Chapter 13: The Spinal Cord and Spinal Nerves

Chapter 13: The Spinal Cord and Spinal Nerves

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

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

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

Internal Anatomy of Spinal Cord

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

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.

Cervical Plexus Formed by the anterior rami of C1-C5. Phrenic nerves- important nerves from the cervical plexuses.

Brachial plexus Formed by the anterior rami of C5-C8 & T1. Supplies the shoulders and upper limbs. Roots trunks divisions cords nerves.

Brachial plexus continued Important nerves that arise from the brachial plexuses are Axillary nerve Musculocutaneous nerve Radial nerve Median nerve Ulnar nerve

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.

P.472-473: 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.

Injuries to the Brachial Plexus

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.

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.

Distribution of Nerves from the Lumbar and Sacral Plexuses

Coccygeal Plexus Formed by the anterior rami of S4-S5 and the coccygeal nerves. Supplies a small area of skin in the coccygeal region.

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.

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.

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.

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

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

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.

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

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.

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

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.

Spinal nerve 4 MOTOR NEURON excited Ascending interneuron Interneuron 5 EFFECTORS (flexor muscles) contract and withdraw leg 4 MOTOR NEURONS excited Descending interneuron 2 SENSORY NEURON excited 3 Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments 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.

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

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.