Functions of the nervous system -Feeling physical sensations -Recruiting skeletal muscle for actions -Reacting with reflex actions Subdivisions of the nervous system graph The two main types of neurons -Alpha motor neuron- a nerve cell under voluntary control that transmits signals to activate muscles -Sensory neuron- transmits sensations like heat, cold, pain, etc to the CNS The structure of a neuron -Soma or cell body- contains the nucleus of the cell -Dendrites- fingerlike projections that receive signals from previous neurons or receptors -Axon- a tail-like structure that stretches from the soma to the next neuron The process of depolarization in neural function 1) At rest, a neuron is negative in its interior due to a large amount of positively-charged sodium ions outside its membrane 2) At rest, a neuron is negative in its interior due to a large amount of positively-charged sodium ions outside its membrane 3) If enough neurotransmitters bind to the dendrite surface, and enough sodium gets in, the neuron “depolarizes” and sends the signal down its length 4) As the signal transmission travels down the axon, the cell will “repolarize” and become negative again Common neurotransmitters -acetylcholine -Epinephrine -dopamine Details of the neuromuscular junction -The end of a neuron’s axon is called a terminal branch - The NMJ is a small gap (called a synapse between neurons) where neurotransmitter chemicals can be released to bind to muscle membranes - Just as signals between neurons function, if enough sodium enters a muscle cell due to the neurotransmitter, the cell will depolarize/fire and contract Motor unit details and neuron/fiber ratios -Motor Unit- The term for a single α-motor neuron and all of the fibers it innervates -A motor unit is only comprised of one type of muscle fiber and its neuron (fast-twitch, etc) -Neuron to fiber ratios determine type of movement 1:100 is a fine motor skill (eye movement) 1:800 is a gross motor skill (bending knee) The difference between afferent and efferent pathways -Afferent pathways send information to your central nervous system from your muscles - Efferent pathways send signals from the central nervous to your muscles Definition of proprioceptors and basic function - Specialized receptors that detect body movement or position - These are found in muscle bellies, tendons, joints, and in the inner ear - they help explain how we know where our limbs are in space when we close our eyes Types: - Muscle spindle - located in several places throughout a muscle, spindles transmit information on muscle length and stretch - Golgi Tendon Organ - located within tendons, it detects the amount of tension generated by a muscle into the tendon and bone Specific shoulder movement possibilities of the scapula -Elevation -Depression - Abduction/protraction - Adduction/retraction - Upward rotation - Downward rotation - Anterior tilt - Posterior tilt The anterior and posterior muscles of the shoulder girdle Anterior: -Pectoralis minor -Serratus anterior -Subclavius Posterior: -Levator scapulae -Rhomboids -Trapezius Movement and stabilizing actions of the rhomboids - They cause downward rotation, adduction, and elevation of the scapula - They work as isometric stabilizers when the arms are abducting (being pulled downward) The four distinct parts of the trapezius The ligaments of the shoulder joint -Coracohumeral ligament- attaches the coracoid process of the scapula to the head of the humerus -Glenohumeral ligament- attaches the glenoid fossa of the scapula to the head of the humerus -Coracoacromial ligament- attaches the coracoid and acromion processes Be able to recognize a shoulder movement description -Flexion: forward and upward rotation on the sagittal plane -Extension: a return from flexion on the sagittal plane -Hyperextension: extreme backward rotation on the sagittal plane Identify which muscle does not affect the shoulder joint when given choices The primary muscles involved in moving the glenohumeral joint include: -Pectoralis Major -Deltoids -Biceps/Triceps Brachii -Supraspinatus/Infraspinatus -Latissimus Dorsi -Teres Major Radius and ulna interactions with the humerus -The ulna of the forearm and the humerus form a hinge type joint at the elbow -The radius, however, interacts with the humerus in an almost ball-andsocket arrangement -The elbow, therefore, is only capable of flexion and extension, but the forearm can be pronated and supinated based on movements of the radius Anatomy of the elbow joint -The proximal end of the ulna is called the olecranon, which is considered the elbow -The radius, ulna, and humerus intersection is surrounded by a capsule with a synovial membrane -The joint is strengthened by the annular, radial collateral, and ulnar collateral ligaments Radio-ulnar joint details and specifics -There are 2 joints between the radius and ulna of the forearm: the proximal and distal -The proximal radio-ulnar joint shares the same capsule as the humeroulnar joint -Both joints are considered pivot joints, due to the fact that the long bones of the forearm pivot around each other in pronation and supination Details of elbow extension Extension -Triceps- most powerful elbow extensor, but also functions as extensor of the shoulder joint due to the long head’s origin on the scapula -Anconeus- only purpose is elbow extension, and serves to begin the movement until the triceps is in best mechanical position -Note: these muscles are recruited in active extension, not when gravity or the flexors are allowing the arm to straighten Identify which muscle is not a flexor of the wrist when given choices Flexors of the wrist -Flexor carpi radialis -Flexor carpi ulnaris -Palmaris longus The divisions of the nervous system (as presented in the graph) The differences between muscle spindles and GTOs (with example actions) -Muscle Spindles- located throughout muscle cells, it is activated as a safety mechanism when the muscle is being stretched too fast, and contracts the muscle to prevent the muscle from tearing -Golgi Tendon Organ- located within the tendons, it detects the amount of resistance being generated by the muscle. If there is too much resistance it inhibits signals to the alpha motor neuron and prevents contraction The particulars of motor unit recruitment -A motor unit is only comprised of one type of muscle fiber and its neuron -In low demand actions 1) there are few motor units recruited 2) there is a low level of stimulation - in high demand action 1) there are many motor units recruited 2) there is a high level of stimulation - slow twitch fibers are always activated because of the low threshold of sodium required, following intermediate, then fast which have higher threshold requirements for sodium The joints of the shoulder girdle with descriptions -Acromioclavicular articulation - the joint between the acromion process of the scapula and the distal clavicle -Sternoclavicular articulation - joint between the proximal end of the clavicle and the lateral border of the sternum Abduction/protraction of the scapula -Lateral movement of the scapula away from the spinal column -Due to the rounded contour of the ribcage, the scapulae also slightly tilt forward on the outside and slightly rotate upwards when abducting -This movement is observed as a person brings their arms together in the front Glenohumeral articulation anatomy and movement basics -Shallow ball and socket joint between the humerus and the glenoid fossa of the scapula that allows movement not seen in most of the body -Flexion/Extension -Hyperextension -Abduction/Adduction -Outward/Inward Rotation -Horizontal Adduction/Abduction -Circumduction The shoulder cuff muscles and their example functions -Supraspinatus, Infraspinatus, Teres Minor -These 3 muscles function as both stabilizers and primary movers of the shoulder joint -Some of the functions include depression of the head of the humerus to allow maximum range of flexion and extension, and prevention of dislocation when the arms are abducted Be able to list and describe 3 shoulder joint injuries -Dislocation: can be forward, downward, or posterior; the head of the humerus slips out of the glenoid fossa and rests below either the coracoid or acromion processes -Rotator cuff tears: usually caused by fast or sudden arm motions -Shoulder impingement: tissue between the humeral head and the acromion is pressed; there are many causes including age Be able to list and describe 3 forearm/wrist injuries Forearm fractures -Typically the radius and ulna break together -Most common from a direct blow or falling onto an outstretched arm Elbow dislocation -The radius and ulna are displaced from the elbow joint -Occurs when the arm is hyperextended and rigid during a fall Sprained/strained wrist -Common injury caused by a hyperextended hand during a fall -The tendon attachments are injured along with occasional carpal fractures
