Reading Notes - Chapter 1

1.1 - the nervous system is made of specialized cells

• Neurons (nerve cells) → arranged into the circuits that underlie all forms of behavior (reflexes and cognition) (brain contains 80-90 billion)

  • Receives inputs from other cells

  • Integrates inputs

  • Distributes processed information to other neurons

  • All neurons have a nucleus which contains chromosomes made of DNA strands, cellular organelles (mitochondria), translation of genetic instructions (via ribosomes)

• Glial cells (glia) → provides support functions and information processing

• Ramon y Cajal (1852-1934) → found that neurons aren’t continuous with one another and helped establish the neuron doctrine:

1. Neurons and other cells of brain are structurally, metabolically, and functionally independent

2. Information is transmitted between neurons across gaps called synapses

• Synapses → gaps between neurons (there are roughly a quadrillion in the brain)

• Four principal divisions of the neuron →

1. Input zone → dendrites (cellular extensions that may be covered in dendritic spines) are where neurons receive information via synapses from other neurons

2. Integration zone → neuron’s cell body (soma) integrates information that was received to determine whether or not to send a signal

3. Conduction zone → the axon (nerve fiber) (has two functions: rapid transmission of electrical signals along outer membrane of the axon and slower transportation of substances within the axon, to and from the axon terminals (like a pipe)) carries neuron’s own electrical signals away from the cell body (sometimes it is aided by a myelin (insulating sheath) and axon may split into axon collaterals (branches))

4. Output zone → axon terminals (synaptic boutons) transmit neuron’s signals across synapses to other cells

• Diversity in shapes and sizes of neurons →

  • Motor neurons (motoneurons) → trigger movements - are large with long axons reaching out to synapse on muscles, causing muscular contractions

  • Sensory neurons → convey info from sense organs to brain

  • Interneurons → receive info from other neurons, process it, and pass integrated info to other neurons (most of the neurons of the brain)

Varying sizes of neural structures:

Different shapes of neurons:

• Multipolar neurons → many dendrites and a single axon (most common)

• Bipolar neurons → single dendrite at the end of the cell and have a single axon on the other end (common in sensory systems like vision)

• Unipolar neurons (monopolar neurons) → single extension identified as an axon for its entire length. One end has the branching dendrite-like input and integration zone where the axon arises directly, leading to a distant output zone with its axon terminals. Cell body branches off the axon part way along its length (transmit touch and pain info from the body into the spinal cord)

Synapses (info is transmitted through synapses) → 

• Presynaptic neuron → info transmitted from axon terminal of a presynaptic neuron

  • Contain synaptic vesicles (tiny hollow spheres) that contain molecules of neurotransmitter (chemical used for presynaptic neuron to communicate with postsynaptic cells)

  • Electrical activity in the axon → synaptic vesicles fuse to presynaptic membrane and rupture, release the neurotransmitter molecules into the synaptic cleft → cross cleft → released neurotransmitter molecules interact with matching neurotransmitter receptors that stud the postsynaptic membrane → receptors capture and react to molecules → alter level of excitation of the postsynaptic neuron

• Postsynaptic neuron → receptive surface that receives info

• Three principal components of a synapse → 

  • Presynaptic membrane

  • Synaptic cleft → gap of 20-40 nanometers that separates presynaptic and postsynaptic neurons

  • Postsynaptic membrane

Neuroplasticity → capacity of neurons to continually remodel their connections with other neurons

Axon integrates and then transmits info

• Axon hillock → distinctive enlargement on the cell body that the neuron’s axon projects away

• Axonal transport → substances (enzymes and structural proteins) are conveyed through the interior of the axon from the cell body to the axon terminals where they are used

  • Anterograde transport → moves materials toward the axon terminals

  • Retrograde transport → moves used materials back to the cell body for recycling

Glial cells protect and assist neurons → provide neurons with raw materials, chemical signals, and specialized structural components. Four types of glial cells in the human nervous system →

• Oligodendrocytes (applies to brain and spinal cord) and Schwann cells (applies to the rest of the body) → wrap around successive segments of axons to insulate them with myelin sheaths (between the patches of myelin are uninsulated patches of axonal membrane called nodes of Ranvier)

  • Result is increase in the speed that electrical signals pass down the axon

    

• (paired with microglia cells) Astrocytes → weave around and between neurons (help form tough outer membranes that swaddle the brain and they also secrete chemical signals that affect synaptic transmission and the formation of synapses)

(paired with astrocytes) Microglia cells → they contain and clean injury sites

1.2 - the nervous system extends throughout the body

• Gross neuroanatomy of the nervous system (cell bodies, dendrites, axons, glial cells for this tissue) → the neural structures that are visible to the unaided eye

• The central and peripheral nervous systems:

  

• Peripheral nervous system → collection of nerves that extend throughout the body (motor (transmit info from spinal cord and brain to muscles and glands) and sensory nerves (convey info to the CNS))

1. Somatic nervous system → supplies neural connections mostly to the skeletal muscles and sensory systems of the body (cranial (nerve connected directly to the brain) and spinal nerves (nerve that emerges from the spinal cord))

   1. The cranial nerves → nerve connected directly to the brain

      

2. Spinal nerves → nerve that emerges from the spinal cord

2. Autonomic nervous system → provides the main neural connections to the internal organs

   1. Sympathetic nervous system → fight-or-flight response, generally prepares the body for action

   2. Parasympathetic nervous system → prepares the body to relax and recuperate

Central nervous system → brain and spinal cord

• Anatomical conventions for describing the anatomy of the brain

  • Planes: 

    • Sagittal plane → divides the body/brain into right and left portions

    • Coronal plane → front and back

    • Horizontal plane → upper and lower

  • Directions:

    • Medial → towards middle

    • Lateral → towards side

    • Ipsilateral → on same side

    • Contralateral → on opposite side

    • Superior → above

    • Inferior → below

    • Basal → towards bottom

    • anterior/rostral → front

    • posterior/caudal → back

    • Proximal → near

    • Distal → far

    • Afferent → carrying action potentials toward the brain or toward one region of interest from another region of interest

    • Efferent → carrying action potentials away from the brain or away from one region of interest toward another region of interest

    • Dorsal → back (like dorsal fin on animals back)

    • Ventral → towards belly

      

Outer surface of brain:

• Cerebral hemispheres → one of the two halves of the forebrain

• Cerebral cortex → outer covering of the cerebral hemispheres, which consists largely of nerve cell bodies and their branches

• Gray matter → areas of the brain dominated by cell bodies and don’t have myelin. Mostly receives and processes info

• White matter → light-colored layer of tissue, consisting of myelin sheathed axons that lies underneath the gray matter of the cortex. Mostly transmits info

• Gyri → ridges of tissue from folding of the cortex

• Sulci → valley of the cortical surface

• Four major cortical regions of each cerebral hemisphere:

  • Frontal lobe → front

  • Parietal lobe → between frontal and occipital lobes

  • Temporal lobe

  • Occipital lobe

  • Boundaries between lobes

    • Sylvian fissure → divides temporal love from other regions

    • Central sulcus → divides frontal and parietal lobes

  • Precentral gyrus → in front of the central sulcus, receives somatosensory info from the entire body (motor control) (primary motor cortex)

  • Postcentral gyrus → behind the central sulcus, receives somatosensory info from the entire body (sense of touch) (primary somatosensory cortex)

  

• Corpus callosum → main band of axons that connects the two cerebral hemispheres

Development of subdivisions within brain:

• CNS in vertebrate of young embryo → looks like tube

  • Neural tube → embryonic structure that corresponds with the future brain and spinal cord. It is walls made of cells 

  • Filled with fluid

• Few weeks after conception, neural tube shows swellings…

  • Forebrain → front of the neural tube and brain. In mature vertebrate, contains cerebral hemispheres, the thalamus, and the hypothalamus

  • Midbrain → middle of brain

  • Hindbrain → rear of brain. In mature vertebrate, contains the cerebellum, pons, and medulla

• Fetus - 50 days

  • Telencephalon → front of fetal forebrain that becomes cerebral hemisphere in adult brain

  • Diencephalon → back of fetal forebrain that becomes thalamus and hypothalamus in adult brain

    

• Brainstem → midbrain, pons, medulla combined

• Nuclei → collection of neuronal cell bodies within the central nervous system

Tracts → bundles of axons

1.3 - the brain shows regional specialization of functions

Cerebral cortex performs complex cognitive processing

• Layers of cortical neurons - there are 6

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  • Cortical columns → vertical columns that constitute the basic organization of the cerebral cortex

  • Neurons in the cerebral cortex…

    • Pyramidal cell → pyramid-shaped cell body found in cerebral cortex (usually in layer III or V)

Nuclei are hidden beneath cerebral cortex

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• Basal ganglia → group of forebrain nuclei including the caudate nucleus, globus pallidus, and putamen, found within the cerebral hemispheres

  • Need for skill learning and control of movement

• Limbic system → group of brain nuclei that innervate each other to form a network (implicated in emotions and learning)

• Amygdala → limbic structure involved in emotional regulation, odor perception, aspects of memory

• Hippocampus → medial temporal lobe structure for learning and memory

• Fornix → fiber tract extending from the hippocampus to the mammillary body (important for memory and learning)

• Cingulate gyrus → strip of cortex in limbic system used for many cognitive functions like directing attention

• Olfactory bulb → processes smell

• Thalamus → paired structures that direct flow of sensory info to and from the cortex

• Hypothalamus → part of diencephalon, ventral to the thalamus (involved in hunger, thirst, temperature regulation, sex, and more) (controls pituitary gland which is the brains interface with the hormonal systems of the body)

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Midbrain has sensory and motor components

• Tectum → top of midbrain, has two pairs of bumps for sensory processing

  • Superior colliculi → processes visual info, involved in direction of visual gaze and visual attention

  • Inferior colliculi → process auditory info

• Tegmentum → main body of the midbrain with several structures…

  • Substantia nigra → innervates the basal ganglia and is major source of dopaminergic projections to the basal ganglia

  • Periaqueductal gray → involved in pain perception

  • Reticular formation → collection of neurons important in sleep and arousal

Brainstem controls vital body functions:

• Cerebellum → used for motor coordination, cognition, learning, motor control

• Pons → contains nerve fibers and motor control/sensory nuclei that connects the midbrain to the medulla

Medulla → posterior part of the hindbrain, continuous with spinal cord (conveys all major motor and sensory fibers to and from the body) (drive respiration, heart rate)

1.4 - specialized support systems protect and nourish the brain

Brain floats in layers of membranes - 3 layers of protective membranes (meninges)

• Dura mater → tough outer layer

• Pia mater → delicate layer

• Arachnoid → webby substance makes subarachnoid space that suspends brain in bath of watery liquid

• Cerebrospinal fluid (CSF) → watery liquid that suspends the brain

  • Meningitis → when meninges are inflamed by infections

  • Meningiomas → tumors that can form in the meninges
    

Brain needs FLUIDS!

• Ventricular system → system of fluid-filled cavities inside the brain

• Lateral ventricle → lateral portion of the ventricular system within each hemisphere of the brain

  • Lined with choroid plexus (lines ventricles by filtering blood)

• Third ventricle → conducts cerebrospinal fluid through narrow passage (cerebral aqueduct) to the fourth ventricle

• Fourth ventricle → cavity within the pons that receives cerebrospinal fluid from third ventricle and releases it to surround brain and spinal cord

• Hydrocephalus → ballooning of the ventricles at the expense of the surrounding brain which happens when the circulation of the cerebrospinal fluid (CSF) is blocked

• Glymphatic system → lymphatic system in the brain that removes waste, moves nutrients, and signals compounds

  • Glymphatic clearance → happens when we sleep. Prevents the accumulation of substances that damage neurons

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• Blood

• Cerebral arteries → 3 pairs of arteries within the skull that supplies blood to the cerebral cortex

• Blood-brain barrier → mechanisms that make the movement of substances from blood vessels into cells more difficult in the brain than in other body organs, giving the brain greater protection from exposure to some substances found in blood. The protective property of cerebral blood vessels that impedes the movement of some harmful substances from the bloodstream into the brain

• Stroke → clot, a narrowing, or a rupture interrupting the supply of blood to a region of the brain

• Transient ischemic attack (TIA) → temporary blood restriction to part of the brain that causes stroke-like symptoms that quickly resolve, which serves as a warning of elevated stroke risk

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1.5 - Techniques for studying structure and function of the nervous system

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• Autoradiography → staining technique that shows the distribution of radioactive chemicals in brain tissue

• Diffusion tensor imaging (DTI) → variant of MRI

  • Exploits a signal associated with the diffusion of water within axons in order to visualize axonal fiber tracts within the brain (this kind of research is called tractography)

• Functional near-infrared spectroscopy (fNIRS, also called optical imaging) → detectors pick up reflections of this light as it bounces back out through the scalp–shifts in the wavelengths of the reflected light are associated with local changes in blood flow and cortical activity during ongoing behavior

  • Spatial resolution is less than fMRI or PET

  • Is noninvasive, fast, and inexpensive

• Magnetoencephalography (MEG) → large array of ultrasensitive detectors measures the minuscule magnetic fields produced by the electrical activity of cortical neurons

  • Construct real-time maps of brain activity during ongoing cognitive processing

  • Studies rapidly shifting patterns of brian activity in cortical circuits that fMRI is too slow to track

1.6 - Research design in behavioral neuroscience

• Control group → in research, a group of individuals that are identical to those in an experimental group in every way except that they do not receive the experimental treatment or manipulation

• Within-participants experiment → an experiment in which the same set of individuals is compared before and after an experimental manipulation

• Between-participants experiment → an experiment in which an experimental group of individuals is compared with a control group of individuals

• Conserved → in the context of evolution, referring to a trait that is passed on from a common ancestor to two or more descendant species

• Reductionism → scientific strategy of breaking a system down into increasingly smaller parts in order to understand it

• Levels of analysis → scope of an experimental approach

  • A scientist may try to understand behavior by monitoring molecules, nerve cells, brain regions, or social environments or using some combination of these levels of analysis