Chapter 13: The Spinal Cord and Spinal Nerves

Copyright 2009, John Wiley & Sons, Inc. Spinal Cord Anatomy Protective structures: Vertebral column and the meninges provide protect the spinal cord and provide physical stability. a. Dura mater, b. Arachnoid, c. Pia mater Epidural space, subdural space and subarachnoid space Copyright 2009, John Wiley & Sons, Inc.

Spinal Cord Anatomy

External Anatomy of the Spinal Cord Two enlargements: cervical and lumbar Conus medullaris Filum terminale Cauda equina Posterior (dorsal root) & anterior(ventral) root Posterior (dorsal root) ganglion Spinal nerve Copyright 2009, John Wiley & Sons, Inc.

External Anatomy of Spinal Cord

Internal Anatomy of the Spinal Cord Anterior median fissure Posterior median sulcus Gray and white commissures Central canal Anterior, posterior & lateral gray horns Anterior, posterior & lateral white columns Copyright 2009, John Wiley & Sons, Inc.

Internal Anatomy of Spinal Cord

Copyright 2009, John Wiley & Sons, Inc. Spinal Nerves 31 pairs; mixed nerves. Cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5) and coccygeal. Connective tissue coverings of spinal nerves: Epineurium, perineurium and endoneurium: Fascicles Copyright 2009, John Wiley & Sons, Inc.

Spinal Nerves

Distribution of Spinal Nerves Spinal nerves branch and their braches are called rami: Posterior (dorsal) ramus Anterior (ventral) ramus Plexuses: a network of axons Anterior rami except T1-T11 form plexuses. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Cervical Plexus Formed by the anterior rami of C1-C5. Phrenic nerves- important nerves from the cervical plexuses. Formed by the anterior rami of C1-C5. Phrenic nerves- important nerves from the cervical plexuses. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Brachial plexus Formed by the anterior rami of C5-C8 & T1. Supplies the shoulders and upper limbs. Roots → trunks → divisions → cords → nerves. Copyright 2009, John Wiley & Sons, Inc.

Brachial plexus continued Important nerves that arise from the brachial plexuses are Axillary nerve Musculocutaneous nerve Radial nerve Median nerve Ulnar nerve Copyright 2009, John Wiley & Sons, Inc.

Injuries to the Brachial Plexus Erb-Duchenne palsy (waiter’s tip)- loss of sensation along the lateral side of the arm. Wrist drop- inability to extend the wrist and fingers. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Median nerve palsy- numbness, tingling and pain in the palm and fingers. Ulnar nerve palsy- inability to abduct or adduct fingers Winged scapula- the arm cannot be abducted beyond the horizontal position. Copyright 2009, John Wiley & Sons, Inc.

Injuries to the Brachial Plexus

Copyright 2009, John Wiley & Sons, Inc. Lumbar Plexus Formed by the anterior rami of L1-L4. Supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs. Femoral nerves, obturator nerves. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Sacral Plexus Formed by the anterior rami of L4-L5 and S1-S4. Supplies the buttocks, perineum, and lower limbs. Gives rise to the largest nerve in the body- the sciatic nerve. Copyright 2009, John Wiley & Sons, Inc.

Distribution of Nerves from the Lumbar and Sacral Plexuses Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Coccygeal Plexus Formed by the anterior rami of S4-S5 and the coccygeal nerves. Supplies a small area of skin in the coccygeal region. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Dermatome Dermatome is the area of the skin that provides sensory input to the CNS via one pair of spinal nerves or the trigeminal nerve. Copyright 2009, John Wiley & Sons, Inc.

Sensory and Motor Tracts The name of the tract often indicates its location in the white matter and where it begins and ends. The white matter contains both sensory and motor tracts. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Reflex A reflex is an automatic, sudden, involuntary response to a stimulus. When the integration takes place in the spinal cord, the reflex is a spinal reflex. Copyright 2009, John Wiley & Sons, Inc.

Copyright 2009, John Wiley & Sons, Inc. Reflex Arc The pathway followed by nerve impulses that produce a reflex is a reflex arc. A reflex arc includes: a. sensory receptor b. sensory neuron c. integrating center d. motor neuron e. effector Copyright 2009, John Wiley & Sons, Inc.

Reflex Arc 1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) MOTOR NEURON integrating center to effector) EFFECTOR (muscle or gland that responds to motor nerve impulses) Interneuron 2 3 4 5 1 SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) MOTOR NEURON integrating center to effector) Interneuron 2 3 4 1 SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) INTEGRATING CENTER (one or more regions within the CNS that relay impulses from sensory to motor neurons) Interneuron 2 3 1 SENSORY NEURON (axon conducts impulses from receptor to integrating center) SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential) 2 1 SENSORY RECEPTOR (responds to a stimulus by producing a generator or receptor potential)

Copyright 2009, John Wiley & Sons, Inc. The Stretch Reflex Causes contraction of a skeletal muscle in response to stretching of the muscle. Monosynaptic reflex. Patellar or knee-jerk reflex: Stretching of a muscle →activation of muscle spindles →sensory neuron →spinal cord→motor neuron → muscle contraction. Ipsilateral. Copyright 2009, John Wiley & Sons, Inc.

Stretch Reflex

1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited MOTOR EFFECTOR (same muscle) contracts and relieves the stretching Antagonistic muscles relax Motor neuron to antagonistic muscles is inhibited Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron Inhibitory interneuron To brain Spinal Nerve + – 2 3 4 5 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited MOTOR Antagonistic muscles relax Motor neuron to antagonistic muscles is inhibited Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron Inhibitory interneuron To brain Spinal Nerve + – 2 3 4 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited Within INTEGRATING CENTER (spinal cord), sensory neuron activates motor neuron Inhibitory interneuron To brain Spinal Nerve + – 2 3 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited To brain Spinal Nerve + 2 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) Antagonistic muscles relax

Copyright 2009, John Wiley & Sons, Inc. The Tendon Reflex Polysynaptic reflex. Control muscle tension by causing muscle relaxation when muscle tension is great. Sensory receptors- Golgi tendon organs. ↑ Tension applied to the tendon → tendon organ stimulation → nerve impulse → spinal cord →motor neuron causes muscle relaxation and relieves tension. Copyright 2009, John Wiley & Sons, Inc.

Tendon Reflex

1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 – EFFECTOR (muscle attached to same tendon) relaxes and relieves excess tension Within INTEGRATING CENTER (spinal cord), sensory neuron activates inhibitory interneuron Excitatory interneuron Antagonistic muscles contract Spinal nerve MOTOR NEURON inhibited Inhibitory SENSORY NEURON excited + To brain Increased tension stimulates RECEPTOR (tendon) Motor neuron to antagonistic muscles is excited 2 3 4 5 1 – Within INTEGRATING CENTER (spinal cord), sensory neuron activates inhibitory interneuron Excitatory interneuron Antagonistic muscles contract Spinal nerve MOTOR NEURON inhibited Inhibitory SENSORY NEURON excited + To brain Increased tension stimulates RECEPTOR (tendon) Motor neuron to antagonistic muscles is excited 2 3 4 1 Within INTEGRATING CENTER (spinal cord), sensory neuron activates inhibitory interneuron Excitatory interneuron Spinal nerve Inhibitory SENSORY NEURON excited + To brain Increased tension stimulates RECEPTOR (tendon) 2 3 – 1 Spinal nerve SENSORY NEURON excited To brain Increased tension stimulates RECEPTOR (tendon) 2 + 1 Increased tension stimulates SENSORY RECEPTOR (tendon)

Flexor (Withdrawal) Reflex Polysynaptic reflex Ipsilateral. Stepping on a tack (stimulus) → nerve impulse → activation of the interneuron → activation of the motor neuron →muscle contraction →withdrawal of the leg. Copyright 2009, John Wiley & Sons, Inc.

Flexor (Withdrawal) Reflex

1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 + Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited MOTOR NEURONS EFFECTORS (flexor muscles) contract and withdraw leg Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments Ascending interneuron Interneuron Descending Spinal nerve 2 3 4 5 1 + Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited MOTOR NEURONS Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments Ascending interneuron Interneuron Descending Spinal nerve 2 3 4 1 + Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments Ascending interneuron Interneuron Descending Spinal nerve 2 3 1 + Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) SENSORY NEURON excited 2 1 Stepping on tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron)

Crossed Extensor Reflex Polysynaptic reflex. Contralateral reflex. Contraction of muscles that extend joints in the opposite limb in response to a painful stimulus. Stepping on a tack (stimulus) → nerve impulse →activation of several interneurons → activation of the motor neurons → muscle contraction causing flexion of the leg stepping on a tack & extension on the opposite side. Copyright 2009, John Wiley & Sons, Inc.

Crossed Extensor Reflex Copyright 2009, John Wiley & Sons, Inc.

1 2 3 4 5 1 2 3 4 1 2 3 1 2 1 + Ascending interneurons EFFECTORS (extensor muscles) contract, and extend left leg SENSORY NEURON excited Spinal nerve Within INTEGRATING CENTER (spinal cord), sensory neuron activates several interneurons MOTOR NEURONS Descending Withdrawal of right leg (flexor reflex) Flexor muscles contract and with- drawright leg Stepping on a tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) in right foot Extension of left leg (crossed extensor reflex) 2 3 4 5 Interneurons from other side 1 + Ascending interneurons SENSORY NEURON excited Spinal nerve Within INTEGRATING CENTER (spinal cord), sensory neuron activates several interneurons MOTOR NEURONS Descending Withdrawal of right leg (flexor reflex) Stepping on a tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) in right foot Extension of left leg (crossed extensor reflex) 2 3 4 Interneurons from other side 1 + Ascending interneurons SENSORY NEURON excited Spinal nerve Within INTEGRATING CENTER (spinal cord), sensory neuron activates several interneurons Descending Withdrawal of right leg (flexor reflex) Stepping on a tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) in right foot 2 3 Interneurons from other side 1 SENSORY NEURON excited Withdrawal of right leg (flexor reflex) Stepping on a tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) in right foot 2 + 1 Withdrawal of right leg (flexor reflex) Stepping on a tack stimulates SENSORY RECEPTOR (dendrites of pain-sensitive neuron) in right foot

Copyright 2009, John Wiley & Sons, Inc. End of Chapter 13 Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein. Copyright 2009, John Wiley & Sons, Inc.