lobes of the Cerebrum

  • Frontal lobe, parietal lobe, temporal lobe, and occipital lobe.

  • Major functions associated with lobes:
      - Frontal Lobe: Decision making, motor function.
      - Parietal Lobe: Sensory processing.
      - Temporal Lobe: Auditory processing.
      - Occipital Lobe: Visual processing.

Page 10: Gyrus and Sulcus Identification

Key Features

  • Central Sulcus: Divides frontal and parietal lobes.

  • Precentral Gyrus: Primary motor cortex.

  • Postcentral Gyrus: Primary sensory cortex.

Page 11: Insular Lobe

  • The insular lobe is enclosed by the opercula of the frontal, temporal, and parietal lobes. It plays a role in consciousness and perception of bodily states.

Page 12: Insula

  • Important for various functions including emotional responses, perception of taste, and autonomic control.

Page 13: Motor and Sensory Regions of the Cerebral Cortex

Primary Areas

  • Primary Motor Cortex: Located in the precentral gyrus; responsible for motor signals.

  • Primary Sensory Cortex: Located in the postcentral gyrus; responsible for receiving sensory input.

  • Somatic Motor Association Area (Premotor Cortex): Processes and plans motor actions.

  • Somatic Sensory Association Area: Integrates sensory data from multiple sources.

  • Broca's Area: Associated with speech production.

  • Wernicke's Area: Associated with understanding speech.

  • Visual Cortex: Processes visual information.

  • Auditory Association Area: Processes auditory data for understanding.

Page 14: Ventricular System and Components

  • Lateral Ventricle: Largest ventricles located in the cerebral hemispheres.

  • Third Ventricle: Located between the thalamus.

  • Fourth Ventricle: Found between the cerebellum and brainstem.

  • Choroid Plexus: Structures producing cerebrospinal fluid.

Page 15: Anatomy of Spinal Cord and Nerves

  • The spinal cord ends at the conus medullaris, with the filum terminale anchoring it to the coccyx.

  • The Cauda Equina is formed by spinal nerves extending below the conus medullaris.

Page 16: Cranial Meninges

Functions

  • Dura Mater: Tough outer layer providing protective encasement.

  • Arachnoid Mater: Middle layer housing the cerebrospinal fluid in the subarachnoid space.

  • Pia Mater: Delicate inner layer adhering to the brain surface.

Page 17: Blood-Brain Barrier and Composition

  • Structures that control substances entering the CNS and protect from pathogens and toxins.

Page 18: Spinal Cord Overview

Gross Anatomy

  • Composed of:
      - Cervical enlargement
      - Lumbosacral enlargement
      - Conus medullaris
      - Filum terminale
      - Cauda equina
      - Anterior and posterior median fissures and sulcus.

Page 19: Spinal Cord Cross-section

Features

  • Gray Matter:
      - Organized into horns including anterior, lateral, and posterior horns.

  • White Matter:
      - Organized into columns that contain ascending and descending tracts.

Page 20: Spinal Nerve Structure

Components

  • Each spinal nerve divides into anterior (ventral) and posterior (dorsal) rami.

  • Dorsal Root Ganglion: Contains the sensory neurons for that segment.

Page 21: Dermatome and Myotome Maps

Definition

  • Dermatome: Skin area supplied by a specific spinal segment.

  • Myotome: Muscle group innervated by a single spinal nerve root.

Page 22: Peripheral Nervous System

Overview of PNS

  • Composed of nerves and ganglia outside CNS which connect to limbs and organs.

Page 23: Cranial Nerves Summary

Total of 12 Pairs

  • Primarily serve the head and neck regions. Only the vagus nerve extends into thoracic and abdominal cavities.
      - Mainly mixed nerves but three are sensory only:
        1. Olfactory (CN I)
        2. Optic (CN II)
        3. Vestibulocochlear (CN VIII)

Page 24: Mnemonic for Cranial Nerves

Device to Remember Order:

  • "Oh, Oh, Oh, To Touch And Feel Very Green Vegetables, AH!"
      - Each initial corresponds to the first letter of each cranial nerve:
        1. Olfactory
        2. Optic
        3. Oculomotor
        4. Trochlear
        5. Trigeminal
        6. Abducens
        7. Facial
        8. Vestibulocochlear
        9. Glossopharyngeal
        10. Vagus
        11. Accessory
        12. Hypoglossal

Page 25: Specific Cranial Nerve Functions

Examples

  • Olfactory Nerve (CN I): Responsible for smell.

  • Optic Nerve (CN II): Responsible for vision.

  • Trigeminal Nerve (CN V): Responsible for sensation of the face and motor functions such as biting and chewing.

  • Facial Nerve (CN VII): Involved in facial expressions, taste sensations, and glandular secretions.

  • Vagus Nerve (CN X): Extends into viscera, involved in regulating heart rate and digestion.

Page 26: Summary of Functions of the Cranial Nerves

  • Each nerve has specific sensory, motor, or autonomic function related to various parts of the body, ensuring coordinated actions and responses.

Conclusion

  • Understanding the organization and functions of the nervous system is crucial for grasping how the body controls and coordinates all its actions, responses to internal and external stimuli, and maintains homeostasis. This information forms the basis for further learning in anatomy, physiology, and medical sciences.

Overview of Extremity Nerves

Upper Extremity Nerves

  • Brachial Plexus: Network of nerves originating from spinal nerves C5 to T1, responsible for motor and sensory function in the upper limb.
      - Major branches include:
        - Musculocutaneous Nerve: Innervates the anterior compartment of the upper arm,(coracobrachialis, biceps, and medial brachialis) controlling flexion of the elbow.

    •  Once it enters the forearm, it is purely sensory innervation by giving rise to the lateral antebrachial cutaneous n. (causes sensations in lateral forearm

    • Axillary Nerve: Innervates the deltoid and teres minor muscles, responsible for shoulder abduction.

      • Gives rise to the lateral brachial cutaneous nerve n.

      • Radial Nerve: Innervates extensor muscles of the arm and forearm, controlling wrist and finger extension.

        • radial= INE: triceps, lateral brachiallis, ECRL, and BRR, posterior brachial cutaneous and posterior antebrachial cutaneous

        • deep radial= INE= supinator, ED, EDM, ECRB, and ECU and then gives rise to the posterior interosseus nerve

        • posterior interosseous n= INE= EI and ABD PL, EPL, and EPB

        • superficial radial n= does NOT innervate muscles but gives crosses the snuffbox and is responsible for sensations to the lateral and back parts of hand, but NOT to the skin of the distal phalanges
              - Median Nerve: Innervates most of the anterior forearm muscles (excpet FCU and .5 FDP because that’s for ulnar n.

        • INE the themar muscles of hand (except ADD P because ulnar n. took that) and the lateral 2 lumbericals

        • responsible for thumb opposition. Enters hand through the CARPAL TUNNEL.
              - Ulnar Nerve: NO INE in upper arm, Innervates1.5 forearm muscles (FCU and .5 FDP) and hand muscles (hypothemar, first 2 lumbericals, all interossei, and ADDP/deep FPB from themar), particularly important for fine motor control in the hand.

Lower Extremity Nerves

  • Lumbar and Sacral Plexuses: Networks of nerves that arise from the lumbar and sacral spinal nerves, serving the lower limbs and pelvis.
      - Major branches include:
        - Femoral Nerve: Innervates the quadriceps muscle, pectineus, sartorious, and iliacus crucial for knee extension.

    • Femoral nerve branches into the anterior femoral cutaneous nerve which INE skin of the anterior and lateral thigh

    • Femoral nerve also branches into the saphenous nerve which goes into the adductor hiatus with the femoral artery and vein and follows down the lower leg to INE the skin of the medial lower leg and foot

  •   - Obturator Nerve: Innervates the medial compartment of the thigh, affecting hip adduction. INE all adductor muscles like the ADD longus, magnus, brevis, gracilis and pectineus and also the obsturator externus
        - Sciatic Nerve: The largest nerve in the body, it branches into the tibial and common fibular (peroneal) nerves, providing motor and sensory functions to the lower leg and foot. IInnervates all hamstring muscles except the biceps femoris short head.
          - Tibial Nerve: Innervates the posterior compartment (tibialis posterior, FHL, FDL, gastrocnemius, soleous, plantaris, and popliteus) of the leg and the plantar aspect of the foot, responsible for plantarflexion and toe flexion. At the level of the foot the tibial nerve splits into the medial and lateral plantar nerves

    • the medial plantar nerve innervates ABD H, FDB, FHB, and 1st lumberical

    • the lateral plantar nerve innervates FDMB, ABD DM, ADD H, QP, and lateral 3 lumbericals, and dorsal and plantar interossei
            - Common Fibular Nerve: Wraps laterally around the neck of the fibula and branches into the deep and superficial peroneal nerves which Innervate the anterior and lateral compartments of the leg, affecting dorsiflexion and eversion of the foot.

      • deep peroneal nerve= INE anterior compartment muscles like the tibialis anterior, EHL/B, EDL/B, and FT

      • superfifical peroneal nerve= INE the lateral compartment muscles like the FL and FB

    • BOTH the tibial and common fibular nerves gives rise to the sural nerve. The sural (calf) nerve runs superficially down the posterior leg, below the lateral malleolus, and is responsible for sensations in the posterior/lateral parts of the lower leg and llateral foot

Functions and Importance

  • Understanding the anatomy and function of upper and lower extremity nerves is essential for diagnosing and treating nerve injuries, understanding movements, and designing rehabilitation strategies.