Spinal Cord & Nerves Ch 13

The Spinal Cord

Peripheral Nervous System cranial nerves- 12 pr spinal nerves- 31 pr

The Spinal Cord white matter grey matter dorsal root pia mater ventral root pia mater spinal nerves arachnoid dura mater

The Spinal Cord vertebra spinal cord spinal nerve

Nerve Pathways into the Spinal Cord sensory pathway motor pathway

Neuron-To-Neuron Transmission synapses Interaction Between Neurons

Spinal Nerves

Spinal Cord

Spinal Nerves

Spinal Nerves

Cervical Plexus Formed by ventral rami of C1–C4 Innervates skin and muscles of the neck, ear, back of head, and shoulders Phrenic nerve Major motor and sensory nerve of the diaphragm (receives fibers from C3–C5)

Cervical Plexus

Brachial Plexus Formed by ventral rami of C5–C8 and T1 (and often C4 and T2) It gives rise to the nerves that innervate the upper limb Major branches of this plexus: Roots—five ventral rami (C5–T1) Trunks—upper, middle, and lower Divisions—anterior and posterior Cords—lateral, medial, and posterior

Brachial Plexus Roots (ventral rami): C4 Dorsal scapular C5 Nerve to subclavius C6 Suprascapular Upper Posterior divisions C7 Middle Trunks Lateral C8 Lower Cords Posterior T1 Long thoracic Medial Medial pectoral Lateral pectoral Axillary Upper subscapular Musculo- cutaneous Lower subscapular Thoracodorsal Radial Medial cutaneous nerves of the arm and forearm Median Ulnar (a) Roots (rami C5 – T1), trunks, divisions, and cords Anterior divisions Posterior divisions Trunks Roots Figure 13.9 (a)

Brachial Plexus: Nerves Axillary—innervates the deltoid, teres minor, and skin and joint capsule of the shoulder Musculocutaneous—innervates the biceps brachii and brachialis and skin of lateral forearm Median—innervates the skin, most flexors and pronators in the forearm, and some intrinsic muscles of the hand Ulnar—supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand Radial—innervates essentially all extensor muscles, supinators, and posterior skin of limb

Musculocutaneous nerve Ulna Radius Ulnar nerve Median nerve Axillary nerve Anterior divisions Posterior divisions Trunks Roots Humerus Radial nerve Musculocutaneous nerve Ulna Radius Ulnar nerve Median nerve Radial nerve (superficial branch) Dorsal branch of ulnar nerve Superficial branch of ulnar nerve Digital branch of ulnar nerve Muscular branch Median nerve Digital branch (c) The major nerves of the upper limb Figure 13.9 (c)

Thoracic Nerves T3-T12 11 intercostal nerve 1 subcostal nerve

Lumbar Plexus Arises from L1–L4 Innervates the thigh, abdominal wall, and psoas muscle Femoral nerve—innervates quadriceps and skin of anterior thigh and medial surface of leg Obturator nerve—passes through obturator foramen to innervate adductor muscles

Lumbar Plexus

Sacral Plexus Arises from L4–S4 Serves the buttock, lower limb, pelvic structures, and perineum Sciatic nerve Longest and thickest nerve of the body Innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot Composed of two nerves: tibial and common fibular

Sacral Plexus

Functional Divisions of the Peripheral Nervous System Afferent Division Sensory (advances) neuron – goes toward CNS Efferent Division Motor (exits) neuron- leaves CNS Somatic Nervous System Autonomic Nervous System A Typical Motor Neuron

Spinal Reflex Arc sensory neuron motor neuron stretch receptor interneuron stretch receptor motor neuron patellar ligament Spinal Reflex Arc

Quadriceps (extensors) Hamstrings (flexors) 1 Quadriceps strongly contracts. Golgi tendon organs are activated. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) + Excitatory synapse – Inhibitory synapse Figure 13.18, step 1

Quadriceps (extensors) Hamstrings (flexors) 1 Quadriceps strongly contracts. Golgi tendon organs are activated. 2 Afferent fibers synapse with interneurons in the spinal cord. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) + Excitatory synapse – Inhibitory synapse Figure 13.18, step 2

Quadriceps (extensors) Hamstrings (flexors) 1 Quadriceps strongly contracts. Golgi tendon organs are activated. 2 Afferent fibers synapse with interneurons in the spinal cord. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) 3a Efferent impulses to muscle with stretched tendon are damped. Muscle relaxes, reducing tension. + Excitatory synapse – Inhibitory synapse Figure 13.18, step 3a

Quadriceps (extensors) Hamstrings (flexors) 1 Quadriceps strongly contracts. Golgi tendon organs are activated. 2 Afferent fibers synapse with interneurons in the spinal cord. Interneurons Quadriceps (extensors) Spinal cord Golgi tendon organ Hamstrings (flexors) 3a Efferent impulses to muscle with stretched tendon are damped. Muscle relaxes, reducing tension. 3b Efferent impulses to antagonist muscle cause it to contract. + Excitatory synapse – Inhibitory synapse Figure 13.18, step 3b

Effector- part of body that responds to a motor nerve impulse Reflex Arc Sensory receptor Sensory neuron Integration center Motor neuron Effector- part of body that responds to a motor nerve impulse

Damage of the spinal cord above C3 can result in_____? INQUIRY What is a reflex? Damage of the spinal cord above C3 can result in_____? In which portion of the spinal cord do the interneurons lie? What kind of peripheral nerve fiber carries motor impulses outward to smooth muscles and glands of internal organs?