Nervous System I: CNS Flashcards
What are the 2 categories of cells in the nervous system?
- Neurons
- Glia (aka. Neuroglia)
What are neurons?
(~ 100 billion): specialized cells for reception, transduction and conduction of stimuli. They rapidly conduct signals (action potentials) from one part of a neuron to another, and these signals are then transmitted to other neurons.
What are Glia (aka. Neuroglia)?
the support cells of the nervous system. They account for ~70% of all cells in the brain.
What is the basic unit/cell of nervous tissue?
neurons
What are the features of neurons?
- DENDRITES (usually many; they receive inputs)
- CELL BODY/SOMA (nucleus and organelles)
- AXON (cell output; may be <1 mm or > 1 metre)
- AXON TERMINALS (often many).
What are the 2 types of axons?
may be myelinated or unmyelinated.
What does myelin act as?
acts as insulation & increases speed
What is the basic role of neurons?
Transmit action potentials from cell to cell through connections called synapses.
How many axons are in a neuron?
only 1
What are the types of glia in the CNS?
- Astrocytes
- Oligodendrocytes
- Microglia
What are the types of glia in the PNS?
- Schwann cells
- Satellite cells
What is the role of astrocytes in the CNS?
provide physical and metabolic support, secrete growth factors, limit neurotransmitter diffusion.
What is the role of Oligodendrocytes in the CNS?
myelination of axons.
What is the role of Microglia in the CNS?
immune cells of the brain, activated during inflammation.
Which of the glias is the most abundant?
Astrocytes!
What is the role of the Schwann cells in the PNS?
myelination of axons.
What is the role of the Satellite cells in the PNS?
support cells found within ganglia.
What type of rxn is taking place at the synapse?
a biochemical rxn!
What is the CNS made up of?
brain + spinal cord
What is the PNS made up of?
i. Cranial nerves
ii. Spinal nerves (aka. peripheral nerves)
iii. Associated structures: Ganglia & Mechanoreceptors and proprioceptors
What are the cranial nerves?
12 pairs attached to the brain.
What are the spinal nerves (aka peripheral nerves)?
31 pairs attached to the spinal cord.
What are the associated structures?
• Ganglia
• Mechanoreceptors and proprioceptors
What are ganglia? Include an ex
clusters of nerve cell bodies.
Dorsal root ganglia (sensory) are one example.
What are Mechanoreceptors and proprioceptors?
specialized structures that detect touch, stretch, vibration, joint position. (aka pain, temp, touch, etc.)
What NS are the 2 types of matter apart of?
the CNS
What is gray matter made up of?
is made up of NEURONAL CELL BODIES and DENDRITES (sites of synaptic connections). Glia are also present.
(stain can absorb it)
What particular type of glia are also present in gray matter?
astrocytes!
What is gray matters function?
Relaying and processing of information occurs in the gray matter.
What is the outer surface of the brain that is a layer of gray matter called?
cerebral cortex
What is a collection of gray matter found within the brain called?
a nucleus
Where are synapses mostly found on?
dendrites!
What does white matter consist of?
MYELINATED AXONS and constitutes the “wiring” of the brain.
Why is white matter called “white matter”?
because of the high lipid content of myelin. (white even when unstained)
What does brain function depend on?
connectivity
(damaged white matter will not work/function)
What are axons with similar functions and connections that are organized into bundles may be referred to as (within the white matter)?
tract (bundle of white matter connecting 2 things), fasciculus, pathway, or lemniscus.
What is the corpus callosum? & What does it connect?
is the largest white matter structure in the brain.
It connects the left and right cerebral hemispheres.
What does the CNS consist of?
Consists of the brain and spinal cord.
What are the brains 3 main divisions?
- Forebrain
- Midbrain
- Hindbrain (continuous with the spinal cord)
What is the forebrain? & what does it consist of?
(largest part of the brain)
- Telencephalon (Cerebrum)
- Diencephalon
What is the midbrain (Mesencephalon)?
Short, narrow “stalk” that connects the forebrain and hindbrain.
What does the Hindbrain consist of?
- Pons
- Medulla oblongata (continuous with the spinal cord)
- Cerebellum
What does the telencephalon consist of?
• Cerebral cortex (gray matter)
• White matter (axons)
• Ventricles
• Basal nuclei
What are the ventricles?
cavities within the brain filled with cerebrospinal fluid [CSF]
What are basal nuclei?
gray matter, involved in motor function
What does the cerebrum consist of?
consists of the cerebral cortex and white matter.
How is the cerebrum divided?
It is divided into two CEREBRAL HEMISPHERES.
The outer surface of the hemispheres is made up of GYRI (ridges, singular - GYRUS) and SULCI (grooves, singular - SULCUS), i.e., lateral sulcus.
Deeper sulci are called fissures: i.e., the LONGITUDINAL CEREBRAL FISSURE - separates the hemispheres.
Why is there gyri & sulci?
to increase SA (more neurons –> greater intelligence)
What are the 4 lobes of the brain?
- Frontal
- Parietal
- Occipital
- Temporal
Which lobe is the largest of the 4 lobes?
Frontal lobe!
What is the frontal lobe responsible for?
for VOLUNTARY MOTOR FUNCTION, including speech.
It also controls “higher functions” – social behaviour, decision making, emotions, abstract reasoning, intellect, personality.
What separates the frontal & parietal lobes?
the CENTRAL SULCUS
What houses the primary motor cortex?
the PRE-CENTRAL GYRUS
What is the primary motor cortex?
responsible for activating the motor neurons of the spinal cord on the OPPOSITE SIDE OF THE BODY (origin of corticospinal tract).
- right hemisphere controls left side of body
What can lesions to the frontal lobe result in?
paralysis, cognitive deficits, and behavioural changes.
What is the post-central gyrus?
is the site of the PRIMARY SOMATOSENSORY CORTEX, which is responsible for conscious perception of sensation.
What is the primary somatosensory cortex?
responsible for conscious perception of sensation.
What is the function of the parietal lobe?
It receives somatosensory information (pain, temperature, touch, proprioception - awareness of our body positions) FROM THE OPPOSITE SIDE OF THE BODY.
- also critical for interpretation and understanding of sensory input.
(dyslexia is linked to function of parietal lobe)
What can lesions of the parietal lobe produce?
can produce deficits in processing sensory information.
What is the parietal lobe separated from the occipital lobe by?
the PARIETO-OCCIPITAL SULCUS.
What is the function of the occipital lobe?
Gyri on the medial surface are the site of the PRIMARY VISUAL CORTEX, responsible for conscious perception of VISION.
What are the two halves of the primary visual cortex are separated by? & how do they receive visual info?
calcarine sulcus.
Each side receives visual information FROM THE OPPOSITE VISUAL FIELD (“RIGHT SEES LEFT”).
The remainder of the lobe is critical for interpretation of visual information (“What is it?” Where is it?).
What can lesions to the occipital lobe do?
Lesions can produce visual deficits, including blindness.
- if damage in brain, than eyes won’t see
What is the temporal lobe separated by?
Separatedfrom the frontal and parietal lobes by the LATERAL SULCUS/FISSURE.
Where is the primary auditory cortex within the temporal lobe?
The gyri in the superior part of the lobe are the site of the PRIMARY AUDITORY CORTEX, responsible for perception of sound.
What is the temporal lobe imp. for?
It is important for interpreting sound, especially language and language formation.
What is the inferior surface of the temporal lobe the site of?
the PRIMARY OLFACTORY CORTEX.
Where is the hippocampus? What is its function?
The HIPPOCAMPUS is contained within the temporal lobe - critical for memory formation.
What are the 3 imp. concepts of cortical function? Explain each
- Functional Localization: different sites within the cortex are associated with specific functions. (motor activity, somatosensory, etc.)
- Bilateral symmetry: one half of the body is represented in each cerebral hemisphere. Also, the left side of brain controls the right side of the body and vice versa. (useless if they aren’t connected)
- Cortical functions depend on connectivity: the left and right hemispheres are connected and the lobes are connected to each other. The cortex is also connected to the diencephalon and spinal cord.
What does the basal nuclei include? & what is it involved in?
Includes the CAUDATE, PUTAMEN, and GLOBUS PALLIDUS.
Involved in regulating motor activity. (don’t generate/produce movement!)
What can lesions to the basal nuclei produce?
Lesions produce movement disorders called DYSKINESIAS, which commonly result in either increased involuntary movement (HYPERKINESIA; i.e., Huntington’s chorea) or decreased/slowed movements (HYPOKINESIA; i.e., Parkinson’s disease).
What is the cause of Huntington’s disease?
caused by death of neurons in the caudate nucleus.
Where is the diencephalon?
Region of the forebrain located between the cerebrum and the midbrain. (in heart/middle of brain)
What are the principle components of the diencephalon?
the THALAMUS and HYPOTHALAMUS.
What is the function of the thalamus?
RELAYS ALL SENSORY INFORMATION (EXCEPT SMELL) to the cerebral cortex – required for conscious appreciation of senses.
What does the hypothalamus regulate?
regulates the PITUITARY GLAND (endocrine system) and the AUTONOMIC NERVOUS SYSTEM - fight or flight response, cardiovascular activity.
What does the midbrain consist of? & what does it contain?
Consists of axons (mainly) and a number of nuclei.
Contains the nuclei of 2 cranial nerves (CN III and CN IV).
What is imp. about the midbrain?
Almost all tracts that enter or exit the cerebral hemispheres pass through the midbrain - a small but critical region.
Site of the SUBSTANTIA NIGRA (important for regulating motor activity, lost in Parkinson’s disease).
What is the substantia nigra imp. for?
(important for regulating motor activity, lost in Parkinson’s disease).
What does the hindbrain consists of?
consists of the PONS, MEDULLA OBLONGATA, and CEREBELLUM.
- embryonic origins of these areas
What does the brainstem consist of?
consists of the MIDBRAIN, PONS, and MEDULLA.
(more imo. than hindbrain)
Where is the pons positioned b/t?
The pons is positioned between the midbrain and the medulla (the medulla is continuous with the spinal cord).
Where are the Cranial nerves V, VI, VII, and VIII attached to?
the pons.
Where are the Cranial nerves IX, X, XI and XII attached to?
the medulla.
What has connections with all 3 parts of the brainstem?
the cerebellum
What is the functional importance of the brainstem?
Small lesions (even mm) can cause big problems!
- Motor and sensory tracts – interruption of these tracts produces profound motor/sensory deficits - paralysis.
- Cranial nerve nuclei – lesions produce deficits in motor/sensory innervation of the head and neck – can affect eye movements, facial expressions, and chewing.
- Other nuclei - reticular formation - lesions may produce coma or even cause cardiac and respiratory arrest.
What does the cerebellum contain? & what is it connected to?
Contains more neurons than the rest of the CNS combined!
- highly folded structure as a result!
Connected to the midbrain, pons, and medulla.
What is the cerebellum imp. for?
Important for MAINTAINING BALANCE (doesn’t produce!): receives inputs from the vestibular apparatus of the inner ear.
Important for FINE MOTOR COORDINATION: receives input from cerebrum (via the pons) and proprioceptors (from the spinal cord).
Important for automatic/non-conscious adjustments in posture and locomotion.
(if can’t touch finger to nose smoothly & precisely than problem in cerebellum - feedback not working)
What is the Neurocranium?
The brain is encased by 8 bones of the skull (neurocranium).
• Six of the bones correspond to the lobes of the brain:
• FRONTAL (n=1)
• PARIETAL (n=2)
• TEMPORAL (n=2)
• OCCIPITAL (n=1)
• The last two bones are the ETHMOID and SPHENOID bones.
• The weakest part of the skull (and one of the thinnest) is called the PTERION.
Describe Cranial Fossae
• Anterior cranial fossa – frontal lobe
• Middle cranial fossa – temporal lobe
• Posterior cranial fossa - cerebellum
What are the meninges?
The brain and spinal cord are covered by 3 membranous layers collectively referred to as the meninges.
What are the 3 meninges?
- Dura Mater (outermost layer)
- Arachnoid Mater
- Pia Mater (innermost)
What does mater mean?
mother (therefore protect, organize/compartmentalizing, & get you where you need to be/conduit)
What are the function of the meninges?
- PROTECTION (together with the cerebrospinal fluid, skull, and vertebral column).
- COMPARTMENTALIZATION of the cranial cavity. They provide structural support for the brain and spinal cord.
- CONDUIT for cerebrospinal fluid (subarachnoid space) and venous blood (venous sinuses). Allows these fluids to circulate.
Describe the dura mater
- Tough, dense outer layer - “TOUGH mother”.
- It is tightly attached to the inner surface of skull
(NO SPACE between them).
What is the dura mater supplied by?
the MIDDLE MENINGEAL ARTERY, which lies right underneath the pterion!
Describe the several infoldings of the dura mater
There are several infoldings or DURAL SEPTA that form separate compartments within the skull. These include the 1) FALX CEREBRI – separates the cerebral hemispheres, and the TENTORIUM CEREBELLI (tent over cerebellum) – separates the cerebellum from the cerebral hemispheres
Where are venous sinuses found?
Venous sinuses are found where the edges of the dural septa meet the skull.
Describe the arachnoid mater
- Thin, middle layer that is firmly attached to the dura (no space between arachnoid and dura).
- It has a filmy, spider web-like appearance.
- The arachnoid “bridges” over the gyri and
sulci of the brain. - There are many small extensions of the arachnoid that connect to the pia mater.
Describe the Pia mater
- Innermost and thinnest layer of the meninges. It is very delicate and translucent, which makes it difficult to see.
- It is firmly attached to the outer surface of the brain and closely follows the contours of the gyri and sulci.
- Easier to see in the spinal cord.
Describe the meningeal spaces in the skull
- Normally, the only space present between the meningeal layers is the SUBARACHNOID SPACE (between the arachnoid and pia). It is filled with cerebrospinal fluid.
- Superficial cerebral blood vessels (arteries and veins) are found in this space.
- The subarachnoid space is continuous with the VENTRICLES, which are also filled with CSF.
- Under pathological conditions meningeal layers may separate to form an EPIDURAL SPACE (between dura and skull) or a SUBDURAL SPACE (between arachnoid and dura).
