* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Nervous System
Signal transduction wikipedia , lookup
Membrane potential wikipedia , lookup
Haemodynamic response wikipedia , lookup
Neural coding wikipedia , lookup
Subventricular zone wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Metastability in the brain wikipedia , lookup
Psychoneuroimmunology wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Multielectrode array wikipedia , lookup
Microneurography wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Central pattern generator wikipedia , lookup
Axon guidance wikipedia , lookup
Node of Ranvier wikipedia , lookup
Resting potential wikipedia , lookup
Neurotransmitter wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Optogenetics wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Neural engineering wikipedia , lookup
End-plate potential wikipedia , lookup
Electrophysiology wikipedia , lookup
Biological neuron model wikipedia , lookup
Single-unit recording wikipedia , lookup
Synaptic gating wikipedia , lookup
Circumventricular organs wikipedia , lookup
Chemical synapse wikipedia , lookup
Development of the nervous system wikipedia , lookup
Synaptogenesis wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Nervous system network models wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Neuroregeneration wikipedia , lookup
The Nervous System (Section 9.1) Although closely linked, the endocrine system and nervous system play different roles. In comparison, Complexity Structure Communication Response Time Nervous System Endocrine System More structurally complex; can integrate vast amounts of information and stimulate a wide range of responses Less structurally complex System of neurons that branch throughout the body Endocrine glands secrete hormones into the bloodstream where they are carried to the target organ Neurons conduct electrical signals directly to and from specific targets; allows find pinpoint control Hormones circulate as chemical messengers throughout the body cells via the blood stream; most body cells are exposed to the hormone and only target cells with receptors respond Fast transmission of nerve impulses up to 100/second Make take minutes, hours, or days for hormones to be produced, carried by blood to target organ, and for response to occur The Nervous System The nervous system contains more than 1 billion nerve cells in the brain alone! Overview: of the Nervous System: Nervous System Central Nervous System brain Spinal cord Peripheral Nervous System Somatic (voluntary) Nerves acts as a coordinating system for incoming and outgoing messages The Nervous System has three overlapping functions: sensory motor Autonomic (involuntary) Nerves sympathetic parasympathetic relay information between the CNS and organs of the body 1. Sensory input: is the conduction of signals from sensory receptors to integration centers of the nervous system. 2. Integration: is a process by which information from sensory receptors is interpreted and associated with appropriate responses of the body. 3. Motor input: is the conduction of signals from the processing center to effector cells (muscle cells, gland cells) that actually carry out the body’s response to stimuli These functions involve both parts of the nervous system: The Central Nervous System (Section 9.3) Consists of the BRAIN and SPINAL CORD Spinal Cord = carries sensory nerve messages from sensory receptors to the brain, and relays motor nerve messages from the brain towards target cells in muscles and organs o Emerges from skull from foramen magnum, extends down through a channel in your backbone o Consists of white matter (consists mostly of myelinated axons) and grey matter (consists of mostly of cell bodies, mostly unmyelinated axons, glial cells, and blood capillaries) Cerebrospinal fluid = surrounds CNS (brain and spinal cord); acts as a sock absorber and transport medium (nutrients, chemicals, removal of wastes, etc) o is a connection between CNS and endocrine system Brain = formed from a concentration of nerve tissue and acts as a coordinating center of the nervous system o is protected by the skull and meninges (a protective three layer thick membrane that surrounds the brain and spinal cord) o meninges controls which chemicals can ultimately reach the brain o consists of three distinctive regions: forebrain, midbrain, and hindbrain. Sections of the Brain Forebrain: reason, intellect, memory, language, and personality information on right side does not = info on left generally on right (visual patterns or spatial awareness) generally on left (verbal skills) hemispheres are joined by a bundle of nerves called corpus collosum = allows communication between hemispheres Sections Olfactory lobes Cerebrum Cerebral Cortex Cerebrum Lobes Frontal Lobes Temporal Lobe Parietal Lobe Occipital Lobe Function (x2) process information about smell 2 hemisphere; largest and most developed coordinates sensory info & motor actions largest and most developed divided into four (4) lobes (see below) surface of cerebrum made of grey matter highly folded (deep folds = fissures) Function motor area control movement of voluntary muscles (e.g walking and speech) linked to intellectual activities and personality sensory areas are associated with vision and hearing linked to memory and interpretation of sensory information sensory areas are associated with tough and temperature awareness linked to emotions and interpreting speech sensory areas are associated with vision interprets visual information Midbrain: located directly below cerebral cortex relay center for eye and ear reflexes Sections Thalamus Hypothalamus Hippocampus Basal Ganglia Function integrative center connecting many different parts of the brain together master control center of automatic nervous system (ANS) integrates the ANS and endocrine system short term memory many parts; responsible for crude motor movements injury leads to rigidity, Parkinson’s and Huntington’s disease mediates emotional feelings mediates between forebrain & hindbrain The Hindbrain: Sections Medulla Oblongata Pons “bridges” Cerebellum Function joins spinal cord to cerebellum controls involuntary muscle action coordinating centre for the ANS e.g breathing, heart rate, blood vessel activity, swallowing, vomiting, digestion…) acts as relay station by sending nerve messages between the cerebellum and medulla controls limb movements, balance and muscle tone e.g. walking, hand-eye coordination, etc) Peripheral Nervous System (Section 9.1) The peripheral nervous system (PNS) resides or extends outside the central nervous system (CNS) - brain and spinal cord. main function of the PNS is to connect the CNS to the limbs and organs. PNS is not protected by bone or by the blood-brain barrier, leaving it exposed to toxins and mechanical injuries. divided into: o the somatic nervous system (voluntary) – sensory system- brings info from sensory receptors to CNS, and motor system- carries signals from CNS to target cells o the automatic (involuntary) nervous system – sympathetic – increase energy expenditure, and parasympathetic – increase activity of energy concerving activities (saves energy) both consits of a collection of nerve cells Nerve Cells: The nervous system includes two main types of cells: o Neurons = conduct messages; identified as excitable. Specialized for transmitting chemical and electrical signals from one location in the body to another. o Supporting cells = (glial and Schwann cells) provide structural reinforcement as well as protect, insulate, and assist neurons; identified as non-excitable (nonconducting) Structure of the Neuron: All neurons contain three parts: o Dendrites: receive info form sensory receptors or other nerves and conduct impulse to cell body; short and extensively branched o Cell body: (aka Soma) contains nucleus, organelles and cytoplasm. The cell body of most neurons are located in the CNS (others in ganglia) o Axon: extension of cytoplasm: carries impulse away from cell body to other neuron or effector; branched into synaptic terminals Many axons are covered by a fatty protein called the myelin sheath = insulation of nerve impulse (these axons are said to be myelinated) Myelin sheath is formed from specialized glial cells called Schwann cells *purpose is to prevent loss of charge – insulate Areas between the myelin sheath = nodes of Ranvier. The nerve impulse actually jumps from node to node (speeding impulse) see diagram on next page All PNS nerves have a thin membrane called the neurillemma = promotes regeneration of damaged axons. Some nerve cells within the brain and spinal cord do NOT have myelin or neurillemma (celled grey matter), therefore these cells are incapable of regeneration. Damage to these cells is permanent. There has been some success with reattaching and regenerating nerves. Stem cell research has also led to new possibilities for neuron regeneration. *See pg. 415 for more info. There are three major classes of neurons: 1. sensory neurons (aka afferent): convey information awy from sensory receptors towards the CNS; most synapse with interneurons 2. motor neurons (aka efferent): convey impulses away from CNS towards efferent cells. 3. interneurons: act as a link between sensory neurons and motor neurons (located predominantly in CNS - the spinal cord and brain) Organization of Neurons Neurons are arranged in groups, or circuits, of two or more kinds of neurons: Complex circuits = like those associated with most behaviours) involve integration by interneurons in the CNS Convergent circuits = messages from several neurons come together at a single neuron; permits integration of information from several sources Divergent circuits = messages from a single neuron spreads out to several neurons; permits transmission of information from several sources Reverberating circuits = circular circuits in which the signal returns to its original source; believed to play a role in memory storage Reflex Arc = simplest circuit (group arrangement)/pathway does not involve the brain = very quick involves synapses between sensory neurons and motor neurons (e.g. knee jerk reflex) Nerve body cells are also often arranged into clusters, which allow for the coordination of activities by only a part of the nervous system o a nucleus is a cluster of nerve cell bodies within the brain o a ganglion is a cluster of nerve cell bodies in the peripheral nervous system The Electrochemcial Impulse (Section 9.2) Neurons send messages using electrical charges (ions) Electrochemical gradient across the membrane creates a voltage potential across the membrane The electrical nature of the nervous system was first identified by Luigi Galvani (1910) o During experiments he discovered that the leg muscle of a dead frog could be made to twitch by electrical stimulus HOW? Nerve cells have a rich supply of negative and positive ions in and outside of the cell, but the ion concentration are dissimilar in the inner and outer environments The membrane of the nerve cell however, is permeable to only SOME ions in the solution – opportunity for an electrochemical gradient Formation of the electrical impulse Signal transmission along neurons depends on voltage potentials created by ionic imbalance across the membrane Ranges from – 50 to -100 mV (millivolts) in animals 1. Resting Neuron: the membrane of a neuron at rest is said to be charged (polarized) because of a potential difference across the membrane (called the resting potential) neuron has a rich supply of positive and negative ions within and outside of the cell, but membrane is impermeable to negative ions (stay on inside of cell) potential difference is created by an unequal concentration of positive ions on both sides of the membrane o high concentration of K+ inside o high concentration of Na+ outside resting membrane is more permeable to K+, thus more K+ ions leave than Na+ ions enter – inside becomes more negative active transport by sodium-potassium pump help maintain this gradient (i.e actively pumps K+ into cell) resting potential = -70mV (millivolts) 2. Stimulation of the nerve leads to depolarization the action potential (nerve impulse) is the rapid change in the membrane potential of an excitable cell, caused by stimulus triggered opening/closing of voltage-gated ion channels o stimulus causes Na+ ion channels to open, allowing Na+ to rush back into cell (concentration gradient) – increases membrane permeability to Na+ o Once the voltage inside the cell becomes positive the ion channels slam shut! o Depolarization = diffusion of sodium ions into cell resulting in a charge reversal o Sodium-potassium pump restores resting potential o Repolarization = process of restoring the original polarity pf the nerve membrane The action potential moves in a wave of polarization down the axon (nerve fibre) o See figure 7, p. 421 for direction of movement of action potential Threshold potential = a stimulus must be a above a critical intensity and duration to stimulate a nerve o Vary with the type of neuron o Increasing the intensity of the stimulus will NOT increase the speed of the transmission nor the intensity of the response (all or nothing response) o Different intensities of stimulus are detected because: Different neurons have different thresholds Frequency of the stimulus changes Refractory period = brief interval of time following the firing of a neuron which it is incapable of a second response (waiting period) Synaptic Transmission Active potential down the axon, but then what? There are small spaces between neurons, or between neurons and their effectors (i.e muscle cells), called synapses (synaptic cleft) A single neuron may branch many times a tits end plate (axon terminals) and join (make connections with) many different neurons Small vesicles containing chemicals called neurotransmitters are located in the end plates of axons. When the nerve impulse reaches the end of the axon it causes the chemicals to be released into the synaptic cleft. Chemicals diffuse across synapse to the dendrites of the next neuron causing a depolarization in that neuron..signal continues Note: the neuron that releases the chemicals is called a presynaptic nerve, while the neuron after the synaptic cleft is called the postsynaptic nerve. Neurotransmitters Allow neurons to communicate across synapses: Acetylcholine = acts as an excitatory neurotransmitter causes Na+ channels to open in postsynaptic neuron resulting in depolarization How does this stop? Cholinesterase = is an enzyme released from the postsynaptic membrane to destroy acetylcholine – Na+ channels closed