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Homeostasis External environment changes drastically Internal environment (inside our bodies) must stay the same Homeostasis is the ability of an organism to maintain its internal make-up. For your internal environment to remain constant you must have a 1. Monitor (detect the problem) 2. Control (fix it) Example 1) Oxygen concentration in blood. Monitor = Oxygen chemoreceptor in aortic arch Control = Medulla Oblongata If not enough O2 in blood, chemoreceptor detects problem Medulla oblongata commands diaphragm & intercostals to work harder Oxygen debt is soon solved chemoreceptor stops detecting problem Medulla Oblongata stops trying to fix it our bodies use 2 mechanisms for controlling our internal make-up. 1. Nerves and the nervous system 2. Hormones and the endocrine system Nervous System The human body is made up of two nervous systems. Central Nervous System CNS Peripheral Nervous System PNS 10 Central Nervous System Yellow Brain and spinal cord. 11 Peripheral Nervous System Blue Green Red Orange Connects the CNS with the rest of the body nerves that leave the spine 12 PNS can be divided into: Somatic Nervous System voluntary control Nerves leading to skeletal muscles fast nerve transmission (myelinated neurons) Autonomic System Nervous Involuntary Automatic functions slower nerve transmission (unmyelinated neurons) 13 Autonomic Nervous System Controls things like heart rate, blood pressure, breathing rate, digestion Divided into two halves: Sympathetic Parasympathetic 14 Sympathetic Nerves which transmit impulses during times of stress Speed up functions like blood pressure and heart rate… Nerves from spinal cord Parasympathetic. Nerves which transmit impulses when the body is attempting to return back to normal after a time of stress. Slows heart rate and blood pressure… Nerves from brain. 15 16 General Properties of all Neurons The basic unit of the nervous system is the neuron. A nerve is a bundle of these neurons. Neurons are specialized to conduct an electrical impulse. All neurons have the same basic components: Dendrite -- receive stimuli Cell body -- contains nucleus and cell organelles Axon -- long cylinder carrying impulse to next neuron or to effector. 17 Axons can be up to 1 meter in length. Sometimes, the axon of a neuron can have an insulating cover called a myelin sheath white made up of Schwann Cells speeds up impulse transmission appears like sausages the naked spaces of axon in between myelinated sections (sausages) are called NODES OF RANVIER every 1 mm along the axon. 19 20 21 22 Neurons can be categorized based on their function Sensory Neurons Interneurons Brings information to the CNS. Located in ganglia next to the spinal cord in the dorsal root. Found only in brain and spinal cord (CNS). Form link between sensory and motor neurons. Motor Neurons Carries impulses from CNS to effectors (muscles or glands) 23 The somatic nervous system controls all voluntary systems within the body except for reflex arcs. These are what we call reflexes. They protect the body quickly when presented with a stimulus that the body perceives as being dangerous. Although reflex arcs send secondary signals to the brain during the reflex action, the primary response is "hard wired" through the spinal cord. 24 Certain stimuli, such as touching a hot surface, cause a reflex arc the nerve impulse travels up the sensory nerve through an interneuron in the spine down the appropriate motor nerves result = jerk the hand away from the hot surface. This automatic response system allows for extremely fast reaction times. 25 A reflex arc must always include 5 components: 1. Receptor (pain receptor…) 2. Sensory neuron 3. Interneuron 4. Motor neuron 5. Effector (muscles) 26 29 30 A nerve impulse can actually be thought of as an electrical signal from one place to another. This can be achieved by pumping charged particles in and out of the neuron. Sodium and Potassium play important roles. There is lots of sodium and potassium around the neuron. 32 In reality, there is a proton pump that will transport potassium into the neuron and sodium out of the neuron. 35 There are also channels that will allow certain ions to diffuse back across the membrane of the neuron. Potassium Channels Sodium Channels 37 The Goal… To have a charge difference across the membrane. The electrical potential This is achieved by having one channel open and the other closed. 39 At rest, the inside of the neuron is negative relative to the outside inside is said to be -70 millivolts (mv) The neuron is POLARIZED. It is polarized because the inside of the neuron and the extracellular fluid are oppositely charged. When electrical charges are separated in this way, they have the potential to do work should they be permitted to come together. 42 Resting Potential Summary Polarization occurs because of the unequal ion distribution. Polarization is mainly due to 3 main factors: 1. 2. 3. The outward diffusion of potassium ions The sodium pump is actually slightly more efficient than the potassium pump (more sodiums out than potassiums in – approximately 3:2) The presence of large diameter negatively charged anions that are stuck inside the neuron. 43 Electrical, chemical, or mechanical stimulus will alter the resting potential by causing sodium to leak back into the neuron. “Sneaks” through the sodium channel. This changes the polarity slightly If the stimulus is strong enough to bring the inside to about -55 mv, a THRESHOLD has been reached. Once this occurs, the sodium channels immediately open wide and potassium channels close. 44 The rapid influx of sodium causes a momentary reversal in polarity . Depolarization Membrane potential shoots to about +40 mv. This sharp rise and fall of action potential is called a spike. This could be described as a slight electrical disturbance in the neuron. The action potential is an electric current strong enough to induce the collapse of the resting potential in the adjacent area of the neuron. 48 49 50 51 52 As the wave of depolarization moves along the axon, the normal polarized state is quickly reestablished behind it. Must get back to Positive outside and Negative inside. Sodium channels close, and potassium channels open. 53 54 55 56 The sodium and potassium pumps soon reestablishes resting potential ion separation. 57 58 59 60 61 62 63 64 65 The amount of time it takes to repolarize is called the refractory period approximately 1 ms (millisecond) During this time the axon cannot transmit an action potential no matter how great the stimulus. During repolarization, the rapid pumping of sodium causes a momentary hyperpolarization. Too much positive outside Inside is about - 85mv Resting state is established when potassium re-enters the neuron. 66 + 40 0 -55 -70 67 + 40 0 -55 -70 68 Neurons and Impulse Transmission Follow the “all-or-none” principle a stimulus above the threshold level, whether strong or VERY strong produces the same strength of signal transmission. More stimulus (i.e. more painful) = more impulses generated, NOT a stronger impulse. An impulse does not diminish in strength as it travels along a neuron. 69 We already know that having a myelin insulation on an axon will speed its impulse transmission. This is because the impulse will jump from node to node. In this way, sodium and potassium do not have to undergo exchanges along the entire length of the axon Sodium and potassium pumps and channels are active only at each NODE OF RANVIER. This is where the axon can actually exchange ions with the extra cellular fluid. 70 Getting the impulse from one neuron to the next. Adjacent neurons in a nerve fiber do not actually touch end to end. The junction between them is called a synapse. The gap is called a synaptic cleft. 73 The gap between the terminal axon of one neuron and the dendrite of the next is about 0.02 m. one millionth of an inch When the nerve impulse (depolarizing wave) reaches the synaptic knob, it must jump to the next neuron. impulse moves from axon of a pre-synaptic neuron to dendrite of a post-synaptic neuron. 75 Each synaptic knob (terminal axon) has vesicles that will produce and secrete neurotransmitters. When the impulse reaches the synaptic knob, the membrane surrounding the knob becomes permeable to calcium. The calcium causes the vesicles to fuse to the membrane of the knob emptying their neurotransmitters into the synaptic cleft. 76 A neurotransmitter is a chemical that will signal the next neuron’s dendrites to send an impulse down its axon. Important neurotransmitters are… acetylcholine -- most common neuromuscular junctions, brain, internal organs usually has an excitatory effect on post-synaptic dendrite. noradrenalin (norepinephrine) same thing but involved in the sympathetic nervous system 77 HOW DOES IT REALLY HAPPEN?? Acetylcholine is released from vesicles in the pre-synaptic axon it diffuses across the synaptic cleft it lands on receptor sites on the postsynaptic dendrite 78 Its purpose is to partially depolarize the membrane of the post-synaptic dendrite. 79 This excites the post-synaptic neuron sodium channels on post-synaptic dendrites open depolarization (charge reversal) action potential is achieved wave of depolarization spreads across post-synaptic neuron Problem: If acetylcholine remains in the receptor site, the sodium channels will remain open repeated stimulation of muscle Solution: Cholinesterase (an enzyme released into synaptic cleft) breaks down acetylcholine. Once sodium channels close, the neuron begins recovery. 81 Troubles… Nerve gas inactivates cholinesterase. the amount of acetylcholine in synaptic cleft increases with each successive nerve impulse repeated stimulation of muscle life-threatening spasms 82 The acetylcholine from one axon terminal is usually not enough to cause depolarization of the postsynaptic neuron. Usually, neurotransmitters from a few different pre-synaptic knobs are needed to induce an action potential This is known as summation. 83 Some neurotransmitters are not excitatory but rather inhibitory. These cause post-synaptic potassium channels to open fully Hyper-polarization more potassium will flow out (diffusion) more positive charges outside neuron Resting potential is now even more negative Need higher stimulus to overcome threshold and initiate action potential 84 85 M.S. Multiple Sclerosis Deterioration of the myelin sheath scar tissue on axon no impulse transmission impaired neural function loss of coordination tremor paralysis 86 Nerve Damage due to injury Parkinson’s Disease If damaged neurons are covered by the thin membrane called neurilemma, regeneration is likely (only in peripheral nervous system) No neurilemma = no chance of regeneration Involuntary muscle contractions Insufficient production of dopamine (a neurotransmitter) Alzheimer’s Disease loss of memory decreased production of acetylcholine 87 The Central Nervous System The Peripheral Nervous System Ear Eye -Identify the principal structures of the CNS and PNS -Explain their functions in regulating somatic and autonomic systems Spinal Cord runs down neck and back inside the spine receives information from skin & muscles sends motor commands for movement controls reflex activities Brain more complex functions coordination of homeostasis perception movement intellect emotions 90 Spinal Cord Structure White matter outer layer consists of motor and sensory axons myelinated Grey matter inner layer contains cell bodies of motor neurons and interneurons. 91 92 93 Central cavity contains cerebrospinal fluid Sensory Neurons pass through dorsal root have cell bodies in the dorsal root ganglion Motor Neurons leave the spinal cord through the ventral root. 94 95 96 31 pairs of mixed nerves nerves that contain both motor and sensory neurons 97 98 3 pounds one of the largest organs in body soft squishy 99 Protected by 3 layers of membranes called Meninges Dura Mater -- outer (next to skull) Arachnoid -- middle Pia Mater -- inner Infection (and swelling) of meninges is called … MENINGITIS 102 Surrounds the brain Lies in between the Pia Mater and the Arachnoid layer. Shock absorption brings nutrients, hormones and WBC to parts of brain Circulates between meninges and central canal of spinal cord Drains into veins 103 Doctors drill into spine Extract cerebrospinal fluid Test for infection Meningitis 104 Divided into Forebrain Midbrain Hindbrain Hindbrain Forebrain Controls pattern & image formation memory learning emotions Includes: Thalamus Hypothalamus Cerebrum Relay center for information on its way to cerebrum sensory information is sorted out sent to appropriate higher brain centers Regulation of homeostasis source of hormones (ADH, Oxytocin - uterine contractions) pituitary gland is connected to hypothalamus thermostat hunger thirst sexual response mating behaviors fight-or-flight response pleasure / rage biological clock when we sleep when our sex drive peaks 2 cerebral hemispheres left -- controls the right side of body Logical thought right -- controls the left side of body Creative thought The two halves of the brain communicate with each other through the corpus callosum a thick white band of fibers Outer gray matter is called cerebral cortex 2 cerebral hemispheres left -- controls the right side of body right -- controls the left side of body communicate with each other through the corpus callosum Outer gray matter is called cerebral cortex each hemisphere is divided into 4 lobes 4 lobes in each hemisphere frontal -- near the forehead speech, personality, precise movements temporal -- by your ears hearing smell parietal-- top of your head taste reading body position occipital -- back of your head vision Largest part of the brain most complex different parts of the cortex are in charge of different parts of the body. Hindbrain Small region relay center between forebrain & hindbrain forebrain & eyes Vision vision is controlled in the forebrain vision reflexes & some perceptual functions are controlled here 132 133 134 138 139 140 141 Hindbrain Called the “brain stem” lower brain Coordinates large-scale body movements like walking. Medulla Oblongata Pons Cerebellum Autonomic & homeostatic functions breathing, heart rate, blood pressure, vasoconstriction/vasodilatation, swallowing, digestion, vomiting … Here, motor axons from the mid and forebrain cross from one side of the CNS to the other SIDE!!!. as a result, right side of brain controls left side of body, and visa versa. just above medulla oblongata relay center between the cerebellum and the cerebral cortex Smooth coordination of movement Hand-eye coordination Balance Organizes information about position of joints length of muscles visual & auditory activity Nerves that leave the brain and spine Cranial nerves nerves that leave the brain Lead to organs of the head & upper body parasympathetic system Vagus Nerve = important cranial nerve Spinal nerves nerves that leave the spine Lead to the whole body sympathetic system 151 When both the sympathetic and parasympathetic systems innervate the same effector, they are called antagonistic. I.e. Heart Sympathetic = speed up Parasympathetic = slow down 157