Lecture 2: Nervous system I Flashcards
2 categories of cells in nervous system
Neurons
Glia
What are neurons?
Specialized cells for rapid communication
Reception, transduction and conduction of stimuli
Conduct action potential from one part of a cell to another which is then transmitted to other cell
What are glia?
aka Neuroglia
Support cells of the nervous systems
What is the basic unit/cell of nervous tissue
Neurons
Parts of neurons
Dendrites (many, receive inputs)
Cell body (cell nucleus and organelles)
Axon (cell output, variable length)
Axon terminals (often many)
Myelination of axons
May be myelinated or unmyelinated
Myelin acts as an insulation for axons and is important for propagation
Specialization of neurons
Specialized for generating and propagating impulses from cell to cell
Where do axons commonly terminate?
On a neuron where it forms a synapse
What is a synapse?
Site of signal transduction between neurons
What type are most synapses?
Chemical
What are synapses targets for?
Drugs
ex: Serotonin Reuptake Inhibitors (SRIs)
Neuroglia in CNS
Astrocytes
Oligodendrocytes
Microglia
Neuroglia in PNS
Schwann cells
Satellite cells
Where are astrocytes found?
In white and gray matter
Functions of astrocytes
- Physical / Structural support
- Secreting Growth Factors (important for
keeping neurons alive) - Metabolic support
- Transmitter ‘scavengers’ (limit diffusion)
- Ionic and pH balance of environment
Function of oligodendrocytes
provide the myelin sheaths around axons in the CNS (required for rapid conduction of the action potential)
Which cells are targeted in multiple sclerosis?
Oligodendrocytes
Proper communication is impossible in MS
Function of microglia
macrophages of the nervous
system
protect against viruses, bacteria, and tumor cells.
When are microglia activated in CNS?
Inflammation
Function of Schwann cells
myelin producing cells of the PNS
Function of satellite cells
support cells of the PNS found within ganglia (collection of neuronal cell bodies outside the CNS)
What are the components of the CNS?
Brain and spinal cord
Components of the PNS
Outside CNS
Cranial nerves (12 pairs attached to brain)
Spinal nerves (31 pairs attached to cord)
Associated structures
What are the associated structures of the PNS?
Ganglia (clusters of nerve cell bodies where synaptic transmission occurs)
Sensory nerve endings (detect pain, temperature, touch, muscle tension etc.)
In which nervous system is gray and white matter found?
CNS
What does the gray matter of the CNS consist of?
Neuronal cell bodies and dendrites (site of synaptic connections)
Function of connections of dendrites in grey matter
These connections are the basis of relaying and processing of information
Which part of the brain is composed of grey matter?
The surface of the brain is largely a layer of gray matter (cerebral cortex)
What is a nucleus (gray matter)?
A collection of neuronal cell bodies that have a similar function
What does white matter consist of?
axons (usually myelinated)
Function of white matter
constitutes the ‘wiring’ of the brain (white because of high lipid content of myelin)
Brain function depends on connectivity
What is a tract, fasciculus, pathway, or lemniscus?
Axons of similar functions and connections that are organized into bundles in the white matter
What is the largest bundle of white matter?
Corpus callosum
connects left & right cerebral hemispheres
(see figures)
Orientation in the nervous system
See figure
3 main sections of brain
- Forebrain,
- Midbrain, and
- Hindbrain (continuous with spinal cord)
See figure
What is the biggest section of the brain?
Forebrain
Parts of forebrain
i. Telencephalon (Cerebrum)
ii. Diencephalon
(see figure)
Structure of midbrain (mesencephalon)
Short, narrow “stalk” that connects forebrain with hindbrain
Parts of hindbrain
i. Pons
ii. Cerebellum
iii. Medulla (continuous with Spinal Cord)
(See figure)
Parts of telencephalon
Cerebral Cortex (Gray matter)
White matter (axons)
Ventricles (cavities within the brain filled with cerebrospinal fluid [csf])
Basal Ganglia/Basal Nuclei (Gray; Motor)
What are cerebral hemispheres made of?
gyri (ridges) and sulci (grooves)
Other name for deep sulk
Fissures
ex: longitundinal fissure that separates hemispheres
What are the 4 lobes of the brain?
- Frontal
- Parietal
- Occipital
- Temporal
(see figure)
Functions of cerebral cortex?
Functional localization
Contralateral Nature
Cortical functions
Functional localization of cerebral cortex
Different sites within cortex
have different functions
Contralateral nature of cerebral cortex
Motor and Sensory Cortex:
Left side of brain corresponds to right side of body
Cortical functions of cerebral cortex
Depend on connectivity
The left and right hemispheres are connected and lobes are connected to each other
cortex is connected to thalamus & Spinal Cord (afferent and efferent)
Function of frontal lobe
Movements/motor
behavior
speech
decision making
feelings
abstract thinking
intellect, personality,
Location of central sulcus of the frontal lobe
separates it from parietal lobe
What is located in the pre-central gyrus of the frontal lobe?
primary motor cortex
Responsible for activating the motor neurons of the spinal cord on opposite side of body (origin of corticospinal/pyramidal tract)
(see figure)
Important gyrus in frontal lobe
Post-central gyrus
Function of post-central gyrus in parietal lobe
site of primary somatosensory cortex;
i.e., conscious perception of somatosensation
Receives somatosensory information (pain, temp., touch, proprioception,) from opposite side of body
(see figure)
What is parietal lobe critical for?
interpretation & understanding of sensory input
Important gyrus in occipital lobe
Medial surface
site of primary visual cortex; i.e., conscious perception of vision
Receives visual information from opposite visual field (“right sees left”)
What is the occipital lobe’s function?
critical for interpretation & understanding of visual information (“What is it?” Where is it?)
Important gyri on temporal lobe
Gyri on floor of lateral sulcus
site of primary auditory cortex; i.e., perception of sound
Important for interpreting sound, esp. language and language formation
Where is the site of the primary olfactory cortex
inferior surface of temporal lobe
Where is the Hippocampus?
Contained within temporal lobe
Role of Hippocampus
Memory formation
What is included in the basal nuclei?
Caudate, putamen, & globus pallidus
Function of basal nuclei
Involved in regulating motor activity
Lesions to basal nuclei
produce movement disorders called dyskinesias: involuntary or diminished movement (either hyperkinetic or hypokinetic)
What disease is associated with death of neurons in caudate nucleus?
Huntingtons
Where is the diencephalon?
Area between the cerebrum and midbrain
see figure
Primary components of diencephalon
thalamus and hypothalamus
Function of thalamus
relays ALL sensory information (except smell) to the cerebral cortex (conscious appreciation of senses)
Function of Hypothalamus
Regulates autonomic nervous system activity
e.g., fight or flight response, visceral activity, cardiovascular activity, etc.
Components of midbrain
Consists of fibres (mainly) and a number of nuclei
Nuclei of 2 cranial nerves (CN III and CNIV)
Importance of midbrain
Almost all fibres that enter or exit the cerebral hemispheres pass through the midbrain
(small but critical)
Site of substantia nigra (important in regulating motor activity; lesioned in P.D.) and reticular formation (RF) (important in consciousness and arousal)
Components of hindbrain
pons
medulla
cerebellum
(see figure)
Parts of brainstem
Midbrain, Pons, and Medulla
What cranial nerves are attached to the pons?
V, VI, VII, VIII
What cranial nerves are attached to the medulla?
IX, X, XI and XII
What brain structure has connections with all three components of the brainstem?
Cerebellum
Lesions of fibre tracts of brainstem
interruption of these fibre tracts produces profound motor / sensory deficits and deficits in autonomic function
Lesions of cranial nerves of brain stem
produce deficits in motor/sensory innervation of head and neck
Lesions of other nuclei in brainstem
coma
cardiac and respiratory arrest
cerebellar deficits (cardiac & resp. centres, and centre resp. for consciousness)
What is the cerebellum connected to?
Midbrain, pons and medulla
Importance of cerebellum
maintaining equilibrium: receives inputs from vestibular apparatus of inner ear
fine motor coordination: receives input from cerebrum (via pons) & proprioceptors - from spinal cord
automatic/non-conscious adjustments in posture and locomotion
What happens if there are lesions to cerebellum?
Disturbances in Gait and Coordination
Three meninges of brain
Dura
Arachnoid
Pia
Dura mater
tough, dense layer tightly attached to inner surface of skull (no space)
Arachnoid mater
thinner layer attached to dura; extensions from arachnoid to pia Meninges
(‘spider-web’ like)
What separates the arachnoid and pia mater?
subarachnoid space which contains CSF, which contains nutrients
Pia mater
very thin translucent layer attached to cortical surface; follows contours of the gyri
Function of meninges
- Protection (together with CSF, skull, vertebral column)
- Compartmentalization of cranial cavity which provides structural support and suspends spinal cord within the dural sleeve
- Conduit for cerebrospinal fluid (subarachnoid space) and venous blood (venous sinuses)
Infolding/septa/reflections of dura mater
Falx cerebri (cerebral falx): lies in longitudinal fissure between hemispheres
Tentorium cerebelli (cerebellar tentorium): tent over cerebellum, separates cerebellum from occipital lobe
(see figure)
Where are the venous sinuses of the meninges?
Within the margins of the septa (form along the attachments of dural infoldings)
Is there space between the dura and the arachnoid?
No
How close is the arachnoid to the sulci and gyri of the brain?
Arachnoid bridges over
Inner surface of arachnoid
irregular and many small strands ( Arachnoid trabeculae, like a spider-web) span the subarachnoid space (filled with cerebro-
spinal fluid) to connect to the pia mater
Figure of meninges
see figure
What is the only space in the skull under normal conditions?
subarachnoid space (between arachnoid & pia); filled with csf
Cerebral blood vessels are present in this space
What is the subarachnoid space continuous with?
Ventricles (also filled with CSF)
What is an epidural space?
Under pathological conditions meningeal layers may separate to form a space between dura and skull
What is a subdural space?
Under pathological conditions meningeal layers may separate to form a space between arachnoid and dura
What is an epidural hematoma?
can form with a blow to the temple where the middle meningeal artery lies between the dura and the skull
It can leak blood and the blood will separate the separate the dura from the skull
What is a subdural hematoma?
forms when vessels (veins) passing between the arachnoid and the dura leak blood into the subdural space (separates dura and arachnoid)
