Nervous System Nervous Tissue &Brain Structure of Nervous System CNS (Central Nervous System) Includes: Brain in cranium Spinal Cord enclosed in spinal cavity Peripheral Nervous System Located outside CNS and consists of nerves that connect the CNS with the rest of the body Functions of the Nervous System: 1. Sensory Function Gather information from inside the body and the outside environment Nerves carry the information to the CNS 2. Integrated Function Sensory information brought to CNS is processed or interpreted 3. Motor Function Motor nerves convey info. from CNS toward the muscles and glands of the body Motor nerves carry out plans made by the CNS Information must travel along the motor nerves from CNS to all the skeletal muscles Micro: Cells of the Nervous System Neuroglia (glial cells) nerve glue most abundant of nerve cells Miotic cells often give rise to brain tumors most are located ion CNS Function: support, protect, insulate, nourish, and generally care for the delicate neuron Some participate in phagocytosis Some assist in secretion of Cerebro-spinal Fluid (CSF) DO NOT conduct nerve impulse Most common: Astrocytes and Ependymal cell Neurons Most important in the transmission of information. Enables the nervous system to act as a vast communication network. Many shapes/sizes: some have measured 4 ft long Non-miotic: do not replicate nor replace themselves when injured Generally do not give rise to malignant brain tumors Parts of a Neuron: Dendrite - Tree-like structures that receives information from other neurons and then transmit the information towards the cell body One neuron may have thousands of dendrites Cell Body contains the nucleus and is essential for the life of the cell Axon long extension that transmits information away from the cell body Myelin Schwann Cells peripheral nervous system Oligodendrits CNS Nodes of Ranvier Axon Terminals extensive branching at the end of the axon store neurotransmitters Structures: Axon Myelin Sheath white fatty material covering most long nerve fibers of the peripheral and central nervous system Protects/insulates the axon myelination begins at the fourth month of fetal life teenage yrs. EX. Movement of an infant are much slower and less coordinated than that of an older child Ex. restricting fat intake of children is unwise because they are still laying down myelin Formation is different in peripheral and central nervous system Neurilemma Layer of specialized cell around the myelin sheath that are called Schwann cells specific to the peripheral nervous system Schwann cells form the myelin sheath Neurolemma is important in the regeneration of a severed nerve Nodes of Ranvier Areas of axon not covered by myelin, appear regularly along axon 7 Types of Neurons Sensory Neuron (afferent neuron) carries information from the periphery toward the CNS Motor Neuron (efferent neuron) carries information from the CNS toward the periphery Sensory/Motor Neuron are found in both CNS and the peripheral nervous system Interneuron Forms the connections between the sensory and the motor neurons Play a role in thinking, learning and memory To Remember: S Sensory A Afferent M Motor E Efferent White Matter Vs Gray Matter! White Matter is white because of the myelin Myelinated fibers are gathered together in the CNS tracts Gray Matter Composed of primarily cell bodies, interneuron, and unmyelinated fibers What is a nerve impulse? Think of how fast the information from a stubbed toe travels? Nerve Impulse: an electrical signal that conveys information along a neuron. Caused by a series of events called Action Potential process of polarization, depolarization and repolarization electrical charge inside the cell moves from its negative(-) resting state to its positive depolarized state (+) and back to its negative resting state (-) 12 Polarization: Resting State When a neuron is polarized.... I ntracellular composition is more (-) than outside the neuron As long as neuron is polarized, no nerve impulse is being transmitted k+ and fewer anions are pumped into the neuron by an ATP-driven pump K+ tends to leak out of the cell, decreasing positive charge Decreased (+) charge and the trapped anions in the cell make the intracellular more (-) = polarized! Depolarization : Stimulated When a neuron is stimulated.... A change occurs in the cells electrical state... The inside of the cell becomes more positive Neuronal membrane allows Na+ to cross the membrane into the cell (diffuses into the cell) As the cell changes from (-) to (+) = depolarized! 13 Repolarized: Recovery Quickly, the inside of the cell becomes more (-)...returning to its resting state....repolarization! Neuronal membrane undergoes a second change: stops additional diffusion of Na+ into the cell allows K+ to diffuse out of the cell, leaving (-) charged ions to remain inside cell outward movement of K+ causes repolarization! Refractory period - is when the cell is unable to accept another stimulus until its repolarize! The changes associated with the action potential (nerve impulse) are due to specific ions across the cell membrane of a neuron. 14 Speedy Nerve Impulse: Myelination affects speed... nerve impulse arrives at axon but can not develop on any part that is covered w/ myelin... it is conducted at the Nodes of Ranvier (bare axonal membrane) Nerve impulse jumps from node to node to the end of axon saltatory conduction Saltatory conduction increases speed in which the impulse travels along the nerve fiber = why myelinated fibers are considered fast conductors 15 Across the Neurons: Synapse = space Synaptic cleft is caused because the axon terminal of the neuron does not physically touch the dendrite of another Neurotransmitters: Axon terminals contain vesicles that store chemicals (neurotransmitters) Most Common: ACh (acetylcholine) & norepinephrine Other CNS transmitters: epinephrine, serotonin, glutamate, GABA (gamma-aminobutyric acid), endorphins 16 Inactivators - are substances that terminate the activity of the neurotransmitters after they have completed their task EX. Acetycholinesterase terminates ACh Receptors - dendrites of a neuron contain receptor sites on the cell membrane where neurotransmitters attach Each receptor site is specific to a neurotrasmitter (accepts only the transmitters that fit) 17 1. Nerve impulse travels along neuron 2. Impulse causes the vesicles to fuse with the axon terminal membrane 3. Vesicles open and release neuro- transmitter into synaptic cleft 4. Neurotransmitter diffuses across synaptic cleft and binds to the receptor sites on the dendrite cell membrane 5. Membrane change is responsible for the formation of a new nerve impulse in the dendrite of the second neuron 6. The nerve impulse travels toward the cell body and the axon of the second neuron Events at the Synapse: 18 19 Brain: Structure & Function Brain is located in the cranial cavity Only 2% body weight - yet requires 20% of oxygen supply Glucose is the primary source of energy for the brain EX. Hypoglycemia effects include mental confusion, dizziness,convulsions, LOC, and death Divided into four major areas: Cerebrum, Diencephalon, Brain Stem, Cerebellum 20 Cerebrum: Largest part of the brain Divided into Rt and Lft Cerebral hemispheres Joined together by the corpus callosum - bands of white matter that form a large fiber tract - allows rt/lft hemispheres to communicate Each hemisphere has four major lobes: frontal, parietal, temporal, occipital What Matters? Cerebral Cortex - thin layer of gray matter on the outermost portion of the cerebrum, composed of primarily cell bodies and interneurons (Gray Color- no myelin sheath) Allows for high performance tasks; learning, reasoning, language, memory White matter - most of the cerebrum located directly below cortex and composed of myelinated axons (white color) forms connections between parts of brain and spinal cord 20 21 Markings! Surface of the cerebral cortex has bumps (convolutions)and grooves (sulci) Formed by folding arrangement of the cerebral cortex - this pattern increases the amount of cerebral cortex (thinking tissue) Intelligence is related to the amount of cerebral cortex and to the number of convolutions/sulci - more intelligent species EX. Humans have more than elephants 21 22 Lobes of the Cerebrum 22 23 Frontal Lobe: Frontal Lobe: plays a key role in: voluntary motor activity, personality, emotional and behavioral expression high-level tasks, learning, thinking, making plans Primary motor cortex - where nerve impulses originate for voluntary muscle movement Each body part is controlled by a specific area of the cerebral cortexEach body part is controlled by a specific area of the cerebral cortex Complicated movements require more brain tissueComplicated movements require more brain tissue EX. The movements of the hand are much more delicate than movements of the foot...there is more brain tissue devoted to the hand than the foot! - Brocas area: motor speech, movements of the mouth/tongue to form words - Damage to this area (stroke/infarct) person develops a type of aphasia (know what they want to say - but cant say it) - Frontal eye field: controls voluntary movements of the eye Decussation - is the crossing over of fibers, when the fibers from one side of the brain innervate the opposite side of the brain. Explains rt sided paralysis or left sided paralysis 24 Parietal Lobe: Primary Somatosensory area Primarily concerned with receiving general sensory information from the body: from skin and muscles sensations of temperature, pain, light touch, proprioception (sense of where your body is) concerned w/ reading, speech, taste 24 25 Temporal Lobe Primary auditory cortex - area that allows hearing - temporal lobe damage causes cortical deafness Olfactory area - receives information from nose Taste buds - areas on the tongue that send sensory information to both temporal and parietal lobes Wernickes area - is a broad region that is located in the parietal and temporal lobe - concerned with the translation of thought into words Damage to this area result in severe deficits in language comprehension 25 26 Occipital Lobe Located in the back of the head - underlying the occipital bone Visual cortex - receives sensory information from the eyes - where it is interpreted as sight Concerned with many visual reflexes and vision-related functions (reading) Damage to this area causes cortical blindness 27 Functions involving Many Cerebral Lobes Speech Area: Includes many areas of the brain - usually located in the left hemisphere Allows you to understand words, written and spoken - after you gather your thoughts Brocas area directs the muscles to speak Association Area: Large areas of the cerebral cortex Areas concerned with analyzing, interpreting and integrating information EX. Primary auditory cortex collects info from the ear - surrounding area (auditory association area) identifies and gives meaning to the sound Patches of Gray: scattered throughout cerebral white matter are patches of gray matter (basal nuclei) helps regulate body movements and facial expressions Neurotransmitter (dopamine) responsible for the activity of basal nuclei Parkinsons- deficiency of dopamine characterized by problems with movement,rigidity,slow speech,drooling, mask-like facial expression Treatment with dopamine or dopamine-like drugs usually used to treat symptoms 27 28 Diencephalon Located beneath the cerebrum and above the brain stem Thalamus Relay station for most sensory fibers traveling from the lower brain and spinal cord to the sensory area of the cerebrum EX. when a pain stimulus reaches the thalamus -we are then aware of pain...as the input moves from thalamus to cerebrum we are then aware of the exact location and type of pain Hypothalamus located directly below the thalamus helps regulate many body processes: body temperature, water balance, metabolism helps regulate functions of the autonomic (involuntary) nerves, has an effect on blood pressure and respirations Pituitary - located under the hypothalamus Function is controlled by hypothalamus Affects directly/indirectly almost every hormone in the body 28 29 Brain Stem Connects spinal cord w/ higher brain structures Midbrain - extends from the lower diencephalon to the pons relays sensory and motor information reflex centers for hearing and vision Pons (bridge) - extends from midbrain to the medulla oblongata Acts as a bridge for information Plays an important role regulating breathing Medulla Oblongata - connects the spinal cord with the pons relays sensory and motor information Control heart rate, blood pressure and respiration Vital Center 29 30 Medulla Oblongata-cont. Extremely sensitive to certain drugs: Narcotics - an overdose of opioids depresses the medulla oblongata (resp center) possibly causing death Vomiting center (emetic center) located in the medulla oblongata can be activated either directly or indirectly Direct activation: stimuli from the cerebral cortex (fear), from sensory organs (bad odors,pain, distressing sights), signals from equilibrium of inner ear (spinning) Indirect activation: signal from digestive tract via the vagus nerve 30 31 Cerebellum Concerned with coordination of voluntary muscle activity Integrates all the incoming information to produce a smooth,coordinated muscular response Damage to the cerebellum produces jerky muscle movements and difficulty maintaining balance - they may appear intoxicated 32 33 Structures Across Divisions of the Brain Limbic System: The emotional brain Parts of the cerebrum and the diencephalon Functions emotional states and behaviors: when the limbic system is stimulated by microelectrodes extreme pleasure or rage can be induced Memory Area: Memory is the ability to recall thoughts and images Includes frontal,parietal,occipital, and temporal lobes, the limbic system and the diencephalon short-term memory:lasts seconds to few hours long-term memory: lasts years to decades 34 Reticular Formation: Sleep-wake cycle and consciousness special mass of gray matter extends through the brain stem into the cerebral cortex signal from the reticular formation to the cerebral cortex stimulates us - keeping us awake and tuned in very sensitive to the effects of medication and alcohol EX. combination of benzodiazapines (tranqilizers) and alcohol can damage the reticular formation causing permanent unconsciousness Consciousness is a state of wakefullness - depends on the RAS (reticular activating system) Different LOC: alertness,attentiveness,relaxation unattentiveness Consciousness/Sleep/Coma 35 Sleep occurs when the RAS is inhibited or slowed - cause of sleep? we do not know! Stages of sleep: REM, NREM Sleep progresses from 4 stages of NREM to REM REM (rapid eye movement)- fluctuating BP, P, R, Most dreaming occurs in REM sleep REM sleep deprivation can lead to mental/physical distress Coma is a sleep-like state with several stages ranging from light to deep coma Light coma - some reflexes are intact; patient may respond to light,sound,sound, touch and painful stimuli Deep coma -these reflexes are gradually lost Damage to the RAS is associated w/ a state of deep coma- can be permanent 36 Protecting the Central Nervous System CNS has an elaborate protective system Protects the delicate brain and spinal cord from injury - neuronal tissue can not be repaired. Consists of four structures: 1. Bone 2. Meninges 3. CSF (cerebro-spinal fluid) 4. Blood-brain barrier 36 37 Bone cranium - encases brain Vertebral column - encases spinal cord Meninges 3 layers of connective tissue surround the brain and spinal cord Dura Mater - thick, tough outermost layer of connective tissue Subdural space - space beneath the dura mater Arachnoid layer- middle, spiderweb-like layer Subarachnoid space - space between arachnoid layer and the pia mater CSF circulates in this space and cushions the rain and spinal cord Pia mater - very thin inner most layer membrane contains blood supply an directly covers the brain and spinal cord 37 38 To Remember: Meninges form a brain PAD P Pia Mater A Arachnoid layer D Dura Mater Meningitis : inflamed or infected meninges, very serious because it could easily reach the brain sometimes causing irreversible brain damage. Lumbar puncture - retrieval of CSF, able to identify bacterial or viral organism 39 CSF Cerebrospinal Fluid CSF is formed within ventricles of the brain by the choroid plexus - the rate in which CSF is formed must equal the rate in which is drained Clear fluid similar in composition to plasma composed of water,glucose,protein, and ions (NA+, Cl-) Protects, cushions the brain from jarring Delivers nutrients to brain and removes waste Blood-brain Barrier Arrangement of cells - glial astrocytes associated with the blood vessels that supply the brain and spinal cord cells select the substances that enter the CNS from the blood - O2 and glucose are readily accepted and block potentially harmful substances Not all harmful substances are blocked EX. Alcohol 39