Quiz 5 Nervous System pt 1 Flashcards
Central Nervous System involves the:
Brain
Spinal Cord
Peripheral Nervous System involves the:
Nerves
- Afferent Neurons
- Efferent Neurons
- Sympathetic Autonomic Control
- Parasympathetic Autonomic Control
Afferent Neurons
sensory neurons
- sense stimulus and send info about the stimulus to CNS e.g. smell, light
Efferent Neurons
motor neurons
- carry signals away from CNS, initiating action
Somatic Motor Neurons
(Efferent Neurons)
skeletal muscle
Autonomic Motor Neurons
(Efferent Neurons)
cardiac muscle (heart), glands, smooth muscles in the body; “hollow tubes”
Sympathetic Nervous System
(Autonomic Motor Neurons)
FIGHT OR FLIGHT
e.g. blood pressure, sweat, digestion stops
Parasympathetic Nervous System
(Autonomic Motor Neurons)
REST OR DIGEST
- counteracts effects of sympathetic nervous system (starts digestion again, lowers BP)
- optimal level of functioning exists in the parasympathetic nervous system
Enteric Nervous System
bowels, small intestine
Neuron
- is a nerve cell, fully differentiated, and capable of transmitting a nervous (electrical) impulse
Nervous Tissue
- composed of neurons
- therefore our brain, spinal cord, and nerves are all cariations of neuronal arrangement
3 basic structures of a neuron
Cell Body (Soma): interpretation and protein synthesis; also contains nucleus
Dendrites: branched projections acting to propogate electrochemical stimulation received from other neural cells to the cell body (soma).
Axon: conducts/transmits electrical impulses away from the soma to different neurons, glands, or muscles; “nerve fibers”
White Matter/Grey Matter
White Matter: myelinated axon
Grey matter: unmyelinated axon, dendrite, or soma
Neurons and signal direction
A neuron is only capable of carrying a signal in one direction along its axon, thus the distinction between sensory and motor neurons.
(A bundle of axons w/in CNS is referred to as a tract; a bundle of axons outside the CNS is referred to as a nerve)
Synapse
- the junction between the axon terminal and there the axons lead (muscle, other neuron, gland)
- transmission of a signal across the synapse may be electric, but is more commonly chemical (involving a neurotransmitter)
Neuronal Membrane
(Channels and Pumps)
the membrane of a neuron is impermeable to most ions such as Na+, K+, Cl-, and Ca+, however, many distint channels and gates exist for their passage, but most notably:
Voltage Gated Channels: “Na+ stay high, K+ stay low”?
Na/K ATPase Pump: re-establish resting membrane (push Na+ out, K+ in)
Slow leak ion channels: K+ leaks out slowly (but faster than Na+)– creates + outside and - inside
Resting Membrane Potential
A membrane at rest has a higher concentration of sodium on the outside and potassium on the inside of the cell. Potassium slowly leaks out creating a negative charge on the inside of the resting membrane; measured in millivolts
Action Potential
- a rapid change in membrane potential and is the mechanism by which a nerve signal is transmitted
- muscle cells, cardiac cells, and neural cells all support an action potential though slight variations exist among the differing tissue types
- the ability to support an action potential is characterized by the term ‘excitable’ tissue
RESTING STAGE
DEPOLARIZATION STAGE (Na+ channels open, flooding inside the cell)
REPOLARIZATION STAGE (K+ channels open, flood out of the cell) ATP pump kicks in?
Saltatory Conduction
- occurs along the myelinated axons allowing for a more rapid and energy conserving signal transmission
- able to “skip” all the gates… jumps from one node to the next
Neurotransmitters
- are chemicals released into the synapse once an action potential reaches the end of the axon
- its release is calcium dependent, and its action is determined by the postsynaptic receptor
- the resulting action may last milliseconds or days and include:
– opening or closing of membrane channels
– enzyme activation on the postsynaptic structure
– altered cell metabolism
– altered gene expression
Two Major classes of neurotransmitters exist:
Large molecule NT: neuropeptides/neurohormones
- insulin, growth hormone, prolactin, melanocyte stimulating hormone
Small molecule NT: have a more rapid and shorter duration of action
- dopamine, seratonin, histamine, acetylcholine, norepinephrine
The obvious variable in a neuron’s ability to carry a signal is:
Alterations in Neuronal Transmission
Ion concentration
- neurotransmitter deficiencies, demyelination, damage to the neuron
Alterations in Neuronal Transmission cont…
- neuroregeneration* is possible through axonal regrowth assuming the cell body of that neuron is in tact
- also, extracellular changes of endogenous and exogenous matter must be considered with respect to ingestion, metabolism, and excretion ability
(e. g. a drop in extracellular pH will result in increased excitability of a neuron while a rise in pH will result in the opposite effect) - Low oxygen levels may decrease synaptic activity
Alterations in Neuronal Transmission Cont
(synaptic fatigue and synaptic facilitation)
Synaptic Fatigue: occurs if stimulation is too rapidly repeated
Synaptic Facilitation: occurs if repetitive stimulation is followed by a brief period of rest, then re-stimulation
Ganglia
- masses of soma and dendrites in a close proximity; “clusters of cell bodies” (the term plexus is used to describe groupings of various ganglia)
Two Ganglia of note:
Dorsal Root Ganglia (spinal ganglia) of the sensory neurons
Autonomic Ganglia of the autonomic motor neurons
- sympathetic ganglia are paraspinal
- parasympathetic ganglia are close to their effector organ
- Somatic motor neuron cell bodies are located within the spinal cord at various levels, thus no ganglia
