Anatomy & Physiology The Nervous System COMPONENTS OF THE NERVOUS SYSTEM Nerve CellsThe nervous system is the body's information gatherer, storage center and control system. Its overall functions are to collect information about the body's external/internal states and transfer this information to the brain (afferent system), to analyze this information, and to send impulses out (efferent system) to initiate appropriate motor responses to meet the body's needs. The system is composed of specialized cells, termed nerve cells or neurons, the functional unit of the nervous system that communicate with each other and with other cells in the body. A neuron has three parts: the cell body, containing the nucleus dendrites, branch-type structures with synapses that receive or conduct incoming signals or information from another cell and transmit the message to the cell body. the axon, a long projection that carries impulse away from the body or conduct outgoing signals emitted by the neuron. Axons are encased in a fat-like sheath, called myelin, which acts like an insulator and, along with the Nodes of Rangier, speeds impulse transmission. Neurotransmitter- a communicate messages from one neuron to another or from a neuron to a specific target tissue.
Major Divisions of the Nervous System The nerves of the body are organized into two major systems: the central nervous system (CNS), consisting of of the brain and spinal cord, the peripheral nervous system (PNS), the vast network of spinal and cranial nerves linking the body to the brain and spinal cord. The PNS is subdivided into: the autonomic nervous system (involuntary control of internal organs, blood vessels, smooth and cardiac muscles), consisting of the sympathetic NS and parasympathetic NS the somatic nervous system (voluntary control of skin, bones, joints, and skeletal muscle). Brain Structures The brain, the body's "control central," is one of the largest of adult organs, consisting of over 100 billion neurons and weighing about 3 pounds. It is typically divided into four parts: the cerebrum; the cerebellum; the diencephalons (thalamus, hypothalamus, sometimes classed as cerebral structures); and the brain stem(medulla oblongata, pons, midbrain), which is an extension of the s spin spinal cord. Parts of the Brain CerebrumThe largest division of the brain, the cerebrum, consists of two sides, the right and left cerebral hemispheres, which are interconnected by the corpus callosum. The two hemispheres are "twins," each with centers for receiving sensory (afferent) information and for initiating motor (efferent) responses. The left side sends and receives information to/from the right side of the body, and vice versa. Various intellectual functions are concentrated in either the left or right hemispheres. CerebellumThe cerebellum, the second largest brain structure, sits below the cerebrum. Like the cerebrum, the cerebellum has an outer cortex of gray matter and two hemispheres. It receives/relays information via the brain stem. The cerebellum performs 3 major functions, all of which have to do with skeletal-muscle control:
Diencephalons The diencephalons, located between the cerebrum and the midbrain, consists of several important structures, two of which are the: Thalamus: large, bilateral (right thalamus/left thalamus) egg-shaped mass of gray matter serving as the main synaptic relay center. Receives/relays sensory information to/from the cerebral cortex, including pain/pleasure centers. Hypothalamus: a collection of ganglia located below the thalamus and intimately associated with the pituitary gland. It has a variety of functions: senses changes in body temperature; controls autonomic activates and hence regulates the sympathetic and parasympathetic nervous systems; The four lobes perform specific functions: frontal – largest lobe, located in the front of the skull, functions are for concentration, abstract thinking, information storage or memory, and motor function. It also contains Boca's area, critical for motor control of speech. Responsible also in large part for a person’s affect, judgment, personality, and inhibitions. parietal - a predominantly sensory lobe located near crown of the head. Coordinates afferent information dealing with pain, temperature, form, shape, texture, pressure, and position. temporal - located around the temples that handles dreams, memory, and emotions. Center for auditory function. occipital - posterior lobe of the cerebral hemisphere located at the lower back of the head governs vision interpretation.
STRUCTURES PROTECTING THE BRAIN The brain is contained in the rigid skull, which protects it from injury. The major bones of the skull are the frontal, temporal, parietal, and occipital bones. Three layers of meninges that made up of fibrous connective tissues that cover the brain and spinal cord. It also provide protection, support, and nourishment.
The dura materis the most superior of the meningeal layers. Its name means "hard mother" in Latin and it is tough and inflexible. This tissue forms several structures that separate the cranial cavity into compartments and protect the brain from displacement. The dura mater also forms several vein-like sinuses that carry blood which has already given its supply of oxygen and nutrients to the brain back toward the heart.
The arachnoid mater is the middle layer of the meninges. In some areas, it projects into the sinuses formed by the dura mater. These projections are the arachnoid granulations or villi. They transfer cerebrospinal fluid, the fluid found in the ventricles, back into the bloodstream.
The pia mater is the innermost layer of the meninges. Unlike the other layers, this tissue adheres closely to the brain, running down into the sulci and fissures of the cortex. It fuses with the ependyma, the membranous lining of the ventricles to form structures called the choroid plexes which produce cerebrospinal fluid. CEREBROSPINAL FLUID Purpose Cerebrospinal fluid is a clear liquid produced within spaces in the brain called ventricles. It is also found inside the subarachnoid space of the meninges which surrounds both the brain and the spinal chord. Function The cerebrospinal fluid has many putative roles including mechanical protection of the brain, distribution of neuroendocrine factors and prevention of brain ischemia. The prevention of brain ischemia is made by decreasing the amount of cerebrospinal fluid in the limited space inside the skull. This decreases total intracranial pressure and facilitates for blood perfusion. It acts as a cushion for the neuraxis, also bringing nutrients to the brain and spinal cord and removing waste from the system.
CEREBRAL CIRCULATION Cerebral circulation is refer to the movement of blood through the network of blood vessels supplying the brain. The arteries deliver oxygenated blood, glucose and other nutrients to the brain and the veins carry deoxygenated blood back to the heart
ArteriesAn intricate arterial structure supplies the brain with oxygen-rich blood. At the brain stem, two vertebral arteries, entering through the first cervical vertebrae, join to form the basilar artery. The basilar artery along with two internal carotid arteries, entering through holes at the base of the skull, interconnect at the Circle of Willis. From there, the anterior and middle cerebral arteries arise; the posterior cerebral artery arises from the basilar system.
Veins The venous drainage of the cerebrum can be separated into two subdivisions: superficial and deep. The superficial system is composed of dural venous sinuses, which have wall composed of dura mater as opposed to a traditional vein. The dural sinuses are, therefore located on the surface of the cerebrum.
The blood-brain barrier (BBB) is a membranic structure that acts primarily to protect the brain from chemicals in the blood, while still allowing essential metabolic function. It maintains homeostasis by restricting the entrances of potentially harmful chemicals from the blood, and by allowing the entrance of essential nutrients. The blood brain barrier is both a physical barrier and a system of cellular transport mechanisms. THE SPINAL CORD The spinal cord is a fundamental component of the central nervous system. It is an elongated, cylindrical structure extending from the level of the foramen magnum, through the vertebral canal, to the upper border of the second lumbar vertebra. At its uppermost point, the spinal cord is contiguous with the medulla oblongata. CRANIAL NERVES Twelve pairs of cranial nerves emerge from the lower surface of the brain and pass through the foramina of the skull.
sensory cranial nerves (I, II, VIII)
motor (III, IV, VI, XI, and XII)
mixed (V, VII, IX, and X).
The table below shows the lists of the names and primary functions of the cranial nerves.
THE SPINAL NERVES There are a total of 31 bilaterally-paired spinal nerves : 8 cervical nerves (C1-C8) 12 thoracic nerves (T1-T12) 5 lumbar nerves (L1-L5) 5 sacral nerves (S1-S5) 1 coccygeal nerve (Co) Inside the spinal cord, there is grey matter, surrounded by white matter. From out of the grey matter, two dorsal roots (one on the left side, and one on the right side) and two ventral roots emerge. (Dorsal means back, ventral means front.)
The dorsal roots contain afferentsensoryaxons, that are sensory and transmit sensory impulses from the spicific areas of the body. The sensory may be somatic, carrying information about pain, temperature, touch, position sense.
The ventral roots contain efferentmotoraxons similarly continue out from the spinal column. These roots are motor and transmit impulses from the spinal cord to the body, and these fibers are also either somatic or visceral.
AUTONOMIC NERVOUS SYSTEM The autonomic nervous system (ANS) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation. Its main components are;
SYMPHATHETIC NERVOUS SYSTEM
Promotes a "fight or flight" response, corresponds with arousal and energy generation, inhibits digestion:. Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles. Dilates pupils and relaxes the lens, allowing more light to enter the eye.
PARASYMPHATHETIC NERVOUS SYSTEM
Promotes a *rest and digest" response; promotes calming of the nerves and return to regular function, enhances digestion. Dilates blood vessels leading to the GI tract, increasing blood flow. This is important following the consumption of food, due to the greater metabolic demands placed on the body by the gut. The parasympathetic nervous system can also constrict the bronchiolar diameter when the need for oxygen has diminished.
ASSESSMENT: THE NEUROLOGIC EXAMINATION The following is a widely accepted format for the neurologic exam, consisting of six subdivisions: 1. Mental Status2. Cranial Nerves3. Motor Exam 4. Reflexes5. Coordination and Gait6. Sensory Exam Equipment Needed Reflex Hammer 128 and 512 (or 1024) Hz Tuning Forks A Snellen Eye Chart or Pocket Vision Card Pen Light or Otoscope Wooden Handled Cotton Swabs Paper Clips General Considerations Always consider left to right symmetry Consider central vs. peripheral deficits
MENTAL STATUS A mental status examination (MSE) is an assessment of a patient's level of cognitive (knowledge-related) ability, appearance, emotional mood, and speech and thought patterns at the time of evaluation. It is one part of a full neurologic (nervous system) examination and includes the examiner's observations about the patient's attitude and cooperativeness as well as the patient's answers to specific questions. The purpose of a mental status examination is to assess the presence and extent of a person's mental impairment. A complete MSE is more comprehensive and evaluates the following ten areas of functioning: Appearance. The examiner notes the person's age, race, sex, civil status, and overall appearance. These features are significant because poor personal hygiene or grooming may reflect a loss of interest in self-care or physical inability to bathe or dress oneself. Movement and behavior. The examiner observes the person's gait (manner of walking), posture, coordination, eye contact, facial expressions, and similar behaviors. Problems with walking or coordination may reflect a disorder of the central nervous system. Affect. Affect refers to a person's outwardly observable emotional reactions. It may include either a lack of emotional response to an event or an overreaction. Mood. Mood refers to the underlying emotional "atmosphere" or tone of the person's answers. Speech. The examiner evaluates the volume of the person's voice, the rate or speed of speech, the length of answers to questions, the appropriateness and clarity of the answers, and similar characteristics. Thought content. The examiner assesses what the patient is saying for indications of hallucinations, delusions, obsessions, symptoms of dissociation, or thoughts of suicide. Dissociation refers to the splitting-off of certain memories or mental processes from conscious awareness. Thought process. Thought process refers to the logical connections between thoughts and their relevance to the main thread of conversation. Irrelevant detail, repeated words and phrases, interrupted thinking (thought blocking), and loose, illogical connections between thoughts, may be signs of a thought disorder. Cognition. Cognition refers to the act or condition of knowing. The evaluation assesses the person's orientation with regard to time, place, and personal identity; long- and short-term memory; ability to perform simple arithmetic; general intellectual level or fund of knowledge; ability to think abstractly; ability to name specified objects and read or write complete sentences; ability to understand and perform a task; ability to distinguish between right and left. Judgment. The examiner asks the person what he or she would do about a commonsense problem, such as running out of a prescription medication. Insight. Insight refers to a person's ability to recognize a problem and understand its nature and severity.
CRANIAL NERVES I - Olfactor To discern smells. The patient is asked to identify the odor. II - Optic Examine the Optic Fundi Test Visual Acuit Screen Visual Fields by Confrontation Test Pupillary Reactions to Light III - Oculomotor Observe for Ptosis Test Pupillary Reactions to Light IV - Trochlear Test Extraocular Movements (Inward and Down Movement) V - Trigeminal Test Temporal and Masseter Muscle Strength Test the Three Divisions for Pain Sensation If you find and abnormality then: Test the Corneal Reflex VI - Abducens Test Extraocular Movements (Lateral Movement) VII - Facial Observe for Any Facial Droop or Asymmetry Ask Patient to do the following, note any lag, weakness, or assymetry Test the Corneal Reflex VIII - Acoustic Screen Hearing Test for Lateralization (Weber test) Compare Air and Bone Conduction (Rinne test) Vestibular Function is Not Normally Tested
IX - GlossopharyngealSee Vagus NerveX - VagusListen to the patient's voice, is it hoarse or nasal?Ask Patient to Swallow Ask Patient to Say "Ah"Test Gag Reflex (Unconscious/Uncooperative Patient)XI - AccessoryFrom behind, look for atrophy or assymetry of the trapezius muscles. Ask patient to shrug shoulders against resistance. Ask patient to turn their head against resistance. Watch and palpate the sternomastoid muscle on the opposite side. XII - HypoglossalListen to the articulation of the patient's words. Observe the tongue as it lies in the mouth Ask patient to: Motor Observation Involuntary Movements Muscle Symmetry Left to Right Proximal vs. Distal Atrophy Pay particular attention to the hands, shoulders, and thighs. Gait Muscle Tone Ask the patient to relax. Flex and extend the patient's fingers, wrist, and elbow. Flex and extend patient's ankle and knee. There is normally a small, continuous resistance to passive movement. Observe for decreased (flaccid) or increased (rigid/spastic) tone.
Muscle Strength Test strength by having the patient move against your resistance. Always compare one side to the other. Grade strength on a scale from 0 to 5 "out of five": Grading Motor StrengtH Grade Description 0/5 - No muscle movement 1/5 - Visible muscle movement, but no movement at the joint 2/5 - Movement at the joint, but not against gravity 3/5 - Movement against gravity, but not against added resistance 4/5 - Movement against resistance, but less than normal 5/5 - Normal strength Test the following: Flexion at the elbow (C5, C6, biceps) [p513] Extension at the elbow (C6, C7, C8, triceps) Extension at the wrist (C6, C7, C8, radial nerve) Squeeze two of your fingers as hard as possible ("grip," C7, C8, T1) Finger abduction (C8, T1, ulnar nerve) Oppostion of the thumb (C8, T1, median nerve) Flexion at the hip (L2, L3, L4, iliopsoas) Adduction at the hips (L2, L3, L4, adductors) Abduction at the hips (L4, L5, S1, gluteus medius and minimus) Extension at the hips (S1, gluteus maximus) Extension at the knee (L2, L3, L4, quadriceps) Flexion at the knee (L4, L5, S1, S2, hamstrings) Dorsiflexion at the ankle (L4, L5) Plantar flexion (S1)
REFLEXES Deep Tendon Reflexes The patient must be relaxed and positioned properly before starting. Reflex response depends on the force of your stimulus. Use no more force than you need to provoke a definite response. Reflexes should be graded on a 0 to 4 "plus" scale: Tendon Reflex Grading Scale Grade Description 0 Absent 1+ or + Hypoactive 2+ or ++ "Normal“ 3+ or +++ Hyperactive without clonus 4+ or ++++ Hyperactive with clonus Biceps (C5, C6) The patient's arm should be partially flexed at the elbow with the palm down. Place your thumb or finger firmly on the biceps tendon. Strike your finger with the reflex hammer. You should feel the response even if you can't see it. Triceps (C6, C7) Support the upper arm and let the patient's forearm hang free. Strike the triceps tendon above the elbow with the broad side of the hammer. If the patient is sitting or lying down, flex the patient's arm at the elbow and hold it close to the chest. Brachioradialis (C5, C6) Have the patient rest the forearm on the abdomen or lap. Strike the radius about 1-2 inches above the wrist. Watch for flexion and supination of the forearm.
Abdominal (T8, T9, T10, T11, T12)
- Use a blunt object such as a key or tongue blade.
Stroke the abdomen lightly on each side in an inward and downward direction above (T8, T9, T10) and below the umbilicus (T10, T11, T12).
Note the contraction of the abdominal muscles and deviation of the umbilicus towards the stimulus.
Knee (L2, L3, L4) Have the patient sit or lie down with the knee flexed. Strike the patellar tendon just below the patella. Note contraction of the quadraceps and extension of the knee. Ankle (S1, S2) Dorsiflex the foot at the ankle. Strike the Achilles tendon. Watch and feel for plantar. Point-to-Point Movements Ask the patient to touch your index finger and their nose alternately several times. Move your finger about as the patient performs this task. Hold your finger still so that the patient can touch it with one arm and finger outstretched. Ask the patient to move their arm and return to your finger with their eyes closed. Romberg Be prepared to catch the patient if they are unstable. Ask the patient to stand with the feet together and eyes closed for 5-10 seconds without support. The test is said to be positive if the patient becomes unstable (indicating a vestibular or proprioceptive problem). Gait Ask the patient to: Walk across the room, turn and come back Walk heel-to-toe in a straight line Walk on their toes in a straight line Walk on their heels in a straight line Hop in place on each foot
DIAGNOGTIC EVALUATION. Neurological tests to evaluate patients may include: computerized tomography (CT ) or computer assisted tomography (CAT) scans -- forms of radiology or imaging that use computers to construct two-dimensional pictures of selected parts of the body. Dye may be injected into a vein to obtain a better picture. electroencephalogram (EEG) -- a procedure that records the brain's continuous electrical activity by means of electrodes attached to the scalp. magnetic resonance imaging (MRI) -- an advanced method of imaging the brain using a very strong magnet, without radiation. electromyogram (EMG) -- a procedure that measures and records electrical activity from the muscles and nerves with mild electrical shocks to stimulate the nerves. arteriogram (angiogram) -- a procedure that provides a scan of arteries going to and through the brain. cerebral spinal fluid analysis (spinal tap) -- a procedure used to make an evaluation or diagnosis by examining the fluid withdrawn from the spinal column. evoked potentials -- procedures that record the brain's electrical response to visual, auditory, and sensory stimuli. myelogram -- a procedure that uses dye injected into the spinal canal to make the structure clearly visible on x-rays. neurosonography -- a procedure that uses ultra high frequency sound waves that enable the physician to analyze blood flow in cases of possible stroke. other procedures