Summary of Book Chapters
Neuronale en hormonale regulatie (AB_1168)
Vrije Universiteit Amsterdam
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- Neuronale en Hormonale regulatie Hoorcolleges
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- Neuronale en hormonale regulatie
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- Summary Neuronal and hormonal regulation: book " Anatomy and Physiology ", FH Martini, E. F. Bartholomew
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Neuronal & Hormonal Regulation
Chapter 12
Anatomically, the nervous system has three divisions: - CNS consists of brain and spinal cord, it is responsible for integrating, processing and coordinating sensory data and motor commands. - PNS (peripheral nervous system) includes all nervous tissue outside the CNS and ENS. The PNS consists of two divisions: o Afferent brings sensory information to the CNS from receptors in peripheral tissues and organs o Efferent carriers motor commands from the CNS to muscles, glands and adipose tissue. These target organs are called effectors. The efferent divisions consist of two subdivisions: Somatic controls skeletal muscle contractions Autonomic automatically regulates smooth muscle, cardiac muscle, glandular secretions and adipose tissue subconsciously. It includes a parasympathetic and sympathetic division, which commonly have antagonistic effects. - ENS (enteric nervous system) is an extensive network of neurons and nerve networks in the walls of the digestive tract. Although the para- and sympathetic divisions influence ENS activities, the ENS initiates and coordinates many complex visceral reflexes locally without instructions form the CNS. It has about 100 million neurons, at least as many as the spinal cord.
Structure of neurons: - Perikaryon is the cytoplasm around the nucleus. Its cytoskeleton contains neurofilaments and neurotubules. Furthermore, it contains organelles that provide energy and synthesize organic materials. The numerous mitochondria, free and fixed ribosomes and membranes of rough RER give the perikaryon a coarse, grainy appearance. Some areas of the perikaryon contain clusters of RER and free
ribosomes. These regions, which stain darkly with cresyl violet, are called Nissl bodies. This is the gray matter seen in gross dissection of the brain and spinal cord. - Bundles of neurofibrils extend into the dendrites of the axon, providing internal support. - Dendrites extend and branch out from the cell body. Typical dendrites are highly branched, and some branches are studded with fine 0 to 1 μm long projections called dendritic spines, which participate in synapses. In the CNS, a neuron receives information from other neurons primarily at the dendritic spines, which may represent 80–90 percent of the neuron’s total surface area. - Axoplasm , or cytoplasm of the axon, contains neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria, and various enzymes. The axolemma , the plasma membrane of the axon, surrounds the axoplasm. In the CNS, the axolemma may be exposed to the interstitial fluid or, as we’ll see, it may be covered by the cellular processes of neuroglia. The base, or initial segment , of the axon in a typical neuron joins the cell body at a thickened region known as the axon hillock. - An axon may branch along its length, producing side branches known as collaterals. Collaterals enable a single neuron to communicate with several other cells. The main axon trunk and any collaterals end in a series of fine extensions called telodendria. - The movement of materials between the cell body and axon terminals is called axonal (axoplasmic) transport. These materials travel the length of the axon on neurotubules in the axoplasm, pulled along by protein “molecular motors,” called kinesin and dynein, which use ATP. The ‘slow stream’ transports some materials at rates of a few millimetres per day. The ‘fast stream’ moves materials as high as 1000 mm/day, but average is 300 mm/day. o Kinesin carries materials from the cell body to the axon terminal; anterograde flow o Dynein carries materials from the axon terminal to the cell body; retrograde flow
Astrocytes largest and most numerous neuroglia in the CNS, they are packed with microfilaments. Functions: - Maintaining BBB - Creating a 3D framework for the CNS. Provide structural support through their cytoskeleton. - Repairing damaged nervous tissue - Guiding neuron development - Controlling the Interstitial Environment (1) regulating the concentration of sodium ions, potassium ions, and carbon dioxide; (2) providing a “rapid-transit system” for transporting nutrients, ions, and dissolved gases between capillaries and neurons; (3) controlling the volume of blood flow through the capillaries; (4) absorbing and recycling some neurotransmitters; and (5) releasing chemicals that enhance or suppress communication across axon terminals.
Ependymal cells line the central canal and ventricles (these are filled with cerebrospinal fluid; CSF ), where they assist in producing and monitoring CSF.
Oligodendrocytes are like astrocytes, but smaller with fewer processes. The plasma membrane near the tip of each process of an oligodendrocyte expands to form a relatively enormous pad, and the cytoplasm there becomes very thin. This flattened “pancake” wraps around the axolemma, forming concentric layers of plasma membrane. This membranous wrapping is called myelin. It serves as electrical insulation and increases the speed at which an action potential travels along the axon.
Many oligodendrocytes cooperate in forming a myelin sheath along the length of an axon. Such an axon is said to be myelinated. Each oligodendrocyte myelinates segments of several axons. The large areas of the axon that are wrapped in myelin are called internodes.
In dissection, myelinated axons appear glossy white, primarily because of the lipids in the myelin. As a result, regions dominated by myelinated axons are known as the white matter of the CNS.
Unmyelinated axons are not completely covered by oligodendrocytes. Such axons are common where short axons and collaterals form synapses with densely packed neuron cell bodies. Areas containing neuron cell bodies, dendrites, and unmyelinated axons have a dusky gray color, and make up the gray matter of the CNS.
Microglia are phagocytic cells; they are the least numerous and smallest neuroglia in the CNS. Microglia migrate through nervous tissue engulfing cellular debris, wastes and pathogens.
Two types of neuroglia in the PNS: - Satellite cells surround neuron cell bodies in ganglia. They regulate the interstitial fluid around the neurons, much as astrocytes do in the CNS. - Schwann cells either form a thick, myelin sheath or indented folds of plasma membrane around peripheral axons in all parts of the PNS. Wherever a Schwann cell covers an axon, the outer surface of the Schwann cell is called the neurolemma. It shields the axon from contact with interstitial fluids. A myelinating Schwann cell can only myelinate one axon.
In the PNS, Schwann cells play a part in repairing damaged nerves. In the process known as Wallerian degeneration , the axon distal to the injury site degenerates, and macrophages migrate into the area to clean up the debris.
(Video PNS Regeneration after injury)
(Video Membrane Potential)
Graded , or local, potentials are changes in the membrane potential that cannot spread far from the site of stimulation.
As the plasma membrane depolarizes, sodium ions are released from its outer surface. These ions, along with other extracellular sodium ions, then move toward the open channels, replacing ions that have already entered the cell. This movement of positive charges parallel to the inner and outer surfaces of a membrane that spreads the depolarization is called a local current.
Type Size Speed Function A 4-20 μm 120 m/s Carry sensory information; position, balance, delicate touch and pressure on skin
Motor neurons that control skeletal muscles B 2-4 μm 18 m/s Carry information to and from CNS
Deliver temperature, pain, general touch
Instructions to smooth muscle, cardiac muscle, glands, etc. C >2 μm 1 m/s Carry information to and from CNS
Deliver temperature, pain, general touch
Instructions to smooth muscle, cardiac muscle, glands, etc.
There are two types of synapses - Electrical synapses have a physical contact between cells. The pre- and postsynaptic membranes of the two communicating cells are locked together at gap junctions. - Chemical synapses send chemical signals to another cell, often a second neuron. o (1) the axon terminal of the presynaptic cell , which sends a message o (2) the postsynaptic cell , which receives the message. A narrow space called the synaptic clef separates the two cells
A synaptic delay of 0.2-0 msec occurs between the arrival of the action potential at the axon terminal and the effect on the postsynaptic membrane.
Excitatory neurotransmitters cause depolarization and promote the generation of action potentials.
Inhibitory neurotransmitters cause hyperpolarization and suppress the generation of action potentials.
Different types of NTs Biogenic amines
- NE (Norepinephrine) aka noradrenaline - Dopamine has inhibitory and excitatory effects. The inhibitory effects play an important role in our precise control of movements (Parkinson). - Serotonin Inadequate serotonin production can have widespread effects on a person’s attention and emotional states and may be responsible for many cases of severe chronic depression. Amino acids - GABA (Gamma-aminobutyric acid) generally has an inhibitory effect. ±20% of the synapses in the brain release GABA. In the CNS, GABA appears to play a role in anxiety. Function remains not completely understood. Neuropeptides - Neuromodulators (NMs) alter the rate of NT release by the presynaptic neuron or change the postsynaptic cell’s response to NTs. In general, they o Have long-term effects that are relatively slow to appear o Trigger responses that involve several steps and intermediary compounds o May affect the presynaptic membrane o Can be released alone or along with a NT - Neuromodulators called opioids have effects like those of the drugs morphine, etc. because they bind to the same group of postsynaptic receptors. Three main classes of opioids in the CNS are: o Enkephalins is a pentapeptide involved in regulating nociception (neural processes of encoding and processing actual or potential damaging stimuli) in the body o Endorphins act to increase feelings of pleasure and well-being and to reduce pain and discomfort o Dynorphins functions are related to learning and memory, emotional control, stress response and pain Dissolved Gases - NO (nitric oxide) is generated by axon terminals that innervate smooth muscle in the walls of blood vessels in the PNS, and at synapses in several regions of the brain - CO (carbon monoxide)
Functionally NTs and NMs fall into one of three groups: - Direct effects i., Ach, glutamate and aspartate - Indirect effects by second messengers i., epinephrine, dopamine, serotonin, histamine and GABA bind to GPCRs.
Postsynaptic potentials are graded potentials that develop in the postsynaptic membrane in response to a NT. Two major types develop at neuron-to-neuron synapses: - EPSP (excitatory postsynaptic potential) is a graded depolarization caused by the arrival of a NT at the postsynaptic membrane. An EPSP results from the opening of chemically gated ion channels in the plasma membrane that lead to membrane depolarization. For example, the graded depolarization produced by the binding of ACh is an EPSP. Because it is a graded potential, an EPSP affects only the area immediately surrounding the synapse. - IPSP (inhibitory postsynaptic potential) is a graded hyperpolarization of the postsynaptic membrane. For example, an IPSP may result from the opening of
From the spinal nerve form branches containing nerve fibres that carry sensory/motor information. These branches are called rami communicantes. A typical spinal nerve has a white & grey ramus communicans , containing myelinated and un-myelinated axons respectively. Furthermore, a spinal nerve contains a posterior ramus , providing sensory and motor innervation to the skin and muscles of the back, and anterior ramus , supplying the ventrolateral body surface, structures in the body wall, and the limbs.
Not exam material The spinal meninges , a series of specialised membranes surrounding the spinal cord, provide the necessary physical stability and shock absorption. Blood vessels branching within these layers deliver oxygen and nutrients to the spinal cord. It consists of 3 layers: - Dura mater is tough and fibrous. It forms the outermost layer of the spinal cord. It contains dense collagen fibres oriented along the longitudinal axis of SC. Between the dura mater and the wall of the vertebral canal lies the epidural space , it contains areolar tissue, blood vessels and protective padding of adipose tissue. - Arachnoid mater is the middle meningeal layer. The surface between the dura and arachnoid mater is covered by simple squamous epithelia. The region between the pia and arachnoid mater is called the subarachnoid space , which is filled with CSF. There is a delicate network of collagen & elastic fibres. - Pia mater is the innermost meningeal layer. Its meshwork of elastic and collagen fibres that is firmly bound to the underlying neural tissue. These connective tissue fibres are interwoven with those that span the subarachnoid space, firmly binding the arachnoid to the pia mater. Along the length of the SC, paired denticulate ligaments extend from the pia mater through all meningeal layers. It prevents lateral movement. At the foramen magnum of the skull, the spinal meninges are continuous with the cranial meninges.
The areas of grey matter on each side of the SC are called horns. There are posterior , lateral and anterior horns. The narrow bridges of grey matter posterior and anterior to the central canal are grey commissures. Masses of grey matter within the CNS are called nuclei. On each side of the SC, in medial to lateral sequence, are somatic motor nuclei that control (1) muscles that position the pectoral girdle, (2) muscles that move the arm, (3) muscles that move the forearm and hand, and (4) muscles that move the hand and fingers.
The white matter on each side of the SC can be divided into three regions called columns. The posterior white columns lie between posterior horns and the posterior median sulcus.
The billions of interneurons of the CNS are organised into a few hundred to a few thousand neuronal pools – functional groups of interconnected neurons. Neuronal pools can be - Scattered involving neurons in several regions of the brain - Localised with neurons restricted to one specific location in the brain or spinal cord Each pool has a limited number of input sources and output destinations. Each pool may contain both excitatory and inhibitory neurons. The output of the entire neuronal pool may stimulate or depress activity in other parts of the brain or spinal cord, affecting the interpretation of sensory information or the coordination of motor commands. The pattern of interaction among neurons provides clues to the functional characteristics of the pool, these are called neural circuits and there are 5 circuit patterns: - Divergence is the spread of information from one neuron to several neurons, or from one pool to multiple pools. Considerable divergence occurs when sensory neurons bring information into the CNS, because the information is distributed to neuronal pools throughout the SC and brain. - Convergence is when several neurons synapse on a single postsynaptic neuron. Several patterns of activity in the presynaptic neurons can therefore have the same
effect on the postsynaptic neuron. Through convergence, the same motor neurons can be subject to both conscious and subconscious control. - In serial processing information is relayed in a stepwise fashion. This pattern occurs when sensory information is relayed from one part of the brain to another. - Parallel processing occurs when several neurons or neuronal pools process the same information simultaneously. Divergence must take place before parallel processing can occur. As a result, many responses can occur simultaneously. - In reverberation collateral branches of axons somewhere along the circuit extend back toward the source of an impulse and further stimulate the presynaptic neurons. Reverberation is like a positive feedback loop involving neurons: Once a reverberating circuit has been activated, it will continue to function until synaptic fatigue or inhibitory stimuli break the cycle. Reverberation can take place within a single neuronal pool, or it may involve a series of interconnected pools. Highly complicated examples of reverberation among neuronal pools in the brain may help maintain consciousness, muscular coordination, and normal breathing.
Reflexes , which are rapid and automatic responses to specific stimuli, preserve homeostasis by making quick adjustments in the function of organs or organ systems.
(Watch video on reflexes)
The route followed by nerve impulses to produce a reflex is called a reflex arc. It contains five steps: 1. Arrival of stimulus and activation of receptor These receptors, the dendrites of sensory neurons, respond to stimuli that cause or accompany tissue damage. 2. Activation of a sensory neuron When the dendrites are stretched, this causes a graded depolarization that leads to the formation and propagation of action potentials along the axons of the sensory neurons. This information reaches the spinal cord by way of a posterior root. 3. Information processing in the CNS Information processing begins when excitatory neurotransmitter molecules, released by the axon terminal of a sensory neuron, arrive at the postsynaptic membrane of an interneuron. The neurotransmitter produces an excitatory postsynaptic potential (EPSP), which is integrated with other stimuli arriving at the postsynaptic cell at that moment. 4. Activation of a motor neuron The axons of the stimulated motor neurons carry action potentials into the periphery. 5. Response by a peripheral effector The release of neurotransmitters by the motor neurons at axon terminals then leads to a response by a peripheral effector.
- Brainstem is connected to the cerebral hemispheres by the diencephalon. It contains a variety of important processing centres and nuclei that relay information headed to or from the cerebrum or cerebellum. It consists of three major sections: o The midbrain contains nuclei that process visual and auditory information and control reflexes triggered by these stimuli. I., your immediate, reflexive responses to a loud, unexpected noise. It also contains centres that help maintain consciousness. o The pons of the brain connects the cerebellum to the brainstem. In addition to, tracts and relay centres, the pons contains nuclei involved with somatic and visceral motor controls. o The MO connects the brain to the SC. The inferior portion of the MO resembles the spinal cord in that it has a narrow central canal. It relays sensory information to the thalamus and to centres in other portions of the brainstem. Furthermore, it contains major centres that regulate autonomic function, such as heart rate, blood pressure and digestion.
Embryology of the Brain
The CNS begins as a hollow cylinder known as the neural tube. In the cephalic (front end of the body, especially nose and mouth), portion of the neural tube, three swellings called the primary brain vesicles develop. The prosencephalon and rhombencephalon are form secondary brain vesicles. - Prosencephalon , forebrain o Telencephalon forms cerebrum o Diencephalon forms the thalamus - Mesencephalon , midbrain. The walls thicken and it becomes a narrow passageway, much like the central canal of the SC. - Rhombencephalon , hindbrain o Metencephalon The posterior forms the cerebellum, the anterior develops into the pons. o Myelencephalon is closer to the SC and becomes the MO.
After the development of brain structures from the vesicles, they expand to form chambers called ventricles. The ventricular system is composed of four ventricles.
Each cerebral hemisphere contains a large lateral ventricle. A thin plate of brain tissue separates the two lateral ventricles. The diencephalon contains the third ventricle. The two lateral ventricles are not directly connected, but each communicates with the third through an interventricular foramen.
The midbrain has a slender canal known as the cerebral aqueduct. This passageway connects the third to the fourth ventricle. It is situated between the posterior surface of the pons and the anterior of the cerebellum. It extends into the superior portion of the MO, where it narrows and becomes continuous with the central canal of the SC.
Ependymal cells , a type of neuroglia, line the ventricles. These cells produce CSF.
Summary of Book Chapters
Vak: Neuronale en hormonale regulatie (AB_1168)
Universiteit: Vrije Universiteit Amsterdam
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Gerelateerde documenten
- Neuronale en Hormonale regulatie Hoorcolleges
- Samenvatting, Neuronale en hormonale regulatie, Anatomie van het Zenuwstelsel I , Compleet
- Neuronale en hormonale regulatie - samenvatting Martini H12-16
- Neuronale en hormonale regulatie
- Overzicht aandoeningen NHR
- Summary Neuronal and hormonal regulation: book " Anatomy and Physiology ", FH Martini, E. F. Bartholomew