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

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.
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Cervical Plexus 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.
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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.
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 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.
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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.
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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.

Coccygeal Plexus   Formed by the anterior rami of S4-S5 and the coccygeal nerves.
Supplies a small area of skin in the coccygeal region.
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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.
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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.
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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.
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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
Interneuron SENSORY NEURON (axon conducts impulses from 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) (axon conducts impulses from integrating center to effector) 5 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. Copyright 2009, John Wiley & Sons, Inc.

Stretch Reflex

Stretching stimulates SENSORY RECEPTOR (muscle spindle) 5 EFFECTOR (same muscle) contracts and relieves the stretching SENSORY NEURON excited MOTOR NEURON excited Spinal Nerve – 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.
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Tendon Reflex

5 EFFECTOR (muscle attached to same tendon) relaxes and relieves excess tension Inhibitory interneuron MOTOR NEURON inhibited Increased tension stimulates SENSORY RECEPTOR (tendon) SENSORY NEURON excited Spinal nerve – + + 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.
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Flexor (Withdrawal) Reflex

5 EFFECTORS (flexor muscles) contract and withdraw leg + Spinal nerve + MOTOR NEURON excited Ascending interneuron Interneuron + Descending interneuron MOTOR NEURONS excited + + SENSORY NEURON excited Within INTEGRATING CENTER (spinal cord), sensory neuron activates interneurons in several spinal cord segments 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.
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Crossed Extensor Reflex Copyright 2009, John Wiley & Sons, Inc.

Flexor muscles contract and with drawright leg + + + 5 EFFECTORS (extensor muscles) contract, and extend left leg

End of Chapter 13
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