Nervous Tissue/Brain; Blood supply to Brain (Ch. 14-15, 23.3) Flashcards
What does the nervous system (NS) include?
All neural tissue in the body (neurons and glial cells)
What is included in the central nervous system (CNS)?
Brain
Spinal Cord
What is included in the peripheral nervous system (PNS)?
Cranial nerves
Spinal nerves
Ganglia
All neural tissue outside the CNS
What are NS fxns?
Collect information
–monitor external and internal changes (sensory input from PNS)
Process and evaluate information
–process sensory input and determines response
Respond to information
–dictates response by activating effector organs
What are the 2 divisions of the NS?
CNS
PNS
What is the functional organization of the NS?
NS branches into: Sensory NS and Motor NS
Sensory NS branches into: Somatic Sensory and Visceral Sensory
Motor NS branches into: Somatic Motor and Autonomic Motor
What is Somatic Sensory?
Free nerve endings in almost all body tissues
Includes receptors for pain, touch, pressure, vibration, temperature…
Also proprioception (sense of body in space) in skin, body wall, and limbs
“Special” senses = vision, taste, hearing, balance, smell
What is Visceral Sensory?
Sensations from the organs (digestive and urinary tracts, reproductive organs, etc.)
Stretch, temperature
What is Somatic Motor?
aka Voluntary NS (b/c we can control it)
–motor nerves carry impulses from the brain to the skeletal muscles and somatic tissues, which creates voluntary movement
Contraction of skeletal muscles
What is Autonomic Motor?
aka Autonomic NS (ANS) or involuntary nervous system
Regulates contraction of smooth and cardiac muscle and gland secretion
We cannot control this
Subdivides into sympathetic and parasympathetic
What is Sympathetic (under ANS)?
“fight or flight”
What is Parasympathetic (under ANS)?
“resting and digesting”
What are the 2 types of cells in nervous tissue?
Neurons and Glia
What are neurons?
Neurons transmit electrical signals
“nerve cells”
What are glia?
“nerve glue”
Supporting cells
What is included in the structure of a neuron?
Soma (cell body)
Dendrites
Axons
Myelin
Structure of a Neuron: what are soma?
(cell body)
Contains nucleus, cytoplasm, organelles
Structure of a Neuron: what are dendrites?
receive signal, transmit to cell body
Structure of a Neuron: what are axons?
transmits signal to axon terminals (note direction of signal movement)
Structure of a Neuron: what is myelin?
Insulates neuron, helps propagate signal
Describe the signal pathway of dendrites and axons.
Dendrite –> cell body –> axon –> axon terminal (end of axon)
What is a synapse?
A synapse is a site where an axon connects with another cell (another neuron cell or muscle and gland cells)
What are the 4 types of Glia (of the CNS)?
- ependymal cells
- microglia
- oligodendrocytes
- astrocytes
In general, glia support and protect the neurons. Each type has slightly different functions though (*do NOT need to know functions for lecture exam)
What are Schwann cells? What are Satellite cells? Where are they found?
Found in Glia of the PNS
Schwann cells: myelinate axons of PNS
Satellite cells: found in ganglia, surround the neuron cell body
What are nerves?
A nerve is defined as a collection of axons in the PNS
The axons are arranged in parallel and wrapped in CT
A nerve can contain myelinated and/or non-myelinated, sensory and/or motor axons
What is included in the structure of a nerve?
Myelin sheath, Axon, Fascicle
Each axon is surrounded by myelin sheath (Schwann cells)
Groups of axons are nerve fascicles
Groups of fascicles = nerve
What are the 3 layers of nerve structure (from superficial to deep)?
- Epineurium: surrounds entire nerve
- Perineurium: surrounds fascicle
- Endoneurium: surrounds axon and myelin sheaths
What 3 things protect the brain?
Meninges
Cerebrospinal fluid (CSF)
Blood brain barrier (BBB)
What are meninges?
They’re membranes that surround and protect the brain
What is CSF?
It cushions the brain
What is the BBB?
It protects the brain from exposure to toxins
What are functions of the meninges?
Cover and protect CNS
Enclose and protect blood vessels to CNS
Contain and circulate CSF
What are the 3 meninges (superficial to deep)?
- Dura mater
- Arachnoid mater
- Pia mater
What is Pia Mater?
Innermost layer, follows curves of brain, very delicate, lots of blood vessels
What is Arachnoid Mater? What is the space associated with this mater?
Arachnoid mater is superficial to pia mater
Subarachnoid space: weblike threads attach to arachnoid mater to pia mater. Filled with CSF
What is Dura Mater?
(hard mother) - outermost layer
2 layers of dense fibrous CT (meningeal and periosteal). In some spots, separate to form dural sinuses (drainage for brain) inside.
What are the 2 layers of dense fibrous CT in the dura mater?
Meningeal and Periosteal
What are dural venous sinuses? What are the 4 specific sinuses?
Drain blood from brain and drain into internal jugular veins.
Include: superior saggital sinus, straight sinus, transverse sinus, sigmoid sinus (drains into jugular vein)
What are the ventricles? How many are there?
4 interconnected cavities or expansions within the brain for circulating CSF
Lateral ventricles (2) communicate with the third ventricle via interventricular foramen
Third ventricle drains into fourth ventricle via cerebral aqueduct
Discuss CSF. What does it do? What does it protect the brain from?
Brain and spinal cord “float” in CSF - prevents damage/crushing
Resists compressive forces, cushions against trauma
Feeds brain, removes wastes, carries chemical signals
How is CSF made? Where does it travel? How much is processed/circulated each day?
- Made in choroid plexus
- Flows through ventricles and into subarachnoid space
- Flows through subarachnoid space
- Absorbed into dural sinuses
~500 mL/d is processed/circulated
What are fxns of the brain?
Controls HR, respiration, BP, and maintains homeostasis
Innervation of head, neck, and viscera
High level tasks - intelligence, consciousness, memory, emotion, behavior
What are the 4 main parts of the brain?
Cerebrum
Diencephalon
Cerebellum
Brain Stem
What is Gray Matter?
Located on the outer part of the brain (cerebellar and cerebral cortex) and also the innermost regions.
Unmyelinated neurons and neuron cell bodies
What is White Matter?
Made of myelinated (and some non-myelinated) axons
Deep to gray matter
What is the Diencephalon?
Surrounded by the cerebral hemispheres
What ventricle does the Diencephalon contain?
the 3rd ventricle
What composes the Diencephalon?
Thalamus = lateral walls Hypothalamus = floor Epithalamus = roof
Discuss the Thalamus. What are functions?
Lateral walls of the 3rd ventricle
Relays somatosensory, visual, and auditory info (all except smell)
**Any part of the brain (sensory or not) that communicates with the cerebral cortex must go through the thalamus
Thalamus = gatekeeper
Discuss the Hypothalamus. What does it do?
Main visceral control center of the body, regulates many activities:
- -controls ANS
- -regulates body temperature
- -regulates hunger/thirst
- -regulates sleep-wake cycles
- -controls endocrine system
- -controls emotional responses
- -controls motivational behavior
- -formation of memory
Discuss the Epithalamus. What does it include?
Forms roof of third ventricle
Includes pineal gland (endocrine function) and a few brain nuclei.
What is the Brain Stem?
Composed of Medulla, Pons, and Midbrain
What are the 4 general fxns of the Brain Stem?
- Passageway for fiber tracts between cerebrum and spinal cord
- Cranial nerves and innervation of the face and head
- Automatic behaviors needed for survival
- Integrates auditory and visual reflexes
Where is the Midbrain located?
Located between diencephalon and pons.
Internal cavity is cerebral aqueduct.
Midbrain: Discuss the Tectal Plate, Superior Colliculus, and Inferior Colliculi.
Tectal Plate: integrates auditory and visual reflexes
Superior Colliculus: acts for visual reflexes
Inferior Colliculi: respond to sound
What is the Pons?
Located between the midbrain and medulla. Separated from cerebellum by 4th ventricle.
It’s a bridge between brainstem and cerebellum (motor)
What is the Medulla Oblongata?
Most caudal part of the brainstem; continuous with the spinal cord.
Pyramidal tracts carry voluntary motor output from cerebrum to brainstem.
Fibers “decussate” so left brain controls right side of body, and right brain controls left side of brain
What is the Cerebellum?
Makes up ~11% of mass of brain.
Smoothes and coordinates body movements, helps maintain posture and equilibrium
Connected to brainstem via cerebellar peduncles.
Cerebellum
2 hemispheres connected by vermis
Folia are leaflike folds that increase surface area
Outer cortex is gray matter; White matter is arbor vitae
Cerebellum: Processing
Receives info from cerebrum on movements planned
Compares planned movements with current body position
Sends instructions back to cerebral cortex to readjust/refine motor commands
How many hemispheres are in the Cerebrum? How many lobes are in EACH hemisphere? What are they named?
Cerebrum is divided into 2 halves (L and R hemispheres)
Each hemisphere is divided into 5 distinct lobes: Frontal, Parietal, Occipital, Temporal, and Insula
–lobes named for overlying bones
What are Gyri and Sulci?
Gyri are ridges of brain tissue. Ridges allow for more cerebral cortex to fit in the cranial vault. Includes: Precentral and Postcentral Gyri
Sulci are grooves between the gyri. Sulci to know: central, parieto-occipital, and lateral.
What is the Cerebrum responsible for?
Intelligence, complex thinking
What are the 3 functional areas of the Cerebrum?
- Sensory - conscious awareness of sensation
- Association areas - integrate information
- Motor areas - voluntary motor functions
What is the Primary Somatosensory Cortex?
Receives info from somatic senses (touch, pressure, vibration, pain, proprioception) and enables conscious awareness of senses. Located in post central gyrus (parietal lobe)
What is Sensory Homunculus?
Each region of the sensory cortex receives sensory stimuli from a specific body region, so a “map” can be created
Amount of cortex used for sensory info is NOT related to absolute size but to amount of info (lips and fingertips are most sensitive)
What 2 cortexes are included in the Sensory Cortical Regions?
Primary Visual Cortex
Primary Auditory Cortex
What is the Primary Visual Cortex?
Posterior/medial occipital lobe. Receives visual info from retina of eye
What is the Primary Auditory Cortex?
In the temporal lobe. Receives and processes auditory info from inner ear
What is the Primary Motor Cortex?
Located in precentral gyrus (dorsal portion of frontal lobe).
Controls voluntary skeletal muscle activity
Other motor areas include Broca’s
What is the Motor Homunculus?
As with sensory homunculus, human body represented spatially in primary motor cortex
Face and hand are very large because of need for very precise motor control
Broca’s Area
Motor speech area. Controls motor movements for speech
If damaged, can understand speech but cannot speak fluently.
Lower portion of LEFT frontal lobe (only)
Wernicke’s Area
Multimodal association area. Recognition and understanding of speech.
If damaged, can speak but not comprehend language.
Posterior section of LEFT superior temporal lobe (only)
What hemisphere are Broca’s Area and Wernicke’s Area located?
Left hemisphere
Discuss White Matter of the Cerebrum.
Corpus Callosum: largest, most visible band of commissural fibers that connect 2 hemispheres.
Association fibers: short fibers that connect regions in the same hemisphere
Discuss deep Gray Matter of the Cerebrum
Basal nuclei (ganglia): involved in motor control.
Composed of caudate nucleus, putamen, and globus pallidus.
Work with the cerebral nuclei to control movement.
Start, stop and regular the intensity of voluntary movements
Discuss the Limbic System
Involved with emotion and motivation. Creating, storing, and retrieving memories.
Cingulate gyrus: emotional response
Hippocampus: stores memory
Various nuclei
All are linked together by the fornix.
Arteries of the Head (lateral right view)
The R and L common carotid arteries both ascend into the neck and head and divide into internal and external carotid arteries.
Internal and external carotid arteries feed the head, brain, and orbital regions.
What does the Internal Carotid Artery supply?
Supplies anterior brain and eyes
Blood supply for brain
Internal carotid divides into anterior and middle cerebral arteries.
Anterior cerebral artery joins anterior communicating artery.
Middle cerebral artery supplies parts of temporal and parietal lobes (= ~80% of cerebrum)
R and L vertebral arteries fuse to become basilar artery, which divides into posterior cerebral arteries
These are connected by posterior communicating arteries
Cerebral Arterial Circle (aka Circle of Willis)
Anastomosis to protect brain’s blood supply (allows rerouting of blood flow).
Formed by posterior cerebral arteries (L and R), posterior communicating arteries (L and R), internal carotid arteries (L and R), anterior cerebral arteries (L and R), and the anterior communicating artery.