Gross neuroanatomy

Anatomical features of the nervous system that are apparent to the naked eye.

Neurophysiology

The study of the life proccesses of neurons.

Chemical neuroanatomy

The distribution of key chemicals, such as transmitters and enzymes, within the structure of the nervous system.

Neuropharmacology

 Also called psychopharmacology. The study of the effects of drugs on the nervous system and behavior.

How many neurons do our brains contain?

100 billion to 150 billion neurons.

Cajal argued that neurons are...

Contiguous – at each point of contact between neurons is a tiny gap.

Neuron doctrine

1. the brain is composed of separate neurons and other cells that are independent structurally, metabolically, and functionally.
2. information is transmitted from cell to cell across tiny gaps.

Glial cells

Important participants in information processing, but because neurons are generally larger and produce readily measured electrical signals, we know much more about them than about glial cells. Glial cells are nonneural brain cells that provide structural, nutritional, and other types of support to the brain. Some glial cells wrap around axons, forming a myelin sheath.

Mitochondria

A cellular organelle that provides metabolic energy for the cell’s processes.

Cell nucleus

Contains the cell’s genetic instructions.

Ribosomes

Structures in the cell body where genetic information is translated (proteins are produced).

4 structural divisions specialized for info processing in the neuron

1. Input zone. Dendrites receive info from other neurons.
2. Integration zone. A cell body region (or soma) contains the nucleus and may receive additional synaptic contacts. Inputs are combined and transformed by specialized structures that serve as an integration zone. This zone is typically part of the cell body.
3. Conduction zone. A single extension, the axon transmits the cell’s electrical impulse away from the cell body.
4. Output zone. Specialized swellings at the end of the axon, the axon terminals, are the output zone. They communicate the cell’s activity to other cells.

In many neurons the axon is only ____________________ long.

A few micrometers

But in neurons that connect the spinal cord to the rest of the body, the axons may reach more than ________ in length.

A meter.

Multipolar neurons (sorting neurons by shape)

Have many different dendrites and a single axon, and they are the most common type.

Bipolar neurons (sorting neurons by shape)

Have a single dendrite at one end of the cell and a single axon at the other end. This type of neuron is especially common in the sensory systems, such as the retina.

Monopolar neurons (sorting neurons by shape)

Have a single extension (or process), usually thought of as an axon, that branches in two directions after leaving the cell body. One end is the receptive pole (the input zone); the other the output zone. Such cells transmit touch information from the body to the spinal cord.

Sorting neurons by size

Vertebrate nerve cell bodies range from 10 micrometers to 100 micrometers in diameter. Larger neurons tend to have more complex inputs and outputs, cover greater distances, and convey information more rapidly than smaller ones.

Sorting neurons by function – motoneurons

Contact muscles or glands, providing a pathway for the brain and spinal cord to control body movements and organ function.

Sorting neurons by function – sensory neurons

They are directly affected by environmental stimuli; respond to light, a particular odor, or touch.

Sorting neurons by function – interneurons

These constitute the vast majority. They receive input and send output to other neurons (hence the name).

Neuronal transmission

 -the neuronal cell body and dendrites receive information across synapses (20-40nm). The gap is small to enhance control of the information transmission.

-dendrites have a branched arborization pattern to facilitate contacts.

-information is transmitted from the presynaptic neuron to the postsynaptic neuron.

Cell membrane

An important part that will allow certain particles to cross, and certain other ones not to cross. It has a hydrophilic head group (likes water), and a hydrophobic head group (hates water). It is semi-permeable membrane. Some particles will be able to get through; others won’t. Special proteins allow chemicals to cross the membrane. This is crucial to normal activity of a neuron.

Some glial cells support neural activity

Glial cells can also directly affect neuronal functioning by providing neurons with raw materials and chemical signals that alter neuronal structure and excitability. Glial cells come in 4 basic forms: astrocyte, microglial, oligodendrites, and Schwann cells.

Edema

The swelling of glial cells which happens in response to brain injury. This damages nurons and is responsible for many symptoms of brain injury.

Astrocyte

A star shaped glial cell with numerous processes in all directions. The formation of new synapses, synaptic signaling, and the dynamic control of local blood flow are all directly coordinated by these and neurons working together. Communicate amongst themselves and with neighboring neurons to modulate neurons’ responses.

Microglia

Very small glial cells that act as phagocytes (engulf and break down neurons) and protect the brain from invading microorganisms – representatives from immune system.

Oligodendrocytes

Extensions wrap wound axons of neurons which act as a myelin sheath; increases speed and efficiency of axonal conduction

Schwann Cell

Perform same function as glial cells, but in the peripheral nervous system.

Node of Ravier

A small gap where the axonal membrane is exposed between each pair of myelinated segments.

Multiple sclerosis

A disorder characterized by widespread degeneration of myelin.

Golgi stains

Fill the whole cell, including details like dendritic spines. Used to characterize the variety of cell types in a region. This stains only a small number of cells, each of which stands out dramatically to the rest of the unstained ones.

Nissl stains

Outline all cell bodies because the dyes are attracted to RNA, which encircles the nucleus. These allow us to measure cell body size and the density of cells in particular regions.

Autoradiography

Cells are manipulated into taking photographs of themselves. Animals are injected by a radioactively labelled drug. When the drug has reached its target, thin sections of brain tissue are placed on slides and covered with photographic emulsion. Radioactivity emitted by the labeled drug in the tissue “explodes” the emulsion –like light striking film—producing a collection of fine, dark grains wherever the drug has become selectively concentrated.

Immunocytochemistry (aka immunohistochemistry)

Brain slices are exposed to antibodies that are selective to a particular cellular protein of interest. After allowing time for the antibodies to attach to molecules of the target protein, unattached antibodies are rinsed off and chemical treatments make the antibodies visible. This process reveals only those cells that were making the specific protein.

Immediate early genes (IEGs)

A class of genes that show rapid but transient increases in expression in cells that have become active. C-fos is a IEG that is commonly used to identify activated neurons through immunocytochemistry.

In Situ hybridization

Using radioactively labeled lengths of nucleic acid, identifies neurons that contain a specific mRNA message. This is equivalent to idntifying the cells in which a gene of interest has been turned on.

Horseradish peroxidase (HRP)

An enzyme found in the roots of horseradish. Used to determine the cells of origin of a particular set of axons. Acts as a tracer of pathways because it is taken up into the axon at the terminals and transported back to the cell body.

3 principal components of the synapse

1. The presynaptic membrane, on the axon terminal of the presynaptic neuron.
2. A specialized postsynaptic membrane on the surface of the dendrite or cell body of the postsynaptic neuron.
3. A synaptic cleft, the gap of about 20 to 40nm that separates the presynaptic and postsynaptic membranes.

Synaptic vesicles

Small spheres in the presynaptic axon terminals, about 30-140nm in diameter. Each contains a specialized chemical substance, or neurotransmitter.

Neurotransmitter

A specialized chemical substance that the neuron uses to communicate with postsynaptic neurons.

In response to electrical activity in the axon, these vesicles…

…fuse to the presynaptic membrane and release molecules of neurotransmitter into the cleft.

After flowing across the cleft, the NT…

…produces electrical changes in the postsynaptic cell that may be either excitatory or inhibitory.

Receptor

A protein in the postsynaptic membrane that captures and reacts to molecules of a transmitter or hormone. A large number of synapses can cover the surfaces of the dendrites and cell body because each synapse is so small.

Dendritic spines

An outgrowth along the dendrite of a neuron that increases the surface area of the dendrites, allowing for extra synaptic contacts.

Axon hillock

A cone-shaped area from which the axon originates out of the cell body. This is the neuron’s integration zone, giving rise to the electrical impulses that carry the neuron’s message along the axon toward its targets.

Axon collaterals

A branch of an axon from a single neuron. Because of this, a single nerve cell can exert influence over a wide array of other cells. At the end it divides into numerous fine branches. At the ends of these are the axon terminals that make synaptic contacts on other cells, or innervate them.

Axonal transport

The transportation of materials from the neuron cell body to distant regions in the dendrites and axons, and from the axon terminals back to the cell body.

3 components of the peripheral nervous system (PNS)

1. Cranial nerves: a nerve that is connected directly to the brain.
2. Spinal nerves (aka somatic nerve): a nerve that emerges from the spinal cord.
3. Autonomic nervous system: a regulatory system that primarily controls the viscera (internal organs)

All 3 communicate sensory information to the CNS and transmit commands from the CNS to the body.

Cranial Nerves

Serve chiefly the sensory and motor systems of the head. Pass through small openings in the skull to enter and leave the brain.

3 cranial nerves that are exclusively sensory pathways to the brain

Olfactory

Optic

Vestibulocochlear

5 cranial nerves that are exclusively motor pathways from the brain

Oculomotor

Trochlear

Abducens nerves innervate muscles to move the eye

Spinal accessory nerves control neck muscles

Hypoglossal nerves control the tongue.

The remaining cranial nerves which have both sensory and motor functions

Trigeminal serves facial sensation through some axons and controls chewing movements through other axons.

Facial nerves control facial muscles and receive taste sensation

Glossopharyngeal nerves receive sensation from the throat and control the muscles there.

Vagus nerve extends far from the head, running to the heart, liver, and intestines.

The spinal nerves

Along the length of the spinal cord are 31 pairs of spinal nerves (aka somatic nerves), with one member of each pair for each side of the body. Each spinal nerve consists of the fusion of two distinct branches, called roots, which are functionally different. The dorsal (back) root of each spinal nerve consists of sensory projections from the body to the spinal cord. The ventral (front) root consists of motor projections from the spinal cord to the muscles.

The name of the spinal cord is the same as what it’s connected to: cervical, thoracic, lumbar, sacral, and coccygeal segments.

The Autonomic Nervous System - Autonomic Ganglia

Aggregates of neurons found in various locations in the body outside of the CNS. They are controlled by the CNS. The ANS spans both the central and peripheral nervous systems.

Preganglionic autonomic neurons

The central neurons that innervate the ganglia

Postganglionic neurons

The ganglionic neurons that innervate the body.

3 divisions of the autonomic nervous system

1. sympathetic nervous system
2. parasympathetic nervous system
3. enteric nervous system

Sympathetic nervous system

One of two systems that compose the ANS. Arises from the thoracic and lumbar spinal cord. These cells send their axons a short distance to innervate the sympathetic chain (a chain of ganglia that runs along each side of the spinal column, part of the sympathetic nervous system). Sympathetic nervous system prepares the body for action: blood pressure increases, the pupils wide, and the heart quickens. (4 Fs!)

Parasympathetic nervous system

One of two systems that compose the autonomic nervous system. Arises from both the cranial nerves and the sacral spinal cord. Parasympathetic ganglia are not collected in a chain as sympathetic ganglia are, but are dispersed throughout the body, usually near the organ affected. These two systems often act in opposite directions, and the result is very accurate control.

Enteric nervous system

A local network of sensory and motor neurons that regulates the function of the gut. Innervated by both sympathetic and parasympathetic neurons.

We can’t control the autonomic nervous systems voluntarily.

Sagittal plane

The plane that bisects the body into right and left halves.

Coronal plane

The plane that divides the body into a front (anterior) and back (posterior). Aka fronal plane or transverse plane.

Horizontal plane

Divides the brain into upper and lower parts.

Medial

Towards the middle.

Lateral

Towards the side.

Ipsilateral

Relative to one location, a second location is ipsilateral if it is on the same side of the body and contralateral if it is on the opposite side of the body.

The head end

Anterior or Rostral

The tail end

Posterior or caudal

Nearest

Proximal

Towards the periphery or towards the end of a limb.

Distal

Towards the bottom of the head/brain.

Ventral

The top of the head/brain.

Dorsal

Afferent/efferent

We call an axon, tract, or nerve afferent if it carries information into a region that we’re interested in, and efferent if it carries information away from the region of interest.

(Afferents Arrive, Efferents Exit).

Within the central nervous system...

nucleus =  _______________

tract =  ______________

nucleus = a collection of neurons

tract = a bundle of axons 

Within the peripheral nervous system...

Ganglia = _________________

Nerves = _________________ 

Ganglia = a collection of neurons

Nerves = a bundle of axons