1. Protective structures: Vertebral column and the meninges provide protect the spinal cord and...

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

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Two enlargements: cervical and lumbar Conus medullaris Filum terminale Cauda equina Posterior (dorsal root) &

anterior(ventral) root Posterior (dorsal root) ganglion Spinal nerve

4

Anterior median fissure Posterior median sulcus Gray and white commissures Central canal Anterior, posterior & lateral gray horns Anterior, posterior & lateral white

columns

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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:

Fascicles8

Spinal nerves branch and their braches are called rami: Posterior (dorsal) ramusAnterior (ventral) ramus

Plexuses: a network of axonsAnterior rami except T1-T11 form plexuses.

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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.

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Formed by the anterior rami of C5-C8 & T1.

Supplies the shoulders and upper limbs.

Roots → trunks → divisions → cords → nerves.

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Important nerves that arise from the brachial plexuses are

Axillary nerve Musculocutaneous

nerve Radial nerve Median nerve Ulnar nerve

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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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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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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.

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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 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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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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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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The pathway followed by nerve impulses that produce a reflex is a reflex arc.

A reflex arc includes:a. sensory receptorb. sensory neuronc. integrating centerd. motor neurone. effector

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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

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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.

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1 Stretching stimulatesSENSORY RECEPTOR(muscle spindle)

Antagonisticmuscles relax


SENSORYNEURONexcited

To brain

SpinalNerve

+

+

2



MOTORNEURONexcited

EFFECTOR(same muscle)contracts andrelieves thestretching

Antagonisticmuscles relax

Motor neuron toantagonistic musclesis inhibited

Within INTEGRATINGCENTER (spinal cord),sensory neuron activatesmotor neuron

Inhibitoryinterneuron

To brain

SpinalNerve

+

–+

+

2

3

45

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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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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

+

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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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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

+

+

+

+

+

+

+

+

+

23

4

5

4

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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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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

+

+ +

+ +

+ +

+

+

+


+

+

+

33

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1. Protective structures: Vertebral column and the meninges provide protect the spinal cord and...

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