SA Medical - General Medicine And Imaging of Disease

The Optics of Vision Physical Principles of Optics Slower velocity than air. Refractive Index of a transparent substance is the ratio of its velocity in air to the velocity in the transparent object. Perpendicular - The direction light travels is always perpendicular to the wave front, When light passes through an angulated surface, it is bent (refracted) at some angle if the refractive indices of the two media are different. The angle depends on the refractive index of the barrier material and the angle between the two surfaces.  Refractive Principles and their Application to Lenses    A Convex Lens - Converge Light that passes the lens perimeter is refracted - bent toward the center - to make perpendicular to the wavefront.    A Concave Lens - divergence Light through the lens perimeter are refracted away from the midline - bent away - to make themselves perpendicular to the wave front.    Focal Length of the Lens Focal Length of a lens is the distance beyound

Pain Sensation: fast and Slow Pain Classification Fast Pain Slow Pain All pain receptors are free nerve endings Three types of Stimuli Pain receptors are activated by mechanical, thermal and chemical stimuli Mechanical and thermal stimuli - fast pain Chemical stimuli - slow pain No adaptation, progressively greater as the pain stimulus  continues, this is called hyperalgesia Two separate pathways of Pain transmission A-delta fibers fast - 6 to 30m/s - Mechanical and thermal stimuli C-Fibers slow - 0.5 to 2m/s  neospinothalamic tract - A-delta fibers paleospinothalamic tract - C-fibers The neospinothalamic tract is used in pain localisation Activity in the paleospinothalamic system may impart unpleasant perception of pain. paleospinothalamic pathway Brain and Spinal Cord: Internal Pain Suppression system The periaqueductal gray  the periadueductal gray of the midbrain and the rostral pons receives input from the ascending pain pathways in addition to descending proje

General Organisation; the tactile and Position senses The somatic senses can be divided into three main components Mechanoreceptors  Thermoreceptors Nociception - pain and damage discriminative - precisely localised touch  Crude - poorly localised - proprioception - touch, pressure, vibration and the senses of static body position and movement Exterioceptive sensation  Visceral sensations Detection and Transmission of Tactile Sensation Even though touch, pressure and vibration are often classified as separate and distinct sensations, they are each detected by the same general class of tactile receptors: the Mechanoreceptors Free nerve endings - skin and in the cornea of the eye Meissner's corpuscule -    The   tactile corpuscles of Wagner and Meissner   (Fig. 936)   are oval-shaped bodies.   These tactile corpuscles occur in the papillæ of the corium of the hand and foot, the front of the forearm, the skin of the lips, the mucous membrane of the tip of the t

SENSORY RECEPTORS Five basic types of Sensory Receptors Mechanoreceptors Thermoreceptors Nocioreceptors Photoreceptors Chemoreceptors Sensory Receptors are highly sensitive to one particular type of stimulus - "the labeled line" priciple. sensory modality anteriolateral system (spinothalamic tract) - pain Receptors transduce a physico-chemical stimulus into a Nerve Impulse The Sensory fiber linked to each receptor exhibits "threshold phenomena" The receptor potential is proportional to stimulus intensity frequency Sensory receptors adapt their stimuli either partially or completely over time accomodation Receptors are classified as slowly adapting or rapidly adapting Slowly adapting receptors Tonic receptors Rapidly adapting receptors rate receptors or movement receptors Physiological Classification of receptors Two different schemes have been devised to classify the entire range of peripheral nerve fibers Types A and C  Fiber diameter and c

The general design of the Nervous system: The Nervous system includes both sensory and motor systems interconnected by complex integrative mechanisms neuron Soma several dendrites single axon sensory receptors sensory neuron motor response Motor response memory Function of the Central Nervous System This is based upon interactions that occur between neurons at specialised junctions called synapses synaptic terminals or synaptic boutons synaptic cleft synaptic vesicles neurotransmitter agent Chemical synapses and electrical synapses are the two most prevalent types of synapses in the brain chemical synapses presynaptic element - releases neurotransmitter agent that bind to the postsynaptic neuron - which is excited or inhibited electrical synapse gap junctions Neurotransmitter Release is Calcium Dependent voltage gated calcium channels calcium moves into the terminal Action of a Neurotransmitter is Determined by its Postsynaptic Receptor Rec

Female Hormonal system: Gonadotropin-releasing hormone (GnRH) from the hypothalamus that stimulates FSH and LH secretion from the anterior pituitary. GnRH is inhibited by circulating estrogen and progesterone LH is secreted from the basophillic cells of the anterior pituitary gland and stimulates the development of the corpus luteum in the ovaries. FSH  is secreted from the basophillic cells of the anterior pituitary gland in response to GnRH and stimulates the follicles in the ovaries. Estrogen and Progesterone are the steroid hormones secreted by the follicle and corpus luthium of the ovary.  Corpus luteum x Section of the ovary. 1. Outer covering. 1’. Attached border. 2. Central stroma. 3. Peripheral stroma. 4. Bloodvessels. 5. Vesicular follicles in their earliest stage. 6, 7, 8. More advanced follicles. 9. An almost mature follicle. 9’. Follicle from which the ovum has escaped. 10.  Corpus luteum . Monthly Menstrual or Ovarian Cycle Follicular Development At th

Spermatogenesis Sper mato genesis is the process of formation of spermatocytes from spermatogonia Sper minog enesis is the process of transformation of the spermatids, which are still epitheloid to sperm cells Male Sex Hormones Testosterone is an anabolic steroid hormone secreted by Leydig cells of the testis Gonadotropin-releasing hormone increases release of the LH and FSH from the anterior pituitary gland LH stimulates testosterone formation by the Leydig Cells, and FSH stimulates sperm ato genesis and sperm ino genesis Inhibin is forced by Sertoli cells and inhibits FSH secretion The Male Sexual Act Male Infertility Androgen dysfunction with normal sperm cell production Isolated dysfunction of sperm cell production with normal androgen levels Combined androgen and sperm cell production defects MALE REPRODUCTIVE PHYSIOLOGY A. Testes Structure and Function 1. Seminiferous tubules 2. Sert