Anatomy and Physiology Basics

Introduction

• Anatomy and Histology studies how cells, organs, tissues, and organ systems are assembled.
• Physiology explores the functions of these components.

Anatomical Language

• Cranial refers to toward the head.
• Caudal refers to toward the tail.
• Dorsal refers to toward the back.
• Ventral refers to toward the belly.
• Medial refers to toward the median plane.
• Lateral refers to toward the side.
• Proximal indicates toward the body or origin.
• Distal signifies further from the body or origin.
• Terms like cranial, caudal, dorsal, palmar, and plantar are used to describe directions within limbs.

Planes of Dissection

• Dorsal plane runs parallel to the back.
• Transverse plane runs perpendicular to the long axis.
• Sagittal plane divides the body into left and right sections.

Body Cavities

• The diaphragm is a musculature structure that divides the trunk.
• The trunk divides into the cranial thoracic cavity and the caudal abdominal cavity.
• The thoracic cavity's dorsal aspect is the spine ribs, ventral aspect is the sternum, lateral aspect is ribs, cranial aspect is the thoracic inlet (rib no.1), and caudal aspect is the diaphragm.
• The abdominal cavity's dorsal aspect is the spine and muscle, lateral aspect is the muscle, ventral aspect is the muscle, cranial aspect is diaphragm, caudal aspect is pelvic inlet.

Tissue Section

• Longitudinal sections involve tissue being cut along the longest axis of an organ.
• Transverse sections involve tissue being cut perpendicular to the longest axis of an organ.
• Oblique sections involve tissue being cut at an angle between transverse and longitudinal.

Homeostasis

• Homeostasis refers to essential regulatory processes for maintaining optimal body conditions, for cellular/enzyme function.
• Enzyme function depends on the correct pH, osmolarity, and body temperature.

Regulating Body Systems

• The Nervous System uses interconnected nerves that carry electric signals between body parts.
• The Endocrine System uses wireless, blood-borne chemicals to carry body signals.

Nervous System Components

• The Central Nervous System (CNS) includes the brain & spinal cord and processes information.
• Sensory Nerves are receptors and afferent neurons which detect stimuli.
• Motor Nerves are efferent neurons which trigger responses in organs.
• Neurons are electrically excitable nerve cells that transmit electrical & chemical signals.
• Central Nervous System (CNS) role is processing sensory inputs and desired responses.
• Efferent Nerves are responsible for carrying out responses (movement, hormone release).
• Unconscious Processes and functions occur automatically.

Endocrine System

• Hormones transport via blood or interstitial fluid.
• Target Cells are cells that respond with the right receptors.
• Endocrine Glands include the pituitary, thyroid, adrenal, and pancreas.
• Feedback Regulation uses feedback mechanisms.

Feedback Loops

• Feedback Loops maintains a regulated variable at its set point (blood pressure / temperature).
• Negative Feedback loops counteract change when something is detected.
• Positive Feedback loops increase the stimulus when something is detected e.g. contractions stimulate even stronger contractions in birth, rather than negative feedback loops which aim to return to normal.

Feed Forward Systems

• Feed-forward systems are anticipatory systems that prevent negative feedback loops.
• Dry mouth stimulates drinking leading to increasing water in the blood, preventing dehydration and stopping the dehydration feedback loop.

Neuroendocrine System

• The Nervous System (NS) is associated with quick responses resulting in behavioral change to avoid heat/cold.
• The Endocrine System (ES) is associated with slow responses affecting growth, reproduction, and metabolism.

Body Fluid

• Water makes up roughly 60% of body weight.
• Intracellular Fluid (ICF) is about 40% of body mass (2/3 of total body water).
• Extracellular Fluid (ECF) is about 20% of body mass (1/3 of total body water).
• Interstitial Fluid (ISF) is around 80% of ECF, found between cells.
• Plasma is about 20% of ECF and is the fluid portion of blood for circulation and blood pressure.
• The ICF and ECF have different compositions for excitable cells.
• Different compartments contain differing proportions of ions.
• ICF features a high potassium concentration.
• ECF features a high sodium concentration.
• An animal's water amount impacts the concentrations of ions and proteins.
• Osmolarity is almost the same in both ICF and ECF, so water isn't osmotically moving until something goes wrong.

Musculoskeletal System - Muscles

• Muscles facilitate contraction for movement.
• Muscles help stabilize joints.
• Muscles contribute to bladder strength.
• Muscles facilitate shivering for warmth.

Skeletal, Cardiac, and Visceral Muscle

• Skeletal muscle is striated, enables voluntary contraction, and uses the somatic nervous system.
• Cardiac muscle is striated, enables involuntary contraction, and uses the autonomic nervous system.
• Visceral muscle is smooth, enables involuntary contraction, and uses the autonomic nervous system.

Skeletal Muscle

• Attaches to bones for leverage.
• Muscle contraction is a voluntary process that relaxes passively.
• Myofibers are long, cylindrical cells.
• Myocytes (muscle cells) fuse forming muscle fibers, which contain many myofibrils.
• Each myofibril comprises myofilaments called actin and myosin for muscle contraction.
• Thick myofilaments (dark) are myosin.
• Thin myofilaments (light) are actin.
• Muscle fibers are connected by connective tissue.

Structure

• Origin is the portion of muscle attached to the least moveable or most proximal bone.
• Belly is the central, fleshy part of muscle.
• Insertion is the distal or most moveable attachment.
• Muscle shortening depends on the length of fibers, with longer fibers allowing greater capacity.
• Muscle power corresponds to the cross-sectional area.
• Muscles are stronger, joining tendons at an angle.

Bones

• Bones support the body, provide a framework, protect organs, and act as levers for muscles.
• Bones are living tissue with growth, repair capabilities, and blood/nerve supply, subject to disease.

Long Bone Structure

• Epiphysis forms the end zones (spongy).
• Diaphysis forms the central part (hollow medullary cavity).
• Metaphysis is the growth zone (plate).

Joints

• Joints are sites of articulation.
• Joints represent the union of two or more bones via soft tissue or cartilage.
• Articular surfaces consist of the head (rounded proximal articular surface) and condyle (large, round articular surface).
• Surface anatomy includes raised or rough surfaces (muscle attachment), foramen (hole), sulcus (groove), fossa (depression), and elevation (line, crest, tubercle, tuberosity, spine).

Bone Structure

• Compact (dense or cortical) Bone is the hard external layer.
• Spongey (cancellous) Bone is a porous network of spicules with trabeculae for a light but strong framework.
• Medullary Cavity (Shaft) is surround by contact bone and the the site of red/yellow bone marrow.
• Periosteum is the outer fibrous layer (tendon/ligament attachment, blood vessels)
• Hyaline Cartilage covers the articular surfaces, and id glassy.
• Nutrient Artery is the main blood supply, which enters mid-shaft.

Bone Types

• Long bones are cylindrical and often act as levers.
• Short bones are the same length in all dimensions and suited to complex movements.
• Flat bones are expanded in two directions and provide sites for muscle attachment/soft tissue protection.
• Irregular bones do not fit other categories
• Sesamoid bones are found within tendons to help prevent tendon wear
• Splanchnic bones develop in soft organs.

Axial Skeleton

• The Skull & Mandible, including the skull proper, mandible, hyoid apparatus, and middle ear bones.
• Skulls contain a cranium(brain case) and face (nasal cavity), separated by the ethmoid bone.
• Most bones are paired, young animal bones are separated by sutures.
• Vertebrae share a basic structure, but vary in size and shape.
• Cervical vertebrae (7 in all mammals) including the Atlas (C1) & Axis (C2).
• Thoracic vertebrae have large spinous processes.
• Lumbar vertebrae have cranially directed transverse processes.
• Sacral vertebrae are fused, creating the pelvic roof.
• Caudal vertebrae become progressively simpler toward the tail.

Appendicular Skeleton

• Appendicular Skeleton is divided into girdle and a free appendage.
• Forelimb includes the pectoral girdle (scapula) and pectoral limbs
• The Hindlimb includes the pelvic girdle (pelvis) and pelvic limbs
• Plantigrade means walking on the entire sole of the foot.
• Digitigrade means weight is borne on toes.
• Unguligrade means weight is borne on toes and toes are incorporated into a hoof.

Excitable Cells

• The Nervous system comprises excitable cells that send signals.
• Muscles, the digestive tract, sweat glands, and arteries and veins feature excitable cells.

Composition

• ISF contains potassium.
• ESF contains sodium.
• The cell membrane is impermeable
• Ions move by transport and diffusion to equalize

Potassium and Sodium

• K+ features leaky channels leading to concentration gradient.
• Na+ A- does does not have open channels through the membrane.

Sodium Potassium ATPase Pump

• Uses ATP energy to maintain EC Sodium and IC Potassium.
• Three sodium ions are expelled, and two potassium ions enter the cell through the exchanger.
• Without the pump, potassium would be lost, rendering cells electrically non-functional.
• More ions are expelled than are replaced, the cell membrane are mostly equal.

Membrane Potential

• The difference in charges surrounding the membrane.
• Neurons and Muscles are excitable.
• Cells at rest are at potential with charges dependent on polarisation, depolarisation, repolarisation, and hyperpolarisation.

Membrane Potential

• Voltage-gated Sodium Channels open to change of voltage.
• As the channel opens from the voltage change, the gates let the sodium move towards a depolarisation.
• Large stimuli open more channels, which forms a graded potential relative to size.

Action Potential

• With the action potential achieved, the sodium channels open and trigger a large influx of Na+.
• The Voltage gated K+ channels ensure K+ returns to negative values (homeostasis).

All or Nothing

• Action potentials fire consistently when stimuli are at full strength, and are unable to produce further responses.
• The AP moves forward on the axon, preventing it from re-firing immediately.
• Refractory period refers to the period after an action potential where another action potential cannot occur, or needs a higher stimulus.
• Absolute refractory period: Na+ channels are already open and will not re-open until resting.
• Relative refractory period: A second AP can be triggered, but needs a stronger stimulus.

AP Conduction

• Works like a 'wave'; breakdown: depolarizes excites and depolarizes the next membrane until they reach threshold.
• Triggers and sets off identical APs along way.
• Keeps strong through the travel due to all-or-nothing process.
• Allows for reliable and fast communication.

Synaptic Transmission

• AP Arrives at Presynaptic Terminal -Action potential arrives at presynaptic terminal, causing voltage-gated Ca²+ channels to open.
• Neurotransmitter Release & Binding -Calcium influx causes acetylcholine (ACh) and binds to receptors. -Opens Na⁺ channels and allows ions to enter.
• Muscle Cell Depolarization -Causes sodium influx and muscle cell depolarization.
• Termination of Signal -Acetylcholine esterase (AChE) breaks down ACh to cease stimulation, and prevent overstimulation.
• Sarcolemma & Excitation-Contraction Coupling -The sarcolemma spreads the AP and triggers muscle contraction.

Muscle Power

• Tension is mechanical force of a contracting muscle to move object.
• Muscle Power depends on the muscle mass.
• Isotonic contraction shortens a contracted muscle for movement.
• Isometric contraction cannot shorten a contracted muscle and used for posture.

Muscle Shortening

• Sliding filament proteins slide past each other in the sarcomere.
• Z-plates pull towards each other, increasing thin/thick filament overlap.

Thin and Thick Filaments

• Action binds to tropomyosin.
• During binding to action, calcium binds to troponin, travels along myosin, then the ATP/action product creates ADP that helps the movement along the filament.

Excitation Contraction Coupling

• Action potential and coupling of actin and myosin prompts contraction.

1. Calcium travels into the nerve cell, triggers sodium channels, and cause the action potential.
2. AP enters T-Tubule and opens SR to release channels.
3. Calcium transports channels to release cytosol of muscle fibres.
4. Binds to troponin and wraps away from actin.
5. Myosin (little feet on thick filament) to bind to actin for the flexing to movement and drag the thin filament.
6. Excess calcium is pumped to SR.
7. Muscle contracts only enough calcium balance release from action potential/being taken back by ATPase pumps. -ATP binding separates ADP and phosphorus to activate little feet movement.

Motor Unit

• One motor neuron and all muscle cells form with endings.
• Neurons activated and stimulate muscle cells.
• Muscles can be activated through motor units. -With neurons controlling muscle.
• Muscle Twitch occurs through action of single fibers: repeated action in the event of calcium reaching thresholds to a tetanic contraction.

Muscle Fatigue

• With skeletal muscle frequency/high frequency, fibers weaken in tension/reduce from fatigue.
• Failure/reduced calcium from less ATP.

Muscle Fibres

• Hypertrophy corresponds to growing the muscle fibre.
• Muscle Atrophy corresponds a decrease in muscle fibre.

Joints

• Sites of bone articulation with soft tissue/cartilage.

Structural Classification

• Fibrous Joints
• joined by tissue or lacking, with ulna and radius.
• Cartilaginous
• joining cartilage and not containing a joint, yet contain shock a joint.
• Synovial
  • joints the joint cartilage and moblie, and made of different capsule (with bones). -Synovial is made of of articular joints capsule that contains fluids and plane-like qualities
  • includes joints, membranes , cartilages that create bone movements.

Functional Classification

• All Joints have degree of movement

Endocrine notes

• Exocrine relates to to the bloodstream or parts ovaries, pancreas and hypothalamus.

Hormones

• Protein and Amine hormones help the cells the cell with membrane-based amino acids and function.
• Steriods create cholesterol which carry fat soluble proteins to activate processes.