Chapter 13- Neuroscience Flashcards
The two major divisions of the nervous system are:
Central nervous system (CNS)
Peripheral nervous system (PNS)
In general, what does the nervous system do?
It enables organisms to receive and respond to stimuli from their external and internal environments.
Neurons
The functional units of the nervous system.
Converts stimuli into electrochemical signals that are conducted through the nervous system.
Which responds to stimuli quicker, the nervous system or the endocrine system?
The nervous system.
What is a neuron?
An elongated cell consisting of several dendrites, a cell body and a single axon.
Soma
Also called the cell body. Contains the nucleus and controls the metabolic activity of the neuron.
Axon
A long cellular process that transmits impulses away from the cell body.
Myelin
Sheath that insulates axons, makes conduction faster.
Oligodendrocytes
Produce myelin in the central nervous system.
Schwann cells
Produce myelin in the peripheral nervous system.
Nodes of ranvier
Gaps between segments of myelin.
Axons end:
Swellings known as axon terminals or synaptic buttons or knobs.
Neurotransmitters
Released from axon terminals into the synapse, which is the gap between the axon terminal of one cell and the dendrites of the next cell.
4 types of cells in the CNS
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
2 types of cells in the PNS
Satellite
Schwann
Astrocytes
Maintain the integrity of the blood brain barrier, regulate nutrient and dissolved gas concentrations, and absorb and recycle neurotransmitters.
Oligodendrocytes
Myelinate CNS axons as well as provide structural framework for the CNS.
Microglia
Remove cellular debris and pathogens.
Ependymal cells
Line the brain ventricles and aid in the production, circulation, and monitoring of cerebral spinal fluid.
Satellite cells
Surround the neuron cell bodies in the ganglia.
Schwann cells
Enclose the axons in the PNS and aid in the myelination of some peripheral axons.
Two neurotransmitters often found in the nervous system:
Norepinephrine and acetylcholine
Precursor of norepinephrine
Dopamine
Where does synthesis of norepinephrine begin? Where does it end?
Begins: axoplasm of the terminal nerve endings of adrenergic fibers
Ends: Inside the vesicles of the fibers
Outline the basic steps in the synthesis of norepinephrine:
Tyrosine is converted to DOPA through the process of hydroxylation
DOPA undergoes decarboxylation to become dopamine
dopamine is transported into vesicles of adrenergic fibers, where it undergoes hydroxylation to become norepinephrine
Where is , norepinephrine is transformed into epinephrine?
In adrenal medulla– through methylation
How is acetylcholine made?
Choline + acetyl-CoA
What are neurons specialized for?
To receive signals from sensory receptors or from other neurons in the body and transfer this information along the length of the axon
Action potentials
Impulses that travel the length of the axon and invade the never terminal, causing the release of neurotransmitter into the synapse.
Resting potential
The potential difference between the extracellular space and the intracellular space when a neuron is at rest.
True or false: at rest, a neuron is polarized
True
Why is there a potential difference at rest?
A result of an unequal distribution of ions between the inside and outside of the cell.
What is a typical resting membrane potential?
-70 millivots (inside is more negative than the outside)
What is the resting membrane potential caused by?
-ly charged compounds are trapped on the side.
Also, inside is selectively permeable to K+, leaving it to travel down its concentration gradient to outside and to leave a net - charge on the inside.
Neurons are impermeable to Na+, leaving cells permeable
Which side of the membrane in more concentrated by each ion?
The concentration of K+ is higher inside than outside. Na+ is higher on the outside than inside.
How is gradient restored after action potential?
The pump uses energy to transport 3 Na+ out and 2 K+ in.
Outside cell:
Na+»_space; K+
net positive charged
Inside cell
K+» Na+
net negative charge
Active transport of K+ is
Two K+ inside
Active transport of Na+ is
3 Na+ outside
Passive transport of K+ is
K+ outside
Passive transport of Na+ is
Na+ inside
Depolarization
Inside of the cell= less negative
Action potential is generated by
If the cell becomes depolarized (excited)
Minimum threshold membrane potential
The level at which an action potential is initiated (-50 mV)
Which phases do depolarization, repolarization and hyperpolarization occur?
Depolarization: Phase 1
Repolarization: Phase 2
Hyperpolarization: Phase 3
When does an action potential begin?
When voltage-gated channels open in response to depolarization, which allows Na+ to rush down its electrochemical gradient into the cell, causing inside to be a lot more positive than outside.
Repolarization
The voltage-gated Na+ channels close, K+ channels open, K+ goes outside of cell down its electrochemical gradient
Hyperpolarization
When neuron shoots past its resting potential and becomes even more negative on the inside than normal
Refractory period
Immediately after an action potential, a period when it is difficult or impossible to initiate another action potential.
All or none response
Action potential with a consistent size and duration is produced when the threshold membrane potential is reached
Nerves fire maximally or not at all
Stimulus intensity is coded by:
the frequency of action potentials
What direction is information transferred?
From dendrite to to synaptic terminal
Impulses are faster when:
Axons have large diameter and are heavily myelinated.
Synapse
Gap between the axon terminal of one neuron (presynaptic neuron) and the dendrites of another neuron (postsynaptic neuron).
Effector cells
cells in muscles or glands that neurons might communicate with.
Neurotransmitters are in
In the membrane bound vesicles of nerve terminals
How is neurotransmitter released?
When an action potential arrives at the nerve terminal and depolarizes it, the synaptic vesicles fuse with the presynaptic membrane and and release neurotransmitters into the synapse.
What happens after neurotransmitters are released into the synapse?
Neurotransmitters diffuse across the synapse and act on receptor proteins on postsynaptic membrane. It will lead to depolarization of postsynaptic cell and cause an action potential.
How is a neurotransmitter removed from the synapse?
Taken back up into the nerve terminal
May also be degraded by enzymes located in the synapse
it way also diffuse out of the synapse
Curare
Blocks postsynaptic acetylcholine receptors so that acetylcholine cannot interact with receptor. Leads to paralysis by blocking nerve impulses to muscles.
Botulism toxin
Prevents the release of acetylcholine from the presynaptic membrane. Leads to paralysis.
Anticholinesterases
Used as nerve gases as in insecticide Parathion. Inhibit the activity of acetylcholinesterase enzyme– hence acetycholine is not degraded and continues to affect the postsynaptic memrane. This results in no coordinated muscular contractions taking place.
Nervous system of protozoa or unicellular organisms:
Possess no organized nervous system. May respond to touch, heat, light and chemicals.
Nervous system of Cnidaria
Simple nervous system called nerve net. Limited centralization. Some jellyfish have clusters of cells and pathways that coordinate the relatively complex movements needed for swimming.
Nervous system of annelida
Possess of primitive central nervous system consisting of a defined ventral nerve cord and an anterior “brain” of fused ganglia
Nervous system of anthropoda
Brains are similar to annelids but more specialized sense organs are present
Afferent neurons
In vertebrates– neurons that carry sensory information about the external and internal environment or the brain or spinal cord.
Efferent neurons
Neurons that carry motor commends from the brain to the spinal cord to various parts of the body
Interneurons
Neurons that participate only in local circuits, linking sensory and motor neurons in the brain and spinal cord; their cell bodies and nerve terminals are in the same located.
Plexus
A network of nerve fibers.
Nerves are essentially ________
bundles of axons connected with connective tissue
Ganglia
Neuronal cell bodies that cluster together– in PNS
Nuclei
Neuronal cell bodies that cluster together– in CNS
CNS consists of
Brain and spinal cord
The brain is a mass of:
Neuron
What do the functions of the brain include?
Interpreting sensory information, forming motor plans, and cognitive function.
Inner and outer portions of the brain?
Inner- white matter (myelinated axons)
Outer- gray matter (cell bodies)
What can the brain be divided into?
Forebrain, midbrain, and hindbrain
Prosencephalon
Forbrain
What does the forebrain consist of?
The telencephalon and diencephalon.
Major component of the telencephalon
Cerebral cortex– highly convulated gray matter that can be seen on the surface of the brain.
What does the cerebral cortex do?
It processes and integrates sensory input and motor responses and is important for memory and creative thought.
Olfactory bulb
Center of reception and and integration of olfactory input.
What does the diencephalon contain?
Thalamus and hypothalamus
Thalamus
Relay and integration center for the spinal cord and cerebral cortex.
Hypothalamus
Controls visceral functions such as hunger, thirst, sex drive, water balance, blood pressure, and temperature regulation. Also important part in endocrine system control.
Mescencephalon
Midbrain
Midbrain
Relay center for visual and auditory impulses. Important role in motor control.
Rhombencephalon
Hindbrain
Hindbrain
posterior part of the brain that consists of cerebellum, the pons, and the medulla.
Cerebellum
helps to modulate motor impulses initiated by the cerebral cortex and is important in the maintenance of balance, hand-eye coordination and the timing of rapid movements.
Pons
Act as a relay center to allow the cortex to communicate with the cerebellum.
Medullla
Control many vital functions such as breather, heart rate, and gastrointestinal activity.
Brainstem
Midbrain, pons and medulla
Spinal cord
An elongated extension of the brain that acts as the conduit for sensory information to the brain and motor information from the rbain
True or false: the spinal cord cannot integrate simple motor impulses
FALSE- it can integrate refelxes
Inner and outer part of spinal cord:
Inner: gray matter area containing nerve cell bodies
outer: white matter area containing motor and sensory axons.
Sensory information enters the spinal cord through:
The dorsal horn
Motor information exists the spinal cord through the
ventral horn
Where do sensory fibers synapse for simple reflexes?
Directly on the ventral horn motor fibers
The PNS consist of:
Nerves and ganglia
The sensory nerves that enter the CNS and motor nerves that leave the CNS are a part of the:
PNS
Two primary division of the PNS
Somatic
Autonomic
Somatic
Innervates skeletal muscles and responsible for voluntary movement as well as reflex arcs
Autonomic
Involuntary regulates internal env– no conscious control.
The ANS innervates
Cardiac and smooth muscle
Where is smooth muscle located?
Blood vessels, digestive tracts, bloadder, bronci
what is ANS important for?
Blood pressure control, gastrointestinal motility, excretory purposes, respiration, and reproductive proceses
ANS subdivisions
Sympathetic and parasympathetic
Sympathetic
Flight or fight. Increases BP and heart rate. Uses norepinephrine as its primary neurotransmitter
Parasympathetic
Acts to conserve energy and restore body to resting activity after exertion.
Lowers heart rate.
Vagus nerve neurotransmitter
Acetylcholine
Lens
Symp: None
ParaSymp: Accomodation
Iris
Symp: Dilates pupil
ParaSymp: Constricts pupil
Salivary glands
Symp: vasoconstriction: dry
ParaSymp: secretion
Sweat glands
Symp: secretion (specific)
ParaSymp: secretion (generalized)
Heart (force and rate)
Symp: increases
ParaSymp: decreases or stays the same
Peripheral blood vessels
Symp: constriction
ParaSymp: dilation
Visceral blood vessels
Symp: constriction
ParaSymp: dilation
Lungs
Symp: vasodilation, bronchodilation
ParaSymp: bronchoconstriction, secretion
Gastrointestinal tract
Symp: decreases peristalsis and secretion
ParaSymp: increases peristalsis and secretion
Rectum and anus
Symp: Inhibits smooth muscle in rectum and constricts sphincter
ParaSymp: Increases smooth muscle tone and relaxes sphincter
Adrenal medulla
Symp: None
ParaSymp: Secretion
Bladder
Symp: Relaxation of detruser muscle and constriction of internal sphincter
ParaSymp: Contraction of the detrusor muscle and inhibition of internal sphincter
Genitalia
Symp: Ejaculation
ParaSymp: Penile erection and engorgement of clitoris and labia
Eye detects and transmits
light energy, photos and transmits information about intensiry, color and shape to the brain
Sclera
A thick opaque layer that covers the eyeball– white of the eye
Choroid
Beneath the sclera- helps supply the terina with blood.
Dark and pigmented area that reduces the reflection in the eye
Retina
innermost layer, contains photoreceptors that sense light
Cornea
Transparent
at the front of the eye and bends and focuses light rays
Pupil
Rays travel from cornea
opening- diameter is controlled by the pigmented and muscular iris
Iris
responds to the intensity of light in the surroundings
Light makes pupil
constrict
Lens
Suspended behind the pupil. Shape and focal length of lens is controlled by ciliary muscles, and focuses image onto retina.
Photoreceptors
tranduce light into action potentials.
Cones
Respond to high intensity illumination and are sensitive to color
rods
detect low intensity illumination and are important in night vision
Cones contain
Three different pigments that absorb red, green and blue wavelengths
Rod contains
only one pigment rhodopsin- only one single wavelength
Bipolar cells
What photoreceptor cells synapse onto
Bipolar turn synapse onto:
ganglion cells
Axons of the ganglion cells bundle to form:
optic nerve
Optic nerve conducts
visual information to the brain
blindspot
where optic nerve exists the eye
No photoreceptors present
Fovea
small area of the retina, densely packed with cones and important for high acuity vision.
Vitreous humor
Jelly like material that maintains shape and optical properties
Aqueous humor
watery substance that fills space between lens and the cornea
Myopia
nearsightedness- image focused in front of retina
Hyperopia
farsightedness- image focused behind retina
Astigmatism
Irregularly shaped cornea
Cataracts
develop when lens become opaque; light cannot enter eyes, and blindness results
Glaucoma
increase of pressure in the eye because of blocking of the outflow of the aqueous humor, which results in optic nerve damage
Function of the ear
Transduces sound energy (pressure waves) into impulses perceived by the brain as sound.
Sound waves pass thorugh
outer ear- auricle(external ear) and auditory canal
At end of auditory canal= tympanic membrane (eardrum) of the middle ear
Vibrates at the same freq. as incoming sound
Ossicles (malleus, incus, and stapes) amplify stimulus and trasmit it through oval window, which leads to fluid filled inner ear
Inner ear- cochlea and vestibular apparatus, which maintains equilibrium
Vibrations of ossicles exerts pressure of cochlea, stimulating hair cells in the basilar membrane to transduce the pressure into action potentials, which travel cia the auditory nerve to the brain
