* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Nervous System - s3.amazonaws.com
Neuromuscular junction wikipedia , lookup
Neural oscillation wikipedia , lookup
Embodied language processing wikipedia , lookup
End-plate potential wikipedia , lookup
Neurophilosophy wikipedia , lookup
Biochemistry of Alzheimer's disease wikipedia , lookup
Brain morphometry wikipedia , lookup
Mirror neuron wikipedia , lookup
Microneurography wikipedia , lookup
Artificial general intelligence wikipedia , lookup
Biological neuron model wikipedia , lookup
Neural coding wikipedia , lookup
Selfish brain theory wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Synaptogenesis wikipedia , lookup
Haemodynamic response wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Human brain wikipedia , lookup
History of neuroimaging wikipedia , lookup
Cognitive neuroscience wikipedia , lookup
Neuroeconomics wikipedia , lookup
Neuroregeneration wikipedia , lookup
Aging brain wikipedia , lookup
Neuropsychology wikipedia , lookup
Neurotransmitter wikipedia , lookup
Neural engineering wikipedia , lookup
Brain Rules wikipedia , lookup
Optogenetics wikipedia , lookup
Neuroplasticity wikipedia , lookup
Single-unit recording wikipedia , lookup
Central pattern generator wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Development of the nervous system wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Metastability in the brain wikipedia , lookup
Circumventricular organs wikipedia , lookup
Synaptic gating wikipedia , lookup
Stimulus (physiology) wikipedia , lookup
Nervous system network models wikipedia , lookup
Nervous System Biology 30 Nervous System Function • Did you know that 1 cm3 of your brain contains about 50 million neurons (nerve cells)? • Each neuron may communicate with thousands of other neurons forming intricate networks that control our functions and store our thoughts. • The nervous system has 3 major functions. – Sensory input moves signals from our various sense organs to the brain. – Integration is the interpretation of those signals and the formation of an appropriate response. – Motor output is the conduction of signals to the body’s effectors – muscles and glands. Nervous System Function The Neuron Dendrite – receives information from receptors or other neurons and conducts nerve impulses toward the cell body. Synaptic Knob – aids in nerve impulse transmission Cell Body – contains nucleus and organelles Nodes of Ranvier – gaps within the myelin sheath Impulses jump from node-to-node therefore speeding up the impulses Neurillemma – delicate membrane that promotes regeneration of damaged neurons Only found in myelinated neurons Myelin – a fatty protein the axon Axon – conducts nerve impulses away fromthat the covers cell body Composed of Schwann cells, which help regenerate damaged neurons Insulate the axon allowing nerve impulses to travel faster Myelination is only found outside the brain and spinal cord Types of Neurons Sensory Neurons (Afferent Neurons) – conducts nerve impulse from sense organs to the brain and spinal cord (CNS) Interneuron (Association Neuron) – found within the CNS No myelination Intergrates and interprets sensory information and relays information to outgoing neurons Motor Neuron (Efferent Neurons) – conducts nerve impulses from CNS to muscle fiber or glands (effectors) • The two major components of the nervous system are the central nervous system (CNS) consisting of the brain and spinal column and the peripheral nervous system (PNS) consisting of a vast network of neurons held together by connective tissue in bundles we call nerves. • The PNS also contains ganglia (s: ganglion) which are the cell bodies of • neurons found in the nerves. • A quick summary of the parts of the nervous system can be seen in the knee-jerk reflex. • When the patellar tendon is tapped, sensory neurons detect the stretching and send a signal to the CNS (in this case, the spinal • cord). • The information goes to a motor neuron and to an interneuron. • The motor neuron stimulates the contraction of the quadriceps muscle which extends the leg, while the interneuron sends an inhibitory signal to the flexor muscle. Threshold Levels Threshold Level – minimum level of stimulus required to produce a response (action potential) Stimulus Muscle Contraction 1 mV -- 2 mV -- 3 mV 5N 4 mV 5N All-or-None Response – neuron either fires maximally or not at all. Variation in response is due to the number of neurons firing or the frequency in which they fire. Neural Ion Transport • Nerve impulses are initiated by the movement of sodium (Na+) and potassium (K+) and changes the polarity (+ and -) along the cell membrane. The movement is controlled in two ways: – Protein Gates – voltage sensitive gates which open when the neural membrane is stimulated. Ion move in and out by diffusion. – Sodium-Potassium Pumps – actively transports Na+ and K+ ions across the neural membrane Nerve Impulse Nerve impulse animation Resting Potential Resting Membrane Action Repolarization Potentialor (Depolarization) Refractory Period •Characterized byby ~+ve charge ononthe outside •Characterized •Characterized by ~-ve ~+ve charge charge on the the •Time takes toonrestore the ~-veit charge the inside outside outside ion~Na+/K+ concentration. No impulse maintaining ~+ve ~-vecharge charge on onthe thepolarity inside inside can occur during this time (1 are open •Na+ gates are closed, some of the K+and gates ~Na+ ~K+ gates open Na+ rushes to 10 milliseconds) (allowing to leak of the K+ membrane) in•OnceK+ polarity is out reversed gates open and K+ •Na+/K+ pumps pump Na+ in 2 K+ •Na+/K+ pumps pump outpolarity 3has Na+reached and pump •Occurs rushes once out tothe restore neuron the threshold out and K+ in to restore the •Resting level potential is about -70 mV (millivolts) ion concentration. •Na+ gates open and Na+ rushes in, reversing polarity Measuring Potential Transmission Across A Synapse • Steps in neural transmission: – Nerve impulse causes synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft. – Neurotransmitters diffuse across to the postsynaptic membrane – Neurotransmitters bind with postsynaptic receptors in a lock-and-key fit. – Neurotransmitters can result in excitation or inhibition of next neuron. If excitatory the sodium gates of the next neuron open and the action potential continues Neurotransmitters Norepinephrine excitatory Acetylecholine ––mostly excitatory Dopamine Serotonin – excitatory/Inhibitory - excitatory Norepinephrine, also called noradrenaline Acetylcholine released where nerves Dopamine Serotonin affects isisnormally brain processes involved inthat is atemperature neurotransmitter that doubles part-time meet muscles (neuromuscular junction) control movement, regulation, emotional sensory response, and as aability As amood neurotransmitter, and ishormone. therefore responsible for muscle theperception, to experience and pleasure control. However, and pain.it norepinephrine helps regulate arousal, contraction. After acetylcholine Regulation plays a major of dopamine role intoemotional plays astimulates crucial disorders role dreaming, moods. As ahealth. hormone, it its receptors, itand is quickly inactivated and in our such mental as and depression, physical suicide, impulsive acts to increase pressure, constrict destroyed byand an blood enzyme known as behavior, aggression blood vessels and increase heart rate cholinesterase responses that occur when we feel stress. Vertebrate Nervous System • In all vertebrates, the CNS consists of the brain and spinal cord, although the ability to integrate stimuli varies greatly from fish to humans. • The spinal cord, buried inside the vertebrae, receives sensory information from the skin and muscles and integrates simple responses such as the knee-jerk reflex. • The brain includes homeostatic centers that keep the body functioning smoothly; sensory centers that integrate data from sense organs; and centers of emotion and intellect. • The brain also sends out motor commands to muscles. Vertebrate Nervous System • The CNS is serviced by a vast network of capillaries that secrete cerebrospinal fluid into the fluid-filled spaces of the brain (ventricles) and spinal cord (central canal). • These capillaries are quite selective in allowing nutrients to pass into the brain, but not waste products. • This selective mechanism is called the blood-brain barrier and helps maintain a stable environment for the brain. • The brain and spinal cord are protected cerebrospinal fluid under tough connective tissues called the meninges. • Infection of these layers is called meningitis and is extremely serious. • The white matter of the CNS is mainly myelin-coated axons and the gray matter is mostly neuron cell bodies and dendrites. • Cranial nerves carry to or from the brain to our eyes, nose, ears. • Spinal nerves carry information to and from the muscles and skin. Reflex Arcs • Reflexes are autonomic, involuntary responses to changes occurring inside or outside the body. • Pathways of a reflex arc: – Receptor generates nerve impulses due to stimulation – Sensory neurons carries impulse to interneurons in the grey matter of the spinal cord – Interneurons pass impulse to motor neurons – Motor neurons stimulate effectors – Effector receives impulse and reacts; glands secrete or muscles contract. Organization of the Nervous System Peripheral Nervous System • The PNS consists of cranial (12) and spinal nerves that extend outside the CNS – Somatic System contains sensory neurons from sense organs and motor neurons to the muscles – voluntary control. – Autonomic System contains sensory neurons from viscera and motor neurons to control glands, heart and smooth muscle of internal organs – involuntary control. Autonomic Nervous System • Sympathetic Pathway: Fight or flight – Neurons run from the thoracic lumbar Parasympathetic Pathway region of the spinal cord and into the Neurons run from the sacral part of the associated organs spinal cord to the associated organs – Used in emergency situations and Release ACh and promotes a relaxed associated with the fight or flight response state reducing the effects of the – Axons release norepinephrine as a sympathetic pathway neurotransmitter (inhibits digestion, accelerates heart rate ad breathing rate) CNS – Spinal Cord • Spinal cord is surrounded by vertebrae; Spinal cord communicates brain is enclosed inside •Functions a center for reflexshell arcs brainare andwrapped spinal • •Communicates The brain and between spinal cord nerves in three membranes (called meninges) •Grey matter (letter H) – made from that are filled with cerebrospinal fluid unmyelinated neurons that cushions and protects. •White matter carries information in tracts to and from the brain •Tracts cross over. Left side of the body is controlled by the right side of the brain and the right side of the body is controlled by the left side of the brain. The Brain • The brain evolved from a set of three hollow bulges at the anterior end of the neural tube called the forebrain, midbrain, and hindbrain. • This evolutionary progression is recapitulated (to repeat the principal stages or phases) during embryonic development, especially in mammals and birds, as these structures become more complex and specialized. • Evolution of the most complex vertebrate behavior correlates to the development of the cerebrum. • This portion of the forebrain undergoes the greatest amount of development in humans who have the largest brain surface area (gray matter) relative to body size of all animals. • With over 100 billion interconnected neurons the human brain has more integrative power than any computer. • The ancestral hindbrain and midbrain, now called the brain stem, has become the medulla oblongata and the pons. • All sensory and motor neurons carrying information to and from the higher brain pass through here. • Another development of the hindbrain, the cerebellum, acts as the coordination centre for body movement. • Although you may consciously plan to go for a walk, the cerebellum provides the complex coordination required by integrating sensory input about your movement with the necessary signals to the motor neurons connected to the various muscles used. • The greatest sophistication occurs in the forebrain, consisting of the thalamus, hypothalamus and cerebrum. • The thalamus acts as a switchboard sending information to the appropriate higher centers of the brain for further interpretation. • The hypothalamus controls the pituitary gland and the secretion of many hormones. • The hypothalamus also regulates body temperature, blood pressure, hunger, thirst, pleasure and the “fight or flight” response. It also regulates our biological clock that maintains our circadian rhythm. • It is highly susceptible to the effects of drugs and its normal functioning can be impaired making the person addicted. • The cerebrum is the largest and most sophisticated part of our brain. • A thick band of nerve fibers called the corpus collosum connects the left and right cerebral hemispheres. • Under the corpus collosum are clusters of neuron cell bodies called the basal ganglia (or basal nuclei) that are important in • motor coordination. • Degeneration of the basal ganglia occurs in Parkinson’s disease and results in tremors eventually followed by paralysis. • The cerebral cortex is a mosaic of specialized, interactive regions. • 5 mm thick, the cerebral cortex accounts for 80% of the brain’s total mass with some 10 billion neurons and hundreds of billions of connections. • This is where our reasoning, imagination, artistry and personality exist. • It integrates input from our senses and regulates our voluntary movements. • Oddly, each hemisphere receives information from and controls movement on the opposite side of the body. • The corpus collosum communicates between the two hemispheres. • At the boundary between the frontal lobe and the parietal lobe is the motor cortex and the somatosensory cortex. • The somatosensory cortex receives touch, pain and temperature from the body. • Across the fissure, the corresponding motor cortex controls body movements. • Neurons associated with the head are located at the bottom of the fissure and those of the toes are at the top. • There are considerably more neurons associated with the face and hands than others. • Language results from some extremely complex interactions among several association areas. • Reading, writing, and speaking involve rapid interactions between our visual association area in the occipital lobe (to process the shape of words on a page), the auditory association area in the temporal lobe, and the speech areas of the parietal and frontal lobes. • Lateralization refers to the specialization of the hemispheres of the brain. • The left hemisphere becomes adept at language, logic, and mathematical operations. • It has a bias for detailed skeletal motor control and processing of fine visual and auditory details. • The right hemisphere is stronger and spatial relations, pattern and facial recognition, musical ability, and emotional processing in general. In about 10% of people, this lateralization may be reversed or not observed. Brain Stroke Hemorrhage Brain Cross Section (Vertical)