Clinical Physiology 5-8 PDF

Clinical Physiology VIII Gastrointestinal Anatomy & Physiology In Relation to the Abdominal Exam BMS 100 Week 9 The GI system The Alimentary Canal – basic structure and function of: Esophagus Stomach Small Intestine Large Intestine The Digestive Accessory Organs – basic structure and function of: Li...

Clinical Physiology VIII Gastrointestinal Anatomy & Physiology In Relation to the Abdominal Exam BMS 100 Week 9 The GI system The Alimentary Canal – basic structure and function of: Esophagus Stomach Small Intestine Large Intestine The Digestive Accessory Organs – basic structure and function of: Liver & Gall Bladder Pancreas The Alimentary Canal Tubular structure that: ▪ Makes direct contact with food (or former food) ▪ Has a typical set of histologic layers that surround a lumen Composed of: ▪ Oral cavity and pharynx (future lectures) ▪ Esophagus ▪ Stomach ▪ Small Intestine Duodenum, jejunum, ileum ▪ Large intestine Cecum, appendix, ascending, transverse, descending colon, rectum The Accessory Digestive Organs All of these organs are derived embryologically as “outgrowths” of the early alimentary canal All of these organs function as glands that secrete substances into the alimentary canal ▪ The liver and pancreas have additional very important functions that impact the rest of the body Include: ▪ Salivary glands (future lectures) ▪ Liver & gall bladder ▪ Pancreas What, in general, does the alimentary canal do? Propulsion – food is moved along the “tube” as it is digested Secretion – two types: ▪ Hormonal secretions that impact digestion, secretion, and overall metabolism ▪ Fluid or mucous secretions that aid propulsion and digestion Digestion ▪ Chemical – enzymes and acid break chemical bonds in food material or substances facilitate enzymatic interactions ▪ Mechanical – movements of the canal mix food, break it apart, and increase the SA:volume ratio of food What, in general, does the alimentary canal do? Absorption (movement from lumen → bloodstream) ▪ Water – we ingest over 1 L of water today, and secrete 4 – 6 L of water into the canal ▪ Macro- and micronutrients Immune function ▪ Protection from ingested microbes that are harmful ▪ Aiding microbes that are useful ▪ “Educating” the immune system about whether something that has been ingested is harmful or harmless Layers of the Alimentary Canal Mucosa – epithelial lining, lamina propria, muscularis mucosa Type of epithelium varies from organ to organ ▪ Columnar with villi for absorption/secretion, cuboidal or squamous for protection from abrasion ▪ Goblet cells are usually present in the epithelial layer → mucous secretion ▪ Neuroendocrine cells – cells that are interspersed among the epithelium and release signals in response to different nutrients or chemical conditions in the lumen Layers of the Alimentary Canal Mucosa – epithelial lining, lamina propria, muscularis mucosa Lamina propria – site of: ▪ blood and lymphatic vessels ▪ Immune tissue (resembles looselystructured lymphatic nodules, known as MALT) Muscularis mucosa ▪ Alters the shape of the mucosa to optimize mixing and exposure of the epithelial cells to lumen contents Layers of the Alimentary Canal Submucosa – loose connective tissue with larger blood vessels and lymphatics ▪ Larger glands can be found here ▪ Very large lymphatic nodules can also be found in the submucosa of the proximal small intestine ▪ A plexus (network) of neurons exist in the submucosa Known as Meissner’s (submucosal) plexus – tends to regulate secretions and convey sensory info about what’s in the lumen Layers of the Alimentary Canal Muscularis - usually just an inner and an outer layer ▪ Inner layer – “circular layer” – smooth muscle fibres concentrically surround the lumen When it contracts, it “squeezes” the lumen shut ▪ Outer layer – “longitudinal layer” – smooth muscle fibres run along the length of the canal When it contracts, it “shortens” the canal ▪ Another plexus – Auerbach’s or myenteric plexus – regulates the movements of these muscular layers Found between the two layers Layers of the Alimentary Canal Outer layer – adventitia or serosa ▪ Adventitia – in the esophagus – connective tissue that anchors the esophagus in the chest cavity ▪ Serosa – Loose connective tissue that is covered by a simple squamous mesothelium The mesothelium secretes fluid that collects in the abdominal (peritoneal) cavity Source of peritoneal fluid The serosa is continuous with what is known as the visceral peritoneum More in later lectures Layers of the Alimentary Canal Peritoneal cavity = fluid filled gap between the wall of the abdomen and the organs contained within the abdomen ▪ Visceral is formed by the serosa of the alimentary canal and the capsule of the liver The mesothelium secretes fluid that collects in the abdominal (peritoneal) cavity ▪ Parietal is the inner lining of the abdominal wall The parietal peritoneum is extremely sensitive to inflammation and other chemical irritants Peritoneal cavity - FYI Esophagus Tube that extends from the pharynx to the stomach, only role is propulsion of food to the stomach ▪ 25 cm long tube located retrosternally ▪ Upper esophageal sphincter – when it closes, it pushes food from the pharynx to the esophagus ▪ Lower esophageal sphincter – limits movement of stomach acid into the esophagus → relaxes to receive swallowed food ▪ Stratified squamous epithelium, adventitia instead of serosa Stomach A sack that can expand to receive and store ingested food Muscular movements accomplish mechanical digestion (churning and breaking up food into acidic chyme) and propulsion into the small intestine Also has a role in chemical digestion ▪ Acid denatures proteins and kills ingested bacteria ▪ Secreted enzymes help to digest protein (collagen in particular) The stomach also tells you when you’re “full” ▪ Role in regulating food intake Stomach Mucosa has low columnar cells that have a wide range of functions: ▪ Parietal cells – secrete acid and intrinsic factor IF is needed for absorption of B12 ▪ Other cells secrete mucous to protect the lining or digestive enzymes specialized for digesting proteins Muscularis has 3 layers ▪ Innermost layer is the oblique layer Pyloric sphincter – regulates the amount of acidic chyme that enters the duodenum Small Intestine Main digestive organ: ▪ Site of most chemical digestion, absorption, and secretion in the alimentary canal ▪ Largest surface area – makes sense given its function 3 separate components – but no true anatomic distinction between them ▪ Duodenum – short, C-shaped tube that receives chyme from the stomach and overlies the head of the pancreas ▪ Jejunum – both the duodenum and jejunum have specialized immune tissue (Peyer’s patches) ▪ Ileum – longest portion, main function is reabsorption of bile salts, micronutrients/vitamins, and water Small Intestine Highly folded epithelium (microvilli), mucosa (villi) and submucosal layers (circular folds) meant to optimize surface area ▪ Columnar epithelium with many microvilli ▪ interspersed with goblet cells and cells that secrete chemical messengers into the blood Messengers help regulate propulsion, overall metabolic function, secretions from the pancreas or liver Large Intestine Main function is absorption of water from stool, storage of stool, and housing the majority of the microbes in the gut ▪ Negligible role in nutrient absorption Low columnar cells with fewer microvilli, plenty of goblet cells Muscular layer is unique ▪ Continuous circular muscle layer ▪ Longitudinal muscle layer is separated into bands that do not completely surround the canal Accessory Organs – Liver, Gallbladder, and Pancreas These organs don’t contact ingested substances directly ▪ They all have ducts that convey their secretions to the lumen of the duodenum ▪ The pancreas has important endocrine functions related to overall nutrient metabolism ▪ The liver has very wide array of important metabolic functions Liver Roles of the liver: ▪ Carbohydrate metabolism ▪ Protein synthesis and degradation Most proteins secreted into the bloodstream are from the liver ▪ Lipid metabolism ▪ Detoxification of molecules so that they can be secreted into the bile and defecated ▪ Making hydrophobic molecules water soluble so that they can be eliminated by the kidney ▪ Storage of vitamins and minerals ▪ Synthesis of bile – essential for lipid digestion ▪ Endocrine – secretion of IGF-1, important hormone regulating growth Gall Bladder and Pancreas Gall bladder – storage and modification of bile ▪ Contraction → bile release into the duodenum Pancreas: ▪ Exocrine – secretes digestive enzymes that are crucial for carbohydrate, protein, and lipid chemical digestion These enzymes are secreted into the pancreatic duct, which drains into the duodenum ▪ Endocrine – secretes hormones that impact glucose, protein, and lipid metabolism into the bloodstream Insulin, glucagon, and somatostatin Basic Physical Exam of the Abdomen Bowel sounds Abdominal discomfort Pain vs. tenderness Guarding vs. rigidity Organomegaly Hepatomegaly Bowel Sounds May be… ▪ Increased (hyperactive) Diarrhea, gastroenteritis, inflammatory bowel disease, laxative use, gastrointestinal bleed Or early bowel obstruction (often described as a high-pitched “tinkling” sound ▪ Decreased (hypoactive) Often suggests more emergent conditions Bowel obstruction, peritonitis, intestinal ischemia ▪ How long should we listen before assuming absence of bowel sounds? Abdominal Pain vs. Tenderness Abdominal pain is present regardless of whether you palpate (press) the abdomen ▪ Tenderness = pain in a region where you palpate ▪ I.e. tender to light or deep palpation Abdominal pain is one of the most challenging presentations ▪ “Deep” or visceral pain can come from stretching, ischemia, or chemical irritation of a component of the alimentary tract or accessory organ ▪ Sometimes pathologies in the thorax (heart attacks, pneumonia) can also present as abdominal pain Guarding vs. Rigidity Guarding is voluntary contraction of the abdominal musculature due to abdominal discomfort ▪ Can be exacerbated by anxiety ▪ Can be serious pathology, but often less serious Rigidity is involuntary contraction of the abdominal musculature, usually accompanied by severe pain ▪ More serious pathology ▪ Due to chemical irritation of the parietal peritoneum lining or “rubbing” of an inflamed organ against it Bile (ruptured cholecystitis), infected material (ruptured or ischemic intestinal wall), pancreatic secretions (pancreatitis), gastric or duodenal contents (perforated peptic ulcer) Inflamed structure rubbing against the parietal peritoneum – appendicitis, diverticulitis Abdominal Pain Often the location of the abdominal pain is helpful – see diagram ▪ Abdominal pain in the three areas in the “centre” can be visceral pain from the alimentary tract or accessory organs Can also be due to irritation of the parietal peritoneum ▪ Abdominal pain in the six regions on the “sides” are often due to irritation of the parietal peritoneum Can also be due to visceral pain from non-GI organs Abdominal Pain – basic locations (FYI) Epigastric: - stomach, esophagus, duodenum, pancreas, bile ducts, sometimes liver Hypochondriac: right side commonly liver, gall bladder, left can be stomach Umbilical: small intestine, cecum, appendix Lumbar – Splenic injury, renal disease Hypogastric: most of the large intestine, bladder Right iliac – appendicitis Left iliac – diverticulitis (large intestine) Right & left iliac – reproductive organs Hepatomegaly (Enlarged Liver) A palpable liver does not necessarily indicate hepatomegaly (an enlarged liver) Pathologic changes in consistency could be noted – from the normal softness to an abnormally firm or hard liver ▪ Pathologies often also cause an increase in the size of the liver Pathologies and their findings: ▪ Liver cirrhosis – large liver with firm, nontender edge ▪ Hepatocellular carcinoma – large liver that is firm and an irregular edge. May or may not be tender Clinical Physiology VII Fundamental Physiologic Basis of the Dermatologic Exam Dr. Hobson BMS 100 Week 7 Function Protective barrier Mechanical, chemical or thermal injuries Important barrier to infection Reduces heat, fluid, electrolyte loss Key for regulating body temperature Provides sensory information Limited importance in waste removal and vitamin synthesis (vitamin D) Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Micro-Anatomy Of The Skin Largest and heaviest organ 8 lbs, 1.5 - 2 m2 Layers Epidermis Dermis Subcutaneous Thickness varies Thick – palms and soles Epidermis is 0.4 – 1.4 mm thick Thin – everywhere else Epidermis is 0.075 – 0.15 mm Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Epidermal Layers From outermost to innermost: Stratum corneum Stratum lucidum ▪ only in thick skin Stratum granulosum Stratum spinosum Stratum basale Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Stratum Corneum Location: most superficial layer Layer Size: 15-30 cell layers Function – most important component of the barrier ▪ Prevents penetration of microbes ▪ Prevents dehydration ▪ Mechanical protection Skin cells here are dead, full of keratin and filaggrin ▪ Held together by tight junctions, desmosomes ▪ Filaggrin helps keratin aggregate into large macrofibrils Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Stratum Lucidum Location: immediately below s. corneum ▪ Only found in thick skin of the palms, soles, and digits Layer Size: 3-5 cell layers Function ▪ Protection, similar to s. corneum ▪ These cells are dead, just like the s. corneum Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Stratum Granulosum Location: between the s. corneum and s. spinosum Layer Size ▪ 3-5 cell layers, becoming compacted and flattened Function ▪ Living cells that are re-organizing keratin and associating it with filaggrin and other proteins ▪ Lamellar granules – lipid-rich, layered granules that help reduce water loss Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Stratum Spinosum Location: superficial to the s. basale Layer Size ▪ 8-10 cell layers – in most skin this is the thickest layer ▪ Very thick in thick skin Function ▪ Very busy synthesizing keratin, proto-filaggrin, and other proteins ▪ Eventually keratin becomes 50% of the cell mass of keratinocytes ▪ Thick bundles of keratin called tonofibrils are linked to desmosomes Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Stratum Basale Location: deepest epidermal layer Layer Size: single layer Function ▪ Stem cells divide and give rise to all of the layers ▪ Melanocytes: Synthesize and distribute melanin to keratinocytes ▪ Wide range of sensory receptors More later this semester ▪ Resident immune cells Langerhans cells – more next semester Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Keratin structure Fibrous protein – strong, often flexible long proteins that have a relatively simple, repeating secondary structure ▪ All have many hydrophobic amino acid residues → insoluble in water -keratin – alpha-helical protein with many levels of structure: ▪ Single “strand” protein arranged in an alpha helix → ▪ Two strands coiled around each other – “coiled coil” → The two strands interact with each other at sites of hydrophobic amino acid residues Rich in alanine, valine, leucine, isoleucine, methionine, phenylalanine (all hydrophobic) Keratin structure Keratin structure cont… ▪ Protofilament – long chains of two coiled coils ▪ Protofibril – two long chains of protofilaments ▪ Additional levels of structure lead to microfibrils (4 protofibrils, also known as tonofibrils) and macrofibrils (many microfibrils, filaggrin helps formation) Keratin can be flexible, or can be remarkably hard ▪ Keratin is held together by H-bonds and varying numbers of disulphide bonds These cross-link individual fibres to each other ▪ “Hardness” depends on the number of disulphide bonds Rhinoceros horn – 18% of the residues are cysteines (disulphide bonds) Keratin structure The alpha-helix is a right-handed coil, coiled-coil left-handed ▪ i.e. coiled in opposite directions ▪ Increases strength of the fibre Hard keratin is “just keratin” with no filaggrin, phospholipids ▪ Hair, nails https://www.labxchange.org/library/pathway/lx-pathway:13a6c8ad-792a-4e89a9ca-84d568afb286/items/lx-pb:13a6c8ad-792a-4e89-a9ca84d568afb286:html:5f9058df Dermal Layers From outermost to innermost: Papillary Layer Reticular Layer Note the blood vessels Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Papillary Layer Superficial 1/5 Loose CT ▪ fine elastic fibers, type III and type I collagen Interlocks dermis and epidermis ▪ Papilla = “fingers” ▪ Dermal papillae are vascularized ▪ Also contains sensory receptors Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Reticular Layer Dense irregular CT - type I collagen and elastic fibers ▪ Usually thickest layer of the skin – thickest over the back (4 mm) Houses ▪ Hair follicles ▪ Nerves, arteries, veins, and lymphatics ▪ Sebaceous and sudoriferous (sweat) glands ▪ Some adipose tissue ▪ Smooth muscle cells ▪ Some sensory receptors Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Collagen fibres - structure Type I, II, and III collagen are fibril-forming collagens ▪ Type I collagen forms 90% of the body’s collagen, and has the most structural strength ▪ many cells produce collagens – in the dermis, it is the fibroblast ▪ Final assembly for these fibril-forming collagens actually occurs in the extracellular space Collagen is a “coiled-coil” structure as well, but is not an -helix ▪ Three collagen -chains (themselves twisted) are coiled around each other – this is called tropocollagen ▪ The tight “twisting” of the -chains is accomplished by a unique amino acid sequence https://commons.wikimedia.org/wiki/File:Tropocollagen.svg Collagen fibres - structure Amino acid sequence: Gly-X-Y ▪ Often “X” is proline (but not always) ▪ Often “Y” is hydroxyproline (but not always) The glycine has a very small R-group ▪ It fits well into the tightly-twisted triple helix Hydroxyproline and proline have rigid, “kinked” structures ▪ These provide the sharp “twists” or “kinks” in the molecule The hydroxylated proline (and lysine, when it’s there) are ideal for covalent cross-linking of the collagen https://commons.wikimedia.org/wiki/File:Tropocollagen.svg Collagen Vitamin C is crucial to collagen formation and crosslinking of hydroxylated a.a.s More in later Biomedicine classes https://commons.wikimedia.org/wiki/File:Tropocollagen_crosslinkage_lysyl_oxidase_(EN).svg Collagen synthesis… a brief overview Fibroblasts (or other cells) produce tropocollagen fibres that have some degree of hydroxylation and glycosylation that are secreted into the ECM Outside of the cell, the tropocollagen molecules are assembled into fibrils and fibres ▪ These fibrils and fibres are also linked to proteoglycans and glycoproteins Junqueira’s Basic Histology, p. 118, fig. 5-20 Hair Follicle What is it? An epidermal in-growth into the dermis (invagination) that builds a long structure formed from hard keratin = a hair ▪ All hair follicles, although found in the dermis, are derived from the epidermis ▪ Specialized keratinocytes Are there areas of the skin completely without hair? Palms and soles Lips, genital structures (glans penis, labia minora, clitoris) The face has a lot of hair – 600 hairs/cm2; most other areas have around 60/cm2 ▪ Roughly 5 million hairs total Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Hair - structure Hair bulb – bulbous part at the base of the follicle Dermal papilla “contacts” the bulb, supplying a capillary network Keratinocytes at the papilla are very similar to the stratum granulosum and spinosum (hair matrix) – site of active cell division ▪ Only found in the bulb Melanocytes in the bulb transfer melanosomes to keratinocytes Hair shaft itself has 3 layers: ▪ Medulla ▪ Cortex ▪ Cuticle Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Hair Histology Hair shaft: Medulla: lightly keratinized Cortex: filled with hard keratin Cuticle: the structure of the keratinocytes is more easily seen – looks like “tiles” or “shingles” Technically, not called the hair shaft until it passes beyond the epidermis Mescher, A. Junqueira’s Basic Histology Text and Atlas 15th ed. Fig 18-14, p. 385 Hair Structure Arrector pili – a bundle of smooth muscle cells that pull the shaft into a more erect position ▪ Why? ▪ Innervated by the sympathetic nervous system, found on same side as the sebaceous gland Hair root plexus – very sensitive mechanoreceptors ▪ Myelinated nerves ▪ Desensitize rapidly Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Hair Growth Three phases ▪ Anagen – longer period of mitotic activity and growth ▪ Catagen – arrested growth and regression of the hair bulb ▪ Telogen – cellular inactivity, often → hair shedding At the beginning of the next anagen phase, epidermal stem cells produce progenitors ▪ The progenitors give rise to the matrix of the new hair bulb ▪ Stem cells are located in the outer layer of the follicle, the external root sheath, near the attachment points of the arrector pili Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Hypodermis/subcutaneous tissue/superficial fascia Lower most layer Contains loose areolar and adipose tissue Important in stabilizing the position of the skin in relation to underlying tissues Fat storage area, insulates against excessive heat loss Superficial region contains vessels Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Pigmentation Skin colouration: Hemoglobin: red blood cells in vasculature below epidermis If deoxygenation occurs (hypoxia) then the skin looks relatively “blue” cyanosis Carotene: yellow pigment from plants in the diet Melanin: pale yellow to black pigment produced by melanocytes Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e For future dermatology lectures: Function and regulation of sebaceous glands Function and regulation of suderiferous (sweat glands) More disorders! Physical Exam: Recalling The Skin Exam How would you describe a skin lesion? What are the important things to note? Morphology: general shape, size, color and appearance Distribution: Is there a pattern? What area of the body does it affect? Inspection – How do you describe a skin lesion? Description 5mm Flat Lesion Macule Patch Flat + Raised Papule Plaque Solid Bump (Round-topped, no fluid) Papule Nodule round, solid, no fluid in it Serous fluid filled Vesicle Bulla(e) Pustule (cyst) Abscess or also a cyst Depends on the structure - has to be epithelial lining Pus-filled Inspection – How do you describe a skin lesion? Some extras… Cyst: any pocket of fluid (infected or not) lined by epithelium Abscess: a pocket of purulent fluid (bigger than a pustule) – not lined by epithelium Ulcer: a defect in the epidermis, down at least to dermis level, usually due to impairment of healing/re-epithelialization Vascular lesions : include telangiectasias (dilated arterioles, venules that one can see with the naked eye) and hemangiomas (many different types of vessel-rich, red or violet growths) Scale – accumulation or excess shedding of the stratum corneum – can be dry or waxy-feeling. Remember atopic dermatitis from Monday? Defects in the moisture barrier (filaggrin) and/or tight junctions → antigens “getting past” the epidermal barrier over and over → recruitment of immune cells repetitive episodes of itchy, erythematous, edematous macular-papular rash Distribution: extensor surfaces, face, scalp https://commons.wikimedia.org/wiki/File:Atopic_dermatitis_child.JPG Atopic dermatitis (eczema) under the microscope Early → late Note the edema in the epidermis (1), the lymphocytes and mast cells (2), and eventually the hyperkeratotic skin (from scratching it so much) (3) 1 1,2 Kumar et. al., Robbins and Cotran Pathologic Basis of Disease 9th ed. Fig 25-22, p. 1155 3 3 1 1 2 2 2 2 2 2 Psoriasis Extremely common Pathogenesis is not well understood: Chronic inflammatory condition that appears to have an autoimmune basis Epidermal hyperproliferation – they divide really quickly Abnormal differentiation of epidermal keratinocytes What is this?! Kumar et. al., Robbins and Cotran Pathologic Basis of Disease 9th ed. Fig 25-25, p 1157 Psoriasis What does it look like? Morphology? Distribution? Vitiligo Pathogenesis is not well understood: disorder of skin pigmentation Immune system attacks the cells that produce melanin (what were those again?) Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e Vitiligo What does it look like? Morphology? Distribution? The Hair Cycle - reminder Anatomy & Physiology, 2e. Chapter 5 https://openstax.org/books/anatomy-and-physiology-2e An approach to hair loss FYI Alopecia areata Prevalence is 0.1-0.2% lifetime risk of developing 1.7% 0.7-3% of patients seen by dermatologists M:F = 1:1, affects Any age Pathophysiology NK cells and cytotoxic T-cells attack the hair follicle (adaptive immune system) More likely in those that are genetically susceptible ~ 20% associated with stressful events Severe infection, trauma Severe psychologic stress Alopecia areata Clinical Features Patchy hair loss that does not scar – hair will re-grow Stressful event tends to predate hair loss by 1 – 6 months 80-90% have only 1 patch of hair loss Most often affects scalp, can affect beard Re-growth tends to occur about 1 year later Androgenetic Alopecia Prevalence – 50% of men at least 13% of women premenopause, > 50% women older than 65 Usually begins to be detectable at age 40 Pathophysiology Gradual conversion of terminal hairs to vellus hairs - inherited Greatly dependent on androgen exposure over time in men Androgens may be less responsible in women Androgenetic Alopecia Clinical features: Hair loss over the crown for both sexes For men: Posterior and lateral scalp are spared See next slide For women: Mid-frontal hair loss Vertex, temporal regions spared; often frontal hair-line preserved If rapid, should check for diseases → androgen excess Often larger psychosocial impact on women AGA in males Acute Telogen Effluvium Common disorder, but no good epidemiologic studies Nonscarring alopecia characterized by acute - subacute diffuse hair shedding caused by a metabolic or hormonal stress or by medications => hair loss occurs 2-3 months later Stressor causes anagen hair to enter telogen – remember that? Generally, recovery is spontaneous and occurs within 6 months, unless a background of pattern alopecia is present A chronic form with a more insidious onset and a longer duration also exists Hair Pull Test - FYI What does it indicate? A positive hair pull test indicates active hair shedding and can be seen in TE and in active stages of AA or different scarring alopecias Procedure: Select 50 to 60 hairs and holds the bundle close to the scalp between the thumb, index finger, and long finger. Firmly pull on the bundle using slow traction as the fingers slide down the hair shaft, avoiding a fast and forceful tug. Location: performed at the vertex, parietal areas, and the occipital area of the scalp. Count the pulled hairs and discard broken hairs Hair Pull Test - FYI Interpretation: If more than 10% of the hairs in each bundle are removed from a scalp area, the hair pull test is considered positive. Alopecia Areata If fewer than 10% are removed, then the hair loss can usually be attributed to normal shedding. If a test is positive in more than 1 scalp region, the clinician must consider telogen effluvium. Other hair disorders (ie, alopecia areata) may only have a positive hair pull test in the affected area. Clinical Physiology VI Fundamental Physiologic Basis of the Neurologic Exam – part 2 BMS 100 Week 6 The Neurologic System Basic functional Anatomy of the Nervous System Cranial Nerves Types of information conveyed by cranial nerves Cranial nerve anatomy and function Major Somatic Sensory Pathways Dorsal column-medial lemniscal system Spinothalamic tract Neurologic Physical Exam – Part II Cranial nerve exam Assessing dermatomes Cranial Nerves Nerves that “emerge from the brain” and exit via skull foramina ▪ All other nerves exit the spinal cord and travel through the intervertebral foramina Cranial nerves carry a wide variety of information: ▪ Special sensory information Special senses – sight, sound, taste, smell, “balance” ▪ Somatic motor information Somatic motor = skeletal muscles that we have voluntary control over ▪ Somatic sensory information Somatic sensory = sensations that we can perceive OTHER THAN the special senses ▪ Motor and sensory information to/from structures that we cannot control or perceive Mostly autonomic nervous system to glands/organs or from organs Cranial Nerves – general anatomy The nuclei (cell bodies) in the brain that communicate to the cranial nerves are mostly found in the brainstem – some exceptions: ▪ Olfactory (CN I) – projects to the cortex (mostly ▪ Optic (CN II) – projects to the thalamus ▪ CN III and IV – nuclei are found in the midbrain ▪ CN V, VI, VII, VIII – nuclei are found in the pons ▪ CN IX, X, XI, XII – nuclei are (mostly) found in the medulla Inferior view – cranial nerves Cranial Nerve I Function – sense of smell (special sense) ▪ From the superior part of the nasal cavity → olfactory bulb → many different locations in the temporal and frontal lobes ▪ Skull entry/exit point: Axons penetrate the skull via the tiny holes in the cribriform plate (ethmoid) How do we test it? ▪ Ask the patient to identify a couple of distinctive smells (eyes closed if necessary) ▪ i.e. coffee, peppermint ▪ Loss of sense of smell = anosmia Infections (COVID is famous for it), head injuries Cranial Nerve I Cranial Nerve II Function – vision (special sense) ▪ From the retina (back of the eye) → thalamus → occipital lobe (cortex) There are other connections between the optic nerve and the brain other than through the thalamus – mostly for mediating reflex eye and head movements ▪ Skull entry/exit point: optic foramen (canal) How do we test it? ▪ The Snellen eye chart (central vision) ▪ Peripheral field tests (peripheral vision) ▪ Observation of the back of the eye (ophthalmoscope) Assesses the retina (the “light sensor”) ▪ Others – pupillary movements, rapid involuntary eye movements Cranial Nerve II Cranial Nerve III, IV, VI Main Function: Eye movements (somatic motor) ▪ CN III: from the midbrain → muscles around the eye As well, CN III projects to your pupillary muscles (dilation, constriction) and your levator palpebrae superioris muscle (helps elevate your eyelid) ▪ CN IV: from midbrain → one of the muscles around your eye (superior oblique) ▪ CN VI: from the pons → one of the muscles around your eye (lateral rectus) ▪ Skull entry/exit point for all: superior orbital fissure We’ll discuss the actions of all of these eye muscles in detail for later… but for now: ▪ CN III – most eye movements and control of pupils ▪ CN IV – directs your gaze down and outwards ▪ CN VI – directs gaze laterally (abducts eyeball) Cranial Nerves III, IV, VI Cranial Nerves III, IV, VI How do we test them? ▪ You can see that these nerves innervate very small, quick, coordinated muscles that help us to control our eye movements ▪ Test them by: 1. Ask patient to “follow your finger with their eyes” 2. Move your finger so that you draw a big “H” in the air in front of them Eyes should smoothly follow your finger 3. Shine a light into the patient’s eyes and hold an object close to patient’s eyes Pupils should constrict in response Cranial Nerves III, IV, VI Cranial Nerve V Two major functions: 1. Sensation over the face, scalp, nasal cavity and cornea (somatic sensation) ▪ Sensations include touch, pain, proprioception for facial muscles and tongue ▪ Cornea = clear, tough outer part of the eye that overlies the iris ▪ Exits from the pons, leaves skull through: Superior orbital fissure: cornea, forehead, scalp, eyelids, nasal mucosa (upper face, scalp) Foramen rotundum: face over the maxillary part of the face, including maxillary teeth (mid-face) Foramen ovale: lower jaw, proprioception for tongue (lower face, mouth – but NOT taste) Cranial Nerve V Two major functions: 2. Motor function (somatic motor) for the muscles of mastication (chewing) and some neck, middle ear muscles ▪ Main muscles – temporalis, masseters, pterygoids ▪ Exits through the foramen ovale How do we test it? 1. Sensory – sharp, dull, and light touch over the face 2. Strength of jaw clenching and movements of the jaw Cranial Nerve V Sharp sensation → break the wooden “stick” of the cotton swab Cranial Nerve VII The trickiest nerve: Functions: 1. Facial movements OTHER THAN the tongue, eye muscles, and muscles of mastication (somatic motor) ▪ Remember from anatomy? Eye opening? Pursed lips? Raised eyebrows? ▪ Controls many skeletal muscles in the head – actually controls more muscles than any other nerve in the body 2. Taste from the anterior 2/3 of the tongue (special sense → taste) 3. Autonomic motor input to glands (“autonomic” motor) ▪ Salivary and tears ▪ Nasal glands (nasal secretions) 4. Somatic sensation from the ear canal (somatic sensory) Cranial Nerve VII – keeping it simple Simplified anatomy: ▪ Exits/enters the pons → passes through the internal acoustic meatus and facial canal, exits through the stylomastoid foramen ▪ Many branches – if you’re really curious, check out this excellent, free reference: https://www.ncbi.nlm.nih.gov/books/NBK526119/#!po=6. 25000 How do we test it? ▪ Pretty simple – you ask the patient to use her facial muscles (make particular faces at you) Cranial Nerve VII Cranial Nerve VIII Hearing apparatus: ▪ Sound waves enter the ear canal → vibration of the tympanic membrane ▪ Tympanic membrane vibrations → movements of tiny bones in the middle ear (malleus, incus, stapes) all of these bones act as levers to increase the amplitude of sound vibrations ▪ Vibrations transmitted from the stapes into the cochlea (snail-looking thingy) within the inner ear ▪ Vibrations in cochlear fluid move hairs in the cochlea → ▪ Hairs transduce vibrations into electrical impulses → ▪ Electrical impulses are carried by CN VIII Cranial Nerve VIII Function - Hearing and balance (special senses) ▪ From inner ear → internal acoustic meatus → pons From pons it passes through the thalamus and synapses in the temporal lobe for the perception of sound Hearing – how do we test it? ▪ Whisper to patient to test for auditory acuity ▪ Tuning forks – allow you to tell if there’s a problem with the nerve or with the ear canal → ear drum → cochlea pathway Tuning forks can be “heard” by conduction of the tuning fork vibration through the bones of the skull If you “hear” the tuning fork better when it’s sending vibrations through your skull (versus being held up to your ear) → ▪ have a problem with sound conduction through the ear canal, ear drum, or the tiny bones of your middle ear Cranial Nerve VIII Cranial Nerve VIII Balance and equilibrium – how do we test it? ▪ We’ve already covered this a bit – the gravity- and motion-detecting apparatus of the ear feeds important information to the cerebellum Vestibular apparatus ▪ If the vestibular apparatus or the vestibular component of CN VIII is compromised, balance is impaired Can be observed when patient is standing with eyes closed (tends to fall over) or with abnormalities in gait (tends to veer to one side or the other) ▪ Many patients with impaired vestibular function are also very nauseous and have rapid, involuntary eye movements (nystagmus) Cranial Nerve IX Function: 1. Swallowing – (somatic motor) 2. Sensation from the pharynx, part of the external ear (somatic sensory) and from chemoreceptors/baroreceptors in the carotid body (“autonomic sensory”) 3. Taste from posterior 1/3 of tongue (special sensory) 4. Innervation of a salivary gland – parotid (“autonomic motor”) ▪ Nerve enters/exits through the jugular foramen in the skull and projects to/leaves the medulla How do we test it? ▪ Stimulate the posterior aspect of the pharynx (careful – this causes a gag reflex) ▪ The soft palate and tongue elevate (CN X) when stimulation is detected (CN IX) ▪ Not the most helpful test – many healthy people have a diminished gag reflex Cranial Nerve IX Cranial Nerve X We’ll talk much more about CN X as we discuss the autonomic nervous system ▪ It projects to a wide variety of organs such as the lungs, heart, liver, and gastrointestinal tract (among others) ▪ Nerve is called the vagus nerve (“vagus” means “wanderer”) Major functions: ▪ Pharyngeal muscles –swallowing - and laryngeal muscles vocal cords (somatic motor) ▪ Parasympathetic nervous system input to the visceral organs discussed above (“autonomic motor”) “Rest and digest” aspect of the autonomic nervous system ▪ Sensation from the visceral organs it impacts (“autonomic sensory”) and some of the pharynx and external ear (“somatic sensory”) ▪ Sensory input from aortic baroreceptors and chemoreceptors (“autonomic sensory”) Cranial Nerve X How do we test it? ▪ Usually by listening to the patient’s voice – if hoarse, then it may be due to damage of the vagus motor input to the vocal cords ▪ Ask the patient to say “ahhhh” → elevation of the palate is part of the somatic function of the vagus nerve ▪ We don’t usually test the function of parasympathetic nervous system at the vagus nerve level Cranial Nerve X Cranial Nerve XI Function – innervation of the sternocleidomastoid and trapezius (somatic motor) ▪ CN XI isn’t really a true cranial nerve – the neuronal cell bodies are actually located in the cervical spinal cord this nerve travels into the skull (foramen magnum)… and then back out again (jugular foramen) How do we test it? ▪ Turning the head against resistance ▪ Shrugging the shoulders Cranial Nerve XI Cranial Nerve XII Function – innervation of the tongue (somatic motor) ▪ Key for speech and swallowing ▪ Exits the medulla and passes through the hypoglossal canal How do we test it? ▪ Ask the patient to stick out her tongue, and move it side to side If the tongue is deviated or the patient can’t follow these instructions, then damage could be at the level of the nerve, medulla, or motor cortex Cranial Nerve XII The foramina – from MSK anatomy The foramina – from MSK anatomy The major sensory pathways - review The special senses are all carried via the cranial nerves – all will eventually project to the cortex ▪ Vision – occipital lobe ▪ Sound – temporal lobe ▪ Taste and smell – inferior-lateral frontal lobes The other senses – pain, touch, vibration, proprioception, temperature – all project to the postcentral gyrus in the parietal lobe ▪ Touch, vibration, proprioception – dorsal column-medial lemniscal system ▪ Pain, temperature – spinothalamic tract ▪ These two pathways have somewhat different anatomy Major sensory pathways Dorsal column-medial lemniscal system ▪ Neurons that receive sensory input (first order neurons) send their axons to the dorsal horn (gray matter of spinal cord) and then project into the dorsal columns (white matter of spinal cord) ▪ These axons stay on the same side until they enter the medulla After entering the medulla, they synapse on another neuron → ▪ The next neuron (second-order neuron) crosses to the other side of the medulla, and then synapses with another neuron in the thalamus (third order neuron) → The third order neuron projects to the post-central gyrus Dorsal Column System and Spinothalamic Tract Major sensory pathways Spinothalamic Tract ▪ Neurons that receive sensory input (first order neurons) send their axons to the dorsal horn (gray matter of spinal cord) → and then synapse with another cell in the dorsal horn (second-order neuron) ▪ The axon of the second order neuron crosses over in the gray matter, then sends its axon up to the brain in the lateral and anterior white matter of the spinal cord → ▪ The second-order neuron synapses with another neuron in the thalamus (third-order neuron) → Third order neuron synapses with a neuron in the postcentral gyrus Dorsal Column System and Spinothalamic Tract Testing sensation Each spinal nerve collects information from a part of the body and sends it to the thalamus and to the prefrontal gyrus ▪ Loss of sensation can be at the level of the spinal nerve, the spinal cord, the thalamus (rare) or at the level of the cortex ▪ We “map out” neurologic deficits in sensation by testing “dermatomes” Specific dermatomes aren’t always the same among individuals ▪ some areas of the body will be supplied by one spinal nerve in one person and a totally different spinal nerve in someone else Classic Dermatomes These dermatomal maps that correspond to the spinal nerves were drawn out many decades ago Significant variation between individuals has been confirmed in numerous studies Example of “old” and less accurate diagram → Dermatomes you can (sort of) bank on The dermatomes illustrated here are a little more consistent across individuals ▪ In general, more peripheral regions (hands, feet) have a little more variability across individuals) ▪ i.e. thumb – literature suggests C6, C7 can variably contribute Testing dermatomes Sharp – usually a “somewhat” sharp object ▪ A splintered wooden tongue depressor or cotton swab, for example ▪ Spinothalamic tract Dull or soft – cotton swab ▪ Dorsal column-medial lemniscal Vibration sense – tuning fork on bony prominence ▪ Dorsal column-medial lemniscal Sharp sensation → break the wooden “stick” of the cotton swab Reliable-ish dermatomes Level Area C2 Scalp C3 Front of Neck C4, C5 Shoulder C8, T1 Little finger T4 Nipple-level T10 Umbilicus L2 Thigh L4 malleoli, medial anterior lower leg L5 Malleoli, lateral anterior leg S1 Lateral posterior leg, lateral plantar foot S3, S4, S5 Perineal area Clinical Physiology V Fundamental Physiologic Basis of the Neurologic Exam – part 1 Dr. Fast BMS 100 Week 5 The Neurologic System Divisions of the Nervous System Central, peripheral, enteric Major anatomic structures of the central and peripheral nervous system Basic Functional Anatomy of the Nervous System Components of the motor system and their roles Components of the sensory system relevant to the motor system The Neurologic Physical Exam – Part 1 Reflexes Cerebellar signs Other signs that evaluate the motor system Nervous tissue - review 1. The peripheral nervous system detects a stimulus and relays it to the central nervous system (sensory) 2. The central nervous system (brain, spinal cord) integrates this information → a response 3. The response is carried to effectors (muscles, glands, blood vessels) via the peripheral nervous system (motor) Nervous tissue - review The cells of the nervous system include: Neurons – an excitable cell that: ▪ receives a stimulus from a neuron or a receptor dendrites ▪ integrates it (ranks it, compares it to other stimuli) Cell body, axon hillock ▪ Passes along another stimulus if it is adequately stimulated axon Nervous tissue - review Axons are carried in bundles ▪ Nerves in the peripheral system ▪ Tracts in the central nervous system Most neuronal cell bodies reside in the CNS, with a few exceptions: ▪ Dorsal root ganglia – neuronal cell bodies for the axons that bring most sensory information from the PNS to the CNS ▪ Autonomic ganglia – help regulate the activities of the autonomic nervous system ▪ Enteric ganglia – help regulate the activity of the gut Overview of the Nervous System The Central Nervous System Structures Brain Cerebrum Cortex Basal Ganglia Limbic structures Thalamus Hypothalamus Cerebellum Brainstem Midbrain Pons Medulla Functions – the Cerebrum Cerebral Cortex Responsible for most of our “higher functions” ▪ Formation, storage, retrieval of memory Together with the limbic structures ▪ Speech & language ▪ Abstract thinking, math, planning and executing plans Also responsible for “what we’re conscious of” ▪ Perception (i.e. what we consciously sense) ▪ Voluntary movements, both simple and complex Basic Functional Anatomy of the Cortex Frontal Lobe Simple movements – precentral gyrus Complex motor plans – anterior portions + precentral gyrus Motor aspects of speech – anterior and inferior to the precentral gyrus Planning, abstract thinking, social behaviour (executive functions) – distributed throughout frontal and parietal lobes Basic Functional Anatomy of the Cortex Parietal Lobe Perception of touch, temperature, vibration – postcentral gyrus Perception of “where our limbs are” (proprioception) – postcentral gyrus Memory, executive functions, abstract reasoning – distributed throughout the parietal lobe Basic Functional Anatomy of the Cortex Temporal Lobe Hearing Scent, taste Recognition of speech Memory ▪ In cooperation with the limbic structures below it Basic Functional Anatomy of the Cortex Occipital Lobe Vision Areas that relate visual stimuli to “actual things” – i.e. association cortex Memories related to what has been seen Memory and the Cerebrum General statements about memory: Memory formation requires attention and structures that “process” and form new memories Attention → prefrontal loge Memory “processors” → the structures of the limbic lobe below the temporal lobe ▪ Hippocampus, amygdala Memory “storage” → Memories tend to be stored in the cortex “close to” the sensation they’re associated with i.e. – memory of a voice or word is likely in or close to the temporal lobe The Cerebrum – the Basal Ganglia Structures that lie below the cortex, close to the middle of the parietal and temporal lobes Serve to refine and regulate behaviours or movements ▪ Movements to be “inhibited” → tics, unnecessary movements, non-speech vocalizations ▪ They allow or “encourage” intended movements Impaired in several diseases – when they lose function: ▪ ▪ ▪ ▪ Tremors, rigidity, difficulty initiating movements Random, purposeless movements Tics, vocal utterances Personality changes Deep Structures in the Cerebrum Basal ganglia: ▪ Striatum ▪ Globus pallidus ▪ Subthalamic nuclei Limbic structures ▪ Approximate location of the amygdala and hippocampus: The Thalamus and Hypothalamus Thalamus – major roles Relays information from sensory receptors in the peripheral nervous system to the cortex ▪ Joint/limb position and movement ▪ Pain, touch, temperature Relays information from brain areas to refine motor planning ▪ Cerebellum, basal ganglia Hypothalamus – major roles Controls much of the endocrine system, along with the pituitary gland Regulates temperature, activity of the autonomic nervous system, fluid balance Some thalamic nuclei modulate emotion and memory formation The Thalamus and Hypothalamus The Cerebellum About 10% of the mass of the brain ▪ Highly folded, complex structure General function: ▪ Compares information from the receptors that sense: Joint position and movement Gravity and equilibrium ▪ Uses this information to adjust movements that are formulated in the prefrontal cortex It very quickly “error-corrects” movements that are planned by comparing them to data from the receptors described above The Cerebellum The Brainstem Composed of the midbrain, pons, and medulla Many functions that will be explored next day ▪ Cranial nerve nuclei are found throughout the brainstem All of the pathways that bring sensory information into the brain (from the PNS) or send motor information out of the brain (to the PNS) pass through the brainstem ▪ We will discuss discrete structures and functions next week Central Nervous System – Spinal Cord Like the brain ▪ isolated from the peripheral nervous system and rest of the body by a set of membranes (meninges) ▪ bathed in unique extracellular fluid (cerebrospinal fluid) ▪ Neurons or axons do not usually regenerate after they have been damaged Regeneration is common after damage to axons in the PNS Different (simpler) structure than the brain ▪ Dorsal components tend to carry sensory information to the brain ▪ Ventral components tend to carry motor information away from the brain to effectors (muscles in particular) Functional Anatomy – Spinal Cord Gray matter (yellow-coloured in this picture): ▪ Mostly cell bodies mixed with unmyelinated or lightlymyelinated axons ▪ Divided into two horns Ventral horns – cell bodies of neurons that activate skeletal muscles Dorsal horns – cell bodies of neurons that relay and integrate sensory information White matter ▪ Divided into columns – these are myelinated axons, no cell bodies Functional Anatomy – Spinal Cord Gray matter (yellowcoloured in this picture): ▪ Mostly cell bodies mixed with unmyelinated or lightly-myelinated axons ▪ Divided into two horns White matter ▪ Divided into columns – these are myelinated axons, no cell bodies ▪ Dorsal, lateral, and ventral columns Functional Anatomy – Spinal Cord Gray matter ▪ Dorsal horn – cell bodies and axons that integrate and transmit sensory information to the brain Which sensations? ▪ Ventral horn – mostly cell bodies of neurons that control skeletal muscles Functional Anatomy – Spinal Cord White matter ▪ Dorsal columns – proprioception (joint/limb position), vibration sense, fast pain fibres – sensory to brain ▪ Anterior and lateral columns – pain, temperature, itch – sensory to pain ▪ Anterior columns – motor information to skeletal muscles General Motor Systems Corticospinal tract: ▪ Motor plan formed (prefrontal cortex) → ▪ Activation of neurons in the primary motor cortex (prefrontal lobe) → ▪ Axons travel through the brainstem (medullary pyramids) and cross over to the opposite side → ▪ Activation of primary motor neurons in the ventral horn that stimulate skeletal muscle contraction OR ▪ Activation of motor neurons in the ventral horn that modify reflexes Lateral corticospinal tract – fine movements of extremities Anterior corticospinal tract – movements of the trunk Corticospinal tract – simplified Synapses are not shown Note the location of the ascending, sensory tracts as well It’s estimated that up to 90% of corticospinal output is to “shut down” reflexes that would oppose voluntary movements General Motor Systems Cerebellar modification of motor plans: cerebellum integrates information from proprioceptors (spinocerebellar tract) and the inner ear (vestibulocerebellar tract) ▪ Keeps the cerebellum “up-to-date” on the actual position of the body in general and specific joints compares this information with information from the motor “plan” generated by the frontal lobe ▪ relayed through the pons cerebellum “adjusts” the motor plan by communicating (via the thalamus) with the frontal lobe and refining the movements relayed by the corticospinal tract Sensory Pathways and the Motor System The motor system depends heavily on input from receptors about the position of a joint, tension across a joint, and tension in a skeletal muscle ▪ Together, these are known as proprioceptors Proprioceptors inform the cortex, the cerebellum and neurons in the spinal cord about the actual position of the body ▪ Dorsal column-medial lemniscal system proprioceptor → dorsal horn → dorsal column → thalamus → post-central gyrus of the parietal lobe ▪ Spinocerebellar system propriceptor → dorsal horn → dorso-lateral columns → cerebellum Reflexes A motor reflex is a fast, involuntary sequence of muscular movements that: ▪ do not need higher brain centres – brainstem or spinal cord circuits are adequate ▪ are simple – usually only a connections between groups of neurons are needed ▪ have a protective or stabilizing function – they help you pull away from a painful stimulus or help you stand ▪ need to be inhibited in order to perform purposeful, complex movements The inhibition often comes from higher brain centres Muscle spindle = a proprioceptor that senses muscle stretch As the muscle is stretched: ▪ activates the muscle to contract against the stretch by stimulating the motor neuron in the ventral horn ▪ inhibits the antagonist muscle Stretch caused by hitting the tendon with a reflex hammer Reflexes – the stretch reflex Types of reflexes Stretch reflex – helps to maintain posture Tendon reflex ▪ When a tendon is stretched, the antagonist muscle contracts and the agonist relaxes ▪ Thought to help prevent tearing the tendon during excessive force generation Withdrawal reflex ▪ In response to a painful stimulus, muscles of flexion are activated to withdraw a limb Plantar reflex ▪ In response to an irritating stimulus, the foot plantar flexes (foot flexes “down”) and the toes curl The Neurological Physical Exam Deep Tendon Reflexes (DTRs) ▪ These are simple stretch reflexes activated by striking the tendon with a reflex hammer → contraction of the agonist muscle ▪ Examples – patellar reflex, triceps reflex ▪ Causes of absent DTRs: normal variation (some people are really difficult to get reflexes from) damage to sensory or motor nerves innervating the muscle being tested ▪ Causes of excessive DTRs loss of inhibition of reflexes from higher brain centres – usually the corticospinal tract (so damage to the corticospinal tract) Reflexes are easier to interpret as abnormal when they are asymmetrical – one side greater/less than the other side The Neurological Physical Exam Plantar reflex ▪ When the lateral side of the foot is stroked firmly, the foot should plantar flex (ankle moves foot downwards) and toes should curl ▪ This develops as we learn to walk – it depends on the corticospinal tract providing specific feedback to particular segments of the spinal cord (S1) ▪ If the foot dorsiflexes and the toes spread, this indicates that the corticospinal input to the lower limb is poor ▪ an “upgoing” plantar reflex is usually an abnormal finding Cerebellar Tests in the Neurological Exam Cerebellar tests include: ▪ rapid alternating movements (RAMS) ▪ point-to-point movements (i.e. patient touches his nose then rapidly touches your finger, and repeats) ▪ heel to shin movements ▪ Gait – how coordinated is the patient’s gait? All of these tests rely on the ability of the cerebellum to evaluate the body’s position and provide feedback to the rest of the motor system If the cerebellum has lost function, then these movements are often clumsy, uncoordinated, and slow Romberg sign This test is thought to evaluate the function of the dorsal columns ▪ Sensory input from proprioceptors to the cerebellum and the parietal cortex – key for joint and limb position sensing Patient stands with feet together and closes her eyes ▪ If the patient loses balance and starts to fall (support the patient!), indicates that the dorsal columns could be damaged visual input is no longer available to help the patient keep her balance Corticospinal tract test – pronator drift The brain structures in the corticospinal tract can be damaged in a wide variety of ways ▪ stroke, trauma, demyelinating disease, tumours ▪ structures include the precentral gyrus and prefrontal cortex Corticospinal tract damage often results in a pattern of loss of muscle strength – extensors and supinators of the arm are weaker than the pronators or flexors Patient stands with arms outstretched, palms up, hand open, eyes closed ▪ The arm “drifts” to a more pronated position, the hand closes, and the arm tends to descend