SBI4U Unit 4 Homeostasis - Nervous System PDF

SBI4U - Unit Four - Homeostasis - Nervous and Endocrine System Nervous System Communication system 100 billion nerve cells in your brain alone 2 main divisions to a vertebrate nervous system 1. Central Nervous System (CNS) Brain and spinal cord Coordinating cent...

SBI4U - Unit Four - Homeostasis - Nervous and Endocrine System Nervous System Communication system 100 billion nerve cells in your brain alone 2 main divisions to a vertebrate nervous system 1. Central Nervous System (CNS) Brain and spinal cord Coordinating centre 2. Peripheral Nervous System (PNS) Nerves that carry info between the CNS and the rest of the organ systems Somatic Nerve System: voluntary (nerves you can control) connected to skeletal muscles and skin Autonomic Nerve System: involuntary (nerves you can’t control) connected to other organ systems (e.g. circulatory, digestive, respiratory) Autonomic System Sympathetic System “Fight or flight” mode involves cortisol and adrenaline Increased heart rate, breathing rate, blood flow, blood pressure Reduced digestion Much harder on the body Parasympathetic System “Rest and digest” mode Increased digestion Resting HR, breathing rate, blood flow, BP Stress Activates the Sympathetic System (fight or flight) Releases cortisol and epinephrine (adrenaline) - both hormones Cortisol increases HR, BP, and breathing rate Chronic stress leads to overactivation of the sympathetic system, wearing the body down over time Neurons  Nerve cells that send electrochemical signals to each other and other parts of the body A nerve is a bundle of many neurons Reflex Arc The simplest nerve pathway is called a reflex arc Typically occurs in the spinal cord Contains 5 essential components receptor sensory neuron (afferent) interneuron motor neuron (efferent) effector Sensory Neurons (Afferent Neurons) unipolar carry impulses from sensory receptors to CNS e.g. photoreceptors in eyes (light), thermoreceptors in skin Motor Neurons (Efferent Neurons) multipolar carry impulses from the CNS to effectors (muscles, organs, glands… AKA things that produce a response) Interneurons bipolar connects sensory and motor neurons (found mostly in the CNS) Nervous System - Communication Nerve Cell Anatomy Cell body nucleus and majority of cytoplasm Dendrites projections of cytoplam that carry impulses toward the cell body Axon extension of cytoplasm that carries nerve impulses away from the cell body Axon Terminal impulses end and chemical is released Myelin Sheath insulated covering (fatty protein) over the axon of some nerves, “myelinated” prevents loss of charge Nodes of Ranvier regularly occuring gaps between sections of the Myelin Sheath Signal Transmission Nerve impulses jump from one node to another - increases speed of the impulse non-myelinated nerves carry impulses at a slower rate axon diameter also effects speed narrower = faster Neurons in the brain have less myelination on the axons than those located in the spinal cord axons in spinal cord are longer and therefore the signal needs to travel faster  Mass of less-myelinated neurons - gray matter - found mostly in the brain and inner section of the spinal cord Mass of highly-myelinated neurons - white matter - found mostly in the peripheral NS (nerve system) and outer section of the spinal cord Action Potential Firing an action potential is an “all-or-none” response to a stimulus that has reached the THRESHOLD POTENTIAL Threshold examples: “just enough” pressure change on the skin “just enough” temperature change to notice If the threshold is not reached, the neuron does not fire an action potenital; even if there is a stimulus, it’s just not enough Sodium Potassium Pump Neurons maintain a resting potential by constantly moving Na+ out and K+ across the concentration gradient When the threshold is reached, the cell opens Na+ channels and as those ions rush in, the cell is depolarizing Neuron Communication Once the electrical imulse reaches the axon terminal and hits the threshold, it releases chemicals called neurotransmitters Neurotransmitter moves across the synapse gap between the axon terminal of one neuron and the dendrite of another neuron Neurotransmitters will bind to receptors of dendrites - when enough bind to receptors, it starts the action potential Neurotransmitters Acetylcholine sent from motor neurons to the muscle and tissue Glutamate GABA Dopamine responsible for motor function, learning and memory, addiction Serotonin associated with happiness and pleasure Epinephrine Norepinephrine SSRIs Selective Serotonin Reuptake Inhibitors Antidepressant and anit-anxiety medication Prevents serotonin from going back to the axon terminal from the synapse Allows serotonin to bind to receptor multiple times, eliciting more pleasure and happy feeling The Brain Composed of three main parts cerebrum (forebrain) cerebellum (hindbrain)  controls fine motor coordination brainstem connects brain to spinal cord Medulla Oblongata - controls circulatory and respiratory system Cerebrum Composed of grey matter The folds (fissures) create more surface area allows faster and greater neural activity (more communication between neurons) Most neural activity of the cerebrum occurs on the surface Corpus Callosum highway of axons that allows the left and right hemispheres to communicate Lobes of the Cerebrum Frontal Lobe contains prefrontal cortex and motor cortex Parietal Lobe contains primary sensory cortex Occipital Lobe Temporal Lobe Parts of the Cerebrum Prefrontal Cortex in front of frontal lobe in charge of all planning, decision making, goal setting, time management develops during high school fully develops around age 18 Motor Cortex coarse motor movement Sensory Cortex tactile (touch) Frontal Lobe thinking, personality, consciousness, inhibition Temporal Lobe long term memory, hearing Parietal Lobe sensory centre, where all sensory input is processed Occipital Lobe vision Limbic System AKA the Primitive Brain Composed of white matter Thalamus relays sensory signals, regulates consciousness Hypothalamus controls all needs and processes requiring hormones including: thirst, huger, sleep, BP, fight or flight, sugar intake Pituitary Gland  receives signal from hypothalamus to release hormones to regulate endocrine system Hippocampus short-term memory processing, spatial memory Amygdala emotional centre What Protects the Brain? Skull first line of protection, composed of bone Meninges two membranes filled with cerebrospinal fluid hold the brain and spinal cord in place, act as shock absorber Blood-Brain Barrier thin membrane between blood vessels and the brain only water and small molecules like glucose and ions get through keeps out substances that would be harmful to the brain Concussions and CTE Concussion Traumatic force causes the brain to hit or bounce against the skull Leads to shearing of the axons in the affected areas Can have long-term effects Chronic Traumatic Encephalopathy (CTE) Caused by repeated traumatic blows to the head over a long period of time Brain slowly degenerates over a long period of time Changes to personality, mood swings, and memory loss Can lead to dementia and early death Senses Vision Parts of the Eye Sclera tough outer layer Cornea protects the eye and redirects light into the eye Pupil opening for light Lens thickens for “near” focus and flattens for “far” focus (made of protein that becomes cloudy with age - cataracts) Iris controls the amount of light entering the pupil Retina photoreceptor layer (rods and cones) Macula part of the retina that contains most of the cones  Optic Disk optic nerve and blood vessels exit eyeball and there are no photoreceptors (blind spot - brain fills in the picture) Note: the eye uses Rapid Eye Movement to determine changes in picture The Retina Photoreceptors are found in the retina Rods - detect low levels of light, night vision Cones - detect different wavelengths or colours, fine detail detects Red, Blue, Green light 6 million cone receptors Sends signals along optic nerve Vision Optic nerve sends sensory input from the eye to the occipital lobe where it is processed Hearing Outer Ear Pinna direct sound waves into ear canal Sound waves vibrate the tympanic membrane (eardrum) Middle Ear Vibrations of sound are amplified by 3 tiny bones called with ossicles which tap on the cochlea Ossicles: hammer anvil stirrup Inner Ear Cochlea - spiral-shaped organ filled with fluid vibration from the ossicles virbates the fluid inside and activates hair cells the further the vibration goes in the cochlea, the higher the frequency of sound input from the hair cells is sent to the auditory nerve fluid in the cochlea also detects and determines your balance Hearing The auditory nerve sends sensory input from the cochlea to the auditory cortex in the temporal lobe where it is processed Tinnitus May be caused from damage to cochlea Neurons will produce this noise if it does not detect a stimulus Touch Mechanoreceptors pick up touch stimulus It is sent to sensory neurons which send signals to the spinal cord The signal travels up the spinal cord to the thalamus which redirects the signal to the Primary Sensory Cortex Homunculus Map/model of where the most neurons are located in the body (LOTS in face, lips, HANDS) Phantom Limb Syndrome When amputees loose limbs, the signal to those dedicated neurons in the cortex disappears To prevent itself from dying the neuron will connect to neurons belonging to another body part Amputees can still feel their missing limb if they touch the other body part