Lecture 2: Nervous System 1 cont, 2, and 3 Flashcards
Two major efferent systems:
Somatic Nervous System
Autonomic Nervous System
The SNS innervates _____ _____, which is under ______ control.
skeletal muscle
voluntary
Cell bodies of the SNS lie in
the CNS
SNS axons extend
into the periphery to innervate one or more neuromuscular junctions
The ANS is under ______ control and innervates
involuntary
all peripheral effectors that is not skeletal muscle
Axons of ANS motor neurons inside the CNS synapse where?
On neurons in the peripheral autonomic (motor) ganglia
Ganglionic neurons of the ANS control
peripheral effectors
Preganglionic fibers
Part of the ANS
Axons that extend from the CNS to a ganglion
Postganglionic fibers
Part of ANS
Axons connecting ganglionic cells with the peripheral effectors
The basic structural unit of the nervous system is the
Neuron
Three parts of a neuron
- Cell body
- Dendrites
- Axon
Cell bodies
- Contains the nucleus and other organelles
- Serves as the nutritional center of the neuron
Dendrites
Cytoplasmic extensions that receive stimuli and conduct impulses to the cell body
Axon (nerve fiber)
Conducts impulses away from the cell body
Axon arises from
a thickened region of the cell body called the axon hillock
Action potentials first appear
at the initial segment of the axon
Collaterals
Branches along the length of the axon
Collaterals enable a single neuron to
communicate with several other cells
The main axon trunk and collaterals end in
fine extensions called telodendria
Synaptic knobs (terminal button)
Located at the tips of the telodendria, they form synaptic connections with other cells
Communication between cells at synapse most often involves the release of ______ by the ______ _____
neurotransmitters
Synaptic knob
Motor end plate
specialized portion of the muscle cell membrane immediately under the synaptic knob
Four functional segments of the neuron
- Receptive segment
- Initial segment
- Conduction segment
- Transmissive (Effector) segment
Receptive segment of neuron
- Receives and processes synaptic inputs from numerous other neurons.
- Resolutions of these processes will be passed on to the next segment only if it is sufficiently stimulated
Initial segment of neuron
The trigger zone of the neuron, where processed neural information from the receptive segment is converted to a nerve impulse (action potential).
The initial segment of a neuron has a _____ threshold because it has many _____ channels
low
sodium
Conduction segment of neuron
Conveys the results of neural processing of receptive segment via nerve impulses to the terminal segment
Transmissive (Effector) segment of neuron
Contains axon terminals that convert the stimulation of the nerve impulse to release chemical neurotransmitters at its synapses, which exert influences upon receptor sites of an effector cell
The two types of transport systems that carry materials from the cell body to the axon terminals and back:
Slow axonal transport (axoplasmic flow)
Fast axonal transport
Slow axonal transport is a ____-way transport away from cell body
one
How fast is slow axonal transport?
moves 1-5mm/day
Bulk of the movement in slow axonal transport is in
the axoplasm
Slow axonal transport is accompanied by
peristaltic waves of the axon membrane
Purpose of slow axonal transport
to supply materials necessary to maintain axons and dendrites.
Does slow axonal transport require ATP?
Yes
Fast axonal transport speed
400-2000 mm/day
What does fast axonal transport move?
Varies organelles and materials that form the membranes of the axolemma, synaptic bulbs, and synaptic vessels away from the cell bodies.
Also transports acetylcholinesterase
Does fast axonal transport require ATP?
Yes
Kinesin
transport protein for moving material along microtubules, from the cell body to the axonal terminal (anterograde transport)
Retrograde flow
When cells are returned to the cell body to be recycled or degraded
When can retrograde flow be detrimental?
It can carry the rabies virus and the tetanus toxin into the CNS, producing potentially fatal results
Transport protein for retrograde flow?
dynein
What is the membrane potential and what is it measured in?
The separation of charges across a membrane.
Measured in millivolts (mV)
Resting membrane potential
potential for electrical activity along the plasma membrane of a resting neuron
What two major factors contribute to the resting membrane potential?
- The distribution of ions across a membrane
- The relative permeability of the membrane to Na- and K+
In a resting neuron, the membrane permeability to __ is about 50 to 100 times greater than it is to __
K
Na
