Cells of the Nervous system

Astrocytes

(Astroglia) Star shaped, symmetrical. Structural support for neurons. Transports substances between neurons and capillaries (blood-brain barrier). Scar tissue formation. Enhance brain activity by providing fuel to active brain regions.

Types of brain tumours

1. Gliomas - Arise from glial cells, account for half of all brain tumours 2. Meningiomas - attach to the meninges and grow entirely outside the brain 3. Metastatic tumours - transfer of tumour cells from one region of the body to another (cancer that spreads to the brain from elsewhere)

Multiple Sclerosis

A chronic disease of the central nervous system marked by damage to the myelin sheath. Plaques occur in the brain and spinal cord causing tremor, weakness, incoordination, paresthesia, and disturbances in vision and speech. Proposed causes include; bacterial or viral infection, pesticides, CNS immune response

Alzheimer's disease

A degenerative dementia associated with loss of memory and other cognitive impairments (problems with language, disorientation), behaviour issues, and changes in mood. Disease associated with abnormal clumps of proteins (plaques) and bundles of fibres (Tangles) in the brain. Patients show a loss of up to one third of their brain volume in advances cases, particularly in the limbic system.

Synapse

A junction (gap) where information is transmitted from one neuron to the next. Usually between an end foot of the axon of one neutron and a dendritic spine of another neuron.

Myelin

A layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next.

Dendrites

A neuron's bushy, branching extensions that receive messages and conduct impulses toward the cell body. 10-20 in each neuron.

Axon

A threadlike extension of a neuron that carries nerve impulses away from the cell body. Begin at one end of cell body, at *axon hillock*. Can have several branches called *axon collaterals*. The lower tip of the axon can further divide into smaller branches - *teleodendria*. At the end of that, is the *terminal button* (end foot)

Interneurons

AKA; Association neurons. Neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs.

Microglia

Act as phagocytes, eating damaged cells and bacteria, act as the brains immune system. Originate in the blood as offshoot of immune system, migrate throughout the brain. They invade regions with cell damage to aid in repair and scavenge and remove debris and dead cells (phagocytosis)

How do we see a brain cell?

Anatomists first remove most of the water from the brain by soaking it in formaldehyde. The brain is then sliced thin (sectioned) and stained with various dyes to distinguish the cells of interest from surrounding cells. The cells now places under the microscope for viewing.

Blood-Brain Barrier

Astrocytes make a protective barrier between blood vessels and the brain. End feet of astrocytes attach to cells of blood vessel, causing cells to bind together. Tight junctions prevent substances from entering the brain through blood vessel walls. Downside: many useful drugs (including antibiotics) cannot pass through blood-brain barrier.

Dendritic retraction

Characterized by marked brain atrophy (brain volume loss). Neurons can change shape, grow, shrink throughout life. In Alzheimer's, the atrophy not associated with widespread cell death but instead to shrinkage of neurons, in part through dendritic retraction (reduction in branches)

5 types of glial cells

Ependymal cell, astrocyte, microglial cell, oligodendroglial cell, Schwann cell

Two cells which help repair neurons

In the PNS, microglia and schwann cells help repair neurons (both are glial cells)

Neurons

Individual cells in the nervous system that receive, integrate, and transmit information. Three basic subdivisions; *Dendrites, Cell body (soma), and Axon.

Cell Body

Largest part of a typical neuron; contains the nucleus and much of the cytoplasm. Integrates the information.

Brain tumours

Mass of new tissue that undergoes uncontrolled growth

Oligodendroglia

Myelinate CNS axons; do not clear the debris or stimulate or guide regeneration

Two main types of cells of the nervous system

Nerouns, and Gilal cells (pl. glia)

Amyotrophic Lateral Sclerosis

Neurodegenerative motor neuron disease. Motor neurons control voluntary muscle activity (speaking, walking, swallowing, breathing) ALS defined by death of upper and lower motor neurons in the motor cortex of the brain, the brain stem and the spinal cord. Time from diagnosis to death averages 3-4 years

Sensory neurons

Neurons that carry incoming information from the sensory receptors to the central nervous system.

Motor Neurons

Neurons that carry outgoing information from the central nervous system to the muscles and glands.

Spinal Cord Injury

Paralysis - Loss of sensation and movement due to nervous system injury. In the CNS, following spinal cord injury, repair does not take place, axon regrowth may even be inhibited. Axon regeneration following spinal injury is the best hope of returning useful function.

Dendritic spines

Protrusions from dendrite, point of contact with axons from other neurons, they increase the surface area, allow more information to be gathered.

Types of neurons

Sensory, Motor, Interneurons

Ependymal Cells

Small ovoid cells found in the walls of the ventricles. Ependymal cells make and secrete cerebrospinal fluid (CSF) that fills the ventricles. CSF is constantly formed and flows through the ventricles towards base of brain where it is absorbed into blood vessels.

Neural Connections

The appearance of each neuron reveals something about the connections that it must make. In general, neurons with large cell bodies have extensions that are very long; neurons with small cell bodies have short extensions. Neurons are in constant communication. Neurons either excite other neurons, or they inhibit other neurons.

Neuron Hypothesis

The idea that the unit of the brain structure and function is the neuron or nerve cell. Proposed by Cajal, who used the Golgi stain to show that the nervous system was made up of discrete cells. Cajal and Golgi won the Nobel prize for medicine in 1906

Schwann Cell

Type of glia in the PNS, Supporting cells of the peripheral nervous system responsible for the formation of myelin.

Information flow in neuron

dendrites --> cell body --> base of axon --> axon --> axon terminus --> terminal button

Glial Cells

supportive cells of nervous system that guide growth of new neurons; forms myelin sheath; holds neuron in place; provides nourishment and removes waste