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BIOB32H3 Lecture Notes - Tendon Reflex, Functional Group, Cervical Plexus

Biological Sciences
Course Code
Kenneth Welch

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The Spinal Cord and Spinal Nerves
General Organization of the Nervous System
Divisions of the Nervous System
Brain and spinal cord
In the white matter, axons arranged in tracts and columns
Remainder of nervous tissue
Gross Anatomy of the Spinal Cord
Adult spinal cord
Localized enlargements provide innervation to limbs
31 segments
each segment has a pair of dorsal roots and a pair of ventral roots
Filum terminale
Conus medularis
Spinal nerves extend off cord
Mixed nerves
Spinal meninges
Provide physical stability and shock absorption
Three layers
Dura mater
Pia mater
Dura mater
Covers spinal cord
Tapers to coccygeal ligament
Epidural space separates dura mater from walls of vertebral canal
Interior to dura mater are the subdural space, the arachnoid and the subarachnoid
Subarachnoid space contains CSF
Pia mater
Meshwork of elastin and collagen fibers
Innermost meningeal layer
Denticulate ligaments extend from pia mater to dura mater
Sectional anatomy of the spinal cord
White matter is myelinated and unmyelinated axons
Gray matter is cell bodies, unmyelinated axons and neuroglia
Projections of gray matter toward outer surface of cord are horns
Horns of spinal cord
Posterior gray horn contains somatic and visceral sensory nuclei
Anterior gray horns deal with somatic motor control
Lateral gray horns contain visceral motor neurons
Gray commissures contain axons that cross from one side to the other
White matter
Divided into six columns (funiculi) containing tracts
Ascending tracts relay information from the spinal cord to the brain
Descending tracts carry information from the brain to the spinal cord
Spinal Nerves
31 pairs of spinal nerves
Nerves consist of:
Spinal nerves
White ramus (myelinated axons)
Gray ramus (unmyelinated axons that innervate glands and smooth muscle)
Dorsal ramus (sensory and motor innervation to the skin and muscles of the back)
Ventral ramus (supplying ventrolateral body surface, body wall and limbs)
Each pair of nerves monitors one dermatome
Nerve plexus
Complex interwoven network of nerves
Four large plexuses
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Principles of Functional Organization
General organization
Sensory neurons
Deliver information to CNS
Motor neurons
Distribute commands to peripheral effectors
Interpret information and coordinate responses
Neuronal pools
Functional group of interconnected neurons
Neural circuit patterns
Serial processing
Parallel processing
An introduction to reflexes
Reflexes are rapid automatic responses to stimuli
Neural reflex involves sensory fibers to CNS and motor fibers to effectors
Reflex arc
Wiring of a neural reflex
Five steps
Arrival of stimulus and activation of receptor
Activation of sensory neuron
Information processing
Activation of motor neuron
Response by effector
Reflex classification
According to
Site of information processing
Nature of resulting motor response
Complexity of neural circuit
Innate reflexes
Result from connections that form between neurons during development
Acquired reflexes
Learned, and typically more complex
More reflex classifications
Cranial reflexes
Reflexes processed in the brain
Spinal reflexes
Interconnections and processing events occur in the spinal cord
Somatic reflexes
Control skeletal muscle
Visceral reflexes (autonomic reflexes)
Control activities of other systems
Monosynaptic reflex
Sensory neuron synapses directly on a motor neuron
Polysynaptic reflex
At least one interneuron between sensory afferent and motor efferent
Longer delay between stimulus and response