Sept 23 - Central Nervous System Flashcards
Name the two categories of cells in the CNS
Neurons and Glia (aka Neuroglia)
What are neurons?
They are specialized cells for rapid communication; reception, transduction and conduction of stimuli. They conduct signal (action potential) from one part of cell to another and which is then transmitted to other cells. They are specialized for generating and propagating impulses from cell to cell
What are glia cells?
The support cells of the nervous system. They have have numerous functions
Describe neurons
They are the basic unit/cell of the nervous tissue. One consists of dendrites, a cell body, an axon and axon terminals. The axon may be myelinated or unmyelinated
What are dendrites?
The site of inputs (excitatory or inhibatory)
Where does an axon commonly terminate?
On a neuron, where it forms a synapse
What is a synapse?
Site of signal transmission between neurons. Most synapses are chemical, i.e., a chemical/transmitter is released from an axon terminal (synaptic button) to act on a specific receptor on the post-synaptic cell
Name the three types of glia cells in the CNS
Astrocytes, Oligodendrocytes and Microglia
Name the two types of glia cells in the PNS
Schwann cells and Satellite cells
Where are astrocytes found? What are their function?
They are found in white matter and gray matter. Their functions include: physical/structural support, secreting growth factors, metabolic support, transmitter “scavengers” and ionic and pH balance of the environment. Basically, keeping neurons happy
What is the role of oligodendrocytes?
They function to provide the myelin sheaths around axons in the CNS (required for rapid conduction of the action potential). These cells are targeted in multiple sclerosis
What are microglia? What is their function?
They are the macrophages of the nervous system (ie. immune cells of the CNS). Their function is to protect against viruses, bacteria and tumour cells (digest invading cells; act as antigen-presenting cells in the CNS). They are activated during inflammation in the CNS, as well as after a stroke, to remove the dead cells
What are Schwann cells?
They are the myeline producing cells of the PNS
What are Satellite cells?
They support the cells of the PNS found within the ganglia
Name the two components of the nervous system
The central nervous system (the brain and spinal cord) and the peripheral nervous system (everything outside of the CNS)
Name the three components of the PNS
Cranial nerves, spinal nerves and associated structures (ganglia and sensory nerve endings)
How many cranial nerves are there?
12 pairs attached to brain
How many spinal nerves are there?
31 pairs attached to the spinal cord
What are ganglia?
Clusters of nerve cell bodies where synaptic transmission occurs
What are sensory nerve endings?
They detect pain, temperature, touch, muscle tension, joint movement, etc.
What is proprioception?
What allows you to know where your limbs are in space without even seeing them
How is the CNS divided?
Into gray matter, white matter and glial cells
What is gray matter?
It consists of neurons embedded within glia (neuropil is processes of glia and neurons within gray matter). In the brain, aggregation of gray matter is called a nucleus
What is white matter?
It consists of nerve fibres/axons embedded in glial cells (white because of high lipid content of myelin)
What are glial cells?
(i.e. glia/neuroglia) They are support cells for neurons
What does gray matter and white matter have in common?
They both contain glia (support cells of the CNS) and they blood vessels
With regard to gray and white matter, how does the brain and the spinal cord differ?
In the brain, gray matter is on the outside and white matter is on the inside. In the spinal cord gray matter is on the inside (butterfly-shape) and white is on the outside
What are ventricles?
Fluid filled cavities
Name the three sections of the brain
Forebrain, midbrain and hindbrain (the hindbrain is continuous with the spinal cord)
Name the two components of the forebrain
Telencephalon (Cerebrum)
Diencephalon
What is another name the for the midbrain? Describe the midbrain
Mesencephalon
Short, narrow “stalk” that connects forebrain with hindbrain
Name the three components of the hindbrain
Pons, cerebellum and medulla (the medulla is continuous with the spinal cord
What is the brain stem
It is the composed of the midbrain, pons and medulla
Name the four components of the telencephalon
Cerebral cortex (gray matter), white matter (axons), ventricles (fluid-filled), basal ganglia/basal nuclei (gray;motor)
What are gyri (gyrus)?
The ridges of the brain
What are sulci (sulcus)?
The grooves of the brain. Deeper sulci are called fissures (i.e., longitudinal cerebral fissure which separates the hemispheres)
Name the four lobes of the brain
Frontal, parietal, temporal and occipital
What are the three important concepts in cortical function
- Functional localization
- Contralateral nature of motor and sensory cortex
- Cortical functions depend on connectivity
Explain functional localization
Different sites within the cortex have different functions; there is a division of labour
Explain Contralateral nature of motor and sensory cortex
The left side of the brain corresponds to the right side of the body and the right side of the brain corresponds to the left body
Explain “Cortical functions depend on connectivity”
The left and right hemispheres are connected and lobes are connected to each other and cortex is connected to thalamus and spinal cord (afferent and efferent)
What is the role of the frontal lobe?
Movements/motor, behaviour, speech, decision making, feelings, abstract thinking, intellect, personality, etc.
What is the central sulcus?
It separates the frontal lobe from the parietal lobe
What does the pre-central gyrus do?
It houses the primary motor cortex; it is responsible for activating the motor neurons of the spinal cord on opposite sides of the body (origin of corticospinal/pyramidal tract)
What is the role of the parietal lobe?
It receives somatosensory information from the opposite side of the body. It is critical for interpretation and understanding of sensory input
What is the post-central gyrus?
It is the primary somatosensory cortex, i.e., conscious perception of somatosensation
What is somatosensory information?
Pain, temperature, touch, proprioception, vibration
What separates the parietal and occipital lobe?
The parietoccipital sulcus
What is the role of the occipital lobe?
It receives visual information from opposite visual field (“left sees right”). The remainder of the lobe is critical for interpretation and understanding of visual information (“What is it? Where is it?”)
What is the role of the gyri on the medial surface of the occipital lobe?
It the site of the primary visual cortex, i.e., conscious perception of vision
What is the role of the temporal lobe?
It is important for interpreting sound, especially language and language formation. It is also responsible for “higher order” function, e.g., interpreting visual information
What is the role of the gyri on the floor of the lateral sulcus of the temporal lobe?
Perception and interpretation of sound
What is the role of the inferior surface of the temporal lobe?
It is the site of the primary olfactory cortex
What is the role of the hippocampus? Where do you find it?
The hippocampus is contained within the temporal lobe. It is responsible for memory formation
What is the basal nuclei?
It is gray matter deep in the brain, not seen externally.
What makes up the basal nuclei?
The caudate nucleus, the putamen and the globus pallidus
What is the function of the basal nuclei?
It is involved in regulating motor activity
What is the result of lesions in the basal nuclei?
Lesions produce movement disorders called diskinesias: involuntary or diminished movement (either hyperkinetic or hypokinetic). Huntington’s disease is associated with the death of neurons in the caudate nucleus
What is the diencephalon?
It is the area between the cerebrum and the midbrain. It forms the wall of the third ventricle (a narrow midline structure) between the 2 lateral ventricles of the cerebral hemispheres and the fourth ventricle
What composes the diencephalon?
It consists of the hypothalamus, the thalamus (largest), the subthalamus and the epithalamus
What are the functions of the diencephalon?
Sensory, motor and autonomic
Describe the sensory function of the diencephalon
The diencephalon is responsible for all sensory information (except smell). It is initially processed in the thalamus before being relayed to the cerebral cortex (conscious appreciation of senses)
Describe the motor function of the diencephalon
It is important in regulating motor activity via connections with basal nuclei and cerebral cortex
Describe the autonomic function of the diencephalon
It regulates autonomic nervous system activity; e.g., fight or flight response, visceral activity, cardiovascular activity, etc.
Describe the midbrain
It consists of fibres (mainly) and a number of nuclei. The nuclei of 2 cranail nervers (CN III and CN IV) are found in the midbrain. Almost all fibres that enter and exit the cerebral hemispheres pass through the midbrain. It is the site of substantia nigra and reticular formation
What is substantia nigra?
It is important in regulating motor activity. It is lesioned in Parkinson’s disease
What is reticular formation?
It is important in consciousness and arousal. It responsible for keeping us alive (cardiovascular system, breathing, sleep-awake cycle, etc.)
What does the hindbrain consist of?
The hindbrain consists of the pons, the medulla (oblongata) and the cerebellum
What is the brainstem?
It is the midbrain, the pons and the medulla. The pons ins connected to the midbrain and the medulla. The medulla is continuous with the spinal cord. The cerebellum has connections with all 3 components of the brainstem
Describe the pons
It is the a larger expansion (relative to the midbrain) made up of fibres (ascending/sensory and descending/motor) cranial nerve nuclei (V, VI, VII and VIII) and reticular formation and pontine nuclei (together with fibres traveling from pontine nuclei to cerebellum, which is the main input to the cerebellum)
Describe the medulla
It is caudal to the pons and continous with the spinal cord. It is made up of fibres (ascending/sensory and descending/motor), cranial nerve nuclei (IX, X and XII) and reticular formation (critical for control of cardiovascular and respiratory systems)
Describe the importance of the cerebellum
It is important in maintaining equilibrium: it receives inputs from vestibular apparatus of inner ear. It is important in fine motor coordination: it receives input from the cerebrum (via pons) and proprioceptors (from spinal cord). It is important for automatic/non-conscious adjustments in posture and locomotion
What are meninges?
The brain and spinal cord are covered with 3 membranous layers: the dura mater, the arachnoid mater and the pia mater
What are the functions of the 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 CSF (subarachnoid space) and venous blood (venous sinuses)
Describe the dura mater
Tough dense layer; in cranium is closely apposed to bone (i.e., no space). Infoldings/septa/reflections separate comparments within the cranium include the falx cerebri (sagittal midline) and the tentorium cerebelli - tent over cerebellum. Venous sinuses are within the margins of the septa
What is the falx cerebri?
It is an arched fold of dura mater that separates the cerebral hemispheres
What is the tentorium cerebelli?
it is an extension of dura mater that separates the cerebellum and the occipital lobe
Describe the arachnoid
Thin middle layer closely apposed to dura (no space between arachnoid and dura). The arachnoid “bridges over the gyri and sulci of the brain. The inner surface is irregular and many small strands (like a spider-web) span the subarachnoid space (filled with CSF) to connect to the pia mater
Describe the pia mater
Innermost and thinnest layer. It is very delicate (transparent) and closely associated with the outer surface of the brain. It closely follows the gyri and sulci of the brain
Describe the “epidural and subdural spaces” of the CNS
Normally there are no spaces within the skull. The cranial epidural space is a “potential space” between the dura and the skull. The subdural space (between the arachnoid and the dura) is also a “potential space). However under pathological conditions, these meningeal layers may separate to form a real space: epidural and subdural
Describe 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 dura from the skull
Describe a subdural hematoma
Forms when vessels (veins) passing between the arachnoid and the dura leak blood into the subdural space (separates dura and arachnoid). There is less pressure compared to an epidural hematoma and symptoms may not appear right away
Describe the subarachnoid space
The subarachnoid space is filled with CSF. It is continuous with the ventricles (cavities within the brain filled with CSF). Blood vessels are present in this space
