Exam 2: Basic Neuroanatomy Flashcards
The Nervous System
Approximately 100 billion neurons in the
nervous system, and each of these neurons
may communicate directly with as many as
2,000 other neurons; This provides at least 1 trillion points of communication.
Divisions of the Nervous
System
Central Nervous System (CNS); Peripheral Nervous System (PNS)
Central Nervous System
Brain (cerebrum, cerebellum, subcortical
structures, brainstem) and spinal cord; All components housed within bone (skull or vertebral column)
Peripheral Nervous System
12 pairs of cranial nerves and 31 pairs of spinal
nerves as well as sensory receptors; Components are housed outside of the bone
Autonomic nervous system (ANS)
Governs involuntary activities of the visceral muscles
(i.e., glandular secretions, heart and digestive
functions). Comprised of: Sympathetic System and Parasympathetic System.
Sympathetic System
Subsystem that responds to
stimulation through energy expenditure (i.e., increase in blood pressure, dilation of pupils, goosebumps;
“fight or flight response”)
Parasympathetic System
System that counters the responses of the sympathetic system (i.e., slowing heart rate, reducing blood pressure, pupillary constriction, etc.)
Somatic Nervous System
Somatic nervous system governs the
aspects of bodily function that are under
our conscious and voluntary control.
The motor component of the somatic
system is divided into 2 parts:
◦ Pyramidal system-largely responsible for
initiation of voluntary motor acts
◦ Extrapyramidal system-responsible for
background tone and movement supporting the
primary motor acts
Nervous system is comprised of:
◦ Neurons-functional building blocks of the
nervous system; function is to transmit
information
◦ Glial Cells- critical players in the development of
synapses; provide structural support for neuron,
and play an important role in storing information
in long term memory
General structure of the neuron includes:
◦ Soma: cell body
◦ Dendrite: transmits information towards
the soma
◦ Axon: transmits information away from
the soma
Two ways neurons respond to stimulation
The neuron’s response is the mechanism for
transmitting information through the
nervous system:
◦ Excitation-stimulation that causes an increase of
activity of the tissue stimulated
◦ Inhibition- stimulation to a neuron that reduces
the neuron’s output
Important landmarks of the neuron:
Axon Hillock
Myelin Sheath
Nodes of Ranvier
Telodendria
Synaptic Vesicles
Neurotransmitters
Synaptic Cleft
Axon hillock
Junction of axon with soma
Myelin Sheath
White, fatty wrapping of axon; functions to speed up neural conduction
Nodes of Ranvier
Areas between myelinated segments; also important in conduction
Telodendria
Long, thin projections at axon endpoint; have terminal buttons at the end
Synaptic Vesicles
Found within terminal (end) buttons and contain neurotransmitters
Neurotransmitters
Compounds responsible for activating next neuron in chain of neurons
Synaptic Cleft
Gap between 2 neurons where neurotransmitter released
Synapse
-When neuron is stimulated, axon discharges
neurotransmitter into synaptic cleft
-Adjacent neuron responds
-Information enters generally at dendrite and
exits at axon
Neurons can either be:
◦ Presynaptic – those “upstream” from the
synapse
◦ Postsynaptic – stimulated by presynaptic
neurons
Different types of neurons
-Monopolar (unipolar)-neurons with a single,
bifurcating process arising from soma
-Bipolar-have 2 processes
-Multipolar-more than 2 processes
Cerebrum
-Largest structure of nervous system
-Weighs about 3 lbs
-Made up of billions of neurons
-Divided into left and right hemispheres
-Wrapped in 3 meningeal linings
-Most highly evolved and organized structure of the
human body
Anatomy of the Cerebrum: Meningeal Linings
-The triple layer meningeal lining serves
important protective and nutritive functions
-3 meningeal layers:
◦ Dura mater-tough bilayered lining; most superficial
◦ Arachnoid mater-lacey, spider-like structure where many blood vessels for the brain pass
◦ Pia mater- thin, membranous covering that closely contours the brain; major arteries and veins serving surface of brain course within this layer
Traumatic Brain Injury
TBI is one of leading causes of death in
individuals under 24 years of age
◦ Transportation-related injuries exceed falls, assaults, sports, firearms
◦ Seatbelts reduce death due to MVA by 50%
◦ Use of helmets reduced frequency of TBI in
motorcycle accidents by 20 to 50%; up to 85% for
bikes
Ventricles
Spaces within the brain through which CSF (cerebral spinal fluid) flows
◦ Right lateral ventricle
◦ Left lateral ventricle
◦ Third ventricle
◦ Fourth ventricle
-Within each ventricle is a choroid plexus, an accumulation of tissue that produces CSF
-These cavities are suited to act as buffers for the delicate brain tissue
Cerebrospinal Fluid
Central Nervous System (CNS) is bathed in cerebrospinal fluid (CSF)
◦ Provides cushion for delicate and dense neural tissue as well as some nutrient delivery and waste removal.
-CSF is the clear, fluid product of the choroid
plexus in each ventricle
-The volume in CNS is ~125mL, replenished
every 7 hours
-Fluid is under constant pressure that
changes with body position
-Life-threatening conditions develop should
something occlude the pathway of CSF
Circulation of CSF
-Begins in each of the lateral ventricles
coursing through foramina of Monro to 3rd
ventricle.
-Then flows to cerebral aqueduct to 4th
ventricle, where drains into subarachnoid
space and freely circulates around brain and
spinal cord.
-Courses around cerebellum and cerebrum to
exit through arachnoid granulation in sinuses
of dura mater
-Absorbed by venous system