Chapter 12 Flashcards
Nerve
A bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord
How many pairs of cranial nerves emerge from the brain?
Twelve
How many pairs of spinal nerves emerge from the spinal cord?
31
Sensory receptor
Structure of the nervous system that monitors changes in the external or internal environment
What divisions is the PNS system divided into
Sensory division and motor division
Sensory or afferent division
Conveys input into the CNS from sensory receptors in the body provides the CNS with sensory information about the somatic senses and special senses
Motor or Efferent division
Conveys output from the CNS two effectors further subdivided into somatic nervous system and autonomic nervous system
Somatic nervous system
Conveys output from the CNS to skeletal muscles only because it can be consciously controlled the action of this part of the PNS is voluntary
Autonomic nervous system
Conveys output from the CNS to smooth muscle cardiac muscle and glands not normally under conscious control the action of the ANS is involuntary
What are the two main branches of the autonomic nervous system?
Sympathetic nervous system and parasympathetic nervous system And enteric nervous system
Parasympathetic nervous system
Rest and digest activities
Sympathetic nervous system
Supports exercise or emergency action “fight or flight” response is
Enteric nervous system
Confined to the wall of the G.I. tract helps regulate the activity of the smooth muscles and glands of the G.I. tract
What are the three basic functions of the nervous system?
- Sensory
- integrative
- motor
Sensory function
Sensory receptors detect internal stimuli examples blood pressure or external stimuli the information is not carried into the brain and spinal cord
Integrative function
The nervous system processes sensory information by analyzing it and making decisions for appropriate responses an activity known as integration
Motor function
After sensory information is integrated if the nervous system may all it an appropriate motor response by activating effectors (muscle and glands) through cranial and spinal nerves
Electrical excitability
The ability to respond to a stimulus and convert it into an action potential
Action potential
An electrical signal that propagates along the surface of the membrane of a neuron
What’s the cell body of the neuron known as
Perikaryon or soma
What’s the term for free ribosomes in clusters of rough endoplasmic reticulum of the neuron?
Nissl bodies
Neurofibrils
Composed of bundles of intermediate filaments that provide the cell shape and support
Microtubules
System moving materials between the cell body and axon
Lipofuscin
A pigment that occurs as clumps of yellowish brown granules in the cytoplasm a product of neuronal lysosome is that accumulates as a neuron ages
Ganglion
Collection of neuron cell bodies outside the CNS
Nerve fiber
General term for any neuronal process that emerges from the cell body of a neuron most have two kinds of processes dendrites and axons
Dendrites
Receiving or input portions of a neuron contain numerous receptor sites for binding chemical messengers from other cells usually short tapering in highly branched
Axon
Propagates nerve impulses towards another neuron, a muscle fibre, or a gland cell. an axon is a long, thin, cylindrical projection that often joins to the cell body at a cone shaped elevation called the axon hillock
Axon hillock
Cone shaped elevation on the axon
Initial segment
Part of the axon closest to the axon hillock
Trigger zone
Junction of the axon hillock and initial segment where nerve impulses arise
Axoplasm
Cytoplasm of axon
Axolemma
Plasma membrane of the neuron
Axon collaterals
Side branches on length of an axon
Axon terminal
Branch off the axon end
Synapse
Site of communication between two Neurons or between a neuron and an effectorcell
Synaptic bulbs and varicosities
The swelling at the tips of the axon terminal which contain many tiny sacs called synaptic vesicles that store neurotransmitters
What stores neurotransmitters?
Synaptic vesicles
Slow axinal transport
Convey’s axoplasm in One Direction only from the cell body toward the axon terminals supplies new exoplasm to developing or regenerating axons and replenishes exoplasm and growing and mature axons
Fast axonal transport
Capable of moving materials a distance of 200 to 400 mm per day uses proteins that function as motors to move materials along the surfaces of microtubules of the neuron cytoskeleton can move material in both directions away from and towards the cell body
Fast axonal transport - Anterograde
Occurs in a forward direction moves organelles in synaptic vesicles from the cell body to the axon terminals
Fast axonal transport - retrograde
Occurs backward direction moves membrane vessicles and other cellular material from the axon terminals to the cell body to be degraded or recycled as well as substances that enter the neuron at the axon terminals
Multipolar neurons
Have several dendrites in one axon
Bipolar neurons
One main dendrite and one axon
Unipolar neurons
Have den droids and one axon that are fused together to form a continuous process that emerges from the cell body also called pseudo unipolar neurons
Purkinje cells
Found in the cerebellum
Pyramidal cells
Found in the cerebral cortex of the brain
Sensory neurons or afferent neurons
Contain sensory receptors at their distal ends or are located just after sensory receptors the sensory neuron forms an action potential in its axon then the action potential is conveyed into the CNS through cranial or spinal nerves; most are unipolar
Motor neurons or efferent neurons
Convey action potentials away from the CNS to effectors in the periphery through cranial or spinal nerves; most are multi polar in structure
Interneurons or association neurons
Mainly located within the CNS between sensory and motor neurons interneurons integrate incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neuron; most are multi polar and structure
Neuroglia
 “Glue” that holds nervous tissue together, smaller than neurons, do not propagate or generate action potentials, are able to multiply and divide
What are the CNS neuroglia?
Astrocytes, oligodendrocytes, microglia, and ependymal cells
Peripheral nervous system neuroglia?
Schwann cells and satellite cells
Astrocytes
Star shaped cells have many processes and are the largest and most numerous of the neuroglia two types protoplasmic and fibrous
Protoplasmic astrocytes
How many short branching processes are found in gray matter
Fibrous astrocytes
located mainly in white matter
What are the functions of astrocytes?
- Contain microfilaments like give them strength which enables them to support Neurons
- Processes of astrocytes wrapped around blood capillaries isolate neurons of the CNS from various potential harmful substances in blood by secreting chemicals that maintain unique selective permeability, The endothelial cells create a blood brain barrier
- In embryo astrocytes agree chemicals that appear to regulate growth migration in interconnection of neurons in the brain
- Help maintain appropriate chemical environment for the generation of nerve impulses
- Play a role in learning and memory by influencing the formation of neural synapses
Oligodendrocytes
Resemble astracites but are smaller in contain fewer processes these processes form and maintain the myelin sheath around CNS axons. Can myelinate several axons
Myelin sheath
Multilayered lipid and protein covering around some axons that insulates them and increases the speed of nerve impulse conduction
Microglial cells or microglia
Small cells with slender processes that give off numerous spine like projections function as phagocytes
Ependymal cells
Cuboidal to calmer cells arranged in a single layer that possesses microvilli and cilia these cells line the ventricles of the brain and central canal of the spinal cord. functionally produce, possibly monitor, and assist in the circulation of cerebral spinal fluid and form the blood-cerebrospinal fluid barrier
Schwann cells
Located in the PNS
Myelinates only a single axon
But can enclose as many as 20 or more unmyelinated axons. Participate in axon regeneration
Satellite cells
Flat cells surround the cell bodies of neurons of PNS ganglia, regulate the exchanges of materials between neuronal’s cell bodies and interstitial fluid
Neurolemma
Outer nucleated cytoplasmic layer of the Schwan cell which encloses the myelin sheath found only around axons in the PNS, aids regeneration by forming a regeneration tube that guides stimulates regrowth of the axon
Nodes of Ranvier
Gaps in the myelin sheath each Schwan cell wraps one axon segment between two nodes
Tract
Bundle of axons that is located in the CNS that interconnect neurons in the spinal cord and brain
White matter
Composed primarily of myelinated axons
Gray matter
Contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. The nissl bodies impart a gray colour and there’s little to no myelin in these areas
What are the two types of electrical signals used to communicate between neurons?
- Graded potential’s
- Action potentials
Grated potentials
Used for short distance communication
Action potentials
communication over long distances within the body‘s
What are the four types of ion channels?
- Leaky channels
- Ligand- gated channels
- Mechanically-gated channels
- Voltage-gated channels
Leak channels
Randomly alternate between opening clothes positions
Ligand gated channel
Opens and closes in response to the binding of a ligand stimulus wide variety of chemical ligands including neurotransmitters, hormones, and particular ions
Mechanically gated channel
Opens or closes in response to mechanical stimulation in the form of vibration, touch, pressure, or tissue stretching; the force distorts the channel from its resting position opening the gate
Voltage gated channel
Opens in response to a change in membrane potential; voltage gated channels participate in the generation and conduction of action potential’s in the axons of all types of neurons
why does resting membrane potential exist?
Because of a small buildup of negative ions in the cytosol along the inside of the membrane and an equal buildup of positive ions in the extracellular fluid along outside surface of the membrane
What’s the typical resting membrane inside a neuron?
-70
Polarized
So the exhibit of membrane potential
What are the three major factors that arise from the resting membrane potential?
- Unequal distribution of ions in the ECF and cytosal
- Inability of most anions to leave the cell
- Electrogenic nature of the Na + -K + ATPases
Graded potential
Small deviation from the resting membrane potential that makes the membrane either more polarized or less polarized
Hyperpolarizing graded potential
When the response makes a membrane more polarized (inside more negative)
Depolarizing graded potential
And the response makes the membrane less polarized (inside less negative)
Decremental conduction
 The flow of current is localized and spreads to adjacent regions along the plasma membrane in either direction from the stimulus source for a short distance and then gradually dies out as the charges are lost across the membrane through leak channels
Summation
Process by which graded potentials add together
Action potential or impulse
Rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to resting state. Two phases depolarizing phase and re-polarizing phase
Depolarizing phase
The negative membrane potential becomes less negative reaches zero and then becomes positive
Re-polarizing phase
The membrane potential is restored to the resting state of -70 MV following three polarizing pay is there may be an after hyperpolarizing phase
After-Hyperpolarizing phase
The membrane potential temporary becomes more negative than the resting level
Threshold
An action potential occurs in the membrane of an axon when depolarization reaches a certain level called threshold
Subthreshold stimulus
An action potential will not occur in response to this it’s a week deep polarization they cannot bring the membrane potential to threshold
Super threshold stimulus
Strong enough to deepalize the membrane above threshold has the same amplitude as an action potential caused by a threshold stimulus 
What are the two separate gates on a voltage gated Na+?
Activation gate and inactivation gate
Refractory period
The period of time after an action potential begins during which an excitable cell cannot generate another action potential in response to a normal threshold stimulus
Absolute refractory period
Even a very strong stimulus cannot initiate a second action potential
Relative refractory period
The period of time during which is second action potential can be initiated but only by larger than normal stimulus
Propagation
When an action potential keeps it strength as it spreads along the membrane
What are the two consequences of flow of current across the membrane only at the nodes of Ranvier?
- Action potentials appear to leap from node to node so it travels much faster
- opening a smaller number of channels only at the nodes is more energy efficient, using less ATP
What are factors that affect the speed of propagation?
- Amount of myelination
- Axon diameter
- Temperature
What are the three major classifications of nerve fibers?
- A fibres
- B fibres
- C fibers
A fibers
- Largest diameter axons
- have a brief absolute refractory period
- conduct nerve impulses
- the axons of sensory neurons that propagate impulses associated with touch pressure position of joints and some thermal and painless sensations
- axons of motor neurons
B fibers
- Myelinated and exhibit saltatory conduction at speeds up to 15 m/s -somewhat longer absolute refractory period
- conduct sensory nerve impulses from the viscera to the brain and spinal cord
- constitute all of the axons of the autonomic motor neurons that extends from the brain and spinal chord to the ANS
C fibers
- Smallest diameter axons all on myelinated nerve impulses -propagation along to C fibre ranges from .5 to 2 m/s
- exhibit the longest absolute refractory period conduct some sensory impulses for pain, touch, pressure, heat, and cold from the skin and painless impulses from the viscera
Ionotropic receptor
Type of neurotransmitter receptor that contains a neurotransmitter binding site and an ion channel they are components of the same protein
Metabotropic receptor
A type of neurotransmitter receptor that contains the neurotransmitter binding site but lacks an ion channel is part of instruction but is coupled to a separate ion channel by type of membrane proteins called a g protein they are not part of the same protein
Inhibitory postsynaptic potential
Hyperpolarizing postsynaptic potential
Excitatory postsynaptic potential
Depolarizing postsynaptic potential
How is the Nero transmitter removed from the synaptic cleft?
- Diffusion
- Enzymatic degradation
- Uptake by cells
Spatial summation
Summation of postsynaptic potential’s in response to stimuli that occur at different locations in the membrane of a postsynaptic cell at the same time
What determines the effect on the postsynaptic neuron?
The sum of all excitatory and inhibitory effects
