Bio: Nervous System Flashcards
The nervous system enables organisms to..
The NS enables organisms to receive and respond to stimuli from external and internal environments
Neuron
Functional unit of the NS.
Converts stimuli into electrochemical signals, which are conducted through NS.
Is the ES or NS faster at responding to stimuli
NS
4 kinds of invertebrate NS
Protozoa
Cnidaria
Annelida
Arthropoda
Protozoa NS
unicellular. no organized NS.
respond to stimuli such as touch, heat, light, chemicals
Cnidaria
Nerve net
limited centralization
jellyfish.
annelida
Earthworms
Possess a PRIMITIVE CNS with defined ventral nerve cord and anterior “brain” of fused ganglia (nerve cell body clusters)
Nerve pathways from receptors to effectors
arthropoda
Arthropod brains are similar to annelid brains.
Arthropods are more specialized sense organs.
compound or simple eyes
tympanum for sounds
Neuron Structure
basic building block of NS.
Elongated cell of several dendrites, cell body, single axon.
Dendrite
cytoplasmic extensions of the cell body that receive information and transmit it to the cell.
Cell body
soma
long cellular process that transmits impulses away from cell body
Myelin
Most mammalian axons are sheathed by it.
allows for faster impulses.
Made by glial cells. (oligodendrocytes in CNS
Schwann cells produe yelin in PNS)
Nodes of anvier
gasps between myelin
Synaptic terminals
axons end. synaptic boutons or knobs
Neurotransmitters are released from?
synaptic terminals into synapse clef in gap between axon terminals of one cell and dendrites of next cell
Function of Neuron
receive signals from sensory receptors or other neurons.
Transfer this info along axon.
Action potentials
Impulses that travel the length of axon and invade nerve terminal, causing NT replease into synapse.
When a neuron is at rest potential difference between extracellular space and intracellular space is
Resting potential
Resting potential charge
Neuron is polarized here at -70 mV.
inside of neuron is more negative than the outside.
Due to selective ionic permeability of neuronal cell membrane and is maintained by active transport by sodium potassium pump.
Sodium potassium pump
Because transmission of action potentials lead to disruption of ionic gradients, the gradients are restored by Na/K pump.
uses ATP transports 3 NA OUT for every 2 K in.
AT REST. pump ensures hi conc of K inside neuron than outside and opposite for Na.
How is the resting potential created?
neuron is selectively permeable to K, so K diffuses down its concentration gradient, leaving net negative INSIDE.
Neurons at rest are impermeable to NA so that the cell remains polarized at -70 mV.
Negative proteins are trapped INSIDE cell
Action potential
if a cell is sufficiently excited or DEPOLARIZED (inside becomes less negative), then an action potential is gen
Minimum threshold membrane potential
-50 mV.
level at which AP is initiated
Ion channels in nerve cell membrane open in response to
Changes in voltage.
That’s why theyre called voltage gated ion channels
When does an action potential begin
When voltage gated Na channels open in response to small changes inmembrane potential that lead to depolarization thus letting na to rush down its electrochemical gradient, causing a rapid depolarization.
Then the Na channels close, and K channels open, letting K to come in and repolarize to a negative potential
Hyperpolarization
Neuron may shoot past the resting potential and become even more negative inside than normal.
Refractory period
very difficult or impossible to initiate another action potential… It represents the time Na+ channels need to recover from inactivation.
Describe AP
all or none.
nerve fires maximally or not at all.
stimulus intensity is coded by action potential frequency
Impulse propagation
axons can propagate AP bidirectionally.. but information transfer only goes dendrite to synaptic terminal.
Why do synapses operate in one direction?
Because refractory periods make the backward travel of AP impossible.
The greater the diameter of the axon and the more heavily it is myelinated… the FASTER or SLOWER? the impulses will travel?
FASTER.
Myelin increases conduction velocity by insulating axon so that the membrane is permeable to ions only in the nodes of Ranvier.
Synapse
Gap between axon terminal of one neuron (presynaptic) and the dendrites of another neuron (postsynaptic)
How else can neurons communicate?
Neurons also may communicate with postsynaptic cells other than neurons, such as cells in muscles or glands called effector cells.
What does the nerve terminal contain?
neurotransmitters. membrane bound vesicles full of cemical messengers
When do the synaptic vesicles fuse with presynaptic membrane?
When the AP arrives at the nerve terminal and depolarizes it… the synaptic vesicles fuse with the presynaptic membrane and release NT into the synapse.
NT diffuses across synapse and acts on receptor proteins of the postsynaptic membrane.
How do you remove a NT from synapse?
Taken back up into the nerve terminal via an uptake carrier protein.It’ll be reused or degraded
It can be degraded by enzymes in synapse (acetylcholinesterase inactivates acetylcholine)
Diffuse out of synapse.
Effect of drugs on synapses
Curare
Botulism toxin
Anticholinesterase
Curare: block postsynaptic acetylcholine receptors so that acetylcholine cant interact with the receptor… paralysis by blocking nerve impulses to muscles.
Botulism toxin: prevents result of acetylcholine from presynaptic membrane and results in paralysis
Anticholinesterase: used as nerve gases. inhibit acetylcholinesterase. Acetylchoine isn’t degraded in the synapse and continues to affect postsynaptic membrane.no coordinated muscular contractions can happen
Afferent neurons
Neurons that carry sensory info about EXTERNAL or INTERNAL environment TO BRAIN or SPINAL CORD.
Efferent neurons
Neurons that carry MOTOR commands FROM BRAIN or SPINAL CORD to various parts of body
Interneurons
Some neurons only participate in local circuits.
link sensory and motor neurons in brain and spinal cord.
Cell bodies and nerve terminals in same location
What is a nerve
Bundles of axon covered with connective tissue.
What is a cluster of neuronal cell bodies?
In the periphery: GANGLIA
In the CNS: NUCLEI
NS
-Central - brain -spinal cord
Peripheral -somatic -autonomic (-sympathetic -parasympathetic)
CNS
Brain and spinal cord
Brain
mass of neurons
outer gray matter (Cell bodies) and inner white matter (myelinated axons)
Forebrain, midbrain, hindbrain
Forebrain
T,O,D(t and h)
Telencephalon-> cerebral cortex. highly convoluted gray matter that can be seen on the outside of the brain. important for integrating sensory input and motor responses. and vip for memory and creative thought.
Olfactory bulb: center for reception and integration of olfactory
Diencephalon-> has thalamus and hypothalamus
Thalamus->relay and integration center for spinal cord and cerebral cortex
Hypothalamus-> visceral functions… hunger.. thirst.. sex..wter bal..blood p.. temp.. endocrinesystem via feedback
Midbrain
relay center for visual and auditory impulse
Als in motor control
Hindbrain
Posterior of brain madeof cerebellum, pons, medulla
CEREBELLUM: modulate motor impulses initiated by cerebral cortex and importance for maintenance of balance, handeye coord. timing of rapid movememnts.
PONS-> relay center to allow cortex to communicate with cerebellum
MEDULLA-> breathing, heart rate, GI
Midbrain. pons. medulla. equals BRAINSTEM
Spinal cord
Elongated extension of brain that is a conduit for sensory information to brain and motor information from brain
spinal cord can integrate reflexes.
outer is whitematter containing motor and sensory axons. inner graymatter containing nerve cell bodies.
Sensory information enters the spinal cord through
the dorsal horn
Cell bodies of these sensory neurons are in the dorsal root ganglia
all motor information exits the spinal cord through the
ventral horn.
reflex, sensory fibers synapse directly on ventral horn motor fibers.
PNS
nerves and ganglia
sensory nerves which enter CNS and motornerves which leave CNS are part of PNS.
Two primary divisions
SOMATIC. AUTONOMIC NS. both have motor and sensory comp
SOMATIC ns
innervates skeletal muscles
voluntary move
AUTONOMIC ns
involuntary ns.
body’s internal enviro without conscious control
ANS innervates cardiac and smooth muscles (blood vess, dig tract, bladder, bronchi)
VIP in bp control, GI motility excretory, resp, rep,
composed of sympathetic andparasympatheic
Sympathetic NS
fight or flight. emergency increases bp, hr, blood flow to skeletal, dilate bronchioles to increasegas exchange. decrease gut motility. Use norepinenephrine as primary NT
Parasympathetic NS
conserve enrgy. restore body to rest.
lower hr. increase gut motility.
VAGUS NERVE. uses acetylchoine as a NT to innervate many thoracic and abdominal viscera
Eye
detects photons and transmits info to brain.
eyeball
covered by sclera (thick, opaque)
Under sclera is choroid (supplies retina with blood. choroid is dark, pigmented area that reduces reflection in eye)
innermost layer is retina that has photoreceptors that sense light
cornea
transparent part at front of eye.
bends focuses light rays into pupil, whose diameter is controlled by pigmented, muscley iris.
iris responds to intensity of light. light goes through lens, which is behind pupil.
lens’s shape and focal length are controlled by ciliary muscles. Lens focuses image on to retina
What is in retina
Photoreceptors. transduce light into AP.
cones hi intensity illumination. contain 3 diff pigments that absorb rgb
Rods low intensity illumination. rod pigment rhodopsin absorbs one wavelength
Bipolar cells
photoreceptor cells synapse onto bipolar cells which in turn synapse onto ganglion cells. which bundle to form optic nerves which conduct visual info to brain.
blind spot
point at which optic nerve exits the eye. no photoreceptors.
fovea
small area of retina packed with cones. vip for high acuity vission
eye contains jellylike material called
vitreous humor.
helps maintain shape and optical props
aqueous humor is made by eye and exits through ducts to join venous blood.
Eye disorders
myopia, hyperopia, astigmatism. cataracts. glaucoma
nearsight. farsight. weird cornea shape. opaque lens. increase pressure in eye due to blociking of outflow of aqueous humor.
ear
transduces sound energy aka pressure waves into impulses perceived by brain as sound
sound waves pass through 3 regions as they enter ear
outer ear (auricle and auditory canal) to tympanic membrane (eardrum where vibrates at same frequency as incoming sound.) -> 3 ear bones(malleus, incus, and stapes) amplify stimulus and transmit into inner ear (cochlea and vestibular apparatus) for equilibrium.
Vibration of ossicles exerts pressure on cochlea fluid, stimulating
hair cells in basilar membrane to transduce pressure into AP, which travel via auditory/cochlear nerve to brain for processing.
