Assessment The finger-to-nose test is a convenient method of assessing upper limb co-ordination: 1. Position your finger so that the patient has to fully outstretch their arm to reach it.
Ask the patient to touch their nose with the tip of their index finger and then touch your fingertip. Ask the patient to continue to do this finger to nose motion as fast as they are able to. Interpretation When patients with cerebellar pathology perform this task they may exhibit both dysmetria and intention tremor: Dysmetria: refers to a lack of coordination of movement.
Intention tremor: a broad, coarse, low-frequency tremor that develops as a limb reaches the endpoint of a deliberate movement. Be careful not to mistake an action tremor which occurs throughout the movement for an intention tremor. The presence of dysmetria and intention tremor is suggestive of ipsilateral cerebellar pathology.
Finger to nose test Finger-to-nose test Rebound phenomenon Rebound phenomenon is a reflex that occurs when a patient attempts to move a limb against resistance that has been suddenly removed.
Assessment 1. Ask the patient to close their eyes and position their arms outstretched in front of them with their palms facing upwards. Explain to the patient that you are going to apply some downward resistance on each arm and that they should try to maintain the current position of their arms as you apply that resistance. Observe the movement of the limb being assessed.
Interpretation In healthy individuals, when the resistance is removed the limb will usually move a short distance upwards i. This is the normal reflex that results in rebound phenomenon. An exaggerated version of rebound phenomenon is suggestive of spasticity e. A complete absence of the phenomenon, caused by a failure of the antagonist muscles to contract, is suggestive of cerebellar disease.
Rebound phenomenon Tone Assessment Assess tone in the muscle groups of the shoulder, elbow and wrist on each arm, comparing each side as you go: 1. Ask the patient to relax and allow you to fully control the movement of their arm. Feel for abnormalities of tone as you assess each joint e.
Interpretation Hypotonia can be caused by an ipsilateral cerebellar lesion. As a result, it is advisable not to put too much weight on this sign or the lack of it. Assess tone Assess tone Dysdiadochokinesia Dysdiadochokinesia is a term that describes the inability to perform rapid, alternating movements, which is a feature of ipsilateral cerebellar pathology.
Ask the patient to place their left palm on top of their right palm. Then ask them to turn over their left hand and touch the back of it onto their right palm. Now ask them to return their left hand to the original position left palm on right palm. Ask the patient to now repeat this sequence of movements as fast as they are able until you tell them to stop.
It is often useful to demonstrate the sequence of movements to the patient to aid understanding. Observe the speed and fluency by which the patient is able to carry out this sequence of rapidly alternating movements. Repeat the assessment with the other hand. Interpretation Patients with cerebellar ataxia may struggle to carry out this task, with their movements appearing slow and irregular. The presence of dysdiadochokinesia suggests ipsilateral cerebellar pathology.
Assess for dysdiadochokinesia Lower limbs Tone Although tone can be re-assessed in the lower limbs, it is often not required in a cerebellar OSCE exam if you have already comprehensively assessed tone in the upper limbs.
Assessment Briefly assess tone in the muscle groups of the hip, knee and ankle on each leg, comparing each side as you go: 1. With the patient lying on the examination couch, roll each leg to assess tone in the muscles responsible for the rotation of the hip.
Lift each knee briskly off the bed warning the patient first and observe the movement of the leg. In patients with normal tone, the knee should rise whilst the heel remains in contact with the bed the heel will typically lift off the bed if there is increased tone. Explain to the patient that you are now going to assess their reflexes by tapping gently on their leg with a tendon hammer it is useful to show the patient the tendon hammer at this stage.
Make sure to hold the tendon hammer handle at its end to allow gravity to aid a good swing. If a reflex appears absent make sure the patient is fully relaxed and then perform a reinforcement manoeuvre by asking the patient to clench their teeth together whilst you simultaneously tap the tendon.
Tap the patellar tendon with the tendon hammer making sure to hold the tendon hammer handle at its end to allow gravity to aid a good swing. If a reflex appears absent make sure the patient is fully relaxed and then perform a reinforcement manoeuvre.
Assess knee jerk reflex Assessment The heel-to-shin test is a convenient method of assessing lower limb co-ordination: 1. Ask the patient to place their left heel on their right knee and then run it down their shin in a straight line. Then ask them to return their left heel to the starting position over the right knee. Now ask them to repeat this sequence of movements in a smooth motion until you tell them to stop. Repeat the assessment with the right heel on the left leg.
Interpretation Dysmetria i. A note of caution: weakness e. As a result, power should be assessed before any diagnostic conclusions are drawn. Heel-to-shin test.
Functions of the Nervous System To carry out its normal role, the nervous system has three overlapping functions. Monitoring changes. Much like a sentry, it uses its millions of sensory receptors to monitor changes occurring both inside and outside the body; these changes are called stimuli, and the gathered information is called sensory input. Interpretation of sensory input. It processes and interprets the sensory input and decides what should be done at each moment, a process called integration.
Effects responses. It then effects a response by activating muscles or glands effectors via motor output. Mental activity. The brain is the center of mental activity, including consciousness, thinking, and memory. This function depends on the ability of the nervous system to detect, interpret, and respond to changes in the internal and external conditions.
It can help stimulate or inhibit the activities of other systems to help maintain a constant internal environment. Anatomy of the Nervous System The nervous system does not work alone to regulate and maintain body homeostasis; the endocrine system is a second important regulating system. Organization of the Nervous System We only have one nervous system, but, because of its complexity, it is difficult to consider all of its parts at the same time; so, to simplify its study, we divide it in terms of its structures structural classification or in terms of its activities functional classification.
Structural Classification The structural classification, which includes all of the nervous system organs, has two subdivisions- the central nervous system and the peripheral nervous system. Central nervous system CNS. The CNS consists of the brain and spinal cord, which occupy the dorsal body cavity and act as the integrating and command centers of the nervous system Peripheral nervous system PNS.
The PNS, the part of the nervous system outside the CNS, consists mainly of the nerves that extend from the brain and spinal cord. Functional Classification The functional classification scheme is concerned only with PNS structures. Sensory division. The sensory, or afferent division, consists of nerves composed of nerve fibers that convey impulses to the central nervous system from sensory receptors located in various parts of the body.
Somatic sensory fibers. Sensory fibers delivering impulses from the skin, skeletal muscles, and joints are called somatic sensory fibers. Visceral sensory fibers. Those that transmit impulses from the visceral organs are called visceral sensory fibers. Motor division. The motor, or efferent division carries impulses from the CNS to effector organs, the muscles and glands; the motor division has two subdivisions: the somatic nervous system and the autonomic nervous system.
Somatic nervous system. The somatic nervous system allows us to consciously, or voluntarily, control our skeletal muscles. Autonomic nervous system. The autonomic nervous system regulates events that are automatic, or involuntary; this subdivision, commonly called involuntary nervous system, has two parts: the sympathetic and parasympathetic, which typically bring about opposite effects.
Nervous Tissue: Structure and Function Even though it is complex, nervous tissue is made up of just two principal types of cells- supporting cells and neurons. Neuroglia include many types of cells that generally support, insulate, and protect the delicate neurons; in addition, each of the different types of neuroglia, also simply called either glia or glial cells,has special functions.
These are abundant, star-shaped cells that account for nearly half of the neural tissue; astrocytes form a living barrier between the capillaries and neurons and play a role in making exchanges between the two so they could help protect neurons from harmful substances that might be in the blood.
These are spiderlike phagocytes that dispose of debris, including dead brain cells and bacteria. Ependymal cells. Ependymal cells are glial cells that line the central cavities of the brain and the spinal cord; the beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective cushion around the CNS.
These are glia that wrap their flat extensions tightly around the nerve fibers, producing fatty insulating coverings called myelin sheaths. Schwann cells. Schwann cells form the myelin sheaths around nerve fibers that are found in the PNS. Satellite cells. Satellite cells act as protective, cushioning cells. Neurons Neurons, also called nerve cells, are highly specialized to transmit messages nerve impulses from one part of the body to another.
Cell body. The cell body is the metabolic center of the neuron; it has a transparent nucleus with a conspicuous nucleolus; the rough ER, called Nissl substance, and neurofibrils are particularly abundant in the cell body. The armlike processes, or fibers, vary in length from microscopic to 3 to 4 feet; dendrons convey incoming messages toward the cell body, while axons generate nerve impulses and typically conduct them away from the cell body.
Axon hillock. Neurons may have hundreds of the branching dendrites, depending on the neuron type, but each neuron has only one axon, which arises from a conelike region of the cell body called the axon hillock. Axon terminals. These terminals contain hundreds of tiny vesicles, or membranous sacs that contain neurotransmitters.
Synaptic cleft. Each axon terminal is separated from the next neuron by a tiny gap called synaptic cleft. Myelin sheaths. Most long nerve fibers are covered with a whitish, fatty material called myelin, which has a waxy appearance; myelin protects and insulates the fibers and increases the transmission rate of nerve impulses. Nodes of Ranvier. Because the myelin sheath is formed by many individual Schwann cells, it has gaps, or indentations, called nodes of Ranvier. Classification Neurons may be classified either according to how they function or according to their structure.
Functional classification. Functional classification groups neurons according to the direction the nerve impulse is traveling relative to the CNS; on this basis, there are sensory, motor, and association neurons.
Sensory neurons. Neurons carrying impulses from sensory receptors to the CNS are sensory, or afferent, neurons; sensory neurons keep us informed about what is happening both inside and outside the body. Motor neurons. The third category of neurons is known as the interneurons, or association neurons; they connect the motor and sensory neurons in neural pathways. Structural classification. Structural classification is based on the number of processes extending from the cell body.
Multipolar neuron. If there are several processes, the neuron is a multipolar neuron; because all motor and association neurons are multipolar, this is the most common structural type. Bipolar neurons.
Neurons with two processes- an axon and a dendrite- are called bipolar neurons; these are rare in adults, found only in some special sense organs, where they act in sensory processing as receptor cells.
Unipolar neurons. Brain Because the brain is the largest and most complex mass of nervous tissue in the body, it is commonly discussed in terms of its four major regions — cerebral hemispheres, diencephalon, brain stem, and cerebellum. Cerebral Hemispheres The paired cerebral hemispheres, collectively called cerebrum, are the most superior part of the brain, and together are a good deal larger than the other three brain regions combined.
The entire surface of the cerebral hemispheres exhibits elevated ridges of tissue called gyri, separated by shallow grooves called sulci. Less numerous are the deeper grooves of tissue called fissures, which separate large regions of the brain; the cerebral hemispheres are separated by a single deep fissure, the longitudinal fissure.
Other fissures or sulci divide each hemisphere into a number of lobes, named for the cranial bones that lie over them. Regions of cerebral hemisphere. Each cerebral hemisphere has three basic regions: a superficial cortex of gray matter, an internal white matter, and the basal nuclei. Cerebral cortex. Speech, memory, logical and emotional response, as well as consciousness, interpretation of sensation, and voluntary movement are all functions of neurons of the cerebral cortex.
Parietal lobe. Occipital lobe. The visual area is located in the posterior part of the occipital lobe. Temporal lobe. The auditory area is in the temporal lobe bordering the lateral sulcus, and the olfactory area is found deep inside the temporal lobe. Frontal lobe. The primary motor area, which allows us to consciously move our skeletal muscles, is anterior to the central sulcus in the front lobe.
Pyramidal tract. The axons of these motor neurons form the major voluntary motor tract- the corticospinal or pyramidal tract, which descends to the cord. Speech area. The speech area is located at the junction of the temporal, parietal, and occipital lobes; the speech area allows one to sound out words.
Cerebral white matter. The deeper cerebral white matter is compose of fiber tracts carrying impulses to, from, and within the cortex.
Corpus callosum. One very large fiber tract, the corpus callosum, connect the cerbral hemispheres; such fiber tracts are called commisures. Fiber tracts. Association fiber tracts connect areas within a hemisphere, and projection fiber tracts connect the cerebrum with lower CNS centers. Basal nuclei. There are several islands of gray matter, called the basal nuclei, or basal ganglia, buried deep within the white matter of the cerebral hemispheres; it helps regulate the voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex.
Diencephalon The diencephalon, or interbrain, sits atop the brain stem and is enclosed by the cerebral hemispheres. The thalamus, which encloses the shallow third ventricle of the brain, is a relay station for sensory impulses passing upward to the sensory cortex.
The Four Brain Lobes Each hemisphere of the mammalian cerebral cortex can be broken down into four functionally and spatially defined lobes: frontal, parietal, temporal, and occipital.
The frontal lobe is located at the front of the brain, over the eyes, and contains the olfactory bulb. The frontal lobe also contains the motor cortex, which is important for planning and implementing movement.
The temporal lobe is located at the base of the brain by the ears. It is primarily involved in processing and interpreting sounds. It also contains the hippocampus, which processes memory formation. The occipital lobe is located at the back of the brain. It is primarily involved in vision: seeing, recognizing, and identifying the visual world. Cerebrum Function The cerebrum directs the conscious or volitional motor functions of the body.
These functions originate within the primary motor cortex and other frontal lobe motor areas where actions are planned. Upper motor neurons in the primary motor cortex send their axons to the brainstem and spinal cord to synapse on the lower motor neurons, which innervate the muscles. Damage to motor areas of cortex can lead to certain types of motor neuron disease. This kind of damage results in loss of muscular power and precision rather than total paralysis.
The olfactory sensory system is unique in that neurons in the olfactory bulb send their axons directly to the olfactory cortex, rather than to the thalamus first. Damage to the olfactory bulb results in a loss of the sense of smell. Its potential functions can be placed into four non-exclusive categories: discriminating among odors, enhancing sensitivity of odor detection, filtering out background odors, and permitting higher brain areas involved in arousal and attention to modify the detection or the discrimination of odors.
Speech and language are mainly attributed to parts of the cerebral cortex. Cerebral Lobes The cortex is divided into four main lobes: frontal, parietal, occipital, temporal. Learning Objective Distinguish between the frontal, temporal, parietal, and occipital lobes of the cerebral cortex Key Takeaways Key Points Each lobe contributes to overall functionality of the brain and each lobe has many different roles.
The frontal lobe is involved in conscious thought. The parietal lobe is important for spatial reasoning. The occipital lobe is required for visual processing. The temporal lobe contributes to language and face recognition. Key Terms frontal lobe: The frontal lobe is an area in the brain of mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes.
In humans, it contributes to a number of higher cognitive functions including attention, planning, and motivation. This region is involved in auditory perception, speech and vision processing, and the formation of long-term memory as it houses the hippocampus. Cerebral lobes: The four lobes frontal, parietal, occipital, and temporal of the human brain are depicted along with the cerebellum. Brain lobes were originally a purely anatomical classification, but we now know they are also associated with specific brain functions.
The telencephalon cerebrumthe largest portion of the human brain, is divided into lobes like the cerebellum. There are four uncontested lobes of the telencephalon: The Frontal Lobe The frontal lobe is an area in the mammalian brain located at the front of each cerebral hemisphere and positioned anterior to in front of the parietal lobe and superior and anterior to the temporal lobes.
Cerebellar Examination – OSCE Guide
It is separated from the parietal lobe by a space between tissues called the central sulcus and from the temporal lobe by a deep fold called the lateral Sylvian sulcus. The precentral gyrus, forming the posterior border of the frontal lobe, contains the primary motor cortex, which controls voluntary movements of specific body parts. The frontal lobe contains most of the dopamine-sensitive neurons in the cerebral cortex.
The dopamine system is associated with reward, attention, short-term memory tasks, planning, and motivation. Dopamine tends to limit and select sensory information that the thalamus sends to the forebrain. A report from the National Institute of Mental Health indicates that a gene variant that reduces dopamine activity in the prefrontal cortex is related to poorer performance in that region during memory tasks; this gene variant is also related to slightly increased risk for schizophrenia.
The frontal lobe is considered to contribute to our most human qualities. Damage to the frontal lobe can result in changes in personality and difficulty planning.
Nervous System Anatomy and Physiology
The frontal lobes are the most uniquely human of all the brain structures. The Parietal Lobe The parietal lobe is a part of the brain positioned above superior to the occipital lobe and behind posterior to the frontal lobe. The parietal lobe integrates sensory information from different modalities, particularly spatial sense and navigation.
For example, it comprises the somatosensory cortex and the dorsal stream of the visual system. This enables regions of the parietal cortex to map objects perceived visually into body coordinate positions. Several portions of the parietal lobe are also important in language processing. Also, this lobe integrates information from various senses and assists in the manipulation of objects. Portions of the parietal lobe are involved with visuospatial processing.
The Occipital Lobe The two occipital lobes are the smallest of the four paired lobes in the human cerebral cortex. Located in the rearmost portion of the skull, the occipital lobes are part of the forebrain. At the front edge of the occipital there are several lateral occipital gyri separated by lateral occipital sulci.
The occipital lobe is involved in the sense of sight; lesions in this area can produce hallucinations. The Temporal Lobe The temporal lobe is a region of the cerebral cortex located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobes are involved in many functions, such as retaining visual memories, processing sensory input, comprehending language, storing new memories, feeling and expressing emotion, and deriving meaning.
The temporal lobe contains the hippocampus and plays a key role in the formation of explicit long-term memory, modulated by the amygdala. These lobes are divided by two fissures — the primary fissure and posterolateral fissure. Fig 1. Zones There are three cerebellar zones. In the midline of the cerebellum is the vermis.
Either side of the vermis is the intermediate zone. Lateral to the intermediate zone are the lateral hemispheres. Functional Divisions The cerebellum can also be divided by function.
There are three functional areas of the cerebellum — the cerebrocerebellum, the spinocerebellum and the vestibulocerebellum. Cerebrocerebellum — the largest division, formed by the lateral hemispheres. It is involved in planning movements and motor learning. It receives inputs from the cerebral cortex and pontine nuclei, and sends outputs to the thalamus and red nucleus.
This area also regulates coordination of muscle activation and is important in visually guided movements. Spinocerebellum — comprised of the vermis and intermediate zone of the cerebellar hemispheres.
It is involved in regulating body movements by allowing for error correction. Spinal Cord The cylindrical spinal cord is a glistening white continuation of the brain stem.
The spinal cord is approximately 17 inches 42 cm long. Major function. The spinal cord provides a two-way conduction pathway to and from the brain, and it is a major reflex center spinal reflexes are sonoff esp32 at this level. Enclosed within the vertebral column, the spinal cord extends from the foramen magnum of the skull to the first or second lumbar vertebra, where it ends just below the ribs. Like the brain, the spinal cord is cushioned and protected by the meninges; meningeal coverings do not end at the second lumbar vertebra but instead extend well beyond the end of the spinal cord in the vertebral canal.
Spinal nerves. In humans, 31 pairs of spinal nerves arise from the cord and exit from the vertebral column to serve the body area close by. Cauda equina. Gray Matter of the Spinal Cord and Spinal Roots The gray matter of the spinal cord looks like a butterfly or a letter H in cross section. The two posterior projections are the dorsal, or posterior, horns; the two anterior projections are the ventral, or anterior, horns. Central canal. The gray matter surrounds the central canal of the cord, which contains CSF.
Dorsal root ganglion. The cell bodies of sensory neurons, whose fibers enter the cord by the dorsal root, are found in an enlarged area called dorsal root ganglion; if the dorsal root or its ganglion is damaged, sensation from the body area served will be lost.
Dorsal horns. The dorsal horns contain interneurons. Ventral horns. The ventral horns of gray matter contain cell bodies of motor neurons of the somatic nervous system, which send their axons out the ventral root of the cord. The dorsal and ventral roots fuse to form the spinal nerves.
White Matter of the Spinal Cord White matter of the spinal cord is composed of myelinated fiber tracts- some running to higher centers, some traveling from the brain to the cord, and some conducting impulses from one side of the spinal cord to the other. Because of the irregular shape of the gray matter, the white matter on each side of the cord is divided into three regions- the dorsal, lateral, and ventral columns; each of the columns contains a number of fiber tracts made up of axon with the same destination and function.
Sensory tracts. Tracts conducting sensory impulses to the brain are sensory, or afferent, tracts. Motor tracts. Those carrying impulses from the brain to skeletal muscles are motor, or efferent, tracts. Peripheral Nervous System The peripheral nervous system consists of nerves and scattered groups of neuronal cell bodies ganglia found outside the CNS. Each fiber is surrounded by a delicate connective tissue sheath, an endoneurium.
Groups of fibers are bound by a coarser connective tissue wrapping, the perineurium, to form fiber bundles, or fascicles. Finally, all the fascicles are bound together by a tough fibrous sheath, the epineurium, to form the cordlike nerve. Mixed nerves. Nerves carrying both sensory and motor fibers are called mixed nerves. Sensory nerves. Nerves that carry impulses toward the CNS only are called sensory, or afferent, nerves.
Motor nerves. Those that carry only motor fibers are motor, or efferent, nerves. Cranial Nerves The 12 pairs of cranial nerves primarily serve the head and the neck. Fibers arise from the olfactory receptors in the nasal mucosa and synapse with the olfactory bulbs; its function is purely sensory, and it carries impulses for the sense of smell.
Fibers arise from the retina of the eye and form the optic nerve; its function is purely sensory, and carries impulses for vision. Fibers run from the midbrain to the eye; it supplies motor fibers to four of the six muscles superior, inferior, and medial rectus, and inferior oblique that direct the eyeball; to the eyelid; and to the internal eye muscles controlling lens shape and pupil size.
Fibers run from the midbrain to the eye; it supplies motor fibers for one external eye muscle superior oblique. Fibers emerge from the pons and form three divisions that run to the face; it conducts sensory impulses from the skin of the face and mucosa of the nose and mouth ; also contains motor fibers that activate the chewing muscles.
Fibers leave the pons and run to the eye; it supplies motor fibers to the lateral rectus muscle, which rolls the eye laterally. Fibers leave the pons and run to the face; it activates the muscles of facial expression and the lacrimal and salivary glands; carries sensory impulses from the taste buds of the anterior tongue. Fibers emerge from the medulla and run to the throat; it supplies motor fibers to the pharynx throat that promote swallowing and saliva production; it carries sensory impulses from the taste buds of the posterior tongue and from pressure receptors of the carotid artery.
Fibers emerge from the medulla and descend into the thorax and abdominal cavity; the fibers carry sensory impulses from and motor impulses to the pharynx, larynx, and the abdominal and thoracic viscera; most motor fibers are parasympathetic fibers that promote digestive activity and help regulate heart activity.
Fiber arise from the medulla and superior spinal cord and travel to muscles of the neck and back; mostly motor fiber that activate the sternocleidomastoid and trapezius muscles. Fibers run from the medulla to the tongue; motor fibers control tongue movements;; sensory fibers carry impulses from the tongue.
Spinal Nerves and Nerve Plexuses The 31 pairs of human spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord. Dorsal rami. The smaller dorsal rami serve the skin and muscles of the posterior body trunk. Ventral rami. The ventral rami of spinal nerves T1 through T12 form the intercostal nerves, which supply the muscles between the ribs and the skin and muscles of the anterior and lateral trunk.
Cervical plexus. The cervical plexus originates from the C1-C5, and phrenic nerve is an important nerve; it serves the diaphragm, and skin and muscles of the shoulder and neck.
Brachial plexus. The axillary nerve serve the deltoid muscles and skin of the shoulder, muscles, and skin of superior thorax; the radial nerve serves the triceps and extensor muscles of the forearm, and the skin of the posterior upper limb; the median nerve serves the flexor muscles and skin of the forearm and some muscles of the hand; the musculocutaneous nerve serves the flexor muscles of arm and the skin of the lateral forearm; and the ulnar nerve serves some flexor muscles of forearm; wrist and many hand muscles, and the skin of the hand.
Lumbar plexus. The femoral nerve serves the lower abdomen, anterior and medial thigh muscles, and the skin of the anteromedial leg and thigh; the obturator nerve serves the adductor muscles of the medial thigh and small hip muscles, and the skin of the medial thigh and hip joint.
Sacral plexus. The sciatic nerve largest nerve in the body serves the lower trunk and posterior surface of the thigh, and it splits into the common fibular and tibial nerves; the common fibular nerve serves the lateral aspect of the leg and foot, while the tibial nerve serves the posterior aspect of leg and foot; the superior and inferior gluteal nerves serve the gluteal muscles of the hip.
It is composed of a specialized group of neurons that regulate cardiac muscle, smooth muscles, and glands. At every moment, signals flood from the visceral organs into the CNS, and the automatic nerves make adjustments as necessary to best support body activities.
The ANS has two arms: the sympathetic division and the parasympathetic division. Preganglionic neurons. The preganglionic neurons of the parasympathetic division are located in brain nuclei of several cranial nerves- III, VII, IX, and X the vagus being the most important of these and in the S2 through S4 levels of the spinal cord. Craniosacral division.
The parasympathetic division is also called the craniosacral division; the neurons of the cranial region send their axons out in cranial nerves to serve the head and neck organs. Pelvic splanchnic nerves. In the sacral region, the preganglionic axons leave the spinal cord and form the pelvic splanchnic nerves, also called the pelvic nerves, which travel to the pelvic cavity.
Anatomy of the Sympathetic Division The sympathetic division mobilizes the body during extreme situations, and is also called the thoracolumbar division because its preganglionic neurons are in the gray matter of the spinal cord from T1 through L2.
Ramus communicans. The preganglionic axons leave the cord in the ventral root, enter the spinal nerve, and then pass through a ramus communicans, or small communicating branch, to enter a sympathetic chain ganglion. Sympathetic chain. The sympathetic trunk, or chain, lies along the vertebral column on each side.
Splanchnic nerves. After it reaches the ganglion, the axon may synapse with the second neuron in the sympathetic chain at the same or a different level, or the axon may through the ganglion without synapsing and form part of the splanchnic nerves. Collateral ganglion. The splanchnic nerves travel to the viscera to synapse with the ganglionic neuron, found in a collateral ganglion anterior to the vertebral column.
Physiology of the Nervous System The physiology of the nervous system involves a complex journey of impulses. Action potential initiation and generation.
Graded potential. Locally, the inside is now more positive, and the outside is less positive, a situation called graded potential. Nerve impulse. The outflow of positive ions from the cell restores the electrical conditions at the membrane to the polarized or resting, state, an event called repolarization; until a repolarization occurs, a neuron cannot conduct another impulse.
Saltatory conduction. Fibers that have myelin sheaths conduct impulses much faster because the nerve impulse literally jumps, or leaps, from node to node along the length of the fiber; this occurs because no electrical current can flow across the axon membrane where there first half corect score exact predictions fatty myelin insulation.
The Nerve Impulse Pathway How the nerve impulse actually works is detailed below.