The Nervous System The Spinal Cord-part of the CNS found within the spinal column The spinal cord communicates with the sense organs and muscles below the level of the head Bell-Magendie Law-the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information to the muscles and glands Dorsal Root Ganglia-clusters of neurons outside the spinal cord
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The Nervous System The Spinal Cord-part of the CNS found within the spinal column The spinal cord communicates with the sense organs and muscles below.
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The Nervous System
The Spinal Cord-part of the CNS found within the spinal column
The spinal cord communicates with the sense organs and muscles below the level of the head
Bell-Magendie Law-the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information to the muscles and glands
Dorsal Root Ganglia-clusters of neurons outside the spinal cord
Spinal Cord
• Extends from foramen magnum to second lumbar vertebra
• Segmented– Cervical
– Thoracic
– Lumbar
– Sacral
• Gives rise to 31 pairs of spinal nerves
• Not uniform in diameter throughout length
The spinal cord and spinal nerves
Gross anatomical structures of the spinal cord
A. Two enlargements of the spinal cord occur in
regions where the amount of gray matter is greater than
others; regions of sensory/motor control of the limbs.
1. Cervical enlargement - nerves supply the shoulder and
upper limbs;
2. Lumbar enlargement - nerves supply the pelvis and the
lower limb.
B. Conus medullaris: region at the end of the spinal cord
where the tissue tapers into a cone shape; approximately
in region of L2.
C. Filum terminale: connective tissue, continuous with
the pia mater of the spinal cord.
D. Cauda equina: extension of nerves exiting from the
base of the spinal cord; appears like a horse's tail.
Cross Section of Spinal Cord
Cross Section of Spinal Cord
• White matter:• Myelinated axons
forming nerve tracts• Fissure and sulcus• Three columns:
– Ventral – Dorsal– Lateral
• Gray matter:• Neuron cell cell bodies,
dendrites, axons• ‘Horns’:
– Posterior (dorsal)– Anterior (ventral)– Lateral
• Commissures:– Gray: Central canal – White
(see later for white matter pathways)
Spinal CordIn the spinal cord, the grey matter is found in the centre (the butterfly shape) and the white matter surrounds it. The opposite arrangement is found in the cortex of the brain. Notice the surrounding dura mater .
See ANS lecture
‘Plexus’:intermingling / merging of nerves and subsequent re-organisation--> distribution of peripheral nerves is different from that of spinal nerves
Dermatomal Map• Skin area supplied with sensory innervation by spinal nerves
Equivalent for motor output to muscle groups:Myotome
CNS
PNSsensory motor motor sensory
spinal nerves (31p) cranial nerves (12p)
spinal cord brain
The Organisation of the Nervous System
• Sensory information has to be passed on from the spinal cord to the brain ascending pathways (red)
• Commands from the brain have to be sent out to the PNSdescending pathways (green)
Ascending (afferent) spinal tracts:
• Pathways that carry sensory information to a conscious level
Basic principle of information flow:
• receptor(e.g. pain receptor in skin)
• primary sensory neurone (cell body in dorsal root ganglia)
• second order neurone (in the spinal cord or brainstem)
• third order neurone (in thalamus)
• target area: cortexsomatosensory (somatic sensory) area (postcentral gyrus) of the cortex
Light touch
Conscious perception
Example
Sensory information travels to the brain via 3 main pathways:
To somatosensory cortex (see lecture 3!):1) Spinothalamic system (lateral and anterior tract):somatosensory information to brain:pain and temperature, light touch, pressure, tickle, itch