The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system consists of nerves that go to the skin and muscles and is involved in conscious activities. The autonomic nervous system consists of nerves that connect the CNS to the visceral organs such as the heart, stomach, and intestines. It mediates unconscious activities. Show
Structure of a NerveA nerve contains bundles of nerve fibers, either axons or dendrites, surrounded by connective tissue. Sensory nerves contain only afferent fibers, long dendrites of sensory neurons. Motor nerves have only efferent fibers, long axons of motor neurons. Mixed nerves contain both types of fibers.A connective tissue sheath called the epineurium surrounds each nerve. Each bundle of nerve fibers is called a fasciculus and is surrounded by a layer of connective tissue called the perineurium. Within the fasciculus, each individual nerve fiber, with its myelin and neurilemma, is surrounded by connective tissue called the endoneurium. A nerve may also have blood vessels enclosed in its connective tissue wrappings. Cranial NervesTwelve pairs of cranial nerves emerge from the inferior surface of the brain. All of these nerves, except the vagus nerve, pass through foramina of the skull to innervate structures in the head, neck, and facial region. The cranial nerves are designated both by name and by Roman numerals, according to the order in which they appear on the inferior surface of the brain. Most of the nerves have both sensory and motor components. Three of the nerves are associated with the special senses of smell, vision, hearing, and equilibrium and have only sensory fibers. Five other nerves are primarily motor in function but do have some sensory fibers for proprioception. The remaining four nerves consist of significant amounts of both sensory and motor fibers. Acoustic neuromas are benign fibrous growths that arise from the balance nerve, also called the eighth cranial nerve or vestibulocochlear nerve. These tumors are non-malignant, meaning that they do not spread or metastasize to other parts of the body. The location of these tumors is deep inside the skull, adjacent to vital brain centers in the brain stem. As the tumors enlarge, they involve surrounding structures which have to do with vital functions. In the majority of cases, these tumors grow slowly over a period of years. In other cases, the growth rate is more rapid and patients develop symptoms at a faster pace. Usually, the symptoms are mild and many patients are not diagnosed until some time after their tumor has developed. Many patients also exhibit no tumor growth over a number of years when followed by yearly MRI scans. Spinal NervesThirty-one pairs of spinal nerves emerge laterally from the spinal cord. Each pair of nerves corresponds to a segment of the cord and they are named accordingly. This means there are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve. Each spinal nerve is connected to the spinal cord by a dorsal root and a ventral root. The cell bodies of the sensory neurons are in the dorsal root ganglion, but the motor neuron cell bodies are in the gray matter. The two roots join to form the spinal nerve just before the nerve leaves the vertebral column. Because all spinal nerves have both sensory and motor components, they are all mixed nerves. Autonomic Nervous SystemThe autonomic nervous system is a visceral efferent system, which means it sends motor impulses to the visceral organs. It functions automatically and continuously, without conscious effort, to innervate smooth muscle, cardiac muscle, and glands. It is concerned with heart rate, breathing rate, blood pressure, body temperature, and other visceral activities that work together to maintain homeostasis. The autonomic nervous system has two parts, the sympathetic division and the parasympathetic division. Many visceral organs are supplied with fibers from both divisions. In this case, one stimulates and the other inhibits. This antagonistic functional relationship serves as a balance to help maintain homeostasis.  1 A sensory neuron is also known as a(n) ____________ neuron. 2 A neuron usually has one long, single extension of the cell called the _____________ that connects it to neighboring neurons. 3 The difference between a neuron of the central nervous system and a ganglion cell is based on their… 4 Glial cells connect afferent and efferent neurons. 5 Nerves are typically a bundle of axons covered by connective tissue. 6 The most abundant cells in the central nervous system are the ganglion cells. 7 The covering of many axons is the ______ sheath, which is laid down by the __________. 8 The resting potential of a nerve cell is approximately… 9 Following depolarization of a neuron's cell membrane, the calcium pump restores the ion gradients of the resting membrane. 10 During the progression of an action potential down the axon of a nerve cell, the __________ ions move across the cell membrane. 11 When the ionic reversal occurs across the plasma membrane of an axon during an action potential, the membrane is said to be… 12 The most common neurotransmitter found in pheripheral nervous system chemical synapses is 13 Electrical synapses are the most common in the animal kingdom and are adapted for escape reaction because they are very fast. 14 Action potentials are self-propagating and once started proceed with a rapid change in intensity. 15 The most primitive nervous system is the ___________ found in cnidarians. 16 Unlike invertebrate nervous systems, the nerves emanating from the spinal cord are separated into a dorsal sensory root and a ventral… 17 Reflexes may be… 18 The flatworms are the first to show differentiation into a peripheral and a central nervous system. 19 Development of a brain at the anterior end of the animal is known as cephalization. 20 A reflex arc involves, at the very least, a receptor, an afferent neuron, the central nervous system, and a motor neuron. 21 The simplest reflex, such as the knee-jerk reflex, involves ___ neurons. 22 The three principle divisions of the simplest vertebrate brain are the prosencephalon, the mesencephalon, and the… 23 The medulla controls… 24 The cerebellum is responsible for control of equilibrium and balance. 25 The thalamus system passes sensory material to higher brain centers. 26 Which one of the following is involved in regulation of functions involving homeostasis and also produces several neurohormones? 27 The efferent division of the peripheral nervous system includes the… 28 In times of stress, the ___________system is predominant in action. 29 If a person is relaxing, he is using what division of the nervous system? 30 What kinds of receptors allow a person to determine where his body parts are relative to the others? 31 Which of the following is probably the most ancient and universal sense in the Animal Kingdom? 32 Nerves from the parasympathetic division emanate from the brain and the thoracic region of the spinal cord. 33 The parasympathetic and sympathetic nervous divisions are usually antagonistic in action. 34 Taste buds have a short life and are continuously replaced. 35 The semicircular canals are responsible for sensing sound waves in higher vertebrates. 36 Lateral lines of fish have receptor cells called________that sense changes in water pressure. 37 In many invertebrates, the statolith is responsible for determining the change in position of the animal, while the organ of similar function in vertebrates is the labyrinth. 38 Arthropods may have compound eyes composed of units called… 39 Upon stimulation by light, rhodopsin is changed in shape and, ultimately this sets into motion a series of reactions that results in a nerve impulse produced by the rod. 40 Rods are most adapted for diurnal vision, and are in highest concentration in the fovea centralis. 41 The _________ of the vertebrate eye is composed of rods and cones. 42 The chambers of the eyes are filled with… 43 In higher vertebrates, focusing is accomplished by… 44 Recent research has focused on the possibility of pheromonal communication in humans. The best-established example is that of menstrual cycle synchronization that occurs in women living together in dormitories. 45 Taste sensations are categorized as which of the following? 46 Taste discrimination depends on assessment by the brain of the relative activity of many different taste receptors. This assessment is similar to color vision in vertebrates. 47 Pacinian corpuscles are very small chemoreceptors that register deep touch and pressure in mammalian skin. 48 Pain receptors are relatively unspecialized nerve fiber endings that respond to a variety of stimuli signaling possible or real damage to tissues. 49 Hair cells form an important sensory component of several mechanoreceptors found in both invertebrate (statocysts) and vertebrate (vestibular organs) organs of equilibrium. What do bundles of axons from ganglion cells make up?Ganglion cell axons exit the retina through a circular region in its nasal part called the optic disk (or optic papilla), where they bundle together to form the optic nerve.
What do the axons of ganglion cells converge to form?The axons of ganglion cells converge to form the optic nerve, which carries the visual information to the brain.
What structure of the eye is a bundle of ganglion axons that carries information to the brain?optic nerve, second cranial nerve, which carries sensory nerve impulses from the more than one million ganglion cells of the retina toward the visual centres in the brain. The vast majority of optic nerve fibres convey information regarding central vision.
Where do the axons of retinal ganglion cells synapse?Retinal ganglion cells (RGCs) are the output neurons of the retina. In the retina, RGCs synapse with bipolar and amacrine cells in the inner plexiform layer (IPL) to receive excitatory and inhibitory synaptic inputs respectively.
What is ganglion cells?1. Overview. Ganglion cells are the final output neurons of the vertebrate retina. Ganglion cells collect information about the visual world from bipolar cells and amacrine cells (retinal interneurons). This information is in the form of chemical messages sensed by receptors on the ganglion cell membrane.
What neurons have axons that form the optic nerve?The axons of the ganglion neurons of the retina form the optic nerves that go into the cranium and are joined to each other at a point called the optic chiasm.
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Bundles of axons from ganglion cells make up the ______.
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