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At the end of this chapter the student should be able to:-Define the term neuroanatomy and the functional essence.-Classify the components of the nervous system.-Give the different parts of the brain and related structures-Give the different components of the autonomic nervous system.-Describe the sensory and autonomic ganglia. NEUROANATOMY DEFINED...
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... typical neuron is made up of a cell body (also known as the soma or perikaryon) containing cytoplasm (neuroplasm) and nucleus, and prolongations from the cell body known as neurites or nerve processes. The neurites are the dendrites and axon (Figure 2.2). ...
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... lying outside the central nervous system are provided by sheaths of covering by the Schwann cells. The Schwann cells provides covering for the axon by invaginating and wrapping up the axis cylinder and in this process the axon comes to be suspended in a fold of membrane known as the mesoaxson (Figure 2.3). The deposition of fat between layers of the mesoaxon results in the formation of the myelin sheath. ...
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... deposition of fat between layers of the mesoaxon results in the formation of the myelin sheath. The external membrane covering of the myelin sheath which is also derived from the Schwann cell is referred to as the neurilenma (Schwann cell sheath)( Figure 2.4). Where the sheath of one Schwann cell meets that of the next, the axon is unprotected with the membrane and this region is called the node of Ranvier. ...
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... cells are necessary for the regeneration of damaged axons by the process of regeneration of nerves (See Degeration and Regereration of nerve). Similarly, the presence of myelin sheath increases the speed of impulse conduction in the axon through its insulating properties ( Figure 2.4). ...
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... are atypical bipolar neurons. They are at first bipolar but with further development the processes converge at one side of the cell body forming a T -shape at the end, one branch of the T -division being the dendrite from the peripheral process while the other is the axon extending centrally (Figure 2.6). Typical locations of these nerve types in the body include Dorsal root ganglia of spinal nerves. ...
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... Type 1: These are neurons whose axons have considerable course outside the part of the gray matter in which its cell body lies. The type I neurons constitute the bulk of the neurons which form the peripheral nerves and main fibre tracts in the central nervous system (Figure 2.5). ...
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... axons are localized in the gray matter and do not leave that part of the gray matter in which their cell bodies lie. They are found in the retina, cerebral and cerebellar cortices (Figure 2.8). Amacrine neurons: Neurons may fail to possess a true axon and function as interneurons. ...
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... they are inhibitory or neuromodulatory interneurons. Amacrine cells are found in the retina and olfactory bulb (Figure 2.5). ...
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... endoneurium hold the individual nerve together and facilitates their coming together in bundles enclosed by a thicker layer of connective tissue called the perineurium. The bundle of nerves enclosed by the perineurium is known as a fascicule ( Figure 2.4). A nerve tract may contain many fascicules enveloped by an epineurium (Figure 2.9). ...
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... bundle of nerves enclosed by the perineurium is known as a fascicule ( Figure 2.4). A nerve tract may contain many fascicules enveloped by an epineurium (Figure 2.9). Collections of cells bodies of neurons form gray matter of the central nervous system. ...
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... process of formation of the myelin sheath has been described in Figure 2.3. The myelin sheath being inert serves as an electrical insulator to increase the velocity of conduction by providing a fodder for the electrical impulses across the axons. ...
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... the existing relationships differ from the myelinated fibres. In the unmyelinated fibres, the Schwann cell cytoplasm invaginates the fibres but there are no developing mesoaxon to spiral round them (Figure 2.10). Many of such unmyelinated axons may invaginate into a single Schwann cell cytoplasm. ...
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... myelin sheath, if present, breaks up. The Schwann cells which does not depend for its life on the neuron survives and multiplies in number to help in the regenerative process (Figure 2.11). ...
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... the junction sites linking two neurons are referred to as synapses (Figure 2.13). For an action potential to pass from one exicitable cell to another it must cross a synapse. ...
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... the same neuron in a chain of interconnected neurons can be a postsynaptic neuron to one group and a presynaptic neuron to another group of neurons. A single neuron may have thousands of synaptic junctions on its dendrites and cell body (Figure 2.13). ...
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... may be classified according to the parts of the neuron which is involved in the formation of the pre and post synaptic junctions: -Axodendritic: in this type an axon terminal establishes contact with the dendrite of a receiving neuron (Figure 2.14) -Dendroaxonic: In this type the dendrites forms the presynaptic cell with the axon of a receiving neuron. ...
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... free nerve endings are sensory nerve endings which do not show any structural specialization. These endings are widely distributed throughout the body and are numerous particularly in relation to hair where they are abundant in relation to hair follicles (Figure 2.16). They may be mechanoreceptors as in the hair or thermoreceptors and nociceptors. ...
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... are the largest glial cells and are of two types: the protoplasmic astrocytes and the fibrous astrocytes. Structurally they are star shaped with branching processes that are terminally enlarged to form vascular feet (Figure 2.19). The processes of the protoplasmic astrocytes are irregular while the processes of the fibrous astrocyte are straight. ...
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... the oligodendrocytes are oval cells with processes which functions to produce the myelin sheath covering nerve fibres in the central nervous system. These are mainly the axons of the white matter (Figure 2.18). ...
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... microglial cells are round cells with processes which are macrophagic in function (Figure 2.18). They are the only glial cells that are mesodermal in origin while the rest of the other glial cells are ectodermal. ...
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... are the simple cuboidal ciliated epithelial cells that forms the inner lining of the neural tube and ultimately the ventricles of the brain. It gets modified in later life to secret the cerebrospinal fluid (Figure 2.18). ...
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... gray matter are distributed at the depths of the cerebrum (thalamus, hypothalamus, subthalamus, basal ganglia-putamen, globus pallidus, nucleus accumbens, septal nuclei), cerebellum (deep cerebellar nucleidentate nucleus, globose nucleus, emboliform nucleus, fastigial nucleus). Cerebral neurons: Histologically, the neurons found in the cerebrum are six different types namely pyramidal neurons, stellate neurons fusiform neurons, horizontal neurons of Cajal, Martinotti cells and Golgi type 11 cells (Figure 3.2). The different layers of the cortex contain these different cell types in varying quantities. ...
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... gastrulation, neural crest cells are situated at the border of neural plate and non-neural ectoderm (Figure 4:2). After neurulation the neural crest cells from the roof plate of the neural tube undergo an epithelial to mesenchymal transition, delaminating from the neuroepithelium and migrating extensively to generate a prodigious number of differented cell types including: Notochord signals leads to formation of neural plate ...
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... surface subdivisions: The most prominent fissure on the superior surface is the fissure prima (primary fissure) (Figure 8.2). This V-shaped fissure has the apex directed dorsally cutting into the vermis. ...
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... third order neurons in the thalamus end by carrying the sensations to the cerebral cortex (Figure 11.2). The neurons of the ascending tract may be involved with the following activities: -The central processes of the first order neurons may ascend or descend to end in the upper or lower segments of the cord. ...
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... the axons of the second order neurons which form the anterior and lateral spinothalamic tracts cross over to the other side of the cord across the white commissure (Figure 11.2). ...
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... is therefore the dorsal part (the alar lamina) and a ventral part (the basal lamina). The alar lamina contains sensory (afferent) while the basal lamina contains motor (efferent) cells. A third type of cell appears in each lamina, the special branchial efferent and afferent cell of cranial nerves supplying the derivation of pharyngeal arches (see Fig. 12.1). Thus proceeding laterally from the midline, cranial nerve nuclei are arranged ...
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... consequence of further development some of the cranial nerve nuclei retain their embryonic positions but some migrate deeper into brainstem (Figure 12.2). ...
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... ganglion is situated in a shallow bony depression at the apex of the patrous bone and serves as the first cell station for the sensory fibres of the trigeminal nerve. It is from this ganglion that the three divisions of the trigeminal radiate forwards in the lateral wall of the cavernous sinus ( figure 12.3). The three divisions are the ophthalmic, the maxillary and the mandibular divisions. ...
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... tunnels the bone between the organs of equilibrium and hearing to reach the internal ear before turning downwards to escape through the stylomastoid foramen. It next reaches the parotid gland before dividing into its numerious branches which reach the scalp to neck (figure 11.6) Figure 12.6: Distribution of the facial nerve. ...
Context 32
... body is large. The body of the Fifth lumbar is largest which accounts for the prominence of the lumbosacral articulation (Figure 17.12). Some peculiarities of the sacrum require mentioning. ...
Context 33
... typical neuron is made up of a cell body (also known as the soma or perikaryon) containing cytoplasm (neuroplasm) and nucleus, and prolongations from the cell body known as neurites or nerve processes. The neurites are the dendrites and axon (Figure 2.2). ...
Context 34
... lying outside the central nervous system are provided by sheaths of covering by the Schwann cells. The Schwann cells provides covering for the axon by invaginating and wrapping up the axis cylinder and in this process the axon comes to be suspended in a fold of membrane known as the mesoaxson (Figure 2.3). The deposition of fat between layers of the mesoaxon results in the formation of the myelin sheath. ...
Context 35
... deposition of fat between layers of the mesoaxon results in the formation of the myelin sheath. The external membrane covering of the myelin sheath which is also derived from the Schwann cell is referred to as the neurilenma (Schwann cell sheath)( Figure 2.4). Where the sheath of one Schwann cell meets that of the next, the axon is unprotected with the membrane and this region is called the node of Ranvier. ...
Context 36
... cells are necessary for the regeneration of damaged axons by the process of regeneration of nerves (See Degeration and Regereration of nerve). Similarly, the presence of myelin sheath increases the speed of impulse conduction in the axon through its insulating properties ( Figure 2.4). ...
Context 37
... are atypical bipolar neurons. They are at first bipolar but with further development the processes converge at one side of the cell body forming a T -shape at the end, one branch of the T -division being the dendrite from the peripheral process while the other is the axon extending centrally (Figure 2.6). Typical locations of these nerve types in the body include Dorsal root ganglia of spinal nerves. ...
Context 38
... Type 1: These are neurons whose axons have considerable course outside the part of the gray matter in which its cell body lies. The type I neurons constitute the bulk of the neurons which form the peripheral nerves and main fibre tracts in the central nervous system (Figure 2.5). ...
Context 39
... axons are localized in the gray matter and do not leave that part of the gray matter in which their cell bodies lie. They are found in the retina, cerebral and cerebellar cortices (Figure 2.8). Amacrine neurons: Neurons may fail to possess a true axon and function as interneurons. ...
Context 40
... they are inhibitory or neuromodulatory interneurons. Amacrine cells are found in the retina and olfactory bulb (Figure 2.5). ...
Context 41
... endoneurium hold the individual nerve together and facilitates their coming together in bundles enclosed by a thicker layer of connective tissue called the perineurium. The bundle of nerves enclosed by the perineurium is known as a fascicule ( Figure 2.4). A nerve tract may contain many fascicules enveloped by an epineurium (Figure 2.9). ...
Context 42
... bundle of nerves enclosed by the perineurium is known as a fascicule ( Figure 2.4). A nerve tract may contain many fascicules enveloped by an epineurium (Figure 2.9). Collections of cells bodies of neurons form gray matter of the central nervous system. ...
Context 43
... process of formation of the myelin sheath has been described in Figure 2.3. The myelin sheath being inert serves as an electrical insulator to increase the velocity of conduction by providing a fodder for the electrical impulses across the axons. ...
Context 44
... the existing relationships differ from the myelinated fibres. In the unmyelinated fibres, the Schwann cell cytoplasm invaginates the fibres but there are no developing mesoaxon to spiral round them (Figure 2.10). Many of such unmyelinated axons may invaginate into a single Schwann cell cytoplasm. ...
Context 45
... myelin sheath, if present, breaks up. The Schwann cells which does not depend for its life on the neuron survives and multiplies in number to help in the regenerative process (Figure 2.11). ...
Context 47
... the junction sites linking two neurons are referred to as synapses (Figure 2.13). For an action potential to pass from one exicitable cell to another it must cross a synapse. ...
Context 48
... the same neuron in a chain of interconnected neurons can be a postsynaptic neuron to one group and a presynaptic neuron to another group of neurons. A single neuron may have thousands of synaptic junctions on its dendrites and cell body (Figure 2.13). ...
Context 49
... may be classified according to the parts of the neuron which is involved in the formation of the pre and post synaptic junctions: -Axodendritic: in this type an axon terminal establishes contact with the dendrite of a receiving neuron (Figure 2.14) -Dendroaxonic: In this type the dendrites forms the presynaptic cell with the axon of a receiving neuron. ...
Context 50
... free nerve endings are sensory nerve endings which do not show any structural specialization. These endings are widely distributed throughout the body and are numerous particularly in relation to hair where they are abundant in relation to hair follicles (Figure 2.16). They may be mechanoreceptors as in the hair or thermoreceptors and nociceptors. ...
Context 51
... are the largest glial cells and are of two types: the protoplasmic astrocytes and the fibrous astrocytes. Structurally they are star shaped with branching processes that are terminally enlarged to form vascular feet (Figure 2.19). The processes of the protoplasmic astrocytes are irregular while the processes of the fibrous astrocyte are straight. ...
Context 52
... the oligodendrocytes are oval cells with processes which functions to produce the myelin sheath covering nerve fibres in the central nervous system. These are mainly the axons of the white matter (Figure 2.18). ...
Context 53
... microglial cells are round cells with processes which are macrophagic in function (Figure 2.18). They are the only glial cells that are mesodermal in origin while the rest of the other glial cells are ectodermal. ...
Context 54
... are the simple cuboidal ciliated epithelial cells that forms the inner lining of the neural tube and ultimately the ventricles of the brain. It gets modified in later life to secret the cerebrospinal fluid (Figure 2.18). ...
Context 55
... gray matter are distributed at the depths of the cerebrum (thalamus, hypothalamus, subthalamus, basal ganglia-putamen, globus pallidus, nucleus accumbens, septal nuclei), cerebellum (deep cerebellar nucleidentate nucleus, globose nucleus, emboliform nucleus, fastigial nucleus). Cerebral neurons: Histologically, the neurons found in the cerebrum are six different types namely pyramidal neurons, stellate neurons fusiform neurons, horizontal neurons of Cajal, Martinotti cells and Golgi type 11 cells (Figure 3.2). The different layers of the cortex contain these different cell types in varying quantities. ...
Context 56
... gastrulation, neural crest cells are situated at the border of neural plate and non-neural ectoderm (Figure 4:2). After neurulation the neural crest cells from the roof plate of the neural tube undergo an epithelial to mesenchymal transition, delaminating from the neuroepithelium and migrating extensively to generate a prodigious number of differented cell types including: Notochord signals leads to formation of neural plate ...
Context 57
... surface subdivisions: The most prominent fissure on the superior surface is the fissure prima (primary fissure) (Figure 8.2). This V-shaped fissure has the apex directed dorsally cutting into the vermis. ...
Context 58
... third order neurons in the thalamus end by carrying the sensations to the cerebral cortex (Figure 11.2). The neurons of the ascending tract may be involved with the following activities: -The central processes of the first order neurons may ascend or descend to end in the upper or lower segments of the cord. ...
Context 59
... the axons of the second order neurons which form the anterior and lateral spinothalamic tracts cross over to the other side of the cord across the white commissure (Figure 11.2). ...
Context 60
... is therefore the dorsal part (the alar lamina) and a ventral part (the basal lamina). The alar lamina contains sensory (afferent) while the basal lamina contains motor (efferent) cells. A third type of cell appears in each lamina, the special branchial efferent and afferent cell of cranial nerves supplying the derivation of pharyngeal arches (see Fig. 12.1). Thus proceeding laterally from the midline, cranial nerve nuclei are arranged ...
Context 61
... consequence of further development some of the cranial nerve nuclei retain their embryonic positions but some migrate deeper into brainstem (Figure 12.2). ...
Context 62
... ganglion is situated in a shallow bony depression at the apex of the patrous bone and serves as the first cell station for the sensory fibres of the trigeminal nerve. It is from this ganglion that the three divisions of the trigeminal radiate forwards in the lateral wall of the cavernous sinus ( figure 12.3). The three divisions are the ophthalmic, the maxillary and the mandibular divisions. ...
Context 63
... tunnels the bone between the organs of equilibrium and hearing to reach the internal ear before turning downwards to escape through the stylomastoid foramen. It next reaches the parotid gland before dividing into its numerious branches which reach the scalp to neck (figure 11.6) Figure 12.6: Distribution of the facial nerve. ...
