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Chapter 13 Spinal Cord, Nerves and Reflexes


Chapter 13 Spinal Cord, Nerves and Reflexes Spinal cord is the information highway between brain and body The spinal cord is protected by: a. the vertebral column – PowerPoint PPT presentation

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Title: Chapter 13 Spinal Cord, Nerves and Reflexes

Chapter 13Spinal Cord, Nerves and Reflexes
  • Spinal cord is the information highway between
    brain and body
  • The spinal cord is protected by
  • a. the vertebral column
  • b. meninges
  • c. cerebrospinal fluid

Anatomy of the Spinal Cord
  • 1. Spinal cord begins as a continuation of the
    medulla oblongata and terminates at about the L1
  • Thick as a finger
  • 2. Cervical and lumbar enlargements serve as
    points of origin for nerves to the extremities
  • 31 pairs of spinal nerves
  • 3. Distal end is tapered and called the cauda
    equina (horses_____)

Meninges of the Spinal Cord
  • The meninges are three fibrous coverings that
    enclose the spinal cord and brain
  • a. innermost layer is the pia mater
  • b. middle layer is the arachnoid
  • c. outermost layer is the dura mater
  • There is a PAD around the spinal cord
  • Inflammation of the meninges is known as

Meninges of Vertebra Spinal Cord
  1. ____________
  2. ____________
  3. ____________

Spinal Tap/ Epidural
  • Placing a needle in the subarachnoid space is
    called a spinal tap (lumbar puncture)
  • Used to diagnose pathologies and to introduce
  • Headache is a frequent side effect, WHY?
  • Spinal tap must be given below L1, Why?
  • An Epidural is typically used for anesthesia

  • 1. White Matter- myelinated (Why white?)
  • 2. Gray Matter- unmyelinated (Why gray?)
  • 3. ______ (Alma Mater)

  • Spinal cord
  • Gray matter forms an H-shaped inner core
  • Surrounded by white matter
  • Brain
  • A thin outer shell of gray matter covers the
    cerebral hemispheres

Cross-Sectional Anatomy of the Spinal Cord
  • Gray matter is shaped like the letter H or a
    butterfly and surrounded by white matter divided
    into 3 columns
  • Gray matter neuron cell bodies
  • White matter myelinated axons
  • Gray matter is divided into horns (posterior,
    anterior and lateral).
  • The posterior horn is the area of the posts

Gray Matter in the Spinal Cord
  • Pair of dorsal or posterior horns
  • totally sensory
  • Pair of ventral or anterior horns
  • totally motor fibers
  • Connected by gray commissure

Spinal Tracts
  • Ascending tracts come from the periphery to head
    up and are called __________, _________
  • Descending tracts head down and to the periphery
    are called ________, _________
  • Decussation means that the fibers cross
  • Contralateral means origin and destination are on
    opposite sides while ipsilateral means on same

The Motor and Sensory Brains
  • The Grand prix (Pronounced grand pre) is a
    motor car race

Sensory Homunculus
  • Demonstrates that the area of the cortex
    dedicated to the sensations of various body parts
    is proportional to how sensitive that part of the
    body is.

Motor Homunculus http//
Noisy Neighbors
  • Neurons that control your right arm and right leg
    dwell near each other in the _______ gyrus on the
    left side of your brain.
  • Experiment 1 Polish the desk with a clockwise
    circling motion of your right hand. Now start
    your right foot circling clockwise.
  • When neurons controlling your arm and leg are
    near each other they work well together.
  • Experiment 2 Now reverse the rotation direction
    of your right foot.
  • Tough to do, why? When neurons near each other
    are called on to do different work they disturb
    each other.

Neighbors Across Town
  • Your left arm and left leg are across town in
    the _____ precentral gyrus from your right and
    left arm and leg.
  • Experiment 3 Using you left arm to buff the top
    of your desk in a clockwise direction. This time
    rotate your right leg counterclockwise.
  • This should pose no problem because the control
    centers for the two limbs are found on opposite
    sides of the brain, so they dont bother each

Abbreviate Version
  • 1. While sitting at your desk, lift your right
    foot off the floor and make clockwise circles.
    2. Now, while doing this, draw the number '6'
    in the air with your right hand. Your foot will
    change direction

  • 1. Spinothalamic tract
  • 2. Posterior (Dorsal) Columns
  • These travel UP the spinal cord

Spinothalamic Tract
  • Pain and temperature
  • Decussation of the second order neuron occurs in
    spinal cord

Dorsal Columns
  • Vibration, proprioception
  • Two Dorsal columns on each side of the spine
  • 1. Fasciculus gracile
  • carry signals from the leg
  • (remember gracilis muscle of the leg)
  • 2. Fasciculus cuneatus
  • carry signals from the arm
  • Decussation of in
  • medulla
  • Third neuron in thalamus carries signal to ___
    ___ of the brain

PROPRIOCEPTION Awareness of your body in space

2 Motor Tracts
  • Called the Pyramidal Tracts
  • 1. Anterior (Ventral) Corticospinal
  • 2. Lateral Corticospinal
  • These travel DOWN the spinal cord

Corticospinal Tract
  • Coordinates limb movements
  • Two neuron pathway start in the
  • upper motor
  • neuron in _____ _____ of the brain

Crossing the TractsRemember that the medulla has
two Ls
Decussates in MEDULLA Decussates in SPINE
DorsaL Column Tracts X
Spinothalamic Tract X
LateraL Corticospinal X
Anterior Corticospinal X
The Spinal Nerves
  • 31 pairs of spinal nerves
  • a. 8 pairs of cervical nerves (C1-C8)
  • b. 12 pairs of thoracic nerves (T1-T12)
  • c. 5 pairs of lumbar nerves (L1-L5)
  • d. 5 pairs of sacral nerves, (S1-S5)
  • e. 1 pair of coccygeal nerves
  • Spinal nerves exit superior to their vertebrae
    for C1-C7 nerves only. C8 nerve-coccyx nerves
    exits inferior to their vertebrae

Spinal Nerves (Cont.)
  • Roots points of attachment for each spinal nerve
    to a segment of the spinal cord
  • Posterior, or dorsal (sensory), root contains
    sensory nerve fibers, conducts nerve impulses
    into the spinal cord
  • The ganglion contains the cells bodies of the
    sensory neurons
  • Anterior, or ventral (motor), root contains motor
    neuron axons and conducts impulses from the cord
  • Cell bodies are located in the gray matter

Branches of a Spinal Nerve
After passing through its intervertebral foramen
(IVF), a spinal nerve divides into a dorsal and
ventral branch called rami Spinal nerve
branches, except for T2-T12, form a network of
nerves called a plexus
Nerve Plexus
  • Two UP
  • Cervical plexus, C1 to C5
  • supplies neck and phrenic nerve to the diaphragm
  • Brachial plexus, C5 to C8 and T1
  • supplies upper arm and shoulder, multiple nerves
  • Two DOWN
  • Lumbar plexus, L1 to L4
  • supplies anterior thigh genitalia
  • Femoral nerve
  • Sacral plexus, L4- S4
  • supplies butt lower leg
  • Sciatic nerve

Cervical Plexus- Clinical
  • Damage to the cervical plexus can effect the
    diaphragm muscle.
  • Damage to the spinal cord in the origin of the
    phrenic nerves (C3-C5) causes respiratory arrest.
  • Breathing stops because the phrenic nerves no
    longer send impulses to the diaphragm.
  • Classic anatomy C3, 4 and 5 keeps the diaphragm

The Cervical Plexus, C1 to C5
Brachial Plexus
  • Nerves of the upper extremities
  • Axillary nerve to deltoid and teres minors and
    arm pit
  • Musculocutaneous nerve to flexors of arm and
    forearm and cutaneous sensation of forearm
  • Median nerve to anterior forearm, palm and first
    3 ½ fingers (thumb, index finger, middle finger
    and lateral half of ring finger)
  • Ulnar nerve of anteriomedial forearm, palm and
    last 1 ½ fingers (medial half of ring finger,
    small finger)
  • Radial nerve to the posterior forearm and dorsal
    surface of hand

The Brachial Plexus, C5 to T1
Brachial Plexus- Clinical
  • Injury to the brachial plexus
  • Crutch palsy (Axillary nerves),
  • Wrist drop (Radial nerve)
  • Carpal tunnel syndrome (Median nerve)
  • Decreased sensation, thumb and wrist and pain
  • Tunnel of Guyon (Ulnar nerve)
  • decreased adduction, abduction of fingers, and
    flexing wrist, and sensation over little finger

The Lumbar Plexus, L1 to L4
Lumbar Plexus- Clinical
  • Injury to the femoral nerve
  • An inability to extend the leg
  • loss of sensation in the skin over the
    anteromedial aspect of the thigh.

The Sacral Plexus, L4- S4
Sacral Plexus- Clinical
  • The largest nerve in the body arises from the
    sacral plexus called the sciatic nerve.
  • A large as your small finger
  • Injury to the sciatic nerve results in pain from
    the buttock down the back of the leg, foot drop,
    an inability to dorsiflex the foot, and loss of
    sensation over the leg and foot.
  • Sciatica Inflammation of the sciatic nerve
  • A few causes include herniated (slipped)
    intervertebral disc, sacroiliac subluxation,
    piriformis syndrome

  • Dermatome skin sensation
  • All spinal nerves except C1 innervate segments of
    the skin
  • Helps diagnosis nerve problems
  • Shingles acute infection of the peripheral
    nerves by the herpes zoster virus
  • The virus goes from the posterior horn and down
    the sensory nerves causing pain and skin

Reflex Arc
  • Simplest type of neural pathway
  • 1. receptor
  • 2. sensory neuron
  • 3. motor neuron
  • 4. effector
  • Example The flexor (withdrawal) reflex is
    ipsilateral and is a protective withdrawal reflex
    that moves a limb to avoid pain
  • Brain is NOT involved in a reflex

The Muscle Spindle
  • Stretch receptors that monitor the length of
    skeletal muscles (biceps, triceps, petellar and
    achilles reflexes)
  • Golgi Tendon organs are stretch receptors in the
    tendon of a muscle.

Reflexes- Clinical
  • Reflexes are used to diagnose disorders and
    locating injured tissue.
  • Absent usually not pathological
  • Absent unilaterally damage may be somewhere
    along a nerve pathway on that side.
  • Hyperreflexia Brain abnormality
  • Clinically important reflexes
  • 1) Biceps (C5), Triceps (C7)
  • 2) Petellar (L4), Achilles reflex (S1)
  • 3) Babinski sign (Pathological reflex

Upper/ Lower Motor Neuron Disease
  • Paralysis
  • Upper motor neuron spastic
  • Lower motor neuron flaccid
  • UMN / LMN
  • UMN Brain
  • LMN peripheral nerves

Reflexes Hyperactive Absent
Atrophy Absent Present
Fasciculation Absent Present
Tone Increased Decreased
CNS Nerve Injury
  • In the CNS, injury to the brain or spinal cord
    can be permanent.
  • Injury is followed by spinal shock
  • A loss of reflex activity called areflexia
  • Anti-inflammatory drugs given at time of trauma
    may decrease swelling
  • Spinal cord injury may result in paralysis which
    may be classified as
  • monoplegia (one limb), diplegia (two limbs),
    paraplegia (both lower limbs), hemiplegia (one
    side), or quadriplegia (all limbs).
  • Para Beside near alongside

Polio and ALS
  • Diseases that cause destruction of motor neurons
    and result in skeletal muscle atrophy
  • Poliomyelitis is caused by poliovirus spread by
    contaminated water from fecal matter
  • weakness progresses to paralysis and possible
    respiratory arrest
  • Amyotrophic lateral sclerosis
  • sclerosis of spinal cord
  • paralysis and muscle atrophy

Spina Bifida Vera
  • Congenital defect
  • Failure of vertebral arch to close
  • Causes a lack of covering for the spinal cord
  • Mothers can reduce risk by taking folic acid
    supplement before pregnancy
  • Spina Bifida occulta is a benign anamaly

  • Sexually transmitted disease
  • Three stages
  • Causes degeneration of the dorsal column
  • Symptoms will be loss of _______ and _______
  • (Dorsal column signs)