Ch2: Neuroanatomy Overview and Basic Definitions Flashcards
The Nervous System
- Perhaps the most beautiful, elegant, and complex system in the body.
- Its interconnected networks perform processing that is simultaneously local and distributed, serial and parallel, hierarchical and global.
- Structures of the nervous system can be described on multiple levels: in terms of macroscopic brain divisions; connecting pathways and cell groupings; individual brain cells; and, ultimately, receptors, neurotransmitters, and other signaling molecules.
Neighborhood Effects
Lesions almost invariably affect neighboring regions as well and are often critical in localizing neuroanatomical lesions
The Human Nervous System can be divided into the…
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
Central Nervous System (CNS)
Brain and Spinal Cord
Peripheral Nervous System (PNS)
Everything Else!
- Cranial nerves and ganglia
- Spinal nerves and dorsal root ganglia
- Sympathetic and parasympathetic nerves and ganglia
- Enteric Nervous System
During embryological development the CNS arises from a sheet of ectodermal cells that folds over to form the…
Neural Tube
Neural Tube
Forms several swellings and outpouchings in the head that eventually develop into the brain, while the part of the neural tube running down the back of the embryo forms the spinal cord
The fluid-filled cavities within the neural tube develop into the…
Brain ventricles, which contain cerebrospinal fluid (CSF).
Parts of the Human Nervous System
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Embryological Development of the Central Nervous System
(A) View of developing nervous system from the back. The neural tube has formed various vesicles that give rise to the different parts of the central nervous system (B) View of developing nervous system from the side. (C) Parts of adult central nervous system
The developing brain has three main divisions:
- The forebrain (prosencephalon)
- The midbrain (mesencephalon)
- The hindbrain (rhombencephalon)
Forebrain/Prosencephalon
The largest part of the nervous system in humans, and it is further subdivided into the telencephalon and diencephalon.
Telencephalon (Forebrain/Prosencephalon)
(meaning “end brain” in Greek) Made up of the cerebral hemispheres and includes structures discussed later in this chapter such as the cerebral cortex, white matter, and basal ganglia.
Diencephalon (Forebrain/Prosencephalon)
Composed of the thalamus, hypothalamus, and associated structures.
Midbrain/Mesencephalon
A relatively short and narrow region connecting the forebrain and hindbrain.
Hindbrain/Rhombencepalon
Composed of the pons and cerebellum (metencephalon) together with the medulla (myelencephalon)
The midbrain, pons, and medulla together form a connection between the…
Forebrain and the spinal cord.
Brainstem
Made up of the midbrain, pons, and medulla
- The most evolutionarily ancient part of the human brain and is the part that most closely resembles the brains of fish and reptiles.
- Controls many of the most basic bodily functions necessary for survival, such as respiration, blood pressure, and heart rate.
Cerebrospinal fluid is formed mainly by vascular tufts lying within the ventricles called…
Choroid Plexus
CSF circulates from the … to the .., and then leaves the ventricular system via foramina in the … to percolate around the outside surface of the brain and spinal cord.
lateral ventricles, third ventricle, fourth ventricle
-Once it leaves the ventricular system, CSF travels in the space between the arachnoid and pia and is ultimately reabsorbed into the venous system.
Meninges
Three membranous protective layers that cover the Central Nervous System
List the Meninges from inside to outside
Mnemonic = PAD
Pia, Arachnoid, Dura
Orientation and Planes of Section
Structures above the midbrain, the orientation of the nervous system is the same with respect to the ground as in reptiles. At the midbrain and below, however, there is a rotation of 90° because in the standing position the spinal cord is approximately perpendicular to the ground in humans.
Example: Above the midbrain, the anterior commissure is… and the posterior commissure is… (Orientation of the Central Nervous System)
Rostral, Caudal
Example: Below the midbrain, the anterior horn of the spinal cord is… and the posterior horn of the spinal cord is… (Orientation of the Central Nervous System)
Ventrail. Dorsal
Example: Below the midbrain, the superior cerebellar peduncle is… and the inferior cerebellar peduncle is… (Orientation of the Central Nervous System)
Rostral, Caudal
Anatomical Planes of Section
(A) Horizontal (axial, transverse) plane. (B) Coronal plane. (C) Sagittal plane
-Sagittal plane= left–right axis
-Coronal plane= anterior–posterior axis,
-Horizontal plane= superior–inferior axis.
(When a plane of section lies somewhere between the three principal planes, it is referred to as oblique. )
Microscopically, the nervous system is composed of…
Nerve cells, or neurons, and support cells called glial cells (glia)
Neurons
The basic units of signaling in the nervous system, although glial cells may contribute as well
A typical neuron has
A cell body containing the nucleus, relatively short processes called dendrites, which receive most inputs to the cell, and long processes called axons, which carry most outputs
Multipolar Neurons
(Most mammalian neurons) They have several dendrites and several axons
-Often, a single axon arising from the cell body will travel for a distance, and then one or several axon collaterals branch off the main axon to reach different targets
Bipolar Neurons
(Some neurons) Have a single dendrite and a single axon arising from the cell body.
- Bipolar cells are often sensory neurons, such as those involved in vision or olfaction
- Some bipolar neurons are called pseudo-unipolar, since their processes are initially fused and then split to produce two long axons.
(ex. dorsal root ganglion sensory neurons)
Unipolar Neurons
Both axons and dendrites arise from a single process coming off the cell body, occur mainly in invertebrates.
Typical Mammalian Neuron
(A) The neuron mainly receives inputs on the dendrites and cell body and conveys signals via axonal electrical conduction to reach synapses, which send outputs to other neurons. (B) Inset showing axonal myelin sheath and node of Ranvier. (C) Inset showing main elements of presynaptic and postsynaptic terminals
Synapses
Specialized regions where communication between neurons mainly takes place
- Classically, synapses carry information from the axon terminals of one neuron to the dendrites of the next neuron.
- However, there are also axo-axonic and dendro-dendritic synapses, and some forms of communication can even occur in reverse, traveling from dendrites back to axons
Chemical Synapses
Chemical neurotransmitter molecules, stored mainly in synaptic vesicles, are released from presynaptic terminals of the neuron
- They then bind to neurotransmitter receptors on the postsynaptic neuron, giving rise to either excitation or inhibition of the postsynaptic neuron.
- In some cases, communication also takes place at electrical synapses where direct electrical coupling of neurons occurs through specialized junctions.
Neurons are … and … active.
electrically and chemically
Action Potential
A transient voltage change that occurs when excitatory synaptic inputs combine with endogenous transmembrane currents to sufficiently excite a neuron, lasting about 1 millisecond.
- Action potentials can travel rapidly throughout the length of a neuron, propagating at rates of up to about 60 meters per second along the cell membrane.
- Classically, action potentials are initiated at the axon hillock and initial segment by integration of inputs from the dendritic end of the neuron and then travel along the axon to reach presynaptic terminals, where communication can occur with the next neuron.
- Action potentials trigger release of neurotransmitter molecules from synaptic vesicles, allowing chemical communication with the postsynaptic cell
Myelin Sheaths
Lipid, formed by specialized glial cells that often insulate axons and speed the rate of action potential conduction
Oligodendrocytes and Schwann Cells
The myelin-forming glial cells in the CNS are oligodendrocytes; in the PNS they are Schwann cells.
Nodes of Ranvier
Voltage gated ion channels that are concentrated in short, exposed segments of the axon
Conduction of action potentials from node to node occurs rapidly by a process called…
Saltatory Conduction
Two general types of functions of Chemical neurotransmitters
- To mediate rapid communication between neurons through fast excitatory or inhibitory electrical events known as excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs).
- Neuromodulation, generally occurring over slower timescales.
Fast EPSPs and IPSPs
Occur on the timescale of tens of milliseconds and rapidly move the membrane voltage of the postsynaptic neuron between states more or less likely to fire an action potential.
-The postsynaptic neuron summates EPSPs and IPSPs arising from many presynaptic inputs
Neuromodulation
Includes a broad range of cellular mechanisms involving signaling cascades that regulate synaptic transmission, neuronal growth, and other functions. Neuromodulation can either facilitate or inhibit the subsequent signaling properties of the neuron
Glutamate (Important Neurotransmitters)
Location of Cell Bodies -Entire CNS Main Projections -Entire CNS Receptor Subtypes -AMPA/Kainate: Excitatory Neurotransmission -NMDA: Modulation of synaptic Plasticity -Metabotropic: Activation of second messenger systems
GAMA (Important Neurotransmitters)
Location of Cell Bodies -Entire CNS Main Projections -Entire CNS Receptor Subtypes -GABAA, GABAB: Inhibatory Neurotransmission
Acetylcholine: Spinal Cord Anterior Horns (Important Neurotransmitters)
Main Projections
-Skeletal Muscles
Receptor Subtypes
-Nicotinic: Muscle Contraction
Acetlylcholine: Autonomic Preganglionic Nuclei (Important Neurotransmitters)
Main Projections
-Autonimic Ganglia
Receptor Subtypes
-Nicotinic: Autonomic Functions
Acetlylcholine: Parasympathetic Ganglia (Important Neurotransmitters)
Main Projections
-Glands. smooth muscle, cardiac muscle
Receptor Subtypes
-Muscarinic: Parasympathetic Functions
Acetlylcholine: Basal forebrain: Nucleus basalis. Medial septal nucleus, and nucleus of diagonal band (Important Neurotransmitters)
Main Projections
-Cerebral Cortex
Receptor Subtypes
-Muscarinic and nicotinic: Neuromodulation
Acetlylcholine: Pontomesencephalic region: pedunculopontine nucleus and laterodorsal tegmental nucleus (Important Neurotransmitters)
Main Projections
-Thalamus, cerebellum, pons, and medulla
Receptor Subtypes
-Muscarinic and nicotinic: Neuromodulation
Acetlylcholine: Striatum: caudate, putamen (Important Neurotransmitters)
Main Projections
-Striatum: caudate, putamen
Receptor Subtypes
-Muscarinic and nicotinic: Neuromodulation
Acetlylcholine: Cerebral Cortex (Important Neurotransmitters)
Main Projections
-Cerebral Cortex
Receptor Subtypes
-Muscarinic and nicotinic: Neuromodulation
Acetlylcholine: Retina (Important Neurotransmitters)
Main Projections
-Retina
Receptor Subtypes
-Muscarinic and nicotinic: Neuromodulation
Norepinephrine: Sympathetic Ganglia (Important Neurotransmitters)
Main Projections
-Smooth Muscle, Cardiac Muscle
Receptor Subtypes
-alpha and beta subtypes: Sympathetic functions
Norepinephrine: Pons (locus ceruleus and lateral tegmental area) (Important Neurotransmitters)
Main Projections
-Entire CNS
Receptor Subtypes
-α1A–D, α2A–D, β1–3: Neuromodulation
Dopamine: Midbrain (substantia nigra, pars compacta, and ventral tegmental area) (Important Neurotransmitters)
Main Projections
-Striatum, prefrontal cortex, limbic cortex, nucleus accumbens, amygdala
Receptor Subtypes
-D1–5: Neuromodulation
Dopamine: Retina (Important Neurotransmitters)
Main Projections
-Retina
Receptor Subtypes
-D1,2,: Neuromodulation
Serotonin (Important Neurotransmitters)
Location of Cell Bodies
-Midbrain, pons and medulla: raphe nuclei
Main Projections
-Entire CNS
Receptor Subtypes
-5-HT1A–F, 5-HT2A–C, 5-HT3–7: Neuromodulation
Histamine (Important Neurotransmitters)
Location of Cell Bodies -Hypothalamus: tubero-mammillary nucleus; midbrain: reticular formation Main Projections -Entire Brain Receptor Subtypes -H1-3: Mainly excitatory neuromodualtion
Glycine (Important Neurotransmitters)
Location of Cell Bodies -Spinal cord; possibly also brainstem and retina Main Projections -Spinal cord, brainstem, and retina Receptor Subtypes -Glycine: Inhibatory Neurotransmission
Peptides. (Important Neurotransmitters)
Location of Cell Bodies -Entire CNS Main Projections -Entire CNS Receptor Subtypes -Numerous: Neuromodulation
In the CNS, the most common excitatory neurotransmitter is…
Glutamate
In the CNS, the most common inhibatory neurotransmitter is…
GABA
In the PNS, the main transmitter at neuromuscular junctions is…
Acetylcholine
Which neurotransmitters are important in the autonomic nervous system?
Acetylcholine and Norepinephrine
White Matter
Areas of the CNS made up of mainly myelinated axons
Gray Matter
Areas made up mainly of cell bodies
Most of the local synaptic communication between neurons in the CNS occurs in the…
Gray matter, while axons in the white matter transmit signals over greater distances
Cerebral Cortex
Unique mantle of gray matter that covers the surface of the cerebral hemispheres (far more developed in higher mammals than other species)
What lies beneath the cerebral cortex and conveys signals to and from the cortex?
White matter
Nuclei
Large clusters of cells located deep within the cerebral hemispheres and brainstem where gray matter is also found (ex. Basal ganglia, thalamus, and brainstem nuclei)
Gray Matter and White Matter in the Central Nervous System
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In the cerebral hemispheres where are gray and white matter found?
The gray matter cortex is outside, while the white matter is inside.
In the spinal cord, where are gray and white matter found?
White matter pathways lie on the outside, while the gray matter is in the center (opposite the cerebral hemisphere)
In the brainstem, where are gray and white matter found?
Gray matter and white matter regions are found both on the inside and on the outside, although most of the outside surface is white matter.
Several different names with similar meaning are used for white matter pathways in the CNS, including…
Tract, fascicle. lemniscus, and bundle
Commissure
A white matter pathway that connects structures on the right and left sides of the CNS
Peripheral Nerves
Axons in the PNS that form bundles (also can simply be called nerves)
Ganglia
Clusters of cell bodies in the PNS
Afferent
Pathways carrying signals toward a structure (afferents arrive, efferents exit)
Efferent
Pathways carrying signals away from a structure (afferents arrive, efferents exit)
Peripheral nerves convey … information about the environment to the CNS and carry … from the CNS to the periphery.
Afferent sensory, efferent signals for motor activity
The nervous system develops in segments, segments in the head expand and fuse together, forming the…
Cerebral hemispheres and brainstem and 12 pairs of cranial nerves exit these segments
The nervous system develops in segments, the spinal nerves arise from the segments of…
The spinal cord. Each segment gives rise to both sensory and motor nerve roots on each side of the body.
The Spinal Cord
(A) Cervical, thoracic, lumbar, sacral and coccygeal (C, T, L, S, Co) spinal cord segments and nerves in relation to vertebral bones. (B) Dorsal sensory roots and ventral motor roots arise at each segment.
Throughout the nervous system, motor systems tend to be more …, and sensory systems more … The same holds true for the spinal cord.
Ventral or anterior, Dorsal or posterior.
Dorsal nerve roots conver mainly…
Sensory information into the dorsal spinal cord
Ventral nerve roots carry mainly…
Efferent motor signals from the ventral spinal cord to the periphery.
The segments and nerve roots of the spinal cord are named according to…
The level at which they exit the bony vertebral canal. Thus, there are cervical, thoracic, lumbar, and sacral nerve roots
During development, the bony vertebral canal increases in length faster than the spinal cord. Therefore, the spinal cord ends at the level of the…
First or second lumbar vertebral bones. Below this the spinal canal contains a collection of nerve roots known as the cauda equina (Latin for “horse’s tail”), which continue down to their exit point
The sensory and motor nerve roots join together a short distance outside the spinal cord and form…
A mixed sensory and motor spinal nerve
Brachial Plexus and Lumbosacral Plexus
Control of the arms and legs requires much more signal flow than does control of the chest and abdomen.
- The nerves controlling the extremities give rise to elaborate meshworks referred to as the brachial plexus for the arms and the lumbosacral plexus for the legs.
- Also, the spinal cord contains a relatively increased amount of gray matter in these segments, causing the overall thickness of the cord to be greater. These regions of the cord are called the cervical enlargement and the lumbosacral enlargement, respectively.
Brachial Plexus and Lumbosacral Plexus
Control of the arms and legs requires much more signal flow than does control of the chest and abdomen.
- The nerves controlling the extremities give rise to elaborate meshworks referred to as the brachial plexus for the arms and the lumbosacral plexus for the legs.
- Also, the spinal cord contains a relatively increased amount of gray matter in these segments, causing the overall thickness of the cord to be greater. These regions of the cord are called the cervical enlargement and the lumbosacral enlargement, respectively.
The PNS includes some specialized neurons that are involved in controlling such automatic functions as…
Heart rate, peristalsis, sweating, and smooth muscle contraction in the walls of blood vessels, bronchi, sex organs, the pupils, and so on.
-These neurons are part of the autonomic nervous system.
The autonomic nervous system has the following two major divisions
Sympathetic and Parasympathetic DIvisions
Autonomic Nervous System
The sympathetic division is shown on the left, and the parasympathetic division is shown on the right
Sympathetic Division
Arises from thoracic and lumbar spinal levels T1 to L3 (the thoracolumbar division). It releases the neurotransmitter norepinephrine onto end organs and is involved in such “fight or flight” functions as increased heart rate and blood pressure, bronchodilation, and increased pupil size.
Parasympathetic Division
In contrast, arises from the cranial nerves and from sacral spinal levels S2 to S4 (the craniosacral division). It releases acetylcholine onto end organs and is involved in more sedentary functions, such as increasing gastric secretions and peristalsis, slowing the heart rate, and decreasing pupil size. The sympathetic and parasympathetic pathways are controlled by higher centers in the hypothalamus and limbic system as well as by afferent sensory information from the periphery.
Enteric Nervous System
Considered a third autonomic division and consists of a neural plexus, lying within the walls of the gut, that is involved in controlling peristalsis and gastrointestinal secretions.
Sulci
The cerebral cortex is not a smooth sheet, but rather has numerous infoldings or crevices
Gyri
The bumps or ridges of cortex that rise up between the sulci
The cerebral hemispheres have four major lobes:
The frontal, temporal, parietal, and occipital
Cerebral Cortex: Frontal, Parietal, Temporal, and Occipital Lobes
(A) Lateral view of left hemisphere. (B) Midsagittal view of right hemisphere
Frontal Lobes
Appropriately, located in the front of the brain and extend back to the central sulcus of Rolando. The frontal lobes are separated inferiorly and laterally from the temporal lobes by an especially deep sulcus called the Sylvian fissure, or lateral fissure. (The term fissure is sometimes used to refer to deep sulci.)
Parietal Lobes
Bounded anteriorly by the central sulcus and antero-inferiorly by the Sylvian fissure. However, the parietal lobes have no sharp demarcation from the posterior temporal lobes or from the occipital lobes when viewed from the lateral side of the brain. When viewed from the medial aspect, the parieto-occipital sulcus can be seen more easily, separating the parietal from the occipital lobes
Insular Cortex
Another region of the cerebral cortex
-Lies buried within the depths of the sylvian fissure
Frontal Operculum and Parietal Operculum,
Lip of frontal cortex anteriorly and parietal cortex posteriorly that covers the insula
Interhemispheric Fissure
Separates the two cerebral hemispheres in the midline; Also known as the sagittal or longitudinal fissure
Corpus Callosum
A large, C-shaped band of white matter that connects both homologous and heterologous areas in the two hemispheres (meaning “hard body”)
On the lateral surface, the frontal lobe is bounded posteriorly by the…
Central Sulcus
The gyrus running in front of the central sulcus is called the…
Precentral Gyrus
The remainder of the lateral frontal surface is divided into the … by the …
Superior, middle, and inferior frontal gyri, Superior and inferior frontal sulci.
The lateral temporal lobe is divided into … by the …
- Superior, middle, and inferior temporal gyri.
- Superior and inferior temporal sulci.
The most anterior portion of the parietal lobe is the…
Postcentral gyrus, lying just behind the central sulcus
What does the intraparietal sulcus divide?
The superior parietal lobule from the inferior parietal lobule.
What does the intraparietal sulcus divide?
The superior parietal lobule from the inferior parietal lobule.
The inferior parietal lobule consists of what to gyri?
Supramarginal gyrus (surrounding the end of the Sylvian fissure) and the angular gyrus (surrounding the end of the superior temporal sulcus).
Corpus Callosum
Clearly visible on the medial surface
-Consists of the rostrum, genu, body, and splenium
Cingulate Gyrus
(Cingulum means “girdle” or “belt”) Surrounds the corpus callosum, running from the paraterminal gyrus anteriorly to the isthmus posteriorly.
Cingulate Sulcus
Has a marginal branch running up to the superior surface that forms an important landmark, since the sulcus immediately in front of it, on the superior surface, is the central sulcus.
Cingulate Sulcus
Has a marginal branch running up to the superior surface that forms an important landmark, since the sulcus immediately in front of it, on the superior surface, is the central sulcus.
The central sulcus does not usually extend onto the medial surface, but the region surrounding it is called the…
Paracentral Lobule
Lingula
The portion of the medial occipital lobe below the calcarine fissure
Cuneus
The portion above the calcarine fissure
Precuneus
Just in front of the cuneus, the medial parietal lobe
Orbital Frontal Gyri
Can be seen on the inferior surface
-Lay on tio of the orbital plate of the frontal bone above the eye
Olfactory SUlcus
More medially, (containing the olfactory bulb and tract) separates the orbital frontal gyri from the gyrus rectus (meaning “straight gyrus”).
Occipitotemporal Sulcus
On the inferior surface of the temporal lobe, separates the inferior temporal gyrus from the occipitotemporal, or fusiform, gyri.
Collateral sulcus
More medially, continues anteriorly as the rhinal sulcus, separates the fusiform gyri from the parahippocampal gyrus.
Primary Motor Cortex
Lies in the precentral gyrus in the frontal lobe
-This area controls movement of the opposite side of the body.
Primary Somatosensory Cortex
In the postcentral gyrus in the parietal lobe and is involved in sensation for the opposite side of the body.
The precentral and postcentral gyri are separated by the …
Central sulcus and that (as in the spinal cord) motor areas lie anterior to somatosensory areas.
Primary Visual Cortex
In the occipital lobes along the banks of a deep sulcus called the calcarine fissure
-Represents visual inputs from the opposite visual field. Thus, the left half of the visual field for each eye is mapped to the right primary visual cortex
Primary Auditory Cortex
Composed of the transverse gyri of Heschl, which are two fingerlike gyri that lie inside the Sylvian fissure on the superior surface of each temporal lobe
-Information reaching the primary auditory cortex is less lateralized and represents more of a mixture of inputs from both ears (the input from the opposite ear is slightly stronger, but this is usually not clinically detectable).
Higher-order sensory and motor information processing takes place in the…
Association cortex
Primary Sensory and Motor Cortical Areas
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Sensory and motor pathways are usually…
Topographically organized.
- -This means, adjacent areas on the receptive (or motor) surface are mapped to adjacent fibers in white matter pathways and to adjacent regions of cortex.
- For example, in primary motor and primary somatosensory cortex, regions representing the hand are adjacent to regions representing the arm, and so on
Somatopic
maps on the cortex are sometimes called the motor or sensory homunculus (“little man”).
Retinotopic
Adjacent retinal areas are mapped in this fashion onto the primary visual cortex
Tonotopic
Adjacent regions of the cochlea, sensing different frequencies, have this representation on the primary auditory cortex.
Somatotopic Maps in the Cortex
Somatosensory homunculus in postcentral gyrus of left hemisphere and motor homunculus in precentral gyrus of right hemisphere
Neocortex
Makes up the majority of the cerebral cortex which has 6 cell layers, labeled I through VI, counting from the surface inward
-In a few regions associated with the limbic system, less than six layers are present.
Layer I of the Neocortex (Cortical Layers)
Contains mainly dendrites of neurons from deeper layers as well as axons.
Name: Molecular Layer
Alternative Name: N/A
Main Connections: Dendrites and axons from other layers
Layers II and III of the Neocortex (Cortical Layers)
Contain neurons that project mainly to other areas of cortex.
(II)
Name: Small Pyramid Layer
Alternative Name: External Grannular Layer
Main Connections: Cortical-Cortical Connections
(III)
Name: Medium Pyramid Layer
Alternative Name: External Pyramidal Layer
Main Connections: Cortical-Cortical Connections
Layer IV of the Neocortex (Cortical Layers)
Receives the majority of inputs from the thalamus
Name: Grannular Layer
Alternative Name: Internal Grannular Layer
Main Connections: Recieves inputs from thalamus
Layer V of the Neocortex (Cortical Layers)
Projects mostly to subcortical structures other than the thalamus, such as the brainstem, spinal cord, and basal ganglia
Name: Large Pyramidal Layer
Alternative Name: Internal Pyramidal Layer
Main Connections: Sends outputs to subcortical structures (other than thalamus)
Layer VI of the Neocortex (Cortical Layers)
Projects primarily to the thalamus. In addition to these connections, numerous other circuits exist between and within the cortical layers that are beyond the scope of this discussion
Name: Polymorphic layer
Alternative Name: Multiform layer
Main Connections: Sends outputs to thalamus
Layers of the Neocortex Brain illustration from K. Brodmann.
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