9/29/2017. Lecture 8, Part A: Chapter 11: The Nervous System. The Nervous System Coordinates many of the body s functions

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1 Lecture 8, Part A: Chapter 11: The Nervous System The Nervous System Coordinates many of the body s functions Central Nervous System (CNS): Brain and spinal cord Peripheral Nervous System (PNS) Nervous system outside of central nervous system 2 parts: Sensory Division of PNS carries information to CNS Motor Division of PNS carries information from CNS to other parts of body Somatic Division: controls skeletal muscle Autonomic Division: controls smooth muscle, cardiac muscle, and glands Neurons Neurons (nerve cells) and nervous system connective tissue make up all parts of the nervous system Neurons generate and transmit impulses through the body 3 Types: Sensory Neurons of PNS: respond to stimuli and transmit info to CNS Interneurons of CNS: transmit impulses between parts of CNS Motor Neurons of PNS: transmit impulses away from CNS Structure of a Neuron Cell Body Dendrites Axon Structure of a Neuron Cell Body Large, round, central part of cell Contains nucleus and most of organelles Dendrites Extensions that transmit signals (electrical impulses) toward cell body More than 1 per neuron Axons Extensions that transmit signals away from cell body Only 1 per neuron 7 1

2 Myelin sheath Composed of fatty cells called Schwann Cells (in peripheral nervous system) which wrap around the axon Forms protective covering Gaps in Myelin = Nodes of Ranvier How are Signals Sent? All living cells have an electrical charge across their membranes ( membrane potentials ) Anions (-) are more concentrated inside cell and cations (+) are more common outside cell Only excitable cells (muscle cells and nerve cells) can generate large changes in their membrane potentials These excitable cells have gated ion channels that can regulate movement of ions across membrane in response to stimuli Stimulus may be chemical (via neurotransmitters) or electrical (via changes in membrane potential) Neurons Initiate Action Potentials Neurons at rest have a resting potential of -70mV Meaning, the inside of the cells are negatively charged relative to the outside of the cells The sodium-potassium pump removes three Na+ ions for every two K+ ions it allows inside the cell This helps maintain the negative membrane potential Resting potential of neuron can change in response to signals from other neurons These transient changes in membrane potential can vary in size and are called graded potentials They fade away from the region of the cell membrane that is affected They may also be summed in space and time (summation) The cell membrane may become: Depolarized = having a membrane potential closer to zero Repolarized = returning to resting potential Hyperpolarized = having a membrane potential that is more negative than the resting potential If enough ion channels are opened up to depolarize the membrane, an action potential is generated Occurs once the threshold is met through summation of graded potentials In neurons, only occurs in axons Spreads rapidly down axon 2

3 The result: the inside of the membrane rapidly becomes temporarily more positive than the outside Followed by a gradual re-polarization 12 Signals are regenerated along axons Sodium ions (Na+) entering cell depolarize membrane Action potential is generated in the neighboring region, opening more sodium gates Is spread forward, jumping from node to node (gaps in the Myelin sheath where plasma membrane is in contact with extracellular fluid) = saltatory conduction Myelin-coated axons transmit signals more rapidly Signals transmitted at approximately 1 mile/hour in nonmyelinated axons 400 miles/hour in myelinated axons Action Potentials are All-Or-None and Self-Propagating An action potential (or impulse ) is like the firing of a gun once you reach the threshold ( pull the trigger ), the nerve fires Pulling the trigger lightly, or pulling it harder than necessary, won t affect the firing of the gun Action potentials travel down the axon at a constant rate and amplitude Neuroglial Cells Support and protect neurons Some help maintain composition of extracellular fluid Some provide physical support The Schwann Cells of the myelin sheath of axons in the PNS are a type of neuroglial cell In the CNS, the protective sheath is composed of oligodendrocytes This sheath degenerates once an axon is destroyed Make up about 80% of cells in the nervous system Nerve cells cannot be replaced Highly specialized Lose ability to divide Nerve damage is difficult to deal with Axons that have been cut in the PNS can potentially grow back together and/or reestablish connections to muscle tissue Schwann Cells do not degenerate Severed axons in brain or spinal cord cannot regenerate, however 18 3

4 Oligodendrocytes degenerate after axon is destroyed 18 We do generate new brain cells into adulthood Discovered in 1998; new cells found in the hippocampus Area involved with memory and learning Mice living in stimulating environments and exercised vs. those in standard cages Those in the enhanced environment had more new brain cells in the hippocampus Performed better on learning tasks Application to humans: physical exercise and mental activity may result in greater learning capacity New neurons have also been identified in human brain Must come from adult stem cells in brain 19 Severity of spinal cord injury depends on where the spinal cord is injured High in neck (2 nd or 3 rd cervical vertebrae) disrupts signals to muscles controlling breathing Below 5 th vertebra in neck paralyzes legs and arms (quadriplegia) Below nerves that control arms, only legs are paralyzed (paraplegia) Brain damage Neurons are energetically expensive and require much oxygen Biggest single-organ oxygen consumption: 1)liver (20.4%) 2)brain (18. 4%) 3)heart (11.6%) Lack of oxygen to brain cells (within 4-5 minutes) often results in death of nerve cells The longer the amount of time without oxygen, the greater the damage Synapses How are impulses transmitted from neuron to neuron? Small gaps (synapses) separate adjacent neurons Ends of neurons are branched, ending in a terminal bouton Postsynaptic and presynaptic neurons When nerve impulse reaches the terminal bouton, stimulates release of neurotransmitters Travel across the gap (synaptic cleft) to receptors on the next (postsynaptic) neuron When enough neurotransmitters bind to receptors, an action potential is generated

5 Many pesticides work by disrupting the nervous system Cause build-up of neurotransmitters in synaptic cleft, making the neuron continue to fire In people exposed to pesticides, can cause headache, blurred vision, rapid pulse, & sweating Exposure to organophosphates in children can result in learning disorders and behavioral problems Children living near an agricultural area where malathion and parathion were used experienced reduced visual acuity (Ishikawa 1970) Organophosphate pesticides have also been shown to reduce intellectual functioning, abstract thought, and simple motor skills Malathion used extensively to control crop pests and mosquitos Over 600,000 pounds applied annually in California EPA regulates pesticides, and has not found Malathion to pose unreasonable risks But evidence is mounting against it (EPA was even prepared to list it as a carcinogen) Anesthetics also work by temporarily disrupting neurotransmitters associated with producing pain signals May block neurotransmitter production (pre-synaptic) May block post-synaptic receptors minute break Brain Housed inside skull Spinal cord Housed inside vertebral canal Meninges three layers of connective tissue that surround brain and spinal cord Space between middle and innermost layer filled with cerebrospinal fluid; provides cushioning The Brain Cerebrum 5

6 29 Largest part of brain Left and right cerebral hemispheres Thin outer layer composed of gray matter: the cerebral cortex; highly folded Each cerebral hemisphere divided into four lobes: frontal, temporal, occipital, and parietal lobes The types of processing that occur in each lobe differ between the left and right hemispheres During development, left hemisphere becomes specialized for Language Math Logic Speed-optimized activities Processing of visual and auditory details Right hemisphere becomes specialized for Pattern recognition Face recognition Emotional processing Cerebral cortex has 3 main functions processed in 3 general areas of cerebrum: Receive sensory input (sensory cortex) Integrate sensory information (association cortex) Generate motor responses (motor cortex) Consciousness resides in the cerebral cortex (See Figure 11.15, 11.16, and 11.17) Einstein s Brain Not unusually large overall Actually slightly smaller than the average male brain Part of brain associated with mathematical thought (parietal lobe) was 15% wider than the average brain The groove extending from front to back of brain (sulcus) didn t extend all the way back Might have allowed more neurons to connect across sides of the brain May also have had more glial cells (cells which support neurons activity) 36 6

7 Cerebellum Second-largest structure of brain Located below cerebrum Controls many unconscious body functions (movement) Coordinates contraction of muscles, allowing smooth motion Thalamus Located beneath cerebrum Relay center receives sensory information (except smell) and relays the information to sensory and association cortex Hypothalamus Beneath the thalamus Control many automatic responses, such as appetite, body temperature, and blood pressure Limbic System Controls instinctive behavior (e.g. fight-or-flight response, territoriality, etc.) Also important in emotions (fear, anger, etc.) Stimulating different parts of the limbic system with electrodes can make a person feel rage, calmness, joy, or other emotions Brain stem Connects brain to spinal cord Controls many automatic body functions, such as heart rate, blood pressure, breathing, and swallowing Spinal Cord A ropelike aggregation of nervous tissue Nerves extending from spinal cord connect to skin, muscles, bones and organs of body YouTube video: Neurons How They Work Human Brain Disorders/Diseases of the Nervous System Multiple Sclerosis Cause: damage to Myelin sheath Thought to be an autoimmune disorder (body attacking its own cells) Demyelination of axons reduces efficiency of signal transmission Eventually, the axons themselves may be destroyed Symptoms: mild weakness; tingling/numb feeling in part of the body; blurred vision; 42 7

8 slurred speech Repeated attacks may continue to damage nervous system Eventually, loss of vision and increased weakness 42 Stroke Cause: lack of blood flow to part of brain Can result from an artery breaking inside brain, or when an artery supplying brain with blood is blocked Parts of brain die As a result, often lose muscle control in part of body Other parts of brain may take over this function and partial or complete recovery is possible Video: brain plasticity 43 Alzheimer s Disease Progressive loss of mental function Generally in people over 65 Early symptoms: forgetfulness and irritability Causes not known May be related to previous brain injury Parkinson s Disease Deterioration of parts of brain that control movement Symptoms: shaking hands or head (tremors) Speaking may eventually become difficult Falls become more frequent Memory and thinking eventually deteriorate Cause: lack of dopamine Can be treated with levadopa Ultimate cause unknown Chemical pollutants may contribute Fetal cell transplants may be helpful in restoring dopamine production Brain Tumors Benign or malignant Benign: do not grow out of control, but can put pressure on parts of brain 8

9 46 9/29/ Can be removed surgically Malignant tumors Grow rapidly Can spread to other parts of body May be caused by exposure to carcinogenic chemicals Oil refining, drug manufacturing, rubber manufacturing industries Viruses and genetics may also play a role A brain tumor virus? A 2002 study by neurosurgeon Charles Cobbs found a common virus in nearly all brain tumors he studied CMV cytomegalovirus a form of the herpes virus Found in 80% of the population Usually harmless; fatigue Was active in the brain tumors, but dormant in other tissues Glioblastoma Multiforme a deadly form of brain cancer Senator Ted Kennedy died from this disease August, 2009 Potential for a vaccine Can we improve the function of our brains through exercise? Video: exercise makes you smarter: Bonus Activity What is an action potential? Explain the role of sodium and potassium ions. What characteristic of an axon increases the speed of transmission of an action potential? Do action potentials decrease in strength as they travel down an axon? Compare the sensory and motor divisions of the peripheral nervous system. Compare the autonomic and somatic divisions of the motor division of the PNS. Break Bio 1102, Lec. 8, Part B: Chapter Sensory Mechanisms 52 Receptors Receive & Convert Stimuli Receptors: a structure specialized to receive certain stimuli Types of receptors: Mechanoreceptors: respond to mechanical energy such as sound, changes in fluid pressure, touch or pressure, stretching, or forces generated by gravity or acceleration Thermoreceptors: respond to heat or cold 9

10 Pain receptors: respond to tissue damage or excessive temperature or pressure Chemoreceptors: respond to chemicals Photoreceptors: respond to light Some receptors adapt to continuing stimuli Receptor adaptation: the ability for some receptors to ignore inputs Stops sending signal to CNS, even though stimulus is still present Example: sensation of wearing a ring Skin receptors for light touch and olfactory receptors adapt rapidly Receptors for pain, joint and muscle receptors, and silent receptors associated with homeostasis, adapt slowly or not at all Somatic and Special Senses Somatic sensations: originate from receptors present at more than one location in the body Examples: temperature, touch, vibration, pressure, pain, and awareness of position or movement Special sensations: originate from receptors that are restricted to a particular part of the body Examples: taste, smell, vision, hearing, and balance The Eye Located in eye sockets in skull 6 small muscles attach eye and control movement Three layers of eye Outer protective layer (white sclera, but clear in front forming cornea) Middle layer (choroid) contains melanin In front of eye, forms the colored iris Smooth muscle of iris controls pupil dilation Opening in iris pupil (where melanin of middle layer is seen, as well as pigmented part of retina) Innermost layer -- retina The Retina Consists of an outer pigmented layer and inner layer of photoreceptors Specialized nerve cells that detect light 2 Types of Photoreceptors Rods: sensitive to low light conditions»dim, grayish images»black-and-white Cones: operate only in brighter light 10

11 »Sharp images»color vision»red, blue, and green cones 59 Different types of animals have the ability to see different parts of the electromagnetic spectrum Dogs and cats mostly see greys, with some blues and yellows Birds, monkeys and humans can see a wide range of colors. Why would we evolve the ability to see this diversity of colors, when animals like cats and dogs can t? Vitamin A (which we derive from Beta Carotene, as found in carrots and other orange fruits & vegetables) necessary for vision Vitamin A needed to produce retinal A form of retinal is bound to rods and cones Light strikes the retinal, causing it to dissociate from the photoreceptor This triggers a signal to the optic nerve Your mom was right! Eat carrots to improve your vision! (to a certain extent) Transmission of visual nerve impulses Rods/cones other neurons ganglion cells (a type of nerve cell), the axons of which unite to form optic nerve visual cortex of brain Focusing of Light Function of the cornea and lens Lens located behind iris Lens held in place and adjusted by thin ligaments that attach to smooth muscle in the ciliary body Changing shape of the lens focuses light Cataracts 11

12 63 9/29/ A clouding of the lens Occurs with age, and also with damage from ultraviolet radiation Risk highest for dark-eyed people Surgery involves removing the lens and replacing it with a plastic one Preventative measures: wear sunglasses that exclude UV radiation Glaucoma Build up of fluid in anterior portion of eye Pressure can damage retina and optic nerve Can lead to blindness Can be treated with eye drops and help drain fluid from the anterior chamber of the eye Nearsightedness (Myopia) Cause: eye too long or lens too strong Result: images far away are fuzzy, while nearby images are in focus (see Fig ) Common (20% of Americans) Can be corrected with glasses, contacts, or surgery Farsightedness (Hyperopia) Cause: eye too short or lens too weak Result: images of far away objects are in focus, but nearby objects are fuzzy Also corrected with glasses, contacts, or surgery Astigmatism Cause: surface of cornea or lens disfigured Result: fuzzy images Corrected with glasses, contacts, or surgery Taste Receptors for taste = taste buds Upper surface of tongue Respond to chemicals in food Dissolved in saliva Enter openings leading to interior of taste bud 5 basic flavors: sweet, sour, bitter, salty, and umami (meaty taste associated with MSG) 68 12

13 Smell Receptors located in roof of nasal cavity Olfactory membrane Olfactory receptor cells have 6-8 projections called olfactory hairs Bind to chemicals in air The Ear: Hearing and Balance Outer Ear, Middle Ear, and Inner Ear Outer Ear Auricle Ear lobe External auditory canal Transmits sound waves to middle ear Middle Ear Located within temporal bone of skull Eardrum separates middle ear from external auditory canal Eardrum vibrates when sound waves strike it 3 bones in middle ear: hammer, anvil, and stirrup Hammer: attached to ear drum; vibrates when eardrum vibrates Anvil: attached to hammer; rocks back and forth when hammer vibrates Stirrup: attached to anvil; moves when anvil moves; attaches to a membrane in inner ear (oval window) Inner Ear Large cavity in temporal bone Contains the cochlea a snail-shaped boney structure Contains auditory receptors (hair cells) and fluid Vibrations in fluid stimulate hair cells Hair cells send impulses to auditory cortex of brain Hearing Loss Conduction Deafness: occurs when sound waves cannot be conducted to inner ear Example: as a result of ear infections, scar tissue may build up, causing bones of middle ear to fuse together Treated by hearing aids (transmit sound waves through skull to inner ear) Nerve deafness: results from damage to hair cells May result from very loud noises which damage the hair cells 13

14 74 9/29/ Hearing Loss Conduction Deafness: occurs when sound waves cannot be conducted to inner ear Example: as a result of ear infections, scar tissue may build up, causing bones of middle ear to fuse together Treated by hearing aids (transmit sound waves through skull to inner ear) Nerve deafness: results from damage to hair cells May result from very loud noises which damage the hair cells May also result from damage to the nerve leading from the cochlea to the brain Vestibular Apparatus Located near the cochlea 2 main parts: semicircular canal and the vestibule (saccule and utricle) Receptors here detect body position and movement Semicircular canals Tubes of bone filled with fluid Base of each canal contains mechanoreceptors Detect movement of the fluid Detect rotational movement of head Vestibule Consists of utricle and saccule; two fluid-filled chambers Otoliths, hard crystals of bone-like material, float in gel Also contain mechanoreceptors Provide information about gravity Example: acceleration, or your angle with respect to gravity 78 All for today 14