Chapter 12 - Nervous Tissue Flashcards
Nervous system is responsible for all our __, ___ and __.
behaviors
memories
movements
neurology
branch of medical science that deals with normal functioning & disorders of the NS
Major structures of the NS
12 pairs of cranial nerves
31 pairs of spinal nerves
**ganglia **outside CNS - small masses of nervous tissue, mostly neuronal cell bodies
**Enteric plexuses - **help regulate digestive system - neuron networks in walls of GI tract organs
**sensory receptors **- structure of NS that monitors change in internal/external environment
Functions of NS (3)
**1) sensory **- afferent
**2) integrative - **interneurons
**3) motor - **efferent
NS divisions (2)
CNS - brain & spinal cord
**PNS - **cranial & spinal nerves, connects CNS to muscles/glands/sensory receptors
Neurons
functional unit of nervous system
have capacity to produce action potentials - **electrical excitability **
cell body (soma) - contains organelles
**Nissl bodies - **clusters of rough ER
**neurofibrils - **cell shape & support
**microtubules - **assist in moving materials
**dendrites & axons - **processes
**lipofuscin - **yellow/brown pigment granules in cytoplasm
Location for most protein synthesis in Neuron
cell body
Axonal transport
1) slow axonal flow
2) **fast **axonal flow
1) movement in one direction -away from cell body
2) either direction - use or recycling
Structural classification of neurons
1) multipolar
2) bipolar
3) unipolar
Functional classification of Neurons
1) sensory (afferent)
2) motor (efferent)
3) interneurons (association)
Neuroglia
non-neuronal cells
1/2 the volume of CNS
Of CNS: astrocytes, oligodendrocytes, microglia, ependymal
Of PNS: Schwann, satellite
Neuroglia of CNS
1) astrocytes
2) oligodendrocytes
3) microglia
**4) ependymal **
1) support, blood-brain barrier, homeostasis,
2) form **myelin sheath **around axons
3) phagocytes
4) produce cerebrospinal fluid
Neuroglia of PNS
1) schwann cells
**2) satellite **
1) form **myelin sheath **around ONE axon
2) structural support & regulate exchange of materials b/w soma & interstitial fluid
Schwann cell cytoplasm forms outer layer & inner layer is…
**myelin sheath **(100+ layers of schwann cell membrane)
Subdivisions of PNS
**1) Somatic (voluntary) - **cutaneous &special sensory receptors → CNS
motor neurons → skeletal muscle
**2) Autonomic (involuntary) **- sensory- visceral organs → CNS
motor to smooth+cardiac muscle& glands
**A. Sympathetic - **↑ heart rate
**B. Parasympathetic **- ↓ heart rate
**3) Enteric - **involuntary sensory & motor control GI tract
function independently of ANS & CNS
Neurons are electrically excitable due to the?
voltage difference across their membrane
Neurons communicate with (2) types of electric signals
1) action potentials - long distance
2) graded potentials - short distance
Resting membrane potential
What is potential energy difference at rest?
When neuron is at rest,
negativeions alonginsideof cell membrane &positive ions along outside
-70mV
At rest, Neuron is said to be _____
polarized
Resting potential exists because? (3)
1) ion concentration differs from inside to outside
**- **ECF has lots of Na+ & Cl-
cytosol has lots of K+
**2) inability of most anions to leave cell - **membrane permeability differs for Na+ & K+
3) Electrogenic nature of Na+/K+ ATPase
- inward flow of Na+ cant keep up with outward flow of K+ ( Na+ pumped out as fast as it leaks in)
this removes more positive than it brings in
Graded potential
occur mainly in?
dendrites & neuronal cell bodies
**small **deviation from resting potential of -70mV
hyperpolarizing vs depolarizing
**hyperpolarizing - **membrane becomes more negative
**depolarizing - **membrane become more positive
Graded potential
The signals are graded, meaning they vary in… and are? (2)
1) **amplitude (size), **
depending on the strength of the stimulus
2) localized
**Action Potential (impulse) **
a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and then restore it to resting state (repolarization)
All-or-none principle of Action Potentials
if stimulus reaches **threshold, **the action potential produced is always the same
stronger stimulus does NOT produce large impulse
(3) phases of an action potential
1) depolarizing phase
2) repolarizing phase
3) hyperpolarizing phase
1) depolarizing phase
At rest: inactivation Na+ gate = **open, **activation gate = closed
chemical/mechanical stimulus → graded potential reaches threshold (-55mV) → Na+ channels open → inactivation gate **closes → **membrane potential = +30mV
2) repolarizing phase
when threshold potential reached (-55mV) → K+ channels open (much slower than Na+ channels) → once K+ channels are **open, **Na+ channels are closed again → K+ outflow returns membrane potential to -70mV
3) hyperpolarizing phase
if enough K+ leaves cell, membrane potential reaches -90mV
K+ channels close & membrane potential returns to resting potential (-70mV)
Refractory period
Period of time during which neuron can not generate another action potential
**Absolute refractory period **vs Relative refractory period
**absolute - (depolarzing + repolarizing phase) **
even very strong stimulus can not begin another AP
inactivated Na+ channels must return to resting state
**refractory - **(hyperpolarizing phase) **
A suprathreshold stimulus will be able to start AP
K+ channels still open but Na+ channels are closed
**Conduction - **(2) types
1) continuous
2) saltatory
1) **unmyelinated + muscle fibers - **step-by-step depolarization of each portion of the length of the axolemma (axon plasma membrane)
2) **myelinated axons - **depolarization only at nodes of Ranvier (gaps in myelin sheath) where there is a high density of voltage-gated ion channels
current carried by ions flows through ECF from node to node
Factors that affect speed of propagation (3)
**1) amount of myelination - **faster along myelinated axon
**2) axon diameter - **larger = faster
**3) temperature - **higher temp = faster
The propagation speed of a nerve impulse is not related to __ __
stimulus strength.
**Fiber types (3) **
**- **diameterm, absolute refractory period (ARP), myelinated/unmyelinated, sensory/motor
**A fibers - **largest, longest ARP
- myelinated somatic sensory & motor to skeletal muscle
**B fibers - **medium, faster ARP
- **myelinated **visceral sensory & autonomic preganglionic (CNS → ANS relay station)
**C fibers - **smallest, fastest ARP
- **unmyelinated **sensory & autonomic motor
(2) types of **synapses **
1) electrical
2) chemical
Electrical Synapse
ionic current spreads to next cell through gap junctions
faster, two-way transmission & capable of synchronizing groups of neurons
AP conduct directly between plasma membrane of adjacent neuron through gap junctions)
Chemical synapse
one-way information transfer from presynaptic to postsynaptic neuron
plasma membranes do not touch, seperated by **synaptic cleft **
1) axodendritic
2) axosomatic
3) axoaxonic
1) from axon to dendrite
2) from axon to **cell body **
3) from axon to axon
Signal transmission at chemical synapse
Action potential reaches end bulb and voltage-gated Ca2+ channels open → Ca2+ inward flow triggers release of neurotransmitters → cross synaptic cleft & bind to ligand-gated receptors → channels open on postsynaptic neuron & ions flow across
Both ____________ and ____________ neurotransmitters are present in the CNS and PNS
the same ____________ may be excitatory in some
locations and inhibitory in others.
inhibitory & excitatory
neurotransmitter
Important neurotransmitters include? (8)
acetylcholine, glutamate, aspartate, gamma aminobutyric acid, glycine, norepinephrine, epinephrine, and
dopamine.
Neural circuits
involved in many important activities such as? (3)
functional groups of neurons that process specific types of information
breathing, short-term memory. waking up
Types of neural circuits (5)
1) simple series
2) diverging
3) converging
4) reverberating
5) parallel after-discharge
