Transcript Spinal_Cord_Power_Point

Chapter 13:
The Spinal Cord and Spinal
Nerves
Spinal Cord Anatomy
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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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Spinal Cord Anatomy
External Anatomy of the Spinal Cord
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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
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External Anatomy of Spinal Cord
Internal Anatomy of the Spinal Cord
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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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Internal Anatomy of Spinal Cord
Spinal Nerves
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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:
 Fascicles
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Spinal Nerves
Distribution of Spinal Nerves
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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
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Formed by the anterior
rami of C1-C5.
Phrenic nervesimportant nerves from
the cervical plexuses.
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Brachial plexus
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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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Brachial plexus continued
Important nerves that
arise from the brachial
plexuses are
 Axillary nerve
 Musculocutaneous
nerve
 Radial nerve
 Median nerve
 Ulnar nerve
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Injuries to the Brachial Plexus
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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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Injuries to the Brachial Plexus
Lumbar Plexus
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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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Sacral Plexus
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Formed by the anterior
rami of L4-L5 and S1S4.
Supplies the buttocks,
perineum, and lower
limbs.
Gives rise to the largest
nerve in the body- the
sciatic nerve.
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Distribution of Nerves from the
Lumbar and Sacral Plexuses
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Coccygeal Plexus
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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
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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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Sensory and Motor Tracts
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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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Reflex
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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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Reflex Arc
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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
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Reflex Arc
2 SENSORY NEURON
(axon conducts impulses from
receptor to integrating center)
1 SENSORY RECEPTOR
(responds to a stimulus
by producing a generator
or receptor potential)
Interneuron
3 INTEGRATING CENTER
(one or more regions within the CNS
that relay impulses from sensory to
motor neurons)
4 MOTOR NEURON
(axon conducts impulses from
integrating center to effector)
5 EFFECTOR
(muscle or gland that
responds to motor
nerve impulses)
The Stretch Reflex
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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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Stretch Reflex
To brain
1 Stretching stimulates
SENSORY RECEPTOR
(muscle spindle)
+
2 SENSORY
NEURON
excited
EFFECTOR
+
5 (same muscle)
contracts and
relieves the
stretching
–
4 MOTOR
NEURON
excited
Spinal
Nerve
+
3 Within INTEGRATING
CENTER (spinal cord),
sensory neuron activates
motor neuron
Antagonistic
muscles relax
Motor neuron to
antagonistic muscles
is inhibited
Inhibitory
interneuron
The Tendon Reflex
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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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Tendon Reflex
To brain
Inhibitory
interneuron
5 EFFECTOR
(muscle attached
to same tendon)
relaxes and
relieves excess
tension
4 MOTOR NEURON
inhibited
+
++
2 SENSORY
NEURON
excited
–
Increased tension
stimulates
1 SENSORY
RECEPTOR (tendon)
+
Spinal
nerve
3 Within INTEGRATING
+
Antagonistic
muscles
contract
CENTER (spinal cord),
sensory neuron activates
inhibitory interneuron
Motor neuron to
antagonistic
muscles is excited
Excitatory
interneuron
Flexor (Withdrawal) Reflex
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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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Flexor (Withdrawal) Reflex
+
Spinal
nerve
+
4 MOTOR
NEURON
excited
Ascending
interneuron
+
+
Interneuron
+
+
5 EFFECTORS
(flexor muscles)
contract and
withdraw leg
Descending
interneuron
+
+
4 MOTOR
NEURONS
excited
+
+
3 Within INTEGRATING CENTER
2 SENSORY
NEURON
excited
(spinal cord), sensory neuron
activates interneurons in several
spinal cord segments
1 Stepping on tack stimulates
SENSORY RECEPTOR (dendrites
of pain-sensitive neuron)
Crossed Extensor Reflex
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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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Crossed Extensor Reflex
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+
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Spinal
nerve
+
Ascending
interneurons
4 MOTOR
NEURONS
excited
5 EFFECTORS
(extensor muscles)
contract, and extend
left leg
+
+
Flexor muscles
contract and withdrawright leg
Interneurons
from other side
+
+
+
Descending
interneurons
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+
+
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+
4 MOTOR
NEURONS
excited
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+
3 Within INTEGRATING CENTER
2 SENSORY
(spinal cord), sensory neuron
activates several interneurons
NEURON
excited
1 Stepping on a tack
Withdrawal of right leg
(flexor reflex)
stimulates SENSORY
RECEPTOR (dendrites of
pain-sensitive neuron) in
right foot
Extension of left leg
(crossed extensor reflex)
End of Chapter 13
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