Ch. 2: Functional Neuroanatomy

Class: Biological Psychology

Neuron (nerve cell)

the basic unit of the nervous system, each composed of a cell body, receptive extention(s) (dendrites), and a transmitting extension (axon)

• receives inputs from other cells, integrates those inputs, and then distributes the processed information to other neurons

• defines and controls all our abilities and behaviors, from the simplest reflexes to the most complex intellectual processes

• from vast ensembles of circuits that intricately process information

Glial Cells (glia)

non-neuronal brain cells that provide structural, nutritional, and other types of support to the brain

• can also communicate with each other and with neurons, and they directly affect neuronal functioning by providing neuron with raw material and chemical signal that alter neuronal structure and excitability

• come in 4 basic forms

• insulate and isolate synapses to prevent one from affecting the other

• continue to divide throughout life, and consequently they form many of the types of tumors that may arise in the brain

• some glial cells respond to brain injury by changing in size (swelling)

Neuron Doctrine

the hypothesis that the brain is composed of cells that are distinct structurally, metabolically, and functionally

• proposed that:

  • the cells of the brain are independent from one another structurally, metabolically, and functionally

  • the information is transmitted from 1 neuron to the next across tiny gaps (synapses)

Synapse

the tiny gap between neurons where information is passed from one neuron to the other

• Santiago Ramon y Cajal proposed that although neurons come very close to one another, they aren’t continuous with one another, and instead argued that at each point of contact between neurons, a tiny gap keeps the cells separate (synapses)

Cell Body (soma)

the region of a neuron that’s defined by the presence of the cell nucleus

• contains a variety of cell organelles found in all somatic cells

• contains the nucleus & bundles information up in the axon hillock

• manufactures various materials, such as enzymes and structural proteins, under the guidance of the DNA contained in the cell nucleus

4 functional zones of neurons

1. Input Zone

2. Integration Zone

3. Conduction Zone

4. Output Zone

1. Input Zone

the part of a neuron that receives information from other neurons or from specialized sensory structures

Dentrite

one of the extensions of the cell body through which synaptic inputs are received

• my be elaborately branched to accommodate synaptic contacts from other neurons

2. Integration Zone

the part of the neuron that initiates nerve electrical activity

• usually corresponds to the neuron’s axon hillock

• the cell body combines/integrates the information that the neuron has received to determine whether or not to send a signal of its own

3. Conduction Zone

the part of the neuron over which the nerve’s electrical signal may be actively propagated

• usually corresponds to the cell’s axon

Axon

a single extension from the nerve cell that carries action potentials from the cell body to other neurons

• carries/conducts the neuron’s own electrical signal away from the cell body

• 2 functions:

  • rapid transmission of electrical signals along the outside of the axon

  • the much slower transportation of substances inside the axon

  • (and to and from he axon terminals)

Axon Collateral

a branch of axon from a single neuron

4. Output Zone

the part of a neuron, usually corresponding to the axon terminals, at which the cell sends information to another cell

Axon Terminal (synaptic bouton)

the end of an axon or axon collateral, which forms a synapse on a neuron or other target cell

• specialized swellings at the ends of the axon

Neuron Size

• vertebrate nerve cells vary tremendously in size (10 to 100 micrometers

• larger neurons tend to have more-complex inputs and outputs, cover greater distances, and/or convey information more rapidly than smaller neurons

• size of neurons vary depending on their activity level and rate of protein synthesis

3 Principal Forms of Nerve Cells

1. Multipolar Neurons

2. Bipolar Neurons

3. Unipolar Neurons

Multipolar Neurons

a nerve cell that has many dendrites and a single axon

• most common type of nerve cell

• dendrites and the cell body (which receives synapses) are the input zone

Bipolar Neurons

a nerve cell that has a single dendrite at one end and a single axon at the other end

• common in sensory systems, such as vision

• dendrites and the cell body (which receives synapses) are the input zone

Unipolar Neurons (Monopolar Neuron)

a nerve cell with a single branch that leaves the cell body and then extends in 2 directions: one end is the receptive pole, the other is the output pole

• transmit touch information from the body into the spinal cord

• dendrites is the input zone

Interneurons

a neuron that is neither a sensory neuron nor a motor neuron; it receives input from and sends output to other neurons

• conveys information only in short distances

• have a complex dendrite

• make up the hugely intricate networks and circuits that perform the complex functions of the brain

Motor Neuron (Motoneuron)

a nerve cell that transmit motor messages, stimulating a muscle or gland

• neurons that connect the brain and spinal cord to the rest of the body have axon of up to a meter in length

• contain long axons reaching out to synapse on muscles, causing them to contract in response to commands from the brain

Sensory Neurons

a neuron that is directly affected by changes in the envrionment, such as light, odor, or touch

• carry messages from peripheral tissue (EX: sensors in the skin) back to the spinal cord and the brain

• have many different shapes depending on what sense they detect

Arborization

the elaborate branching of the dendrite of some neurons

• an arrangement of a neuron’s dendrite reflects the complexity of the neuron’s information-processing function

Presynaptic

referring to the region of a synapse that releases neurotransmitters

• information is transmitted from the axon terminal of the presynaptic neuron to the receptive surface of the postsynaptic neuron

Postsynaptic

referring to the region of a synapse that receives and responds to neurotransmitter

• information is transmitted from the axon terminal of the presynaptic neuron to the receptive surface of the postsynaptic neuron

3 Components of a Synapse

1. Presynaptic Membrane

2. Synaptic Cleft

3. Postsynaptic Membrane

Presynaptic Membrane

the specialized membrane of the axon terminal of the neuron that transmits information by releasing neurotransmitter

• is the axon terminal of the presynaptic membrane

Synaptic Cleft

the space between the presynaptic and postsynaptic membranes

• a gap of about 20-40 nanometers that separates the presynaptic and postsynaptic neurons

Postsynaptic Membrane

the specialized membrane on the surface of the cell that recieves information by responding to neurotransmitter from a presynaptic neuron

• is on the dendrite or cell body of the postsynaptic neuron

• contains a high density of receptors

• because each synapse occupies a very small patch of the postsynaptic neuron, a large number of synapses can cover the surfaces of the dendrites and cell body

Synaptic Vesicles

a small, spherical structure that contains molecules of neurotransmitter

• each 30-140nm in diameter

Neurotransmitter (synaptic/chemical transmitter)

the chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons

• communication starts when the synaptic vesicles fuse with the presynaptic membrane and rupture, releasing their payload of neurotransmitter molecules into the cleft

Receptor (receptor molecule)

a protein that binds and reacts to molecules of a neurotransmitter or hormone

• results in local changes in the electrical excitation of the postsynaptic cell

  • postsynaptic cell = neuron → increased likelihood that the postsynaptic neuron will release its own neurotransmitter

  • molecules of neurotransmitter generally don’t enter the postsynaptic neuron; they simply bind to the receptors momentarily to induce a response, and then detach and diffuse away

Neural Plasticity (Neuroplasticity)

the ability of the nervous system to change in response to the experience or the environment

• the continual remodeling of the connections between neurons

• Dendritic Spines: studding the dendrites of man neurons are outgrowths; increasing the surface area of dendrites allow for extra synaptic contacts

  • the number and structure may be rapidly altered by experiences

Axon Hillock

a cone-shaped area from which the axon originates out of the cell body

• functionally, the integration zone of the neuron (gathers and integrates information from all the synapses on the dendrite and cell body, then converts the processed information into a code of electrical impulses that carries the neuron’s message down the axon toward it target)

Histology

the scientific study of the composition of tissues

Nissl Stain

a cell stain that reveals all cell bodies by staining RNA

• allows us to measure cell body size and the density of cells in particular region

Golgi Stains

a cell stain that fills a small proportion of neurons with a dense dark pocket

• label only a minority of neurons in a sample, but affected cells are stained very darkly and completely reveling fine structures of cell structure

Autoradiography

a histological technique that shows the distribution of radioactive chemicals in tissues

Immunohistochemistry (IHC)

a technique in which labeled antibodies are used to visualize the histological distribution of specific proteins

• involves creating antibodies against a protein of interest

• these antibodies attach themselves to their target proteins within the neurons in a brain slice, thereby revealing the distribution of only hose neurons that make the target protein

In Situ Hybridization

a technique in which labeled complementary nucleic probes are used to identify cells expressing specific messenger RNA transcripts, reflecting the activation of specific genes of interest

Tract Tracers

a compound used to identify the routes and interconnections of neuronal projections

Innervate

to provide neural input

• neurons have 1 axon which divides into several axon collaterals, allowing the neuron to innervate/influence numerous postsynaptic cells

Axonal Transport

the transportation of materials between the neuronal cell body and axon terminals

• works in both directions:

  • anterogrande transport: moves material toward the axon terminals

  • retrograde transport: moves used materials back to the cell body for recycling

4 Basic Forms of Glial Cells

1. Astrocytes

2. Microglial Cell

3. Oligodendrocytes

4. Schwann Cells

Astrocytes

a star-shaped glial cell with numerous processes (extensions) that run in all directions, weaving among neurons

• EX: some form sucker-like end feet on blood vessels, regulating local blood flow to provide more supplies to neurons when they’re active

• receive synapses directly from neurons and surround and monitor the activity of nearby neuronal synapses

• directly participate in the transmission of neurons

• involved in the formation of new synapses, as well as the pruning of surplus synapses that is a normal part of brain development

• directly influence local brain chemistry, so they’ve been implicated in diseases that result from changes in neuronal excitability

• increasingly implied in degenerative processes

Microglial Cell (microglia)

extremely small glial cells that remove cellular debris from injured or dead cells

• remarkably active: continualy extending and withdrawing very find processes that, when they contact a site of damage, form a spherical containment zone around the injury

• migrate to sites of injury or disease in the nervous system to remove debris from injured or dead cells

• also involved in aspects of pain perception and neuronal remodeling

Oligodendrocyte

a type of glial cell that forms myelin in the central nervous system

• perform myelination

• each cell providing myelin beads to several nearby axons

• provide chemical signals (trophic signals) that enhance the structural integrity of axons

Schwann Cell

a glial cell that forms myelin in the peripheral nervous system

• perform myelination

• do the ensheathing/covering of the axon in myelin

• a single cell ensheathes a limited length of a single acon

Myelination

the process of covering axons in myelin

• glial cells wrap sections of the axon in multiple layers of myelin, giving the axon the appearance of a string of slender beads

• between adjacent beads, nodes of Ranvier remained exposed

• result: a large increase in the speed with which electrical signals pass down the axon, jumping from one node to the next

• many thin, short axons lack myelin but are still surrounded by oligodendrocytes or Schann cells, which segregate the unmyelinated axons

Myelin

the fatty insulation around an axon, formed by glial cells, that speeds the conduction of action potentials

nodes of Ranvier

a gap between successive segments of the myelin sheath where the axon membrane is exposed

• uninsulated patches of axonal membrane that remains exposed

Edema

the swelling of tissue, such as in the brain, in response to injury

• damages neurons and is responsible for many symptoms of brain injuries

Multiple Sclerosis

literally “many scars”; a disorder characterized by widespread degeneration of myelin

• the loss of the insultating myelin sheath from axons in various regions of the brain can have severe consequences tht vary depending on the region that is affected, ust as losing the outer insulation from a computer cable ca cause short ircuits and the loss of vital information

Gross Neuroanatomy

anatomical features of the nervous system that are apparent to the naked eye

• formed from neuronal cell bodies, dendrites, axons, and glia mass that form its tissues

• visible to the naked eye

Peripheral Nervous system

the portion of the nervous system that includes all the nerves and neurons outside the brain, skull, and spinal cord

Central Nervous System (CNS)

the portion of the nervous system that includes the brain and the spinal cord

Nerves

a collection of axons bundled together outside the central nervous system

Motor Nerves

transmit information from the spinal cord and brain to the muscles, organs, and glands

Sensory Nerves

a nerve that conveys sensory information from the periphery (body) into the central nervous system (spinal cord and brain)

2 Peripheral Nervous Systems

1. Somatic Nervous System

2. Autonomic Nervous System

Somatic Nervous System

the part of the peripheral nervous system that provides neural connections to the skeletal musculature

• the main pathway through which the brain controls movement and receives sensory information from the body and from the sensory organs of the head

Nerves that make up the Somatic Nervous System

1. Cranial Nerves

2. Spinal Nerves

Cranial Nerves

a nerve that is directly connected to the brain

• humans have 12 pairs of cranial nerves: one left-sided and one right-sided nerve in each pair that serve the sensory and motor systems of the head and neck

• these nerves pass through small openings in the skull, directly entering or leaving the brain without ever joining the spinal cord

• are exclusive sensory pathways to the brain: the olfactory nerve conveys smell, the optic nerve carries visual information, and the vestibulocochlear nerve is concerned with hearing and balance

• 5 pairs of nerves for the motor pathways from the brain: oculomotor, trochlear, and abducens nerves innervate muscles to move the eye; the spinal accessory nerves control neck muscles; the hypoglossal nerves control the tongue

• sensory and motor function nerves:

  • trigeminal carries facial sensation through some axons, and it controls chewing movements through other axons

  • facial nerves control facial muscles and recieve some sensation

  • glossopharyngeal nerves receive additional taste sensations and sensations from the throat and control throat muscles

  • vagus nerve extends far from the head, innervating the heart, liver, and intestines; primary route by which the brain both controls and receives information from many visceral organs and participates in varied functions like sweating, digestion, and heart rate

Spinal Nerve (somatic nerve)

a nerve that emerges from the spinal cord

• 31 pairs emerge at regularly spaced intervals through openings in the backbone

  • 8 cervical

  • 12 thoracic

  • 5 lumbar

  • 5 sacral

  • 1 coccygeal

• one member of each pair of spinal nerves serves each side of the body

• each nerve consists of the fusion of 2 distinct branches, called roots

Dorsal Root

the branch of a spinal nerve, entering the dorsal horn of the spinal cord, that carries sensory information from the peripheral nervous system to the spinal cord

• consists of sensory projections from the body to the spinal cord

Ventral Root

the branch of a spinal nerve, arising from the ventral horn of the spinal cord, that carries motor messages from the spinal cord to the peripheral nervous system

• consists of motor projections from the spinal cord to the muscles

Cervical

referring to the topmost 8 segments of the spinal cord in the neck region

Thoracic

referring to the 12 spinal segments below the cervical (neck) portion of the spinal cord, corresponding to the chest

Lumbar

referring to the 5 spinal segments that make up the upper part of the lower back

Sacral

referring to the 5 spinal segments that make up the lower part of the lower back

Coccygeal (tailbone)

referring to the lowest spinal vertebra

Autonomic Nervous System

the part of the peripheral nervous system that supplies neural connections to glands and to smooth muscles of internal organs

• is the brain’s main system for controlling the organs of the body

Autonomic Ganglia

collections of nerve cell bodies, belonging to the autonomic division of he peripheral nervous system, that are found in various locations and innervate the major organs

• found in the body outside of the CNS

• autonomic neurons within the brain and spinal cord send their axons to innervate neurons in the ganglia, which in turn send their axons to innervate all the major organs

Preganglionic

literally,”before the ganglion”; referring to neurons in the autonomic nervous system that run from the central nervous system to the autonomic ganglia

Postganglionic

literally,”before the ganglion”; referring to neurons in the autonomic nervous system that run from the autonomic ganglia to various targets in the body

• these cells in the sympathetic chain send axons throughout the body, innervating all of the major organ systems

3 Major Divisions of the Autonomic Nervous System

1. Sympathetic Nervous System

2. Parasympathetic Nervous System

3. Enteric Nervous System

Sympathetic Nervous System

a component of the autonomic nervous system that run from the autonomic ganglia to various targets in the body

• found in the middle parts of the spinal cord: the thoracic and lumbar regions

• send their axons only a short distance, innervating the sympathetic chain of autonomic ganglia that runs along each side of the spinal column

• prepares the body for action: blood pressure increases, inhibited digestion, the pupils of the eyes dilate, and the heart rate quickens

  • flight or flight response

• uses the neurotransmitter norepinephrine to accelerate activity

Sympathetic Chain

a component of the autonomic nervous system that arises from the thoracic and lumbar spinal cord

Parasympathetic Nervous System

a component of the autonomic nervous system that arises from both the cranial nerves and the sacral spinal cord

• helps the body to relax, recuperate, and prepare for future action

  • heart rate slows, blood pressure drops, and digestive processes are activated

  • rest and digest response

• its axons travel a longer distance before terminating in the parasympathetic ganglia

  • parasympathetic ganglia are dispersed throughout the body, usually positioned near the organs they affect

• uses the neurotransmitter acetylcholine, which slows activity down

Norepinephrine (noradrenaline)

a neurotransmitter produced and released by sympathetic postganglionic neurons to accelerate organ activity

• produced in the brainstem and found in projections throughout the brain

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Acetylcholine

a neurotransmitter produced and released by parasympathetic postganglionic neurons, by motor neurons, and by neurons throughout the brain

Enteric Nervous System

an extensive mesh-like system of neurons that governs the functioning of the gut

• a local network of sensory and motor neurons that regulates the functioning of the gut, under the control of CNS

• regulates digestive activities of the gut

• maintains fluid and nutrient balances in the body

Spinal Cord

funnels sensory information from the body up to the brain and conveys the brain’s motor commands out to the body

• contains circuits that perform local processing and that control simple units of behavior (like reflexes)

Cerebral Hemispheres

the right and left halves of the forebrain

Cerebral Cortex

the outer covering of he cerebral hemispheres that consists largely of neuronal cell bodies and their branches

• thick sheet of brain tissue

• arranged in 6 distinct layers:

  • Layer 1: is distinct because it has few cell bodies

    • Layers 1, 2, & 3: receive input from layer 4 and integrate information

  • Layer 4: receives axon from sensory systems

  • Layers 5 & 6: have many neurons with large cell bodies; send axons to other brain areas, especially motor output

Gyrus (Gyri)

a ridged or raised portion of a convoluted brain surface

Sulcus (Sulci)

a furrow of a convoluted brain surface

• folding up the tissue in this way increases the amount of cortex that can be jammed into the skull

4 Major Cortical Regions (Lobes)

1. Frontal

2. Parietal

3. Temporal

4. Occipital

• each lobe of the hemisphere is continuously communicating among themselves and with their counterparts in the other hemisphere, their collaboration producing the seamless experiences and complex behaviors that distinguish us as individuals

Frontal LobeCorpus Callosum

the most anterior portion of the cerebral cortex the main band of axons that connects the two cerebral hemispheres

• allows the brain to act as a single entity during complex processing

Parietal Lobe

large region of cortex lying between the frontal and occipital lobes of each cerebral hemisphere

• receive sensory information from the body and participate in spatial cognition

Temporal Lobe

large lateral cortical region of each cerebral hemisphere, continuous with the parietal lobe posteriorly and separated from the frontal lobe by the Sylvian fissure

• auditory information is directed here

• damage here can impair hearing

Occipital Lobe

large region of cortex covering much of the posterior part of each cerebral hemisphere

Sylvian Fissure (Lateral Sulcus)

a deep fissure that demarcates the temporal lobe from other regions of the hemisphere

Central Sulcus

a fissure that divides the frontal lobe from the parietal lobe

Postcentral Gyrus

the strip of parietal cortex, just behind the central sulcus, that receives somatoosensory information from the entire body

Sagittal Plane

the plane that disects the body into right and left halves

Coronal/Frontal/Transverse Plane

the plane that divides the body into a front (anterior) and a back (posterior) part

Horizontal Plane

the third main plane, which divides the brain into upper and lower parts

Medial

towards the middle

Lateral

towards the side