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Chapter 11

BIOL 2404 Chapter Notes - Chapter 11: Lumbosacral Plexus, Peripheral Nervous System, Anterior Ramus Of Spinal Nerve

Course Code
BIOL 2404

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Chapter 11: Central and Peripheral Nervous System
Spinal Cord
Major communication link between the brain and the PNS (spinal nerves)
Participates in the integration of incoming information and produces
responses through reflex mechanisms
Gives rise to 31 pairs of spinal nerves
Cervical and lumbosacral enlargements give rise to the spinal nerves
of the limbs
Nerves from the end of the spinal cord form the cauda equina
Shorter than the vertebral column
Meninges of the Spinal Cord
Three meningeal layers surround the spinal cord. From superficial to deep
they are
Dura mater
Arachnoid mater
Pia mater
The epidural space is between the periosteum of the vertebral canal and the
dura mater
The subarachnoid space is between the arachnoid mater and the pia mater
Spinal Cord Cross Section
The spinal cord consists of peripheral white matter and central gray matter
White matter is organized into columns (funiculi), which are subdivided into
tracts (fasciculi or pathways), which consist of ascending and descending
Gray matter is divided into horns
The dorsal horns contain sensory axons that synapse with
The ventral horns contain the neuron cell bodies of somatic motor
The lateral horns contain the neuron cell bodies of autonomic motor
The gray and white commissures connect each half of the spinal cord
Spinal nerves arise from the spinal cord in numerous rootlets
The rootlets combine to form a ventral root and a dorsal root
The dorsal root contains sensory axons
The ventral root has motor axons
Spinal nerves have sensory and motor axons
Stereotypic, unconscious, involuntary responses to stimuli
Maintain homeostasis
Two general types:
Somatic reflexes
Mediated through the somatic motor nervous system and
includes responses that
Remove the body from painful stimuli
Keep the body from suddenly falling
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Cause movement because of external forces
Autonomic reflexes
Mediated through the ANS and are responsible for maintaining
variables within their normal ranges
Blood pressure
Blood carbon dioxide levels
Water intake
A reflex arc is the functional unit of the nervous system
Sensory receptors respond to stimuli and produce action potentials in
sensory neurons
Sensory neurons propagate action potentials to the CNS
Interneurons in the CNS synapse with sensory neurons and with
motor neurons
Motor neurons carry action potentials from the CNS to effector organs
Effector organs, such as muscles or glands, respond to the action
Spinal Reflex
Convergent and divergent pathways interact with reflexes
Reflexes are integrated within the brain and spinal cord
Higher brain centers can suppress or exaggerate reflexes
Stretch Reflex
Muscle spindles detect the stretch of skeletal muscles and cause the muscle
to shorten reflexively
Golgi Tendon Reflex
Golgi tendon organs respond to increased tension within tendons and cause
skeletal muscles to relax
Withdrawal Reflex
Activation of pain receptors causes contraction of muscles and the removal of
some part of the body from a painful stimulus
Structure of Nerves
Individual axons are surrounded by the endoneurium
Groups of axons (fascicles) are bound together by the perineurium
Fascicles form the nerve and are held together by the epineurium
Spinal Nerves
There are 31 pairs of spinal nerves
Eight cervical
Twelve thoracic
Five lumbar
Five sacral
One coccygeal
Spinal nerves have specific cutaneous distributions called dermatomes
Spinal Nerves and Plexuses
Spinal nerves branch to form rami
The dorsal rami supply the muscles and skin near the middle of the
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