3 Introduction to Nerve and Glial cells Flashcards
Describe the Central Nervous system
Central Nervous System (CNS)
- composed of the Brain and Spinal Cord
- located in the cranial cavity and spinal cavity
Function:
- to interpret incoming sensory information and issue outgoing instructions
Describe the peripheral nervous system
Nerve fibres:
- Spinal nerves - carry impulses to and from the spinal cord
- Cranial nerves - carry impulses to and from the brain
And cell bodies outside of the CNS
- Ganglia (functions as a relay station)
Function: to conduct impulses to and from CNS
- afferent (sensory) nerves go towards CNS
- efferent (motor) nerves go away from CNS
Describe the branches of the PNS
PNS:
- Efferent (motor)
- Afferent (sensory)
Describe the branches of the Efferent (motor) nervous system
Efferent (motor): - Somatic (voluntary) - Autonomic nervous system > Parasympathetic NS > Sympathetic nervous system
Name the 2 types of nerve tissue cells
- Neuron/nerve cell
- Neuroglia
Describe a neuron/nerve cell
The structural and functional unit of nerve tissue
- Specialised to receive stimuli and conduct impulses
A neuron is composed of a cell body with processes called:
- Dendrites: receives impulses
- Axon: transmit impulses away from the cell body
Name the different types of neurons:
Neurons have different shapes reflecting differing functions:
- Motor neurons
- Sensory neurons
- Interneurons
Describe motor neurons
Motor neurons
- have a large cell body to support the axon
- and because of their numerous dendritic processes, classes as multipolar neurons
Describe sensory neurons
Sensory neurons
- commonly pseudo-unipolar
- characterised by a short process from their cell body, which later divides into a peripheral branch (conducting impulses from the receptor organ toward the cell body)
- and a central branch that continues from the cell body into the CNS
Describe interneurons
Interneurons
- Small, simple cells with short processes that provide local connection within the CNS
Discuss the histology of neurons
Neurons are highly metabolically active:
- maintenance of massive area of the cell membrane and developing electrochemical gradients
This is reflected in the histological appearance:
- Nucleus is large and rounded with a large nucleolus reflecting a high degree of transcriptional activity
- Abundance of RER for protein synthesis seen in H&E staining as blue-stained granules: Nissl substance
- Nissl substance is found in the cell body (aka perikaryon) and dendrites, but not the axon
The start of the axon (as it leaves the cell body) is called the Axon hillock
- this is where the AP is first generated
Describe neuroglia
These are the non-neuronal, non-excitable cells of the nervous system
- Their function is to support, insulate, and nourish the neurons
They are found in CNS and PNS, as different types
Name the peripheral neuroglial cells
- Schwann Cells
- Satellite cells
Describe Schwann cells
as peripheral neuroglia
Schwann Cells
- Responsible for myelinating the axons
- One Schwann cell myelinates only one axon
- Their product (myelin) can be seen in histological samples surrounding the axons and Schwann cell nucleus
Myelin is an insulating sheath wrapped around the axons
- functioning to increase the speed of conduction along axons
- NCV is increased even further with gaps called Nodes of Ranvier
Describe Satellite Cells
as peripheral neuroglia
Satellite cells
- they surround neuron cell bodies within a ganglion
- and are responsible for regulating the environment
Name the Central neuroglial cells
- Oligodendrocytes
- Astrocytes
- Microglia
- Ependymal cells
Describe oligodendrocytes
as central neuroglia
Oligodendrocytes
- these myelinate CNS axons
- seen by small nuclei that are surrounded by rings of cytoplasm (halo)
- (found in grey matter)
Describe Astrocytes
as central neuroglia
Astrocytes
- maintain the blood-brain barrier
- provide structural support
- and most abundant neuroglial cell
Two different types:
- Fibrous: found in white matter
- Protoplasmic: found in grey matter
Describe astrocytes histologically
Astrocytes:
- large nuclei
- no clear cytoplasm
- numerous protrusions in a radial pattern give the characteristic star-like appearance
Describe microglia
as central neuroglia
Microglia
- responsible for phagocytosis of debris, waste and pathogens
- seen as a rod-shaped nucleus with no clear border
Describe Ependymal cells
as central neuroglia
Ependymal cells
- line ventricles and spinal cord
- responsible for maintaining Cerebral Spinal Fluid (CSF)
- epithelial-like, and have cilia
Describe the tissue structure of the PNS
These are peripheral nerves with specialised nerve endings
- Synapses
Peripheral nerve
- bundle of nerve fibres which carry sensory and motor information to and from the CNS (and supporting Schwann cells)
- held together by Connective Tissue
Location of cell bodies
- within the CNS
- outside of the CNS (peripheral ganglia)
Describe the location of cell bodies within the CNS
Cell bodies within the CNS:
- Located in the brain, brain stem, and spinal cord
- Motor neuron cell bodies that innervate skeletal muscles
- Axons leave CNS and travel in peripheral nerves to the skeletal muscles
- CNS to effector organ - a single neuron
Describe the location of cell bodies outside the CNS
Cell bodies outside the CNS
- Peripheral ganglia
- Ganglia = clusters of neuronal cell bodies and nerve fibres
- Sensory neuron cell bodies (somatic and visceral component)
- Receptor - through a ganglion - spinal cord or brainstem
Describe the connective tissue involved in the nervous tissue/nerves
Individual nerve fibres and associated Schwann cells are held together by three distinctive components of CT:
- Endoneurium: loose CT surrounding individual axons
- Perineurium - specialised CT surrounding the nerve fascicle. Collagen fibrils are present, but fibroblasts are absent
- Epineurium - dense irregular CT surrounding and binding nerve fascicles into a common bundle. May also include adipose tissue
Describe the Histology of the CNS
- Consists of the brain and spinal cord
- Protected by skull and vertebrae
- Surrounded by CT membranes - meninges
- Floats in ECF (this occupies the space between the two inner meninges)
Describe the connective tissue in the CNS
3 sequential CT membranes covering the brain and spinal cord:
- Dura mater:
> outermost - thick sheet of dense CT - Arachnoid layer:
> lies beneath the dura mater
> arachnoid trabeculae - loose CT and elongated fibroblasts - Pia mater:
> lies directly on the surface of the brain and spinal cord
> delicate CT layer
What is white matter?
White matter:
- axons of nerve cells, associated glial cells and blood vessels
What is gray matter?
Gray matter:
- neuronal cell bodies, dendrites, initial unmyelinated portions of axons and glial cells
Describe the brain, and where the white and gray matter lies
In the brain:
- gray matter forms an outer layer of the cerebral cortex
- whereas the white matter forms the inner core
Describe the spinal cord, and where the white and gray matter lies
In the spinal cord:
- gray matter exhibits a butterfly-shaped inner substance
- whereas the white matter occupies the periphery
