Compendium Review Five -- Nervous Function

Katie Meyers

Compendium Five – Nervous Function

Introduction to the Nervous System

• Nervous System
• 2 parts
• Central Nervous System
• Spinal cord
• Brain
• Peripheral Nervous System
• Contains nerves
• Is made up of 2 systems
• Somatic System
• Autonomic System
• Sympathetic Division
• Parasympathetic Division
• 3 functions
• Nervous Tissue – 2 types
• Neurons
• 3 types
• 3 parts
• Neuroglia

Resting Potential, Action Potential, Synapse

• Resting potential
• Action potential
• Synapse

Sensation

• Sensation
• Sensory receptors
• 2 kinds
• 4 categories
• 3 types
• Specific, or special, senses
• Taste
• Smell
• Vision
• Hearing
• Equilibrium

Drug Abuse

• Drug abuse
• Drug addiction
• 6 most popular drugs
• Alcohol
• Nicotine
• Cocaine
• Methamphetamine
• Heroin
• Marijuana

Introduction to the Nervous System

• Nervous system
• 2 parts

• (found at http://library.thinkquest.org/28807/media/nerve2.gif)
• Central Nervous System (CNS) – consists of brain and spinal cord, both of which are protected by bone (vertebrae and skull, respectively)

• (found at http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19588.jpg)
• Where sensory info is received and motor control is initiated
• Composed of two nervous tissue types – grey matter and white matter
• Grey matter – contains cell bodies and short, nonmyelinated fibers
• White matter – contains tracts – bundles of myelinated axons that run together
• Spinal Cord

• (found at http://www.infovisual.info/03/img_en/024%20Spinal%20cord.jpg)
• From brain base through large opening in skull (foramen magnum) and into vertebral canal formed by openings in the vertebrae
• Provides means of communication between the brain and the peripheral nerves leaving the spinal cord
• If severed, loss of voluntary control and sensation occurs – called paralysis
• Center for thousands of reflex arcs
• Central Canal
• Contains cerebrospinal fluid
• Also contains neurons, motor neurons, and interneurons
• The interneurons communicate with the sensory and motor neurons
• Grey Matter – shaped like the letter “H”
• White Matter – occurs around grey matter; contains ascending tracts that take info to the brain, as well as descending tracts that take info from the brain
• Brain

• (found at http://www.medem.com/MEDEM/images/ama/ama_brain_stroke_lev20_thebraineffectsstroke_01.gif)
• Has four ventricles – two lateral ventricles, third ventricle, and fourth ventricle
• The two lateral ventricles contain the cerebrum
• The third ventricle contains the diencephalon
• The fourth ventricle contains the brain stem and cerebellum
• Cerebrum (also called telencephalon)
• Largest portion of the human brain
• Last center to receive sensory input and carry out integration before commanding voluntary motor response
• Communicates and coordinates with other brain parts
• Has two halves, or hemispheres (remember that it is located in two ventricles)
• Sulci (shallow grooves) separate the hemispheres into lobes
• Four lobes – frontal lobe, parietal lobe, occipital lobe, temporal lobe
• Each lobe is associated with a particular function
• Cerebral cortex – gray matter that covers cerebral hemispheres
• Contains motor, sensory, and associated areas
• Contains the primary motor and somatosensory areas of the brain
• Somatosensory area has primary taste, visual, auditory, and olfactory areas
• Association areas – where integration occurs
• Visual association area – associates new visual info with previously received visual info
• Auditory association area – does the same with auditory info as the visual association does with visual info
• Somatosensory association area – processes and analyzes sensory info from skin and muscles
• Processing centers
• Receive info from other association areas
• Perform higher-level analytical functions
• Central white matter – makes up much of the rest of the cerebrum
• Diencephalon
• Contains hypothalamus and thalamus
• Hypothalamus – regulates hunger, sleep, thirst, body temperature, and H2O balance; control pituitary gland, therefore serving as the link between the nervous and endocrine systems
• Thalamus – is two masses of grey matter on the sides and roof of the third ventricle; is the receiving end for sensory input except for smell
• Also has pineal gland, which secretes melatonin
• Cerebellum
• Has two portions, both of which are made up of primarily white matter
• Receives…
• Sensory input from eyes, ears, joints, and muscles pertaining to the present position in space of parts of the body
• Motor output from cerebral cortex, which, after receiving them, sends impulses by the brain stem to skeletal muscles
• Maintains posture and balance
• Brain stem
• Contains midbrain, pons, and medulla oblongata
• Midbrain – relay system for tracts passing between the cerebrum and spinal cord or cerebellum
• Pons – literally means “bridge”; contains axon bundles that travel between there cerebellum and the rest of the CNS
• Medulla oblongata – contains reflex centers for heartbeat, breathing, blood pressure, vomiting, swallowing, coughing, sneezing, and hiccupping
• Has a reticular formation that is a complex network of grey matter masses and fibers that extend the length of the brain stem
• Limbic system – a system in the brain that is involved with emotions and higher mental functions
• Peripheral Nervous System (PNS) – consists of all of body’s nerves

• (found at http://trc.ucdavis.edu/biosci10v/bis10v/week10/spinalcord.gif)
• Contains nerves
• These nerves are composed of axons (the long part of a neuron)
• All nerves take impulses to and from the CNS
• Cranial nerves come from the brain, 12 pairs per human
• Spinal nerves come from the spinal cord and sprout from the sides of the spinal cord, 31 pairs per human
• Each pair of these spinal nerves serves a specific body area
• Is made up of two systems

• (found at http://universe-review.ca/I10-13-nerves2.jpg)
• Somatic system
• The nerves in this system serve the skin, skeletal muscles, and tendons
• Take sensory info to and motor commands from these areas
• Actions are voluntary
• Reflex arc
• We do not feel pain until our brain receives and interprets the information about the injury
• Autonomic system
• Regulates activity of the cardiac and smooth muscles, as well as the glands
• Autonomic control – involuntary control, e.g. digestive system, glands, heart, blood vessels; maintains all basic body functions
• The loss of autonomic function can be fatal
• Sympathetic and parasympathetic divisions

• (found at http://www.becomehealthynow.com/images/organs/nervous/sympth_parasymth.gif)
• Are opposite each other overall
• Both…
• Function automatically and usually involuntarily
• Innervate all the internal organs
• Utilize two neurons and one ganglion per impulse
• Sympathetic division
• “Fight or flight” – accelerates heartbeat, dilates bronchi
• Inhibits digestive tract
• Pergangliotic fibers (from the mid-spine) are short
• Postgangliotic fibers are long when they are in contact with an organ
• Parasympathetic division
• “Rest and digest” system – promotes internal responses for a relaxed state
• Eye pupils contract
• Promotes food digestion
• Retards heartbeat
• Consists of the cranial nerves and fibers from the bottom portion of the spinal cord
• Pregangliotic fibers long
• Postgangliotic fibers short
• These work together and are connected with each other.
• 3 functions
• Receives sensory input
• Processes information (in brain and spinal cord); or, CNS integration – summing up input received from body
• Motor output – initiating response (muscles result in movement, glands result in secretion); or, CNS generates output as nerve impulses
• Nervous Tissue – 2 types
• Neurons – cells that transmit nerve impulses through the body; main cells of the nervous system

• (found on slide 9 of Nervous Function – BIO 156 PowerPoint presentation)
• Most neurons never die or divide; once they develop, a human has the same ones for life
• 3 types
• Sensory neurons – take nerve impulses from sensory receptors to CNS; detect environmental changes; bring information in
• Interneurons – all in CNS; receive input from sensory neurons and other CNS interneurons
• After receiving such input, they sum up the information before communicating with motor neurons
• Motor neurons – take nerve impulses away from CNS and to effector muscles; send information out
• Effector muscles – carry out responses to environmental changes, internally and externally
• 3 parts
• Cell body – nucleus and other organelles
• Dendrites – short extension that receives input form sensory receptors or other neurons; connect to other cells, usually neurons or muscle cells
• Axon – conducts nerve impulses (carries the message); can be very long
• Long axons have myelin sheath, short ones do not

(found on slide 10 of Nervous Function – BIO 156 PowerPoint presentation)

• Myelin – “a fat-based insulating substance that isolates neurons and helps speed of action potential propagation” (from slide 10 of Nervous Function – BIO 156 PowerPoint presentation)
• Schwann cells (a type of neuroglia) – contain myelin in plasma membrane; these cells wrap around axon; only in PNS – CNS uses oligodendrocytes instead
• Neuroglia – tissue that supports and nourishes neurons

Resting potential, Action potential, Synapse

• Resting potential – when axon is not conducting an electrical impulse

• (found on slide 14 of Nervous Function – BIO 156 PowerPoint presentation)
• Every neuron contains a resting potential
• -65 to -70 millivolts average (measured by comparison of millivolts inside and millivolts outside cell; -65 means there are 65 less millivolts inside the cell than outside the cell)
• Sodium-potassium pump prevents diffusion and maintains levels like -65;
• Pump maintains unequal distribution
• Greater concentration of sodium ions (Na+) outside axon
• Greater concentration of potassium ions (K+) inside axon
• One-third of calories consumed are used to maintain this negative voltage
• Pumps constantly keep this resting state in preparation for action potential to occur
• Action potential – rapid messages transmitted by neurons with cell membrane changes; how neurons carry messages

• (found on slide 15 of Nervous Function – BIO 156 PowerPoint presentation)
• Ability to sense environment, rapidly transmit messages, and respond
• “Ability to rapidly carry an ion diffusion mediated change in voltage along the cell membrane” (from slide 13 of Nervous Function – BIO 156 PowerPoint presentation); charged ions cross by diffusion
• An “all or none” event
• Always has the same strength, the strength of the reaction is determined by how many nerve impulses are generated in a certain time span
• Happens only in neurons and muscle cells of mammals
• Rapid polarity change across the axons of a membrane during the occurrence of a nerve impulse
• -70 to +40 millivolt comparison in an instant
• Stimulus causes Na+ and K+ gates to open; the cell’s membrane “depolarizes”, or opens up
• Na+ opens first, causes +40 millivolt measurement; called depolarization
• K+ opens last, causes millivolt measurement to return to -65; called repolarization
• These two steps combined take 3/1000 of a second to occur
• Refractory period – right after impulse of axon, this ensures sodium gates do not open so action potential cannot move backward
• Here is an example of an action potential

• (found on slide 21 of Nervous Function – BIO 156 PowerPoint presentation)
• Steps in this example
• 1) “Sensory neurons action potential bring in pain information from skin”
• 2) “Neurons of spinal cord process information, take decision”
• 3) “Motor neurons carry output to muscles to move limb away from pain”
• (from slide 21 of Nervous Function – BIO 156 PowerPoint presentation)
• As is evidenced by the above example, action potential is a reflex reaction. A person does not even need to think about the situation; the body does it subconsciously, or on its own.
• Synapse – what happens when action potential arrives at the end of its axon

• (found at http://www.coolschool.ca/lor/BI12/unit12/U12L04/Synapse.gif)
• Happens at axon terminal – a small swelling at the end of each axon
• 3 steps
• 1) Nerve impulse in axon arrives at axon terminal
• 2) Calcium enters terminal and stimulates vesicles (in axon terminal that are carrying neurotransmitters) to merge with sending membrane
• 3) Neurotransmitter molecules released into synaptic cleft, where they then diffuse across the cleft to receiving membrane, where they bind to specific receptor proteins
• When Na+ is diffused into receiving neuron, it causes excitation.
• When K+ is diffused into receiving neuron, it causes inhibition.

Sensation

• Sensation
• Conscious perception of stimuli
• Occurs when nerve impulses arrive at the brain’s cerebral cortex
• Sensory receptors – specialized cells that sense something and interpret what to do, where the signal is coming from, and how “loud” that signal is; dendrites specialized to detect certain stimuli
• Trigger action potential in connecting sensory neurons
• Then, signal travels up the spinal cord and to the brain, where the main “Where? What? “How much/how strong?” interpretation and analyzation
• All over body
• 2 kinds
• Exteroceptors – sensory receptors that pick up information from the outside of the body
  
• Interoceptors – sensory receptors that pick up information from the inside of the body
• 4 categories
• Chemoreceptors – respond to chemical substances in the vicinity, e.g. taste and smell use these
• Pain receptors (also called nociceptors) – naked dendrites that respond to chemicals released by damaged tissues
• Photoreceptors – respond to light energy, e.g. eyes
• Mechanoreceptors – stimulated by mechanical forces, usually resulting in pressure, e.g. hearing, equilibrium, touch
• Thermoreceptors – stimulated by temperature changes, in hypothalamus and skin
• 3 types
• Proprioceptors – mechanoreceptors involved in reflex actions, equilibrium, and posture
• Help us know position of limbs in space
• “Proprioception – gives body position by sensing muscle tension” (from slide 27 of Nervous Function – BIO 156 PowerPoint presentation)
• For example, this allows us to touch our nose with our eyes closed
• Cutaneous receptors – in dermis; makes skin sensitive to touch, pressure, pain, temperature (all of which are sensations)
• Pain receptors – in internal organs; sensitive to chemicals released by damaged tissues
• Sensory brain fields – “For conscious somatic sensory perception, large fields in brain organize information spatially” (from slide 25 of Nervous Function – BIO 156 PowerPoint presentation)

• (found on slide 25 of Nervous Function – BIO 156 PowerPoint presentation)
• Specific, or special, senses; only in the human’s head; 5 total
• Taste

• (found at http://freda.auyeung.net/5senses/taste.jpg)
• A limited sensation that uses the tongue
• About 3,000 taste buds on the human tongue
• Four main taste sensations – sweet, salty, sour, bitter
• A possible fifth sensation called umami; considered to taste flavors like “meaty” or “savory”
• Smell

• (found on slide 30 of Nervous Function – BIO 156 PowerPoint presentation)
• Richer than taste; a very fine-tuned sense
• 80%-90% of taste is due to smell, due to the olfactory cells in the nasal cavity
• How do we smell? The nose is a very complicated organ that recognizes specific proteins and protein patterns and associates them with specific smells.
• Vision

• 
• (found on slide 31 of Nervous Function – BIO 156 PowerPoint presentation)
• Uses primarily the eyes
• Another very fine-tuned sense
• At least one-third of the cerebral cortex takes part in processing visual information
• How do we see? Light comes into the eyes, which is focused by the cornea. The pupil regulates how much light comes in.
• Retina
• “Vision – retina receptors respond to light” (from slide 32 of Nervous Function – BIO 156 PowerPoint presentation)
• 3 neuron layers
• Outermost – has rod and cone cells (also known as photoreceptors)
• Middle – has bipolar cells
• Innermost – has ganglion cells, whose sensory fibers become the optic nerve
• Contains the rhodopsin, which changes shape when light hits it
• Hearing

• (found on slide 33 of Nervous Function – BIO 156 PowerPoint presentation)
• Again, a very fine-tuned sense
• Uses the ears primarily
• Ear – 3 parts
• Outer – contains pinna, auditory canal
• Middle – goes from the eardrum to the bony wall containing the oval window and the round window
• Inner – contains semicircular canals (helps with equilibrium), vestibule (also helps with equilibrium), cochlea (helps with hearing)
• Filled with fluid
• The order in which anatomy is used during hearing – auditory canal, tympanic membrane (eardrum), malleus, incus, stapes, oval window, cochlea, spiral organ, cochlear nerve, brain
• Equilibrium
• Responds to body’s movement
• The anatomy used for equilibrium is in the same apparatus as the inner ear (see above)
• Achieved and aided by – vesibular nerves, proprioceptors, vision
• 2 pathways

• (found on slide 34 of Nervous Function – BIO 156 PowerPoint presentation)
• Rotational Equilibrium Pathway – uses the three semicircular canals in the ear, which have mechanoreceptors, which detect angular and/or rotational head movement
• Gravitational Equilibrium Pathway – uses mechanoreceptors in the utricle and saccule that detect vertical and horizontal head movement
• Utricle and saccule – membranous sacs in the inner ear near the semicircular canals

Drug Abuse

• Drug abuse – when a drug is taken at does level and under circumstances that increase the potential for harmful effects
• Drug addiction – when a person tolerates drug and needs more of it for the same effect
• Can affect fetuses when mother is abusing or addicted to a drug, e.g. a newborn addicted to cocaine
• 6 most popular drugs that are abused and become addicting
• Alcohol
• Is a depressant
• Harmful effects on body and brain
• Damages vital body organs, e.g. liver and brain
• Found in alcoholic drinks (obviously)
• Nicotine
• Is a stimulant
• Found in tobacco, both smoking and chewing
• Very addictive
• Damages vital body parts, e.g. lungs
• Cocaine – “crack”
• Is a stimulant
• Derived from the shrub Erythroxylon coca
• Has euphoric and stimulating effects
• Methamphetamine – “meth”
• Is a stimulant – mimics cocaine reactions
• A synthetic drug made from amphetamine
• Available in powder or crystal form
• “Ecstasy”, or methylenedioxymethametaphine, is similar to meth, but without hallucinations
• Heroin
• Is a depressant
• From the resin or sap of the opium poppy
• Has pain-killing effects
• Marijuana – “joint”
• Is a psychoactive, meaning it effects the mind or mental processes
• Dried parts of the Indian help plant Cannabis sativa