CH 11 - Functional Organization Of Nervous Tissue Flashcards
What are the 3 functions of the nervous system?
Sensory input (afferent), integration, motor output (efferent)
Afferent
Sensory input
Information is gathered from various sensory receptors inside and outside the body to monitor for changes
Integration
The processing and interpretation of incoming information from the sensory input
Efferent
Motor output
Effecting a response by activating or suppressing effectors
What are considered effectors?
Muscles, glands, organs, and tissues
What makes up the central nervous system?
The brain and spinal cord
Also nervous tissue, connective tissue, and blood vessels
What are the functions of the central nervous system?
Process & coordinate:
Internal/external sensory info
Peripheral organ activity
Higher functions (intelligence, memory, learning, emotion)
What makes up the peripheral nervous system?
All neural tissue outside of the CNS
Also cranial/spinal nerves, connective tissue, and blood vessels
What are the functions of the peripheral nervous system?
Carry sensory info to the CNS
Carry motor commands from the CNS
What do somatic sensory neurons monitor?
The external environment and positions within it
Where are the sensory receptors from in somatic sensory?
Skin, skeletal muscle, joints
Where are the sensory receptors from in visceral sensory?
Organs, tissues, smooth muscle
What do visceral sensory neurons monitor?
Internal environment and status of other organ systems
What information comes from special sense organs?
Seeing, hearing, balance & equilibrium, smell, taste
What is the somatic nervous system?
The voluntary nervous system
Effectors: skeletal muscles
Neurons: somatic motor neurons
What is the autonomic nervous system?
The involuntary nervous system
Effectors: everything except skeletal muscles
Neurons: 2 visceral motor neurons
What are the 2 divisions of the autonomic nervous system?
Sympathetic - fight or flight
Parasympathetic - rest and digest
Cranial nerve I
Olfactory
From olfactory receptors
Cranial nerve II
Optic
From retina of eye
Cranial nerve III
Oculomotor
To eye muscles
Cranial nerve IV
Trochlear
To eye muscles
Cranial nerve V
Trigeminal
From mouth and jaw muscles
Cranial nerve VI
Abducens
To eye muscles
Cranial nerve VII
Facial
From taste buds
To facial muscles and glands
Cranial nerve VIII
Vestibulocochlear
From inner ear
Cranial nerve IX
Glossopharyngeal
From pharynx
To pharyngeal muscles
Cranial nerve X
Vagus
From/to internal organs
Cranial nerve XI
Accessory
To neck and back muscles
Cranial nerve XII
Hypoglossal
To tongue muscles
List the spinal nerves.
Cervical nerves (C1-C8)
Thoracic nerves (T1-T12)
Lumbar nerves (L1-L5)
Sacral nerves (S1-S5)
Coccygeal nerve (C0)
What is a neuron?
Highly specialized cells that are the structural units of the nervous system
What is the function of a neuron?
Perform all communication (via nerve impulses), information processing, and control functions of the nervous system
What are 3 characteristics of neurons?
Extreme longevity - lasts a lifetime
Amitotic - cannot regenerate
High metabolic rate - aerobic respiration
What are the 4 regions of a multipolar neuron?
Cell body (soma) - contains the nucleus
Dendrites - short, branched processes off the soma
Axon - a single long process
Telodendria - terminal branches off the axon
Descibe the cytoskeleton of the cell body.
Consists of neurofilaments, neurotubules, microfilaments
Helps maintain shape/structure
Moves materials between cell body and axon
Nuclei
Clusters of cell bodies in the CNS
Ganglia
Clusters of cell bodies in the PNS
Nissl bodies
Free ribosomes and rough endoplasmic reticulum that gives the soma a grey color
Neurofibrils
Bundles of neurofilaments in the soma
Describe and list the functions of dendrites.
Main input region of the neuron that is branched to increase surface area
Convey incoming info as a graded potential toward the cell body
Dendritic spines
Points of contact with other neurons at the end of a dendrite
Describe an axon and its functions.
Conducting component of a neuron
*One per neuron
Carries an action potential away from the cell body
Axoplasm
Cytoplasm of an axon
Axolemma
Plasma membrane of an axon
Axon Hillock
Cone-shaped thickened area of the cell body that joins the initial segment of axon
Trigger zone
Axon hillock plus the initial segment of axon
Axon collaterals
Side branches along the length of the axon
Telodendria (terminal branches)
End branches of the axon
Synaptic knob
Very ends of the axon where neurotransmitters are exocytosed and released into the synaptic cleft
Where are graded potentials generated?
On plasma membranes of dendrites and the cell body
*Becomes an action potential at the trigger zone
Where are action potentials generated?
On axolemma
*Travels to synaptic knobs
Anterograde movement
Movement toward the axon terminal carried out by kinesin
Kinesin
A molecular motor protein
Carries: mitochondria, cytoskeleton elements, membrane components, enzymes, and neurotransmitters
Retrograde movement
Movement toward the cell body carried out by dynein
Dynein
A molecular motor protein
Carries: recycled organelles
Synapse
Specialized site where a neuron communicates with another cell
*Every synapse involves 2 cells
Presynaptic neuron
Neuron that sends the message
Postsynaptic neuron
Neuron that receives the message
*Can be another neuron, a muscle cell, or a gland cell
What are 5 types of synapses?
Neuromuscular junction Neuroglandular junction Axodendritic Axosomatic Axoaxonic
Synaptic cleft
The small gap that separates the presynaptic and postsynaptic membranes
Neurotransmitter
Chemical messengers released at presynaptic membrane into synaptic cleft that affect receptors of the postsynaptic membrane
What are the 3 structural classifications of neurons?
Unipolar, bipolar, multipolar
Describe unipolar neurons.
Found in sensory neurons of PNS
They have very long axons (fused to the dendrites) and a cell body on one side
Describe bipolar neurons.
Rarest, but found in special sensory organs
Cell body is before the trigger zone
Describe multipolar neurons.
Most common type in the body, CNS
Multiple dendrites and one long axon
*All somatic motor neurons are multipolar
What are the 3 functional classifications of neurons?
Sensory (afferent), motor (efferent), interneurons (association neurons)
What do sensory neurons do?
Transmit impulses from sensory receptors in skin/internal organs toward the CNS
*All sensory neurons are unipolar except the bipolar special sense organs
What do motor neurons do?
Carry impulses away from the CNS to the effectors
*All are multipolar
What do interneurons do?
Lie between sensory and motor neurons in neural pathways and shuttle signals through CNS pathways where integration occurs
- Outnumber all other neuron types combined
- Most located within CNS
- More complex the response to a stimulus, the more interneurons will be involved
What are 3 types of sensory receptors?
Interoceptors, exteroceptors, proprioceptors
What do interoceptors do?
Provide info about the internal environment
Monitor internal systems (digestive, urinary..)
and internal senses (taste, pain…)
What do exteroceptors do?
Provide info about the external environment
External senses (touch, temperature...) and distance senses (sight, smell...)
What do proprioceptors do?
Monitor position and movement of skeletal muscle and joints
What are Neuroglia?
The supporting cell to the neuron
*Smaller and 25x higher population
Name the 4 types of glial cells in the CNS, and the 2 in the PNS.
CNS: ependymal cells, microglia, astrocytes, oligodendrocytes
PNS: satellite cells, Schwann cells
Describe ependymal cells.
Line the central canal in the spine and ventricles in the brain
Form an ependyma (simple cuboidal/columnar epithelium)
Forms the blood-CSF barrier
Secretes CSF into ventricles and remove waste from CSF
Describe microglia.
Least numerous and smallest Neuroglia
Long processes that touch/monitor health of nearby neurons
Phagocytic cells
Migrate through neural tissue
List the functions of astrocytes.
Maintain blood-brain barrier with processes that wrap around capillaries
Regulate embryonic neuron development
Control interstitial/chemical environment
Aid learning/memory by forming neuronal synapses
Repair damaged neural tissue
Describe oligodendrocytes.
Aids structural organization by tying clusters of axons together
Wraps axons in a myelin sheath
What does myelination do?
Increases the speed of action potentials
Makes nerves appear white
Nodes of ranvier
Gaps between internodes, and sites of potential axon collaterals
Internodes
Myelinated segments of the axon
Describe satellite cells.
Surround PNS cell bodies
Regulate environment around the neuron (PNS version of the astrocyte)
Describe Schwann cells.
Form a myelin sheath around PNS axons (PNS version of oligodendrocytes)
*Takes multiple Schwann cells to fully enclose axon
Wallerian degeneration (regeneration of peripheral nerve fibers)
Neurolemma
Plasma membrane of a Schwann cell
Voltage
Measurement of electrical potential energy created by the separation of opposite charges
Units of volts (V) or millivolts (mV)
Current
The flow of electrical charge from one point to another that can be used to do work
Units of Amperes (A) or milliamperes (mA)
*Amount of charge (current) that moves between the points depends on voltage and resistance
Resistance
The hindrance to charge flow by a substance through which the current must pass
Unit of ohms
*A measure of how much the membrane restricts ion movement (membrane resistance)
Tell whether the concentrations are higher inside or outside of the cell: sodium, potassium, calcium, chloride.
Sodium: higher outside
Potassium: higher inside
Calcium: higher outside
Chloride: higher outside
What activates a leak channel?
Randomly activates (passive)
- Establishes resting membrane potential
- NOKIA
What are 3 types of gated channels?
Ligand-gated, voltage-gated, mechanically-gated
*Active channels
What activates a ligand-gated channel?
The binding of a specific chemical
*Most common on dendrites/soma
What activates a voltage-gated channel?
Changes in the transmembrane potential (membrane potential)
What activates a mechanically-gated channel?
Physical distortion of membrane surface
*Sensory receptors that respond to touch…
Resting membrane potential
-70mV, but varies with time and cell type
All neural activity begins with a change in resting potential of a neuron
Electrogenic pump
A transport protein that generates voltage across a membrane
*Na+ - K+ ATPase pump contributes to the voltage potential across the plasma membrane (NOKIA)
Electrochemical gradient
Drives the diffusion of ions across a membrane
Made of: Chemical gradient (the ion’s concentration gradient) Electrical gradient (the effect of the membrane potential on the ion’s movement)
Depolarization
Reduction in membrane potential (inner leaflet less negative)
Hyperpolarization
Increase in membrane potential (inner leaflet more negative)
Repolarization
Process of restoring resting membrane potential (return to -70mV) from a less negative number
*Called return to resting potential when going from more negative to resting membrane potential)
Graded potential
Short distance signals that open ligand or mechanically-gated channels
A temporary, localized change in the resting potential that decreases with distance from stimulus
Action potential
Long distance signals along plasma membrane of axon that do not diminish with distance from source
Opens voltage-gated channels
GP -> AP at trigger zone (membrane potential must be -55mV)
*Once initiated at threshold potential (-55mV) cannot be undone “all-or-nothing”
Why can’t action potentials generate from dendrites?
Dendrites only have ligand-gated or mechanically-gated channels, not voltage-gated channels
What happens at -70mV?
Voltage-gated Na+ inactivation gate channels open
Voltage-gated Na+ activation gate channels close
*Graded response from Na+ influx depolarizes to -55mV
What happens at -55mV?
Voltage-gated Na+ inactivation gate channels open
Voltage-gated Na+ activation gate channels open
*Results in rapid Na+ influx, depolarizing to +30mV
What happens at +30mV?
Voltage-gated Na+ inactivation gate channels close
Voltage-gated Na+ activation gate channels remain open
Voltage-gated K+ channels open, resulting in repolarization to -70mV
What happens at the return to -70mV?
Voltage-gated Na+ inactivation gate channels open
Voltage-gated Na+ activation gate channels close
Voltage-gated K+ channels begin slowly closing, resulting in hyperpolarization to -90mV
What happens at -90mV?
Voltage-gated K+ channels fully close, resulting in return to resting potential of -70mV
What are the 2 methods of propagating action potentials?
Continuous propagation and saltatory propagation
Continuous propagation
Occurs in unmyelinated axons
Both activation and inactivation gates of voltage-gated sodium channels open and sodium enters. Sodium that enters segment 1 spreads to segment 2, bringing it to threshold for another AP, while segment 1 repolarizes. Continue down the axolemma until it reaches the synaptic knob
Saltatory propagation
Occurs in myelinated axons
Action potential jumps from node to node between myelinated internodes, for the same reasons as continuous propagation
Faster
What do propagation velocities (speeds of AP propagation) depend upon?
Axon diameter- larger diameter, lower resistance, faster propagation
Degree of myelination- faster in myelinated axons
Temperature- lower temp, slower propagation
Describe type A fibers:
Size
Myelination
Speed/type
Where found
Large
Thick myelin
Fast, saltatory
Somatic sensory neurons, somatic motor neurons
Describe type B fibers:
Size
Myelination
Speed/type
Where found
Medium
Light myelin
Medium, saltatory
Visceral sensory neurons, all pre-ganglionic axons of ANS
Describe type C fibers:
Size
Myelination
Speed/type
Where found
Small
No myelin
Slow, continuous
Some somatic sensory, some visceral sensory, and all post-ganglionic axons of ANS
What are the 2 varieties of synapses?
Electrical and chemical
Electrical synapses
Rare
Presynaptic and postsynaptic membranes are connected by gap junctions
Propagation of AP travels very quickly resulting in the electrically coupled cells having a simultaneous AP
Chemical synapses
Synaptic end bulb releases a neurotransmitter that binds to the postsynaptic plasma membrane, producing a GP there
Common; unidirectional communication
What do excitatory neurotransmitters do?
Promotes the generation of action potentials by causing depolarization
*Neurotransmitters are excitatory or inhibitory depending on what type of channel it opens
What do inhibitory neurotransmitters do?
Suppresses the generation of action potentials by causing hyperpolarization
*Neurotransmitters are excitatory or inhibitory depending on what type of channel it opens
List the 7 steps that happen at a chemical synapse.
- Nerve AP arrives at synaptic end bulb of presynaptic axon
- Voltage-gated calcium channels open and calcium diffuses into neuron
- Increased intercellular calcium concentration triggers exocytosis of neurotransmitters into synaptic cleft
- Neurotransmitters bind to receptors on postsynaptic cell
- Ligand-gated channels open allowing influx/reflux of sodium, potassium, or chloride
- Change in resting membrane potential (depolarization or hyperpolarization)
- If threshold is reached, AP is initiated on the postsynaptic cell (neuron or effector)
Postsynaptic potential
Graded potential that develops in the postsynaptic membrane of the soma or dendrites in response to a neurotransmitter
What are the 2 types of postsynaptic potentials?
Excitatory (EPSP) & inhibitory (IPSP)
Excitatory postsynaptic potential
Graded depolarization caused by neurotransmitter binding to postsynaptic membrane receptors
Results from opening of ligand-gated sodium channels
Increases a postsynaptic neuron’s ability to generate an AP because it is closer to threshold voltage
Inhibitory postsynaptic potential
Graded hyperpolarization caused by neurotransmitters binding to postsynaptic membrane
Results from opening of ligand-gated potassium or chloride channels
Reduces a postsynaptic neuron’s ability to generate an AP because it is father from threshold voltage
Summation
The adding of EPSP’s together in order to increase probability of reaching threshold potential to produce an action potential in the postsynaptic neuron
*Single EPSP’s cannot induce an AP
Spatial summation
Occurs when sources of stimulation arrive simultaneously but at different locations
Causes large amounts of neurotransmitters to be released together that increase depolarization at trigger zone
Temporal summation
Occurs when one synapse receives stimuli occurring in rapid succession
Burts of neurotransmitters are released in quick succession, causing more and more ligand-gated channels to open, increasing degree of depolarization
Why do neurotransmitter effects need to be terminated?
As long as a neurotransmitter is bound to its postsynaptic receptor, it will continue to affect membrane permeability and block additional messages from presynaptic neurons
What are 3 mechanisms to terminate a neurotransmitter’s effects?
Degradation by enzyme, reuptake by cells, diffusion away
Describe degradation by enzymes.
An enzyme will be present on the postsynaptic membrane or synaptic cleft that will break down the neurotransmitter
Describe reuptake by cells.
The neurotransmitter will be taken up by astrocytes or the presynaptic terminal to be stored or destroyed by enzymes via neurotransmitter transporters
Describe diffusion away.
The neurotransmitter will diffuse away from the synapse
Name 2 excitatory amino acids.
Glutamate, aspartate
Name 2 inhibitory amino acids.
Gamma-aminobutyric acid (GABA),
glycine
Neuropeptides
Neurotransmitters consisting of 3-40 amino acids
Numerous and widespread in CNS and PNS
Many function as hormones that regulate physiological responses in the body
Describe substance P.
Found in sensory neurons, spinal cord pathways, and parts of the brain associated with pain
Enhances perception of pain
Neural circuits
Functional groups of neurons that process specific types of information
What are 4 types of neural circuits?
Diverging circuits
Converging circuits
Reverberating circuits
Parallel after-discharge circuits
Describe diverging circuits.
One input, many outputs
An amplifying circuit
Describe converging circuits.
Many inputs, one output
A concentrating circuit
Describe reverberating circuits.
Signal travels through a chain of neurons, each feeding back to previous neurons
An oscillating circuit that controlls rhythmic activity
Describe parallel after-discharge circuits.
Signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell
Impulses reach output cell at different times, causing a burst of impulses called an after-discharge
Rabies
A viral infection of the nervous system transferred to humans by the bites of infected animals that causes brain inflammation, delirium and death
Virus transported via retrograde movement in peripheral nerve axons to the CNS
Multiple sclerosis
Demyelinating autoimmune disease
Symptoms: visual/speech disturbances, muscle weakness/paralysis, urinary incontinence
Neuropathy
Any disease of nervous tissue, particularly degenerative diseases of nerves
Neurotoxin
A substance that is poisonous or destructive to nervous tissue
Shingles
A viral infection of sensory neurons serving the skin, characterized by scaly/painful blisters lasting for weeks, caused by varicella-zoster virus
When dormant, it remains in the sensory ganglia until immune system is weakened
Hansen’s disease (leprosy)
A disease caused by mycobacterium leprae that results in skin sores, nerve damage, and muscle weakness that worsens over time
Not contagious, long incubation period
More common in children
Compare Schwann cells, myelin sheaths, and internodes.
Schwann cell- glial cell responsible for myelinating PNS axons
Myelin sheath- layers of Schwann cell’s plasma membrane that cover the axon
Internode- length of Schwann cell or myelin sheath
Absolute refractory
The period when no action potential can be generated regardless of strength of the stimulus
Transmembrane potential
Potential difference measured in volts or millivolts in plasma membranes
Measured at the inner leaflet, so value will always be negative
