Chapter 12 - Nervous Tissue Flashcards
neurons
functional unit of the nervous system (transmits info)
neuroglia
cells that support and maintain neuronal function
structural classification of neurons is based on…
the number of processes (axons or dendrites) extending from the cell body
-unipolar, bipolar, or multipolar neurons
describe sensory or afferent neurons
- Convey AP into the CNS (central nervous system)
- Occurs through cranial or spinal nerves
describe motor or efferent neurons
- Convey AP from CNS to the periphy
- Cause muscles to do something
describe interneurons
-Mainly located in CNS between sensory and motor neurons
what are the two types of electrical signals that neutrons use?
1.Graded potentials Short distance communication Only within dendrites and cell body – doesn’t travel down axon Determine if AP will ocurr 2.Action potentials Allow for communication over long distances
what is Resting Membrane Potential (RMP)?
- ion channels open or close in response to specific stimui
- More positive charge outside the cell = RMP
- The RMP is negative (-70mV)
Explain the process of maintaining a -70 mV RMP.
- Na+/K+ ATPase pumps out 3 Na+ for every 2 K+ pumped in (net increase of + charge outside cell)
- Leakage channels randomly opened or closed
- More K+ leaks out than Na+ leaks in
explain electrochemical gradiets
- when ion channels are open, specific ions can cross PM down the electrochemical gradient.
- Cations (positive charge) move towards a negatively charged area; Anions (negative charge) move towards a positively charged area
what are the 3 types of gated channels?
- ligand-gated
- voltage gated
- mechanically gated
explain ligand-gated channels.
- respond to a neurotransmitter
- concentrated near synapses, dendrites and cell body of sensory neurons
explain voltage gated channels.
Channels respond to changes in membrane
explain mechanically gated channels
respond to a mechanical or physical deformation
what is a polarized cell?
a cell that exhibits a resting membrane potential
polarized cells have the ability to produce what kind of potential. Explain.
- graded potential
- Open an ion channel, changes the membrane potential
- Spreads for a short distance
depolarizing graded potential
Stimulus causes the cell to be less negatively charged
hyperpolarizing graded potential
Stimulus causes cell to be more negatively charged
When does an action potential occur
if the Axon Hillock reaches -55 mV (threshold)
where do graded potentials occur?
dendrites and cell body, do not travel down the axon
how do graded potentials differ from action potentials?
- travel short distances
- can be added together to create a smaller or larger graded potential
define action potential
- a signal which travels the length of the neuron
- If neuron reaches a threshold potential, an AP is produces and spreads down to axon terminals
- If stimulus is not strong enough = no AP
what are the 2 phases of an action potential?
- depolarizing phase
2. repolarizing phase
what occurs when a graded potential reaches its threshold (-55 mV)
- Voltage-gated Na+ channels open
- Na+ rushes into cell inside becomes more positive
- Membrane potential reaches +30 MV - During the repolarization phase, K+ channels open and K+ rushes outward.
- The cell returns to a more negative state
in action potentials what causes after-hyperpolarization to occur? explain.
- open voltage gated channels let too much k+ flow out of the cell
- membrane potential becomes even more negative (~-90 mV)
- Voltage gates K+ channels close, membrane potential returns to resting
explain the all or none principle for AP
- if a stimulus reaches threshold, the action potential is always the same.
- a stronger stimulus will not cause a larger AP
- If you need a stronger reaction, send more AP’s
what is the absolute refractory period? explain.
- cell cannot generate another AP, no matter how strong the stimulus.
- Period that coincides with the period of Na+ channel activation and inactivation
- Na+ channels must return to resting state before next AP can occur
what is the relative refractory period? explain.
- period of time during which a second action potential can be initiated, but only by a larger-than-normal stimulus.
- When K+ channels are still open, but Na+ channels are resting = hyperpolarizing phase
where does propagation of an AP begin?
axon hillock
how does propagation of an action potential proceed?
- continuous conduction - unmyelinated axons
2. saltatory conduction - myelinated axons
what is the purpose for a myelinated axon?
insulation, increases speed of nerve impulse
what are nodes of ranvier? (neurofibril nodes)
areas of axon without myelin
explain signal transmission at the synapse
1.one-way transfer from a presynaptic neuron to a postsynaptic neuron.
2.AP reaches axon terminals, voltage gated Ca2+ channels open
3.Ca2+ flows in triggering
the release of Neurotransmitters into synaptic cleft.
4.neurotransmitters cross cleft and bind to ligand-gated receptors on postsynaptic membrane
what mades the intensity of graded potentials increase?
increased number of neurotransmitters released to bind to postsynaptic membrane will increase graded potential in post synaptic cell
explain the process of neurotransmitter removal.
Removal is accomplished by:
- Diffusion out of the synaptic cleft
- Loss through enzymatic degradation
- Re-uptake by the cells
neurological regeneration is dependent upon what?
neurilemmocytes
where does neurological regeneration occur? and where does it not?
occurs in the Peripheral Nervous System (in neurilemmocytes) but does not occur in the central nervous system.
In the CNS what occurs if nerve cells become damaged?
astrocytes form scar tissue.
Describe the process of Neuronal Regeneration.
1) Axon is Injured
2) neurolemma forms regeneration tube
3) axon regenerates and re-mylenation occurs
4) Innervation to effector is restored
What are the 2 main divisions of the nervous system.
Central Nervous system
- brain and spinal cord
Peripheral Nervous System
-nervous tissue outside the CNS (nerves and ganglia)
Where do most stimuluses for muscle contraction and gland secretion begin?
central nervous system
what are the divisions of the PNS?
1) Somatic Nervous System (SNS)
2) Autonomic Nervous System (ANS)
3) Enteric Nervous System (ENS)
What are the components of the Somatic nervous system?
1) Somatic sensory neurons (afferent)
- to CNS
2) Somatic motor neurons (efferent)
- Away from CNS to skeletal muscle
3) Interneurons
- between afferent and efferent neurons
What are the components of the autonomic nervous system?
1) Sensory Neurons
- info from sensory receptors in visceral organs (heart, lungs) to CNS
2) Motor Neurons (involuntary)
- impulses from CNS to smooth muscle, cardiac muscle, and glands
name the 2 divisions of the autonomic nervous system
1) Sympathetic (fight or flight)
2) Parasympathetic (rest and digest)
The Enteric Nervous system (ENS) is often referred to as the …..
brain of the gut
what are the responsibilities of the ENS?
- involuntarily controls the GI propulsion
- acid and hormonal secretions
