Nervous System Flashcards
nervous system
enables organisms to receive and respond to stimuli from their internal and external environments. responds faster than endocrine system
Neurons
functional units of the nervous system. a neuron converts stimuli into electrochemical signals which are conducted through the nervous system.
protazoa nervous systems
posses no organized nervous system. single celled organisms may respond to stimuli like heat, touch, light and chemicals
cnidaria
simple nervous systems called nerve net. network of nerves may have limited centraliztion
annelida systems
earthworms possess a primitive central nervous system consisting of ventral nerve cord and anterior brain of fused ganglia. Definite nerve pathways lead from receptors to effectors
arthropoda systems
arthopod brains are similar to those of annelids but more specialized sense organs are present.
neuron structure
it is an elongated cell consisting of several dendrites, cell body, and a single axon.
dendrites
are cystoplasmic extensions of the cell body that receive information and transmit it towards the cell.
cell body
containing the nucleus and controls the metabolic activity of the neuron.
axon
a long cellular process that transmits impulse away from the cell body. most mammalian axons are sheathed by insulating substance called mylein.
myelin
allows axons to conduct impulses faster. it is produced by cells known as glial cells.
Oligodendrocytes
produce the mylein sheath in the central nervous system
Schwann cells
produce the myleain sheath in the peripheral nervous system.
nodes of Ranvier
the gaps between the mylein sheath
synaptic terminals
the axons endings that release neurotransmitters into the synapse, which is the gap between the axon terminals of the one cell and the dendrites of the next.
neurons function
specialized to recieve signals from sensory receptors or other neurons in the body to transfer information along the length of the axon.
action potentials
impulses that travel the axon and invade the nerve terminal thereby cuasing a release of neurotransmitter into the synapse
resting potential
when the neuron is at rest, the potential difference between the extracellular space and the intracellular space. the neuron is polarized
typical resting membrane potential is
-70 millivolts which means that the inside of the neuron is more negative than the outside.
Na+/K+ pump
active transport system that maintains the selective permeability of ions in the neuron membrane. the pump using ATP energy transports 3 Na+ out for every 2 K+ it puts in. Action potentials mess up the gradient and this pump restores it.
At rest the Na+/ K+ pump ensures
that the concentration of K+ is higher on the inside of the neuron and Na+ concentration is higher on the outside.
Action potential (detailed)
if the cell becomes excited or depolarized an action potential is generated. the minimum threshold membrane potential is around -50mV which the level that action potential is generated.
-voltage gated ions in the nerve membrane open in response to the change in voltage
the action potential begins when the Na+ voltage opens and Na+ rushes down its gradient leading to depolarizing. then it closes and K+ voltage does the same. repolarizing the cell.
hyperpolarization
if the neuron skips past the resting potential and becomes more negative inside than normal. this makes it impossible to initiate another action potential.
refractory period
the time the Na+ channels need to recover from inactivation after hyperpolarization.
Synapse operation direction
information will only travel from dendrite to synaptic terminal. they only operate in one direction because refractory periods make backward travel impossible.
impulse propagation
different axons can propagate at diff speeds. the greater the diameter of the axon and more heavily the mylein sheath, the faster the impulses will travel.
Synapse
the gap between the axon terminal of one neuron (called pre-synaptic neuron) and the dendrites of another neuron (post synaptic neuron/ cells) .
effector cells
if neuron is communicating with another cells they are called effector cells.
synapse function
When the action potential arrives at the nerve terminal end, the synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter into the synapse. which fuses across the synapse and acts of the receptor proteins on the postsynaptic membrane. which leads to depolarization of the post synaptic membrane leading to the firing of an action potential.
Neurtransmitter removal from synapse
it can be taken up into the nerve terminal (via uptake carrier), may be degraded by enzymes in the synapse or it may simply diffuse out of the synapse.
Curare
blocks the postsynaptic acetylcholine receptors so that acetylcholine is unable to interact with the receptor. this leads to paralysis by blocking impulses to muscles
Botulism toxin
prevents the release of acetylcholine from the presynaptic membrane and also results is paralysis
anticholinesterases
uses as nerve gases in insecticides, inhibits activity of the acetylcholinesterase enzyme. so it is not degraded in the synapse preventing coordination of muscles
afferent neurons
neurons that carry sensory information about the external or internal environment TO the brain or spinal cord
efferent neurons
neurons that carry motor commands FROM the brain or spinal cord to various parts of the body
interneurons
participate only in local circuits, linking sensory and motor neurons in the brain and spinal cord, plus their cell bodies and nerve terminals are in the same location.
nerves
bundle of axons covered with connective tissue
plexus
a network of nervous
ganglia
neuronal cell bodies clustered together in the periphial system
nuclei
neuronal cell bodies clustered together in the central nervous system
CNS
central nervous system consisting of the brain and the spinal cord
Brain
- mass of neurons that resides in t he skull. -functions include interpreting sensory information, forming motor plans, and cognitive function.
- outer portion is gray matter (cell bodies) and inner white matter (myelinated axons).
- forebrain, midbrain and hindbrain
forebrain telencephalon
- major component is the cerebral cortex highly convoluted gray matter that can be seen on the surface of the brain, processes and integrates sensory input and motor responses an it important for memory and creative thought.
- olfactory bulb is inferior portion: the center for reception and integration of odor input.
forebrain diencephalon
contains the thalamus and the hypothalamus.
thalamus-relay and integration center for the spinal cord and the cerebral cortex
hypothalamus-controls visceral functions and endocrine systems feedback
Mid brain Mesenecephalon
relay center for visual and auditory impulses. also important in motor control
Hind brain
posterior part that contains the cerebelum, medulla and the pons.
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
medulla
controls many vital functions such as breathing, heart rate, gastrointestinal activity.
brain stem
midbrain, pons and medulla
spinal cord
- elongated extension of the brain that acts as a conduit for sensory information to the brain and motor information form the brain.
- outer white area contains motor and sensory axons, inner gray matter contains nerve cell bodies
dorsal horn
where sensory information enters the spinal cord, the cell bodies of these sensory neurons are located in the dorsal root ganglia
ventral horn
all motor information exits the spinal cord here
reflexes
come from areas where the sensory and motor fibers synapse directly onto one another.
PNS
peripheral nervous system- consists of nerves and ganlia. the sensory nerves that enter the CNS and the motor nerves that exit the CNS are part as well. Two divisions are somatic and autonomic.
Somatic nervous system
innervates skeletal muscles and is responsible for voluntary movement
Autonomic nervous system
also the involuntary nervous system, innervates cardiac and smooth muscle. comprised of two divisions sympathetic and parasympathetic which act in opposition to each other
sympathetic nervous system
responsible for the “flight or fight” responses that ready the body for action in an emergency situation. Increases blood pressure, heart rate, skeletal muscles, decreases gut motility, dilates bronchi oles to increase gas exchange. Uses norephinephrine as a primary neurotransmitter
parasympathetic nervous system
acts to conserve energy and restore the body to resting activity levels following exertion. “rest and digest”. exact opposite actions of SNS. the vagus nerve is key. Uses aceytelcholine as its primary neurotransmitter
The eye
detects light energy (as photons) and transmits information about intensity, color, and shape to the brain.
sclera
thick white opaque layer that covers the eyeball
choroid layer
underneath the scleara of the eye that helps to supply the retina with blood. Dark pigmented area that reduces reflection in the eye
retina
innermost layer of the eye which contains photoreceptors that sense light and transduce them into action potentials.
cornea
transparent portion at the front of the eye bends and focuses light rays.
pupil
an opening behind the cornea that the rays of light travels through whose diameter is controlled by the pigmented muscular iris
iris
pigmented portion of the eye that responds to the intensity of light in the surroundings.
lens
suspended behind the pupil, the shape and focal length is controlled by the ciliary muscles and focuses the image into the retina.
photoreceptors cells
located in the retina are cones and rods. they synapse onto bipolar cells, which synapse onto ganglion cells. axons of the ganglion cells bundle to form the optic nerve.
cones
respond to the high intensity illumination of light and are sensitive to color. containing three different pigments that absorb red, green and blue
rods
detect low intensity illumination and are important for night vision. the only pigment contained in rhodopsin.
optic nerve
conducts visual information to the brain. the point at which the nerve exits the eye is the blind spot.
fovea
a small area of the retina is densely packed with cones and is important for high acuity vision.
vitreous humor
jelly like liquid in the eye which helps maintain its shape and optical properties.
aqueous humor
formed by the eye and exits through ducts to join the venous blood.
myopia
nearsightedness occurs when the image is focused in front of the retina
hyperopia
farsightedness occurs when the image is focused behind the retina
astigmatism
caused by an irregular shaped cornea
cataracts
caused the lens to become opaque, light cannot enter the eye and blindness result
glaucoma
is in increase of pressure in the eye due to the blocking of the outflow of the aqueous humor
the ear
transduces sound energy (pressure waves) into impulses of perceived by the brain as sound. sound waves pass through three reigons of the ear first, outer middle and inner
outer ear
consists of the auricle (external ear) and the auditory canal
middle ear
the of the auditory canal is the tympanic membrane (ear drum) which vibrates at the same frequency as the incoming sound. next the three ossicles (males incus and stapes) amplify the stimulus and transmit through the oval window which leads to inner ear
inner ear
fluid filled and consists of the cochlea and the vestibular apparatus, which is involved in equilibrium. vibration of the ossicles exerts pressure on the fluid cochlea stimulating hair cells in the basilar membrane to transduce action potientals that are sent by the auditory nerve to the brain for processing.
