Nervous System Flashcards
Nervous System
responsible for controlling most body functions, enabling organisms to receive and respond to stimuli from their external and internal environments
Neuron
- used to convert stimuli into electrochemical signals through the body
- consists of dendrites, a cell body, and an axon
Dendrites
receive information and transmit it toward the cell body
Cell Body
contains the nucleus and controls the metabolic activity of the neuron
Axon
transmits impulses or action potentials away from the cell body
Myelin
- protects the axons from leaking signals and allows for faster conduction of impulses
- produced by glial cells called oligodendrocytes in the CNS and by Schwann cells in the PNS
Nodes of Ranvier
gaps between segments of myelin where action potential propagates
Synaptic Terminals
this is where axons end and where neurotransmitters are released into the synaps
Synapses
the gap between the axon terminals of one cell and the dendrites of the next cell
Astrocytes (CNS)
maintain the integrity of the blood-brain barrier, regulate nutrient and dissolved gas concentrations, and absorb and recycle nuerotransmitters
Oligodendrocytes (CNS)
myelinate CNS axons as well as provide structural framework for the CNS
Microglia (CNS)
remove cellular debris and pathogens
Ependymal (CNS)
line the brian ventricles and aid aid in the production, circulation, and monitoring of CSF
Satellite Cells (PNS)
surround the neuron cell bodies in the ganglia
Schwann Cells (PNS)
enclose the axons in the PNS and aid in the myelination of some peripheral axons
Resting Potential
- even at rest a neuron is polarized due to unequal distribution of ions between the inside and outside of the cell
- the potential difference at rest between the extra and intracellular space is the resting potential (-70mV)
Action Potential
- the nerve cell body receives both excitatory and inhibitory impulses from other cells
- if the cell body becomes sufficiently excited and depolarized to reach threshold potential, then voltage-gated ion channels located in the nerve cell mambrane open in response
- an action potential begins when voltage-gated Na+ channels open in response to depolarization allow Na+ to rush down its electrochemical gradient into the cell causing further rapid depolarization of the segment of the axon
- Na+ also causes the next portion of the axon toward the terminal to become depolarized, causing voltage-gated Na+ channels to open these as well, continuing the process of moving the action potential toward the terminal
- once the action potential reaches the synaptic terminal, a final voltage-gated channel specific to calcium opens and rushes in and triggers the exocytosis of synaptic vesicles containing neurotransmitters
- after the signal has been propogate through a segment of the axon, the high voltage there causes voltage-gated K+ channels to open
- meanwhile the voltage-gated Na+ channels also close
- together, these processes return the cell to a negative potential in a process called repolarization
- the neuron’s voltage shoots past the resting potential and becomes even more negative inside the normal due to the K+ still being free to leave the cell (hyperpolarization)
Refractory period
a period of time after an action potential during which new action potentials are very difficult or impossible to initiate immediately
Impulse Propagation
- information transfer will occur only in one direction: from dendrite to synaptic terminal b/c synapses operate only in one direction and because refractory periods make the backward travel of action potentials impossible
- different axons propogate action potentials at different speeds
- the greater the diameter of the axons and the more heavily it is myelinated, the faster the impulses travel
- myelin increases the conduction velocity by insulating segments of the axon such that the membrane is permeable to ions only in the nodes of Ranvier
Synapse
- the gap between the axon terminal of one presynaptic neuron and the dendrites of another neuron (postsynaptic)
- neurons may also communicate with postsynaptic cells other neurons (effectors cells)
Curase
blocks postsynaptic nicotinic acetylcholine receptors. leads to muscle relaxation and paralysis by blocking the ability to constrict muscles
Botulinum Toxin
prevents the release of acetylcholine from the presynaptic membrane and also results in paralysis
Anticholinesterases
used as nerve gases and the insecticide parathion
Afferent neurons
carry sensory information about the external or internal environment to the brain or spinal cord
Efferent neurons
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
Plexus
a network of nerve fibers. Neuronal cell bodies cluster together - ganglia in the periphery. In the CNS they are call nuclei
Central Nervous System (CNS)
consists of the brain and spinal cord
Brain (CNS)
- a mass of neurons that resides in the skull
- functions: interpret sensory information, forming motor plans, and cognitive function
- consists of an outer portion of cell bodies (gray matters and an inner portion of myelinated axons called white matter)
Forebrain - prosencephalon (CNS)
- consists of the telencephalon and the diencephalon
- major component of the telencephalon is the cerebral cortex, which is highly convulated gray matter
- the cortex processes and integrates sensory input and motor responses and is important for memory and creative thought
- the olfactory bulb is the center for reception and integration of olfactory input
- the diencephalon contains the thalamus and hypothalamus
Thalamus (forebrain)
a relay and integration center for the spinal cord and cerebral cortex
Hypothalamus (forebrain)
controls visceral functions such as hunger, thirst, sex drive, water balance, blood pressure, and temp regulation also plays an important role of the endocrine system
Midbrain (mesencephalon)
- a relay center for visual and auditory impulses
- also plays an important role in motor control
Hindbrain (Rhombencephalon)
-the posterior part of the brain and consists of the cerebellu, the pons, and the medulla
Cerebellum (Hindbrain)
- a part of the brain stem
- helps 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 (Hindbrain)
- a part of the brain stem
- acts as a relay center to allow the cortext to communicate with the cerebellum
Medulla (Hindbrain)
- a part of the brain stem
- controls vital functions: breathing, heart rate, and GI activity
Spinal Cord
- an elongated extension of the brain that acts as the conduct for sensory info to the brain and motor info from the brain
- a cross section of the spinal cord reveals an outer white matter area containing motor and sensory axons and inner gray matter area containing nerve cell bodies
- sensory info enters the spinal cord through the dorsal horn
- motor info exists the spinal cord through the ventral horn
Peripheral Nervous System (PNS)
- contains the nerves and ganglia
- sensory nerves that enter the CNS and the motor nerves that leave the CNS are part of the PNS
- has two primary divisions: somatic and autonomic
Somatic Nervous System
innervates skeletal muscles and is responsible for voluntary movement as well reflex arc
Autonomic Nervous System
- sometimes called the involuntary nervous system b/c it regulates the body’s internal environment w/o the aid of the conscious control
- includes both sensory and motor fibers
- innervates cardiac and smooth muscle
- comprised of sympathetic and parasympathetic nervous system
Sympathetic Nervous System
responsible for the “flight or fight” response. Increases blood pressure and heart rate. Uses norepinephrine as its primary neurotransmitter
Parasympathetic Nervous System
acts to conserve energy and restore the body to resting activity levels after exertion
The Eye
-detects light energy and transmits information about intensity, color, and shape
Sclera
-a thick layer covering the eyball
Choroid layer
-beneath the sclera and helps supply the retina with blood
Retina
- the innermost layer of the retina
- contains photoreceptors
Cornea
-bends and focuses light rays
Pupil
this is where the rays travel
Iris
controls the diameter of the pupil
Lens
controlled by ciliary muscles
Cones
- respond to high-intensity illumination and are sensitive to color
- absorb red, green, and blue wavelengths
Rods
- detect low-intensity illumination and are important in night vision
- the rod pigment, rhodopsin, only absorbs a single wavelength
Fovea
densely packed with cones and is important for high-acuity vision
Vitreous Humor
helps maintain its shape and optical properties
Aqueous Humor
a more watery substance that fills the space between the lens and the cornea
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 irregularly shaped cornea
Cataracts
develop when the lens becomes opaque, light cannot enter the eye and blindness results
Glaucoma
an increase pressure in the eye because of blocking of the outflow of the aqueous humor, which results in optic nerve damage
Outer Ear
consists of the auricle and the auditory canal
Middle Ear
- consists of the tympanic membrane (eardrum), which vibrates at the same frequency as the incoming sound
- contains three bones that amplify the stimulus and transmit it through the oval window
Inner Ear
consists of the cochlea and the vestibular apparatus stimulating hair cells in the basilar membrane to the transduce the pressure into action potentials, which travel via the auditory nerve to the brain for processing
