Chapter 10 - Nervous System Flashcards
Overview of Nervous System Function:
- Master regulatory system
- Sends and receives information
- Sensory input (detects changes)
- Integration and processing (making decisions)
- Motor output (stimulates muscles and glands to respond)
- Maintains homeostasis
- Acts as center for thought, learning, and memory
Sensory Input
Detects Change
Integration and Processing
Makes Decisions
Motor Output
Stimulates muscles and glands to respond
Main Cell Types of Nervous System:
2 types
Neurons (nerve cells) & Neuroglia
Neurons (nerve cells)
- respond quickly to changes/stimuli
- Conducts electrical impulses via neurotransmitters
What is the Flow of informaiton in the nervous system
Sensory receptor (sensory input) to Brain and spinal cord (integration) to Effector (motor output)
Central Nervous System
CNS
Brain
&
Spinal Cord
Peripheral Nervous System
PNS
- Connects CNS to other body parts
- Consists of cranial nerves and spinal nerves
- two subdivisions: afferent sensory & efferent (motor)
Sensory Division
Sensory receptors perform sensory function (detect changes)
Receptors convert information into impulses
Impulses conducted along peripheral nerves to CNS for integration
Motor Division
Neurons that transmit impulses from CNS to effectors perform motor function
Effectors are muscles or glands outside nervous system
What are the two subdivisions of Motor Division?
Somatic: Transmits voluntary commands to skeletal muscles
Autonomic: Transmits involuntary commands to viscera
Neurons…?
- Very in size and shape
- may differ in length, number, and size of axons and dendrites
Neurons share certain structural features
- Cell body (soma or perikaryon)
- Dendrites
- Axon
Cell body (soma or perikaryon):
Contains nucleus, cytoplasm,
organelles, neurofilaments, chromatophilic substance (Nissl bodies)
Dendrites
Branched receptive surfaces; a neuron may have many
Axon
ransmits impulses and releases neurotransmitters to
another neuron or effector (another neuron, a muscle cell, or a gland
cell); a neuron may have only 1 axon
Structural features of axons
- Axon hillock: Cone-shaped area of cell body from which axon arises
- Collaterals: Branches from axon
- Axon terminal: Specialized endings of extensions from axon
- Synaptic knob: Rounded ending of a synaptic terminal
Schwann cells:
- Neuroglia of the PNS that wrap around some axons in layers
- Myelin: Mixture of fats and proteins that fill layers made by Schwann
cell membranes - Myelin sheath: A wrapped coating around some PNS axons,
composed of layers of Schwann cell membranes and myelin; acts as
electrical insulator - Nodes of Ranvier: Gaps in myelin sheath between Schwann cells
True or False
Not all axons are myelinated
True
Myelinated axons:
- Are coated by a myelin sheath
- Produced by a series of Schwann cells lined up along axon in PNS
- Produced by Oligodendrocytes in CNS
- Groups of myelinated axons in CNS comprise White Matter
- Increase conduction speed for electrical impulses
Unmyelinated axons:
Encased by Schwann cell cytoplasm in PNS, but there is no
wrapped coating of myelin surrounding the axons
Groups of unmyelinated axons in CNS comprise Gray Matter
What are the 3 classifications of neuron by structure?
B.U.M.
- Multipolar neurons
- Bipolar neurons
- unipolar (Pseudounipolar) neurons:
Multipolar neurons:
- Many processes extend from cell body (many dendrites, 1 axon)
- 99% of neurons
- Most neurons of CNS, some in autonomic NS
Bipolar neurons
- Two processes extend from cell body (1 dendrite, 1 axon)
- Not that common
- Eyes, ears, nose
Unipolar (Pseudounipolar) neurons:
- One process extends from cell body
- Two branches that function as 1 axon (peripheral and central
processes) - Cell bodies are mainly found in ganglia of PNS
Classification of Neurons by Function
M.I.S.
- Sensory (Afferent) Neurons:
- Carry impulses from periphery to CNS (brain or spinal cord)
- At distal ends, contain sensory receptors to detect changes
- Most are unipolar, some are bipolar
- Interneurons (Association or Internuncial Neurons):
- Link neurons in the CNS
- Relay information from one part of CNS to another
- Multipolar
- Some cell bodies cluster to form nuclei in CNS
- Motor (Efferent) Neurons:
- Carry impulses from CNS to effectors (muscles or glands)
- Multipolar
- In somatic NS, control voluntary skeletal muscles
- In autonomic NS, control involuntary smooth and cardiac muscle, glands
What are the general Functions of Neuroglia?
- Provide structural support for neurons
- In embryo, guide neurons into position, may stimulate
specialization - Produce growth factors to nourish neurons and remove
excess ions and neurotransmitters - Aid in formation of synapses
What are Astrocytes?
- Connect neurons to blood vessels, exchanging nutrients and growth factors
- Form scar tissue
- Aid metabolism of certain substances
- Regulate ion concentrations, such as
- Part of Blood Brain Barrier
What are Oligodendrocytes?
Myelinate CNS axons; also provide structural support
What are Microglia
Phagocytic cells; also provide structural support
What are Ependyma or ependymal cells:
- Line central canal of spinal cord & ventricles of brain, cover choroid plexuses
- Help regulate composition of cerebrospinal fluid
- Ciliated cuboidal or columnar cells
Schwann Cells:
- Produce myelin sheath found on some peripheral axons
- Speed up speed of nerve impulse transmission
Satellite Cells:
- Support clusters of neuron cell bodies (ganglia)
- Nourish and balance ionic concentrations
Do Mature Neurons divide?
&
If the cell body is injured, what happens to the neuron?
- Mature neurons do not divide
- If cell body is injured, the neuron usually dies
Neuron Regeneration in the PNS:
- If a peripheral axon is injured, it may regenerate
- Axon separated from cell body and its myelin sheath will degenerate
- Schwann cells and neurilemma remain
- Remaining Schwann cells provide guiding sheath for growing axon
- If growing axon establishes former connection, function will return; if not,
function may be lost
Neuron Regeneration in the CNS:
- CNS axons lack neurilemma to act as guiding sheath
- Oligodendrocytes do not proliferate after injury
- Regeneration is unlikely
Neurons communicate with each other at a…?
Synapse
Synapse facts
- A site at which a neuron transmits a nerve impulse to
another neuron - Presynaptic neuron sends impulse
- Postsynaptic neuron receives impulse
- Synaptic cleft separates the 2 neurons
What is Synaptic Transmission:
- Process by which presynaptic neuron sends impulse to
postsynaptic neuron - One-way process, using neurotransmitters to transfer the
message
Synaptic transmission facts continued…
- Transmission of a nerve impulse from one neuron to another
- Released neurotransmitters cross the synaptic cleft and react with
specific receptors in the membrane of postsynaptic neuron - Effects of neurotransmitters vary; some open ion channels and others
close ion channels - Chemically gated ion channels respond to neurotransmitters.
- Local potentials resulting from changes in chemically gated ion
channels are called synaptic potentials.
Excitatory neurotransmitters
increase permeability to Na+ ions, bring
membrane closer to threshold; increase likelihood of generating
impulses
Inhibitory neurotransmitters
move membrane farther from threshold,
decrease likelihood of generating impulses
Excitatory postsynaptic potential (EPSP)
- Membrane change in which neurotransmitter opens Na+ Channels.
- Depolarizes membrane of postsynaptic neuron, as Na+ enters axon.
- Action potential in postsynaptic neuron becomes more likely
Inhibitory postsynaptic potential (IPSP)
- Membrane change in which neurotransmitter opens K+ channels (or Cl−
channels). - Hyperpolarizes membrane of postsynaptic neuron, as K+ leaves axon
- Action potential of postsynaptic neuron becomes less likely
How many neurotransmitters are there?
at least 100
Acetylcholine stimulates…?
skeletal muscle contraction
Neurotransmitters
Neurotransmitters may be monoamines, amino acids, peptides
Neurotransmitters are produced in the rough ER or cytoplasm
When impulse reaches synaptic knob of an axon,
neurotransmitters are released by exocytosis
Impulse Processing
The way the nervous system processes nerve impulses and
acts upon them reflects the organization of neurons and
axons in the brain and spinal cord
Neuronal Pools:
- Groups of interneurons that make synaptic connections with each
other, and are located completely within the CNS - Cell bodies may be in different parts of the CNS
- Interneurons work together to perform a common function
- Each pool receives input from other neurons
- Each pool generates output to other neurons
- Pools may affect other pools or peripheral effectors
Convergence
- One neuron receives input from several neurons
- Incoming impulses often represent information from different types of
sensory receptors - Allows nervous system to collect, process, and respond to information
- Makes it possible for a neuron to sum impulses from different sources
Divergence
- One neuron sends impulses to several neurons, via branching of its
axon - Can amplify an impulse
- Impulse from a single neuron in CNS may activate several motor units
in a skeletal muscle - Impulse from a sensory receptor may reach different regions of the CN
S for processing
