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
Layers of Cerebrum
Cerebrum consists of 2 cerebral hemispheres,
roughly equal halves of brain
◦ Cortex refers to the outer surface of the brain; contains 2 basic cell types:
-Pyramidal cells-involved in motor function (project to more distant regions)
-Nonpyramidal cells-involved in sensory function
(connect to more local regions)
There are 6 Layers of Cerebrum
◦ Outmost layer=glial cells and axons
◦ 2nd and 3rd layer=pyramidal cells
◦ 4th layer= nonpyramidal cells
◦ 5th and 6th layer=pyramidal cells
Landmarks of Cerebrum
Cerebral longitudinal fissure, Gyrus, Sulcus, Lateral Sulcus (Sylvian Fissure), Central Sulcus (Rolandic Sulcus)
Cerebral longitudinal fissure
Separates left and right cerebral hemispheres
Gyrus
A ridge on the cerebral cortex
Sulcus
infolding valleys that separate gyri
◦ (if the groove is deeper or more pronounced it is termed a fissure
Lateral Sulcus (Sylvian Fissure)
divides temporal from frontal & anterior parietal
Central Sulcus (Rolandic Sulcus)
separates the frontal and parietal lobes entirely
Frontal Lobe
-Largest of the lobes
-Predominates in planning, initiation, and
inhibition of voluntary motion, as well as
cognitive function
Some key areas:
◦ Broca’s Area-speech motor planning in
dominant hemisphere
◦ Motor Strip (a.k.a. pre-central gyrus)-site of
initiation of voluntary motor movement
Parietal Lobe
-Primary reception sight for body (somatic) sense
-All senses that reach consciousness terminate within parietal lobe
-Integrates info related to vision, audition, and
somatic sense
Key areas:
◦ Postcentral gyrus-sensory counterpart to the motor strip, primary site of sensory output; receives sensation from various parts of body
◦ Supramarginal gyri-some involvement in motor planning for speech
◦ Angular gyri-important in comprehension of written material
Temporal Lobe
Site of auditory reception and is very
important for auditory and receptive
language processing
Key areas:
◦ Superior temporal gyrus-important in both SLP
and Audiology because along it runs…..
- Heschl’s Gyrus (where all auditory information is projected)
- posterior portion of Wernicke’s area (important in language decoding
Occipital Lobe
Posterior limit of brain; Responsible for receiving visual stimulation, as well as some of the higher-level visual processing
Insula
-AKA the Island of Reil
-Located deep to a region of cerebrum known as the operculum
-Believed to be involved in consciousness and play a role in emotion and the regulation of the body’s homeostasis
Limbic System
Not an anatomically distinct region but is composed of:
◦ Uncus (formed by amygdala)
◦ Thalamus
◦ Parahippocampal gyrus
◦ Cingulate gyrus
◦ Olfactory bulb and tract
◦ Hippocampus
◦ Dentate gyrus
Related to functional relationships to:
◦ Motivation
◦ Sex drive
◦ Emotional behavior
◦ Affect
Myelinated Fibers
Gray matter of the cortex is predominately made up of neuron bodies, whereas white matter represents myelinated axon fibers
-These fibers make up the communication link between neurons (without them there would be no neural function)
There are 3 types of fibers:
◦ Projection Fibers
◦ Association Fibers
◦ Commissural Fibers
Projection Fibers
Connects cortex with distant locations
Association Fibers
Provides communication between regions of the same hemisphere
Commissural Fibers
Runs from one location on a hemisphere to the corresponding location on the opposite hemisphere (mainly the corpus callosum)
Anatomy of the Subcortex: Basal Ganglia
-Group of large nuclei that partially surround
the thalamus
-Important in the control of movement;
regulates voluntary motor activities
-Functions in starting, stopping, and
monitoring arm swinging and gait
Made up of:
◦ Caudate nucleus
◦ Putamen
◦ Globus Pallidus
Anatomy of the Subcortex: Hippocampus
-Involved in memory forming, organizing, and
storing
-As a limbic system structure, it is important
in forming new memories and connecting
emotions and senses, such as smell and
sound, to memories
-Sends memories out to appropriate cerebral
hemisphere for long-term storage and
retrieval
-Also appears to be specialized to recognize
faces of individuals
Anatomy of the Subcortex: Diencephalon
Structures of the Diencephalon:
◦ Thalamus
◦ Hypothalamus
◦ Epithalamus
◦ Subthalamus
Function:
◦ Relays sensory information between brain regions
◦ Controls many autonomic functions of the PNS
◦ Connects structures of the endocrine system with the nervous system
◦ Works in conjunction with the limbic system to
generate and manage emotions and memories
Specific Functions of Diencephalon
-Directing sense impulses throughout the body
-Autonomic function control
-Endocrine function control
-Motor function control
-Homeostasis
-Hearing, vision, taste
-Touch perception
Thalamus
-Large, dual-lobed mass of grey matter
-Involved in sensory perception and
regulation of motor functions
-As a limbic system structure, it connects
areas of the cortex involved in perception
and movement with related parts of the
brain and spinal cord
-As a regulator of sensory information, it
controls sleep and awake states of
consciousness
Hypothalamus
-Control center for many autonomic
functions of PNS
-Connections with structures of endocrine
and nervous systems enable maintenance
of homeostasis
◦ Blood vessel connection between hypothalamus
and pituitary gland
◦ Allows for control of pituitary hormone secretion
-As a limbic system structure, influences
emotional responses
Epithalamus
Secretion of melatonin by the
pineal gland (involved in circadian
rhythms), and regulation of motor pathways
and emotions
Subthalamus
Involved in the control of striated muscle
Circle of Willis
-The arrangement of the brain’s arteries into
the Circle of Willis creates redundancies to
ensure constant blood supply to the brain
-If one part of the circle or one of the arteries
supplying the circle is blocked or narrowed,
blood flow from the other blood vessels can
often preserve the cerebral perfusion
Venous Drainage & Blockage
System of blood vessels called veins that
provide the means of draining carbon
dioxide-laden blood to the lungs from
reoxygenation
Obstruction in cerebrovascular supply typically occurs as:
◦ Thrombus: a foreign body (blood clot) that obstructs blood vessel
◦ Embolism: when a thrombus breaks loose from its site of formation and floats through bloodstream and causes occlusion
Cerebellum
-Responsible for coordinating motor
commands with sensory inputs to control movement
-Communicates with brainstem, spinal cord,
and cerebral cortex by means of superior,
middle and inferior peduncles
-Also plays significant role as memory for
motor functions and even cognitive
processing
-Composed of 2 hemispheres (the vermis
separates the two lobes)
Tracts of Cerebellum
Dorsal spinocerebellar tract, Cuneocerebellar tract, Ventral spinocerebellar tract, Rostral spinocerebellar tract
Dorsal spinocerebellar tract
communicates sensation of temperature, proprioception, and touch from lower body to ipsilateral cerebellum
Cuneocerebellar tract
serves the same function as above but for the arms and upper trunk
Ventral spinocerebellar tract
transmits proprioception info and pain sense from legs and lower trunk
Rostral Spinocerebellar Tract
Serves the same as above for arms and upper trunk
Anatomy of the Brainstem
-Medulla
-Pons
-Midbrain
Cranial Nerves and their nuclei arise from the brainstem and basic bodily functions of life are maintained here
Medulla Oblongata
A portion of the hindbrain that controls
autonomic functions
-Digestion
-Heart and blood vessel function
-Swallowing
-Sneezing
◦ Motor and sensory neurons from midbrain and
forebrain
◦ Relay of nerve signals between the brain and spinal cord
◦ Coordination of body movements
Pons
Description
◦ Connects the cerebral cortex with the medulla
oblongata
◦ Communication and coordination center between the two cerebral hemispheres
◦ Helps in transferring of messages between brain and spinal cord
Function
◦ Arousal
◦ Controlling autonomic functions
◦ Relaying sensory information between cerebrum and cerebellum
◦ Sleep
Midbrain
Midbrain and hindbrain make up the
brainstem; Connects the hindbrain and the forebrain; Involved in auditory and visual responses as well as motor function
Reticular Formation (also called Reticular Activating System)
Function:
◦ Arousal
◦ Attention
◦ Cardiac Reflexes
◦ Motor Functions
◦ Regulates Awareness
◦ Relays nerve signals to the cerebral cortex
◦ Sleep
Location:
◦ The reticular formation is a group of nerve fibers
located inside the brainstem (spans the medulla,
pons and midbrain)
Cranial Nerves
-Cranial nerves I through IV stem from
midbrain
-Cranial nerves V through VIII stem from pons
-Cranial nerves IX through XII stem from
medulla
-Cranial nerves can be efferent, afferent or
mixed
Efferent
Transmit information from brain to spinal nerves.
Afferent
Transmit info concerning the physical state of limbs and trunk to higher brain centers.
Anatomy of the Spinal Cord
-Spinal cord if the information lifeline to and from the periphery of the body
-Made up of a long mass of neurons, with both cell bodies and projections from (and to) those neurons
-Gray portions are neuron cell bodies and white portions are the myelinated fibers of tracts that communicate info to and from brain
-Efferent (motor) tracts, such as corticospinal tract, transmit information from brain to spinal nerves
-Afferent (sensory) tracts, such as spinothalamic tract, transmit info concerning the physical state of limbs and trunk to higher brain centers
More anatomy of spinal cord
-Begins at foramen magnum of skull and courses
through the vertebral canal
-Safely protected by long tube made up of
connective tissue (the meningeal linings)
31 pairs of spinal nerves arise from regions
related to the vertebra
◦ 8 pairs of cervical spinal nerves
◦ 12 pairs of thoracic nerves
◦ 5 pairs of lumbar and sacral nerves
◦ 1 pair of coccygeal nerves
