STRUCTURAL AND FUNCTIONAL ORGANIZATION OF NERVOUS SYSTEM Flashcards
DESCRIBE
The brain
surrounded by the skull and contains about 100 billion neurons
DESCRIBE
Spinal Cord
Connects to the brain and is surrounded by the bones of the vertebral column
contains about 100 million neurons
DESCRIBE
Cranial Nerves
12 pairs of cranial nerves numbered I-XII that emerge from the base of the brain
DESCRIBE
Spinal Nerves
31 Pairs of spinal nerves that emerge from the spinal cord each serving a specific region of the body
DESCRIBE
Sensory Recrptors
Specialized cells that monitor change in the internal and external environment.
(photoreceptors in the retina of the eye)
DESCRIBE
Ganglia
small masses of nervous tissue consisting of neuronal cell bodies that are located outside the brain and spinal cord
(dorsal root ganglion)
DESCRIBE
Enteric Plexus
Extensive network of nerves that are located in the walls of the GI tract that help regulate the digestive system
Tasks of the Nervous System
Smell
Touch
Temp
Producing Speech
Remembering Past Events
Provides signals that control body movement
regulates the operation of the internal organs
3 Basic Functions of the Nervous System
- Sensory function afferent
- Intergrative function
- Motor function (efferent)
DEFINE
Sensory Function afferent
detects int/ext stimuli and carry information into brain and spinal cord via cranial and spinal nerves
DEFINE Integrative Function (information processing)
Perception=awareness of sensory input
Analyzing and storing information to help lead to appropriate responses
DEFIN Motor Function (efferent)
Once integration occurs the brain may elicit motor response to muscles or glands (effectors) via cranial and spinal nerves
HISTOLOGY
Neurons
Provide most of the unique functions of the nervous system
HISTOLOGY
Neuroglia
Function to provide support, nourishment, and protection
PARTS OF A NEURON
Cell Body
Nucleus, cytoplasm with typical organelles
PARTS OF A NEURON
Dendrites
Highly branched structues that carry impulses to the cell body
PARTS OF A NEURON
Axon
conducts away from the cell body toward another neuron, muscle or gland.
PARTS OF A NEURON
Axon Terminals
Contain synaptic vesicles that can release NT
STRUCTURAL CLASSES OF NEURONS
Multipolar
1) Have several or many dendrites and one axon
2) Most common type in brain and spinal cord
STRUCTURAL CLASSES OF NEURONS
Bipolar
Have one dendrite and one axon
retina of eye and inner earr
STRUCTURAL CLASSES OF NEURONS
Unipolar
1) Have fused dendrite and axon
2) Sensory neurons of spinal nerves
NEUROGLIA
characteristics
(a) Support, nourish, and protect neurons
(b) Critical for homeostasis of interstitial fluid around neurons
(c) Cells smaller but much more numerous than neurons
(d) Make up about half the volume of the CNS
NEUROGLIA
Functions
1) Do NOT generate or conduct nerve impulses
2) Support, nourish and protect neurons
3) In case of injury or disease, neuroglia can multiply to fill in space
formerly occupied by neurons
NEUROGLIA
Types
1) Astrocytes form blood brain barrier (CNS)
2) Oligodendrocytes produce myelin in CNS (CNS)
3) Microglia protects CNS cells from disease (CNS)
4) Ependymal cells form CSF in ventricles (CNS)
5) Schwann cells produce myelin around PNS neurons (PNS)
6) Satellite cells support neurons in PNS ganglia (PNS)
MYELINATION
Characteristics
(a) Most axon are surrounded by a myelin sheath
(b) Insulates the axon and speeds up the nerve impulse
(c) Myelin increases from birth to maturity
(d) Nodes of Ranvier: Gaps in myelin along the axon
(e) Disease such as Multiple Sclerosis and Tay-Sachs destroy myelin sheaths
CLUSTERS OF NERVOUS TISSUE
Ganglion
Cluster of cell bodies in PNS
CLUSTERS OF NERVOUS TISSUE
Nucleus
Cluster of cell bodies in CNS
BUNDLES OF AXONS
Nerve
Bundle of axons in PNS
BUNDLES OF AXONS
Tract
Bundle of axons in CNS
White matter
Primarily myelinated axons
Gray matter
Cell bodies, dendrites, unmyelinated axons, axon
terminals, neuroglia
LOCATION OF GRAY MATTER
Brain:
Gray matter in thin cortex surrounds white matter (tracts)
LOCATION OF WHITE MATTER
Spinal cord:
White matter (tracts) surround centrally located gray matter
“H” or “butterfly”
NEURON REGENERATION
PNS neurons
1) Axons and dendrites in the PNS can be repaired if cell body is intact
and Schwann cells functional.
2) These form a regeneration tube and grow axons or dendrites if scar
tissue does not fill the tube
NEURON REGENERATION
CNS neurons
1) Very limited even if cell body is intact
2) Inhibited by neuroglia and by lack of fetal growth-stimulator cues
ACTION POTENTIAL
Action
Action potentials, or nerve impulses, allow for communication between neurons
ACTION POTENTIAL
Requires
1) A resting membrane potential
2) Ion channels
ACTION POTENTIAL
Ion channels
Allow ions to move by diffusion from high to low concentration
a) Leakage channels allow ions to leak through
b) Gate channels open and close on command
c) The distribution of ions produces the resting membrane
potential
ACTION POTENTIAL
Whats necessary for initial event
STIMULUS
1) Triggers resting membrane to become more permeable to Sodium (Na+
)
2) Causes enough Na+ to enter cell so that cell membrane reaches threshold (~
–55 mv)
3) If threshold is reached, an action potential arises(“all or nothing response”)
ACTION POTENTIAL
Depolarizing phase
Voltage gated Na+ channels open ~ as more Na+ enters cell, membrane
potential rises and becomes positive (–70 ~ 0 ~ + 30 mv)
ACTION POTENTIAL
Repolarizing phase
Voltage gated K+ channels open ~ as more K+ leave cell, membrane
potential is returned to resting value (+ 30 ~ 0 ~ –70 mv)
CONDUCTION OF A NERVE IMPULSE
propagation
when nerve impulses travel from where they arise (axon
hillock), along the axon to the axon terminal.
1) Each section triggers the adjacent segment distally as even more
Na+ channels are opened
CONDUCTION OF A NERVE IMPULSE
Continuous conduction
a) In unmyelinated axons, currents flow across adjacent portions of the
plasma membrane
b) Slower form
CONDUCTION OF A NERVE IMPULSE
Saltatory conduction
In myelinated axons, Nodes of Ranvier allow impulses to “leap” from one node to the next
SYNAPTIC TRANSMISSION
(a) Synapses allow neurons to communicate with other neurons or effectors
1) Neuromuscular junction (neuron-muscle fiber)
2) Neuroglandular junction (neuron-gland)
(b) Triggered by action potential (nerve impulse)
(c) Components of synapse:
1) Presynaptic neuron: Sending neuron (releases neurotransmitter)
2) Synaptic cleft: Space between neurons
3) Postsynaptic neuron: Receiving neuron (has receptors that bind to
neurotransmitter)
(d) Action potential arrives at presynaptic neuron’s end bulb
(e) Opens voltage gated Ca2+ channels
1) Ca2+ flows into presynaptic cytosol
(f) Increased Ca2+ concentration causes exocytosis of synaptic vesicles
(g) Neurotransmitter (NT) released into cleft
(h) NT diffuse across cleft and bind to receptors on the postsynaptic cell membrane
(i) NT acts as chemical trigger, opening ion channels which changes the
voltage across the postsynaptic cell membrane
(j) Postsynaptic cell membrane may be depolarized or hyperpolarized,
depending on which ions were admitted
(k) If threshold reached (-55mV) then postsynaptic AP results and nerve
impulse is triggered
(l) One-way transmission: Action potentials can only travel in one direction
from dendrite to axon.
(m)NT removed from cleft via diffusion, destruction by enzymes such as Achase, or transport back into presynaptic cell (recycling)
NEUROTRANSMISSION
Acetylcholine:
Common in PNS
1) Stimulatory (on skeletal muscles)
2) Inhibitory (on cardiac muscle)
NEUROTRANSMISSION
Amino acids
Glutamate, aspartate, gamma aminobutyric acid (GABA)
NEUROTRANSMISSION
Modified amino acids
Norepinephrine (NE), dopamine (DA), serotonin
NEUROTRANSMISSION
2 others
- Neuropeptides such as endorphins
2. Nitric oxide (NO)
ORGANIZATION OF NERVOUS TISSUE
Central Nervous System
(a) Consists of the brain and spinal cord
(b) Source of thoughts, emotions, and memories
ORGANIZATION OF NERVOUS TISSUE
Peripheral Nervous System
(a) Includes all the nervous tissue outside the central nervous system
1) Include the cranial nerves, spinal nerves, ganglia and sensory nerves
(b) Can be subdivided into the
1) Somatic nervous system (SNS)
2) Autonomic nervous system (ANS)
3) Enteric nervous system (ENS)
(c) Somatic Nervous System
1) Sensory neurons: Convey info from head, body wall, and limbs
and from receptors for special senses (vision, hearing, taste smell)
to CNS
2) Motor neurons: Conduct impulses from CNS to skeletal muscles
(voluntary control)
(d) Autonomic nervous system
1) Sensory neurons: Convey information from receptors in the
visceral organs (stomach and lungs) to CNS
2) Motor neurons: Conduct impulses from CNS to smooth muscles,
cardiac muscles, and glands (involuntary control)
a) Sympathetic: “fight or flight”
b) Parasympathetic: “rest and digest”
(e) Enteric Nervous System “Brain of the gut”
a) Sensory neurons: Monitor chemical changes in GI tract, stretching of
walls
b) Motor neurons: Regulate contractions, acid secretion, endocrine cell
secretions
c) Involuntary control
