Nervous - System (receptors, neuroglia & astrocytes)

• corpuscle of touch

• a touch receptor that consists a mass of dendrites

• enclosed by a capsule of connective tissue

Meissner corpuscle

• a touch receptor that consists of free nerve endings that make contact of Merkel cells of the stratum Basale of the skin

Merkel (tactile) disc

• a pressure receptor

• composed of a multilayered connective tissue capsule that encloses a dendrite

Pacinian (lamellated) corpuscle

• a pain receptor that is composed of free nerve endings (bare dendrites)

nociceptor

detect thermal sensations

Thermoreceptors

• resemble nociceptors

• unipolar neurons with free nerve endings (bare dendrites) that serve as sensory receptors

itch receptors & tickle receptors

what determines the type of sensory stimulus that is detected by the unipolar neuron?

the type of sensory receptor found in the dendrites of a unipolar neuron

• contain sensory receptors at their distal ends (dendrites)

• or located just after the sensory receptors

sensory neuron

formation of action potential in a sensory neuron

• appropriate stimulus activates sensory receptor

• sensory neuron forms action potential in its axon

• action potential conveyed into the CNS through cranial or spinal nerves

• convey action potentials away from CNS into the effectors in the PNS through spinal and cranial nerves

Motor or efferent neurons

• mainly located in CNS

• between sensory and motor neurons

• process incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neurons

Interneurons or association neurons

Most sensory neurons are ______ in structure.

unipolar

Most motor neurons are ______ in structure.

multipolar

most interneurons are ______ in structure.

multipolar

• make up about have the volume of the CNS

• derives from the idea of early histologists that they were the “glue” that held nervous tissue together

• generally smaller than neurons but up to 5 to 50 times more numerous

Neuroglia or glia

can the neuroglia generate action potentials?

no

can the neuroglia multiply and divide in the mature nervous system?

yes

what does the neuroglia do in cases of injury or diseases?

The neuroglia multiplies to fill in the spaces formerly occupied by the neurons.

• brain tumors derived from glia

• they tend to be highly malignant and grow rapidly

Gliomas

6 types of neuroglia

• astrocytes

• oligodendrocytes

• microglia

• ependymal

• Schwann cells

• Satellite cells

the 4 types of neuroglia that are only found in the CNS

• astrocytes

• oligodendrocytes

• microglia

• ependymal

the remaining 2 types of neuroglia present in the PNS

• Schwann cells

• Satellite cells

Bases used in classifying the types of Neuroglia present in the CNS:

• size

• cytoplasmic processes

• intracellular organization

• star-shaped cells

• have many processes and are the largest and most numerous among the neuroglia

Astrocytes

2 types of Astrocytes

• Protoplasmic Astrocytes

• Fibrous Astrocytes

• many short branching processes

• this type of Astrocytes are found in gray matter

Protoplasmic Astrocytes

• many long unbranched process

• this type of Astrocytes are located in white matter

Fibrous Astrocytes

the processes of Astrocytes make contact with the following:

• blood capillaries

• neurons

• pia mater

5 functions of Astrocytes:

1. contain microfilaments which gives them considerable strength enabling them to support neurons

2. blood-brain barrier

3. in the embryo, Astrocytes secrete chemicals that regulate growth, migration and interconnection among neurons in the brain

4. maintain appropriate chemical environment for generation of nerve impulses

5. learning and memory by influencing the formation of neural synapses

• created by the endothelial cells

• isolation of neurons of the CNS from various potentially harmful substances in blood

• it restricts the movement of substances between the blood and interstitial fluid of the CNS

blood-brain barrier