Neuroanatomy Study Guide - Midterm #1 (Written)

What are the two structural divisions of the nervous system?

• Central Nervous System (Brain & Spinal cord)

• Peripheral Nervous System (Cranial & Spinal Nerves)

What are the two functional divisions of the nervous system?

• Somatic Nervous System

  • Body wall (muscles, skin, and mucous membranes)

• Autonomic (Visceral) Nervous System

  • Portions of CNS and PNS

  • Smooth muscles and glands of internal organs, blood vessels

  • Returns sensory info from organs —> brain

What is considered to be the rostral portion of the brain?

Cerebrum / Forebrain

The rostral portion of the brain is the most ____________ advanced and has the most ________ functions

The rostral portion of the brain is the most phylogenetically advanced and has the most complex functions

What are the two sections of the cerebrum?

• Telencephalon

• Diencephalon

What comprises the telencephalon?

• Cerebral cortex (gray matter)

• Subcortical white matter

• Basal ganglia (gray masses deep within hemispheres)

White matter has a high ______ content with no ________ or ________.

White matter has a high myelin content with no neuronal cell bodies or synapses

What comprises the diencephalon?

• Thalamus

• Hypothalamus

What are the different parts of the brainstem? What is their order from superior to inferior?

1. Midbrain (mesencephalon)

2. Pons

3. Medulla Oblongata

What comprises the cerebellum?

• Vermis

• Lateral Lobes/Hemispheres (2)

What is a ventricle?

• Spaces within the hollow brain

• Filled with cerebrospinal fluid (CSF)

What is a neuron?

• “Nerve cells”

• Specialized cells that receive and send signals to other cells through extensions / axons

• Encoded through electrical or chemical steps

• Large cell bodies and long axons

What is an interneuron?

• Small cell bodies and short axons

• Transmits impulses locally

What is the definition of nuclei?

Nerve cells grouped together with common functions within the CNS

What is the definition of ganglia?

Nerve cells grouped together with common functions in the PNS

What is a tract (fasciculi)?

• Pathways between groups of neurons in the CNS in the form of fiber bundles

  • Can descend or ascend

  • Pathways may cross (decussate)

What is a column (funiculi)?

Tracts in the spinal cord

What is a commisure?

Horizontal / Lateral Connections

Discuss the symmetry of the nervous system.

• Bilateral symmetry is most apparent in cerebrum and cerebellum

  • Also present in brainstem and spinal cord

• Some higher cortical functions (e.g., language) are more strong in one hemisphere than the other

What is decussation?

The crossing of fiber tracts from one side of the nervous system to the other (e.g., right side of the brain receives information from and controls motor function of the left side of the body)

What are the exceptions to decussation?

• Sternocleidomastoid

  • Left SCM controlled by the left cerebral cortex

• Cerebellar hemispheres control the ipsilateral side

  • (However, decussation still occurs in the cerebellum, it just crosses twice to control ipsilateral side)

What is a brain map?

• Represents the outside world

• Sensory map within the cerebral cortex (homunculus)

• Maps within visual world in occipital, temporal, and parietal lobes

  • Retinotopic - preserve geometric shapes

What is the clinical importance of brain maps?

Helps clinicians localize lesions (focal lesions of the brain may only interfere with just part of the map)

What does it mean if something is afferent?

• Information to the CNS

• Convey sensory stimuli

What does it mean if something is efferent?

• Information from CNS

• Generally motor functions (muscle contraction or secretion from glands)

What are the different parts of a spinal nerve root? What is their function?

• Dorsal → sensory

• Ventral → motor

What would be the typical mechanism of injury of the peripheral nervous system?

• Compression or physical trauma

• Some systemic illnesses (diabetes, toxins / drug exposure)

What would be the effects of an injury of the peripheral nervous system?

• Produces peripheral polyneuropathy (peripheral neuropathy)

  • Causes weakness, numbness, and pain

  • Typically feet are affected first (as well as the hands)

______ neurons are larger than ______ neurons.

Motor neurons are larger than sensory neurons

What is the dendritic zone?

Receptive part of the neuron

What is the synaptic terminal?

Downstream end of an axon

The cell body is the _______ and _______ center

The cell body is the metabolic and genetic center

T/F: The cell body makes up a large part of the neuron’s total volume

False (the cell body makes up a small part of the neuron’s total volume)

The receptive pole of the neuron includes the ________ and _________.

The receptive pole of the neuron includes the cell body and dendrites

What are dendrites? What is their function?

• Branches of neurons that extend from the cell body (long and thin)

  • Branching pattern is complex and determines how a neuron integrates synaptic inputs

• Receives incoming synaptic information

• Acts as resistors, isolating electrical events

What is a dendritic spine? What is their function?

• Small mushroom shaped projections that act as fine dendritic branches and receive synaptic inputs

• Shape of the spine regulates strength of signal

  • e.g., thin neck = smaller influence

• Dynamic and can change shape

  • Changes in shape can strengthen synaptic connections or alter function

What is an axon?

• Long extension arising from a neuron

• Cylindrical tube of cytoplasm covered by a membrane (axolemma)

What does the cytoskeleton consist of?

• Neurofilaments

• Microtubules

What is the function of a microtubule?

Provides framework for fast axonal transport

What is myelin?

Consists of multiple concentric layers of lipid rich membrane produced by Schwann cells (PNS) and oligodendrocytes (CNS)

What are the nodes of ranvier?

Small gaps in axon where myelin is absent

The smallest axons are ___________.

The smallest axons are unmyelinated

What is the function of myelin?

• Acts as an insulator

• Increases speed of impulse conduction

What are the different types of axonal transport?

• Anterograde Transport

• Retrograde Transport

What is anterograde transport?

The transport of materials from the cell body → synaptic terminals

Is anterograde transport fast or slow?

Both, may be fast or slow

What is retrograde transport?

The transport of materials from the synaptic terminals → cell body

T/F: Retrograde transport is similar to rapid anterograde transport?

True

After injury to an axon, the neuronal cell body responds by entering a phase called what?

Axon reaction or chromatolysis

How does regeneration differ between axons damaged in the PNS and CNS?

• PNS: regenerate quickly

• CNS: do not tend to regenerate

What occurs at a synapse?

Transmission of information between neurons (usually occurs between axon terminal to receptive region of receiving neuron)

What is a synaptic junction?

A specialized inter-neuronal complex

What is an axodendritic synapse?

A synapse located between an axon and dendrite

Is an axodendritic synapse considered to be excitatory or inhibitory?

Excitatory

What is an axosomatic synapse?

A synapse between an axon and nerve cell body

Is an axosomatic synapse considered to be excitatory or inhibitory?

Inhibitory

What is an axoaxonic synapse?

A synapse between an axon terminal and another axon

What is the function of an axoaxonic synapse?

Presynaptic inhibition (modulates transmitter release in postsynaptic axon)

What is an electrical synapse (gap junction)?

A specialized junction which involves the release of a chemical transmitter substance or electrical current pass directly from cell to cell

In what type of species are electrical synapses most common?

Most common in invertebrate nervous systems (but found in a small number of sites in mammalian CNS)

What are the three distinct characteristics of an electrical synapse?

1. Synaptic vesicles on pre-synaptic side

2. Synaptic cleft

3. Dense thickening of cell membrane on both sides

Synaptic vesicles contain ___________ and each vesicle contains a small packet (_____) of ____________.

Synaptic vesicles contain neurotransmitters and each vesicle contains a small packet (quanta) of transmitter

What is occurring during depolarization at a synaptic terminal?

1. Influx of calcium which leads to phosphorylation of class proteins called synapsins

2. Synaptic vesicles dock at the presynaptic membrane facing the synaptic cleft

3. Synaptic vesicle fuses with synaptic cleft

4. Synaptic vesicle releases transmitter

What is a transporter molecule?

Takes up transmitters from synaptic cleft (are not calcium dependent)

How are nerve cell bodies grouped?

Grouped characteristically (in many parts of the nervous system)

What is a projection neuron?

Has axons that carry impulses to other parts of the nervous system

Aggregates of tracts in the spinal corder are referred to as….

Columns (or funiculi)

Within the brain, certain axon tracts are referred to as…

Lemnisci

In some regions of the brain, axons are intermingled with dendrites and do not run in bundles so that pathways are difficulty to identify; these web-like networks are called the…

Neuropil

Glia _______ neurons in the brain and spinal cord and _______ form synapses

Glia outnumber neurons in the brain and spinal cord and do not form synapses

What are the important roles of glia?

• Myelin formation

• Guidance of developing neurons

• Maintenance of extracellular K+ levels

• Reuptake of transmitters after synaptic activity

What are the two classes of glia?

• Macroglia

• Microglia

Macroglia refers to…

• Astrocytes

• Oligodendrocytes

What are the principle functions of oligodendrocytes?

Myelin formation in CNS

What are the principle functions of astrocytes?

• Regulate ionic environment

• Reuptake of neurotransmitters

• Guidance of growing axons

Where is macroglia derived from?

Ectoderm

In contrast to neurons, macroglia have the capability to ________ (under some circumstances)

In contrast to neurons, macroglia have the capability to regenerate (under some circumstances).

What are the two classes of astrocytes?

• Protoplasmic

• Fibrous

What are the principle functions of microglial cells?

Immune surveillance of the CNS

What are the characteristics of the protoplasmic class of astrocytes?

• More delicate

• Processes are branched

• Occurs in gray matter

What are the characteristics of the fibrous class of astrocytes?

• More fibrous

• Processes (containing glial fibrils) rarely branched

What are the functions of astrocytes?

• Provide structural support to nervous tissue

• Direct neuronal migration

• Maintain appropriate concentrations of ions (K+) within brain and spinal cord

• Synaptic transmission

• Astrocytes surround endothelial cells within CNS

• Contribute to blood-brain barrier

Where do oligodendrocytes predominate?

White matter

What are microglia?

Macrophage-like cells

What is the function of microglia?

Detect and destroy invaders (such as bacteria)

The extracellular matrix makes up about __% of the total volume of the brain and spinal cord

The extracellular matrix makes up about 20% of the total volume of the brain and spinal cord

What is ionic homeostasis?

Regulation of ion levels in extracellular space (performed by astrocytes)

What is cerebral edema?

• Increase in bulk of the brain

• Can be either vasogenic (extracellular) or cytotoxic (intracellular)

• Must be treated emergently

What is wallerian degeneration?

• If the axon is cut, the part distal to the cut degenerates

• Occurs because materials for maintaining the axon are formed in the cell body and can no longer be transported down the axon (axoplasmic transport)

What is the function of the primary motor cortex?

Voluntary muscle activation

What is the function of the frontal eye field?

Eye movements

What is the function of Broca’s area?

Motor aspects of speech

What is the function of the primary sensory cortex?

Somatosensory

What is the function of the primary visual cortex?

Processing of visual stimuli

What is the function of the visual association cortex?

Processing of visual stimuli

What is the function of the primary auditory cortex?

Processing of auditory stimuli

What is the function of Wernicke’s Area?

Language comprehension

Describe the layout of the motor homunculus.

Describe the layout of the sensory homunculus.

What does the term basal ganglia refer to?

Refers to masses of gray matter deep within the cerebral hemisphere