section 2, chapter 11 cns & pns
DESCRIPTION
nervous system lecture for anatomy & physiologyTRANSCRIPT
Chapter 11, Section 2
Spinal Cord
Spinal Cord
The spinal cord is continuous with
the brain and extends downward
through the vertebral canal.
The spinal cord begins at the foramen
magnum, and terminates between the
first and second lumbar vertebra.
Two regions of the spinal cord are thickened
1. Cervical Enlargement – nerves to upper limbs
2. Lumbar enlargement – nerves to lower limbs
Structure of the
Spinal Cord
31 pairs of spinal nerves arise from the
spinal cord.
• 8 cervical nerves
• 12 thoracic nerves
• 5 lumbar nerves
• 5 sacral nerves
• 1 coccygeal nerve
Figure 11.29 The thirty one
pairs of spinal nerves are
grouped according to the level
from which they arise.
Terminal end of the
Spinal Cord
The spinal cord tapers at its terminal
end into the conus medullaris
Filum terminale – thin cord of connective
tissue arising from the conus medullaristissue arising from the conus medullaris
Cauda Equina “Horse’s tail” – spinal nerves
at the conus medullaris fan outward, creating
a structure that resembles a horse’s tail.
Cross Section of the
Spinal Cord
Anterior Median Fissure &
Posterior Median Sulcus
• Grooves that divide the spinal cord into left and right halves
Central Canal – continuous with ventricles in the brain
The spinal cord consists of white matter
surrounding a core of grey matter.
Central Canal – continuous with ventricles in the brain
Structures of the
Spinal Cord Grey Matter
• Posterior horns – located towards the dorsal surface
• Anterior horns – located towards the ventral surface
• Lateral horns – located in some regions of the spinal cord,
• Grey commissure – connects the left and right grey matter
White Matter
• Posterior funiculus
• Anterior funiculus
• Lateral funiculus
The funiculi (sing. funiculus)
are columns that provide
pathways for axons, called
nerve tracts.
Spinal Nerves
Dorsal Root – Branch of spinal
nerves that carry sensory impulses
towards spinal cord
Dorsal Root Ganglion – Mass of
sensory neuron cell bodies in the
dorsal root of the spinal cord
Ventral Root – Branch of spinal
nerves that carry motor impulses
away from the spinal cord
dorsal root of the spinal cord
Functions of Spinal Cord
• The spinal cord is a conduit for
nerve impulses to and from the
brain and brainstem
• The spinal cord is a center
for spinal reflexes
Reflex Arcs
•Reflexes are automatic, subconscious responses to stimuli within or
outside the body
• Reflexes are the simplest response to a stimulus
• Simple reflex arc (sensory – motor)• Simple reflex arc (sensory – motor)
• Most common reflex arc (sensory – interneuron – motor)
Figure 10.7a. A schematic of a reflex arch.
Reflex Arcs
Five components of a reflex arc.
1. Receptor - detects changes in environment
• Dendritic end of a sensory neuron, or specialized receptor cell
2. Sensory neuron – conveys stimulus to spinal cord
• Passes through Dorsal Root• Passes through Dorsal Root
3. Interneuron – conducts impulse from sensory neuron to motor neuron
4. Motor Neuron – transmits impulse to effector
• Passes through Ventral Root
5. Effector – muscle or gland that produces the reflex
Figure 10.7b the five components of a reflex arc.
Reflex Arcs
Table 11.2 summarizes the components of a reflex arc.
Tracts of the Spinal Cord
• Ascending tracts conduct sensory impulses to the brain
• Descending tracts conduct motor impulses from the brain to
motor neurons reaching muscles and glands
Figure 11.11 Major
ascending and descending
tracts in a cross section of
the spinal cord.
1. Fasciculus gracilis & fasiculus cuneatus
• Within the posterior funiculus of spinal cord
• Conducts sensory information from skin, muscles, and joints
• Sense touch, pressure, and body movement
• Fibers decussate (cross over) in medulla oblongata of brain
2. Lateral Spinothalamic tract
• Conducts sensations of pain and
Ascending Tracts
• Conducts sensations of pain and
temperature to thalamus of the brain
• Fibers decussate in spinal cord
3. Anterior Spinocerebellar tract
• Conducts impulses from
muscles of lower limbs and
trunk to cerebellum
• Coordinate muscle movements
Ascending Tracts
Figure 11.12 sensory impulses originating in skin
touch receptors ascend in the fasciculus cuneatus
tract and cross over in medulla oblongata of the
brain. Pain and temperature information ascends
in the lateral spinothalamic tract, which crosses
over in the spinal cord.
Descending Tracts1. Corticospinal tracts
• Lateral and anterior tracts
• Motor impulses from cerebral cortex to spinal
nerves and outward to various skeletal muscles
• Fibers decussate in medulla oblongata
• Voluntary movement
2. Rubrospinal tract
• Passes through lateral funiculi
• Motor impulses from brain to skeletal muscles• Motor impulses from brain to skeletal muscles
• Coordinate muscles & controls posture
Descending Tracts
Figure 11.13 Most fibers of the corticospinal tract Figure 11.13 Most fibers of the corticospinal tract
originate in the cerebral cortex, cross over in the
medulla, and descend in the spinal cord, where they
synapse with neurons whose fibers lead to spinal
nerves supplying skeletal muscles. Some fibers
cross over in the spinal cord.
End of Chapter 11, Section 2