Biology 3201 Maintaining Dynamic Equilibrium II Nervous System The nervous system is the body system that allows us to feel things. This happens by a network of nerves. There are two main parts of the nervous system 1. Brain 2. Spinal Cord Human Nervous System How the Brain and Spinal Cord are Protected… By 1. Meninges- Spaces around the brain and spinal chord that act as buffer zones. 2. Bone (Skull/Vertebrae)- Act as a shield. 3. Cerebral Spinal Fluid – Absorbs energy when the brain of spinal cord receive a blow. Meninges The Brain Parts we must know: 1. Cerebrum – Sorts and interprets all information from our senses.It is the center of human consciousness. 2. Cerebellum – Controls muscle coordination. Contains 50% of the brain’s neurons. 3. Medulla Oblongata – Controls heart rate, and force of heart contractions. Also controls reflex centers for hiccupping, vomiting, coughing, swallowing. 4. Pons – Functions with medulla to regulate breathing rate; has the reflex centers involved in head movement. 5. Hypothallamus – Controls hunger, body temperature, aggression. 6. Thalamus – Sorts sensory information. 7. Midbrain – Involved in sight and hearing. 8. Corpus Callosum – Series of nerve fibers that connect the left and right sides of the brain. The Peripheral Nervous System • Consists of the autonomic nervous system and the somatic nervous system. – The autonomic nervous system is not consciously controlled. – The autonomic nervous system is made up of the sympathetic and parasympathetic nervous system. • The sympathetic nervous system gets the body prepared for a fight or flight response. • It causes such things as increased heart rate, dilation of pupils, release of adrenaline, etc. (Refer to Figure 12.5) • The parasympathetic nervous system has the opposite effect of the sympathetic nervous system. • The somatic nervous system is in some cases under our control. – It is made up of: • Sensory neurons that carry impulses from the body’s sense organs to the CNS. • Motor neurons that carry impulses away from the CNS to effectors (muscle fibers) that cause a response. (eg. Moving your hand away from a hot stove.) Nervous System Response In order for a nervous system response to occur there must be: 1. Information taken in by the senses (eyes, ears, skin, etc.) 2. Transmission of an impulse by neurons. 3. Interpretation of the impulse by the brain or spinal cord. 4. Effectors (muscle or glands). The result is an impulse giving rise to a response if called a reflex arc. The Neuron The functional Unit of the Nervous system is called the neuron. The PNS consists of nerves, which are neurons held together by connective tissue. 90% of the body nerves are found in the CNS. Capable of living over 100 years. The Neuron The neuron consists of three main parts. 1. Cell body – Contains a nucleus, cytoplasm with mitochondria, lysosomes, a golgi complex and rough ER. 2. An axon – Is the long, cylindrical portion of the neuron. Can be 1mm to 1 m in length. Impulses are passed along the axon by a wave of depolarization. 3. Dendrites – The fingerlike projections that extend from the cell body. The receive signals from other neurons. The Neuron How an impulse is passed The neuron at rest Outside the neuron membrane • +vely charged. • High  of Na+ ions. Lower ’s of K+ and Cl-. Inside the neuron membrane • High  of K+. Lower ’s of Na+ • Dominant anions are proteins, amino acids, phosphates and sulfates. At rest the Na+/K+ pump keeps the ion distribution. Resting potential of the neuron is –70mV. Depolarization • As an impulse passes, there is a change in the charge of the membrane. This is called an action potential. • Na+ channels open that allow ions to pass. • K+ channels close. Repolarization • After the impulse passes the Na+ channels close. • The K+ channels open to allow the ions out of the membrane. • The Na+/K+ pump helps reestablish polarity. The time between neuron impulses in called refractory period. For many neurons this can be ~0.001s. The All-Or-None Response In order for an impulse to occur the stimulus need to be sufficient for the impulse to be sent. Ie. There is a Threshold that needs to be met in order for an impulse to occur. If the Threshold is met then an impulse will be sent along the length of the axon. The strength of the impulse is always the same, there is no mild of stronger impulse. The impulse either occurs or it doesn’t ie. Either all-or-none. The Synapse Once an impulse reaches the Axon terminals, it needs to cross the synaptic gap. Neurotransmitters are released from the presynaptic neuron by exocytosis. Receptor sites on the post synaptic neuron recieves the neurtransmitter. This can cause either an excitatory response or inhibitory response. The enzyme cholinesterase is released quickly to break down the neurotransmitter Acetylcholine. Neurotransmitters • Acetylcholine – Primary neurotransmitter of the somatic and parasympathetic nervous systems. May be excitatory or inhibitory. • Noradrenaline (norephnephrine) – primary neurotransmitter of the sympathetic nervous system. • Glutamate- the neurotransmitter of the cerebral cortex. Makes up ~ 75% of the neurotransmitters in the brain. • GABA (gamma aminobutyric acid) – Most common inhibitory neurotransmitter in the brain. Neurotransmitters Dopamine – Elevates mood and controls skeletal muscles. Seratonin – Involved in alertness, sleepiness, thermoregulation, and mood. Requirements of the Nerve cell Cells within the nervous system require enormous amounts of energy to function. This energy is provided by the processing of glucose and the production of ATP within these tissues, requiring an adequate supply of carbohydrates and oxygen (Na+/K+ pump). ATP energy is required to operate the sodium-potassium pump which convert cellular chemical signals into electrical signals along a nerve cell and in between individual nerve cells (i.e., synapse). Core Lab #1 - Reflex Arc What is a reflex arc? It is the nerve pathway that leads from stimulus to reflex action. Complete Pre-lab Question. Technology for Viewing the Brain 1. EEG (electroencephalograph): Invented by Dr. Hans Borger in 1924. This technology measures electrical activity in the brain. Allows doctors to detect and locate brain tumors and disorders such as epilepsy. EEG Technology Continued 2. Cat Scan: taking a series of cross- sectional X-rays to give a computer generated 3-D picture of any part of the body, including the brain. Technology Continued 3. MRI (Magnetic Resonance Imaging): This technology uses a series of large magnets, radio frequencies and a number of computers to create a detailed view of the brain and other structures in the body. MRI Treating Stroke and Spinal Cord Injury Stroke: Is caused by lack of oxygen to a particular part of the brain causing that portion of the brain to die. Treatments for stroke involve: 1. clot-busting drugs- drawback is that they need to be administered within three hours after the stroke occurs. 2. Asprin may also be administered to a person showing signs of stroke. Asprin decreases the chance of a clot by reducing stickiness of platelets (like the oil that you put in the engine of a car) Treatments for spinal cord injury (none as of yet): There is a large amount of medical research dedicated to finding a way to treating spinal cord injuries. § -Scientists have found a gene that inhibits the regeneration of the spinal cord and the CNS. § -Researchers hope to use this discovery to develop a therapy that will promote regeneration of the neurons in the CNS EEG MRI PET Scan • Shows activity of the brain by giving a coloured scan on a monitor. The more intense the colour the greater the activity. Section 12.3 – The Sense Organs Eye and Ear The Sense Organs: The Human Eye What are the eyes protected by? 1. Eyelashes 2. Eyebrows 3. Eyelids 4. Bones in skull The different parts of the eye: How many can you think of? 1. Lens: The lens is a clear and flexible part of the eye. Its purpose is to focus light onto the retina. The lens is adjusted by ciliary muscles. These adjust the shape of the lens. 2. Iris: The iris opens and closes to control the size of the pupil. Which inturn restricts or allows more light to get into the eye. your iris is the coloured part of your eye. If you have green eyes, it’s because you have a green iris. 3. Retina: The retina is the inner layer of the eye. It is composed of the photoreceptors of the eye, the rods and the cones The retina contains approximately 6 million cones. 4. Rods: The rods are very sensitive to light, but they do no distinguish between different colors. 5. Cones are less sensitive to light but they are able to distinguish between colours. 6. Cornea: The cornea is the transparent, dome-shaped window covering the front of the eye. it is normally clear and has a shiny surface 7. Choroid Layer: Is the middle layer of the eye. Located between the retina and the outer layer of the eye. a. It absorbs light b. Prevents reflection of light within the eye c. The choroids becomes the iris at the front of the eye 8. Fovea: The fovea is located directly behind the lens of the eye. The cones of the eye are concentrated within the fovea. This area of the eye is responsible for producing the most distinct image 9. Pupil: The pupil is the opening in the center of the iris. The size of the pupil determines the amount of light that enters the eye. 10. Blind spot: There is one area in the eye where there are no photoreceptors Because of this there is one place in the eye where you cannot see. Look at page 413 The Eye Links • http://www.nei.nih.gov/health/eyediagram/i ndex.asp • http://www.exploratorium.edu/learning_stu dio/cow_eye/step01.html Go to unitedstreaming.com Pathway of Light Through the Eye 1. Light passes through the cornea • 2. . Then through the iris • 3. If there is a lot of light the pupil then constricts, if there is low amounts of light the pupil will dilate • 4. The lens then adjusts its shape in order to aim the image at the retina. • 5. Light hits the retina. The retina is composed of three layers: 1. ganglion layer 2. Bipolar layer 3. the rod and cone layer. • The rods and cones form the image The image is then transmitted to the ganglion layer via the bipolar layer of the eye. The impulse then exits the eye via the optic nerve Layers of the retina (pg 412) Disorders of the Eye In this course we will learn about 5 disorders of the eye. 1. Cataracts – cloudy or opaque areas on the lens • Get worse with age • Damaged lens can be replaced with an artificial one. 2. Glaucoma – Buildup of aqueous humor between lens and cornea. • The duct that normally drains the fluid becomes blocked. • Can cause nerve damage to nerves that aid in peripheral vision. • Can be helped with drugs. 3. Myopia (Near-sightedness) – Can see objects close up. – Usually caused by the eyeball being too long. – Therefore the image is focused in front of the retina. – Treated with concave lens 4. Hyperopia (Far-sightedness) – Can see objects far away but not close up. – Usually caused by short eyeballs. – The image is focused behind the retina. – Treated with convex lens 5. Astigmatism – Abnormal shaped lens or cornea, resulting in uneven focus. – Treated with uneven lens. Refer to Figure 12.22 in text. Treatments of eye disorders 1. Laser treatment 1. Photorefractive keratectomy (PKU) • Outpatient procedure • Reshapes cornea by removing microscopic amounts of tissue. • Controlled by computer 2. Laser in situ keratomileusis (LASIK) • Helps repair near-sightedness • Knife is used to cut the corneal flap. • Laser is used to remove tissue underneath and flap is replaced. • Controlled by surgeon. • Both treatments are highly successful. 2. Corrective lenses 3. Cornea transplant – When the cornea is beyond repair, a transplant can be performed. – Cornea comes from a donor, but doesn’t need to be matched. Ie any cornea can be used by any person. – Recovery can be up to 12 months. – Prognosis is usually very good. The Ear Parts of the ear 1. Pinna – Channels sound waves into the auditory canal. 2. Tymphanic membrane (ear drum) acts like a drum head and vibrates as sound waves hit it. 3. Ossicles – Malleus (hammer) – picks up vibrations from the ear drum. Vibrates and hits the incus (anvil) – Incus (anvil) – Passes vibrations to the stapes. – Stapes (Stirrup) – Passes vibrations to the Oval Window. 4. Eustachian tube (Auditory tube) – Tube behind the ear drum that allows pressure behind the eardrum to equalize. 5. Semicircular canals – Involved in balance and equilibrium. (Fluid filled) 6. Cochlea – Fluid filled – involved in hearing. Contains very tiny hairs that pick up sound vibrations. 7. Auditory nerve – Takes message away from ear to the CNS. Pathway of Sound in the Ear 1. Pinna focuses sound waves into the auditory canal. 2. Tymphanic membrane vibrates. 3. Vibrations are passed through the ossicles. 4. Sound waves pass through the oval window into the cochlea. 5. Hairs in the cochlea pick up sound and are changed to nerve inpulses. 6. Nerve impulses are taken away by the auditory nerve. Disorders of the Ear There are two main types of deafness that a person can have; they are as follows: 1. Nerve deafness: Nerve deafness is caused by damage to hair cells in the spiral organ of the ear. a. This type of deafness is usually uneven, ie. People with the disorders can hear certain frequencies better than others. b. Damage cannot usually reversed and it continues to get worse as a person gets older. 2. Conduction deafness: This type of hearing disorder is caused by damage to the outer and middle ear a. Conduction deafness affects the transmission of sound waves into the ear. b. This type of hearing disorder doesn’t usually cause total hearing loss. c. Hearing can usually be improved with the use of a hearing aid. 1. Eustachain tube implants: Many children have inner middle ear infections because their Eustachian tube is on an angle that does not allow proper drainage. a. To prevent these infections, doctors can put tubes in the patients ears to allow proper drainage and pressure release. Treatments for Ear Disorders 1. Hearing aids: There are several different types of hearing aids available; 1. Conventional 2. Programmable, and 3. digital aids. a. Conventional hearing aids have a microphone to receive sounds and an amplifier to increase their volume b. Programmable hearing aids have an analog circuit that a professional such as an audiologists can program to the patients needs. c. Digital Hearing aids can shape amplifications across various pitches and frequencies according to individual needs.
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