Nervous Tissue and Lower Limb Anatomy

Divisions of the Nervous System

  • Central Nervous System (CNS): Comprised of the brain and the spinal cord.

  • Peripheral Nervous System (PNS): Divided into sensory pathways and motor pathways.     * Motor Pathways: Subdivided into the Somatic (voluntary) nervous system and the Autonomic (involuntary) nervous system.     * Autonomic Nervous System: Further divided into the Sympathetic division and the Parasympathetic division.

Nervous Tissue Structure and Cellular Composition

  • Primary Components: Nervous tissue is composed of neurons and neuroglia.     * Neurons: Specialized cells that send electrical signals.     * Neuroglia: Cells that support, protect, and nourish neurons.

  • Key Neuron Structures:     * Cell Body: The part of the neuron containing the nucleus and various organelles.     * Nissl Bodies: Granules of rough endoplasmic reticulum (ER) located within the neuron cytoplasm.     * Dendrites: Branching structures that receive impulses and transmit them toward the cell body.     * Axon: The structural part of the neuron that carries nerve impulses away from the cell body.     * Axon Hillock: The cone-shaped area where the axon leaves the cell body.     * Myelin Sheath: Fatty layers that surround and electrically insulate the axon to speed up nerve impulses.     * Nodes of Ranvier: The gaps found between Schwann cells along the axon.     * Schwann Cells: Cells responsible for forming myelin sheaths around axons specifically in the Peripheral Nervous System (PNS).     * Oligodendrocytes: Cells responsible for forming myelin sheaths around axons specifically in the Central Nervous System (CNS).     * Axon Terminals (Synaptic Knobs): The ends of the axon containing membrane sacs called synaptic vesicles.

The Chemical Synapse and Neuromuscular Junction (NMJ)

  • Synapse Definition: The location where a neuron meets another cell (another neuron or an effector).

  • Synapse Components:     * Presynaptic Neuron: The neuron located before the synapse.     * Postsynaptic Neuron: The neuron located after the synapse.     * Synptic Cleft: The physical area or gap where the presynaptic and postsynaptic neurons meet.     * Synaptic Vesicles: Membrane sacs located in the axon terminals that store neurotransmitters.     * Neurotransmitter: The chemical message released by the presynaptic neuron to bind to the postsynaptic neuron.

  • Chemical Synapse Mechanism:     1. An action potential reaches the presynaptic terminal.     2. Voltage-gated Ca2+Ca^{2+} channels open, allowing calcium to enter the cell.     3. Ca2+Ca^{2+} triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft via exocytosis.     4. Neurotransmitters bind to ligand-gated ion channels on the postsynaptic membrane.     5. Ion channels (e.g., Na+Na^{+} channels) open, altering the membrane potential of the postsynaptic cell.

  • Neuromuscular Junction (NMJ): A specific type of synapse involving a motor neuron and muscle fibers.     * Motor Unit: Consists of a single motor neuron and all the muscle fibers it innervates.     * Acetylcholine (ACh): The specific neurotransmitter used at the neuromuscular junction to initiate muscle contraction.

General Classification of Neurons

  • Structural Classification: Based on the number of extensions (processes) attaching to the cell body.     * Unipolar Neurons: Possess one single extension off the cell body; commonly found in the dorsal root ganglion of the spinal cord.     * Bipolar Neurons: Possess two extensions from the cell body; located in special sensory organs such as the retina of the eye.     * Multipolar Neurons: Possess multiple extensions from the cell body; the most abundant neuron type in the human body.

  • Functional Classification: Based on the direction of impulse transmission.     * Sensory (Afferent) Neurons: Transmit impulses from sensory receptors in the skin or organs toward the Central Nervous System (CNS).     * Interneurons: Conduct impulses within the CNS and integrate incoming sensory input to determine the proper motor output.     * Motor (Efferent) Neurons: Carry impulses away from the CNS to effectors, including muscles, organs, or glands.

Osteology of the Lower Limb

  • Femur (Thigh Bone):     * Anterior Markings: Head, neck, greater trochanter, lesser trochanter, intertrochanteric line, lateral epicondyle, medial epicondyle, patellar groove.     * Posterior Markings: Fovea capitis, intertrochanteric crest, gluteal tuberosoty, pectineal line, linea aspera (insertion site for thigh adductors), lateral condyle, medial condyle, intercondylar fossa.

  • Patella (Kneecap): Includes anterior and posterior views; functions within the femoropatellar joint.

  • Tibia (Shin Bone): Supports and distributes weight across the knee to the ankle.     * Markings: Tibial tuberosity (distal attachment for the patellar ligament), medial condyle, lateral condyle, medial malleolus.

  • Fibula: Stabilizes the ankle and supports the muscles of the lower leg.     * Markings: Head, lateral malleolus.

  • Bones of the Foot:     * Tarsals (7 bones): Medial cuneiform (MC), intermediate cuneiform (IC), lateral cuneiform (LC), cuboid (Cu), navicular (N), talus (T), and calcaneous (Ca).     * Metatarsals: Numbered #1 through #5.     * Phalanges (14 bones): Named by number (#1 - #5) and position (proximal, medial, distal).         * Proxmial Phalanx #1 - #5.         * Medial Phalanx #1 - #5.         * Distal Phalanx #1 - #5.

Joints of the Lower Limb

  • Coxal (Hip) Joint: Formed by the acetabulum of the os coxa and the head of the femur. It is a synovial, multiaxial, ball and socket joint.

  • Sacroiliac Joint: Found between the sacrum and the iliac bone.

  • Pubic Symphysis: The joint located between the left and right pubic bones.

  • Knee Joint Complex:     * Tibiofemoral Joint: Formed by the medial and lateral condyles of the femur articulating with the medial and lateral condyles of the tibia. It is a synovial, biaxial, modified hinge joint containing menisci, bursa, and ligaments.     * Femoropatellar Joint: Articulation between the patella and the patellar surface of the femur. It is a synovial plane joint allowing for the gliding of the patella.

  • Tibiofibular Joints:     * Superior Tibiofibular Joint: Located between the tibia and fibula near the knee.     * Inferior Tibiofibular Joint: Located between the distal ends of the tibia and fibula with the lateral malleolus of the fibula near the ankle.

  • Ankle and Foot Joints:     * Talocrural (Ankle) Joint: Articulation between the tibia, fibula, and the proximal end of the talus.     * Tibiotarsal Joint: Specifically the joint between the tibia and tarsal bones.     * Intertarsal Joint: Found between individual tarsal bones.     * Tarsometatarsal Joint: Found between the tarsals and metatarsals.     * Metatarsophalangeal Joint: Found between the metatarsals and phalanges.     * Interphalangeal Joint: Found between the phalanges of the toes.

Myology of the Lower Limb

  • Anterior and Lateral Lower Limb Muscles:     * Sartorius: Originates at the anterior superior iliac spine; inserts at the superior aspect of the medial surface of the tibial shaft near the tibial tuberosity. Actions include flexing and laterally rotating the hip joint and flexing the knee. Innervated by the femoral nerve.     * Tensor Fasciae Latae (TFL): Originates on the pelvis; inserts on the tibia via the iliotibial (IT) band. Actions include hip flexion and hip abduction.     * Quadriceps Group: Main extensors of the leg at the knee. Originates at the iliac spine and inserts at the tibial tuberosity (base of patella). Includes Rectus femoris, Vastus lateralis, and Vastus medialis.     * Tibialis Anterior: Facilitates dorsiflexion (pulling the foot toward the shin) and raising toes upwards.     * Extensor Digitorum Longus: Located in the anterior/lateral leg.

  • Medial Lower Limb Muscles (Adductor Group):     * Gracilis: Most superficial adductor. Originates from the thin aponeurosis on the medial surface of the inferior body of the pubis; inserts on the proximal aspect of the medial surface of the tibia. Actions: Hip adduction, knee flexion, and knee internal rotation.     * Other Adductors: Pectineus, Adductor brevis, Adductor longus.

  • Posterior Lower Limb Muscles:     * Gluteal Group:         * Gluteus Maximus: Major extensor of the hip joint. Originates from the posterior surfaces of the ilium, sacrum, and coccyx; inserts at the gluteal tuberosity of the femur and the iliotibial band. Involved in standing from a sitting position, climbing stairs, and standing erect.         * Gluteus Medius: Action is abduction of the hip.         * Gluteus Minimus: Action is abduction of the hip.     * Hamstring Group:         * Biceps Femoris: Involved in knee flexion and hip extension.         * Semitendinosus: Originates at the ischial tuberosity of the ischium; inserts at the superior and medial aspect of the tibia. Action: Decreases the angle at the knee (flexion).         * Semimembranosus: Involved in knee flexion and hip extension.     * Calf Muscles:         * Gastrocnemius: Large calf muscle involved in plantarflexion (standing on toes), running, and jumping.         * Soleus: Works with the gastrocnemius for plantarflexion at the ankle.         * Achilles (Calcaneal) Tendon: Common insertion for gastrocnemius and soleus onto the calcaneus.

  • Lateral Leg Muscles:     * Fibularis (Peroneus) Longus: Originates on the upper two-thirds of the fibula and intermuscular septa; inserts at the plantar base of the first metatarsal and first cuneiform. Action: Plantarflexes and everts the foot.     * Fibularis (Peroneus) Brevis: Involved in foot movement.

Muscle Movement and Action Predictions

  • Basic Principle: When a muscle contracts, the insertion moves toward the origin.

  • Movement of Femur at the Coxal Joint:     * Flexion (Anterior/Medial muscles): Rectus femoris, Sartorius, Adductor group.     * Extension (Posterior muscles): Gluteus maximus, Biceps femoris, Semimembranosus, Semitendinosus, Adductor group.     * Abduction (Lateral muscles): Gluteus medius, Sartorius, Tensor fascia latae.     * Adduction (Medial muscles): Adductor group.

  • Movement of Tibia at the Tibiofemoral Joint:     * Extension (Anterior thigh muscles): Rectus femoris, Vastus medialis, Vastus lateralis. These muscles increase the angle at the knee joint.     * Flexion (Posterior thigh muscles): Biceps femoris, Semimembranosus, Semitendinosus. These muscles decrease the angle at the knee joint.

  • Movement of Foot at the Tibiotarsal Joint:     * Dorsiflexion (Anterior tibia muscles): Tibialis anterior.     * Plantarflexion (Posterior/Lateral tibia muscles): Gastrocnemius, Fibularis longus.