Nervous System, Microanatomy

Comprised of the nerves that run between the CNS and other tissues

PNS

The brain and spinal cord make up the:

CNS

What are some effector organs of voluntary somatic pathways?

Skeletal muscle (movement)

What are some effector organs of involuntary pathways?

Smooth muscle

Cardiac muscle

Muscle-like epithelial cells (myoepithelial cells) with exocrine glands

Perikaryon is what portion of the neuron?

Cell body

These are part of the neuron, highly branched tapering processes. They end in specialized sensory receptors or form synapses with neighboring neurons from which they receive stimuli.

Dendrites

What is the function of dendrites?

Major sites of information input into the neuron

Axons are commonly referred to as:

Nerve fibers

This the most common neuron, with numerous dendrites from the cell body (may arise from one pole of the body or may extend from all areas of the cell. body surface)

Multipolar neuron

These neurons are a single dendrite, which arise from the pole of the cell body opposite to the origin of the axon. Acts as a receptor for the senses of smell, sight and balance

Bipolar neuron

These neurons are a single dendrite and the axon arise from a common stem of the cell body (formed by the fusion of the first part of the dendrite and axon of a bipolar type of neuron), during embryological development

Pseudo-unipolar neurons

Neuron impulses are conveyed along dendrites towards the nerve cell body, which also means:

Afferent

Axons usually convey impulses away from the nerve cell body, which also means:

efferent

What are the steps of myelination?

1. Invagination

2. Cytoplasm is then excluded so that the inner leaflets of plasma membrane fuse with each other

3. The axon becomes surrounded by multiple layers of membrane which together constitute the myelin sheath

This disease is the main demyelinating disease, a immune-mediated destruction of myelin. It is confined to the CNS and leads to the slowing of axonal conduction and neurological dysfunction. Symptoms relate to the location of the affected white matter.

Multiple Sclerosis

This disease is immune-mediated destruction of myelin in the PNS. Symptoms include a progressive weakness of the limb and weakness of respiratory muscles.

Guillain-Barre syndrome

These structures are located between Schwann cells, which are short intervals where the axon is not covered by a myelin sheath

Nodes of Ranvier

this is a form of conduction, as the action potential travels by jumping from node to node. This greatly enhances the conduction velocity of axons

Saltatory conduction

These are regions that are uncompacted at certain points within the internodal myelin sheath

Schmidt-Lanterman incisures

These are highly specialized intercellular junctions, which allow communication by linking neurons to neurons

Synapses

What are 3 types of synapses?

1. Axodendritic synapse

2. Axosomatic synapses

3. Axoaxonic synapses

What are the steps of condiction of the nerve impulse?

1. Release of neurotransmitter from one neuron

2. Diffusion across the narrow space in the synapse

3. Induces excitation or inhibition in the target neuron or effector cell of that synapse

4. Neurotransmitter attaches to receptors in the opposing plasma membrane

5. Neurotransmitter is cleared from synaptic cleft

6. Frees up the synapses for further signals

These are axon endings at which neurotransmitter chemicals are released to pass the signal to the next cell or end organ

Motor end plates (neuromuscular junctions)

This disease is the most common cause of dementia due to the accumulation of abnormal proteins (Beta amyloid and Tau). There is synaptic dysfunction in the hippocampus and cerebral cortex. the synapse mediating NT transmission is affected.

Alzheimer’s disease

This disease is caused by idopathic destruction of neurons in the substantia nigra, resulting in the loss of dopamine. Symptoms include motor control loss, tremors, rigidity and slowness.

Parkinson’s disease

In histology, if Alzheimer’s is present, what two accumulations can be seen in a biopsy?

1. Plaques P

2. Neurofibrillary

this is a tumor of the peripheral nerve. It is a mixture of cell types, including Schwann cells, fibroblasts, and perineural cells

Neurofibroma

Malignant peripheral nerve sheath tumors (MPNST) arise from:

Peripheral nerve or show nerve sheath differentiation

What are the two types of peripheral neuropathy?

1. Demyelinating neuropathy

2. Axonal neuropathy

What are two benign tumors that can occur in the PNS?

1. Neurofibromas

2. Perineuriomas

This is an autoimmune disease affecting the motor end plate, the most common primary disorder of neuromuscular transmission.

Myasthenia gravis

What cause myasthenia gravis?

1. Receptors may be depleted by binding to autobodies specific for the receptor

2. ACh effects on postsynaptic membrane is reduced

3. Detection of serum antibodies that bind to ACh

How is myasthenia gravis treated?

1. Cholinesterase inhibitors

2. Temporarily prolongs the effects of the ACh signal

3. Leads to improved muscle strength

This movement is from the cell body, using kinesin as a molecular motor.

Anterograde movement

this movement is to the cell body, using dynein.

Retrograde movement

This type of transport carries membrane-bound organelles, around 400 mm/day. It is mediated by microtubular transport mechanisms.

Fast axonal transport

This type of transport carries cytoskeleton elements.

Slow axonal transport

What is gliosis?

Results in the healing in the brain following injury, granulation tissue and fibrous scarring

In the PNS, these cells are highly specialized and envelope all axons. They provide structural and metabolic support.

Schwann cells

In the CNS, myelin sheaths are formed by what cells?

Oligodendrocytes

Rate of conduction of AP is:

proportional to the DIAMETER of the axon

This damage can occur as a result of bleeding within the brain itself (or vessels outside the brain).

Intracranial hemorrhage

What are some causes of intracranial hemorrhage?

1. Trauma

2. Rupture of a cerebral artery aneurysm

What are some causes of a cerebral infarction (stroke)?

1. Cerebral artery atheroma

2. Thrombosis

3. Embolism

What can cause a hemorrhagic stroke?

From bleeding of small intracerebral vessels (reperfusion following reversal of a blockage)

This is an infection of the meninges

Meningitis

This is an infection of the spinal cord

Myelitis

this is an infection of the brain substance

Enchephalitis

How are infections of the CNS typically spread?

hematogenous spread (blood stream)

This disorder is the abnormal regulation of neuronal excitability within the brain, leading to uncontrolled spread of depolarization

Epilepsy

These are large encapsulated sensory receptors that are responsive to pressure, coarse touch and rapid vibration

Pacinian corpuscles

Where are pacinian corpusles located?

1. Deeper layer of the skin

2. Ligaments and joint capsules

3. Some serous membranes

4. Mesenteries

5. Viscera

Free nerve endings associated with hair follicles, function by:

Sense hair position or movement (whiskers)

These structures are robust spindle-shaped structures, found in the deep skin usually in the soles of feet. These structures detect tension.

Ruffini corpuscles

These structures are delicate encapsulated receptors, found in the lining of the oropharynx and in the conjunctiva of the eye

Krause end bulbs

These cells are located in the basal layers of the epidermis. The cytoplasm of these cells contain dense core vesicles with ultrastructural features to those found in synapses.

Merkel cells

A Merkel cell-neurite complex is:

a Merkel cell + adjacent free nerve ending

slow-adapting mechanoreceptor

sensitive to sustained touch and pressure

Merkel cell-based receptor arrays + Meissner corpusle-based arrays can sense:

Fine discriminatory touch (fingert tips, lips)

This structure is a small, encapsulated receptor. It is located in the papillary dermis of the fingertips, soles of feet, nipples, eyelids, lips, genitalia. They are fast adapting mechanoreceptors that detect changes in texture and vibration

Meissner corpusle

What are the two types of intrafusal fibers?

1. Nuclear bag fibers

2. Nuclear chain fibers

Synaptic loss is strongly associated and early sign of what kind of diseases?

Neurodegenerative diseases

Plaques P are accumulations of what substance?

Amyloid

Neurofibrillary tangles are abnormal accumulations of cytoskeletal filaments, which is associated with what protein?

Tau

A classical Lewy body is:

a typical neuromelanin-containing neuron

Inclusions are composed of aggregates of what proteins?

Alpha-synuclein

the motor unit consists of these two structures:

Motor neuron

Muscle fibers

The external lamina is the basement membrane of this cell

Schwann cell

What are the three layers that surround a peripheral nerve?

1. Endoneurium

2. Perineurium

3. Epineurium