pap12e lecture ch13

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

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.


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.


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


1 SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

1SENSORY NEURON(axon conducts impulses from receptor to integrating center)

SENSORY RECEPTOR(responds to a stimulusby producing a generatoror receptor potential)

2 1SENSORY NEURON(axon conducts impulses from receptor to integrating center)


INTEGRATING CENTER(one or more regions within the CNSthat relay impulses from sensory tomotor neurons)

Interneuron

2

3




MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

Interneuron

2

3

4




MOTOR NEURON(axon conducts impulses fromintegrating center to effector)

EFFECTOR(muscle or gland thatresponds to motornerve impulses)

Interneuron

2

3

4 5

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

1 Stretching stimulatesSENSORY RECEPTOR(muscle spindle)

Antagonisticmuscles relax


SENSORYNEURONexcited

To brain

SpinalNerve

+

+

21 Stretching stimulates

SENSORY RECEPTOR(muscle spindle)


Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesmotor neuron

Inhibitoryinterneuron

To brain

SpinalNerve

+

–

+

2

3



MOTORNEURONexcited


Motor neuron toantagonistic musclesis inhibited



To brain

SpinalNerve

+

–

+

+

2

3

4



MOTORNEURONexcited

EFFECTOR(same muscle)contracts andrelieves thestretching


Motor neuron toantagonistic musclesis inhibited



To brain

SpinalNerve

+

–

+

+

2

3

4

5

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.


Tendon Reflex

1

Increased tensionstimulatesSENSORYRECEPTOR (tendon)

1

Spinalnerve


To brain


2 ++

1

Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesinhibitory interneuron

Excitatoryinterneuron

Spinalnerve



+

To brain


++2

3

–

+1

–



Antagonisticmusclescontract

Spinalnerve

MOTOR NEURONinhibited



+

To brain


Motor neuron toantagonisticmuscles is excited

+

+

+

+2

3

4

1

–

EFFECTOR(muscle attachedto same tendon)relaxes andrelieves excesstension



Antagonisticmusclescontract

Spinalnerve

MOTOR NEURONinhibited



+

To brain


Motor neuron toantagonisticmuscles is excited

+

+

+2

3

45

+

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

1 Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)

1

+

Stepping on tack stimulatesSENSORY RECEPTOR (dendritesof pain-sensitive neuron)


+

2

1

+



Within INTEGRATING CENTER(spinal cord), sensory neuronactivates interneurons in severalspinal cord segments

Ascendinginterneuron

Interneuron

Descendinginterneuron

Spinalnerve

+

+

+

+

+

+

2

3

1

+



MOTORNEURONSexcited

MOTORNEURONexcited



Interneuron


Spinalnerve

+

+

+

+

+

+

+

+

+

2

3

4

4

1

+



MOTORNEURONSexcited

MOTORNEURONexcited

EFFECTORS(flexor muscles)contract andwithdraw leg



Interneuron


Spinalnerve

+

+

+

+

+

+

+

+

+

2

3

4

5

4

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


1

Withdrawal of right leg(flexor reflex)

Stepping on a tackstimulates SENSORYRECEPTOR (dendrites ofpain-sensitive neuron) inright foot

1




2

+

1

+

Ascendinginterneurons


Spinalnerve

Within INTEGRATING CENTER(spinal cord), sensory neuronactivates several interneurons

Descendinginterneurons



+

+ +

2

3

+

+ +

+ +

+ +

Interneuronsfrom other side

1

+



Spinalnerve


MOTORNEURONSexcited



Stepping on a tackstimulates SENSORYRECEPTOR (dendrites ofpain-sensitive neuron) inright foot Extension of left leg

(crossed extensor reflex)

MOTORNEURONSexcited

+

+ +

2

3

4

4

+

+ +

+ +

+ +

+

+

+


1

+


EFFECTORS(extensor muscles)contract, and extendleft leg


Spinalnerve


MOTORNEURONSexcited



Flexor musclescontract and with-drawright leg

Stepping on a tackstimulates SENSORYRECEPTOR (dendrites ofpain-sensitive neuron) inright foot Extension of left leg

(crossed extensor reflex)

MOTORNEURONSexcited

+

+ +

2

3

4

4

5

+

+ +

+ +

+ +

+

+

+


+

+

+


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.

pap12e lecture ch13

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