Sensory Organs
SENSORY ORGANS
Introduction The knowledge of the world around us stimulates our sensory organs to provide us with the information of what is going on around us. All sensory information is picked up by the sensory receptors, specialised cells that monitor internal and external conditions. Examples of sensory organs are: SENSE ORGAN Eye Ear (Organ of Corti) Ear (Semicircular Canals) Ear (utricle and saccule) Olfactory mucous membrane Taste Buds Skin Skin Skin Skin Various Muscle Spindle Golgi tendon organ
RECEPTOR Rods and Cones Hair Cells Hair Cells Hair Cells Olfactory Neurons Taste Receptor Cells Nerve Endings Nerve Endings Nerve Endings Naked Nerve Endings Nerve Endings Nerve Endings Nerve Endings
SENSORY MODE Vision Hearing Rotational acceleration Linear acceleration Smell Taste Touch – Pressure Warmth Cold Pain Joint Movement and Position Muscle Length Muscle Tension
All sensory information arrives at the central nervous system (CNS) in the form of action potentials and the stronger the stimulus, the higher the frequency of action potentials. For example, touch, pressure, pain, temperature and taste sensations arrive at the primary sensory cortex. The CNS interprets the nature of the sensory information entirely on the basis of the area of the brain stimulated, it cannot tell between a ‘true’ sensation or a ‘false’ one. For example, when you rub your eyes, you may ‘see’ flashes of light. The stimulus was mechanical rather than visual; the activity was projected to the visual cortex and was experienced as a visual perception. Adaptation is a reduction in sensitivity in the presence of a CONSTANT stimulus. For e.g. ticking of the clock in the background, jumping into a hot bath or cold lake. After a short time, the body reduces the amount of information arriving at the cerebral cortex. Most sensory information is routed towards the spinal cord and triggers involuntary reflexes such as withdrawal reflex e.g. removing the hand from a hot stove. We can
Introduction The knowledge of the world around us stimulates our sensory organs to provide us with the information of what is going on around us. All sensory information is picked up by the sensory receptors, specialised cells that monitor internal and external conditions. Examples of sensory organs are: SENSE ORGAN Eye Ear (Organ of Corti) Ear (Semicircular Canals) Ear (utricle and saccule) Olfactory mucous membrane Taste Buds Skin Skin Skin Skin Various Muscle Spindle Golgi tendon organ
RECEPTOR Rods and Cones Hair Cells Hair Cells Hair Cells Olfactory Neurons Taste Receptor Cells Nerve Endings Nerve Endings Nerve Endings Naked Nerve Endings Nerve Endings Nerve Endings Nerve Endings
SENSORY MODE Vision Hearing Rotational acceleration Linear acceleration Smell Taste Touch – Pressure Warmth Cold Pain Joint Movement and Position Muscle Length Muscle Tension
All sensory information arrives at the central nervous system (CNS) in the form of action potentials and the stronger the stimulus, the higher the frequency of action potentials. For example, touch, pressure, pain, temperature and taste sensations arrive at the primary sensory cortex. The CNS interprets the nature of the sensory information entirely on the basis of the area of the brain stimulated, it cannot tell between a ‘true’ sensation or a ‘false’ one. For example, when you rub your eyes, you may ‘see’ flashes of light. The stimulus was mechanical rather than visual; the activity was projected to the visual cortex and was experienced as a visual perception. Adaptation is a reduction in sensitivity in the presence of a CONSTANT stimulus. For e.g. ticking of the clock in the background, jumping into a hot bath or cold lake. After a short time, the body reduces the amount of information arriving at the cerebral cortex. Most sensory information is routed towards the spinal cord and triggers involuntary reflexes such as withdrawal reflex e.g. removing the hand from a hot stove. We can
References: 1. Rhoades and Pflanzer (1996) Human Physiology 3rd Edition: 2. Vander, Sherman & Luciano (1998) Human Physiology 7th Edition 9 NERVOUS SYSTEM TUTORIAL – NEUROMUSCULAR JUNCTION 1. An adequate stimulus will produce a change in the membrane potential of a sensory receptor cell. This change is known as a(n) (action/generator) potential. 2. The compression of the free nerve endings inside a Pacinian corpuscle causes the opening of (potassium/sodium) channels embedded in the nerve membranes. 3. The number of impulses reaching the brain through all nerve fibers is known as (frequency/population) code of stimulus intensity. 4. Both temperature and pressure receptors are located in the skin. They send their information to the brain via (different/the same) neurons. 5. The (largest/smallest) nerve fibers are more likely to have thick myelin sheaths. 6. The (gray/white) matter of the spinal cord is composed of nerve cells. 7. The (dorsal/ventral) horn of the gray matter of the spinal cord is associated with muscular movement. 8. Reflex behaviors are controlled by the (brain/spinal cord). 9. Muscles are attached to bones by (ligaments/tendons). 10. A flexor and an extensor for the same joint are said to be (antagonistic/synergistic). 11. The (frequency/population) code of muscle contraction refers to the number of individual neurons involved in contraction. 12. For the knee jerk reflex to occur, the (extensor/flexor) action must be inhibited. 13. Cells involved in (fine/gross) movements occupy a larger portion of the motor cortex. 14. The parts of the body that are most densely innervated are the fingers, thumb and lips and are represented by the (smallest/largest) areas of the somatosensory cortex. 15. The stimulation of the (motor cortex/supplemental and premotor areas) brings about a more complex muscular response. 16. When patients are told to think about a particular movement, there is an increase in blood flow to the (motor cortex/supplemental motor area). 17. The (thin/thick) filaments are made of the contractile protein called ‘myosin’. 18. Muscles do not continuously contract because the cross bridges are (prevented/allowed) to bind with the actin molecules. 19. When there is an action potential, it (acts on the contractile proteins directly/increases the cytosolic calcium concentration) 20. Increased calcium ions will bind onto (troponin/tropomyosin) binding site 21. An end-plate potential (EPP) is (much smaller/much larger) than an EPSP 22. Inhibitory potentials (depolarize/hyperpolarize) postsynaptic membranes (are/are not) found in human skeletal muscle. 23. South American arrowhead poison ‘Curare’ (keeps open the ion channels/does not keep channels open). 24. Nerve gas causes (continuous/absent) action potentials 25. Clostridium botulinum bacteria produces a toxin which blocks (the ion channels/Ach being released) 26. When tapping the patellar tendon, this will stretch the (flexor/extensor) muscle which then causes compensatory contraction and the (flexor/extensor) muscle to relax. 27. If your foot stepped on a pin, this will activate the ipsilateral (flexor/extensor) motor neurons and inhibit the (flexor/extensor) motor neuron. 28. If you stand on one leg, the leg that is supporting the weight will activate (the ipsilateral (flexor/extensor) motor neurons and inhibit the (flexor/extensor) motor neuron. 10