mod 1: The Nervous System Flashcards
(158 cards)
1
Q
homeostasis (general definition)
A
tendency of the body to maintain a state of equilibrium. a state of relative stability within the body
2
Q
nervous system (definition, function)
A
elaborate communication system that receives input, processes, integrates, and stores information, and triggers muscle contraction or glandular secretion
3
Q
branches of the nervous system (list)
A
- central nervous system
- peripheral nervous system
- sensory branch
- motor branch
- somatic nervous system
- autonomic nervous system
- sympathetic nervous system
- parasympathetic nervous system
4
Q
central nervous system (components)
A
“CNS”. brain and spinal cord. consists of interneurons (the only place where interneurons can be found)
5
Q
peripheral nervous system (components)
A
nerves and ganglia (collections of nerve cell bodies) outside the brain and spinal cord
6
Q
sensory branch (definition, function)
A
branch of the peripheral nervous system. carries sensory info from receptors (internal or external sensors) to the CNS
7
Q
motor branch (definition, function)
A
branch of the peripheral nervous system. carries info from the CNS to effectors (muscles/glands)
8
Q
somatic nervous system (definition, function)
A
division of peripheral nervous system. controls voluntary movement of skeletal muscles (motor neurons conduct signals from the CNS to skeletal muscles) and from sensory receptors to the CNS (sensory neurons
9
Q
autonomic nervous system (definition, function)
A
division of peripheral nervous system. controls involuntary movement of cardiac and smooth muscles (conducts signals from the CNS to the glands and cardiac and smooth muscles)
10
Q
sympathetic nervous system (definition, function)
A
branch of the autonomic nervous system. “fight, flight, or fright response”. activates the body to cope with some stressor (ex: danger, fear, excitement)
11
Q
parasympathetic nervous system (definition, function)
A
branch of the autonomic nervous system. “rest and digest response”. works opposite to the sympathetic system to bring the body back to normal after stress and oversees digestion, elimination, and glandular function
12
Q
which neurotransmitter is used by the parasympathetic system?
A
acetylcholine
13
Q
which neurotransmitters are used by the sympathetic system?
A
acetylcholine and norepinephrine
14
Q
difference in structure between sympathetic and parasympathetic nervous systems?
A
sympathetic consists of nerves coming from the middle part of the spinal cord and is connected to a cord of ganglia that run down the spinal cord. parasympathetic consists of nerves coming from the very bottom and very top of the spinal cord and have no ganglia
15
Q
neuron (definition, function)
A
basic structural and functional cells of the nervous system. respond to physical and chemical stimuli, conduct electrochemical signals, and release chemicals and regulate bodily processes
16
Q
neuron (structure)
A
the cell body (soma) is where the nucleus is, and it looks like an enlarge bulb off of which are the dendrites (small branches that receive impulses from receptors or other neurons) and the axon, which is a long tail. at the end of the axon are offshoots called axon terminals. the axon may or may not have a myelin sheath, where the myelin sheath cells are called Schwann cells and the spaces between them are called nodes of Ranvier
17
Q
dendrite (definition, function)
A
offshoot of the cell body of a neuron. receives signals from other neurons or from receptors, conducting them to nerve impulses to convey to the cell body
18
Q
neuron cell body (function)
A
integration centre where electrical signals from the dendrites converge and the impulse is conducted on towards the axon
19
Q
axon (function)
A
carries the nerve impulse away from the cell body and towards the axon terminals
20
Q
axon terminals (function)
A
contain chemicals called neural transmitters that are released when a nerve impulse reaches them, moving towards the next destination (another neuron or an effector) and initiating an electrical impulse there
21
Q
myelin sheath (structure, function)
A
consists of Schwann cells wrapped around the axon with nodes of Ranvier between them. allows the nerve impulse to travel from node to node and be much faster. not all neurons have this; those that do are called myelinated and those that do not are unmyelinated
22
Q
nerve (definition, structure)
A
message pathway of the nervous system. made up of many neurons grouped into bundles and surrounded by protective tissue
23
Q
cranial and spinal nerves (definition, amount)
A
cranial: insert into the brain. 12 pairs.
spinal: emirate from the spinal cord. 31 pairs.
24
Q
three main types of neurons? (list)
A
sensory neuron, interneuron, motor neuron
25
sensory neuron (function)
gather information from receptors and transmit impulses to the CNS
26
interneuron (function)
process and integrate incoming sensory information and read outgoing motor information. act as a link between sensory and motor neurons.
27
motor neuron (function)
transmit info from the CNS to effectors
28
receptor (definition)
any kind of internal or external sensor
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effector (definition)
any type of muscle or gland that responds to nerve impulses
30
multiple sclerosis
"MS". disease of central nervous system where the myelin sheath becomes inflamed and may be replaced by scar tissue, slowing nerve impulse transmission or stopping it entirely. also causes damage to blood vessels in the affected area, allowing it to be located in an MRI
31
brain is protected by...?
the skull and meninges
32
meninges (structure, function)
three layers of tough, elastic tissue directly enclosing the brain and spine, also preventing circulation of blood through the cells of the brain and spinal cord from outside (blood-brain barrier)
33
blood-brain barrier (how it works)
nutrient containing blood enters through blood capillaries made of tightly fused epithelial cells, forming a barrier that only lets oxygen, glucose, and lipid-soluble substances through
34
cerebrospinal fluid (definition, function)
fluid that circulates through ventricles (spaces) within the brain and spinal cord, as well as between two layers of the meninges, where it acts as a shock-absorber and cushion for the brain. it also transports hormones, white blood cells, and nutrients across the blood-brain barrier
35
structures of the brain (list)
hindbrain (consists of the cerebellum, medulla oblongata, pons)
midbrain
forebrain (consists of the thalamus, hypothalamus, cerebrum)
36
cerebellum (location/structure, function)
fairly large walnut-shaped structure. below and behind the cerebrum. unconscious coordination of posture, reflexes, and body movements, and fine, voluntary motor skills. receives information from proprioreceptors located within skeletal muscles and joints.
in general: controls muscle balance and coordination
37
medulla oblongata (location/structure, function)
smallish lump at base of brainstem. connects the brain with spinal cord. controls automatic, involuntary responses such as: heart rate, constriction/dilation of blood vessels to control blood pressure, and the rate and depth of breathing, swallowing, and coughing.
in general: controls subconscious activities
38
pons (location/structure, function)
larger lump in front of and above the medulla oblongata. relay centre between the neurons of the right and left halves of the cerebrum, cerebellum, and the rest of the brain.
39
midbrain (location/structure, function)
area above the pons and below the thalamus and hypothalamus. relays visual and auditory information between areas of the forebrain and hindbrain.plays important role in eye movement and control of skeletal muscles.
40
thalamus (location/structure, function)
sits at the base of the forebrain (above the midbrain and within the cerebrum). "the great relay station of the brain". consists of neurons that provide connections between the forebrain and hindbrain and between areas of the sensory system (except smell) and the cerebellum.
41
hypothalamus (location/structure, function)
below the thalamus and roughly in front of the midbrain. regulates body's internal environment and certain aspects of behaviour. controls: blood pressure, heart rate, body temperature, basic drives (i.e. thirst and hunger), emotions (i.e. fear, rage, pleasure). major link between nervous and endocrine system (coordinates actions of the pituitary gland)
42
cerebrum (location/structure, function)
the largest part of the brain--the section surrounding the rest of the forebrain and the midbrain. divided into left and right hemispheres as well as the different lobes. general function: intellect, memory, consciousness, language, interpretation of and response to sensory information.
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structures and lobes of the cerebrum (list)
cerebral cortex, corpus callous, frontal lobe, temporal lobe, parietal lobe, occipital lobe
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cerebral cortex (location/structure)
~5mm thick outer covering of grey matter that covers the internal mass of white matter of the cerebrum. twisted, ridged structure of the brain allows for more grey matter due to increased surface area
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grey matter
nervous tissue that consists of unmyelinated neurons
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white matter
nervous tissue that consists of myelinated neurons
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corpus callous (location, function)
the part of the cerebrum that touches the lateral ventricle (just above the thalamus). white matter that connects the right and left hemispheres of the cerebrum
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frontal lobe (location, function)
front and largest part of the cerebrum
associated with conscious though, intelligence, memory, and personality. controls precise, voluntary muscle movement (the primary motor area) and contains Broca's area.
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Broca's area (location, function)
within the frontal lobe
coordinates muscle movements for speaking and translates thoughts into words. damage to this area would render the person unable to talk but able to understand other people
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temporal lobes (location, function)
stretched below the frontal and parietal lobe. band at around the temple area
mainly responsible for auditory reception (is also linked to understanding speech and retrieving memories) and helps to process visual information. contains Wernicke's area
51
Wernicke's area (location, function)
within the temporal lobe
stores information involved in language comprehension. damage to this area would not affect one's ability to pronounce words correctly but the words would be meaningless and the person would be unable to understand others
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parietal lobes (location, function)
behind the frontal lobe and above the temporal lobe
receives sensory information from skin. processes information about body position and taste
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occipital lobes (location, function)
small part at the very back of the cerebrum
receive and analyze visual information (including recognition of seen objects)
54
PET (procedure, how does it work, main focus)
"positron-emission tomography". patient recieves radioactively-labelled glucose that allows scanners to monitor its consumption in the brain, indicating areas of heightened energy demand and therefore increased activity
55
MRI (procedure, how does it work, main focus)
"magnetic resonance imaging". giant magnet surrounds the patient's head. changes in the direction of the magnetic field cause the brain's hydrogen atoms to emit radio signals, which can be detected, translated, and then displayed as a clear structural or functional image, showing detailed brain structure. one scan can produce images from any direction as it can creates a 3D model.
56
which hemisphere corresponds to which half of the body and why?
the right hemisphere corresponds with the left half of the body and the left hemisphere corresponds with the right half of the body because most sensory and muscle control nerves/receptors cross over at the brain stem
57
which structures protect the spinal cord? (list)
the spinal column (series of backbones/vertebrae), meninges, and cerebrospinal fluid
58
structure of the spinal cord (description)
consists of white matter on the outside and grey matter in a butterfly shape on the inside. in the very centre is the central canal. spinal nerves (that come off the spinal cord, not the ones that make it up) are usually a mixture of motor and sensory neurons. nerves attach to the spinal cord in the ventral (front) and dorsal (back) areas, splitting off into two "roots". the sympathetic nerves have a ganglion at the part where the roots meet but parasympathetic do not.
59
reflex (definition)
inborn, not-learned behaviour that results from the stimulation of a special neural pathway called the reflex arc
60
reflex arc (definition, how it works)
simple connections fo neurons that result in a reflex action. controlled by the spinal cord and therefore occurs before the brain has time to process and voluntarily respond.
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monosynaptic pathway (definition)
involves only one sensory and one motor neuron
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simple reflex (characteristics)
unconscious and not learned. involuntary, rapid
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conditioned reflex (characteristics)
automatic response established by training
64
sensory receptor (definition, function)
cell or group of cells that is specialized to receive stimuli that provide information about the body's external and internal conditions
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type of sensory receptors? (list)
photoreceptors (light), mechanoreceptors (pressure, touch, stretch, motion, etc) , chemoreceptors (solute concentration, individual kinds of molecules), osmoreceptors (osmotic pressure, water movement), thermoreceptors (heat/cold)
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sensation (definition)
the reception and processing by the brain of a nerve impulse sent by an activated sensory receptor
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perception (definition)
interpretation of sensory information by the cerebral cortex
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sensory adaptation (definition)
tendency of sensory neurons to become less sensitive when they are repeatedly stimulated
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taste buds (definition, function)
chemoreceptors on the tongue that detect molecules from one of five basic tastes (sour, sweet, salty, bitter, umami) (specific taste buds only detect on of the five tastes)
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process of tasting (step by step description)
molecules are dissolved in saliva and enter the taste bud, where they activate taste cells to generate a nerve impulse and sensory neurons send that impulse to the gustatory centre (primary taste area) of the parietal lobe for processing
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molecules must be _____ to be detected by taste buds
dissolved in saliva
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olfactory receptor cell (definition, function)
sensory neuron located in the olfactory epithelium that is specialized to receive chemical stimuli and to initiate a nerve impulse
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olfactory epithelium (definition, location, function)
sense organ for smell. a patch of tissue located in the upper part of the nasal cavity. contains mucous-secreting cells and olfactory cells
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process of smelling (step by step description)
odour molecules enter the nasal cavity and are dissolved in mucous secreted by the olfactory glands in the olfactory epithelium. once dissolved, the molecules bind to olfactory cells (each molecule can only bind with its corresponding olfactory cell), causing ion channels in the olfactory cell membrane to open, generating a nerve impulse that travels through the olfactory cell to the directly linked olfactory bulb of the brain. from there, the impulse is sent to the emotional centres of the brain and the frontal lobe, where perception of odour occurs
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relationship between senses of smell and taste
80–90% of what we perceive as taste is actually detected by the sense of smell. molecules from food travel through the nose and stimulate chemoreceptors that then trigger olfactory neurons.
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structures of the eye (list)
```
sclera (external layer)
- cornea
choroid (intermediate layer)
- iris
- pupil
- ciliary muscles
retina (internal layer)
- rods
- cones
- fovea centralis
lens
humours
optic nerve
```
77
external layer of the eye and its components (definition, function)
the sclera is a white, tough fibrous protective layer. towards the front of the eye is the cornea: the transparent part of the sclera that allows light into the eye
78
intermediate layer of the eye and its components (definition, function)
the chorion is a black layer that absorbs stray light rays not detected by photoreceptors and contains blood vessels that nourish the eye. forms the donut-shaped, coloured iris towards the front, the centre opening of which is called the pupil. the iris adjusts the size of the pupil based on light conditions. the ciliary muscles are also part of the chorion, and they attach to the lens and change its shape to focus on things
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internal layer of the eye and its components (definition, function)
the retina is a thin layer of tissue that contains photoreceptors: rods are sensitive to light intensity (level of brightness) and cones are sensitive to colour. the fovea centralis is an area of the retina close to the blind spot (optic nerve) where there is the highest concentration of cones.
80
what are the structures of the eye aside from the sclera, choroid, and retina? (location, definition, function)
the lens is located between the iris and retina. it is flexible, changing shape to direct light towards the retina in a way that will provide the clearest image.
the humours are fluids within the retina-surrounded part of the eye (vitreous humour) and the part between the cornea and iris (aqueous humour). they help maintain the shape of the eyeball and the aqueous humour also provides nutrients for the cornea, which is not reached by blood vessels of the chorion.
optic nerve is connected to the eye at the blindspot and transmits sensory information to the brain
81
accommodation (relating to the eye) (definition)
the ability to change the shape of the lens in order to focus light on the retina
82
cataracts (definition)
grey-white spots on the lens caused by degeneration of lens protein structure due to age
83
astigmatism (definition)
inherited uneven curvature of the cornea
84
myopia (definition, treatment)
nearsightedness. eyeball is elongated and focus falls before the retina. corrected by a concave lens
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hyperopia (definition, treatment)
farsightedness. eyeball is short and focus falls behind the retina. corrected by a convex lens
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tapetum (definition, function)
reflective layer on top of the choroid layer that allows better sight in low light levels
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photopsin (definition)
pigment that absorbs light and starts chemical changes
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process of seeing (rods) (step by step description)
rhodopsin is bleached and broken down into opsin and retinal when hit by enough and the right kind of light. this initiates a nerve impulse in the bipolar cell layer, which transfers the energy to the ganglion cell layer, which transfers the energy directly to the optic nerve. the optic nerve sends the impulse to the optic chasm, which finally transmits the final, 3D image to the occipital lobe
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retinal (definition, function)
derivative of vitamin A. combines with opsin to produce rhodopsin, which makes it possible to see. therefore, lack of vitamin A can cause difficulties seeing
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what photopsins are present in cones and rods?
cone: three different pigments called iodopsins, where each cone only have one type of iodopsin.
rod: rhodopsin
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glaucoma (definition)
malfunction of ducts that drain excess humour from anterior chamber causes pressure buildup in that chamber which causes blood vessels to rupture and the cells then deteriorate due to lack of nutrients
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what are the layers of the retina, from closest to the chorion to farthest? (list)
pigmented cells (specialize to form tapetum in some animals), photoreceptors (rods and cones), bipolar cells, ganglion cells
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optic chiasm (definition, function)
the part in the path the nerve impulse travels from the eyes to the occipital lobe where nerves cross over, allowing the brain to create a single 3D image of the surroundings, rather than the two flat images that the eyes see individually
94
major structures of the ear (be able to label a diagram) (list)
outer ear: pinna, auditory canal
middle ear: tympanum, ossicles, oval window, Eustachian tube
inner ear: cochlea, semicircular canals, vestibule, round window
95
pinna (definition, function)
outside flap made of skin and cartilage. shape enhances sound vibration and focuses them into ear
96
auditory canal (definition, function)
~2.5cm long tube leading to tympanum. amplifies sound waves. hair and earwax prevent foreign material from entering
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tympanum (definition, function)
"eardrum" or "tympanum membrane". round, elastic structure. vibrates in response to sound waves, passing those vibrations on to the ossicles
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ossicles (definition, function)
three tiny, interconnected bones (malleus/hammer, incus/anvil, and stapes/stirrup, in order from the tympanum to the oval window) that greatly amplify the strength of vibration. concentrate vibration into the oval window
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oval window (definition, function)
membrane-covered opening in the wall of the inner ear. transforms vibrations from ossicles to waves in the fluid of the cochlea
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Eustachian tube (definition, function)
tube connecting the middle ear to the throat, allowing pressure differences to be equalized
101
cochlea (definition, function)
fluid-filled. receives vibrations from ossicles through the oval window. the middle chamber of the cochlea contains the organ of Corti, which is the organ of hearing
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round window (definition, function)
small membrane-covered opening between the middle ear and inner ear, beneath the oval window. dissipates sound waves in the inner ear
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organ of Corti (definition, function)
contains hair cells that detect vibrations in the fluid of the inner ear and initiates a nerve impulse that is transmitted to the auditory nerve
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organ of Corti (structure)
rests on the basilar membrane. consists of hair cells that have stereocilia. the far ends of the stereocilia are embedded into the tectorial membrane
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basilar membrane (definition)
one of two parallel membranes that comprise the organ of Corti in the inner ear. the once that moves. hair cells are attached to it
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hair cells (definition)
sensory mechanoreceptors attached to the basilar membrane in the organ of Corti. have stereocilia coming out of them
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tectorial membrane (definition)
one of two parallel membranes found in the organ of Corti. the one that doesn't move. the far ends of stereocilia (projected out of hair cells) are embedded in it
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process of hearing (step by step description)
sound wave passes by the pinna and into the auditory canal of the outer ear. the sound wave hits the tympanum, causing it to vibrate, and causing the tympanum to send vibrations on to the ossicles in the inner ear, which amplify the sound and cause the oval window to vibrate. the oval window's vibration creates pressure waves within the fluid of the cochlea (inner ear). the waves cause the movement of the basilar membrane of the organ of Corti within the cochlea. this causes the stereocilia to bend and move against the tectorial membrane, activating hair cells and causing them to send a nerve impulse to sensory neurons that send the information to the temporal lobe of the brain.
109
pitch (definition)
corresponds to the frequency of a sound (high or low)
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how does the organ of Corti tell apart different pitches?
the organ of Corti stretches all along the spiral of the cochlea. sounds that have a higher pitch are detected by the hair cells closer to the oval window.
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deafness (definition, types)
any type of hearing loss. classified into two types: conduction or perception deafness
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conduction deafness (definition)
deafness caused by damage to the sound conduction system of the outer or middle ear. the nerves and hair cells are fine but insufficient sound waves are actually getting to them
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perception deafness (definition)
"nerve deafness". damage to the organ of Corti, rendering it unable to initiate nerve impulses. the outer structures deliver sound waves to the organ of Corti correctly but the organ of Corti is unable to send the information to the brain
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semicircular canals (location, definition, function)
in inner ear. three tubes that contain mechanoreceptors that detect head and body rotation. responsible for dynamic balance (rotational equilibrium)
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utricle and saccule (location, definition, function)
tiny chambers in the inner ear, below the semicircular canals, that contain otoliths and hair cells, which respond to changes in head position with respect to gravity and movement in one direction. responsible for static balance (gravitational equilibrium)
116
dynamic balance (definition)
"rotational equilibrium". balance resulting when the head and body are moved or rotated
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static balance (definition)
"gravitational equilibrium". balance resulting from changes in the position of the movement of the head in one direction. usually in response to gravity
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otolith (location, definition, function)
tiny particle of calcium carbonate found in the utricle and saccule that contacts the hair cells in these structures and stimulates them
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vestibule (location, definition)
fluid-filled area of the inner ear between the semicircular canals and the cochlea. contains the utricle and saccule
120
process of dynamic balance (step by step description)
when the body moves and rotates, fluid moves within the semicircular canals (which are arranged in all three planes, XYZ). when the fluid moves into the bulges at the base of each canal, it causes the cupula attached to the hair cells within the bulge to move with the flow of the fluid. this causes a bending and tugging on the hair cell stereocilia, which stimulates the hair cell, causing it to send information to the brain.
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cupula (definition, location)
jelly-like covering on hair cells within the semicircular canals and utricle and saccule.
122
process of static balance (step by step description)
when the head is tilted in any direction, it causes the direction of gravity relative to the direction of the head to change. this causes the otoliths within the utricle and saccule to be pulled in the direction of gravity. otoliths are contained in a cupula over the hair cells, so the shift of the otoliths causes the hair cells' sterocilia to bend and stimulate the hair cell.
123
what happens to the impulses from the semicircular canals and the ventricle?
some impulses travel to the spinal cord to be dealt with by reflex while others are send to the cerebellum. this information is combined with input from the eyes
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membrane potential (definition)
form of potential energy resulting from the separation of charges between the inside and outside of a cell membrane. voltage across a cell membrane
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voltage (definition)
electrical potential difference across a membrane as measured by a voltmeter
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polarized membrane (definition)
the state of the cell membrane in an unstimulated neuron in which the inside of the neuron is negatively charged in comparison to the outside of the neuron.
roughly -70mV
127
polarization (definition)
the process of generating a resting membrane potential averaging roughly -70mV
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resting membrane potential (definition)
the voltage across the cell membrane of an unstimulated (resting) cell. averages at -70mV
129
what mechanisms help maintain a polarized membrane? (short descriptions)
1) negatively charge molecules too large to pass through the membrane are present within the neuron.
2) the membrane is impermeable to some small negative ions such as Cl-, which are present within the neuron.
3) sodium-potassium exchange pumps transports 3Na+ out of the cell for every 2 K+ that are transported into the cell
130
process of sodium-potassium pumps (step by step description)
a) carrier protein has a shape that allows it to transport 3 Na+
b) when 3 Na+ are in the protein, ATP is split and a phosphate group attached to the carrier protein
c) the carrier changes shape due to the phosphate group, causing it to release the 3 Na+ outside the neuron and pick up 2 K+
d) the phosphate group is released from the carrier protein
e) resulting shape change causes release of 2K+ into the neuron. return to step a)
NOTE: Na+ and K+ are able to diffuse over the membrane but K+ diffuses out of the neuron more readily than Na+ diffuses in, allowing a charge of -70mV to build up
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depolarization (definition)
the loss of reduction of the negative resting membrane potential
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action potential (definition)
the change in charge that occurs when the gates of the potassium ion channels close and the gates of the sodium ion channels open. a large depolarization event that is conducted along the membrane of a nerve or muscle cell
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threshold stimulus (definition)
weakest possible stimulus needed to stimulate a nerve impulse (initiate action potential)
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repolarization (definition)
restoring the resting membrane potential (-70mV) after depolarization
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refractory period (definition, time, function)
short period of time immediately after an action potential in which the neuron cannot respond to another stimulus. the period of time it takes to re-establish the negative charge inside the neuron and the positive charge outside, restoring the balance of Na+ and K+ ions that is normal in a polarized neuron.
136
threshold potential (definition)
the smallest change in membrane potential that is needed to initiate action potential. bringing the net charge to about -55mV
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all-or-none response (definition)
action that occurs either completely or not at all. generation of action potential is such a response--the magnitude of the stimulus does not impact the magnitude of the action potential
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nerve impulse process (step by step description)
1) the neuron's membrane potential is -70mV. a stimulus of -55mV (threshold potential) is delivered to the neuron, initiating action potential.
2) depolarization: the stimulation causes voltage-regulated Na+ channels in the membrane to open and K+ channels to close, causing Na+ ions to rush into the cell and K+ ions unable to leave, raising the charge to +35mV
3) repolarization: change in voltage causes Na+ channels to close and K+ channels to open, preventing more Na+ to enter and causing K+ to flood out (hyperpolarization causes overshooting and the charge becomes -90mV rather than the resting potential right away)
4) the neuron returns to the resting potential and normal methods of maintaining a charge of -70mV continue
NOTE: this order of events moves throughout the neuron in a single direction due to the refractory period preventing the neuron from stimulating backwards
139
why exactly do myelinated neurons carry nerve impulses faster?
the movement of action potential though the neuron's axon depends on it being able to exchange ions with its environment. the myelin sheath acts as an insulator and prevents ions to move into or out of the neuron where Schwann cells cover it. this causes the positively charged neurons to move past the Schwann cell and to the node of Ranvier (saltatory conduction) (refractory period prevents the charged ions from stimulating in the wrong direction), and this moving past areas surrounded by Schwann cells is faster than the movement of the action potential without skipping past areas
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saltatory conduction (definition)
rapid transmission of a nerve impulse along a myelinated axon. the action potential jumps from one node of Ranvier to another, skipping the myelinated regions of the membrane
141
what two factors determine rate of nerve impulse conduction in an axon?
```
myelin sheath (present = faster)
axon diameter (larger = faster)
NOTE: axon diameter does not have as great an impact as the presence of a myelin sheath
```
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nerve impulse (simple definition)
a series of action potentials
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synapse (definition)
connection between two neurons or a neuron and an effector
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neuromuscular junction (definition)
synapse between a motor neuron and a muscle cell
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synaptic cleft (definition)
space between connected neurons (most have gaps)
146
synaptic knob (definition)
"synaptic terminal". tiny enlarged ending on an axon terminal
147
synaptic vesicle (definition)
a tiny membranous sac that contains neurotransmitters
148
neurotransmitter (definition)
chemical messenger, released from the synaptic knob of a neuron at a synapse, that diffuses across the synaptic cleft, binds to specially shaped protein receptors on the postsynaptic membrane, and stimulates the postsynaptic neuron
149
presynaptic/presynaptic membrane (definition)
the surface membrane surrounding the synaptic knob and facing the synaptic cleft (presynaptic: the neuron that sends the message. postsynaptic: the neuron that receives the message)
150
impulse crossing the synaptic cleft process (step by step description)
1) the impulse travels through the axon and axon terminal to the synaptic terminal
2) synaptic vesicles move forward and fuse with the presynaptic membrane
3) neurotransmitters are released into the synaptic cleft (exocytosis)
4) neurotransmitters bind to receptor proteins and affect the postsynaptic neuron (by causing the opening of of positive or negative ion channels)
5) neurotransmitters are detached from the receptor proteins, broken down by specific enzymes, and reabsorbed by the presynaptic neuron
151
excitatory effect (neurotransmitter) (definition)
the neurotransmitter causes positive ion channels to open (such as Na+ channels) that cause depolarization and may cause action potential if the threshold stimulus is reached or may lower the threshold for future stimulation
152
inhibitory effect (neurotransmitter) (definition)
the neurotransmitter causes negative ion channels to open (or positive K+ channels where this would cause K+ to leave the neuron), resulting in an increased negative charge and increased threshold stimulus. causes hyperpolarization
153
dopamine (function, effects of abnormal production)
FUNCTION: affects brain synapses in the control of body movements. linked to sensations of pleasure such as eating.
EXCESSIVE PRODUCTION: linked to schizophrenia, where a person's perception of reality is greatly distorted
INADEQUATE PRODUCTION: linked to Parkinson's, where neurons are destroyed, causing tremors, slurred speech, and other coordination problems
154
serotonin (function, effects of abnormal production)
FUNCTION: regulates temperature and sensory perception
| INADEQUATE PRODUCTION: linked to depression
155
endorphins (function, effects of abnormal production)
FUNCTION: acts as natural painkillers in synapses in the brain. affects emotional areas of the brain
INADEQUATE PRODUCTION: linked to increased risk of alcoholism
156
norepinephrine (function, effects of abnormal production)
FUNCTION: used by brain and some autonomic neurons. complements actions of epinephrine (hormone), which readies the body to respond to danger or other stressful situations. used by the sympathetic nervous system
EXCESSIVE PRODUCTION: linked to high blood pressure, anxiety, and insomnia
INADEQUATE PRODUCTION: linked to hunger cravings and exhaustion
157
cholinesterase (definition, function)
"acetylcholinesterase". fast acting enzyme. decomposes acetylcholine in the synaptic cleft.
158
acetylcholine (definition, function)
very common neurotransmitter. excitatory. broken down by cholinesterase. used in sympathetic and parasympathetic autonomic nervous systems
