Neurophysiology 1

Question 1

Outline the structure (morphology) of a neuron cell body

Answer 1

They have asoma (or cell body). Maintains the neuron’s structure and provides energy to drive activities. It has a nucleus which contains genetic information. Also contains specialized organelles

Question 2

Describe the basic functions of the nervous system

Answer 2

1. Sensation(sensory functions) : Receiving of information about the internal and external environment. A stimulus enables the nervous system to register the presence of a change from homeostasis or a particular event in the environment.
   Internal vs external stimuli
2. Response(motor functions) : based on the stimuli perceived by sensory structures. Responses can be divided into:
   A. Voluntary or conscious (contraction of skeletal muscle) Voluntary responses are governed by the somatic nervous system
   B. Involuntary (contraction of smooth muscles, regulation of cardiac muscle, activation of glands) involuntary responses are governed by the autonomic nervous system
3. Integrationor association areas.
   This process combines sensory perceptions and/or higher cognitive functions such as memories, learning, and emotion to produce a response. The processing of information (stimuli) that was received by sensory structures and communicated to the nervous system. Stimuli are compared with, or integrated with, other stimuli, memories of previous stimuli, or the state of a person at a particular time. This leads to the specific response that will be generated

Question 3

Explain the functional differences in the responses of the nervous system

Answer 3

1. Conscious perception and voluntary motor responses.
   Facilitated by the somatic nervous system (SNS).
   Voluntary motor response means the contraction of skeletal muscle (not always in the sense that you want to perform them). Some somatic motor responses are reflexes, and often happen without a conscious decision to perform them. Other motor responses become automatic (in other words, unconscious) as a person learns motor skills (referred to as “habit learning” or “procedural memory”).
2. Involuntary control of the body (usually for homeostasis)
   The responsibility of theautonomic nervous system (ANS) which regulates the organ systems of the body. Sensory input for autonomic functions can be from external or internal environmental stimuli via various sensory structures.
   The motor output includes smooth, cardiac muscle and glandular tissue.

*Enteric nervous system.

Question 4

Describe neurons

Answer 4

Specialized cells that can receive and transmit chemical or electrical signals.
Sometimes referred to as nerve cells
Facilitate communication and computation of information.
They are responsible for the electrical signals that communicate information about sensations, and that produce movements in response to those stimuli, along with inducing thought processes within the brain
Have 3 basic functions:
1. To receive signals (or information).
2. Integrate incoming signals (‘determine’ whether or not the information should be passed along).
3. To communicate signals to target cells (other neurons, muscles or glands).
Structure allows the neuron to perform these functions

Question 5

Outline the structure (morphology) of a neuron axon

Answer 5

Axon: connects a neuron with its target cell.
Conducts impulses away from cell body.
Arises from the cell body at a specialized area called the axon hillock.
As the axon hillock narrows, it transitions into the beginning of the axon called the initial segment.
The axon hillock andinitial segment are sometimes referred to as the trigger zone as this is where action potentials are generated.
Towards its end, it splits into many branches with bulbous swellings called axon (or nerve) terminals which synapse onto target cells
Many axons are wrapped by an insulating sheath called myelin, made from glial cells.
There are gaps in this sheath called nodes of Ranvier.
The length of the axon between each gap is referred to as anaxon segment
Neurons are secretory cells with the secretory zone, generally, at the end of the axon, far removed from the cell body where protein synthesis is mostly located.
Within the axon hillock, the cytoplasm changes to a solution of limited components calledaxoplasm.
Transport of proteins and polypeptides to the axonal ending occurs by axoplasmic flow.
Long axon length necessitates special transport systems.

Question 6

Outline the structure (morphology) of neuron dendrites

Answer 6

responsible for receiving most of the input from other neurons
Processes that resemble a tree-like structure.
These projections are also known as dendritic spines.
Usually highly branched, providing locations for other neurons to communicate with the cell body.
Designed to receive information from other neurons at specialized areas of contact calledsynapses.
The dendrites become stimulated by other neurons and conduct the electrochemical charge to the cell body (or, more rarely, directly to the axons).
Incoming signals: excitatory or inhibitory.
A single neuron may have more than one set of dendrites and receive thousands of input signals.

Question 7

Describe axonal transport

Answer 7

Moves compounds bi-directionally along microtubules; may be fast or slow.
Involves molecular motors such as kinesin and dynein
Anterograde (orthograde) transport moves materials away from cell body.
Retrograde transport moves materials toward cell body.

Question 8

Describe the functional zones of a neuron and their importance

Answer 8

From a functional point of view, neurons generally have 4 important zones:
A receptor, or dendritic zone, where multiple local potential changes generated by synaptic connections are integrated.
A site where propagated action potentials are generated (the initial segment in spinal motor neurons, the initial node of Ranvier in cutaneous sensory neurons).
An axonal process that transmits propagated impulses to the nerve endings.
The nerve endings, where action potentials cause the release of synaptic transmitters.

Question 9

Describe the structural classification of neurons

Answer 9

1. Pseudo-unipolar:
   Cell body sits along side of single elongate process. Are exclusively sensory neurons with two unique characteristics.
   A. Their dendrites receive sensory information, sometimes directly from the stimulus itself.
   B. Their cell bodies are always found in ganglia.
   Sensory reception is a peripheral function so the cell body is in the periphery, though closer to the CNS, in a ganglion. The axon projects from the dendrite endings, past the cell body in a ganglion, and into the CNS
2. Bipolar:
   Dendrite and axon arise from opposite ends of cell body. Not very common. They are found mainly in the olfactory epithelium (where smell stimuli are sensed), and as part of the retina
3. Multipolar:
   Have more than 2 processes e.g. multiple dendrites and one axon. All of the neurons that are not unipolar or bipolar. With the exception of the unipolar sensory ganglion cells, and the two specific bipolar cells mentioned above, all other neurons are multipolar.

Question 10

Describe the functional classification of neuron

Answer 10

1. Sensory neurons ‘obtain info’ from internal and external environment and bring signals into the CNS. Sensory (afferent) neurons conduct impulses into CNS
2. Motor neurons ‘obtain’ info from other neurons and carry signals out of the CNS. Motor (efferent) neurons carry impulses out of CNS
3. Interneurons connect one neuron to another. They are only found in the CNS. Interneurons integrate NS activity

Question 11

Describe the schwann cells

Answer 11

These myelinate neurons by wrapping myelin (a protein-lipid complex) around the axon to from a sheath.
The myelin sheath envelops the axon except at its ending and at the nodes of Ranvier, periodic constrictions about 1 mm apart.
The nucleus and cytoplasm of the Schwann cell are on the edge of the myelin sheath.
Myelin electrically insulates axon and dramatically increases the speed of action potential transmission.

*Not all neurons are unmyelinated.

Question 12

Describe the satellite cells

Answer 12

Found in sensory and autonomic ganglia.
Surround the cell bodies of neurons in these PNS ganglia.
They provide support, performing similar functions in the periphery as astrocytes do in the CNS—except for establishing the BBB.

Question 13

Describe the astrocytes

Answer 13

Most numerous type of glial cell and are the most numerous cells in the brain.
Astrocytes have many processes extending from their main cell body (not axons or dendrites like neurons, just cell extensions).
Those processes extend to interact with neurons, blood vessels, or the connective tissue covering the CNS (pia mater) and allow these cells to perform a variety of functions
Are generally, the supporting cells for the neurons in the CNS

Question 14

What are the functions of astrocytes?

Answer 14

Are of different types with a variety of functions including:
1. help regulate blood flow in the brain;
2. maintain the composition of ECF bathing the neuron;
3. regulate communication between neurons at the synapse;
4. regulate adult neurogenesis.

Question 15

What is the blood brain barrier?

Answer 15

Importantly, astrocytes contribute to formation of the blood-brain barrier.
Include endothelial cells, vascular smooth muscle cell, pericytes, the basement membrane and immune cells.
The BBB tightly regulates the movement of molecules, ions and cells between the blood and the CNS.
Protects the CNS from toxins, pathogens, inflammation, injury and disease allowing for proper neuronal function.
Sometimes also an obstacle for drug delivery.

Question 16

Describe oligodendrocytes

Answer 16

Share a similar function to Schwann cells in that they both produce myelin.
One oligodendrocyte will provide the myelin for multiple axon segments, either for the same axon or for separate axons via the few processes that extend from the cell body

Question 17

Describe the microglia

Answer 17

Smaller than most of the other glial cells.
Microglia are related to macrophages and act as scavengers.
Also referred to as CNS-resident macrophages

Question 18

Describe ependymal cells

Answer 18

Line the ventricles of the brain and the central canal of the spinal cord.
This glial cell filters blood to makecerebrospinal fluid (CSF), the fluid that circulates through the CNS.
The extracellular space in nervous tissue does not easily exchange components with the blood due to the BBB.
Thechoroid plexusis a specialized structure in the ventricles where ependymal cells come in contact with blood vessels and filter and absorb components of the blood to produce CSF
Because of this, ependymal cells can be considered a component of the BBB, or a place where the BBB breaks down.
These glial cells appear similar to epithelial cells, making a single layer of cells with little intracellular space and tight connections between adjacent cells.
They also have cilia on their apical surface to promote circulation of the CSF through the ventricular space