Chapter 13/Nervous System
13.1 Overview of the Nervous System
13.2 The Central Nervous System
13.3 The Limbic System and Higher Mental Functions
13.4 The Peripheral Nervous System
13.5 Drug Abuse
13.1 Overview of the Nervous System
There are two major divisions of the Central Nervous System (CNS)
The two divisions are: the brain and the spinal cord
The Peripheral Nervous System (PNS) consists of nerves.
The two systems (CNS and PNS) work together and are connected.
The two divisions are: the brain and the spinal cord
The Peripheral Nervous System (PNS) consists of nerves.
The two systems (CNS and PNS) work together and are connected.
Three specific functions of the nervous system:
(1) Receives sensory input- sensory receptors respond to external and internal stimuli with nerve impulses that travel from the PNS to the CNS.
(2) CNS performs integration- the CSN puts together all of the information it receives from all over the body.
(3) CNS generates motor output- nerve impulses from the CNS travel through the PNS into the muscles and glands.
Nervous Tissue
There are two types of cell in Nervous tissue
(1) Neurons- cells that transmit nerve impulses between parts of the nervous system.
(2) Neuroglia- supports and nourishes neurons.
Neuron Structure
There are three (3) types of neurons:
(1)Sensory Neuron- relays message from sensory receptor to the CNS. (The sensory receptor are structures for detection changes in the environment.)
(2)Interneuron- located entirely within the CNS- receive input from sensory neurons and also receive from other interneurons in the CNS- they compile all of the incoming information (nerve impulses) from the neurons prior to sending message to motor neuron.
(3)Motor Neuron- relays nerve impulses away from CNS to an effector (muscle fiber gland). An effector carries response to environmental changes, either external or internal.
Neurons all have three (3) parts:
1-Cell body- Contains nucleus and other organelles
2-Dendrites- Short extensions that receive signals
3-Axon- Part of the neuron that conducts nerve impulses- can be quite long/called a nerve fiber when present in nerves.
Myelin Sheath- a protective sheath that covers many axons-Schwann Cells is a neuroglia in the PNS-Schwann cells contain myelin in plasma membrane.
In the CNS oligodendrocytes perform the same function- Gaps where the Myelin Sheath is interrupted (broken) is called Nodes of Ranvier.
Long axons usually have myelin sheath and shorted ones do not.
The Nerve Impulse
Nerve impulses convey information within the nervous system.
The nerve impulse and its voltage is measured using a voltmeter and by studying excised axons.
Resting Potential is when the axon is not conducting an impulse.
Resting potential correlates with a difference in ion distribution on either side of axonal membrane.
Concentration of sodium ions is greater outside axons-
Concentration of potassium ions is greater inside ions-
The sodium /potassium pump is responsible for the uneven distribution.
Action Potential is rapid change in polarity across an axonal membrane as the nerve impulse occurs- such as when a stimulus causes the axonal membrane to depolarize to certain level (called threshold) * this occurs in an “all or none” manner.
Sodium Gates Open- action potential occurs-gates of sodium channels open-NA flows into axon-as NA fills axon the membrane potential changes-this is called de-polarization because the charge inside the axon changes from negative to positive.
Potassium Gates Open- gates of potassium open and K flows to outside of axon-as K moves to outside of axon, the action potential changes-this is called re-polarization because the inside of the axon resumes a negative charge as K leaves axon.
The Synapse
The axon branches into many fine endings tipped by small swellings called the axon terminal.
Each axon terminal is close to either the dendrite or the cell body of yet another neuron.
The area of closeness is called the synapse.
Synapse cleft is a tiny gap that separate the sending from the receiving neurons.
Transmission is completed by molecules called neurotransmitters-they are stored in synapse vesicles inside axon terminals-
Here is how it works-
1- nerve impulse reach an axon terminal
2- calcium ions enter the terminal which stimulate synaptic vesicles to merge with the sending membrane
3- neurotransmitter molecules are release into synaptic cleft, travel across cleft to receiving membrane and bind with specific receptor proteins- once events occur the neurotransmitter is removed from cleft-this cycle and removal prevent continuous stimulation (inhibition) of the receiving membranes. Removal makes it possible for new signals to be received and responded to by the cell membrane-
Neurotransmitter Molecules
Acetylcholine, nor epinephrine, dopamine, serotonin, glutamate, GABA are some of the many substances known as neurotransmitters.
Many of the drugs used that affect the nervous system interfere with the actions of the neurotransmitters.
Synaptic Integration-
Neurons have many dendrites plus cell body,- they can have synapses with many other neurons-because of this neurons are the receivers for many signals-either excitatory or inhibitory-
Caffeine is an example of excitatory and heroin is an example of inhibitory-
Integration means to sum up the incoming information whether it be excitatory or inhibitory-the evaluating of the message decides whether an axon will fire or not. Only if the combined signals cause the membrane potential to rise above certain threshold does an action potential occur.
13.2 The Central Nervous System
Spinal cord and Brain make up the CNS-
Sensory information is received and motor control is initiated-the spinal chord and the brain are protected by bone-
(1)Spinal cord is surrounded by vertebrae
(2)Brain is enclosed by the skull
Both are wrapped in meninges for protection-
Spaces between meninges are filled with cerebrospinal fluid-
The brain has four (40 ventricles, which are interconnecting chambers that produce and hold cerebrospinal fluid-
The CNS is made up of two (2 types of nervous tissue)
1- Gray Matter- contains cell bodies and short nonmyelinated fibers
2- White Matter-contains myelinated axons that run together in bundles called tracts.
The Spinal Cord extends from base of brain through large opening in skull called foramen magnum and into vertebral canal formed by openings in vertebrae-
Cross section of spinal cord contains central canal, gray matter, and white matter-individual vertebrae protect the spinal cord-spinal nerves project from cord between the vertebrae -this makes up the vertebrae column-intervertebrael disks separate the vertebrae and if pressure occurs due to slippage, then pain is felt-
Functions of the Spinal Cord
The spinal cord communicates between the brain and peripheral nerves-
Sensory receptors generate nerve impulses which pass through sensory fibers to spinal cord to ascending tracts in brain- gate control theory proposes the tracts in spinal cord have gates which control flow of pain messages from peripheral nerves to brain-motor impulses starting in brain pass down descending tracts to spinal cord and out muscles-
Paralysis occurs when if the spinal cord is severed.
Reflex Action
The spinal cord houses thousands of reflex arcs-
Stimulus make sensory receptors generate nerve impulses- These nerve impulses travel in sensory axons in the spinal cord.
Interneurons take in information and relay signals to motor neurons-skeletal muscle contraction is a response to the stimulus- many signals are sent at one time because each interferon has synapses with several other interneurons and motor neurons-
The spinal cord operates with the internal organs-(involuntary system) such as blood pressure drops, internal receptors respond, motor impulses then cause blood vessels to constrict to increase blood pressure back to homeostasis level.
The Brain
The cerebrum is the largest part of the brain.
Last to receive input before commanding voluntary motor responses-
Communicates to other brain areas: coordination and activities-
Cerebral Hemispheres- two halves of the cerebrum-
Known as the left and right cerebral hemispheres-
Longitudinal fissure divides the two halves-
Sulci (shallow grooves) divide hemispheres into lobes-
The frontal lobe is the most ventral-The parietal lobe is dorsal to the frontal lobe-
The occipital lobe is dorsal to parietal lobe-
The temporal lobe lies inferior to frontal and parietal lobes-
Each of the lobes carry our specific functions:
Figure 13.9/each cerebral is divided into four lobes/lobes contain centers for reasoning and movement, somatic sensing, hearing, and vision.
Frontal Lobe
(1)primary motor area
(2)premotor area
(3)motor speech (Broca’s) area
(4)prefrontal area
Occipital Lobe
(1)primary visual area
(2)visual association area
Cerebral Cortex-thin, outer layer of gray matter that covers cerebral hemispheres-contains over one billion cell bodies-area accounts for sensation, voluntary movement, all thought processes we associate with consciousness.
Primary Motor and Sensory Areas of the Cortex-contains motor and sensory and association areas-
Association Areas- places where integration occurs-
Processing Centers- receive information from other association areas-perform higher level analytical functions-
Central White Matter- A large portion of the cerebrum is made up of “white matter”-
Myelination occurs during childhood and ‘white matter” develops-
During childhood development, neurons become myelinated within tracts of cerebrum and that is why children become more skilled and capable-
Descending tracts from primary area communicate with lower brain centers, lower areas relay information to primary somatosensory area-Due to cross-over in medulla, the left side of cerebrum controls the right side of the body and vice versa-
Diencephalon contains the hypothalamus and the thalamus- (third ventricle)
Hypothalamus helps maintain homeostasis: regulates hunger, thirst, sleep, and body temperature.
Thalamus receives all sensory input: visual, auditory, somatosensory, everything except for smell-
The pineal gland is also located in the diencephalons but its functions are still under study-
Cerebellum is under occipital- separated from brain stem by fourth ventricle-
Cerebrum has two parts-Receives sensory input from eyes, ears and joints-receives motor output from cerebral cortex- maintains posture and balance-
The Brain Stem-Contains the mid-brain, pons, and medulla oblongata-
Mid-brain acts as relay station between cerebrum and spinal cord or cerebellum- relax center for visual, auditory, and tactile responses-
Pons- bridge containing bundles of axons that travel between cerebellum and rest of CNS-
pons works along with medulla oblongata to regulate breathing rate and has reflex centers-
Medulla oblongata- reflex center for regulation of heart beat, breathing, and blood pressure- also reflex center for vomiting, coughing, and sneezing-
Reticular Formation is complex network of nuclei (gray matter and fibers) extend length of the brain stem-Part of the RAS which receives sensory signals and sends them up to the higher centers- motor signals are sent to the spinal cord- RAS arouses cerebrum via thalamus to make person alert-believed to be able to filter out extra stimulus to help person focus on one thing-
13.3 The Limbic System and Higher Mental Functions
Limbic system is primitive/ancient part of brain that is a “functional” grouping and not an “anatomical”-Limbic blends primitive emotions with higher mental functions into whole unit-
Two parts of the Limbic-
1-Amygdala-which can cause experiences to have emotional overtones, also creates the sensation of fear- frontal cortex can over-ride the limbic and make us re-think the situation and prevent strong reactions-
Hippocampus- believed to play large part in learning and memory- believed to be able to communicate with frontal cortex because memories are known to be an important part of decision making.
Higher Mental Functions
Brain research has advanced dramatically because of technological advancements.
Limbic system indicate that the cortical areas work with the lower centers to produce learning and memory-
Memory refers to the ability to hold a thought in mind or to recall-
Learning refers to retaining and then using past memories-
Types of memory:
(1) short term memory- information stored in front part of brain
(2) long term memory- information that is them memorized is associated with long term memory- combines semantic memory (numbers, words) and episodic (persons, events)
Skill Memory- can exist independently of episodic memory- involved in riding a bike or activities that involve motor skills-skill memory involves motor areas of cerebrum below level of consciousness.
Long term memory storage and retrieval- stored in bits in the sensory association areas-
Long Term Potentiation refers to what is believed to be memory storage- after synapses have been firing a lot in a short time period they release more neurotransmitters than previously-
This is thought to be LTP-
Language is dependent on semantic memory- disruptions within the normal pathways are
thought to interfere with comprehension-
Seeing and hearing words is dependent sensory centers in occipital and temporal lobes-
Wernicke’s area damage results in inability to understand speech-
Broca’s area damage results in inability to speak and write-
The left hemisphere of the brain is more global and the right hemisphere is more specific-
Left hemisphere is in control of: verbal, logical, analytical, rational
Right hemisphere is in control of: non-verbal, visuospatial, intuitive, creative
13.4 The Peripheral Nervous System
http://highered.mcgraw-hill.com/sites/dl/free image from unit powerpoint presentation
The PNS lies outside the CNS and contains the nerves.
Cranial nerves arise from the brain
Spinal nerves arise from the spinal cord
All nerves take impulses (messages) to and from the CNS.
Humans have 12 pair of cranial nerves that are attached to the brain- some are sensory, some are motor, and some are mixed- largely involved to the head, neck , and facial areas-
Spinal nerves emerge in 31 pairs from either side of spinal cord-
Roots physically separate the axons of sensory and motor neurons-
Sensory neuron is in a dorsal root ganglion, which is a collection of cell bodies outside the CNS.
Somatic System- nerves in the somatic system serve the skin, skeletal muscles, and tendons-
Some actions are voluntary and some are automatic-
Reflexes are considered automatic-
The “reflex arc” involves only the spinal cord-
The sequence is described in Figure 13.15; Stimulus causes sensory receptors in skin to generate nerve impulses- go from sensory axons to spinal cord, there interneurons send message to motor neurons-motor axons from spinal cord contract and an automatic reflex occurs, such as a hand pulling away from a hot object or a pin prick.
Autonomic System is in the PNS- regulates activity of cardiac and smooth muscles and glands-
Area is divided into the sympathetic and parasympathetic-activation in two areas typically cause opposite responses-
Both (sympathetic and parasympathetic) have the following commonalties:
(1) function automatically and involuntarily
(2) innervate all internal organs
(3)utilize two neurons and one ganglion for each impulse
Sympathetic Division have ganglionic fibers that arise from the middle of spinal cord and terminate in ganglia that lie near cord-the preganglionic fiber is short but the post-ganglionic fiber that makes connection with the organ is long- sympathetic division is highly important during emergency situations _
Parasympathetic Division includes few cranial nerves and fibers that arise from the bottom of the spinal cord- in the parasympathetic system the preganglionic fiber is long and the postganglionic fiber is short because ganglia lie near or in the organ- sometimes referred to as the housekeeper division promotes all internal responses associated with a relaxed state- such as pupil contraction, food digestion, and heartbeat retardation- This system can be thought of as, “The rest and digest” system.
13.5 Drug Abuse
Drugs affect the nervous system, can alter moods and emotional states-
(1) limbic system is affected
(2) promote or decrease action of neurotransmitters
Dopamine is a neurotransmitter that affects the brains reward circuitry-
Drug abuse is describes as, “The continued use of a substance despite negative impact on the individuals life.” Actually, this is my definition of drug dependency not our text book’s definition.
When a person takes a drug at a dose that increases potential for harm it is considered abuse. Drug abuse and dependency involves psychological and or physical dependency.
Cravings are part of the psychological addiction. Physical addiction is when a person needs more of the drug to get the same effects and also when the person stops using the chemical they experience withdrawals.
Alcohol use is the most socially and culturally accepted drug to be used in the world. Alcohol has harmful effects on the human body and the brain. Alcohol crosses the cell membrane, including the blood-brain barrier-In the CNS alcohol acts as a depressant.
Nicotine acts as a stimulant- during smoking it is delivered to the CNS and the mid-brain- increases skeletal muscle activity, heart rate, blood pressure, and digestion. Nicotine is highly addictive.
Cocaine is a powerful stimulant that comes from a shrub- interferes with the re-uptake of dopamine in the synapses in the CNS- continued use of cocaine causes the body to make less dopamine- tolerance leads to withdrawal-
Methamphetamine is a synthetic drug that is a highly addictive stimulant- effects are almost instantaneous- mimics cocaine and has structure similar to dopamine-
Heroin comes from the opium poppy plant- highly addictive depressant on the nervous system- rapidly delivered to the brain and turned into morphine-binds rapidly to opioid receptors for euphoric feelings- depressed breathing, activates the reward center, block pain pathways, and cloud mental functions- risky behaviors put heroin users in danger, such things as “sharing needles” unclean drugs, and risky sexual choices make this addiction very dangerous for disease and other health risks-
Marijuana contains THC and is a plant- THC mimics anadamide, when it reaches the CNS mild euphoria, altered vision and judgment occurs- regular use can cause cravings and make it difficult to stop usage-
Chapter 14/Senses
14.1 Sensory Receptors and Sensations
14.2 Proprioceptors and Cutaneous Receptors
14.3 Senses of Taste and Smell
14.4 Sense of Vision
14.5 Sense of Hearing
14.6 Sense of Equilibrium
14.1 Sensory Receptors and Sensations
Sensory receptors- dendrites specialized to detect certain kinds of stimuli-
Exteroceptors- sensory receptors that detect stimuli from outside the body, such as; taste, smell, vision, hearing, and equilibrium-
Interceptors- receive stimuli from inside the body, such as; pressoreceptors respond to changes in BP, osmoreceptors detect changes in water/salt balance, and chemo receptors monitor ph of blood-
Interceptors are related to homeostasis-
Extroceptors are NOT directly involved with homeostasis/ continuously send messages to CNS about environmental conditions-
There are four types of Sensory Receptors:
(1) chemo receptors- respond to chemicals in area/pain receptors are a specific type-they are naked dendrites that are responding to chemicals released by damaged tissues-
(2) photoreceptors- respond to light energy-stimulation of rod cells results in black and white vision-
(3) mechanoreceptors- stimulated by mechanical forces, usually by some type of pressure- they are responding to fluid-borne pressure waves when gravity/motion changes are felt-pressure receptors are responsible for the sensation of touch-
(4) thermo receptors- stimulated by changes in temperature-response to rising temperature is felt in warmth receptors and cold receptors are used when temperatures go down-
How Sensation Occurs
Sensation is “the conscious perception of stimuli.”
Sensory receptors are the first responders in a reflex arc-
Some sensory receptors are free nerve endings while other nerve endings are specialized-All sensory receptors initiate nerve impulse-
Prior to initiation, nerve impulses carry out integration (the summing up of signals) a particular kind of “integration” is called “sensory adaptation” which is a decrease in the response to stimuli-
Sensory receptor function is very important to homeostasis-it helps maintain a constant for our internal environment-
14.2 Proprioceptors and Cutaneous Receptors
Nerve impulses traveling from muscles, joints, tendons, other internal organs, and skin go to the spinal cord, then to somatosensory areas of cerebral cortex-There are three (3) general types of sensory receptors:
(1) Proprioceptors-mechanoreceptors involved in reflex actions used to maintain muscle tone, equilibrium, and posture- assists us in knowing our body placement in its environment even with the force of gravity constantly putting pressure on us-
(2) Cutaneous Receptors- Skin is made of two layers, the epidermis is composed of the outer layers and the dermis is located underneath- Dermis is a thick connective tissue layer- Dermis contains cutaneous receptors, which are responsible for making skin sensitive to touch, pressure, pain, and the temperature-Dermis is composed of intertwined and many tiny receptors-
Cutaneous receptors that are sensitive to various degrees of touch are: (1)Meissner Corpuscles (touch) (2) Pacinian Corpuscles (pressure) (3) Ruffini Endings (pressure)
Pain Receptors
Skin and internal organs have pain receptors-they are sensitive to chemicals released by damaged tissues-Referred pain is when there is stimulation of internal pain receptors and from internal organs-some internal organs have a referred pain relationship with other body part, such as pain from heart is often felt in left shoulder and arm-
14.3 Senses of Taste and Smell
Taste and smell are known as chemical senses- taste and olfactory cells bear chemo receptors- chemo receptors are divided plasma membrane receptors- the two types are receptors that respond to distant stimuli and receptors that respond to direct stimuli-
Sense of taste:
Adults have approximately 3000 taste buds which are mainly located on the tongue- at least four (4) primary types of taste buds:
(1) sweet -tip of tongue area
(2) sour- sides of tongue area
(3) salty- sides of tongue area
(4) bitter- rear of tongue area
Taste buds open at a taste pore with support cells also elongated taste cells that end in micro villa-impulses travel in sensory nerve fibers that go to brain- they are interpreted at the gustatory cortex and translated-
Sense of Smell:
80-90% perception of our taste is actually due to smell-we have 10-2- million olfactory cells in roof of nasal cavity- olfactory cells end in tufts of five cilia, which bear receptor proteins-
olfactory interpretation is connected to emotion/memory brain centers-
14.4 Sense of Vision
The parts of the eye (optic nerve) and the brain (cerebral cortex) work together for vision-
There are three (3) layers to an eye-
(1) sclera-outer layer- the cornea is part of this area
(2) choroids- vascular for absorption of stray light rays- iris is part of this area, also the pupil inside the iris- behind the iris is the ciliary body- contains the ciliary muscle- controls lens shape for near and far vision- lens is part of this area that divides the eyeball into two compartments (anterior and posterior)
(3) retina-located in posterior compartment filled will gel like vitreous humor-retina contains photoreceptors- fovea centralis is where coned cells are densely packed-vision is most acute in this area-
Function of the Lens
The retina is able to focus images because of the cornea, lens assistance, and the humors-
“Focus” starts with cornea-
Next rays pass through lens and humors-
Light rays are bent (refracted) so they are much smaller than the actual image being viewed-
Visual accommodation happens for close vision- the lens rounds up to assist bringing the image into focus- the ciliary muscle assists when the object of focus is far away- lens shape is controlled by the ciliary muscle- “eye-strain’ occurs because of ciliary contractions used to help focus-
Function of Photoreceptors- once light has been focused on photoreceptors in retina that’s when vision begins- rod cells and cone cells make up the photoreceptors-Rhodopsin is complex
molecule made of protein opsin and retinal-
The retina has three (3) layers of neurons-
1- close to choroids layer are rod/cone cells-
2- middle layer contains bipolar cells
3-inner most layer contains ganglion cells-
There are no rods/cones where optic nerve exit’s the retina so this is a “blind spot” (no vision possible)
The optic nerve carries impulse to visual cortex and on to optic chiasma- the image is split because the two parts of the cortex receive different halves of the visual information- once the brain puts the image information back together again it also has a sense of depth perception -
Abnormalities of the Eye-
Nearsightedness occurs when a person can see better close up and not far away-
Farsightedness is when a person can see objects clearly that are far away but not at close distances-
Astigmatism is when objects appear fuzzy and is caused by an unevenness of the lens or cornea-
Health Focus page 285
Talks about cataracts and glaucoma conditions of the eye. Cataracts are caused because of a lens being cloudy and glaucoma is a build up of fluid inside the eyeball. Surgeries are discussed for both conditions. Lens replacement for cataracts can correct the condition and sometimes eye drops/oral medications can relieve built up pressure in glaucoma. Surgery is the alternative for glaucoma sufferers when medications do not work. Surgery consists of drilling tiny holes 9with a laser) in the iris/cornea area. Lasik surgery is discussed to help people who suffer from presbyopia (difficulty with focus). This condition is very common and is actually present in almost 100% of people around age 55.
14.5 Sense of Hearing
Hearing and balance are both functions of the ear- sensory receptors are located in the inner ear- they consist of hair cells and micro villa (called stereo cilia).
The ear has three (3) divisions:
1- Outer Ear- pinna, which is the outer flap and auditory canal-
2- Middle Ear- begins at tympanic membrane (eardrum) ends at bony wall containing two small openings covered by membrane-
Names of the opens are; oval/round windows-
The outer and middle ear contain air and the next division (inner) contains fluid-
The outer and middle ear contain air and the next division (inner) contains fluid-
3- Inner Ear- three areas (1) semicircular canals (2) vestibule) (3) cochlea
Sound (hearing) begins at auditory canal by means of sound waves, or vibrations-
The middle ear amplifies the sound vibrations- oval window membranes are then struck to send message on to the brain- Volume is interpreted by the brain and is felt as pressure within vestibular canal-
14.6 Sense of Equilibrium
Page 290: figure 14.15 The Mechanoreceptors for equilibrium
Rotational equilibrium- ampullae’s of the semicircular canals have hair cells with stereo cilia embedded in cupula- person turns their head and the cupula is displaced, then bending the stereocilia- nerve impulses go to vestibular nerve to the brain- (rotational or angular head movement)
Gravitational equilibrium- utricle and saccule contain hair cells with stereocilia imbedded in otolithic membrane- head bends, otoliths are displaced making membrane sag and stereocilia bend- when stereocilia bend toward kinocilium 9longest stereocilia) the nerve impulses increase in vestibular nerve- when stereocilia bend away from kinocilium the nerve impulses decrease in vestibular nerve- this DIFFERENCE tells the brain which way to move the head- (vertical or horizontal planes movement)
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