ch 11 Flashcards
basic functions of the human nervous system
master controlling and communication system of the body. 3 functions:
- sensory input (input=afferent): gather information from various sensory receptors inside and outside the body to monitor any changes
- integration: processing and interpreting the incoming information from the sensory input
- motor output (output=efferent): effects a response by activating or suppressing muscles, organs, glands, tissues. muscles, organs, glands, tissues that respond are called effectors
nervous systems division
central nervous system: CNS (brain, spinal cord)
peripheral nervous system: PNS (all neural tissue outside of the CNS)
-input: afferent (sensory division):
—-somatic afferent: sensory receptors from: skin, skeletal muscle, joints; somatic sensory neurons: monitor external environment and positions within it
—–visceral afferent: sensory receptors from: organs, tissues, smooth muscle; visceral sensory neurons: monitor internal environment and status of other organ systems
-output: efferent (motor division)
——-autonomic nervous system (ANS): involuntary NS- visceral motor neurons– sympathetic division (fight or flight) — parasympathetic division(rest and digest)
——-somatic nervous system (sns): voluntary NS: somatic motor neurons- includes reflexes
neuroglia of CNS
ependymal cells: line central canal (narrow passageway in spinal cord) and ventricles (enlarged chambers in brain); form an epithelium (simple cuboidal to simple columnar) called Ependyma; cerebralspinal fluid: fills passageways or spaces in the CNS; form blood-CSF barrier; have cilia and microvilli to circulate CSF
microglia cells: immune cells, least numerous and smallest neuroglia; relative long thorny processes which touch nearby neurons, monitoring their health. phagocytic cells, migrate through neual tissue.
astrocytes: contain microfilaments, processes wrap around blood capillaries: maintain blood-brain barrier, in embryo regulate and guide neuron development, control interstitial environment, play role in learning and memory by influencing formation of neuronal synapses, repair damaged neural tissue
oligodendrocytes: fewer processes than astrocytes; play role in structural organization by tying clusters of axons together; improve functioning of neurons by wrapping axons within a myelin sheath
structure and characteristics of neuron
characteristics: extreme longevity, largely amitotic, exceptionally high metabolic rate
structure: cell body (contains nucleus), dendrites (short and branched processes), axon (single long processes), telodendria (terminal branches of axon)
movement along axon
movement toward synaptic knob is called anterograde movement; carried out by kinesin, mitochondria, cytoskeletal elements, membrane components, enzymes, some neurotransmitters.
movement toward cell body is retrograde movement; carried by dynein; most organelles bring recycled, delivery of signal molecules; important means of intracellular communication
3 functional classifications of neurons
- sensory (afferent neurons) unipolar neurons; transmit impulses from sensory receptors in skin or internal organs TOWARD or INTO the CNS. almost all sensory neurons are unipolar except special sense organs- bipolar neurons
- motor (efferent neurons); carry impulses AWAY from CNS to effectors; all multipolar neurons
- interneurons (association neurons): outnumber all other types combined, most located within the CNS; lie between motor and sensory neurons in neural pathways. shuttle signals through cns pathways where integration occurs, all multipolar neurons but considerable diversity in both size and fiber branching patterns
structural classification of neurons
- mulitpolar: most common in body and CNS, have very long axons, multiple dendrites, one axon. (all somatic motor neurons)
- bipolar: rarest, found in special sensory organs
- unipolar: found in sensory neurons of PNS; have very long axons, fused dendrites and axon, cell body to one side.
sensory receptors (dendrites)
- interoceptors: provides information about internal environment; monitor internal systems and internal senses
- exteroceptors: provides information about external environment; external senses and distance senses
- prprioceptors: monitor position and movement
neuroglia of PNS
satellite cells (amphicytes): surround cell bodies within ganglia, regulate environement around neuron like astrocytes, cover soma. schwann cells (neurolemma cells): form a myelin sheath around peripheral axons, fuctionally similar to oligodendrocytes. vital to regeneration o fperipheral nerve fibers known as wallerian degeneration. whole cell jelly rolls around axon not just processes like oligodendrocytes
nuclei, ganglia, white matter, gray matter
nuclei: clusters of cell bodies in CNS are nuclei
ganglia: clusters of cell bodies in PNS are ganglia
white matter: myelinated axons
gray matter: areas containing cell bodies, dendrites, and unmyelinated axons
the synapse
presynaptic cell= presynaptic neuron: neuron that sends message
postsynaptic cell: cell receives message either neuron to muscle cell, or neuron to glandular cell
synaptic cleft: small gap that separates presynaptic membrane and postsynaptic membrane
neurotransmitter
released into synaptic cleft
chemical messengers
affect receptor of postsynaptic membrane
released at presynaptic membrane. synaptic knob secretory part of neuron
neron fires
trigger zone sends action potential, which open voltage gated channels. Na+ and K+
AP travels to synaptic knob and opens voltage gated Ca2+
dendrites receive this info which causes chemically gated channels to open Na+, K+, Cl-
this causes a graded potential which travels to trigger zone and causes an action potential
graded potential
short distance signals (local)
produced b typical stimulus (any stimulus that opens chemically gated channel produces graded potential)
temporary, localized, short lived change in resting potential.
decreases with distance from stimulus, magnitude varies directly with stimulus strength
essential in initiating action potentials
action potentials
long distance signals
electrical impulse that is propagated along the plasma membrane of axon or sarcolemma
doesnt diminish as it moves away from the source
transition from GP to AP takes place at trigger zone
depolarization
less polarized, meaning less negative -70 mv to -65 mv
repolarization
restoring resting membrane potential -65 mv to -70 mv
hyperpolarization
membrane potential increases (inner leaflet is more polarized)
inner leaflet of plasma becomes more negative than at resting membrane -70 mv -75 mv
4 steps in formation of ap
- depolarization to threshold
- activation of sodium channels and rapid depolarization
- inactivation of sodium channels and activation of potassium channels
- closing of potassium channel
continuous propagation vs saltatory propagation
continuous propagation: unmyelinated axon
saltatory propagation: myelinated axon: ap propagation occurs more rapidly and only happens at node of ranvier. it skips
fiber types
type A: fastest; largest myelinated; somatic motor neurons
type B: lightly myelinated, preganglionic axons of ANS
type C: unmyelinated, smallest type; postganglionic axons of ANS
electrical synapse
very rare in CNS and PNS (eye and brain)
presynaptic and postsynaptic membranes locked together via gap junctions: electrically coupled.
propagation of AP travels very quickly, efficiently and will always occur between coupled neurons
chemical synapses
most common type , unidirectional communication, synaptic terminal releases a neruotransmitter that binds to postsynaptic plasma membrane, produces temporary localized chance in permeability or function of postsynaptic cell
changes affect cell depending on nature and number of stimulated receptors
excitatory neurotransmitter: promotes APs by depolarization
inhibitory neurotransmitter: inhibits APs by hyperpolarization
termination of a neurotransmitter
degradation by enzyme: enzyme present at the postsynaptic membrane or synaptic cleft that breaks down the neurotransmitter
uptake or reuptake by cells: neurotransmitter is taken up by astrocytes or presynaptic terminal by neurotransmitter transporters
diffuses away: neurotransmitter diffuses away from synapse
spatial summation
multiple synapses that are simultaneously resulting in huge numbers of neurotransmitters being released altogether that dramatically increases depolarization at trigger zone
temporal summation
addition of stimuli occurring in rapid succession at single synapse
neurotransmitters
excitatory: glutamate, aspartate
inhibitory: gamma-aminobutyric acid, glycine
neuropeptides
substance p: found in sensory neurons, spinal cord pathways and parts of brain associated with pain
endorphins: inhibit pain by blocking release of substance p
