Nervous System

A nerve visible to the unaided eye contains thousands of individual nerve processes that are grouped together into fascicles. Within a fascicle, staining for myelin shows the bundle of individual nerve processes, each insulated from its neighbors. The myelin sheath is formed from several layers of membrane, visible in the electron microscope. These layers are projections of _________ ______ in the peripheral nervous system. In the central nervous system, the corresponding layers are projections of cells called _____________________

- - schwann cells (PNS) oligodendrocytes (CNS)

The motor portion of the sympathetic system is a chain of _____ motor neurons. The cell body of the first neuron lies in the lateral horn of the spinal cord; its axon leaves the spinal cord between levels T1 and L2. The axon travels within a ventral root, spinal nerve and ventral primary ramus to a _______ ________ _______________

two white ramus communicans.

There are 31 pairs of spinal nerves, __ in the cervical region, ___ in the thoracic region, __ in the lumbar region, __ in the sacral region, __ in the coccygeal region.

8 12 5 5 1

The spinal cord ends at ____; the tapering portion is the conus medullaris. Nerve roots leaving the spinal cord is this region form the _______ __________, so-called because they resemble a horse's tail.

L2 cauda equina

In order to work correctly, muscles must be innervated by motor nerve axons, but also have sensory feedback as to their position and strength of contraction. Part of this sensory input comes from muscle spindles. These are microscopic, so you won't see them on dissection, but you should realize they are present and that a nerve to a muscle contains sensory as well as motor fibers. Sensory nerves innervating the muscle spindles send back information as to strength of contraction and rate of movement of the muscle. Sensory nerves are ____________ (a = toward, think affection); they carry information centrally toward the spinal cord

afferent

The nervous system is divided into the central nervous system (CNS), consisting of the ________ and _________ cord, and the peripheral nervous system (PNS) made up of peripheral nerves (spinal and cranial nerves). Peripheral nerves extend away from the spinal cord or brain to the rest of the body (periphery). Note the high concentration of nerves going to the upper and lower limbs

brain and spinal cord

Nerve fibers in Dorsal primary rami go to _____ _____ muscles and overlying skin Nerve fibers in Ventral primary rami go everywhere else on body wall and limbs

deep back

that area of skin innervated by branches of the two spinal nerves (left and right) found at one vertebral level his includes branches of both dorsal and ventral primary rami.

dermatome

3 layers of meninges

dura mater, arachnoid mater and pia mater.

The meninges surrounding the spinal cord are continuous with the same layers that surround the brain. As the nerve roots continue laterally from the spinal cord, they are still covered by a dural sheath (or sleeve) that includes the ....(2)..? Further laterally, these layers are replaced by the ________________ covering the remaining portions of the peripheral nerve. The subarachnoid space with its CSF in the spinal cord is continuous with the subarachnoid space of the brain, so CSF bathing the brain can be sampled from the subarachnoid space at L4, as done by a ________ _____

dura, arachnoid, and pia. epineurium spinal tap

Motor nerves go to skeletal muscles and control contraction of these muscles. Motor nerves are also called ____________ nerves (e = away; think eject): they carry information outward (away from the spinal cord) to the periphery. At motor nerve terminals, an action potential conducted down the axon leads to release of neurotransmitter contained in synaptic vesicles. In turn, the neurotransmitter acts on receptors on the muscle to trigger the muscle to contract

efferent

Motor fibers ___ ___ skeletal muscles Sensory fibers come from muscles or skin Nerve fibers in Cutaneous nerves are sensory to skin only, not muscle Dorsal roots contain only __________ fibers Ventral roots contain only _______ fibers

go to come from sensory motor

The spinal nerve leaves the vertebral column via a gap between adjacent vertebrae called an __________________ ____________ This is important because damage to the disc separating two vertebrae can lead to pinching of the nerve and neurological symptoms. This is especially likely at L4-L5 and L5-S1, or at C7-C8 and C8-T1, where a more mobile region of the vertebral column meets a less mobile one.

intervertebral foramen.

ventral roots contain only _______ fibers

motor

Nerve cells in the peripheral nervous system are either motor or sensory nerves. The cell bodies and their processes have different relationships. In a motor neuron, the cell body has many short dendrites and one long axon that goes peripherally to a muscle (_______________). A sensory neuron is _________________; the cell body is located at the side of its process. One end of the process goes peripherally to the area being sensed. The other end of the same process goes centrally to the spinal cord, where it may synapse locally or go all the way to the brain. Individual processes are too small to be seen without a microscope.

multipolar psedounipolar

Dorsal and ventral primary ______ contain both sensory and motor fibers

rami

In the head, the parasympathetic system controls ___________ of saliva and mucus from salivary and mucous glands and the ____________ of tears from the lacrimal gland. The sympathetic system controls smooth muscle of blood vessels everywhere, in both the body wall and in the viscera. There is ___ parasympathetic supply to the body wall or the limbs. The _______ and ______ are special cases, receiving both sympathetic innervation (via paravertebral ganglia of the sympathetic chain) and parasympathetic innervation (via the vagus nerve).

secretion..... secretion - no heart and lungs

Dorsal roots contain only ___________ fibers

sensory

Dorsal roots contain only __________ fibers, and ventral roots contain only motor fibers...... but spinal nerves and primary rami contain ______ sensory and motor fibers. Make sure you understand this difference between roots and rami; this will save a good deal of confusion.

sensory .... motor both