Spinal Cords & Spinal Nerves

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Chapter 13: The Spinal Cord and Spinal Nerves:

Chapter 13: The Spinal Cord and Spinal Nerves

Spinal Cord Anatomy:

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

Spinal Cord Anatomy:

Spinal Cord Anatomy

External Anatomy of the Spinal Cord:

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:

External Anatomy of Spinal Cord

Internal Anatomy of the 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:

Internal Anatomy of Spinal Cord

Spinal Nerves:

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:

Spinal Nerves

Distribution of 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.

Cervical Plexus:

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

Brachial plexus :

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:

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:

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.

Slide 15:

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:

Injuries to the Brachial Plexus

Lumbar 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. Copyright 2009, John Wiley & Sons, Inc.

Sacral Plexus:

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:

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

Coccygeal Plexus:

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.

Dermatome:

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:

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.

Reflex:

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.

Reflex Arc:

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

The Stretch Reflex:

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:

Stretch Reflex

Slide 28:

1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) Antagonistic muscles relax 1 Stretching stimulates SENSORY RECEPTOR (muscle spindle) SENSORY NEURON excited To brain Spinal Nerve + + 2 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 MOTOR NEURON excited 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 MOTOR NEURON excited 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

The Tendon Reflex:

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:

Tendon Reflex

Slide 31:

1 Increased tension stimulates SENSORY RECEPTOR (tendon) 1 Spinal ner ve SENSORY NEURON excited To brain Increased tension stimulates SENSORY RECEPTOR (tendon) 2 + + 1 Within INTEGRATING CENTER (spinal cord), sensory neuron activates inhibitory interneuron Excitatory interneuron Spinal ner ve Inhibitory interneuron SENSORY NEURON excited + To brain Increased tension stimulates SENSORY RECEPTOR (tendon) + + 2 3 – + 1 – Within INTEGRATING CENTER (spinal cord), sensory neuron activates inhibitory interneuron Excitatory interneuron Antagonistic muscles contract Spinal ner ve MOTOR NEURON inhibited Inhibitory interneuron SENSORY NEURON excited + To brain Increased tension stimulates SENSORY RECEPTOR (tendon) Motor neuron to antagonistic muscles is excited + + + + 2 3 4 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 ner ve MOTOR NEURON inhibited Inhibitory interneuron SENSORY NEURON excited + To brain Increased tension stimulates SENSORY RECEPTOR (tendon) Motor neuron to antagonistic muscles is excited + + + 2 3 4 5 +

Flexor (Withdrawal) Reflex:

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:

Flexor (Withdrawal) Reflex

Slide 34:

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

Crossed Extensor Reflex:

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:

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

Slide 37:

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

End of Chapter 13:

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.

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