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
.
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