Ch 1 - Nervous System Organization

natural selection

Darwin’s theory that heritable traits that boost an individual’s chance of survival and reproduction will, over the course of many generations, become more common in the population

design principles

physical or engineering principles that can be used to argue that a biological feature is “well-designed”, even though natural selection is not guided by any kind of “designer”

central nervous system (CNS)

in vertebrates, the brain and spinal cord

• the CNS also includes the eye, which develops as an outpocketing of the diencephalon

peripheral nervous system (PNS)

axons and neurons that lie outside of the CNS, including most sense organs and nerves, large parts (but not all) of the autonomic nervous system, and the enteric nervous system

autonomic nervous system

a complex, widespread network of neurons that regulate the body’s vital processes (automatic)

• includes digestion, heart, blood pressure

• acts fairly independently (autonomously) of the CNS

  • contains sympathetic and parasympathetic divisions

enteric nervous system

roughly 200-600 million neurons (in humans) in the lining of the gastrointestinal tract that regulate digestion

centralization

the idea that the majority of neurons (in many but not all animals) tend to be concentrated in a few specific locations, notably the brain, rather than being scattered throughout the body

gray matter

contains neuronal cell bodies and dendrites

• unmyelinated axons and most synapses

  • most of these unmyelinated neurons are interneurons

• area regions → areas of nerve connections and processing

white matter

tissue that contains almost exclusively myelinated axons (w/ myelin sheaths)

• myelinated neurons connect regions of gray matter to each other and to rest of body

• acts as information highway of brain to speed up connections between distant parts of brain and body

fiber tracts

large bundles of axons, usually myelinated

brain nuclei

clusters of neuronal cell bodies w/ similar features, typically segregated from cell bodies that exhibit different sets of features

dorsal

toward the back of the body or the top of the head (in four-legged animals when they hold their head high)

• ambiguous in humans

ventral

toward the abdomen/underside of the body (humans) or the underside of the head (four-legged animals)

rostral

toward the snout (four-legged animals); not defined well in humans

caudal

toward the tail (four-legged animals); not defined well in humans

superior

toward the top of the head (humans)

inferior

toward the bottom of the feet when standing upright (humans)

• for the brain → toward the neck

anterior

toward the front of the body when standing upright (humans)

• for the brain → toward the front of the skull

posterior

toward the back side of the body when standing upright (humans)

• for the brain → toward the back of the skull

medial

toward the organism’s midline

lateral

toward the left or right sides of the body

• for the brain → toward the left or right sides of the skull

midsagittal

the plane that bisects the body or the brain into left and right halves

horizontal

planes that cut through an animal’s brain or body parallel to the ground, when the head and body are held in their normal, standing position

coronal

one of several planes that cut through a human body transversely, at right angles to the body’s long axis

• for the brain → a plane that is parallel to the face and perpendicular to the midsagittal and horizontal planes

ipsilateral

on the same side of the midline

contralateral

on the opposite side of the midline

hindbrain

the part of the brain between the spinal cord and the midbrain

• includes medulla, cerebellum, and pons

medulla

the part of the brain that is closest to the spinal cord

cerebellum

a highly folded part of the hindbrain (in many vertebrates) that is involved in fine-tuning movements (and likely some cognitive processes)

• based on trial-and-error learning

• “little brain”

pons

cluster of neurons lying ventral / inferior to the cerebellum and providing much of its input

midbrain

the region between the hindbrain and the forebrain

colliculus

the dorsal / superior part of the midbrain, usually divided into superior and inferior colliculi

• superior colliculus is called optic tectum in non-mammalian vertebrates

optic tectum (in non-mammalian vertebrates)

the name for the superior colliculus in non-mammalian vertebrates (part of the midbrain)

tegmentum

the ventral / inferior part of the midbrain

brainstem

defined differently by different people

• in this book, refers to medulla, pons, and tegmentum

forebrain

the most rostral / anterior of the brain’s major divisions

• includes diencephalon and telencephalon

diencephalon

the part of the forebrain that is closest to the midbrain

• includes the thalamus and hypothalamus

thalamus

the dorsal / superior part of the diencephalon

• includes medial geniculate nucleus and the lateral geniculate nucleus

hypothalamus

the ventral / inferior part of the diencephalon

• involved in regulating many vital bodily functions

telencephalon

the most rostral part of the forebrain and its largest division in most vertebrates

striatum

a large ventrolateral / inferior (non-cortical) component of the telencephalon

• largest component of the basil ganglia

pallidum

part of the ventral / inferior telencephalon that receives its main input from the striatum

• contains dorsal and ventral subdivisions

cerebral cortex

the layered (laminated) part of the telencephalon

• includes neocortex, olfactory cortex, and hippocampus

laminae

layers, typically of the cerebral or cerebellar cortex

• generally, a neuron is said to be located in whichever lamina contains its cell body

hippocampus

part of the cerebral cortex

• involved in spatial memory and in memory of what happened when and where

piriform cortex

the largest part of the olfactory cortex

• receives input from the olfactory bulb

neocortex

the largest part of the cerebral cortex in humans

• exhibits numerous folds and interacts extensively w/ underlying striatum and the thalamus

cortical area

a region of the cerebral cortex that is functionally and structurally distinct from other cortical areas

• e.g., in its pattern of lamination, connections, and/or physiological responses

gyrus / gyri

an outward fold (or ridge) of the cerebral cortex

sulcus / sulci

an inward fold (or groove) of the cerebral cortex

frontal lobe

the most rostral / anterior lobe of the neocortex

• includes motor cortex and prefrontal cortex

parietal lobe

the region of the neocortex that lies caudal / posterior to the frontal lobe and anterior / rostral to the occipital lobe

• includes somatosensory cortex and areas involved in control of targeted eye, head, and hand movements

temporal lobe

the most ventral / inferior portion of the primate neocortex, bordered caudally / posteriorly by the occipital lobe

• includes auditory cortex and, deep within, the hippocampus and amygdala

occipital lobe

the most caudal / posterior lobe of the neocortex

• includes primary visual cortex and several higher visual cortices

central sulcus

one of the most prominent sulci in primate brains

• lies between primary somatosensory cortex and the primary motor cortex

  • separates frontal lobe from the parietal lobe

insular cortex

a portion of the neocortex that is covered by parts of the frontal (and other) lobes

• has variety of functions

  • e.g., processing of gustatory (taste) information

amygdala

a collection of cell groups in the anterior pole of the human temporal lobe

• functions include the control of strong emotions and emotion-related modulation of memory

olfactory bulb

the most rostral part of the telencephalon in most vertebrates, located on the inferior surface of the frontal lobe in humans

• receives inputs from the olfactory epithelium and projects to olfactory cortex

retina

the multilayered neural structure at the back of the eye that contains photoreceptors, retinal interneurons, and neurons that project through the optic nerve to the brain

dendrites

short branched extension of nerve cell, where impulses are received from other neurons at synapses

• receive messages from other cells

axon

a long and thin neuronal process that remains relatively constant in thickness along its length

• main function is to conduct action potentials over long distances

  • passes messages to terminal branches

action potential

an all-or-none electrochemical signal generated by neurons in response to above-threshold stimulation

synapse

the site where a presynaptic neuron releases neurotransmitter molecules onto a postsynaptic cell or (for electrical synapses) where a presynaptic neuron comes into direct cytoplasmic contact w/ a postsynaptic cell

• in between neurons; where neurotransmitters are released

neurotransmitter

one of many different chemicals that neurons release in order to transmit information from one cell to another

glial cell

one of several non-neuronal cell types that are prominent components of the nervous system

• types → astrocytes, microglia, oligodendrocytes, Schwann cells, ependymal cells

microglia

small star-shaped glial cells that multiply in response to brain injury, migrate to the site of injury, secrete inflammatory molecules, and engulf cellular debris

• act like white blood cells by attacking and destroying pathogens that invade brain

astrocyte

type of glial cell that protects neurons by filtering nutrients out of the blood and prevents chemicals and pathogens from leaving the capillaries of the brain

oligodendrocyte

type of glial cell that wraps itself around axons and produces the myelin sheath around myelinated axons in the CNS

• helps speed up communication in brain

Schwann cell

a type of glial cell that produces myelin sheaths surrounding axons in PNS

ependymal cells

types of glial cell that line capillaries of choroid plexuses and filter blood plasma to produce cerebrospinal fluid

topographic projection

an axonal projection in which neighboring neurons project to neighboring neurons in the target region

divergence

the idea that axons may split into two or more branches that project to different targets

convergence

the idea that neurons may receive input from two or more other neurons

negative feedback loop

a control system in which the system’s output is used to modify the process giving rise to that output in such a way that, overall, less output is produced

positive feedback loop

a control system in which the system’s output is used to modify the process giving rise to that output in such a way that, overall, more output is produced

dual reflex arc model

hypothesis by William James and Theodore Meynert

• long (generally transcortical) reflex arcs modulate the activity of short (usually subcortical) reflex arcs

  • conceptual framework that illustrates how simple, innately determined subcortical reflexes can be modified by learned associations and higher-level processing in the cortex

    • suggests hierarchy in NS → experiences can link basic reflex actions through cortical connections

association fibers

axonal connections that are both divergent and convergent so that each neuron projects to (and receives input from) many other neurons

reverse engineering

the process of trying to understand the inner workings of a system by starting w/ observations a/b its behavior

neuropsychologist

a scientist who explores the neural basis of psychological processes

neuroethologist

scientist who studies the neural mechanisms underlying natural behavior

phrenologist

followers of Joseph Gall who believed that the brain is composed of multiple distinct “cerebral organs”, the size of which is reflected in the shape of the skull

homolog

one biological feature is the homolog of another if both features can be traced back, along continuous history, to a corresponding feature in a common ancestor

• refers to a biological structure in one species that corresponds to a structure in another species b/c they both descended from a common ancestral feature

  • shared revolutionary origin, not necessarily shared current function