Bio 201 Chapter 13 Lecture

Chapter 13: The Spinal Cord and

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

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

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

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 T2-T12 form plexuses.

Cervical Plexus Formed by the anterior rami of C1C5.  Phrenic nervesimportant nerves from the cervical plexuses. 

Brachial plexus Formed by the anterior rami of C5C8 & 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. 

Injuries to the Brachial Plexus  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 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

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.

Stretch 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

Tendon 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.

Flexor (Withdrawal) 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.

Crossed Extensor Reflex

End of Chapter 13