The H or "butterfly" shape , • Ventral horn-larger • Dorsal horn-smaller
Ventral horn: • contains the large somata of autonomic motor neurons . • They receive input from integrator neurons in the cord, and send commands to contract to skeletal muscle in the periphery . Dorsal horn: • contains neuron somata of the connector neurons (not motor) . • They receive input from sensory fibers entering the cord through the dorsal root of the spinal nerve.
The Leptomeninges • Surround the brain and the spinal cord. • The cerebrospinal fluid circulates between 2 meningeal layers called the pia matter and the arachnoid (or pia-arachnoid membranes). • The outer, thicker layer serves the role of a protective shield and is called the dura matter. • The spinal cord is also covered, like the brain, by the pia matter and the arachnoid membranes. • The cerebrospinal fluid circulates around the pia and below the outer arachnoid, and this space is also termed the subarachnoid space. • The dura surrounds the pia-arachnoid of the spinal cord, as it does for the brain. • in spinal cord there is space between the dura mater and the vertebral canal is the epidural (or peridural) space, filled with adipose tissue and it contains a network of blood vessels.
CSF subarachnoid space.
The peripheral nervous system
Constituents of peripheral nervous system 1. Sensory neurons, 2. Ganglia (clusters of neurons) 3. Plexuses: felt works of nerve fibres 4. Nerves and nerve roots. 12 pairs of cranial nerves 31 pairs of spinal nerves Nerve Roots A nerve root is the initial segment of a nerve leaving the central nervous system. 1. A cranial nerve root, the beginning of one of the twelve pairs leaving the central nervous system from the brain stem or the highest levels of the spinal cord; 2. A spinal nerve root , the beginning of one of the thirty-one pairs leaving the central nervous system from the spinal cord.
• Each spinal nerve root consists of the union of a sensory dorsal root and a motor ventral root. • The dorsal root (or posterior root) is the afferent sensory root of a spinal nerve. • The ventral root (anterior root: is the efferent motor roots of a spinal cord. • At its distal end , the ventral root joins with the dorsal root to form a mixed spinal nerve. • Mixed (motor and sensory) peripheral nerve: • Fibers that carry motor input to limbs and fibers that bring sensory information from the limbs to the spinal cord
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- Fall '16