Myelin in the peripheral nervous system derives from Schwann cells, and the distance between nodes of Ranvier determines the conduction rate. The enteric nervous system is the extensive system of neurons located in the walls of the gastrointestinal tract, gallbladder, and pancreas that control the functioning of the gut independently of the sympathetic and parasympathetic systems Furness et al. It has its origin from the abducens nucleus at the lower border of the pons and at the lateral part of the pyramid of the medulla. Ventilation is suppressed during vomiting, and the glottis is closed. The nerve runs from the back of the eye, through the optic canal, and into the middle cranial fossa. Axons from the receptor cells join into approximately 20 small nonmyelinated bundles the olfactory nerves.
They are called white fibers. Trigeminal neuralgia causes episodes of severe, stabbing, electric shock-like pain in the areas of the face, where the branches of the nerve are distributed, i. Synonym: seventh cranial nerve See: illustration; femoral nerve 1. Fracture of the ethmoid bone or lesions of olfactory fibers may result in partial or total loss of smell, a condition known as anosmia Origin Olfactory receptor cells bipolar neurons in the olfactory epithelium of the nasal cavity. The upper eyelid droops ptosis , and the person has double vision. From its surface, it appears to be bilaterally symmetrical.
Contraction of the abdominal muscles produces a large positive intra-abdominal pressure that forces gastric contents past the lower esophageal sphincter and into the esophagus. In , depending on the neurotransmitter released and the type of receptor it binds, the response in the muscle fiber could be either excitatory or inhibitory. This includes both cardiovascular and respiratory functions. The knee-jerk response to the stimulation of the patellar ligament in the knee is an example of a reflex response. Upper motor neurons are often consulted in case of voluntary motor responses.
Reverse peristalsis brings intestinal contents into the stomach from which it can be expelled during vomiting. The enteric nervous system interfaces with the autonomic nervous system but it can also function independently. Individual fibres are usually insulated with a layer of white fatty material called myelin. Sensory The femoral nerve and its branches innervate the skin along the distal anterior thigh, the front and medial side of the knee, and the medial leg and foot. Like the brain, the spinal cord consists of gray matter and white matter. Effect of Damage: In abducens nerve paralysis, the eye cannot be moved laterally; at rest, affected eyeball turns medially internal strabismus. Any of the cordlike bundles of fibers made up of neurons through which sensory stimuli and motor impulses pass between the brain or other parts of the central nervous system and the eyes, glands, muscles, and other parts of the body.
The result is reduced coordination of motility. Alpha motor neurons can receive signals from upper motor neurons for voluntary muscle movement. The somatic system is the part of the that is responsible for carrying motor and sensory information both to and from the. At the spinal cord, upper motor neurons form synapses with lower motor neurons, and release glutamate into the synaptic cleft. A longitudinal fissure separates the left and right hemispheres, but the fissure penetrates only as far as the corpus callosum, a large collection of nerve fibers that communicates information between the two hemispheres. The second axon in the chain, the postganglionic parasympathetic axon, has its cell body in a peripheral ganglion near its target tissue. Sensory The radial nerve innervates skin along the lateral posterior arm via the posterior and lower lateral brachial cutaneous nerves.
Their cell bodies are in the of the spinal cord and they are sometimes called ventral horn cells. It innervates skin on the medial side of the arm. Higher centers return input to the intermediolateral neurons, thereby providing a mechanism for the influence of autonomic function by the emotional state. Motor The major motor branches are the lateral pterygoid, masseteric, deep temporal, and buccal nerves, which innervate the muscles of mastication lateral and medial pterygoids, masseter, and temporalis. When the muscle spindle is stretched, the opening of ion channels generates an action potential in these sensory neurons. It is the only motor nerve that originates from the dorsal surface of the brain between the midbrain and the cerebellum. Either of two nerves, the long ciliary nerve and the short ciliary nerve, that carry sensory axons and postganglionic sympathetic fibers that innervate the ciliary body, iris, and cornea of the eye.
Which of these lethal toxins is used in cosmetic procedures? Muscles consist of fascicles that contain myofibrils, which are the driving forces of muscle contraction. Intraluminal pressures generated by reverse peristalsis are nearly twice as great as those produced by normal phasic intestinal contractions. The ventral branches of the upper four, on either side, unite to form the cervical plexus, and those of the lower four, together with the ventral branch of the first thoracic nerve, form most of the brachial plexus. Synonym: greater superficial petrosal nerve; major superficial petrosal nerve greater superficial petrosal nerve hepatic nerve A somatic motor nerve originating in the hypoglossal nucleus of the hindbrain. Clinical Application: Opioid-Induced Constipation Physicians prescribe opioids as an analgesic to treat persons with a variety of pain conditions ranging from chronic pain resulting degenerative diseases of the back, knees, and hips, other musculoskeletal pain, neuropathic pain, and cancer pain, to acute pain resulting from sprains, strains, fractures, dental work, and surgery.
It travels unilaterally over the face and at one point is located in the parotid salivary gland, which it does not serve. Once two acetylcholine receptors have been bound, an ion channel is opened and sodium ions are allowed to flow into the cell. True diverticula are uncommon and probably congenital. The number of alpha motor neurons innervating a single muscle depends on the extent of fine motor control required at the site. Acetylcholine is the only neurotransmitter released in the synapse between upper and lower motor neurons C. Cardiac and smooth muscles contract without nervous stimulation, while skeletal muscles require excitation by motor neurons to contract. This center coordinates the gastrointestinal muscles and somatic motor systems to expel potentially noxious luminal contents from the gastrointestinal tract.