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Home , Autonomic ganglion, Grey column, Lateral grey column, Pseudounipolar neuron

Introduction Remember studying as a Basic Tissue?

1. Epithelial tissue 2. Connective tissues 3. Muscle tissue 4. Nervous tissue

Well, during this lab you will review these tissues as observed in both the:

i. Central (CNS)- the brain and . ii. Peripheral Nervous System (PNS) - peripheral /ganglia outside the CNS.

Learning objectives and activities Using the Virtual Slidebox:

A Recognize nervous tissue in histological sections and discuss the organization/function of the cells present.

B Examine the features of peripheral nerves in both longitudinal and cross section that allow you to identify them in tissue sections.

C Differentiate between sensory and autonomic (sympathetic/parasympathetic) ganglia.

D Identify the different functional regions and cells of the spinal cord.

E Identify the major layers and cells of the cerebellum ad the .

F Complete the self-quiz to test your understanding and master your learning.

Despite its complexities, the nervous system is composed entirely of two cell types: a network of cells () that transmit signals throughout the nervous system and the glial cells that support them.

Neurons

Examine Slide 1 (16) to investigate the basic structure of a ii

i. Cell body (perikaryon). Most cell bodies are located in the (brain and spinal cord) or in ganglia of the peripheral nervous i system. They contain darkly stained granules called Nissl bodies which are the ribosomes used to manufacture iii in the cell.

iv ii. Dendrites extend from the cell body. These are short, highly branched structures that receive nerve impulses from other neurons. Nissl bodies can be seen extending into the dendrites.

iii. Nucleus and nucleolus. Neurons have a large nucleus with prominent nucleolus. The ribosomes seen in the cell body are assembled in the nucleolus.

iv. hillock and axon The is where the axon branches from the cell body. It contains the Golgi apparatus and is therefore devoid of Nissl bodies. The axon is a single 'fiber' that transmits impulses. Most neurons have an axon surrounded by fat – the sheath – which assists propagation of electrical impulses along the axon.

There are three basic classes of neuron

i. Multipolar neurons Located in CNS Located in PNS Have multiple dendrites and a long axonal process. They convey either somatic motor or visceral/autonomic Skeletal muscle motor information from the CNS.

Examine the following slides Somatic motor to see examples of multipolar neurons: Pre-ganglionic Slide 1 (16) : somatic motor Autonomic Slide 2a (19) : somatic motor Smooth muscle (e.g. vessels or Slide 3a (21) : visceral motor digestive tract)

Post-ganglionic

Visceral motor

ii. Pseudounipolar neurons Have one axon that divides close to the cell body to form two long axonal branches. They convey sensory information to the CNS and their cell bodies are located within the dorsal root ganglion (or cranial nerve ganglia).

Examine Slide 4a (20) to see pseudounipolar (sensory) neurons in a dorsal root ganglion.

iii. Bipolar neurons Have one axon and one . They convey special sensation to the CNS.

Examine Slide 5 (82) to see bipolar neurons in the retina. Glial cells

Glial cells support and protect the neurons.

i. In the CNS There are many different types of glial cell: - - the equivalent of Schwann cells in the CNS - - specialized macrophages that protect CNS neurons - - regulate chemical environment in CNS (blood-brain barrier) - ependymal cells - line ventricles of brain and of spinal cord

Together they form the ‘’ of the CNS known as ‘’.

With the exception of ependymal cells it is very difficult to specifically identify the different types of glial cell within the central nervous system without specific stains. Therefore you will not be asked to do this.

Explore Slide 2b (19) to see glial cells, neuropil and ependymal cells in the CNS.

ii. In the PNS, There are two types of glial cell: - Schwann cells - form the myelin sheath surrounding the axon of the neuron - satellite cells - surround and support neuron cell bodies located in the PNS.

Explore Slide 3b (21) and Slide 4b (20) to see Schwaan cells and satellite cells in the PNS (ganglia). In a typical peripheral nerve individual nerve are bundled together to form a series of layers v. surrounded by connective tissue. These are best seen vi. in cross sections through nerves. iv.

Identify the features of a peripheral nerve in both the iii. longitudinal and cross section shown in Slide 6 (17)

i. External coat of dense irregular connective tissue.

ii. ii. Connective tissue surrounding individual axon bundles that are called fascicles. iii. Thin connective tissue layer surrounding each individual axon and its myelin sheath. iv. Myelin sheath The fatty sheath formed by the surrounding the axon. v. Axon i. The long process of an individual neuron that extends from the cell body. vi. A Na+ channel rich ‘gap’ between adjacent Schwann cells that allows rapid propagation of impulses along an axon. These are only visible in longitudinal sections of nerves. Ganglia are nodular masses of connective tissue and neuron cell bodies surrounded by supporting glial cells (satellite cells). There are two types of ganglia in the PNS: i. Sensory ganglia Located in CNS Located in PNS Collections of cell Dorsal root ganglion bodies that: Satellite cells - convey afferent impulses towards the CNS - are associated with (cranial ganglia) and the spinal cord (dorsal root ganglia) - are tightly clustered and bounded by a CT capsule Examine Slide 4a (20) again to identify the key features - have large nuclei with a central of a sensory ganglion and ensure you can differentiate located nucleolus. this from an . - surrounded by supportive satellite cells (glial cells). - may contain lipofuscin (brown granules containing residuals of oxidation and lysosomal ) Located in CNS Located in PNS ii. Autonomic ganglia Sympathetic ganglion Collections of multipolar, post ganglionic (in sympathetic chain) neuron cell bodies that: - control activity of smooth muscle, glands and cardiac

rhythm Satellite cells - can be located close to the spinal

cord = sympathetic (see Slide 3a) Parasympathetic - can be located close to/within an ganglion = parasympathetic (see (in wall of organ) Slide 7). - are scattered and bounded by a CT capsule - have small nuclei with an Satellite cells eccentric nucleolus. - are each surrounded by Examine Slide 3a (21) of the sympathetic chain and supportive satellite cells (glial Slide 7 (54) which contains a parasympathetic ganglion cells) to identify the key features of autonomic ganglia. Ensure - may contain lipofuscin granules you can differentiate these from sensory ganglia. Different sections through the spinal cord exhibit different functional zones (tracts and ganglia) that have been linked to specific functions around the body. All spinal cord sections have an outer region of composed mainly of neuron axons and an inner area of where neuron cell bodies can be found. In all areas you can recognize a variety of glial cells.

Review the organization and cells of the sacral spinal cord segment shown in Slide 8

Connective tissue - the spinal cord is surrounded by three layers of connective tissue: dura, arachnoid and pia mater. - the dura is often removed during histological preparation

a. Pia mater - a thin visceral layer of connective tissue that adheres to the spinal cord Identify the pia mater - its inner surface is a simple squamous epithelium in - it forms a double fold as it reflects in and out of the ventral median Slide 8a fissure - in some areas it may become artificially separated from the spinal cord during preparation

b. Identify arachnoid - abuts the inner surface of the dura (not seen histologically) mater and arachnoid - has delicate projection called arachnoid trabeculae that extend trabeculae in through the subarachnoid space to the surface of the pia Slide 8b

c. Subarachnoid space - the space between the arachnoid and pia that is bridged by the arachnoid trabeculae Identify subarachnoid - it contains CSF and blood vessels space in - the arachnoid trabeculae collapse during preparation due to loss of Slide 8c CSF making the space look like a layer of loose irregular connective tissue White matter - in the spinal cord this is the outer layer of nervous tissue surrounding the grey matter - contains axons of neurons running from one part of the nervous system to another. - contains glial cells and blood vessels accompanying theses axons. - axons that are going to/coming from specific locations are grouped into functionally related bundles called tracts (although these tracts are indistinguishable from surrounding white matter that is not a component of the tract)

d. Corticospinal tract Identify the - aggregations of the axons of upper motor neurons that are corticospinal tract of traveling from the cerebral cortex within the spinal cord they are white matter in involved in control of motor functions of the body. Slide 8d

e - contains axons of sensory neurons traveling from skin to . Identify the - it has two components: anterior and lateral. spinothalamic tract of - the anterior spinothalamic tract carries info about crude touch. white matter in - the lateral spinothalamic tract carries info about pain/temperature Slide 8e

f. Gracile fasciculus Identify the gracile - it contains the axons of sensory neurons that convey information fasciculus of white regarding from the lower limbs and trunk to the matter in Slide 8f .

Grey matter - in the spinal cord this is the inner layer of nervous tissue deep to the white matter - it is organized into dorsal and ventral horns - it contains the cell bodies of neurons, their dendritic processes and axons and supportive glial cells and blood vessels. - collections of neuron cell bodies with specific functions within the grey matter are often referred to as nuclei. Identify the lateral g. Lateral group/lateral grey column in - composed of sympathetic preganglionic visceral motor neurons Slide 8g which are part of the .

h. Onuf’s nucleus - a collection of neurons in the S1-4 region of the spinal cord. Identify Onuf’s - these neurons that are involved in maintenance of urinary and nucleus in fecal continence Slide 8h - is the origin of the motor fibers that travel in the pudendal nerve Glial cells - there are a variety of glial cells in the spinal cord that get lost in the mass of dendrites, axons and neuron cell bodies - it is not common practice to attempt to identify these cells using standard histological preparations.

i. Neuropil Outline an area of - the general histological term that describes the difficult to neuropil in interpret mass of neuroglia and neuron processes. Slide 8i

j. Glial cell nuclei - glial cells have very sparse cytoplasm and a prominent (often Find the nuclei of glial circular) nucleus making them easy to identify among axons and cells in neuron cell bodies. Slide 8j

k. Central canal - the CSF filled space that runs through the central of the spinal Find the central canal cord and is continuous with the ventricles in the brain. in - it is lined by ependymal cells (a type of glial cell) Slide 8k - it is often squashed closed during sectioning

l. Ependymal cells - the glial cells that line the central canal Find examples of - their apical surface is ciliated which allows them to move CSF ependymal cells in through the central canal Slide 8l - due to the collapse of the central canal they are less distinct than seen in diagrams Different sections through the spinal cord exhibit different functional zones (tracts and ganglia) that have been linked to specific functions around the body. All spinal cord sections have an outer region of white matter composed mainly of neuron axons and an inner area of grey matter where neuron cell bodies can be found. In all areas you can recognize a variety of glial cells.

Review the organization and cells of the cerebellum in Slide 9 and Slide 10

Cerebellum The cerebellum is a portion of the brain lying behind and below the cerebrum; it serves to coordinate both voluntary movements and muscle function in the maintenance of normal posture. Note the cortex of grey matter is located on the outside surface and is composed of three distinct layers. The medulla of white matter is located deep to these. This is the reverse to the organization of white and grey matter seen in the spinal cord.

1. Cortex (grey matter)

a. Molecular layer Identify the molecular - the outermost region of the grey matter cortex layer of the cortex - contains the vast dendritic trees of Purkinje cells Slide 9a and - contains the cell bodies of small multipolar neurons called basket Slide 10a cells.

b. Basket cells Find examples of - the main cells found in the molecular layer basket cells in - have branching dendrites that are dilated and knotty Slide 9b and - with Purkinje cells Slide 10b

Identify the Purkinje c. layer cell layer in - the intermediate layer of grey matter Slide 9c and - contains Purkinje cells and numerous Golgi cells Slide 10c d. Purkinje cells Find examples of - large characteristic neurons of the cerebellum Purkinje cells in - they have a large branching dendritic trees that extend into the Slide 9d and molecular layer Slide 10d

e. Golgi type II cells Find examples of - inhibitory that are seen at the Purkinje layer Golgi cells in - they are larger cells than surrounding granule cells Slide 9e and Slide 10e f. Granular layer Identify the granular - the deepest layer of the grey matter cerebellar cortex layer in - it is composed of a large number of small granule cells which give it Slide 9f and its ‘granular’ appearance Slide 10f

g. Granule cells - the smallest and most numerous neurons in the brain. Identify - emit only four to five dendrites, each of which ends in an granule cells in enlargement called a dendritic claw. Slide 9g and - these enlargements are sites of excitatory input from mossy fibers Slide 10g and inhibitory input from Golgi cells.

2. Medulla (white matter)

h. White matter Identify the white - afferent and efferent nerve fibers travelling within the cerebellum matter of the medulla - it also contains supporting neuroglial cells, and small blood vessels, in Slide 9h and but no neuronal cell bodies. Slide 10h

Cerebrum The cerebrum is the principal portion of the brain. The outer cortex of grey matter contains the cell bodies of nerves that receive and store sensory information, nerves that control voluntary motor activity, and nerves that integrate and coordinate the activity of other nerves, as well as the nerves and neural pathways that constitute memory. The white matter in the medulla contains the axons of these nerves.

1. Cortex (grey matter) The cortex has six layers (Layers 1-6). You are not required to differentiate between all these layers as their boundaries are difficult to see with the exception of the plexiform layer (layer 1).

a. Plexiform/Molecular layer (layer 1) Identify the molecular - consists largely of fibers, most of which travel parallel to the layer of the cortex surface, and relatively few cells, mostly neuroglial cells and Slide 11a and occasional horizontal cells of Cajal (not shown). Slide 12a - you can also see blood vessels entering the cortex here b. Pyramidal cells - found in layers 2-6 Identify pyramidal - can be large or small but have a distinctive triangular shape cells in - are the primary excitation units of the prefrontal cortex and the Slide 11b and corticospinal tract Slide 12b

2. Medulla (white matter) c. White matter Find the white - afferent and efferent nerve fibers travelling within the cerebellum matter in - it also contains supporting neuroglial cells, and small blood vessels, Slide 11c and but no neuronal cell bodies. Slide 12c In addition to all basic tissues, you must be able to identify the following features of the peripheral and central nervous systems:

Neurons Multipolar Spinal cord Pseudounipolar Central canal Bipolar Ependymal cells Cell body (perikaryon) Grey matter Nissl bodies White matter Dendrites Ventral horn Axon Dorsal horn Axon hillock Corticospinal tract Nucleus Spinothalamic tract Nucleolus Ventral median fissure

Glial cells and neuropil Glial cells (in CNS: non-specific) Pia mater Ependymal cells (in CNS) Arachnoid mater Satellite cells (in PNS) Arachnoid trabeculae Schwaan cells (in PNS) Subarachnoid space Neuropil (in CNS)

Peripheral nerve (in longitudinal Cerebellum and cross section) White matter Epineurium Grey matter Perineurium Purkinje cell layer Endoneurium Molecular layer Axon Granular layer Myelin sheath Basket cells Schwann cell Golgi Type II cells Node of Ranvier Granule cells

Ganglia Cerebrum Sensory/Dorsal root ganglion White matter Autonomic/sympathetic Plexiform layer (Layer 1) ganglion Layers 1-6 (collectively) Autonomic/parasympathetic ganglion Neuropil Lipofuscin