Three major functions: 1. Receive sensory input Gather info by monitoring changes or stimuli from inside & outside body 2. Integration of input Process & interpret sensory input & determine action 3. Motor output Carry out response decided by integration usually by muscles (movement) or glands (secretion) Two major parts of nervous system: Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) All nerves (spinal & cranial) outside of CNS Two components: Sensory (afferent) division Info going TOWARD CNS Motor (efferent) division Impulses EXIT from CNS Two subdivisions of motor (efferent): Somatic nervous system voluntary Conscious control of skeletal muscles Autonomic nervous system - involuntary Controls smooth/cardiac muscle & glands Two subdivisions of autonomic that often bring about opposite effects: Parasympathetic stimulate rest & digest activities Ex: stimulate flow of saliva Sympathetic stimulate flight or fight activities Ex: inhibit flow of saliva Classified into two types of cells: 1. Neurons transmit nerve impulses; no cell division (amitotic) 2. Support cells (called neuroglia or glia) that can not transmit nerve impulses; cell division (mitotic) a.Astrocytes b.Microglia c.Ependymal cells d.Oligodendrocytes e.Satellite cells f.Schwann cells Central nervous system (CNS) Peripheral nervous system (PNS) Also known as nerve cells Structure allows them to receive & transmit messages or impulses All have same basic structures Cell body usual cell organelles including nucleus except no centrioles (no mitosis) Processes/fibers arms that extend to/from body To body = dendrites (1-100s) From body = axon (only 1) Must know cell parts: Soma - cell body Nucleus metabolic center of cell Dendrite(s) one or more processes that conducts impulses TOWARD cell body Axon hillock where cell branches out to axon Axon process that conducts impulses AWAY from cell body Myelin whitish, fatty substance found on long axons in CNS; speeds up transmission rate Schwann cells cells that myelinate axons in PNS Myelin sheath membranes wrapped around myelin Nodes of Ranvier gaps in between Schwann cells Axon terminal branched end of axon in which neurotransmitters are stored in vesicles Large concentrations of cell bodies in CNS are in clusters & called nuclei Small concentrations are called ganglia (pl) or ganglion (sing) found in CNS & PNS Bundles of nerve fibers in CNS called tracts, but in PNS are called nerves Myelinated nerve fibers/tracts in CNS called white matter Unmyelinated fibers and cell bodies called gray matter Three types of neurons based on function or direction of nerve impulse: Sensory (afferent) neurons Carry impulses from sensory receptors TOWARD CNS Nerve endings pain & temperature receptors Meissners corpuscle touch receptor Pacinian corpuscle deep pressure receptor Proprioceptors stretch or tension in tendons & muscles Motor (efferent) neurons Carry impulses FROM CNS to organs or muscles Association neurons/interneurons Connect motor & sensory neurons (afferent) (efferent) Three types of neurons based on structure or how many processes extend from body Unipolar Single, very short process from cell body Immediately breaks into peripheral & central axon Unique: dendrites at peripheral end, so axon conducts impulses away and TO cell body Bipolar One axon, one dendrite Very rare, only seen sense organs (eye & nose) Act as receptor cells Multipolar Several processes extend from cell body All motor neurons are multipolar so they are most common Star-shaped Account for ~ 50% of neural tissue Form living barrier between capillaries & neurons therefore make exchanges between them Help protect neurons from harmful substances Pick up extra ions Recapture released neurotransmitters Spiderlike phagocytes (cell eaters) Dispose of debris like dead brain cells & bacteria Covered with cilia Line cavity of brain & spinal cord Beating of cilia help circulate cerebrospinal fluid that fills brain & spinal cord cavity Forms protective cushion around CNS Wrap flat extensions tightly around nerve fibers Produces fatty insulating covering of axons called myelin sheaths in CNS Form myelin around axons in PNS Protective, cushioning cell body in PNS neuron has two distinct properties that differentiate it from any other cell in human body: Irritability - ability to respond to stimuli & convert it to a nerve impulse conductivity - ability to transmit an impulse to other neurons, muscles, or glands Most CNS neurons receive chemical stimulus at plasma membrane (everywhere on neuron), transmits it as electrical signal along axon, & ends as chemical signal at axon terminals Most PNS neurons (sensory organs) receive stimulus as light (eyes), sound waves (ears), pressure (touch), or chemicals (taste & smell) plasma membrane is where nerve impulse begins Plasma membrane at rest is polarized fewer positive ions (K + ) are inside cell than positive ions (Na + ) outside cell More negative (Cl - ) ions inside cell than outside Na + K+K+ K+K+ K+K+ K+K+ K+K K+K+ K+K+ K+K+ K+K a stimulus depolarizes neurons membrane by opening up Na+ gates on membrane, allowing Na+ inside initial exchange of ions is a local depolarization Inside is more + than outside Depolarization starts an action potential in entire neuron Once action potential (nerve impulse) starts, its propagated over entire axon (all or nothing principle) K+ ions rush out of the neuron after Na+ ions rush in, which repolarizes the membrane Na+/K+ pump on membrane restores original configuration by shoving Na+ back out and allowing K+ back in requires ATP outsiders INSIDERS Impulse travels faster when fibers have a myelin sheath Once electrical action potential reaches axon terminals, excites vesicles containing neurotransmitters Vesicles move toward axon terminal membrane & releases neurotransmitter into synaptic cleft Neurons NEVER touch other neurons Neurotransmitters bind to receptors on neighboring neurons dendrites New action potential will start on THAT one The human body uses 50 different neurotransmitters depending on the need Neurotransmitters either excite or inhibit neurons Many drugs act to mimic the effect of neurotransmitters on the brain NameFunction Result from DEFICIT Result from EXCESS AcetylcholineMuscle action, learning, memory Alzheimers, paralysis Muscle spasms EndorphinsDiminish pain sensation, increase pleasure Emotionally unstable, depression Addiction, little pain sensation NorepinephrineAlertness, arousal (flight or fight) Slight depressionAnxiety, panic attacks, rapid heartbeat, nausea, dizziness DopamineMovement, learning, attention, emotion Parkinsons, schizophrenia Schizophrenia SerotoninMood, hunger, sleep, arousal Depression, anxiety, OCD None GABAInhibits nervous system Seizures, tremors, Huntingtons, insomnia Increase blood pressure & heart rate GlutamateMemorySchizophreniaMigraines, seizures, ALS Much communication between neurons on everyday basis is done via reflexes Reflex : rapid, predictable, involuntary responses to stimuli Reflex always occurs in same manner using same neural pathways of both CNS & PNS so they are called reflex arcs Two types of reflexes: Somatic : stimulates skeletal muscles Ex: pull hand away from hot object, blinking when air burst aimed at eyes Autonomic : regulate smooth & cardiac muscles, & glands Ex: secretion of saliva, change in pupil size Reflex arcs have at least 5 elements involved in same arc or pattern: 1. Sensory receptor react to stimulus 2. Sensory neuron connect receptor & CNS 3. Integration center connect neurons 4. Motor neuron connect CNS & effector 5. Effector organ muscle/gland to be stimulated patellar (knee-jerk) reflex is simplest type of reflex two neurons involved Withdrawal reflex (remove from painful stimulus) is more complicated three neurons involved utilizing association neuron Average adult brain weighs 3 lbs Divided into 4 regions: 1. Cerebrum largest region, broken into left & right hemispheres 2. Diencephalon interbrain atop brain stem 3. Brain stem stalk on which brain sits, connects to spinal cord 4. Cerebellum bulbous projection at occipital region, broken into two hemispheres Made of two hemispheres together called cerebrum Encloses other three parts of brain Entire surface made of peaks and valleys Gyrus (gyri) peaks of ridges Sulcus (sulci) shallow valleys Fissures deep grooves separating large regions Function of cerebrum is vast speech, memory, logical & emotional response, consciousness, interpretation of sensation, voluntary movement Sulci & fissures divide cerebrum into lobes (named after cranial bones) Parietal lobe Frontal lobe Temporal lobe Occipital lobe Parietal Lobe Somatic sensory area located just posterior to central sulcus receives & interprets impulses from bodys sensory receptors (NOT special senses) Pain, cold, light touch Spatial map depicting region on body where senses come from and how much brain power is devoted to them is called sensory homunculus Model depiction showing areas of body given more brain power than others Sensory pathways are crossed pathways, meaning left side of brain receives impulses from right side of body & vice versa Itch on right hand interpreted on left side of somatic sensory area. Occipital lobe Visual area located in posterior part Visual cortex sees Visual association area ties object to memories, knowledge Temporal lobe Auditory area bordering lateral sulcus Auditory cortex hears Auditory association area ties sound to object or knowledge Olfactory (smell) area deep inside Frontal lobe Contains primary motor area, just anterior to central sulcus, which allows us control of skeletal muscles Spatial map region called motor homunculus Brocas area located in left hemisphere gives ability to speak Higher intellectual reason Socially acceptable behavior Language comprehension Gustatory complex (taste) Two layers of cerebral hemisphere: Gray matter (cerebral cortex) Outermost layer made out of cell bodies of neurons (no myelin) Ridges allow greater surface area, increasing amount of neurons Several islands of gray matter that jut inward called basal ganglia White matter Deeper cerebral layer made from fiber tracts (bundles of nerve fibers) Major tract called corpus callosum connects right & left cerebral hemisphere AKA interbrain, made of 3 areas: Thalamus relay station for sensory impulses going up to sensory cortex Get rough idea if sensation will be pleasant or unpleasant sensory cortex figures it out Hypothalamus regulates body temperature, water balance (thirst), metabolism (appetite), sex, pain, pleasure, pituitary gland Pituitary gland is attached & secretes hormones Epithalamus pineal gland (secretes hormones) & choroid plexus (knots of capillaries that form cerebrospinal fluid) Made of 3 structures: Midbrain reflex centers for vision & hearing Pons fiber tracts that control breathing Medulla oblongata control heart rate, blood pressure, breathing, swallowing, vomiting Many small gray matter areas that control breathing, blood pressure Running along length is reticular formation which regulates consciousness, awake/sleep cycles Damage here results in permanent unconsciousness or coma Two hemispheres & wrinkly (convoluted) surface Outer cortex is gray matter while inner region is white matter called arbor vitae (tree of life) Provides timing for muscle activity, controls balance & equilibrium Constantly monitors body position & makes adjustments to keep balance As nervous tissue is very soft and delicate, injury to irreplaceable neurons can be catastrophic Three methods of protection: Bony skull & vertebral column Membranes Cerebrospinal fluid Three connective tissue membranes called meninges cover & protect CNS Top: Dura mater (tough mother) Periosteal layer (touches skull) Meningeal layer Middle: Arachnoid mater (spider mother) Looks like a cobweb Bottom: Pia mater (gentle mother) Clings gently but tightly to brain surface Watery broth similar to blood plasma Constantly formed by choroid plexuses Little protein, lots of vitamin C, lots of ions Always circulating among ventricles, canals, & aqueducts in brain Spinal tap removes CSF from lumbar area Brain can not handle tiniest fluctuations of chemicals (all kinds) as other organs can As result, neurons are kept separated from blood borne substances by blood-brain barrier which is composed of least permeable capillaries in human body Only water, glucose, essential amino acids, fats, respiratory gases, and fat-soluble alcohols, nicotine, caffeine, and anesthetics can pass Metabolic wastes (urea), toxins, proteins, most drugs are prevented Nonessential amino acids & K, are always pumped from brain The other component of CNS, its a two-way conduction pathway from PNS & brain composed of neurons with long axons Reflex center where reflexes are determined 17 long spinal cord is continuation of brain stem ending at L2 Starting at L3, branched into 31 pairs of spinal nerves exit vertebral column called cauda equina (horses tail) Cervical 8 pairs Thoracic 12 pairs Lumbar 5 pairs Sacral 5 pairs Covered by meninges for protection Gray matter of spinal cord resembles butterfly Posterior projections = posterior/dorsal horns Anterior projections = ventral/anterior horns Gray matter surrounds central canal which contains CSF Spinal (nerve) fibers entering spinal cord White matter composed of myelinated fiber tracts Divided into three regions: posterior, lateral, anterior columns Two types of tracts Sensory/afferent tracts: conduct sensory impulses TO the brain Motor/efferent tracts: carry impulses FROM brain to skeletal muscles Consists of nerves & scattered groups of ganglia found outside CNS Nerve is bundle of neuron fibers not in CNS Neuron fibers (processes) surrounded by endoneurium Groups of fibers bound by perineurium Whole bundles called fascicles Fascicles bound together by epineurium Nerves carrying both sensory & motor fibers called mixed nerves All spinal nerves are mixed Sensory (afferent) nerves toward CNS Motor (efferent) nerves away from CNS Cranial nerves 12 pairs that serve head and neck Spinal nerves 31 pairs formed by both dorsal & ventral roots of spinal cord Ventral rami (extension) forms four plexuses (network of nerves) which are both sensory & motor Four nerves to know: Sciatic nerve part of sacral plexus Largest nerve in body Serves lower trunk & posterior thigh/leg Inflammation or damage causes sciatica Median nerve Part of brachial plexus Allows flexion of forearm & some hand muscles Pressure on nerve from tendon causes carpal tunnel syndrome Inability to pick up small objects, fine motor control VII Facial nerve 7 th cranial nerve Serves muscles for facial expression, salivary & lacrimal (tear ducts) glands, taste buds Weakening or paralysis causes Bells palsy Vagus Nerve X or 10 th cranial nerve Latin for wandering nerve Controls heart, lungs, stomach, large intestines, spleen, kidney! Involuntary motor branch of PNS that controls smooth muscles, cardiac muscles, glands Information from CNS activates nerves that release neurotransmitters which then signal appropriate muscle/gland Recall two divisions of ANS that have opposite effects: Sympathetic extreme situations (fear, exercise, rage) Parasympathetic rest & conserve energy Three neurotransmitters in ANS: Acetylcholine both sympathetic & parasympathetic Epinephrine sympathetic division Norepinephrine sympathetic division Formation Nervous system formed during first 4 weeks of embryonic development Maternal infection or poor health habits may cause permanent damage Measles causes deafness Smoking decreases oxygen causing low birth weight, others Drugs (OTCs & illegal) can permanently damage Maturation Last areas of CNS to mature is hypothalamus Preemies have problems controlling body temperature Throughout childhood, no neurons grow but in fact become myelinated, allowing neuromuscular control Aging Brain at maximum weight as young adult Next 60+ years, neurons get damaged & die Other unused pathways can take over & be developed Sympathetic nervous system becomes less efficient Premature shrinking of brain occurs when individuals accelerate normal process with lifestyle Boxers, alcoholics, drug abusers Huntingtons Disease Dominant genetic disease (one dominant allele needed) for 50% chance of acquiring it Strikes in middle age (around 50) Massive degeneration of basal nuclei then cerebral cortex Initial symptoms are wild, jerky movements termed chorea (Latin for dance) Usually fatal within 15 years of onset Treated with neurotransmitter (dopamine) blockers Parkinsons Disease Degeneration of dopamine-releasing neurons in substantia nigra (in midbrain) so basal nuclei dopamine targets becomes overactive, causing tremors First sign is pill-rolling tremor of hand Treatment with L-dopa drugs helps some symptoms, but after more neurons are affected, it is ineffective Newer (albeit controversial) treatments include transplanting embryonic substantia nigra tissue, or genetically engineered (stem cells), or cells from fetal pigs Alzheimers Progressive degenerative disease that results in dementia (mental deterioration) Nearly 50% of all people in nursing homes have Alzheimers Begins with short-term memory loss, short attention span, disorientation, loss of language Result of shortage of acetylcholine & structural changes in brain (areas of cognition & memory) Microscopy of tissue shows abnormally large deposits of protein About 5-15% of people over 65 will get this Stroke (Cerebrovascular Accident/CVA) Blood circulation to brain area is blocked resulting in tissue death Blood clot Ruptured blood vessel Area of tissue is initially located by looking at patients symptoms Left cerebral hemisphere results in aphasia (language impairment) Severe strokes kill 2/3 people almost immediately, and remaining 1/3 die within 3 years Mild strokes do not cut off blood flow completely Called temporary brain ischemia or transient ischemic attack (TIA) Not permanent but offer warning signs of CVA later Spinal Cord injuries (SCI) & Paralysis Any damage to the spinal cord resulting from crushing or severing. Cervical injuries Cervical (neck) injuries usually result in full or partial tetra/quadriplegia. Thoracic injuries Injuries at or below the thoracic spinal levels result in paraplegia. T1 to T8 : inability to control the abdominal muscles. T9 to T12 : partial loss of trunk and abdominal muscle control. Lumbar and sacral injuries Decreased control of the legs and hips, urinary system, and anus. There are about 11,000 new cases of spinal cord injury in the U.S. every year. Males account of 82% of all spinal cord injuries and females for 18%. Multiple Sclerosis Autoimmune disease in which myelin sheaths around axon fibers in CNS are gradually destroyed by own immune system Myelin converts to hardened sheaths called scleroses Lack of insulation leads to inability to control muscles Treatment today includes hormone-like substance called interferon Will result in complete inability to function Meningitis Inflammation of meninges due to viruses or bacteria Can be life threatening since can spread to nervous tissue of CNS Diagnosed by spinal tap to look at CSF EEG (electroencephalogram) Assess electric activity of brain impulses Many electrodes are placed on scalp and measurement of activity pattern is recorded Used to diagnose epileptic lesions, tumors PEG (pneumoencephalography) Detection of hydrocephalus (water on brain) Cerebrospinal fluid is drained via spinal tap, air is injected into subarachnoid space Provides clear picture of ventricles Extremely painful for patients recovery takes 2-3 months for CF to return back to normal Not used since 1980s Cerebral angiogram Used to assess condition of cerebral arteries Dye is injected into artery & disperses into brain X-ray is then taken which highlights dye so blood flow can be assessed Stroke victims Computed (Computer- Aided) Tomography (CT or CAT) scan Series of X-rays grouped together by a computer. Used to see tumors, lesions, MS or Alzheimers plaques, infarcts (dead brain tissue) Important in mapping brain prior to surgery MRI scan (Magnetic Resonance Imagery) Used to see tumors, lesions, MS or Alzheimers plaques, infarcts (dead brain tissue) Similar to CT scan but 3D image capabilities PET scan (Positron Emission Tomography) Used to determine sugar (glucose) uptake/usage of cells Faster growing cells (cancer) use sugar faster Active brain areas also use sugar faster Alzheimer, Parkinson, epilepsy, tumors, dementia Patient drinks glucose solution, areas of fast uptake show up on image